iMechanica - research
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en3D-printing biomimetic structures to reveal the mechanics of natural systems
http://imechanica.org/node/21280
<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><strong>Michael M Porter </strong></span></p>
<p><em><span>Natural Engineering Lab, Department of Mechanical Engineering, Clemson University; </span></em><span><em>Zucker Graduate Education Center, N. Charleston, SC, 29405</em></span>
</p><p><span>Biological systems are notoriously difficult to study because many are protected or have limited access; they also exhibit a high variability of forms and properties (no two organisms ever grow exactly alike). For these reasons, many researchers use artificial models to help understand natural phenomena. However, in contrast to the many established technologies used to investigate biological systems – such as microscopes to visualize the microstructures of tissues or treadmills to measure the running speeds of animals – additive manufacturing, or 3D-printing, has only recently entered the field as a new tool of discovery in biological research. </span></p>
<p><span>In short, many biologists, engineers, and designers are working together to create biomimetic models of natural systems to explore their properties and behaviors. This is different from the original intent of biomimicry: “to [innovate] sustainable solutions to human challenges by emulating nature’s time-tested patterns and strategies” (The Biomimicry Institute, 2017). Instead, artificial models of biological systems are designed with CAD software and built with 3D printers, then tested in controlled laboratory environments. The result: a surplus of data to explain biological phenomena without the need for controversial in vivo or invasive testing, and designs that lie outside of the natural morphospace can be created and compared with their natural counterparts to reveal the mechanisms that control their mechanics. </span></p>
<p><span>In recent years, many research groups have created biomimetic analogues of natural materials, structures, and organisms to explore their biomechanics. Here, I highlight a few representative studies that mimic the dermal armors of various fishes via 3D-printing. </span></p>
<p> </p>
<p><strong><span>Figure 1</span></strong><span> shows schematic illustrations of a diversity of fish armors. They can be broadly classified as (A) elasmoid scales, (B) ganoid scales, (C) placoid scales, (D) carapace scutes, and (E) bony plates. Commonly found in striped bass, gars, sharks, boxfishes, seahorses and many other fishes, these armored systems are composed of relatively rigid structures embedded in a more compliant skin and interconnected by various articulation patterns. The interfaces of the rigid elements range from simple overlaps and abutted sutures to more complex peg-and-socket joints. </span></p>
<p><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr2.jpg" alt="Fig. 1" width="659" height="274" /></p>
<p><strong><span>Fig. 1. Representative schematics of common protective armors among living fishes. (A)</span></strong><span> Overlapping elasmoid scales common among most teleosts, such as striped bass; <strong>(B) </strong>interlocking ganoid scales common among gars and bichirs; <strong>(C)</strong> partially imbricated placoid scales common among sharks; <strong>(D)</strong> tessellating carapace scutes common among boxfishes; <strong>(E) </strong>interlocking and overlapping bony plates common among seahorses and related syngnathid fishes. </span><span>Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><span>To better understand the mechanics of these structures, several researchers have performed studies on 3D-printed proxies of the natural armors. In most cases, the natural complexity of the dermal armors is reduced or simplified. This is because 3D-printing currently has many limitations; most machines can only print a few materials (most often polymers) with Young’s moduli up to only a few GPa at resolutions on the order of ~100 μm. However, these design constraints are not necessarily a bad thing. The reduced structures lend themselves nicely to validate analytical and computation results; they can also be built such that only one mechanism is investigated at a time, a strategy that is simply not possible with only natural specimens. </span></p>
<p><span>Below are several figures taken from (Porter et al., 2017) highlighting recent reports that used 3D-printing to study the mechanics of some fish-inspired structures. </span></p>
<p> </p>
<p><strong><span>Figure 2</span></strong><span> shows several versions of overlapping elasmoid-like structures created to explore their mechanics. The biomimetic models were created by: (A) 3D-printing the plates, then casting them in a silicon rubber (Browning et al., 2013); (B) 3D-printing the plates, then gluing them on a silicon base (Ghosh et al., 2014); (C) 3D-printing the plates and supporting matrix with a multi-material machine (Rudykh et al., 2015). In these studies, it was found that interference and frictional contact between adjacent scales cause them to rotate and bend, store energy, and strike a balance of combined protection and flexibility.</span></p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr4.jpg" alt="Fig. 2" width="367" height="343" /></span></p>
<p><strong><span>Fig. 2. Elasmoid scales provide body mobility and puncture resistance. (A) </span></strong><span>Three representative 3D-printed models used to evaluate the effects of scale size, inclination, and overlap; <strong>(B)</strong> 3D-printed model of overlapping scales used to validate analytical models describing the effect of frictional sliding during bending; <strong>(C)</strong> multi-material 3D-printed model of hard scales embedded in a soft substrate subjected to 3-point bending. <strong>(D-F)</strong> Diagrams illustrating the two-dimensional micromechanical behavior of overlapping fishscales in concave bending, which are dependent on the rotation and bending stiffnesses of the scales. Symbols in (D-F): scale length (l</span><span>), separation distance (rl</span><span>), radius of curvature of the skin (R</span><span>) and scale (Rs</span><span>), scale rotation angle (theta</span><span>), scale attachment stiffness (K</span><span>), and scale rigidity (EI</span><span>). </span><span>Scale bars: (A) 25 mm; (C) 10 mm. Images adapted from (A) (Browning et al., 2013); (B) (Ghosh et al., 2014); (C) (Rudykh et al., 2015); (D-F) (Vernerey and Barthelat, 2014). Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>Figure 3</span></strong><span> shows 3D-printed models that replicate the morphology of ganoid scales. In this study, the biomimetic models were scaled up for visualization and manual manipulation. It was found that the morphology of the plates changes across the body of a bichir fish, providing more protection near its head and more flexibility near its tail. These mechanisms were further exploited to design customized armors to cover different body curvatures, including a human shoulder (Duro-Royo et al., 2015). </span></p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr5.jpg" alt="Fig. 3" width="772" height="228" /></span></p>
<p><strong><span>Fig. 3. Ganoid scales provide protection and flexibility. (A-D) </span></strong><span>3D-printed replicas of scales from near the head (A, B) and tail (C, D) of a bichir fish (<em><span>Polypterus senegalus</span></em>); <strong>(E)</strong> schematic illustrating the transition from protection near the head of the fish in blue to flexibility near the tail of the fish in red. <strong>(F) </strong>Illustrations of different body curvatures observed in swimming fishes. The arrows in (B & D) indicate the direction of insertion of the peg-and-socket joints. The coordinate axes indicate the anteroposterior (u), ventrodorsal (v), and lateral (n) directions, with respect to the body of the fish. Images adapted from (Duro-Royo et al., 2015). </span><span>Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>Figure 4</span></strong><span> shows 3D-printed arrays of topologically interlocked structures, which are similar to the overlapping edges of many ganoid scales. Adding the topological interlocks enhances the stiffness, strength and resilience of the structures because contact at the inclined interfaces of the plates redistributes the puncture load through the entire tessellation. For more details on this and related structures, refer to (Martini et al., 2017).</span></p>
<p><span><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr6.jpg" alt="Fig. 4" width="527" height="354" /></span></span></p>
<p><strong><span>Fig. 4. Effect of scale geometry on puncture resistance. (A)</span></strong><span> A 5 x 5 array of simple square scales made of stiff ABS plastic resting on a softer silicon substrate, punctured by a sharp steel needle; <strong>(B)</strong> the same system, with the addition of 45° angles on the sides of the scales to generate topological interlocking between the scales. <strong>(C)</strong> Puncture force-deflection curves for simple and interlocked scales with associated sequences of pictures. Both systems fail by sudden tilting of the indented scale. However, tilting is delayed in the interlocked scales, which increases the puncture resistance by a factor of four. Scale bars: 10 mm. Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>Figure 5 </span></strong><span>shows biomimetic models of shark skin used for hydrodynamic studies. Natural shark skin, shown in panel (A), is composed of several placoid scales that are shaped like tiny hydrofoils. These structures pin vorticities, which reduce static drag and increase the swimming speed of the cartilaginous fishes. In different studies, synthetic models of the shark-like skins were tested to reveal the mechanical effects of the scales (Wen et al., 2014), their patterning (Wen et al., 2015) and their bristled form (Lang et al., 2008).</span></p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr7.jpg" alt="Fig. 5" width="527" height="290" /></span></p>
<p><span><span><strong><span>Fig. 5. Placoid scales (dermal denticles) reduce drag in shark skins. (A) </span></strong><span>Scanning electron micrograph of a natural shark skin (<em>Sphyrna tiburo</em>); <strong>(B)</strong> computer model of biomimetic denticles designed for 3D-printing; <strong>(C)</strong> micrograph of a biomimetic shark skin, showing scale engagement in concave bending and scale separation in convex bending. <strong>(D)</strong> Image of a computer-rendered model of bristled scales used to create a synthetic prototype for experimental testing; <strong>(E)</strong> schematic illustration of the fluid roller bearing effect of drag reduction by bristled scales, showing the primary, secondary, and tertiary vorticities. The axes in (D) indicate the anteroposterior (x), lateral (y), and ventrodorsal (z) directions. Scale bars: (A) 200 μm; (C & D) each denticle is scaled up from the natural ~200 μm to (C) ~1.5 mm long and (D) ~20 mm long. Images adapted from (A-C) (Wen et al., 2014) and (D & E) (Lang et al., 2008). </span><span>Figures and caption taken from (Porter et al., 2017).</span></span></span></p>
<p> </p>
<p><strong><span>Figures 6 & 7</span></strong><span> show images from two studies on 3D-printed models of boxfishes. In the first (Fig 6), 3D-printed models of boxfish bodies were tested in a flow tank to validate computational fluid dynamics studies on their swimming performance. It was found that the boxy shape of the fish increases drag, but enhances maneuverability due to instabilities that promote tighter turning (Wassenbergh et al., 2015). In the second (Fig 7), multi-material models of a boxfish carapace were compressed to reveal the mechanisms that protect the animal from crushing. It was found that the boxy shape promotes buckling of the body; the sutured interfaces between its armored scutes enhances its resistance to crushing (Kenneson, 2016).</span></p>
<p><span><span><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr8.jpg" alt="Fig. 6" width="367" height="313" /></span></span></span></p>
<p><strong><span>Fig. 6. The shape of a boxfish carapace enhances swimming manueverability. (A) </span></strong><span>3D-printed model of a boxfish carapace (~60 mm wide). <strong>(B & C)</strong> Computational fluid dynamics models of (B) the lead-edge pressure waves and (C) the trailing-edge vortices induced during swimming of a boxfish (</span><em><span>Ostracion cubicus</span></em><span>). The color scheme in (B) illustrates the distribution of negative pressure (blue) to postitive pressure (red) on the leading-edge of the carapace. The color scheme in (B) illustrates vorticity flows in the anti-clockwise (blue) and clockwise (red) directions for the front (left), dorsal (top, right) and lateral (bottom, right) views. </span><span>Images adapted from (Van Wassenbergh et al., 2015). Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr9.jpg" alt="Fig. 7" width="367" height="447" /></span></p>
<p><strong><span>Fig. 7.</span></strong><span> <strong>Carapace scutes provide body support in boxfishes. (A-C) </strong>Micro-computed tomography images of the hierarchical organization of a boxfish carapace (</span><em><span>Lactoria cornuta</span></em><span>), showing its (A) ventral surface, (B) tessellation pattern of predominantly hexagonal scutes, and (C) zigzag-like sutures between adjacenet scutes. <strong>(D)</strong> Load-displacement curves illustrating the compressive behaviors of three hypothetical models of 3D-printed boxfish carapaces. The inset (top, left) shows a representative 3D-printed model of a boxfish carapace (~70 mm wide) that was compressed ~15%, where the blue outline shows its orginial shape before loading. The slopes of the load-displacement curves before and after the scutes engage, which is a result of concave bending of the carapace sides, are denoted by the apparent moduli, E1'</span><span> and E2'</span><span>. </span><strong><span>(E-G)</span></strong><span> Magnified models of the three hypothetical carapaces tested, two with a biomimietc armor (orange) covering a flexible skin (yellow) having (E) sutured interfaces or (F) flat interfaces, and another with (G) a flexible skin only. Scale bars: (A) 5 mm; (B) 1 mm; (C) 50 μm; (E-G) 2 mm. Images adapted from (A-C) (Yang et al., 2015). </span><span>Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>Figure 8</span></strong><span> shows images of several sutured interfaces printed for mechanical testing. The 3D-printed models were created to validate analytical models that describe the stress response of the interfaces under loading (Li et al., 2011, 2012, 2013; Lin et al., 2014a, 2014b). It was found that triangular sutures are the best design for high strength and toughness; additional levels of hierarchy, shown in panel (B), further amplify their mechanical properties. In a similar study, jigsaw-like structures were also printed to validate analytical models (Malik et al., 2017).</span></p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr10.jpg" alt="Fig. 8" width="367" height="473" /></span></p>
<p><strong><span>Fig. 8. Suture geometries and hierarchies provide mechanical strength, stiffness, and toughness. (A)</span></strong><span> 3D-printed samples with first-order sutures, where <em>β</em> describes the suture angle measured with respect to the vertical axis of anti-trapezoidal (-11.3°), rectangular (0°), trapezoidal (11.3°), and triangular (22.6°) geometries. The inset (top, right) shows stretching of the softer interfacial layer that bonds the traingular sutures when subject to tension. <strong>(B)</strong> 3D-printed samples with varying levels of suture hierarchy, where N describes the level of hierarchy, as first (1), second (2), or third (3) order. Scale bars: (A) 10 mm (inset: 5 mm); (B) 10 mm. </span><span>Images adapted from (A) (Lin et al., 2014a) and (B) (Lin et al., 2014b). </span><span>Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>Figure 9</span></strong><span> shows images of a seahorse skeleton and biomimetic models used to explain “why the seahorse tail is square” (Porter et al., 2015). In this study, natural square-prism and hypothetical cylindrical models of a seahorse tail skeleton were created to compare their mechanics in bending, twisting, and crushing. It was found that the square structure outperforms the cylindrical one as an armored and grasping appendage.</span></p>
<p><span><img src="http://ars.els-cdn.com/content/image/1-s2.0-S1751616116304398-gr11.jpg" alt="Fig. 9" width="772" height="247" /></span></p>
<p><strong><span>Fig. 9. Bony plates facilitate tail prehensility in seahorses. (A-C) </span></strong><span>Micro-computed tomographs of (A) a seahorse (<em>Hippocampus reidi</em>) and its tail in (B) bending, twisting, and (C) compression. For clarity, the vertebral column is colored magenta, and the bony plates are colored red, yellow, blue, and green. <strong>(D)</strong> Computer-generated images of a hypothetical cylindrical model and a natural square-prism model of a seahorse tail wrapped around a cylinder, illustrating their respective surface contact when grasping.<strong> (E, F) </strong>Images of 3D-printed prototypes compressed just before failure, which occurs when the spring struts disjoin from the 3D-printed plates, illustrating the (E) rotational hinge and (F) linear sliding mechanisms that occur at the overlapping joints of the cylindrical and square-prism structures, respectively. Scale bars: (A) 10 mm; (B & C) 2 mm; (E & F) 3D-printed models are ~60 mm wide. Images adapted from (A-C, E, F) (Porter et al., 2015). </span><span>Figures and caption taken from (Porter et al., 2017).</span></p>
<p> </p>
<p><strong><span>References</span></strong></p>
<p><span>Browning, A., Ortiz, C., Boyce, M.C., 2013. Mechanics of composite elasmoid fish scale assemblies and their bioinspired analogues. Journal of the Mechanical Behavior of Biomedical Materials 19, 75-86.</span></p>
<p><span>Duro-Royo, J., Zolotovsky, K., Mogas-Soldevila, L., Varshney, S., Oxman, N., Boyce, M.C., Ortiz, C., 2015. MetaMesh: A hierarchical computational model for design and fabrication of biomimetic armored surfaces. Computer-Aided Design 60, 14-27.</span></p>
<p><span>Ghosh, R., Ebrahimi, H., Vaziri, A., 2014. Contact kinematics of biomimetic scales. Applied Physics Letters 105, 233701.</span></p>
<p><span>Kenneson, P., 2016. Bioinspired flexible armor: The influence of suture interfaces on tessellated armor plates in bending (B.S. Honors Thesis), Department of Mechanical Engineering. Clemson University.</span></p>
<p><span>Lang, A.W., Motta, P., Hidalgo, P., Westcott, M., 2008. Bristled shark skin: A microgeometry for boundary layer control? Bioinspiration & Biomimetics 3, 046005.</span></p>
<p><span>Li, Y., Ortiz, C., Boyce, M.C., 2011. Stiffness and strength of suture joints in nature. Physical Review E 84, 062904.</span></p>
<p><span>Li, Y., Ortiz, C., Boyce, M.C., 2012. Bioinspired, mechanical, deterministic fractal model for hierarchical suture joints. Physical Review E 85, 031901.</span></p>
<p><span>Li, Y., Ortiz, C., Boyce, M.C., 2013. A generalized mechanical model for suture interfaces of arbitrary geometry. Journal of the Mechanics and Physics of Solids 61, 1144-1167.</span></p>
<p><span>Lin, E., Li, Y., Ortiz, C., Boyce, M.C., 2014a. 3D printed, bio-inspired prototypes and analytical models for structured suture interfaces with geometrically-tuned deformation and failure behavior. Journal of the Mechanics and Physics of Solids 73, 166-182.</span></p>
<p><span>Lin, E., Li, Y., Weaver, J.C., Ortiz, C., Boyce, M.C., 2014b. Tunability and enhancement of mechanical behavior with additively manufactured bio-inspired hierarchical suture interfaces. Journal of Materials Research 29, 1867-1875.</span></p>
<p><span>Malik, I.A., Mirkhalaf, M., Barthelat, F., 2017. Bio-inspired “jigsaw”-like interlocking sutures: modeling, optimization, 3D printing and testing. Journal of the Mechanics and Physics of Solids 102, 224-238.</span></p>
<p><span>Martini, R., Balit, Y., Barthelat, F., 2017. A comparative study of bio-inspired protective scales using 3D printing and mechanical testing. Acta Biomaterialia 55, 360-372.</span></p>
<p><span>Porter, M.M., Adriaens, D., Hatton, R.L., Meyers, M.A., McKittrick, J., 2015. Why the seahorse tail is square. Science 349, aaa6683.</span></p>
<p><span>Porter, M.M., Ravikumar, N., Barthelat, F., Martini, R., 2017. 3D-printing and mechanics of bio-inspired articulated and multi-material structures. Journal of the Mechanical Behavior of Biomedical Materials (in press).</span></p>
<p><span>Rudykh, S., Ortiz, C., Boyce, M.C., 2015. Flexibility and protection by design: Imbricated hybrid microstructures of bio-inspired armor. Soft Matter 11, 2547-2554.</span></p>
<p><span>Van Wassenbergh, S., van Manen, K., Marcroft, T.A., Alfaro, M.E., Stamhuis, E.J., 2015. Boxfish swimming paradox resolved: Forces by the flow of water around the body promote manoeuvrability. Journal of The Royal Society Interface 12, 20141146.</span></p>
<p><span>Vernerey, F.J., Barthelat, F., 2014. Skin and scales of teleost fish: Simple structure but high performance and multiple functions. Journal of the Mechanics and Physics of Solids 68, 66-76.</span></p>
<p><span>Wen, L., Weaver, J.C., Lauder, G.V., 2014. Biomimetic shark skin: Design, fabrication and hydrodynamic function. Journal of Experimental Biology 217, 1656-1666.</span></p>
<p><span>Wen, L., Weaver, J.C., Thornycroft, P.J., Lauder, G.V., 2015. Hydrodynamic function of biomimetic shark skin: Effect of denticle pattern and spacing. Bioinspiration & Biomimetics 10, 066010.</span></p>
</div></div></div><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-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/417">Journal Club Forum</a></div></div></div>Sat, 03 Jun 2017 12:37:50 +0000mmporter21280 at http://imechanica.orghttp://imechanica.org/node/21280#commentshttp://imechanica.org/crss/node/21280SLM Ti-6Al-4V Plastic Anisotropy
http://imechanica.org/node/21356
<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/5109">anisotropic plasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/7060">1D plasticity</a></div><div class="field-item even"><a href="/taxonomy/term/4948">titanium alloy</a></div><div class="field-item odd"><a href="/taxonomy/term/6863">Titanium</a></div><div class="field-item even"><a href="/taxonomy/term/3568">additive manufacturing</a></div><div class="field-item odd"><a href="/taxonomy/term/4371">SLM</a></div><div class="field-item even"><a href="/taxonomy/term/2520">Cyclic Plasticity</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><strong>Cyclic Plasticity and Microstructure of As-built SLM Ti-6Al-4V: The Effect of Build Orientation</strong></span></p>
<p>D. Agius, K.I. Kourousis, C. Wallbrink, T. Song</p>
<p><strong><em>Materials Science & Engineering: A (2017) -- </em></strong><strong>Free access to the full article available at: <a href="https://authors.elsevier.com/a/1VHXL_Ky~FZJ6H">https://authors.elsevier.com/a/1VHXL_Ky~FZJ6H</a></strong></p>
</div></div></div>Tue, 27 Jun 2017 16:31:26 +0000kourousis21356 at http://imechanica.orghttp://imechanica.org/node/21356#commentshttp://imechanica.org/crss/node/21356Reaction diffusion problems in mechanics
http://imechanica.org/node/21355
<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/11686">Reaction diffusion</a></div><div class="field-item odd"><a href="/taxonomy/term/11687">coupled nonlinear PDEs</a></div><div class="field-item even"><a href="/taxonomy/term/11688">time stepping techniques</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>For those interested in this topic, we are organizing a <strong>minisymposium at the European Solid Mechanics Conference</strong> (sponsored by EUROMECH) in Bologna, in 2018, see session 9.2:</p>
<p><a href="http://www.esmc2018.org/drupal8/node/9">http://www.esmc2018.org/drupal8/node/9</a></p>
<p>Some examples are:</p>
<p><strong>Reaction diffusion and Brinkman flow to model chemical reactions and the motion of a contaminated viscous fluid:</strong></p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0021999117303807">http://www.sciencedirect.com/science/article/pii/S0021999117303807</a></p>
<p><a href="https://www.google.it/url?sa=t&source=web&rct=j&url=https://hal.archives-ouvertes.fr/hal-01401903/document&ved=0ahUKEwj0qKrV793UAhUKIMAKHW1gCOUQFggcMAA&usg=AFQjCNGnemUapeyWfy3WDl0OKar9qX3CrA">https://www.google.it/url?sa=t&source=web&rct=j&url=https://hal.archives...</a></p>
<p><strong>Degradation of polymers (temperature, moisture and chemical reactions):</strong></p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S0927024817300673?via%3Dihub">http://www.sciencedirect.com/science/article/pii/S0927024817300673?via%3...</a></p>
<p> </p>
<p><strong>Other well known applications regard biological systems, such as electrophysiology of the hearth, and brain growth models based on Turing instabilities.</strong></p>
<p>Due to the different dynamics and time scales of the fields involved, novel time integration schemes have been developed.</p>
<p> </p>
<p>We encourage participation from any field of mechanics, with original contributions on mathematical modelling, numerical methods, physical evidences related to the exploitation of reaction diffusion systems in mechanics.</p>
</div></div></div>Tue, 27 Jun 2017 11:12:11 +0000marco.paggi21355 at http://imechanica.orghttp://imechanica.org/node/21355#commentshttp://imechanica.org/crss/node/21355What is the physical meaning of Green-Lagrangian strain and Eulerian-Almansi strain measures?
http://imechanica.org/node/21334
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</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>Hello, researchers. I have difficulty in understanding the physical meaning of Green-Lagrangian strain (E) and Eulerian-Almansi strain (A) measures. Mathematically speaking, I can derive the equations of these strains in different ways. But physically speaking, it's a bit harder to understand how these strains (E and A) can be pictured and how to give a proper physical definition for them. In a simple case, considering a uni-axial bar (Please refer the attached file), Engineering strain can be understood easily, but in E and A equations, from where do the squares of the lengths originate? and how does it came into the picture?. or Is E and A are the true strain measures and engineering strain is the linearization of E and A?. How to understand this? I referred several books and online sources, but I failed to understand the clear interpretation of these strain measures (E and A). Would be much appreciated if someone explains me this or give me the useful references to read. Thanks in advance.</p>
</div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/2882">Continuum mechanics; nonlinear elasticity</a></div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/109">Ask iMechanica</a></div></div></div><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>Tue, 20 Jun 2017 19:26:30 +0000Sundaraelangovan selvam21334 at http://imechanica.orghttp://imechanica.org/node/21334#commentshttp://imechanica.org/crss/node/21334Latest progresses on the phase field model for brittle fracture
http://imechanica.org/node/21328
<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/11672">Phase field model of fracture</a></div><div class="field-item odd"><a href="/taxonomy/term/11673">Solid shells</a></div><div class="field-item even"><a href="/taxonomy/term/2202">interface fracture</a></div><div class="field-item odd"><a href="/taxonomy/term/3502">computational methods</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 Fracture mechanician,</p>
<p>In my group we published 2 articles with novelties on the phase field model for brittle fracture:</p>
<p> </p>
<p><strong>1. New formulation that combines the phase field model of brittle fracture and the interface cohesive zone model</strong>, recovering the fundamental solutions by He and Hutchinson on crack deflection vs. penetration at an interface, and further generalizing them to cohesive fracture: <a href="http://www.sciencedirect.com/science/article/pii/S0045782516317066">http://www.sciencedirect.com/science/article/pii/S0045782516317066</a><a href="http://www.sciencedirect.com/science/article/pii/S0045782516317066" target="_blank"></a></p>
<p> </p>
<p><strong>2. Implementation of the phase field model of fracture in solid shells for geometrical and mechanical nonlinear problems</strong>, with ANS and EAS techniques to avoid locking, and with interpolation of the phase field through the thickness:</p>
<p><a href="https://link.springer.com/article/10.1007/s00466-017-1386-3">https://link.springer.com/article/10.1007/s00466-017-1386-3</a></p>
<p> </p>
<p>If you are interested in collaborations on these topics, please contact <a href="mailto:marco.paggi@imtlucca.it">marco.paggi@imtlucca.it</a> </p>
<p> </p>
<p>As ever,</p>
<p>Marco </p>
</div></div></div>Sat, 17 Jun 2017 17:37:59 +0000marco.paggi21328 at http://imechanica.orghttp://imechanica.org/node/21328#commentshttp://imechanica.org/crss/node/21328A cohesive zone framework for environmentally assisted fatigue (code included)
http://imechanica.org/node/21327
<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/8387">hydrogen embrittlement</a></div><div class="field-item odd"><a href="/taxonomy/term/395">cohesive zone model</a></div><div class="field-item even"><a href="/taxonomy/term/11165">Hydrogen diffusion</a></div><div class="field-item odd"><a href="/taxonomy/term/9981">Fatigue crack growth</a></div><div class="field-item even"><a href="/taxonomy/term/248">finite element analysis</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>I hope some of you find this work interesting, the code with the cohesive zone model for fatigue can be downloaded as a user element (UEL) subroutine for Abaqus from <a title="empaneda.com/codes" href="http://www.empaneda.com/codes/">empaneda.com/codes</a></p>
<p>A cohesive zone framework for environmentally assisted fatigue</p>
<p>Susana del Busto, Covadonga Betegón, Emilio Martínez Pañeda</p>
<p>Engineering Fracture Mechanics (2017)</p>
<p><a href="http://www.sciencedirect.com/science/article/pii/S001379441730098X">http://www.sciencedirect.com/science/article/pii/S001379441730098X</a></p>
<p>We present a compelling finite element framework to model hydrogen assisted fatigue by means of a hydrogen- and cycle-dependent cohesive zone formulation. The model builds upon: (i) appropriate environmental boundary conditions, (ii) a coupled mechanical and hydrogen diffusion response, driven by chemical potential gradients, (iii) a mechanical behavior characterized by finite deformation J2 plasticity, (iv) a phenomenological trapping model, (v) an irreversible cohesive zone formulation for fatigue, grounded on continuum damage mechanics, and (vi) a traction-separation law dependent on hydrogen coverage calculated from first principles. The computations show that the present scheme appropriately captures the main experimental trends; namely, the sensitivity of fatigue crack growth rates to the loading frequency and the environment. The role of yield strength, work hardening, and constraint conditions in enhancing crack growth rates as a function of the frequency is thoroughly investigated. The results reveal the need to incorporate additional sources of stress elevation, such as gradient-enhanced dislocation hardening, to attain a quantitative agreement with the experiments.</p>
</div></div></div>Sat, 17 Jun 2017 09:58:26 +0000Emilio Martínez Pañeda21327 at http://imechanica.orghttp://imechanica.org/node/21327#commentshttp://imechanica.org/crss/node/21327ARENA: A constitutive model for high-rate loading of partially saturated soils
http://imechanica.org/node/21321
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>New paper: ARENA model for partially saturated soils. <a title="http://www.parresianz.com/mechanics/Arena-model-paper/" href="http://www.parresianz.com/mechanics/Arena-model-paper/">http://www.parresianz.com/mechanics/Arena-model-paper/</a></p>
<p>-- Biswajit</p>
</div></div></div>Wed, 14 Jun 2017 22:05:09 +0000Biswajit Banerjee21321 at http://imechanica.orghttp://imechanica.org/node/21321#commentshttp://imechanica.org/crss/node/21321Recent Work "Modeling the Energy Storage and Structural Evolution during Finite Viscoplastic Deformation of Glassy Polymers"
http://imechanica.org/node/21319
<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/11668">nonequilibrium thermodynamics</a></div><div class="field-item odd"><a href="/taxonomy/term/10601">Aging and rejuvenation</a></div><div class="field-item even"><a href="/taxonomy/term/11669">glassy polymers</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 enthalpic response of amorphous polymers depends strongly on their thermal and deformation history. Annealing just below the glass transition temperature (Tg) causes a large endothermic overshoot of the isobaric heat capacity at Tg as measured by differential scanning calorimetry, while plastic deformation (cold work) can erase this overshoot and create an exothermic undershoot. This indicates that a strong coupling exists between the polymer structure, thermal response and mechanical deformation. In this work, we apply a recently developed thermomechanical model for glassy polymers that couples structural evolution and viscoplastic deformation, to investigate the effect of annealing and plastic deformation on the accumulation of stored energy during cold work and calorimetry measurements of heat flow. The thermomechanical model introduces the effective temperature as an additional state variable in a nonequilibrium thermodynamics setting, to describe the structural evolution of the material. The results show that the model accurately describes the stress and enthalpy response of quenched and annealed polymers with different plastic pre-deformations. The model also shows that at 30% strain in uniaxial compression, 45% of the applied work is converted into stored energy, which is consistent with experimental data from the literature. </p>
<p> </p>
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</div></div></div>Wed, 14 Jun 2017 07:25:46 +0000Rui Xiao21319 at http://imechanica.orghttp://imechanica.org/node/21319#commentshttp://imechanica.org/crss/node/21319CiteScore 2016 indicates soaring impact of Extreme Mechanics Letters
http://imechanica.org/node/21307
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://www.journals.elsevier.com/extreme-mechanics-letters"><img src="https://www.evise.com/staticcontent/eviseimages/jrnllogo/EVISE_JRNL1369_BANNER.png" alt="" width="600" height="60" /></a></p>
<p><a title="CiteScore" href="https://journalmetrics.scopus.com/" target="_blank">CiteScore </a>is an impact factor based on a 3-year citation window, calculated using data from the Scopus database. <a title="CiteScore" href="https://journalmetrics.scopus.com/" target="_blank">CiteScore </a>is free to use, comprehensive and transparent.</p>
<p>Based on the newly released CiteScore 2016, <a href="https://www.journals.elsevier.com/extreme-mechanics-letters">Extreme Mechanics Letters</a> received a CiteScore of 3.70, which ranks it in <a href="https://www.scopus.com/sourceid/21100376821#tabs=1">95th percentile among all Mechanical Engineering journals and 94th among all Mechanics of Materials journals</a>. This represents a drastic increase of EML’s CiteScore from its 2015 figure (1.30), epitomizing the soaring impact of the journal. </p>
<p><a href="https://www.journals.elsevier.com/extreme-mechanics-letters">Extreme Mechanics Letters</a> publishes rapid communication of research that highlight the role of mechanics in multi-disciplinary areas across materials science, physics, chemistry, biology, medicine and engineering; with an emphasis on the impact, depth and originality of new concepts, methods and observations at the forefront of applied sciences.</p>
</div></div></div>Sat, 10 Jun 2017 02:55:17 +0000Teng Li21307 at http://imechanica.orghttp://imechanica.org/node/21307#commentshttp://imechanica.org/crss/node/21307Bone remodeling: Komarova model
http://imechanica.org/node/21306
<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/289">ABAQUS</a></div><div class="field-item odd"><a href="/taxonomy/term/3333">subroutine</a></div><div class="field-item even"><a href="/taxonomy/term/4573">bone remodeling</a></div><div class="field-item odd"><a href="/taxonomy/term/11665">Komarova model</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 Community,</p>
<p>I make a code public for bone remodeling, using the Komarova model. It was developed by me alone. I provide the code as is, without warranty. </p>
<p>The agreement between my data and the ones from a reference are very good for fixed loading, but deviate for a more intricate loading. Lacking access to Abaqus with a Fortran compiler, I am at present unable to pinpoint the cause for the discrepancy between my data and data from the reference. The code can serve as a starting point and I give directions how to identify the cause for that discrepancy.</p>
<p>The self-coded part of the subroutine ends at the subroutine ODEX. This ODEX-code provides a numerical solution of a system of first order ordinary differential equations and was taken off the shelf. That part of the program was coded by mathematicians. Don't let it bother you, it acts as black box. Mathematical advisory needed !</p>
<p>I recommend to first study the reference [1] as it presents reference solutions for fixed stimulus values.</p>
<p>List of State Variables:<br />01 number of osteoclasts<br />02 number of osteoblasts<br />03 number of inactive osteoclasts <br />04 number of inactive osteoblasts<br />05 number of active osteoclasts <br />06 number of active osteoblasts<br />07 density<br />08 temporal variation of the density<br />09 variation of the density<br />10 Young's modulus<br />11 Poisson's ratio<br />12 density of the elastic energy<br />13 stimulus DELTA_E<br />14 g12<br />15 g21<br />16 speed of the variation of the number of osteoclasts = d(n1)/dt<br />17 speed of the variation of the number of osteoblasts = d(n2)/dt<br />18 omega (defined in [2] after Eq. (11))<br />19 zeta (defined in [2], Eq. (13))</p>
<p> <br /> <br />The following simulations are included in the attachment:</p>
<p>1) the simulations V01, V02, V03. These are the three simulations to [1] with fixed values for the stimulus, defined in the subroutine. Thus, loading or deformation of the FEM model was not required and the input-files to V01, V02, V03 are identical.<br />The Fortran-files differ only in their definition of DELTA_E.</p>
<p>2) V07 defines DELTA_E as given in [2], equation 18. The simulation was not analyzed as V08, with results easier to verify, generated a discrepancy to the expected values, see below. Also, the loading of the model is not as indicated in [2].</p>
<p>3) V08 imposes the stimulus DELTA_E in Fig. 7 from [1]. This stimulus, of course, should follow from external loading of the model. As a preliminary version, the stimulus is defined here as a function of time within the subroutine. The figure referred to was digitized, and a time function allows to interpolate linearly between the time points. Thus, once again, no external loading or deformation of the model was required. </p>
<p>The initial Young's modulus in this simulation follows from the fit formula for the modulus vs. density with the indicated value for the density. There is obviously a misprint in my input-file, the value is presumably a minor error.</p>
<p>The density of an element in my simulation V08 deviates from the one depicted in Fig. 7. This deviation might originate from an inaccuracy in my code. Another possibility is that the authors inadvertently inserted a graph for density vs. time from another simulation. Mind that the strain for that simulation is given as 0.04% in the figure caption and as 0.4% in the text. </p>
<p>I have access to Abaqus at present, but it is not equipped with a Fortran compiler. Thus, I am unable to modify and run simulations with subroutines.</p>
<p>I recommend:<br />a) delete the imposed DELTA_E as given in the subroutine V08.f, and replace it with the definition of eq. (6) in [1].<br />b) define straining of the model to 0.04% or 0.4% in V08.inp.<br />c) compare the output for the stimulus DELTA_E with Fig. 7.</p>
<p>If you do not succeed in reproducing the data from Fig. 7, then proceed to analyze V07.</p>
<p>As I was quite satisfied with my simulations listed unter 1) at this point and did not need the code any more, I discontinued that project at this point.</p>
<p>The zip-file contains:<br />a) all input-files. As the stimulus was defined in the subroutine, the geometry should be arbitrary, provided three directions in space exist as required by the definition of elasticity in the subroutine.<br />b) all Fortran-files. They differ only in their definition of the stimulus DELTA_E.<br />c) A Mathematica-Notebook 'Komarova-model.nb' for the analysis of 1) above, also printed to a pdf-file.</p>
<p>The attachment is a zip-file, but the site does not allow uploading zips. Change the file extension.</p>
<p>The above-mentioned Mathematica-Notebook also provides an analysis of the model in Mathematica, finding a numerical solution to the ordinary differential equations, in addition to the graphical representation of the Abaqus data for the simulations in 1) above. Both solutions generate a very good match to the data depicted in [1].</p>
<p>Abaqus was used in its release 6.9-EF1.</p>
<p>See also<br /><a href="http://imechanica.org/node/13153">http://imechanica.org/node/13153</a><br />for a list of publications that leak their codes in full or at least describe the algorithm in some detail.</p>
<p>You are free to use the code. Please kindly indicate the source of the code. </p>
<p>Kind regards</p>
<p>Frank Richter </p>
<p>References:<br />[3] and [4] were not studied while working on the project</p>
<p>[1] N. Bonfoh, M. Bilasse, P. Lipinski: <br />Modélisation du remodelage osseux <br />Revue de Mécanique Appliquée et Théorique, Vol. 1 (2008), no. 10, pages 717-726 <br /> <br />[2] N. Bonfoh, E. Novinyo, P. Lipinski:<br />Modeling of bone adaptative behavior based on cells activities<br />Biomech Model Mechanobiol, vol. 10 (2011), pages 789–798</p>
<p>[3] S.V. Komarova, R.J. Smith, S.J. Dixon, S.M. Sims, L.M. Wahl:<br />Mathematical model predicts a critical role for osteoclast autocrine regulation in the control of bone remodeling<br />Bone, vol. 33 (2003), pages 206–215</p>
<p>[4] S.V. Komarova:<br />Mathematical Model of Paracrine Interactions between Osteoclasts and Osteoblasts Predicts Anabolic Action of Parathyroid Hormone on Bone<br />Endocrinology, vol. 146 (2005), no. 8, pages 3589–3595</p>
<p></p>
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</div></div></div>Fri, 09 Jun 2017 21:01:02 +0000Frank Richter21306 at http://imechanica.orghttp://imechanica.org/node/21306#commentshttp://imechanica.org/crss/node/21306PhD positions in mechanics of advanced materials at the University of Minnesota
http://imechanica.org/node/21304
<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/2106">PHD position</a></div><div class="field-item odd"><a href="/taxonomy/term/584">mechanics</a></div><div class="field-item even"><a href="/taxonomy/term/11664">acoustics metamaterials</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>PhD positions in the broad area of mechanics of advanced materials and metamaterials are available in the group of Prof. Stefano Gonella (</span><a href="http://personal.cege.umn.edu/~gonella/"><span>http://personal.cege.umn.edu/~gonella/</span></a><span>) at the University of Minnesota. </span></p>
<p><span>Current topics of interest include: 1) N<span class="apple-converted-space">onlinear metamaterials, including soft architected lattices; 2) Topological and non-reciprocal metamaterials; 3) Tunable and programmable multifunctional materials and structures</span>.</span></p>
<p><span>The ideal candidate is a highly motivated and creative student with solid foundations in mechanics and/or physics, coding experience and strong communication skills. </span></p>
<p><span>Applicants must submit a statement of interest, a detailed resume, indicating education, experience and qualifications, and the names and contact of references. <strong>Applications and inquiries should be sent via email to Prof. Stefano Gonella at <a href="mailto:sgonella@umn.edu">sgonella@umn.edu</a></strong>. <strong>Qualified candidates will be contacted to schedule a follow-up phone/Skype interview.</strong> </span></p>
<p><span>The University of Minnesota is one of the most comprehensive and prestigious public universities in the United States. The campus is located in the vibrant heart of the Minneapolis-Saint-Paul metropolitan area (the Twin Cities), one of the fastest-growing economic, artistic and cultural hubs in the nation, just blocks from theaters, museums, professional sports venues and endless outdoors recreation opportunities.</span></p>
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</div></div></div>Fri, 09 Jun 2017 14:26:14 +0000stefanogonella21304 at http://imechanica.orghttp://imechanica.org/node/21304#commentshttp://imechanica.org/crss/node/21304Investigating phase formations in cast AlFeCoNiCu high entropy alloys by combination of computational modeling and experiments
http://imechanica.org/node/21298
<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/11633">high entropy alloys</a></div><div class="field-item odd"><a href="/taxonomy/term/3371">DFT</a></div><div class="field-item even"><a href="/taxonomy/term/4260">phase diagrams</a></div><div class="field-item odd"><a href="/taxonomy/term/11661">HTXRD</a></div><div class="field-item even"><a href="/taxonomy/term/2777">SEM</a></div><div class="field-item odd"><a href="/taxonomy/term/4081">EBSD</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>Selection and thermal stability of phases are important in design of high entropy alloys (HEA). In this study, phase formations in cast AlFeCoNiCu HEA were investigated. Ab-initio molecular dynamics (AIMD) simulations were used to determine crystal structures of phases at different temperatures in equiatomic composition of AlFeCoNiCu. The AIMD results showed a possible coexistence of a face-centered cubic (fcc) phase and a bodycentered cubic (bcc) phase at the room temperature and indicated stabilization of a single fcc phase above 1070 K at the equiatomic composition of AlFeCoNiCu. The phase diagrams of AlFeCoNiCu system were calculated using a modified thermodynamic approach based on CALPHAD and Muggianu's methods. The calculated phase diagrams showed formation of the same two phases at the room temperature, and a phase transformation at about 1010 K to form a single fcc phase. The characterization experiments utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) confirmed the crystal structures and composition of phases determined by AIMD simulations and phase diagram calculations. High temperature XRD (HTXRD) analysis showed a significant increase in weight fraction of the fcc phase at high<br />temperatures confirming the predicted phase transformation.</p>
<p class="MsoPlainText">Materials & Design 127 (2017), Pages 224–232: <strong>Freely access this article until July 28, 2017</strong></p>
<p class="MsoPlainText"><a href="https://authors.elsevier.com/a/1VB1Hy3Zws2Po">https://authors.elsevier.com/a/1VB1Hy3Zws2Po</a></p>
</div></div></div>Thu, 08 Jun 2017 13:54:10 +0000mohsenzaeem21298 at http://imechanica.orghttp://imechanica.org/node/21298#commentshttp://imechanica.org/crss/node/21298Regarding implementation of an integration scheme which avoids the need of contact surface segmentation.
http://imechanica.org/node/21297
<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/7762">computational contact mechanics</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 All,</p>
<p>As FEA is one of the most popular methods for the treatment of contact problems. In that, the overall contact surface is discretized a number of segments and contact integrals are evaluated in a segment-wise manner. In 2005 Fischer and Wriggers [1] presented an integration method which avoids the need of contact surface segmentations and enables the evaluation of contact integrals directly at the slave nodes of contact bodies. </p>
<p>However, I couldn't follow the integration approach presented in [1]. Therefore, seeking help if you could help or suggest me to be able to implement the same in my code. </p>
<p> </p>
<p>Thanks in advance.</p>
<p> </p>
<p>Best regards,</p>
<p>Vishal Agrawal</p>
<p> </p>
<p><strong>Reference</strong><span> </span></p>
<p>[1] K. A. Fischer, P. Wriggers, Frictionless 2D contact formulation for finite deformation based on mortar method, Comput. Mech. 36 (2005)226-244.</p>
</div></div></div>Thu, 08 Jun 2017 13:33:29 +0000Vishal Agrawal21297 at http://imechanica.orghttp://imechanica.org/node/21297#commentshttp://imechanica.org/crss/node/21297Adverse Effects of Polymer Coating on Heat Transport at Solid-Liquid Interface
http://imechanica.org/node/21296
<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/11659">poymers</a></div><div class="field-item odd"><a href="/taxonomy/term/1029">interfaces</a></div><div class="field-item even"><a href="/taxonomy/term/7535">heat conduction</a></div><div class="field-item odd"><a href="/taxonomy/term/93">molecular dynamics</a></div><div class="field-item even"><a href="/taxonomy/term/11660">Solid-liquid interfaces</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>Published in </span><strong>The Journal of Physical Chemistry C</strong><span><strong>: </strong></span><span><a href="http://pubs.acs.org/doi/pdf/10.1021/acs.jpcc.7b02123">http://pubs.acs.org/doi/pdf/10.1021/acs.jpcc.7b02123</a></span></p>
<p><span>The ability of metallic nanoparticles to supply heat to a liquid environment under exposure to an external optical field has attracted growing interest for biomedical applications. Controlling the thermal transport properties at a solid-liquid interface then appears to be particularly relevant. In this work, we address the thermal transport between water and a gold surface coated by a polymer layer. Using molecular dynamics simulations, we demonstrate that increasing the polymer density displaces the domain resisting to the heat flow, while it doesn’t affect the final amount of thermal energy released in the liquid. This unexpected behavior results from a trade-off established by the increasing polymer density which couples more efficiently with the solid but initiates a counterbalancing resistance with the liquid.</span></p>
</div></div></div>Thu, 08 Jun 2017 13:31:09 +0000nuaajsh21296 at http://imechanica.orghttp://imechanica.org/node/21296#commentshttp://imechanica.org/crss/node/21296A ``small'' but interesting riddle from the theory of vibrations
http://imechanica.org/node/21295
<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/612">vibrations</a></div><div class="field-item odd"><a href="/taxonomy/term/180">thermodynamics</a></div><div class="field-item even"><a href="/taxonomy/term/6006">classical physics</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>Here is a ``small'' riddle from classical physics which I recently happened to think of, in connection with my studies of QM. See if it interests you.</p>
<p>See the figure below.</p>
<p><img src="http://imechanica.org/files/vib_string_with_middle_support_touching_it.png" alt=" An ideal vibrating string with a removable support at the mid-point" width="600" height="120" /></p>
<p>There is an idealized string tautly held between two fixed end-supports that are a distance L apart. The string can be put into a state of vibrations by plucking it. There is a third support exactly at the mid-point; it can be removed at will. When touching the string, the middle support does not permit vibrations to pass through it.</p>
<p>Initially, the middle support is touching the string. </p>
<p>At time t_0, the left-half carries a standing wave pattern in the fundamental normal mode (i.e. it is the fundamental mode for the <em>half</em> part on the left hand-side, i.e., its half-wavelength is L/2). Denote its frequency as \nu_1. At this time, the right-half is perfectly quiscent. Thus, energy is present only in the left-half of the system.</p>
<p>At time t_1, the middle support is suddenly removed. Now, disturbances from any of the two halves can freely propagate into the other half.</p>
<p>Assume that at a time t_F >> t_1, the system reaches a steady-state pattern of standing waves.</p>
<p>The issue of interest is:</p>
<p><em>What is/are the frequency/frequencies of the standing waves now present over the entire length L?</em></p>
<p>Mathematically, the fundamental mode for the entire length L as well as <em>any</em> and <em>all</em> of its overtones are possible, provided that their individual amplitudes are such that the law of energy conservation would not get violated.</p>
<p>Practically speaking, however, <em>only</em> the fundamental mode for the total length (L) is observed. </p>
<p>In short:</p>
<p>Thermodynamically, an infinity of tones are perfectly possible. Yet, in reality, only one tone of them gets selected, and that too is always only the fundamental mode (for the new length). What gives?</p>
<p><em>What precisely is the reason that the system gets settled into one and only one option—indeed an extreme option—out of an infinity of them, all of which are, energetically speaking, equally possible?</em></p>
<p>Comments are welcome!</p>
<p>A very verbose version of this problem was posted yesterday at my personal blog, here: [<a href="https://ajitjadhav.wordpress.com/2017/06/07/an-interesting-problem-from-the-classical-mechanics-of-vibrations/" target="_blank">^</a>] </p>
<p>PS: If there is a useful reference where this problem already appears, please do drop a line; thanks in advance.</p>
<p>Best,</p>
<p>--Ajit</p>
<p> </p>
<p> </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">
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</div></div></div>Thu, 08 Jun 2017 09:50:12 +0000Ajit R. Jadhav21295 at http://imechanica.orghttp://imechanica.org/node/21295#commentshttp://imechanica.org/crss/node/21295Postdoc positions in Nonlinear Solid Mechanics, MIT
http://imechanica.org/node/21287
<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/871">postdoc</a></div><div class="field-item odd"><a href="/taxonomy/term/541">job</a></div><div class="field-item even"><a href="/taxonomy/term/584">mechanics</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="form-text"><span>I am in search of two postdocs to join my group, at MIT, on September 1st , 2017, or earlier. These positions will provide a unique flexibility in choice of research topic which will, in general, target problems in nonlinear solid mechanics. See our group website (<a href="http://tal-cohen.wixsite.com/website">http://tal-cohen.wixsite.com/website</a>) for more information on our present research thrusts. Though our primary focus is on theoretical mechanics, candidates with experimental and computational experience are also encouraged to apply.</span></p>
<p class="form-text"><span>Please send applications to <a href="mailto:talco@mit.edu">talco@mit.edu</a> and include a (i) Cover Letter, your (ii) CV, and (iii) <span>Two Recommendation Letters</span>* to be sent separately.</span></p>
<p class="form-text"><span>Applications will be considered only upon submission of all three items listed obove and the positions will remain open until filled. <br /></span></p>
<p class="form-text"><span>* It is the reponsibility of the candidate to arrange for reference letters to be sent.</span></p>
<p class="form-text"><span> </span></p>
<p class="form-text"><span> </span></p>
<p class="form-text"><span> </span></p>
<p> </p>
<p> </p>
</div></div></div>Tue, 06 Jun 2017 14:51:06 +0000TalCohenMIT21287 at http://imechanica.orghttp://imechanica.org/node/21287#commentshttp://imechanica.org/crss/node/21287Seek your input on nano-indentation or basic mechanics of materials
http://imechanica.org/node/21286
<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/4643">Nano-indentation</a></div><div class="field-item odd"><a href="/taxonomy/term/597">mechanics of materials</a></div><div class="field-item even"><a href="/taxonomy/term/11658">material tests</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"><img src="http://blogs.rsc.org/sc/files/2011/08/c1sc00430a_nanoindentation_410_tcm18-206451.jpg" alt="" width="410" height="147" /></p>
<p class="MsoNormal">Dear researchers----We spent more than two years to prepare a research proposal and it was submitted to a federal funding agency (not NSF). Based on one reviewer’s comments, the program manager rejected our proposal. Our title is “A Multi-Scale Approach of Combining Nano-indentation with Computational Mechanics to Predict Impact Behavior of Structural Composite Materials”. I only list these comments related to nano-indentation. Your frank opinion is really appreciated.</p>
<p class="MsoNormal"> Reviewer said 1. “the nano-indentation method employs low velocity impact methods although the actual impact problems for aircraft are high speed, highly dynamic, and highly non-linear problems.”</p>
<p class="MsoNormal"> 2. “It is not clear how the proposed quasi-static method can predict plastic response of a wide range of speed variations.”</p>
<p class="MsoNormal"> 3. “The proposal could also be improved by explaining the methodology to capture delamination using nano-indentation techniques on matrices or on fibers as simulation parameters.”</p>
</div></div></div>Mon, 05 Jun 2017 20:41:06 +0000L. Roy Xu21286 at http://imechanica.orghttp://imechanica.org/node/21286#commentshttp://imechanica.org/crss/node/21286Best journals in the field of welding
http://imechanica.org/node/21283
<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/6227">Friction Stir welding(FSW)</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>Please introduce the best journals and conferences in the field of welding. </p>
<p>Thank you in advance</p>
<p> </p>
<p>Mab</p>
</div></div></div>Mon, 05 Jun 2017 18:23:23 +0000Mab-M21283 at http://imechanica.orghttp://imechanica.org/node/21283#commentshttp://imechanica.org/crss/node/21283Unification of Mechanics and Thermodynamics: Finally Done.
http://imechanica.org/node/21273
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="https://plus.google.com/114459636678637969101/posts/5yGASSkvAmw">https://plus.google.com/114459636678637969101/posts/5yGASSkvAmw</a></p>
<p> </p>
<p> </p>
</div></div></div>Fri, 02 Jun 2017 03:16:58 +0000cemalbasaran21273 at http://imechanica.orghttp://imechanica.org/node/21273#commentshttp://imechanica.org/crss/node/21273On a systematic approach for cracked rotating shaft study: breathing mechanism, dynamics and instability
http://imechanica.org/node/21271
<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/11653">Cracked shafts Breathing crack Rotordynamics Instability</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="Para">We present a systematic approach to deal with the modelling and analysis of the cracked rotating shafts behaviour. We begin by revisiting the problem of modelling the breathing mechanism of the crack.</p>
<p class="Para">Here we consider an original approach based on the form we give to the energy of the system and then identify the mechanism parameters using 3D computations with unilateral contact conditions on the crack lips.</p>
<p class="Para">A dimensionless flexibility is identified which makes the application of the approach to similar problems straightforward. The additional flexibility due to the crack is then introduced in a simple and comprehensive dynamical system (2 DOF) to characterize the crack effects on the dynamical response of a rotating shaft. Many results could help in early crack detection.</p>
<p class="Para"><a href="https://link.springer.com/article/10.1007/s11071-017-3367-7">https://link.springer.com/article/10.1007/s11071-017-3367-7</a></p>
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<thead><tr><th>Attachment</th><th>Size</th> </tr></thead>
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<tr class="even"><td><span class="file"><img class="file-icon" alt="" title="image/jpeg" src="/modules/file/icons/image-x-generic.png" /> <a href="http://imechanica.org/files/stab_cf002.jpg" type="image/jpeg; length=53774" title="stab_cf002.jpg">Floquet stability</a></span></td><td>52.51 KB</td> </tr>
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</div></div></div>Thu, 01 Jun 2017 10:45:42 +0000saberelarem21271 at http://imechanica.orghttp://imechanica.org/node/21271#commentshttp://imechanica.org/crss/node/21271Is the study of Low Cycle Fatigue (LCF) and cyclic plasticity useful for biomedical metals?
http://imechanica.org/node/21268
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>I would like to open a discussion in relation to the following question:</p>
<p><span><em><strong>"Is the study of Low Cycle Fatigue (LCF) and cyclic plasticity useful for biomedical metals?"</strong></em><em><strong><br /></strong></em></span></p>
<p><span>It appears that there is some level of misunderstanding around this issue. Thus, I would be very interested to find out the views of iMechanica community engineers and researchers working on biomedical metals and applications (i.e. implants) on this.</span></p>
<p>In your responses, I would appreciate if you could state if you have previous/current experience-involvement in biomedical engineering.</p>
<p>Regards,</p>
<p><span>K Kourousis</span></p>
<p> </p>
</div></div></div><div class="field field-name-taxonomy-forums field-type-taxonomy-term-reference field-label-above"><div class="field-label">Forums: </div><div class="field-items"><div class="field-item even"><a href="/forum/109">Ask iMechanica</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-above"><div class="field-label">Free Tags: </div><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/2520">Cyclic Plasticity</a></div><div class="field-item odd"><a href="/taxonomy/term/1399">biomedical materials</a></div><div class="field-item even"><a href="/taxonomy/term/1966">low cycle fatigue</a></div></div></div><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>Tue, 30 May 2017 21:14:08 +0000kourousis21268 at http://imechanica.orghttp://imechanica.org/node/21268#commentshttp://imechanica.org/crss/node/21268A very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model
http://imechanica.org/node/21262
<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/27">adhesion</a></div><div class="field-item odd"><a href="/taxonomy/term/691">rough surfaces</a></div><div class="field-item even"><a href="/taxonomy/term/11651">dmt</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 very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model" is in press in Meccanica, can be viewed at <a href="http://rdcu.be/s0lV">http://rdcu.be/s0lV</a> Abstract In the present note, we suggest a single-line equation estimate for adhesion between elastic(hard) rough solids with Gaussian multiple scales of roughness. It starts from the new observation that the entire DMT solution for ‘‘hard’’ spheres (Tabor parameter tending to zero) with the Maugis law of attraction can be obtained using the Hertzian relationship load-indentation and estimating the area ofattraction as the increase of the bearing area geometrical intersection when the indentation is increased by the Maugis range of attraction. The bearing area modelin fact results in a simpler and even more accurate solution than DMT for intermediate Tabor parameters, although it retains one of the assumptions of DMT, that elastic deformations are not affected by attractive forces. Therefore, a solution is obtained for random rough surfaces combining Persson’s adhesiveless asymptotic simple form solution with the bearing area model, which is trivially computed for a Gaussian. A comparison with recent data from extensive numerical computations involving roughness with wavelength from nano to micrometer scale shows that the approximation is quite good for the pull-off in the simulations, and it remarks the primary importance in this regime of a single parameter, the macroscopic well-deﬁned quantity (rms) amplitude of roughness, and small sensitiveness to rms slopes and curvatures.</p>
<p>Cite this article as:Ciavarella, M. Meccanica (2017). doi:10.1007/s11012-017-0701-6</p>
</div></div></div>Thu, 25 May 2017 11:02:00 +0000Mike Ciavarella21262 at http://imechanica.orghttp://imechanica.org/node/21262#commentshttp://imechanica.org/crss/node/21262A theoretical study on the piezoresistive response of carbon nanotubes embedded in polymer nanocomposites in an elastic region
http://imechanica.org/node/21258
<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/18">micromechanics</a></div><div class="field-item odd"><a href="/taxonomy/term/8194">piezoresistivity</a></div><div class="field-item even"><a href="/taxonomy/term/11647">Experimental analysis</a></div><div class="field-item odd"><a href="/taxonomy/term/7567">Strain sensor</a></div><div class="field-item even"><a href="/taxonomy/term/4512">characterization</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>Herein, we report a theoretical study of polymeric nanocomposites to provide physical insight into complex material systems in elastic regions. A self-consistent scheme is adopted to predict piezoresistive characteristics, and the effects of the interface and of tunneling on the effective piezoresistive and electrical properties of the nanocomposites are simulated. The overall piezoresistive sensitivity is predicted to be reduced when the lower interfacial resistivity of multi-walled carbon nanotubes (MWCNTs) and the higher effective stiffness of nanocomposites are considered. In addition, thin film nanocomposites with various MWCNT weight percentages are manufactured and their electrical performance capabilities are measured to verify the predictive capability of the present simulation. From experimental tests, the nanocomposites show clear piezoresistive behaviors, exhibiting a percolation threshold at less than 0.5 wt% of the MWCNTs. Three sets of comparisons between the experimental data and the present predictions are conducted within an elastic range, and the resulting good correlations between them demonstrate the predictive capability of the present model.</span></p>
<p>Published in Carbon: <a href="http://www.sciencedirect.com/science/article/pii/S0008622317305079">http://www.sciencedirect.com/science/article/pii/S0008622317305079</a></p>
</div></div></div>Wed, 24 May 2017 12:56:06 +0000Hamid Souri21258 at http://imechanica.orghttp://imechanica.org/node/21258#commentshttp://imechanica.org/crss/node/21258Measuring the relative density of open cell metal foams
http://imechanica.org/node/21257
<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/11644">relative density</a></div><div class="field-item odd"><a href="/taxonomy/term/11645">metal foams</a></div><div class="field-item even"><a href="/taxonomy/term/11646">open cell</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>Hello,</p>
<p>I would like to know how to measure the density of open cell porous iron foam. I am studying the mechanical behavior of pure iron foams for which I need to compare the relative densities of different foam samples. Could the density of the foams be simply calculated by the mass over the bulk volume (volume of the struts + volume of the pores) of the foam? Can I use Archimedes principle to calculate the foam density given that I have open cells? What is the best method to calculate the foam density? </p>
<p>Best Regards,</p>
<p>Reza</p>
</div></div></div>Tue, 23 May 2017 05:30:24 +0000rezaalavi100021257 at http://imechanica.orghttp://imechanica.org/node/21257#commentshttp://imechanica.org/crss/node/21257Bioinspired Composite Microfibers for Skin Adhesion and Signal Amplification of Wearable Sensors
http://imechanica.org/node/21256
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span>Published in <strong>Advanced Materials:</strong> <a href="http://onlinelibrary.wiley.com/doi/10.1002/adma.201701353/abstract">http://onlinelibrary.wiley.com/doi/10.1002/adma.201701353/abstract</a></span></p>
<p><span><strong>Abstract:</strong> <span>A facile approach is proposed for superior conformation and adhesion of wearable sensors to dry and wet skin. Bioinspired skin-adhesive films are composed of elastomeric microfibers decorated with conformal and mushroom-shaped vinylsiloxane tips. Strong skin adhesion is achieved by crosslinking the viscous vinylsiloxane tips directly on the skin surface. Furthermore, composite microfibrillar adhesive films possess a high adhesion strength of 18 kPa due to the excellent shape adaptation of the vinylsiloxane tips to the multiscale roughness of the skin. As a utility of the skin-adhesive films in wearable-device applications, they are integrated with wearable strain sensors for respiratory and heart-rate monitoring. The signal-to-noise ratio of the strain sensor is significantly improved to 59.7 because of the considerable signal amplification of microfibrillar skin-adhesive films.</span></span></p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="http://imechanica.org/files/Drotlef_et_al-2017-Advanced_Materials.pdf" type="application/pdf; length=3222406">Drotlef_et_al-2017-Advanced_Materials.pdf</a></span></td><td>3.07 MB</td> </tr>
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</div></div></div>Mon, 22 May 2017 12:39:07 +0000mortezaamjadi21256 at http://imechanica.orghttp://imechanica.org/node/21256#commentshttp://imechanica.org/crss/node/21256Recent Advances in Skin Penetration Enhancers for Transdermal Gene and Drug Delivery
http://imechanica.org/node/21255
<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/11641">drug and drug delivery</a></div><div class="field-item odd"><a href="/taxonomy/term/11642">transdermal delivery</a></div><div class="field-item even"><a href="/taxonomy/term/11643">skin penetration enhancers</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>Published in <strong>Current Gene Therapty</strong>: <a href="https://www.ncbi.nlm.nih.gov/pubmed/28494734">https://www.ncbi.nlm.nih.gov/pubmed/28494734</a></span></p>
<p><span><strong>Abstract:</strong> <span>There is a growing interest in transdermal delivery systems because of their noninvasive, targeted, and on-demand delivery of gene and drugs. However, efficient penetration of therapeutic compounds into the skin is still challenging largely due to the impermeability of the outermost layer of the skin, known as stratum corneum. Recently, there have been major research activities to enhance the skin penetration depth of pharmacological agents. This article reviews recent advances in the development of various strategies for skin penetration enhancement. We show that approaches such as ultrasound waves, laser, and microneedle patches have successfully been employed to physically disrupt the stratum corneum structure for enhanced transdermal delivery. Rather than physical approaches, several non-physical routes have also been utilized for efficient transdermal delivery across the skin barrier. Finally, we discuss some clinical applications of transdermal delivery systems for gene and drug delivery. This paper shows that transdermal delivery devices can potentially function for diverse healthcare and medical applications while further investigations are still necessary for more efficient skin penetration of gene and drugs.</span></span></p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="http://imechanica.org/files/Amjadi-MS_0.pdf" type="application/pdf; length=2771573">Amjadi-MS.pdf</a></span></td><td>2.64 MB</td> </tr>
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</div></div></div>Mon, 22 May 2017 12:36:23 +0000mortezaamjadi21255 at http://imechanica.orghttp://imechanica.org/node/21255#commentshttp://imechanica.org/crss/node/21255Designing Nanostructures for Phonon Transport via Bayesian Optimization
http://imechanica.org/node/21254
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><span><span>Published in <strong>Physical Review X</strong></span><strong>: </strong></span><span><a href="https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021024">https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021024</a></span></p>
<p><span>We demonstrate optimization of thermal conductance across nanostructures by developing a method combining atomistic Green’s function and Bayesian optimization. With an aim to minimize and maximize the interfacial thermal conductance (ITC) across Si-Si and Si-Ge interfaces by means of the </span><span class="aps-inline-formula"><span id="MathJax-Element-1-Frame" class="mjx-chtml MathJax_CHTML"><span id="MJXc-Node-1" class="mjx-math"><span id="MJXc-Node-2" class="mjx-mrow"><span id="MJXc-Node-3" class="mjx-mrow"><span id="MJXc-Node-4" class="mjx-mi"><span class="mjx-char MJXc-TeX-main-R">Si</span></span><span id="MJXc-Node-5" class="mjx-mo MJXc-space1"><span class="mjx-char MJXc-TeX-main-R">/</span></span><span id="MJXc-Node-6" class="mjx-mi MJXc-space1"><span class="mjx-char MJXc-TeX-main-R">Ge</span></span></span></span></span></span></span><span> composite interfacial structure, the method identifies the optimal structures from calculations of only a few percent of the entire candidates (over 60 000 structures). The obtained optimal interfacial structures are nonintuitive and impacting: the minimum ITC structure is an aperiodic superlattice that realizes 50% reduction from the best periodic superlattice. The physical mechanism of the minimum ITC can be understood in terms of the crossover of the two effects on phonon transport: as the layer thickness in the superlattice increases, the impact of Fabry-Pérot interference increases, and the rate of reflection at the layer interfaces decreases. An aperiodic superlattice with spatial variation in the layer thickness has a degree of freedom to realize optimal balance between the above two competing mechanisms. Furthermore, the spatial variation enables weakening the impact of constructive phonon interference relative to that of destructive interference. The present work shows the effectiveness and advantage of material informatics in designing nanostructures to control heat conduction, which can be extended to other nanostructures and properties.</span></p>
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</div></div></div>Sun, 21 May 2017 04:45:06 +0000nuaajsh21254 at http://imechanica.orghttp://imechanica.org/node/21254#commentshttp://imechanica.org/crss/node/21254PhD position available on 4D printing of intelligent marine structures at NTNU Trondheim
http://imechanica.org/node/21253
<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/11640">3D/4D Printing; smart materials; marine structures</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>Please check out the official announcement at:</p>
<p><a href="https://www.jobbnorge.no/en/available-jobs/job/138013/phd-position-in-4d-printing-of-intelligent-marine-structures">https://www.jobbnorge.no/en/available-jobs/job/138013/phd-position-in-4d...</a></p>
</div></div></div>Sat, 20 May 2017 19:40:50 +0000Josef Kiendl21253 at http://imechanica.orghttp://imechanica.org/node/21253#commentshttp://imechanica.org/crss/node/21253PhD position within Marine Hydrodynamics available at NTNU Trondheim
http://imechanica.org/node/21252
<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/11639">Isogeometric analysis (IGA); boundary element method; potential flow; fluid-structure interaction; FSI; flexible propellers</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>Please check the official announcement at:</span></p>
<p><a href="https://www.jobbnorge.no/en/available-jobs/job/124853/phd-position-in-computational-modeling-of-fracture-in-thin-walled-structures">https://www.jobbnorge.no/en/available-jobs/job/138439/phd-position-within-marine-hydrodynamics-iv-136-17</a></p>
</div></div></div>Sat, 20 May 2017 19:31:52 +0000Josef Kiendl21252 at http://imechanica.orghttp://imechanica.org/node/21252#commentshttp://imechanica.org/crss/node/21252Characterization of Human Diaphragm at high strain rate loading.
http://imechanica.org/node/21250
<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-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>In this paper, we studied the strain rate dependent failure properties of human diaphragm tissue using uniaxial tensile testing at four strain rates, i.e. 0.0015/s, 65/s, 130/s and 190/s. The custom made quasi-satatic and drop tower based dynamic test setups was used to conduct the tests uptill 200/s strain rate. The engineering stress- strain curves obtained for diaphragm tissue at every strain rates observed bilinear behaviour - initial low strain toe region which typically represents the physiological range in which soft tissue normally operates and a linear region where collagen fibers become taut in direction of loading. Hence, a blinear constitutive model was developed from the stress-strain curves of human daphragm tissues. The failure properties obtained are of value for use in in human body models.</p>
<p>The paper is attached with this post for the interested readers. </p>
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="http://imechanica.org/files/diaphragm.pdf" type="application/pdf; length=6249009" title="diaphragm.pdf">Diaphragm research paper</a></span></td><td>5.96 MB</td> </tr>
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</div></div></div>Fri, 19 May 2017 19:45:07 +0000gaurp21250 at http://imechanica.orghttp://imechanica.org/node/21250#commentshttp://imechanica.org/crss/node/21250