Wei Hong's blog
https://imechanica.org/blog/27
enDepartment Head Position at HKUST
https://imechanica.org/node/24755
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/13003">Department Head</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Helping a friend to post this oppotunity - Head of the Department of Civil & Environmental Engineering at Hong Kong University of Science and Technology. (I am not moving:))<br />More details can be found in the attachment, and applications and querry should be directed to the Search Committee Chair for Headship of CIVL (<a href="mailto:dhcivl@ust.hk">dhcivl@ust.hk</a>).</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Advertisement.pdf" type="application/pdf; length=153791">Advertisement.pdf</a></span></td><td>150.19 KB</td> </tr>
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</div></div></div>Thu, 26 Nov 2020 12:29:27 +0000Wei Hong24755 at https://imechanica.orghttps://imechanica.org/node/24755#commentshttps://imechanica.org/crss/node/24755Multiple Faculty Positions at SUSTech
https://imechanica.org/node/22765
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><strong><span lang="EN-US" xml:lang="EN-US">Faculty Positions in Interdisciplinary Mechanics</span></strong> </p>
<p><strong><span lang="EN-US" xml:lang="EN-US">Department of Mechanics and Aerospace Engineering</span></strong> </p>
<p><strong><span lang="EN-US" xml:lang="EN-US">Southern University of Science and Technology</span></strong></p>
<p><span lang="EN-US" xml:lang="EN-US"><span>The Department of Mechanics and Aerospace Engineering (MAE) at Southern University of Science and Technology (SUSTech) in Shenzhen, China invites applications for multiple tenured or tenure-track faculty positions at all ranks. We seek ambitious and creative candidates who are well versed with the fundamentals of mechanics, have the vision and capability of carrying out interdisciplinary research, and contribute to the collegial and collaborative environment of the department. Researches interfusing solid mechanics with any other disciplines are welcome, such as biomedical engineering, robotics, advanced materials, aerospace materials and structures, human-machine interface, artificial intelligence, energy systems, manufacturing and composites, and data science. The successful candidates are expected to build strong and independent research, advise graduate and undergraduate students, publish in archival journals, and teach both undergraduate and graduate courses in Solid Mechanics. Senior candidates are expected to play leadership roles in research and education. Globally competitive salaries and very attractive start-up packages will be provided.</span></span></p>
<p><span lang="EN-US" xml:lang="EN-US"><span>The MAE Department was established in 2015, and just graduated its first class of students in Summer 2018. The department has two undergraduate programs: Theoretical and Applied Mechanics, and Aerospace Engineering, and possesses state-certified BS, MS and PhD degree programs. The department currently has 19 tenured/tenure-track faculty members, conducting active research in the general areas of fluid mechanics, solid mechanics, computational mechanics, micro and soft materials and devices, aeroengines, unmanned aerial vehicles, aeroacoustics and dynamics.</span></span></p>
<p><span lang="EN-US" xml:lang="EN-US"><span>Established in 2012, SUSTech is a public institution in Shenzhen, a special economic zone in China. Located in the Pearl River Delta region and neighboring Hong Kong, Shenzhen is one of the top four most prosperous cities in China and has been consistently referred to as the leader in technological developments. The mission of SUSTech has been to reform higher education in China and become a world-class institution with a strong emphasis on student learning experience, world-class research, innovation and entrepreneurship. More information can be found at <span><span><a href="http://sustc.edu.cn/"><span><span>http://sustc.edu.cn/</span></span></a></span></span>.</span></span></p>
<p><span lang="EN-US" xml:lang="EN-US"><span>Applicants should submit the following materials: (1) a complete curriculum vita, (2) names, affiliations, and contact information of at least three references, (3) a statement of research and teaching interests and plan, and (4) copies of three representative publications. These application materials should be sent by e-mail to: Professor Wei Hong (<span><span><a><span><span>hongw@sustc.edu.cn</span></span></a></span></span>), Chair, Faculty Search Committee in Interdisciplinary Mechanics. Screening starts immediately and will continue until the positions are filled.</span></span></p>
<p><span lang="EN-US" xml:lang="EN-US"><span>SUSTech values diversity and equal opportunity, international and female candidates are strongly encouraged to apply.</span></span></p>
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</div></div></div>Tue, 16 Oct 2018 07:05:10 +0000Wei Hong22765 at https://imechanica.orghttps://imechanica.org/node/22765#commentshttps://imechanica.org/crss/node/22765Interesting idea on stretchable - sculptures
https://imechanica.org/node/18118
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/437">video</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><iframe src="https://www.youtube.com/embed/yycrty8oOPA" frameborder="0" width="560" height="315"></iframe></p>
</div></div></div>Sat, 28 Mar 2015 18:34:33 +0000Wei Hong18118 at https://imechanica.orghttps://imechanica.org/node/18118#commentshttps://imechanica.org/crss/node/18118Mini-symposium "Computational mechanics of soft matter" on APCOM 2013
https://imechanica.org/node/14584
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3281">soft matter</a></div><div class="field-item odd"><a href="/taxonomy/term/5906">soft material</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Soft materials, such as polymers, foams, gels, granular materials, liquids, and colloids, as well as biological tissues, are known for their low stiffness against mechanical or multi-physics loads. Many of these materials are active: they respond to environmental stimuli in the form of large deformation. Engineering applications increasingly demand accurate way of characterizing and predicting of the multiphysics behaviors of these materials. With the focus on computational methodologies, this mini symposium aims at bringing together researchers working on mechanics of soft materials to exchange recent advances and to inspire new ideas.
</p>
<p>
Researchers are invited to present their recent work on but not limited to the following topics:
</p>
<ul><li>Theoretical models for soft matter.</li>
<li>Recent discoveries on soft materials and soft structures.</li>
<li>Computational methods for the large deformation and the multi-field coupling of soft matter.</li>
<li>Modeling and simulation of soft biological materials and tissues.</li>
<li>Theory and modeling of electro- and magneto-active soft mater.</li>
<li>New applications of soft matters.</li>
</ul><p>
The minisymposium will be held as a part of the <a href="http://www.apcom2013.org/index.html">5TH ASIA PACIFIC CONGRESS ON COMPUTATIONAL MECHANICS & 4TH INTERNATIONAL SYMPOSIUM ON COMPUTATIONAL MECHANICS</a> (APCOM 2013), and will be held on <strong>December 11-14, 2013 in Singapore</strong>.<br />
Please submit your abstract to the minisymposium by <strong>April 30, 2013</strong>.
</p>
<p>
All submissions should be sent to:
</p>
<p>
<a href="mailto:secretariat@apcom2013.org">secretariat@apcom2013.org</a><br />
The abstract (and/or paper) submission should include: <br />
1) "Abstract_template" (in Word documents), and <br />
2) "Abstract_submission_form" (in Excel document). <br />
Download template and submission form here:<br /><a href="uploads/3/1/1/5/3115594/abstract_template.doc">Abstract_template</a>; (To be submitted by 30 April 2013)<br /><a href="uploads/3/1/1/5/3115594/abstrat_submission_form.xls">Abstract_submission_form</a>; (To be submitted by 30 April 2013<br />
together with the Abstract)</p>
</div></div></div>Tue, 23 Apr 2013 19:39:28 +0000Wei Hong14584 at https://imechanica.orghttps://imechanica.org/node/14584#commentshttps://imechanica.org/crss/node/14584Mini-symposium “Fracture and Instabilities in Soft Materials” on ICF13
https://imechanica.org/node/13506
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
We are organizing a mini-symposium, "Fracture and Instabilities in Soft Materials", on the 13th International Conference on Fracture, which will be held during <strong>June 16-21, 2013</strong> in <strong>Beijing, China</strong>. We would like to invite you to submit an abstract on your recent research findings in related areas. The deadline for abstract submission has now been extended to <strong>October 31, 2012</strong>. Instructions on abstract submission can be found at <a href="http://www.icf13.org/"><strong>http://www.icf13.org/</strong></a>. The conference anouncement is at <a href="http://www.icf13.org/wordpress/wp-content/uploads/2012/08/final0830.pdf"><strong>http://www.icf13.org/wordpress/wp-content/uploads/2012/08/final0830.pdf</strong></a>.
</p>
<p>
Please submit your abstract to the <strong>mini-symposium</strong> <strong>no.12<br />
- Fracture and Instabilities in Soft Materials</strong>.
</p>
<p>
<strong>Mini-symposium description:</strong>
</p>
<p>
Soft materials are materials that deform easily under mechanical or multi-physics loads. Examples of soft materials are engineering materials such as polymers, foams, gels, granular materials, liquids, and colloids, as well as biological tissues. Many of these materials are active: they respond to environmental stimuli in the form of large deformation. Engineering applications of these materials increasingly demand mechanical reliability in addition to the active properties. The fundamental understanding on the failure mechanisms of soft materials, including but not limited to instability phenomena, damage, and fracture, has become an interesting and important topic. This mini symposium aims at bringing together researchers working on mechanics of soft materials to exchange recent advances and to inspire new ideas. Researchers are invited to present their recent work on but not limited to the following topics:
</p>
<ul class="unIndentedList"><li> Experimental and theoretical research on fracture of soft materials </li>
<li> Experimental and theoretical research on cavitation and other instability phenomena in soft solids and structures</li>
<li>Microstructure and damage evolution in soft materials </li>
<li> Development of new soft materials with superior mechanical/physical performance</li>
</ul><p>
Wei Hong<br />
Department of Aerospace Engineering<br />
Iowa State University
</p>
<p>
Oscar Lopez-Pamies<br />
Civil and Environmental Engineering<br />
University of Illinois at Urbana-Champaign
</p>
</div></div></div>Tue, 23 Oct 2012 21:50:27 +0000Wei Hong13506 at https://imechanica.orghttps://imechanica.org/node/13506#commentshttps://imechanica.org/crss/node/13506Journal Club Theme of September 2012: Fracture of polymeric gels
https://imechanica.org/node/13088
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/31">fracture</a></div><div class="field-item odd"><a href="/taxonomy/term/821">Journal Club Forum</a></div><div class="field-item even"><a href="/taxonomy/term/1265">gel</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
A polymeric gel consists of a polymer network swollen by small solvent molecules. It could be synthesized from a monomer solution through gelation or from a dry elastomer directly through swelling. The swelling capability attaches unique attributes to polymeric gels, such as 1) the extremely low stiffness, comparable to that of biological tissues, and 2) the coupling between deformation and solvent migration. However, swelling is also often accompanied with the reduction of both toughness and strength (Tsunoda 2000; Tanaka, 2000, Miquelard-Garnier, 2009), which could occur in gels obtained from either synthesis method. The fragility and weakness of gels hinder potential applications such as tissue replacement, tissue scaffold or as stimulus responsive material for sensors and actuators. In addition to promoting structural applications of gels, understand the fracture process of gels may also improve the handling and mouthfeel of many gel ingredients in foods (Lillfor, 2001; Foegeding, 2007) - an area less known to mechanical engineers. </p>
<p>Regular gels that are weak and brittle are often built upon a single type of polymer network. Some novel gels with modified network architecture show significant improve in strength, such as the double network gel (DN gel, Gong et al, 2003), the nano-composite gel (Haraguchi & Takisha, 2002), the topological gel (Mayumi & Ito, 2001), and the model network gel (Malkoch et al, 2006, Ossipov & Hilborun, 2006). This review aims to elucidate the current understanding of 1) the origin of fragility of simple gels 2) general toughening mechanisms of DN gel and nano-composite gel 3) the special role of swelling/diffusion coupling in fracture process of gels.
</p>
<p>
<strong>Swelling embrittlement<br /></strong>The rule of thumb for the strength requirement of polymeric gels in most biomedical applications is a level comparable to the load carrying capacity of nature tissues. For example, cartilage (Kempson 1982), aortic wall (Mohan & Melvin, 1982) and skin (Edwards & Marks 1995), could carry a load on the order of 10 MPa. However, the strength of a gel is usually dependent on the loading condition, sample geometry, and constraints, and thus may not be an objective measure.<br />
The failure mechanisms of gels vary from localized flow (Moller, et al 2008), softening and yielding (Na et al, 2006; Webber et al 2007; Haraguchi 2006), cavitation (Kundo and Crosby, 2009), to fracture (Tanaka, 2000). If we limit the discussion to the macroscopic propagating cracks (with a length scale much larger than the mesh size of the polymer network), a suitable characteristic quantity is the fracture energy, namely the energy required to create unit area of fresh crack face.<br />
To understand the reduction of fracture energy due to swelling, let us start from a generic conceptual picture: a mixture consists of homogeneous rubbery network with a viscous liquid. The cohesion of the material is provided solely from the polymer network, and a crack propagates by scissoring the polymer chains along its path. Besides a small amount of the excess energy of the surface itself, the fracture energy is mainly composed of two dissipation mechanisms. Firstly the energy of stretching an entire polymer chain to its elastic limit is dissipated irreversibly after subsequent chain rupture (Lake & Thomas 1967). Its magnitude is typically ~50 J/m2, and is often referred to as the intrinsic fracture energy. For dry polymers, the second means of dissipation is crystallization and viscoelastic dissipation of the highly stretched polymer network in front of crack tip due to interaction between closely packed chain strands, which is strongly rate dependent with the magnitude ranging from 0 to 105 J/m2 (Gent, 1996). The effect of this dissipation mechanism diminishes in a swollen gel when chains are diluted, and the fracture energy is shown to be strongly correlated with the dynamic loss modulus of a swollen elastomer (Tsunoda et al, 2000). At the high swelling limit (low elastomer fraction), the fracture energy becomes almost rate independent and reduced to the intrinsic fracture energy (Tsunoda et al, 2000; Tanaka 2007). The effect of dilution of chain density due to swelling could be easily corrected by converting the fracture energy into a value measured with respect to the corresponding area in the dry state.
</p>
<p>
<br /><strong>Toughening of novel gels through distributed damage</strong><br />
Although simple polymer network tend to become very brittle when swollen, it has been demonstrated that by modifying the molecular and micro- structure of a gel, the deformation and energy dissipation mechanism could be changed, and the toughness may be increased by orders of magnitude (Tanaka et al, 2005; Lin et al 2010). The toughening mechanism in two tough gels, the DN gel and the nano-composite gel, are explained from a multi-scale perspective. <br />
A DN gel consists of interpenetration networks of a highly extended 1st network of crosslinked polyelectrolyte, and a coiled 2nd network of neutral chains (Gong et al, 2003). The 1st network ruptures with microcracks prior to the 2nd network at finite deformation. Under an increasing deformation, the multiplication of microcracks or damage in 1st network proceeds stably, while the 2nd network remains almost intact, due to the double network topology, even after the 1st network has been shattered into small islands with percolated microcracks (Nakajima et al, 2008). Recently, a new type of DN gel is developed with the 1st network crosslinked by reversible ionic crosslinks (Sun et al,2012). This new DN gel achieves a much higher toughness and has a self-healing capability due to the reforming of the ionic crosslinks. A nano-composite gel undergoes a different damage process. A nano-composite gel consists of a swollen single network imbedded with nano-clay particles (Haraguchi & Takehisha, 2002). The polymer chains absorb and form physical bonds with clay particle, i.e. the clay acts as weak physical crosslinking points attached with a large amount of short chains, and breaks easily before the final failure of the main backbone (Nishida et al 2009). A signature for the damage of stress-active chains in the network for both materials is the significant hysteresis and softening in simple mechanical tests such uniaxial tension and compression (Webber et al, 2007; Zhu et al, 2006; Xiong et al 2008). Both materials are highly heterogeneous before and after damage. For example, the typical length scale for the island structure a damaged DN gel (Nakajima et al, 2008) (and other derivatives based on this structure such as micro-gel reinforced gels (Hu et al, 2012), and micro-voids reinforced gels ((Nakajima et al, 2011)) is on the order of microns, and the typical size of a nano-composite-reinforced gel is in the submicron region (Haraguchi et al, 2006).<br />
For the problem of an advancing macroscopic crack, the microstructural damage leads to the formation of an extended damage zone ahead of the crack tip. The fracture energy has the additional contribution from the dissipation in the damage zone. While the intrinsic fracture energy corresponds to the dissipation at a region of size comparable to merely the mesh size of polymer network (Lake & Thomas, 1967; Hui, 2003), the damage of sacrificial bonds occurs on a much larger length scale, typically several hundreds of microns, which has been observed directly under optical micro scope for double network gels (Yu et al, 2009; Liang et al, 2011). Thus comparing to the rupture a single layer of chains in a simple gel, the fracture energy is amplified by orders of magnitudes. <br />
The toughening effect is determined form the competing process of an extending damage zone against the propagation the actual crack. For a DN gel, it has been shown experimentally that the fracture energy increases with the average chain length of the 2nd network (Nakajima et al, 2009). On the other hand, it is also found that that the fracture energy could be further increased by increase the heterogeneity and weakening of the 1st network, which enables the formation of damage zone at lower strain (Nakajima et al, 2011). Simple models have been developed to relate the energy dissipation in the hysteresis of a simple test to that in the damage zone (Brown 2007; Tanaka 2007). The general mechanism of toughening in all these gels are the same: to sacrifice part of the gel structure (1st network, crosslinks, clay particles, etc) as much as possible in a stable way. The weaker the sacrifice, the larger the damage zone, the tougher the composite gel would be.
</p>
<p>
<br /><strong>Weakening effect of heterogeneity<br /></strong>A simple gel, even without any visible flaw, often breaks easily due to the large amount of defects and heterogeneities in the network, especially for those formed by regular gelation methods such as radical polymerization (Cohen et al,1992; Ikkai & Shibayama 2004). It is found that the magnitude of heterogeneity tends to be amplified by swelling or deformation (Mendes et al, 1996; Basu et al, 2011, Shibayama 2011), which eventually leads to the formation of microcracks. <br />
On the other hand, both the topological network defect and heterogeneous crosslinking problem could be avoided by producing a nearly-homogeneous network using methods such as ‘click chemistry' (Malkoch et al, 2006, Ossipov & Hilborun, 2006), and combining star polymers of the same size (Sakia et al, 2008). Alternatively, one can also enable the network crosslinking point to slide with deformation by producing a ‘topological gel'. Both types of gels could survive much larger stretch than a regular single gel, to almost the ultimate stretch of each chain. These homogeneous gels are, however, not much tougher, and are expected to fracture at a much lower stretch when a notch in the geometry is present.
</p>
<p>
<br /><strong>Effect of solvent </strong><br />
The effect of the solvent and solvent-network interactions to the strength and toughness of gels is relatively less studied. Firstly, solvent may induce a frictional drag on the polymer chains, especially for those dangling chains formed during damage. Secondly, the highly concentrated hydrostatic tension near a crack tip lower the local solvent chemical potential, and causes a converging solvent flow (Wang & Hong, 2012). Despite the diffusional origin of the second effect, the redistribution of solvent takes as short as milliseconds near a microcrack. While the first effect generally stabilizes the fracture process, the second softens the crack tip and promotes fracture (at constant load).<br />
Experiments on highly viscous physical gel has shown that the wetting of propagating crack in dry air could lead to a decrease in fracture energy (Baumberger et al, 2006), increase in propagation velocity of steady state cracks (Baumberger & Ronsin, 2009, 2010), and the initiation of secondary cracks (Baumberger & Ronsin, 2010). Simple analytical model shows that these effects are partly due to the stress-assisted dissociation of physical crosslinks, and the friction between polymer chains and solvent (Baumberger & Ronsin, 2009). While solvent friction is also present in a permanently crosslinked gel (Tanaka et al, 2000), similar observation has not been reported on chemical gels. <br />
The effect of solvent on a weak simple gel may seem minor. However, it could lead to a large improvement on the performance of tough gels by stabilizing crack propagation and increase the damage-zone size. For example, it has been shown that by increasing the viscosity of the swelling medium, the fracture energy of a DN gel could be further improved (Liang et al, 2012).
</p>
<p>
<br /><strong>References<br /></strong>A. Basu, Q. Wen, X. Mao, T. C. Lubensky, P. A. Janmey, A. G. Yodh, Nonaffine displacement in flexible polymer networks, Macromolecules 44, 1671 (2011).<br />
T. Baumberger and O. Ronsin, From thermally activated to viscosity controlled fracture of biopolymer hydrogels, J. Chem. Phys. 130, 061102 (2009).<br />
T. Baumberger and O. Ronsin, A convective instability mechanism for quasistatic crack branching in a hydrogel, Eur. Phys. J. E 31, 51 (2010).<br />
T. Baumberger, C. Caroli, D. Martina, Solvent control of crack dynamics in a reversible hydrogel. Nature Mater. 5, 552 (2006).<br />
H. R. Brown, A model of the fracture of double network gels. Macromolecule.s 40, 3815 (2007).<br />
C. Edwards, R. Marks, Evaluation of biomechanical properties of human skin. Clin. Dermatol. 13, 375 (1995). <br />
Y. Cohen, O. Ramon, I. J. Kopelman, S. Mizrahi, Characterisation of inhomogeneous polyacrylamide hydrogels. J. Polym. Sci., B, Polym.Phys. 30, 1055 (1992). <br />
E. A. Foegeding, Rheology and sensory texture of biopolymer gels. Curr. Opin Colloid. In. 12, 242 (2007).<br />
A. N. Gent, Adhesion and Strength of Viscoelastic Solids. Is There a Relationship between Adhesion and Bulk Properties? Langmuir 12, 4492 (1996).<br />
J. P. Gong, Y. Katsuyama, T. Kurokawa, Y. Osada, Double network hydrogels with extremely high mechanical strength. Adv. Mater. 15, 1155 (2003). <br />
K. A. Grosch, The effect of low-viscosity swelling liquid on the tensile strength of rubber. J. Appl. Polym. Sci. 12, 915-937 (1968).<br />
K. Haraguchi, T. Takehisa, Nanocomposite hydrogels: a unique organic-inorganic network structure with extraordinary mechanical, optical, and swelling/de-swelling properties. Adv. Mater. 14, 1120-1124, (2002).<br />
K. Haraguchi, M. Ebato, T. Takehis, Polymer-Clay Nanocomposites Exhibiting Abnormal Necking Phenomena Accompanied by Extremely Large Reversible Elongations and Excellent Transparency. Adv. Mater.18, 2250 (2006).<br />
J. Hu, T. Kurokawa, K. Hiwatashi, T. Nakajima, Z. L. Wu, S. M. Liang, J. P. Gong, Structure Optimization and Mechanical Model for Microgel-Reinforced Hydrogels with High Strength and Toughness. Macromolecules. 45, 5218 (2012). <br />
C. -Y. Hui, A. Jagota, S. J Bennison and J. D. Londono, Crack blunting and the strength of soft elastic solids, Proc. R. Soc. Lond. A 459, 1489-1516 (2003)<br />
F. Ikkai, M. Shibayamma, Inhomogeneity control in polymer gels. J. Polym. Sci. B 43, 617 (2005).<br />
G. E. Kempson, Relationship between the tensile properties of articular cartilage from the human knee and age. Ann. Rheum. Dis. 41, 508 (1982).<br />
S. Kunku, A. J. Crosby, Cavitation and fracture behavior of polyacrylamide hydrogels. Soft Matter 5, 3963 (2009).<br />
G. J. Lake, A. G. Thomas, The strength of highly elastic materials. Proc. Roy. Soc. A 300, 108 (1967).
</p>
<p>
S. Liang, Z. L. Wu, J. Hu, T. Kurokawa, Q. M. Yu, J. P. Gong, Direct observation on the surface fracture of ultrathin film double-network hydrogels. Macromolecules 44, 3016-3020 (2011).<br />
S. Liang, Z. L. Wu, J. Hu, T. Kurokawa, J. P. Gong, Toughness Enhancement and Stick-Slip Tearing of Double-Network Hydrogels in Poly(ethylene glycol) Solution. Macromolecules 45, 4758 (2012)<br />
P. J. Lillford, Mechanics of fracture in foods. J. Texture Stud. 32, 397 (2001).<br />
W. Lin, W. Fan, A. Marcellan, D. Hourdet, C. Creton, Large Strain and Fracture Properties of Poly(dimethylacrylamide)/Silica Hybrid Hydrogels. Macromolecules 43, 2554 (2010).<br />
M. Malkoch, R. Vestberg, N. Gupta, L. Mespouille, P. Dubois, A. F. Mason, J. L. Hedrick, Q. Liao, C. W. Frank, K. Kingsbury, C. J. Hawker, Synthesis of well-defined hydrogel networks using click chemistry. Chem. Commun. 2774 (2006). <br />
K. Mayumi, K. Ito, The Polyrotaxane Gel: A Topological Gel by Figure-of-Eight Cross-links. Adv. Mater. 13, 485 (2001).<br />
E. Mendes, R. Oeser, C. Hayes, F. Boue, J. Bastide, Small-Angle Neutron Scattering Study of Swollen Elongated Gels: Butterfly Patterns. Macromolecules. 29, 5547 (1996).<br />
G. Miquelard-Garnier, D. Hourdet, C. Creton, Large strain behaviour of nanostructured polyelectrolyte hydrogels. Polymer 50, 481 (2009).<br />
D. Mohan, J. W. Melvin, Failure properties of passive human aortic tissue I - uniaxial tension tests. J. Biomech. 15, 887 (1982).<br />
P. C. F. Moller, S. Rodts, M. A. J. Michels. D. Bonn, Shear banding and yield stress in soft glassy materials. Phys. Rev. E. 77, 041507 (2008).<br />
Y. Na, Y. Tanaka, Y. Kawauchi, H. Furukawa, T. Sumiyoshi, J. P. Gong, Y. Osada, Necking Phenomenon of Double-Network Gels. Macromolecules. 39, 4641 (2006).<br />
T. Nakajima, H. Furukawa, Y. Tanaka, T. Kurokawa, Y. Osada, J. P. Gong, True chemical structure of double network hydrogels. Macromolecules. 42, 2184 (2009). <br />
T. Nakajima, H. Furukawa, Y. Tanaka, T. Kurokawa, J. P. Gong, Effect of Void Structure on the Toughness of Double Network Hydrogels. J. Polym. Sci. B. 49, 1246 (2011).<br />
T. Nishida, H. Endo, N. Osaka, H. Li, K. Karaguchi, M. Shibayama, Deformation mechanism of nanocomposite gels studied by contrast variation small-angle neutron scattering. Phys. Rev. E 80, 030801 (2009).<br />
D. A. Ossipov, J. Hilborun, Poly(vinyl alcohol)-Based Hydrogels Formed by "Click Chemistry". Macromolecules. 39, 1709 (2006).<br />
T. Sakai, T. Matsunaga, Y. Yamamoto, C. Ito, R. Yoshida, S. Suzuki, N. Sasaki, M. Shibayama, U.-i. Chung, Design and fabrication of a high-strength hydrogel with ideally homogeneous network structure from tetrahedron-like macromonomers. Macromolecules 41,5379 (2008). <br />
M. Shibayama, Small-angle neutron scattering on polymer gels: phase behavior, inhomogeneities and deformation mechanisms. Polym. J. 43, 18 (2011).<br />
Jeong-Yun Sun, Xuanhe Zhao, Widusha R.K. Illeperuma, Kyu Hwan Oh, David J. Mooney, Joost J.Vlassak, Zhigang Suo, Highly stretchable and tough hydrogels. Nature. 489, 133 (2012).<br />
K. Tsunoda, J. J. C. Busfield, K. L. Davies, A. G. Thomas, Effect of materials variables on the tear behavior of a non-crystallising elastomer. J. Mater. Sci. 35, 5187 (2000).
</p>
<p>
Y. Tanaka, K, Fukao, Y. Miyamoto, Fracture energy of gels. Eur. Phys. Lett. E. 3, 395 (2000).<br />
Y. Tanaka, R. Kuwabara, Y.-H. Na, T. Kurokawa, J. P. Gong, Y. Osada, Determination of fracture energy of high strength double network hydrogels. J. Phys. Chem. B 109, 11559 (2005). <br />
Y. Tanaka, A local damage model for anomalous high toughness of double-network gels. Eur. phys. Lett. 78, 56005 (2007). <br />
X. Wang, W. Hong, Delayed Fracture in gels. Soft Matter. 8, 8171 (2012).<br />
R. E. Webber, C. Creton, H. R. Brown, J. P. Gong, Large strain hysteresis and Mullins effect of Ttough Double-Network hydrogels . Macromolecules. 40, 2919 (2007).<br />
Q. Wen, A Basu, P. A. Janmey, A. G. Yodh, Non-affine deformation in polymer gels. Soft Matter 8, 8039 (2012).<br />
Q. M. Yu, Y. Tanaka, H. Furukawa, T. Kurokawa, J. P. Gong, Direct observation of damage zone around crack tips in double-network gels. Macromolecules. 42, 3852 (2009). <br />
M. Zhu, Y. Liu, B. Sun, W. Zhang, X. Liu, H. Yu, Y. Zhang, D. Kuckling, H. P. Adler, A novel highly resilient nanocomposite hydrogel with low hysteresis and ultrahigh elongation. Macromolucles. 27, 1023 (2006).
</p>
</div></div></div>Thu, 06 Sep 2012 14:20:09 +0000Wei Hong13088 at https://imechanica.orghttps://imechanica.org/node/13088#commentshttps://imechanica.org/crss/node/13088Modeling mechano-chromatic lamellar gels
https://imechanica.org/node/11637
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1099">hydrogel</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div><div class="field-item even"><a href="/taxonomy/term/6973">photonic gel</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Consisting of alternating swelling and nonswelling polymeric layers (SLs and NLs), lamellar gels are 1D photonic crystals with tunable optical properties. The lamellar structure induces a constraint between the SLs and the NLs, resulting in an anisotropic swelling behavior coupled with deformation. The coupling gives rise to the mechano-chromatic effect, and quantitative understanding of it is the key to many applications. This letter formulates a nonlinear continuum model for lamellar gels by considering the constrained swelling of SLs and the anisotropic deformation in both types of layers. A finite-element method is further developed to simulate the response to non-uniform deformation.</p>
</div></div></div>Wed, 28 Dec 2011 21:05:01 +0000Wei Hong11637 at https://imechanica.orghttps://imechanica.org/node/11637#commentshttps://imechanica.org/crss/node/11637Multiple Faculty Openings at Iowa State University
https://imechanica.org/node/11137
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3194">tenure-track</a></div><div class="field-item odd"><a href="/taxonomy/term/4457">Aerospace engineering</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
The Department of Aerospace Engineering at Iowa State University (<a href="http://www.aere.iastate.edu/">www.aere.iastate.edu</a>) invites applicants for faculty positions in each of the broad areas of Computational Propulsion, Thermal Management & Heat Transfer, and Experimental Robotics & Autonomous Aerospace Systems. Applications are sought for tenured and tenuretrack appointments at the level of Assistant or Associate Professor, and exceptional candidates who qualify for the rank of Full Professor may also be considered for the Dennis and Rebecca Muilenburg Chair in Aerospace Engineering.
</p>
<p>
Iowa State University is a comprehensive, land grant, Carnegie Doctoral/Research Extensive University with an enrollment of over 28,000 students. The College of Engineering comprises 8 departments, with 221 faculty members and annual research expenditures exceeding $75 million. Iowa State's nearly 2000 acre, park-like<br />
campus is located in Ames, Iowa, consistently ranked within the top ten livable small cities in the nation.
</p>
<p>
An earned Ph.D. or equivalent terminal degree in Aerospace Engineering or a closely related field is required at the start date of employment. Underrepresented minorities and women are strongly encouraged to apply. Candidates at the level of Associate or Full Professor must demonstrate a strong record as evidenced by a quality research program, publications, professional recognitions and extramural funding.
</p>
<p>
The Aerospace Engineering Department currently has 23 faculty and is housed in a $50 million state-of-the-art teaching and research complex. The successful applicant will participate in all aspects of the department’s mission, including developing a strong externally funded research program, teaching and supervising students at the undergraduate and graduate levels, and engaging in service to the university.
</p>
<p>
All offers of employment, oral and written, are contingent upon the university’s verification of credentials and other information required by federal and state law, ISU policies/procedures, and may include the completion of a background check. Iowa State University is an Equal Opportunity/Affirmative Action Employer with NSF<br />
ADVANCE funding to broaden the participation of women and underrepresented minorities and enhance the success of all faculty in STEM fields.
</p>
<p>
All interested, qualified persons must apply for this position online by visiting <a href="http://www.iastatejobs.com/">www.iastatejobs.com</a>. Please refer to vacancy #110837 for Computational Propulsion, vacancy #110840 for Thermal Management & Heat Transfer, or vacancy #110839 for Experimental Robotics & Autonomous Aerospace Systems. Please be prepared to enter or attach the following:<br />
1) A detailed resume<br />
2) A concise statement of research plans & teaching interests<br />
3) Full contact information for three references
</p>
<p>
Interested candidates are encouraged to apply early, with review of applications beginning on November 15, 2011. To assure full consideration, applications must be received by December 31, 2011. Review of applications after this date will continue until the positions are filled.
</p>
<p>
Inquiries regarding the faculty search should be directed to Professors Paul Durbin (Computational Propulsion) <a href="mailto:durbin@iastate.edu">durbin@iastate.edu</a>, Alric Rothmayer (Thermal Management and Heat Transfer) <a href="mailto:roth@iastate.edu">roth@iastate.edu</a> or Ashraf Bastawros (Experimental Robotics & Autonomous Aerospace Systems) <a href="mailto:bastaw@iastate.edu">bastaw@iastate.edu</a>. If you have questions regarding this application process, please email <a href="mailto:employment@iastate.edu">employment@iastate.edu</a> or call 515-294-4800 or Toll Free: 1-877-477-7485.
</p>
<p>
Iowa State University does not discriminate on the basis of race, color, age, religion, national origin, sexual orientation, gender identity, genetic information, sex, marital status, disability, or status as a U.S. veteran. Inquiries can be directed to the Director of Equal Opportunity and Compliance, 3280 Beardshear Hall, (515) 294-7612.
</p>
</div></div></div>Sat, 24 Sep 2011 16:11:24 +0000Wei Hong11137 at https://imechanica.orghttps://imechanica.org/node/11137#commentshttps://imechanica.org/crss/node/11137Tenure-Track Faculty Position in Iowa State University
https://imechanica.org/node/9612
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/127">Faculty Position</a></div><div class="field-item odd"><a href="/taxonomy/term/4457">Aerospace engineering</a></div><div class="field-item even"><a href="/taxonomy/term/4860">Iowa State University</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>TENURE-TRACK FACULTY POSITION: The Department of Aerospace Engineering at Iowa State University invites applicants for a faculty position in the area of autonomous space systems. The appointment will start in August 2011. The search is focused at the Assistant and Associate Professor level, but exceptional candidates who qualify for the rank of Full Professor will also be considered. The primary research interests include robotic and human space exploration, on-board autonomy, and space systems analysis, with background in the disciplines of adaptive guidance and control, navigation, and space flight mechanics. A balanced research program with a strong experimental interest is desirable. An earned Ph.D. or equivalent terminal degree in Aerospace Engineering or closely related field is required at the start date of employment. Underrepresented minorities and women are strongly encouraged to apply. Candidates at the level of Associate or Full Professor must demonstrate a strong record as evidenced by a quality research program, publications, professional recognitions and extramural funding. The successful applicant will be participating in all aspects of the department’s mission, including developing a strong externally funded research program, teaching and supervising students at the undergraduate and graduate levels, and participation in service to the university.<br />
The Aerospace Engineering Department currently has 23 faculty. The department is housed in a $50 million state-of-the-art teaching and research complex. Potential applicants are invited to view the department website at <a href="http://www.aere.iastate.edu/">http://www.aere.iastate.edu/</a>. Questions regarding the position may be directed to Prof. Ping Lu at <a href="mailto:plu@iastate.edu">plu@iastate.edu</a>.<br />
All offers of employment, oral and written, are contingent upon the university’s verification of credentials and other information required by federal and state law, ISU policies/procedures, and may include the completion of a background check.<br />
All interested, qualified persons must apply for this position online at:<br /><a href="http://www.iastatejobs.com/">www.iastatejobs.com</a><br />
Please refer to vacancy id# 100876<br />
Please be prepared to enter or attach the following:<br />
1) A detailed resume<br />
2) A concise statement of research plans & teaching interests<br />
3) Full contact information for three references<br />
Review of applications will begin March 15, 2011 and will continue until the position is filled.<br />
Iowa State University is an Equal Opportunity/Affirmative Action Employer with NSF ADVANCE funding to broaden the participation of women and underrepresented minorities and enhance the success of all faculty in STEM fields.</p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/ISU%20Faculty%20Position%202011.pdf" type="application/pdf; length=166038" title="ISU Faculty Position 2011.pdf">ISU Faculty Position 2011.pdf</a></span></td><td>162.15 KB</td> </tr>
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</div></div></div>Wed, 12 Jan 2011 16:33:12 +0000Wei Hong9612 at https://imechanica.orghttps://imechanica.org/node/9612#commentshttps://imechanica.org/crss/node/9612Modeling Viscoelastic Dielectrics
https://imechanica.org/node/8551
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/795">viscoelasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/992">dielectric elastomer</a></div><div class="field-item even"><a href="/taxonomy/term/4112">hong group research</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Dielectric elastomer, as an important category of electroactive polymers, is known to have viscoelastic properties that strongly affect its dynamic performance and limit its application. Very few models accounting for the effects of both electrostatics and viscoelasticity exist in the literature, and even fewer are capable of making reliable predictions under general loads and constraints. Based on the principals of nonequilibrium thermodynamics, this paper develops a field theory that fully couples the large inelastic deformations and electric fields in deformable dielectrics. Our theory recovers existing models of elastic dielectrics in the equilibrium limit. This paper proposes, in a general nonequilibrium state, the mechanism of instantaneous instability which corresponds to the pull-in instability often observed on dielectric elastomers. Most finite-deformation constitutive relations and evolution laws of viscoelastic solids can be directly adopted in the current theoretical framework. As an example, a specific material model is selected and applied to the uniform deformation of a dielectric elastomer. This model predicts the stability criteria of viscoelastic dielectrics and its dependence on loading rate and the effect of pre-stress and relaxation. The dynamic response and the hysteresis behavior of a viscoelastic dielectric elastomer under cyclic electric fields are also studied.</p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
<tbody>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Viscoelastic_Dielectric.pdf" type="application/pdf; length=320369" title="Viscoelastic_Dielectric.pdf">Viscoelastic_Dielectric.pdf</a></span></td><td>312.86 KB</td> </tr>
</tbody>
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</div></div></div>Wed, 14 Jul 2010 21:02:14 +0000Wei Hong8551 at https://imechanica.orghttps://imechanica.org/node/8551#commentshttps://imechanica.org/crss/node/8551JClub July 2010: Mechanics of Ionic Polymer Metal Composites
https://imechanica.org/node/8493
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/821">Journal Club Forum</a></div><div class="field-item odd"><a href="/taxonomy/term/1099">hydrogel</a></div><div class="field-item even"><a href="/taxonomy/term/5363">IPMC</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Ionic polymer-metal composite (IPMC) is a polyelectrolyte (usually Nafion or Femion swollen by simple salt solution) strip or membrane with both sides plated with metal electrodes. It is a particular design of electroactive-polymer device rather than a new class of material. When a voltage is applied between its electrodes, it will bend toward either electrode depending on the polarity (anode for a negatively charged gel), and the magnitude of deformation could be controlled by the electric signal. <span> </span>Reversely, the deformation of an IPMC can generate electric signal or even energy output [<a href="/node/8493/blog#1">1</a>-<a href="/node/8493#4">4</a>]. <span> </span>Therefore IPMC has recently becomes a hot topic in actuation, sensor and energy harvesting applications, especially when integrated with the characteristics of certain gels that are responsive to other environmental stimuli such as pH value or temperature.
</p>
<p class="MsoNormal">
Compared to traditional actuation devices, the IPMC is small, simple, low-cost, resilient, noise-free, biocompatible, works at low voltage and capable of large deformation [<a href="/node/8493#a">a</a>]. <span> </span>However, it also suffers from several problems: its actuation response is non-linear and also followed by non-controllable relaxation, its response is relatively slow, its working voltage is limited by the electrolysis of swelling media, its performance deteriorates in the long term as swelling media evaporates, its operation is time and history dependent, and so on [<a href="/node/8493#5">5</a>, <a href="/node/8493#6">6</a>]. <span> </span>There have been numerous experimental efforts to overcome these problems by changing the swelling media or modifying the structures of polymer matrix and electrodes [<a href="/node/8493#7">7</a>-<a href="/node/8493#10">10</a>].
</p>
<p> </p>
<p class="MsoNormal">
On the other hand, the underlying mechanism of IPMCs has yet to be fully understood. <span> </span>Deformation theories of polyelectrolyte gel [<a href="/node/8493#b">b</a>] were initiated almost at the same time as when Oguro published his first design of IPMC [<a href="/node/8493#11">11</a>]. <span> </span>By using the same frame work, equilibrium and kinetics of bending of IPMC was then calculated [<a href="/node/8493#12">12</a>, <a href="/node/8493#13">13</a>]. <span> </span>It is suggested that free ions drift under electric field, the concentration gradient creates osmotic pressure difference that drives the gel to bend, which is balanced by the elastic resistance of the matrix, while the kinetics is formulated by phenomenological law of porelasticity and diffusion rather than viscoelasticity [<a href="/node/8493#c">c</a>]. <span> </span>Later another stress part is added to include the collective behavior of fixed charges [<a href="/node/8493#14">14</a>-<a href="/node/8493#17">17</a>]. <span> </span>A detail model of this stress is presented for Nafion by Nemat-Nasser [<a href="/node/8493#18">18</a>], who assumes that Nafion contains solution clusters and a hydrophilic polymer matrix, with the detailed morphology determined by the level of hydration, as suggested by materials models [<a href="/node/8493#19">19</a>, <a href="node/8493/edit#20">20</a>]. <span> </span>A double layer of ions forms at phase boundary where the electro-static interaction of the ordered polarized results in a net excess pressure. <span> </span>Although the essential microstructural features are captured, more assumptions have to be made in order to incorporate this effect in the general framework of continuum theory.
</p>
<p> </p>
<p class="MsoNormal">
A nonlinear field theory for polyelectrolyte gels recently proposed [<a href="/node/8493#21">21</a>] provides a way of describing the deformation and electrochemistry of polyelectrolyte gels.<span> </span>The theory suggests that the equilibrium behavior of a polyelectrolyte gel is fully determined by its free-energy density, as a function of strain, electric displacement, and concentration of mobile species.<span> </span>The concept of osmotic pressure, which has often been used without a physical definition [<a href="/node/8493#22">22</a>, <a href="/node/8493#d">d</a>], is introduced as a Lagrange multiplier for the incompressibility constraint. <span> </span>The equations that govern the evolution of polyelectrolyte gels in a nonequilibrium state are formulated, based on the conservation law of all mobile species and the kinetic equations that relates the diffusion flux of mobile species to its driving force, the gradient of the chemical potential.<span> </span>A self-consistent model shall have the chemical potential derived from the free-energy function as well, containing contributions from the elasticity of the polymer, the concentration of mobile species, and the electric field.<span> </span>If specific combinations of the free-energy function and the kinetic laws are chosen, one could recover the Nernst-Planck equation, an evolution equation often used in various models [<a href="/node/8493#15">15</a>, <a href="/node/8493#16">16</a>].<span> </span>Clearly, a gap exists between the microstructure of the material and its free-energy function / kinetic law.<span> </span>The following questions may need to be answered before we can fill in this gap in theoretical understanding.
</p>
<p> <strong>1. The effect of the microstructure and thickness of the electrodes/interfaces</strong> </p>
<p class="MsoNormal">
One of the important conclusions by existing models is that there is an ion-depletion region near the electrode and the deformation is determined by this boundary layer [<a href="/node/8493#18">18</a>]. <span> </span>However, most models simply assume a sharp interface between electrode and polymer matrix. <span> </span>Under such an assumption, in an equilibrium or steady state, the physical laws and a simple dimensional analysis will lead to a result that the bulk of a gel is electroneutral except for the boundary layer, characterized by the Debye length.<span> </span>While an 1D analysis can estimate a bending moment induced by the ultra high stress in the thin boundary layer, 3D continuum mechanics indicates that a surface compressive stress may rather cause surface instabilities such as wrinkle and crease.<span> </span>On the other hand, an effective IPMC design actually needs the electrode metal particles to infiltrate into polymer matrix, and experiments also suggest a strong correlation between the actuation strain and the morphology and thickness of electrodes [<a href="/node/8493#23">23</a>, <a href="/node/8493#24">24</a>]. It is possible that the energy is majorly stored in the “vague” electrode-polymer interface, or the microstructured electrode with finite thickness, rather than in the thin boundary layer between the polyelectrolyte and a mathematically sharp interface?
</p>
<p> <strong>2. Are the basic laws of electrostatics still valid in an electrolyte-metal composite?</strong> </p>
<p class="MsoNormal">
In most existing models of IMPC, the governing equation for the electric field, namely the Poisson-Boltzmann equation, is derived from the Gauss’s law of electrostatics.<span> </span>A homogeneous polyelectrolyte mixture is sometimes treated as a dielectric medium when all charged particles are excluded [<a href="/node/8493#21">21</a>].<span> </span>However, for a material with microstructures of various length scales, the validity of such an assumption has never been discussed.<span> </span>For example, the mixture of metal, polyelectrolyte, and ionic solution at the interfaces, which seems to play an important role, turns out to be a medium that is both an electric conductor and an ionic conductor.<span> </span>Even for the case when the structure is random, a proper way of homogenization is a challenge.<span> </span>Other examples include the microporous structure of Nafion, in which the mobile charges are distributed in order, and the distribution interacts with the macroscopic electric field.
</p>
<p> <strong>3. The origin and mechanism of the electrostatic and ionic contributions to force/stress</strong> </p>
<p class="MsoNormal">
The definition and notation of electrostatic forces in solids have always been controversial, as commented by Zhigang in <a href="node/635" target="_blank">his paper</a> on deformable dielectrics.<span> </span>In a system containing dielectric polymer and solvent, mobile and immobile ions, and even electronic conductors, the “force” or “stress” in a continuum mechanics manner is even hard to imagine.<span> </span>Maybe one should rather avoid ambiguous terms like force and stress.<span> </span>A question that arises naturally is how the charges carried by the polymer network and the mobile ions interact with each other and with external field, and further affect the system as a whole.<span> </span>The answers to such a question have impacts much broader than just calculating the bending of a polymer strip. <span> </span>For example, biological tissues are materials of similar or more complex structures.<span> </span>Qualitatively, it has been argued that the main contributions include the electrostatic repulsions between fixed charges and the osmosis by the concentration difference of mobile ions in the solvent [<a href="/node/8493#25">25</a>].
</p>
<p class="MsoNormal">
An approach often used (e.g. in multiphasic theories) is the introduction of the chemical expansion stress [<a href="/node/8493#26">26</a>] or similarly the eigenstrain [<a href="/node/8493#e">e</a>], the thermodynamic validity of which is put into question recently [<a href="/node/8493#27">27</a>]. <span> </span>Another approach is the use of the Maxell stress in dielectrics through homogenizing the charge distribution.
</p>
<p class="MsoNormal">
Alternatively, one could start from the microstructure of the material and sum over all the ion-ion interactions, an approach similar to statistical physics or atomistic simulations [<a href="/node/8493#28">28</a>].<span> </span>However, similar as one calculating Maxwell stress, careful sum over all interaction pairs need to be performed, which also introduces the question of how microstructures (e.g. electric double layers) will evolve in response to the change in macroscopic fields.
</p>
<p> </p>
<p class="MsoNormal">
IPMC is not only interesting in application, but also one of the model systems of natural soft materials with tunable parameters. <span> </span>Modeling it may sever as the first step towards understanding the mechanics of soft matters.
</p>
<p> </p>
<p class="MsoNormal">
Key References:
</p>
<p class="MsoNormal">
[a<a name="a" title="a" id="a"></a>] <a href="http://iopscience.iop.org/0964-1726/10/4/327">M. Shahinpoor and K. J. Kim, “Ionic polymer-metal composite: I Fundamentals”, Smart Mater. Struct. <strong>10</strong>, 819 (2001)</a>
</p>
<p class="MsoNormal">
[b<a name="b" title="b" id="b"></a>] <a href="http://pubs.acs.org/doi/abs/10.1021/ma00046a058">M. Doi, M. Matsumoto and Y. Hirose, “Deformation of ionic polymeric gels by electric fields” J. Macrocol. <strong>20</strong>, 5504 (1992):</a>
</p>
<p class="MsoNormal">
[c<a name="c" title="c" id="c"></a>] <a href="http://www.unm.edu/~amri/electromechanical.pdf">P. G. deGennes, K. Okumura, M. Shahinpoor and K. J. Kim, “Mechanoelectric effects in ionic gels”, Europhys. Lett.<strong> 50</strong>(4) 513 (2000)</a>
</p>
<p class="MsoNormal">
[d<a name="d" title="d" id="d"></a>] <a href="http://iopscience.iop.org/0964-1726/3/3/012">M. Shahinpoor, “Continuum eletromechanics of ionic polymeric gels as artificial muscles for robtotic applications”, Smart. Mater. Struct. <strong>3</strong>, 367 (1994)</a>
</p>
<p class="MsoNormal">
[e<a name="e" title="e" id="e"></a>] <a href="http://jap.aip.org/japiau/v92/i5/p2899_s1">S. Nemat-Nasser, “Micromechanics of actuation of ionic polymer-metal composites”, J Appl Phys <strong>95</strong> (5): 2899 (2002)</a>
</p>
<p class="MsoNormal">
[f] <a href="http://iopscience.iop.org/0964-1726/12/1/308">K. J. Kim and M. Shahinpoor, “Ionic polymer-metal composite: II Manufacturing technique”, Smart Mater. Struct. <strong>12</strong>, 65 (2003)</a>
</p>
<p class="MsoNormal">
[g] <a href="http://iopscience.iop.org/0964-1726/13/6/009">M. Shahinpoor and K. J. Kim, “Ionic polymer-metal composite: III Modeling and simulations as biomemetic sensors, actuators, transducers and artificial muscles”, Smart Mater. Struct. <strong>10</strong>, 819 (2001)</a>
</p>
<p class="MsoNormal">
[h] <a href="http://iopscience.iop.org/0964-1726/14/1/020">M. Shahinpoor and K. J. Kim, “Ionic polymer-metal composite: IV industrial and medical applications”, Smart Mater. Struct. <strong>13</strong>, 1362 (2004)</a>
</p>
<p> </p>
<p class="MsoNormal">
Other References:
</p>
<p class="MsoNormal">
[1<a name="1" title="1" id="1"></a>] K. Asaka, K. Oguro, Y. Nishimura, M. Mizuhat and H. Takenaka, “Bending of polyelectrolyte membrane-platinum composites by electric stimuli I”, Polymer J. <strong>27</strong>(4) , 436 (1995)
</p>
<p class="MsoNormal">
[2] K. Sadeghipour, R. Salomon and S. Neogi, “Development of a novel electrochemically active membrane and smart material based vibration sensor/damper” Smart Mater. Struct. <strong>1</strong>, 172 (1992)
</p>
<p class="MsoNormal">
[3] M. Shahinpoor, Y. Bar-Cohen, J. O. Simpson and J. Smith, “Ionic polymer-metal composite as biomimetic sensors, actuators and artificial muscles – a review”, Smart Mater. Struct. <strong>7</strong>, 15 (1998)
</p>
<p class="MsoNormal">
[4<a name="4" title="4" id="4"></a>] M. Aureli, C. Prince, M. Porfiri and S. D. Peterson, “Energy harvesting from base excitation of ionic polymer metal composites in fluid environment”, Smart Mater Struct <strong>19</strong>, 015003 (2010)
</p>
<p class="MsoNormal">
[5<a name="5" title="5" id="5"></a>] Y. Bar-Cohen, S. Leary, A. Yavrouian, K. Oguro, S. Tadoro, J. Harrizion, J. Simith and J. Su, “Chanllenges to the application of IPMC as actuators of planerary mechanis”, Proc SPIE Smart Struc. Mater. Sympo. 3987-21 (2000)
</p>
<p class="MsoNormal">
[6<a name="6" title="6" id="6"></a>] X. Bao, Y. Bar-Cohen and S. Lih, “Measurements and macro models of ionomeric polymer-metal composties”, Proc. SPIE Smart Struc. Mater. Sympo. 4695-27 (2002)
</p>
<p class="MsoNormal">
[7<a name="7" title="7" id="7"></a>] S. Nemat-Nasser and Y. Wu, “Comparative experimental study of ionic polymer-metal composites with different backbone ionomer and in various cation forms”, J Appl. Phys. <strong>93</strong>(9), 5255 (2003)
</p>
<p class="MsoNormal">
[8] B. J. Akle, M. D. Bennett and D. J. Leo, “High-strain ionomeric ionic liquid electroactive actuators”, Sens. Actuators, A 126(1), <strong>173</strong> (2006)
</p>
<p class="MsoNormal">
[9] N. Kamamichi, M. Yamakita, T. Kozuki, K. Asaka and Z. W. Luo, “Doping effects on robotic system with ionic polymer-metal composite actuators”, Adv. Rob. 21(1-2), <strong>65</strong> (2007)
</p>
<p class="MsoNormal">
[10<a name="10" title="10" id="10"></a>] S. Liu, R. Montazami, Y. Liu, V. Jain, M. Lin, X. Zhou, J. R. Heflin, Q.M. Zhang, “Influence of the conductor network composites on the electromechanical performance of ionic polymer conductor network composite actuators”, Sensors and Actuators A <strong>157</strong>, 267 (2010)
</p>
<p class="MsoNormal">
[11<a name="11" title="11" id="11"></a>] K.Oguro, Y. Kawami and H. Takenaka, “Bending of an ion-conducting polymer film electrode composite by an electric stimulus at low voltage”, J. Micromachine SOC <strong>5</strong>, 27 (1992)
</p>
<p class="MsoNormal">
[12<a name="12" title="12" id="12"></a>] D. Segalman, W. Witkowski, D. Adolf, M. Shahinpoor, “Electrically-controlled polymeric gels as active materials in adaptive structures”, Smart Mater Struct <strong>1</strong>, 95 (1992)
</p>
<p class="MsoNormal">
[13<a name="13" title="13" id="13"></a>] M. Shahinpoor, “Continuum eletromechanics of ionic polymeric gels as artificial muscles for robtotic applications”, Smart. Mater. Struct. <strong>3</strong>, 367 (1994)
</p>
<p class="MsoNormal">
[14<a name="14" title="14" id="14"></a>] J. Firmrite, H. Struchtrup and N. Djilali, “Transport phenomena in polymer electrolyte membranes I medeling framework”, J Electrochem. SOC <strong>152</strong>(9), A1804 (2005)
</p>
<p class="MsoNormal">
[15<a name="15" title="15" id="15"></a>] R. Luo, H. Li and K. Y. Lam, “Modeling and simulation of chemo-electro-mechanical behavior of pH-electric-senstive hydrogel”, Anal. Bioanal. Chem. <strong>398</strong>, 863 (2007)
</p>
<p class="MsoNormal">
[16<a name="16" title="16" id="16"></a>] M. Porfiri, “Charge dynamics in ionic polymer metal composite”, J Appl Phys <strong>104</strong>, 104915 (2008)
</p>
<p class="MsoNormal">
[17<a name="17" title="17" id="17"></a>] T. Wallmersperger, A. Horstmann, B. Kroplin and D. J. Leo, “Thermodynamical modeling of the eletromechanical behavior of ionic polymer metal composites”, J Intell. Mater. Syst. Struct. <strong>20</strong>(6), 741 (2009)
</p>
<p class="MsoNormal">
[18<a name="18" title="18" id="18"></a>] S. Nemat-Nasser, “Micromechanics of actuation of ionic polymer-metal composites”, J Appl Phys <strong>95</strong> (5): 2899 (2002)
</p>
<p class="MsoNormal">
[19<a name="19" title="19" id="19"></a>] W. Y. Hsu and T. D. Gierke, “Elastic theory for ionic clustering in perfluorinated ionomers”, Macromol. <strong>15</strong>, 101 (1982)
</p>
<p class="MsoNormal">
[20<a name="20" title="20" id="20"></a>] K. A. Mauritz and R. B. Moor, “State of understanding of Nafion”, Chem. Rev. <strong>104</strong>, 4535 (2004)
</p>
<p class="MsoNormal">
[21<a name="21" title="21" id="21"></a>] W. Hong, X. Zhao, Z. Suo, “<a href="/node/5960" target="_blank"><span>Large deformation and electrochemistry of polyelectrolyte gels</span></a>” J Mech. Phys. Solids. <strong>58</strong>, 558-577 (2010).
</p>
<p class="MsoNormal">
[22<a name="22" title="22" id="22"></a>] P.J. Flory, in “Principles of polymer chemistry”, Ithaca, New York, Come11 University Press (1953)
</p>
<p class="MsoNormal">
[23<a name="23" title="23" id="23"></a>] N. Fujiwara, K. Asaka, Y. Nishimura, K. Oguro and E. Torikai, “Preparation of gold-solid polymer electrolyte composite as electric stimuli-responsive materials”, Chem. Mater. <strong>12</strong>, 1750 (2000)
</p>
<p class="MsoNormal">
[24<a name="24" title="24" id="24"></a>] K. Onishi, S. Sewa, K. Asaka, N. Fujiwara and K. Oguro, “Morphology of electrodes and bending response of the polymer electrolyte actuator”, Electrochimica Acta <strong>46</strong>, 737 (2000)
</p>
<p class="MsoNormal">
[25<a name="25" title="25" id="25"></a>] V. C. Mow and X. E. Guo, “Mechano-electrochemical properties of aritcular cartilage: their inhomogeities and anisotrpies”, Annu. Rev. Biomed. Eng. <strong>4</strong>, 175 (2002)
</p>
<p class="MsoNormal">
[26<a name="26" title="26" id="26"></a>] W. M. Lai, J. S. Hou and V. C. Mow, “A triphasic theory for the swelling and deformation behavior of articular cartilage”, J. Biomech. Engr. <strong>113</strong>, 245 (1991)
</p>
<p class="MsoNormal">
[27<a name="27" title="27" id="27"></a>] J. H. Huyghe and W. Wilson, “On the thermodynamical admissibility of the triphasical theory of charged hydrated tissues”, J Biomech. Engr.<strong> 131</strong>, 044504 (2009)
</p>
<p class="MsoNormal">
[28<a name="28" title="28" id="28"></a>] S. A. Rice and N Nagasawa, in “Polyelectrolyte solution, a theoretical introduction”, Academic Press, New York (1961)
</p>
<p>
This review is completed with the help of Xiao Wang.
</p>
</div></div></div>Thu, 01 Jul 2010 21:19:42 +0000Wei Hong8493 at https://imechanica.orghttps://imechanica.org/node/8493#commentshttps://imechanica.org/crss/node/8493SES 2010 Annual Technical Meeting - Call for Papers
https://imechanica.org/node/7938
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/4859">SES 2010</a></div><div class="field-item odd"><a href="/taxonomy/term/4860">Iowa State University</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.
</p>
<p>
Now the conference is open to abstract submission. Please visit the <a href="http://www.ucs.iastate.edu/mnet/ses2010/home.html" target="_blank">conference website</a> and submit your abstract online. The deadline for submitting your abstract is Friday, May 7, at 5pm (CST).
</p>
<p>
<strong>AWARDS SYMPOSIA</strong>
</p>
<ul><li>
<p> A symposia in honor of the contribution of Ray Ogden, the recipient of Prager Medal </p>
</li>
<li>
<p> A symposia in honor of the contribution of Rob Ritchie, the recipient of Eringen Medal </p>
</li>
<li>
<p> A symposia in honor of the contribution of Roger Fosdick, the recipient of SES Medal </p>
</li>
</ul><p>
<strong>BIOENGINEERING MATERIALS, MECHANICS AND STRUCTURES</strong>
</p>
<ul><li>
<p> Single molecule techniques in biophysics and bioengineering </p>
</li>
<li>
<p> Cell Mechanics </p>
</li>
<li>
<p> Biomechanics/Bioimaging: Inducing and Tracking Mechanical Deformations in Tissue and Living Cells for Diagnostics and Therapy </p>
</li>
<li>
<p> Orthopaedic Bioengineering - Nano-Science to Device Level </p>
</li>
<li>
<p> Mechanics of Soft Materials </p>
</li>
<li>
<p> Experimental techniques for multiphysics and multiscale analysis </p>
</li>
<li>
<p> General Biomechanics </p>
</li>
</ul><p>
<strong>FLUID MECHANICS</strong>
</p>
<ul><li>
<p> Symposium on Non-Newtonian Fluid Mechanics in Celebration of the 60th Birthday of K.R. Rajagopal </p>
</li>
<li>
<p> Dynamics and rheology of complex fluids </p>
</li>
<li>
<p> Symposium on Experimental Fluid Mechanics in Single and Multiphase Flows Description </p>
</li>
<li>
<p> Symposium on Microfluidics and Nanofluidics Description </p>
</li>
<li>
<p> Symposium on Fluid Issues in Renewable Energy Systems Description </p>
</li>
<li>
<p> Symposium on Bio-Inspired Fluid Mechanics Description </p>
</li>
<li>
<p> Symposium on Granular Flow Description </p>
</li>
<li>
<p> Symposium on Multiphase Flow Description </p>
</li>
</ul><p>
<strong>MECHANICS OF MATERIALS AND STRUCTURES</strong>
</p>
<ul><li>
<p> Nanomechanics: Beyond Modulus and Hardness </p>
</li>
<li>
<p> Theoretical and Computational Studies of Defects in Crystals and the Mechanical Properties of Solids </p>
</li>
<li>
<p> Strain Rate Effects in Low Impedance Materials </p>
</li>
<li>
<p> Size Scale Effects in Micro/Nano Structured Materials and Composites </p>
</li>
<li>
<p> Phase transformations and mechanichemistry </p>
</li>
<li>
<p> Multifunctional Composite Materials </p>
</li>
<li>
<p> Multiscale modeling of micro/nano structural thin films </p>
</li>
<li>
<p> Instabilities in Solids </p>
</li>
<li>
<p> Multiscale characterization of materials using diffraction methods </p>
</li>
<li>
<p> Failure and Fracture of Heterogeneous and Multilayer Materials </p>
</li>
</ul><p>
<strong>Workshop</strong>
</p>
<ul><li>
<p> Multi-scale and Multi-field Modeling of Materials Processing: State-of-the-art and future Challenges. </p>
</li>
</ul><p>
<strong>NON-DISTRUCTIVE EVALUATION OF MATERIALS</strong>
</p>
<ul><li>
<p> Infrastructural NDE and Structural Health Monitoring </p>
</li>
<li>
<p> Probing Inhomogeneous Media </p>
</li>
<li>
<p> Transforming Theory into NDE Practice </p>
</li>
</ul><p>
<strong>STUDENT PROGRAM</strong>
</p>
<ul><li>
<p> Graduate student paper competition </p>
</li>
<li>
<p> Undergraduate student paper competition </p>
</li>
</ul><p><span class="normal"></span></p>
<p>
</p>
<p></p>
</div></div></div>Wed, 07 Apr 2010 14:19:24 +0000Wei Hong7938 at https://imechanica.orghttps://imechanica.org/node/7938#commentshttps://imechanica.org/crss/node/7938SES 2010 Annual Technical Meeting - Call for Symposia
https://imechanica.org/node/7647
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/74">conference</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/4859">SES 2010</a></div><div class="field-item odd"><a href="/taxonomy/term/4860">Iowa State University</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Dear Colleague:
</p>
<p>
The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.
</p>
<p>
The overarching theme of the conference is multi-scale multi-physics phenomena. The conference will have the following general topical tracks:
</p>
<ul class="unIndentedList"><li>Biomechanics</li>
<li>Computational Methods </li>
<li>Dynamics</li>
<li>Fluid Mechanics</li>
<li>Mechanics of Materials and Structures</li>
<li>Multi-Physics Phenomena</li>
<li>Non-Destructive Evaluations</li>
</ul><p>
The SES2010 website is now up and running (<a href="http://www.ucs.iastate.edu/mnet/ses2010/form1.html" target="_blank">http://www.ucs.iastate.edu/mnet/ses2010/form1.html</a>) and we have begun to populate the site with symposia topics.
</p>
<p>
The organizers invite you to organize a mechanics-related symposium under any of the conference tracks. The proposed symposium should bring the diverse audience in these multidisciplinary fields to expand cooperation, understanding and promotion of efforts and disciplines in these areas. New research results, new developments, and novel concepts are key for the development of these symposia.
</p>
<p>
Symposia consist of two or more five-paper sessions focused on a narrow theme, under one of the general conference tracks. An abstracts will be required for oral presentation per the usual practice at SES meetings.
</p>
<p>
Your duties as Symposium Organizer will be mainly to solicit papers, assign session chairs as needed, ensure that all deadlines are met through the web-based submission and review service, schedule presentations in your symposium, maintain good communication with the local organizers at Iowa State and of course attend the conference.
</p>
<p>
<strong>Please submit your proposed topic directly to the SES2010 organizing committee (<a href="mailto:ses2010@iastate.edu">ses2010@iastate.edu</a>) for approval by March 5, 2010</strong>. The organizing committee will review and combined symposia as deemed appropriate to prevent topic fragmentation and duplications.
</p>
<p>
If you have any questions regarding the SES2010 meeting please feel free to contact one of the organizing committee directly:
</p>
<p>
Ashraf Bastawros, General Chair <a href="mailto:bastaw@iastate.edu">bastaw@iastate.edu</a> <br />
Aerospace Engineering
</p>
<p>
Bulent Biner, <a href="mailto:biner@ameslab.gov">biner@ameslab.gov</a> <br />
Aerospace Engineering
</p>
<p>
Abhijit Chandra, <a href="mailto:achandra@iastate.edu">achandra@iastate.edu</a> <br />
Mechanical Engineering
</p>
<p>
Dale Chimenti, <a href="mailto:chimenti@iastate.edu">chimenti@iastate.edu</a><br />
Aerospace Engineering<br />
Center of Non-Destructive Evaluations
</p>
<p>
Baskar Ganapathysubramanian, <a href="mailto:baskarg@iastate.edu">baskarg@iastate.edu</a><br />
Mechanical Engineering
</p>
<p>
Steve Holland, <a href="mailto:sdh4@iastate.edu">sdh4@iastate.edu</a><br />
Aerospace Engineering<br />
Center of Non-Destructive Evaluations
</p>
<p>
Wei Hong, <a href="mailto:whong@iastate.edu">whong@iastate.edu</a><br />
Aerospace Engineering
</p>
<p>
Hui Hu, <a href="mailto:huhui@iastate.edu">huhui@iastate.edu</a> <br />
Aerospace Engineering
</p>
<p>
Valery Levitas, <a href="mailto:vlevitas@iastate.edu">vlevitas@iastate.edu</a><br />
Mechanical Engineering<br />
Aerospace Engineering
</p>
<p>
Richard LeSar, <a href="mailto:lesar@iastate.edu">lesar@iastate.edu</a><br />
Materials Science & Engineering
</p>
<p>
Thomas Rudolphi, <a href="mailto:rudolphi@iastate.edu">rudolphi@iastate.edu</a><br />
Aerospace Engineering
</p>
<p>
Lester Schmerr, <a href="mailto:lschmerr@iastate.edu">lschmerr@iastate.edu</a><br />
Aerospace Engineering
</p>
<p>
Pranav Shrotriya, <a href="mailto:shrotriy@iastate.edu">shrotriy@iastate.edu</a><br />
Mechanical Engineering
</p>
<p>
Bruce Thompson, <a href="mailto:rbthomps@iastate.edu">rbthomps@iastate.edu</a><br />
Aerospace Engineering<br />
Materials Science & Engineering<br />
Center of Non-Destructive Evaluations
</p>
</div></div></div>Tue, 23 Feb 2010 04:12:14 +0000Wei Hong7647 at https://imechanica.orghttps://imechanica.org/node/7647#commentshttps://imechanica.org/crss/node/7647Surface interactions between two like-charged polyelectrolyte gels
https://imechanica.org/node/7331
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1690">gels</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div><div class="field-item even"><a href="/taxonomy/term/4113">polyelectrolyte</a></div><div class="field-item odd"><a href="/taxonomy/term/4671">surface interactions</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Due to the migration of mobile molecules and ions, a thin diffusive layer of distributed charge - the electric double layer - forms at the interface between a polyelectrolyte gel and a liquid ionic solution. When two polyelectrolyte gels are brought closely together, the electric double layers overlap and interact with each other, resulting in an effective repulsion. The multiphysics coupling nature of soft gels makes their surface interactions significantly different from the interactions between rigid solids. Using the recently formulated nonlinear theory, this paper develops a continuum model to study the surface interactions between two like-charged polyelectrolyte gels, accounting for the coupled electric, concentration, and deformation fields in both the gels and the liquid. Numerical solutions of the surface interactions are obtained and compared with a qualitative scaling law derived via linearization. The results suggest that the structure of double layers, as well as their interactions, depends not only on the concentration of liquid solutions, but more on the bulk properties of the gels such as stiffness and fixed-charge density. This model also provides insights to the mechanism of the low-friction phenomena on the surface of a polyelectrolyte gel.</p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
<tbody>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/24.pdf" type="application/pdf; length=218533" title="24.pdf">Disjoining pressure</a></span></td><td>213.41 KB</td> </tr>
</tbody>
</table>
</div></div></div>Wed, 06 Jan 2010 16:50:07 +0000Wei Hong7331 at https://imechanica.orghttps://imechanica.org/node/7331#commentshttps://imechanica.org/crss/node/7331Electric-field-induced antiferroelectric to ferroelectric phase transition in a mechanically confined perovskite oxide
https://imechanica.org/node/7330
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/3543">ferroelectrics</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div><div class="field-item even"><a href="/taxonomy/term/4670">phase transition</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>The electric-field-induced phase transition was investigated under mechanical confinements in bulk samples of an antiferroelectric perovskite oxide at room temperature. Profound impacts of mechanical confinements on the phase transition are observed due to the interplay of ferroelasticity and the volume expansion at the transition. The uniaxial compressive prestress delays while the radial compressive prestress suppresses it. The difference is rationalized with a phenomenological model of the phase transition accounting for the mechanical confinement.</p>
</div></div></div><div class="field field-name-upload field-type-file field-label-hidden"><div class="field-items"><div class="field-item even"><table class="sticky-enabled">
<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
<tbody>
<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/22.pdf" type="application/pdf; length=263387" title="22.pdf">Tan_PRE_2010.pdf</a></span></td><td>257.21 KB</td> </tr>
</tbody>
</table>
</div></div></div>Wed, 06 Jan 2010 15:57:50 +0000Wei Hong7330 at https://imechanica.orghttps://imechanica.org/node/7330#commentshttps://imechanica.org/crss/node/7330Formation of creases on the surfaces of elastomers and gels
https://imechanica.org/node/5999
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/995">instability</a></div><div class="field-item even"><a href="/taxonomy/term/1265">gel</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div><div class="field-item even"><a href="/taxonomy/term/4141">crease</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>When a block of an elastomer is bent, the compressed surface may form a crease. This paper analyzes the critical condition for creasing by comparing the elastic energy in a creased body and that in a smooth body. This difference in energy is expressed by a scaling relation. Critical conditions for creasing are determined for elastomers subject to general loads and gels swelling under constraint. The theoretical results are compared with existing experimental observations.</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/creases%20on%20elastomers%20and%20gels.pdf" type="application/pdf; length=174554" title="creases on elastomers and gels.pdf">creases on elastomers and gels.pdf</a></span></td><td>170.46 KB</td> </tr>
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</div></div></div>Thu, 09 Jul 2009 20:42:26 +0000Wei Hong5999 at https://imechanica.orghttps://imechanica.org/node/5999#commentshttps://imechanica.org/crss/node/5999Large deformation and electrochemistry of polyelectrolyte gels
https://imechanica.org/node/5960
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/472">large deformation</a></div><div class="field-item even"><a href="/taxonomy/term/1265">gel</a></div><div class="field-item odd"><a href="/taxonomy/term/4112">hong group research</a></div><div class="field-item even"><a href="/taxonomy/term/4113">polyelectrolyte</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Immersed in an ionic solution, a network of polyelectrolyte polymers imbibes the solution and swells, resulting in a polyelectrolyte gel. The swelling is reversible, and is regulated by ionic concentrations, mechanical forces, and electric potentials. This paper develops a field theory to couple large deformation and electrochemistry. A specific material model is described, including the effects of stretching the network, mixing the polymers with the solvent and ions, and polarizing the gel. We show that the notion of osmotic pressure in a gel has no experimental significance in general, but acquires a physical interpretation within the specific material model. The theory is used to analyze several phenomena: a gel swells freely in an ionic solution, a gel swells under a constraint, electric double layer at the interface between the gel and the external solution, and swelling of a gel of a small size.</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/polyelectrolyte.pdf" type="application/pdf; length=432333" title="polyelectrolyte.pdf">polyelectrolyte.pdf</a></span></td><td>422.2 KB</td> </tr>
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</div></div></div>Sat, 04 Jul 2009 15:09:07 +0000Wei Hong5960 at https://imechanica.orghttps://imechanica.org/node/5960#commentshttps://imechanica.org/crss/node/5960Multiple tenure-track faculty positions at Iowa State University
https://imechanica.org/node/4420
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/127">Faculty Position</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
The Department of Aerospace Engineering at Iowa State University invites applications for multiple tenure-track faculty positions at the assistant, associate, or full professor ranks to begin August 2009. Applicants are sought in all areas of aerospace engineering and engineering mechanics but preference will be given to those with interest and expertise in aerospace structures/mechanics of materials, multidisciplinary design and analysis, experimental thermal-fluids, propulsion, wind energy, and wind engineering.
</p>
<p>
The department is also interested in applicants whose expertise and research interests intersect with one or more of the college’s interdisciplinary research and education clusters: biosciences and engineering, energy sciences and technology, engineering for extreme events, information and decision sciences, and engineering for sustainability.
</p>
<p>
Details in the attached pdf file.
</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/ISU%20Aero%20Open%20Positions%20%2B%20CoE%20cluster-hire%202008-09.pdf" type="application/pdf; length=22483" title="ISU Aero Open Positions + CoE cluster-hire 2008-09.pdf">ISU Aero Open Positions + CoE cluster-hire 2008-09.pdf</a></span></td><td>21.96 KB</td> </tr>
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</div></div></div>Wed, 03 Dec 2008 16:31:36 +0000Wei Hong4420 at https://imechanica.orghttps://imechanica.org/node/4420#commentshttps://imechanica.org/crss/node/4420Graduate Research Opportunities at Iowa State University
https://imechanica.org/node/4370
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/616">materials</a></div><div class="field-item odd"><a href="/taxonomy/term/1498">modeling</a></div><div class="field-item even"><a href="/taxonomy/term/1569">experimental</a></div><div class="field-item odd"><a href="/taxonomy/term/2106">PHD position</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
There are currently 5 openings for perspective graduate students (preferably applying for a PhD program) in the area of experimental, theoretical or computational solid mechanics (or combined), starting from Fall, 2009. Recruited students are expected to work with <a href="http://www.public.iastate.edu/~bastaw/">Ashraf Bastawros</a> or <a href="http://www.public.iastate.edu/~whong/">Wei Hong</a>. Possible research topics include: Smart materials/structures, Reliability of micro-electronic devices, Layered structures, Mechanics of soft active materals, etc.
</p>
<p>
Please apply through the university website<br /><a href="http://www.admissions.iastate.edu/apply/index.php">http://www.admissions.iastate.edu/apply/index.php</a>
</p>
<p>
For details on the position and research projects, please contact <a href="mailto:whong@iastate.edu">Wei Hong</a> or <a href="mailto:bastaw@iastate.edu">Ashraf Bastawros</a> with a copy of your application materials.
</p>
<p>
Early starting (Summer 2009 or earlier) is possible
</p>
</div></div></div>Mon, 24 Nov 2008 19:28:48 +0000Wei Hong4370 at https://imechanica.orghttps://imechanica.org/node/4370#commentshttps://imechanica.org/crss/node/4370Inhomogeneous swelling of a gel in equilibrium with a solvent and mechanical load
https://imechanica.org/node/3163
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/447">Finite Element Method</a></div><div class="field-item even"><a href="/taxonomy/term/1101">swelling</a></div><div class="field-item odd"><a href="/taxonomy/term/1265">gel</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p class="MsoNormal">
<span>A network of polymers can imbibe a large quantity of a solvent and swell, resulting in a gel. The swelling process can be markedly influenced by a mechanical load and geometric constraint. When the network, solvent, and mechanical load equilibrate, the gel usually swells by a field of inhomogeneous and anisotropic deformation. We show that this field in the swollen gel is equivalent to that in a hyperelastic solid. We implement this theory in the finite-element package, ABAQUS, and analyze examples of swelling-induced deformation, contact, and bifurcation. Because commercial software like ABAQUS is widely available, this work may provide a powerful tool to study complex phenomena in gels.</span>
</p>
<p>
The source code of the UHYPER program is attached below.
</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="Plain text icon" title="text/plain" src="/modules/file/icons/text-plain.png" /> <a href="https://imechanica.org/files/gel.for_.txt" type="text/plain; length=2378" title="gel.for_.txt">gel.for_.txt</a></span></td><td>2.32 KB</td> </tr>
<tr class="even"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/gel_in_equilibrium_2008_05_06%20submit.pdf" type="application/pdf; length=728767" title="gel_in_equilibrium_2008_05_06 submit.pdf">gel_in_equilibrium_2008_05_06 submit.pdf</a></span></td><td>711.69 KB</td> </tr>
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</div></div></div>Wed, 07 May 2008 20:45:32 +0000Wei Hong3163 at https://imechanica.orghttps://imechanica.org/node/3163#commentshttps://imechanica.org/crss/node/3163Prof. Zhigang Suo and Prof. Frans Spaepen elected to the National Academy of Engineering
https://imechanica.org/node/2681
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/75">mechanician</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/1820">NAE</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Prof. <a href="user/2">Zhigang Suo</a> and Prof. <a href="http://www.seas.harvard.edu/matsci/people/fspaepen/frans.html"><strong>Frans Spaepen</strong></a>, of the Harvard School of Engineering and Applied Sciences, have just been elected to the National Academy of Engineering. They are among <a href="http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=02082008">65 new members</a> elected to the NAE in 2008. Update: Also elected this year is another mechanician, <a href="http://cee.uiuc.edu/Faculty/r-dodds.htm">Robert Dodds</a>, of the University of Illinois. </p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/NAE%20Class%20of%202008.pdf" type="application/pdf; length=89983" title="NAE Class of 2008.pdf">NAE Class of 2008.pdf</a></span></td><td>87.87 KB</td> </tr>
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</div></div></div>Fri, 08 Feb 2008 15:29:41 +0000Wei Hong2681 at https://imechanica.orghttps://imechanica.org/node/2681#commentshttps://imechanica.org/crss/node/2681Drying-induced bifurcation in a hydrogel-actuated nanostructure
https://imechanica.org/node/2487
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/1099">hydrogel</a></div><div class="field-item even"><a href="/taxonomy/term/1265">gel</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
<span>Hydrogels have enormous potential for making adaptive structures in response to diverse stimuli. In a structure demonstrated recently, for example, nanoscale rods of silicon were embedded vertically in a swollen hydrogel, and the rods tilted by a large angle in response to a drying environment (Sidorenko, et al., Science 315, 487, 2007). Here we describe a model to show that this behavior corresponds to a bifurcation at a critical humidity, analogous to a phase transition of the second kind.<br /></span>
</p>
<p>
<span>The structure adapts to the drying environment in two ways. Above the critical humidity, the rods stand vertical, enabling the hydrogel to develop tension and retain water. Below the critical humidity, the rods tilt, enabling the hydrogel to reduce thickness and release water. We further show that the critical humidity can be tuned.<br /><br /></span>
</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/202.pdf" type="application/pdf; length=115331" title="202.pdf">Drying-induced bifurcation in a hydrogel-actuated nanostructure</a></span></td><td>112.63 KB</td> </tr>
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</div></div></div>Sat, 22 Dec 2007 21:56:02 +0000Wei Hong2487 at https://imechanica.orghttps://imechanica.org/node/2487#commentshttps://imechanica.org/crss/node/2487A theory of coupled diffusion and large deformation in polymeric gels
https://imechanica.org/node/1926
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/1099">hydrogel</a></div><div class="field-item even"><a href="/taxonomy/term/1100">diffusion</a></div><div class="field-item odd"><a href="/taxonomy/term/1265">gel</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
A large quantity of small molecules may migrate into a network of long polymers, causing the network to swell, forming an aggregate known as a polymeric gel. This paper formulates a theory of the coupled mass transport and large deformation.<br />
The free energy of the gel results from two molecular processes: stretching the network, and mixing the network with the small molecules. Both the small molecules and the long polymers are taken to be incompressible, a constraint that we enforce by using a Lagrange multiplier, which coincides with the osmosis pressure or the swelling stress. The gel can undergo large deformation of two modes. The first mode results from the fast process of local rearrangement of molecules, allowing the gel to change shape but not volume. The second mode results from the slow process of long-range migration of the small molecules, allowing the gel to change both shape and volume. We assume that the local rearrangement is instantaneous, and model the long-range migration by assuming that the small molecules diffuse inside the gel. The theory is illustrated with a layer of a gel constrained in its plane and subject to a weight in the normal direction. We also predict the scaling behavior of a gel under a conical indenter.
</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Kinetics%202007%2010%2022%20correct.pdf" type="application/pdf; length=274330" title="Kinetics 2007 10 22 correct.pdf">Kinetics 2007 10 22 correct.pdf</a></span></td><td>267.9 KB</td> </tr>
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</div></div></div>Sun, 16 Sep 2007 04:43:00 +0000Wei Hong1926 at https://imechanica.orghttps://imechanica.org/node/1926#commentshttps://imechanica.org/crss/node/1926Dynamics of terraces on a silicon surface due to the combined action of strain and electric current
https://imechanica.org/node/392
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/132">strain</a></div><div class="field-item even"><a href="/taxonomy/term/148">Wei Hong</a></div><div class="field-item odd"><a href="/taxonomy/term/149">Zhenyu Zhang</a></div><div class="field-item even"><a href="/taxonomy/term/163">electromigration</a></div><div class="field-item odd"><a href="/taxonomy/term/312">silicon</a></div><div class="field-item even"><a href="/taxonomy/term/313">step</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>A (001) surface of silicon consists of terraces of two variants, which have an identical atomic structure, except for a 90° rotation. We formulate a model to evolve the terraces under the combined action of electric current and applied strain. The electric current motivates adatoms to diffuse by a wind force, while the applied strain motivates adatoms to diffuse by changing the concentration of adatoms in equilibrium with each step. To promote one variant of terraces over the other, the wind force acts on the anisotropy in diffusivity, and the applied strain acts on the anisotropy in surface stress. Our model reproduces experimental observations of stationary states, in which the relative width of the two variants becomes independent of time. Our model also predicts a new instability, in which a small change in experimental variables (e.g., the applied strain and the electric current) may cause a large change in the relative width of the two variants.</p>
<p> </p>
<p> Preprint available online.</p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Electromigration_Elastic%2011%2003%20suo.pdf" type="application/pdf; length=313300" title="Electromigration_Elastic 11 03 suo.pdf">Electromigration_Elastic 11 03 suo.pdf</a></span></td><td>305.96 KB</td> </tr>
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</div></div></div>Sun, 05 Nov 2006 20:41:03 +0000Wei Hong392 at https://imechanica.orghttps://imechanica.org/node/392#commentshttps://imechanica.org/crss/node/392Tenure-track or Tenured Faculty Positions at Mechanical and Aerospace Engineering, UCSD
https://imechanica.org/node/359
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><strong>MECHANICAL AND AEROSPACE ENGINEERING</strong></p>
<p><strong>POSITION</strong>: The Department of Mechanical and Aerospace Engineering invites applications for one or more <em>TENURE-TRACK</em> or <em>TENURED FACULTY POSITIONS</em> at the Assistant, Associate or Full Professor levels. Successful candidates will be expected to teach undergraduate and graduate courses in Mechanical and Aerospace Engineering and to establish a vigorous extramurally funded research program.</p>
<p><strong>QUALIFICATIONS</strong>: Ph.D. or equivalent degree.</p>
<p><strong>RANK AND SALARY</strong>: Level of appointment commensurate with qualifications; salary based on published UC pay scales.</p>
<p><strong>CLOSING DATE FOR APPLICATIONS</strong>: November 30, 2006.</p>
<p>Send detailed resume, personal statement summarizing teaching experience and research interests, leadership efforts and contributions to diversity, and names/addresses of 5 professional references to:</p>
<p>Search Chair/mae<br />UCSD MAE Department<br />9500 Gilman Drive<br />La Jolla, CA 92093-0411</p>
<p>* * *<br />Inquiries: <a href="mailto:recruitment@maemail.ucsd.edu">recruitment@maemail.ucsd.edu</a><br />Additional Information: <a href="http://maeweb.ucsd.edu">http://maeweb.ucsd.edu</a><br />For applicants interested in spousal/partner employment, please visit the UCSD Partner Opportunities Program website <a href="http://academicaffairs.ucsd.edu/offices/partneropp/">http://academicaffairs.ucsd.edu/offices/partneropp/</a><br />UCSD is an equal opportunity / affirmative action employer with a strong institutional commitment to the achievement of excellence and diversity <a href="http://diversity.ucsd.edu">http://diversity.ucsd.edu</a></p>
</div></div></div>Sat, 28 Oct 2006 17:42:30 +0000Wei Hong359 at https://imechanica.orghttps://imechanica.org/node/359#commentshttps://imechanica.org/crss/node/359Faculty position in computational mechanics engineering science and mechanics department, Penn State University
https://imechanica.org/node/327
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/73">job</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>The Engineering Science and Mechanics Department at The Pennsylvania State University invites applications for a tenure-track faculty position in computational mechanics at the assistant professor level. Exceptional candidates at the associate or full professor level will also be considered. Candidates are sought with a foundation and research interests in mechanics across all scales from the molecular to the macroscopic, including expertise in: efficient massive and nonlinear computations; molecular and multiscale simulations; innovative and efficient approaches to nonlinear FEM for large deformations, inhomogeneities, and/or inclusions; problems with evolving microstructure such as phase transitions and damage evolution; massively parallel simulations of large systems of equations; novel numerical/empirical approaches to modeling multiscale constitutive behavior of composite, biological or otherwise novel material systems.</p>
<p>Multidisciplinary research interests would be advantageous, particularly those related to the department’s strategic thrust areas: health monitoring of machines and people; neural and biomedical engineering; and bionanomaterials and technology. Candidates with teaching interests in numerical methods and engineering mathematics, as well as in emerging areas, are encouraged.</p>
<p>Qualifications for the positions include an earned Doctorate in mechanics or an area appropriate to the applicant’s field of specialization and a proven record of scholarly activities. Duties will include undergraduate and graduate teaching and scholarly research that will advance the state of the art of mechanics and engineering science. Collaboration with Penn State’s Institute for Computational Science, and Center for Computational Mathematics and Applications is encouraged. The department is committed to diversity and fostering a welcoming climate for all.</p>
<p>Review of applications will begin December 1, 2006. Applications will be considered until the position is filled. Please send a curriculum vitae, statement of professional interests, teaching philosophy and the names and addresses of four references to:</p>
<p>Attn: ESM Search Committee Chair<br />Department of Engineering Science and Mechanics<br />212 Earth-Engineering Sciences Building, Box 212<br />The Pennsylvania State University<br />University Park, PA 16802-6812</p>
<p>Electronic applications may be submitted to: <a href="mailto:positions@mail.esm.psu.edu">positions@mail.esm.psu.edu</a></p>
</div></div></div>Mon, 23 Oct 2006 14:27:17 +0000Wei Hong327 at https://imechanica.orghttps://imechanica.org/node/327#commentshttps://imechanica.org/crss/node/327Persistent step-flow growth of strained films on vicinal substrates
https://imechanica.org/node/313
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/132">strain</a></div><div class="field-item even"><a href="/taxonomy/term/147">step flow</a></div><div class="field-item odd"><a href="/taxonomy/term/148">Wei Hong</a></div><div class="field-item even"><a href="/taxonomy/term/149">Zhenyu Zhang</a></div><div class="field-item odd"><a href="/taxonomy/term/274">vicinal</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>We propose a model of persistent step flow, emphasizing dominant kinetic processes and strain effects. Within this model, we construct a morphological phase diagram, delineating a regime of step flow from regimes of step bunching and island formation. In particular, we predict the existence of concurrent step bunching and island formation, a new growth mode that competes with step flow for phase space, and show that the deposition flux and temperature must be chosen within a window in order to achieve persistent step flow. The model rationalizes the diverse growth modes observed in pulsed laser deposition of SrRuO3 on SrTiO3 </p>
<p> <a href="http://link.aps.org/abstract/PRL/v95/e095501" target="_blank"><em>Physical Review Letters</em> <strong>95</strong>, 095501 (2005) </a></p>
<p>Preprint available here </p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/stepflow%2005.07.18.pdf" type="application/pdf; length=217066" title="stepflow 05.07.18.pdf">stepflow 05.07.18.pdf</a></span></td><td>211.98 KB</td> </tr>
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</div></div></div>Tue, 17 Oct 2006 14:09:34 +0000Wei Hong313 at https://imechanica.orghttps://imechanica.org/node/313#commentshttps://imechanica.org/crss/node/313Interplay between elastic interactions and kinetic processes in stepped Si (001) homoepitaxy
https://imechanica.org/node/136
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/144">Si</a></div><div class="field-item even"><a href="/taxonomy/term/145">homoepitaxy</a></div><div class="field-item odd"><a href="/taxonomy/term/146">ES barrier</a></div><div class="field-item even"><a href="/taxonomy/term/147">step flow</a></div><div class="field-item odd"><a href="/taxonomy/term/148">Wei Hong</a></div><div class="field-item even"><a href="/taxonomy/term/149">Zhenyu Zhang</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>A vicinal Si (001) surface may form stripes of terraces, separated by monatomic-layer-high steps of two kinds, </span><span><em>SA </em></span><span>and <span></span></span><span><em>SB</em></span><span><span></span>. <span> </span>As adatoms diffuse on the terraces and attach to or detach from the steps, the steps move.<span> </span>In equilibrium, the steps are equally spaced due to elastic interaction.<span> </span>During deposition, however, </span><span><em>SA</em></span><span><span></span><span> </span>is less mobile than <span></span></span><span><em>SB</em></span><span><span></span>.<span> </span>We model the interplay between the elastic and kinetic effects that drives step motion, and show that during homoepitaxy all the steps may move in a steady state, such that alternating terraces have time-independent, but unequal, widths. <span> </span>The ratio between the widths of neighboring terraces is tunable by the deposition flux and substrate temperature.<span> </span>We study the stability of the steady state mode of growth using both linear perturbation analysis and numerical simulations.<span> </span>We elucidate the delicate roles played by the standard Ehrlich-Schwoebel (ES) barriers and inverse ES barriers in influencing growth stability in the complex system containing </span><span>(<em>SA</em>+<em>SB</em>)</span><span> step pairs.</span></p>
<p> Preprint available in the attachment. </p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/SA-Barrier%2006%209%204%20hong.pdf" type="application/pdf; length=393199" title="SA-Barrier 06 9 4 hong.pdf">SA-Barrier 06 9 4 hong.pdf</a></span></td><td>383.98 KB</td> </tr>
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</div></div></div>Mon, 11 Sep 2006 15:05:54 +0000Wei Hong136 at https://imechanica.orghttps://imechanica.org/node/136#commentshttps://imechanica.org/crss/node/136Error | iMechanica