Plasticity

Dear All,

 I think that many students are looking for some tutorials about writing a UMAT in ABAQUS.

You can find a comprehensive tutorial for elastic problems.

This file contains: 

• Motivation

• Steps Required in Writing a UMAT or VUMAT

• UMAT Interface

• Examples

Example 1: UMAT for Isotropic Isothermal Elasticity

Example 2: UMAT for Non-Isothermal Elasticity

Submitted to the Journal of Applied Mechanics on 2/1/2010. 

 (in Computational Methods for Microstructure-Property Relationships," Springer. Edited by Somnath Ghosh and Dennis Dimiduk)

Dislocation mediated continuum plasticity: case studies on modeling scale dependence, scale-invariance, and directionality of sharp yield-point

Claude Fressengeas, Amit Acharya, Armand Beaudoin

I am working with shape memory alloys (nitinol), and am in that respect investigating fracture behaviour of NiTi, using, among other things, simulations in ABAQUS. ABAQUS doesn't have a material model that include plasticity unless you pay for it. I am wondering if anyone have implemented either of the following models as a UMAT, and if you are willing to share the code with me.

The models I am interested in are:

A post-doc position is available now for one who has recently obtained (or about to get) his/her PhD on computational
geomechanics or computational mechanics. The successful candidate is expected to have strong background of mechanics
and extensive experience on computer programming (e.g., coding in FEM and/or DEM), and is able to work independently.
He/she who has previously worked on multi-scale modeling of material behavior will be particularly welcome to apply. The
initial contract is one year and is extendable to multiple years subject to his/her performance and availability of funding.

(in Journal of the Mechanics and Physics of Solids)

I came upon a recent paper called "Deformation gradients for continuum mechanical analysis of atomistic simulations" by Jonathan A. Zimmerman , Douglas J. Bammann,  and Huajian Gao, International Journal of Solids and Structures 46 (2009) 238–253 where the authors conclude with

My name is Aurelio Tronci and I am a PhD student at the University of Cagliari (Italy). My research topics are related to friction stir welding (FSW). The work done so far has focused on the application of the DOE technique in order to investigate the influence of welding parameters on the microstructural and mechanical properties of aluminum alloys (AA 2198 T3-T8) joints. At the moment I am interested in the development of a thermo-mechanical model of FSW with CFD, but I find it really difficult to find material constants (Sellars and Tegart law) for all the alloys I have to test.

Series on Advances in Mathematics for Applied Sciences - Vol. 80

INELASTICITY OF MATERIALS- An Engineering Approach and a Practical Guide

by 

Article on web

http://www.eng-tips.com/faqs.cfm?fid=1441

The physical basis of material
properties like Young's modulus can be understood by examining
materials on the atomic scale. There are two main things that influence
the value of the modulus:

1.)     The atomic microstructure
2.)     The interatomic bonds.

 So, what is the reason of change of elastic modulus with plastic deformation? Any References??

I have a question regarding the experimental determination of rate independent phenomenological elaso plastic constitutive model.

Since the models are rate independent, does the strain rate in the experiments used to calibrate the model parametes have any influence on the model. I am talking about this in context to the Cap plasticity model used in Abaqus. One has to run a certain number of powder compaction experiments to calibrate the model.

I have a fundamental question regarding flow rules of finite plasticity models especially those used in soil mechanics. In most of the papers and books, I have seen the usage of an associated flow rule with the plastic potential similar to the yield surface. However, I am unable to understand the means of obtaining a non-associative flow rule. I am using Abaqus with cap plasticity model (modified Drucker Prager Cap model) to simulate powder compaction process.

I am currently running a Quasi-Static compression simulation in Abaqus Explicit using the Johnson-Cook Plasticity option. As the strain gets beyond the elastic range, the stress-strain response begins to oscillate +- 5 MPa around the expected curve. Does anyone know why this is happening and/or how to repair the problem?

Thanks, 

D. Barrett Hardin

Dear Mechanical Engineers,

It's my pleasure to be one of your group. I have a question in Abaqus Explicit and all my friends recommended me to as iMechanica as the explicit Abaqus is more popular to you than us as civil engineers.

I’m trying to simulate a tensile test for an elastic-perfectly plastic material as a quasi-static analysis in Abaqus Explicit. I have solved the same problem in Abaqus Standard and the results were fine as follow.

Does anyone knows where I can find any paper discuss the existence of potential functinoal for materials that violate the maximum plastic dissipation principle (due to non-convex yield function and/or non-associately fluw rule)?