research

Stress analysis of composite cylindrical shells with an elliptical cutout  
Erkan Oterkus & Erdogan Madenci & Michael P. Nemeth

Abstract

This paper presents an anharmonic lattice statics analysis of 180 and 90 domain walls in tetragonal ferroelectric perovskites. We present all the calculations and numerical examples for the technologically important ferroelectric material PbTiO3. We use shell potentials that are fitted to quantum mechanics calculations. Our formulation places no restrictions on the range of the interactions. This formulation of lattice statics is inhomogeneous and accounts for the variation of the force constants near defects.

The simple extension tear test-piece also referred to as the trousers sample is widely used to study crack propagation in rubber. The corresponding energy release rate, called tearing energy for rubber materials, was first established by Rivlin and Thomas (Rupture of rubber. I. Characteristic energy for tearing. J. Polym. Sci., 10:291–318, 1953); a second derivation was proposed later by Eshelby (The calculation of energy release rates. In G. C. Sih, H. C. van Elst, and D. Broek, editors, Prospects of Fracture Mechanics, 69–84, Leyden, Noordhoff, 1975).

All metallic, hollow sandwich cylinders having ultralight two-dimensional prismatic cores are optimally designed for maximum thermo-mechanical performance at minimum mass. The heated cylinder is subjected to uniform internal pressure and actively cooled by forced air convection. The use of two different core topologies is exploited: square- and triangular-celled cores. The minimum mass design model is so defined that three failure modes are prevented: facesheet yielding, core member yielding, and core member buckling.

Dr. Jun Lou and Dr. Junlan Wang are co-editing a special issue on Nanomechanics and Nanostructured Multifunctional Materials: Experiments, Theories, and Simulations for Journal of Nanomaterials, an open access journal. Papers on latest developments on all aspects of nanomechanics and nanostructured materials are welcome. Deadline for manuscript submission is September 01, 2007.
 
For more details, please check JNM website

Apply for NSF fellowships to attend 1-week long workshop on cell mechanics, July 31-Aug 3, 2007.

Check out www.ccm.uiuc.edu  

Depolarization field and misfit strain are two important factors that may greatly influence the properties of ferroelectric thin films. The effect of depolarization field on polarization states of single-domain ferroelectric thin films with nonequally biaxial in-plane misfit strains are studied in the present work by numerically solving three coupled Euler-Lagrange equations, which are derived from the minimization of total free energy.

We have recently reported the label-free detection of HCV (Hepatitis C Virus) helicase by using a resonating microcantilever whose surface is functionalized by RNA aptamers as receptor molecules. This work was accepted for publication at Biosensors & Bioelectronics.

Abstract

Abstract 

We study the kinetics of phase transformations in solids using the peridynamic formulation of continuum mechanics. The peridynamic theory is a nonlocal formulation that does not involve spatial derivatives, and is a powerful tool to study defects such as cracks and interfaces.

      This letter describes a method to analyze electromechanical stability of dielectric elastomer actuators.  We write the free energy of an actuator using stretches and nominal electric displacement as generalized coordinates, and pre-stresses and voltage as control parameters.  When the Hessian of the free-energy function ceases to be positive-definite, the actuator thins down drastically, often resulting in electrical breakdown.  Our calculation shows that stability of the actuator is markedly enhanced by pre-stresses.

When an electric voltage is applied across the thickness of a thin layer of an dielectric elastomer, the layer reduces its thickness and expands its area. This electrically induced deformation can be rapid and large, and is potentially useful as soft actuators in diverse technologies. Recent experimental and theoretical studies have shown that, when the voltage exceeds some critical value, the homogenous deformation of the layer becomes unstable, and the layer deforms into a mixture of thin and thick regions.

In a piezoelectric material an applied uniform strain can induce an electric polarization (or vice-versa). Crystallographic considerations restrict this technologically important property to non-centrosymmetric systems. It can be shown both mathematically and physically, that a non-uniform strain can potentially break the inversion symmetry and induce polarization even in non-piezoelectric dielectrics.

2007 Alan T. Waterman Award Winner

Peidong Yang

The National Science Foundation’s Highest Honor