Blog posts
Dislocation pattern formation in finite deformation crystal plasticity
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.
Web workshop - Introduction to Simpleware Software, Nov 28 2018
Join us for this interactive web workshop where we will demonstrate the ease of 3D image processing with Simpleware Software. We will walk you through the workflow of how to build high fidelity models from 3D data for a variety of applications.
Research Position Computational Fracture Mechanics
A research position is available at the Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences in order to conduct a strategic project funded by the COMET-K2 Competence Center on Integrated Research in Materials, Processing and Product Engineering in Leoben.
Crack Growth Testing Beach Marks
Dear Fellow Machanicians,
I want to make some beach marks in fatigue cracks – what are the best loads?
To verify crack growth modelling we have put some notches in square (10×10mm) section steel tensile fatigue specimens – so there's a reasonably controlled initiation – at least location. In some the notch is across one side in others it's just on one corner, 0.5mm deep. I have tried one and didn't get the obvious beach marks I was hoping for.
Modelling of deformation and fracture for a model quasi-brittle material with controlled porosity: Synthetic versus real microstructure
Dear all,
Our group has recently published a paper titled "
Modelling of deformation and fracture for a model quasi-brittle material with controlled porosity: Synthetic versus real microstructure" in Engineering Fracture Mechanics. You can find the accepted manuscript at: https://www.researchgate.net/publication/328762356_Modelling_of_deforma…;
Regards,
Key Activities of ASME Materials Division in IMECE 2018 (Pittsburgh, PA)
Dear Colleagues,
Please see the list of key activities of the Materials Division in IMECE 2018 next week. Everyone is welcome!
Materials Division Executive Committee
On the Structure of Linear Dislocation Field Theory
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.
An efficient convergence test for the fixed point method
The fixed point method consists to find the solution of F(X)=X.
One can not get fixed with the convergence condition |F'(X)|<1 because if the function has an optimum then |F'(X)|=0 even if the solution is not yet reached.
We introduce an efficient convergence test with the condition:
|Xn+1 - Xn| ≤ epsilon1 And |F(Xn+1)-Xn+1| ≤ epsilon2
Will Nemo's balloon burst or not?
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?