research

Rajat Arora        Amit Acharya

Stressed dislocation pattern formation in crystal plasticity at finite deformation is demonstrated for the first time. Size effects are also demonstrated within the same mathematical model. The model involves two extra material parameters beyond the requirements of standard classical crystal plasticity theory. The dislocation microstructures shown are decoupled from deformation microstructures, and emerge without any consideration of latent hardening or constitutive assumptions related to cross-slip. Crystal orientation effects on the pattern formation and mechanical response are also demonstrated. The manifest irrelevance of the necessity of a multiplicative decomposition of the deformation gradient, a plastic distortion tensor, and the choice of a reference configuration in our model to describe the micromechanics of plasticity as it arises from the existence and motion of dislocations is worthy of note.

Amit Acharya          Robin J. Knops         Jeyabal Sivaloganathan

(In JMPS, 130 (2019), 216-244)

Uniqueness of solutions in the linear theory of non-singular dislocations, studied as a special case of plasticity theory, is examined. The status of the classical, singular Volterra dislocation problem as a limit of plasticity problems is illustrated by a specific example that clarifies the use of the plasticity formulation in the study of classical dislocation theory. Stationary, quasi-static, and dynamical problems for continuous dislocation distributions are investigated subject not only to standard boundary and initial conditions, but also to prescribed dislocation density. In particular, the dislocation density field can represent a single dislocation line.

It is only in the static and quasi-static traction boundary value problems that such data are sufficient for the unique determination of stress. In other quasi-static boundary value problems and problems involving moving dislocations, the plastic and elastic distortion tensors, total displacement, and stress are in general non-unique for specified dislocation density. The conclusions are confirmed by the example of a single screw dislocation.

https://www.researchgate.net/publication/328792035_On_the_Structure_of_Linear_Dislocation_Field_Theory

Nemo lives in the ocean near the Great Barrier Reef. One day, he bought a hydrogel balloon which is inflated by an inner pressure p. Will the balloon burst eventually or stay safe?

We introduce our recent works on advanced fabrication and mechanics of hard-magnetic soft materials towards the development of untethered soft machines and robots actuated and controlled by magnetic fields. 

- Abstract

Please see our recent publication in Extreme Mechanics Letters:

Huilong Hou, Peter Finkel, Margo Staruch, Jun Cui & Ichiro Takeuchi, Ultra-low-field magneto-elastocaloric cooling in a multiferroic composite device, Nature Communications 9(1): 4075, (2018).

Beyond piezoelectricity: Flexoelectricity in solids

Jiawang Hong

School of Aerospace Engineering, Beijing Institute of Technology

1. Introduction