Wei Hong's blog

Faculty Positions in Interdisciplinary Mechanics 

Department of Mechanics and Aerospace Engineering 

Southern University of Science and Technology

We are organizing a mini-symposium, "Fracture and Instabilities in Soft Materials", on the 13th International Conference on Fracture, which will be held during June 16-21, 2013 in Beijing, China. We would like to invite you to submit an abstract on your recent research findings in related areas. The deadline for abstract submission has now been extended to October 31, 2012.  Instructions on abstract submission can be found at http://www.icf13.org/. The conference anouncement is at http://www.icf13.org/wordpress/wp-content/uploads/2012/08/final0830.pdf.

Consisting of alternating swelling and nonswelling polymeric layers (SLs and NLs), lamellar gels are 1D photonic crystals with tunable optical properties.  The lamellar structure induces a constraint between the SLs and the NLs, resulting in an anisotropic swelling behavior coupled with deformation.

TENURE-TRACK FACULTY POSITION: The Department of Aerospace Engineering at Iowa State University invites applicants for a faculty position in the area of autonomous space systems. The appointment will start in August 2011. The search is focused at the Assistant and Associate Professor level, but exceptional candidates who qualify for the rank of Full Professor will also be considered.

Dielectric elastomer, as an important category of electroactive polymers, is known to have viscoelastic properties that strongly affect its dynamic performance and limit its application. Very few models accounting for the effects of both electrostatics and viscoelasticity exist in the literature, and even fewer are capable of making reliable predictions under general loads and constraints. Based on the principals of nonequilibrium thermodynamics, this paper develops a field theory that fully couples the large inelastic deformations and electric fields in deformable dielectrics.

The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.

Dear Colleague:

The Society of the Engineering Science is sponsoring the 47th Annual Technical Meeting (SES2010) on October 4-6, 2010 at Iowa State University in Ames, IA. The meeting is held on biannual basis as a standalone meeting to foster and promote the exchange of ideas and information among the various disciplines of engineering and the fields of physics, chemistry, mathematics, bioengineering and related scientific and engineering fields.

Due to the migration of mobile molecules and ions, a thin diffusive layer of distributed charge - the electric double layer - forms at the interface between a polyelectrolyte gel and a liquid ionic solution.  When two polyelectrolyte gels are brought closely together, the electric double layers overlap and interact with each other, resulting in an effective repulsion.  The multiphysics coupling nature of soft gels makes their surface interactions significantly different from the interactions between rigid solids.

The electric-field-induced phase transition was investigated under mechanical confinements in bulk samples of an antiferroelectric perovskite oxide at room temperature. Profound impacts of mechanical confinements on the phase transition are observed due to the interplay of ferroelasticity and the volume expansion at the transition. The uniaxial compressive prestress delays while the radial compressive prestress suppresses it. The difference is rationalized with a phenomenological model of the phase transition accounting for the mechanical confinement.

When a block of an elastomer is bent, the compressed surface may form a crease. This paper analyzes the critical condition for creasing by comparing the elastic energy in a creased body and that in a smooth body. This difference in energy is expressed by a scaling relation. Critical conditions for creasing are determined for elastomers subject to general loads and gels swelling under constraint. The theoretical results are compared with existing experimental observations.

Immersed in an ionic solution, a network of polyelectrolyte polymers imbibes the solution and swells, resulting in a polyelectrolyte gel. The swelling is reversible, and is regulated by ionic concentrations, mechanical forces, and electric potentials. This paper develops a field theory to couple large deformation and electrochemistry. A specific material model is described, including the effects of stretching the network, mixing the polymers with the solvent and ions, and polarizing the gel.

The Department of Aerospace Engineering at Iowa State University invites applications for multiple tenure-track faculty positions at the assistant, associate, or full professor ranks to begin August 2009. Applicants are sought in all areas of aerospace engineering and engineering mechanics but preference will be given to those with interest and expertise in aerospace structures/mechanics of materials, multidisciplinary design and analysis, experimental thermal-fluids, propulsion, wind energy, and wind engineering.

There are currently 5 openings for perspective graduate students (preferably applying for a PhD program) in the area of experimental, theoretical or computational solid mechanics (or combined), starting from Fall, 2009.  Recruited students are expected to work with Ashraf Bastawros or Wei Hong.  Possible research topics include: Smart materials/structures, Reliability of micro-electronic devices, Layered structures, Mechanics of soft active materals, etc.

Prof. Zhigang Suo and Prof. Frans Spaepen, of the Harvard School of Engineering and Applied Sciences, have just been elected to the National Academy of Engineering.  They are among 65 new members elected to the NAE in 2008.  Update:  Also elected this year is another mechanician, Robert Dodds, of the University of Illinois.

Hydrogels have enormous potential for making adaptive structures in response to diverse stimuli.  In a structure demonstrated recently, for example, nanoscale rods of silicon were embedded vertically in a swollen hydrogel, and the rods tilted by a large angle in response to a drying environment (Sidorenko, et al., Science 315, 487, 2007).  Here we describe a model to show that this behavior corresponds to a bifurcation at a critical humidity, analogous to a phase transition of the second kind.

   A large quantity of small molecules may migrate into a network of long polymers, causing the network to swell, forming an aggregate known as a polymeric gel.  This paper formulates a theory of the coupled mass transport and large deformation.

A (001) surface of silicon consists of terraces of two variants, which have an identical atomic structure, except for a 90° rotation. We formulate a model to evolve the terraces under the combined action of electric current and applied strain. The electric current motivates adatoms to diffuse by a wind force, while the applied strain motivates adatoms to diffuse by changing the concentration of adatoms in equilibrium with each step. To promote one variant of terraces over the other, the wind force acts on the anisotropy in diffusivity, and the applied strain acts on the anisotropy in surface stress. Our model reproduces experimental observations of stationary states, in which the relative width of the two variants becomes independent of time. Our model also predicts a new instability, in which a small change in experimental variables (e.g., the applied strain and the electric current) may cause a large change in the relative width of the two variants.