Hi all,

 I am new in the Forum, and I am looking for some informations regarding how to simulate nonlinear material in explicit.

I am tryng to analyse the behaviour of a roller rolling on the sand (or mud), but the results I get with a basic elasto-plastic material are not very accurate, expecially because I cannot set the tension allowed in the sand to be zero.

Other ways to input nonlinearity in Explicit are always refused by ABAQUS. Is there any way to get something more accurate?

Since ABAQUS 6.8, a new feature has been added to the combined hardening
material input.

Let's assume a combined Kinematic and Isotropic hardening case, such as
those happen in metals.

"Half cycle" uni-axial test results has been utilized to model the yield
stress-plastic strain behavior as well as the Kinematic behavior of the
metals.

In the same user interface,  there is an option to choose the number of
back stresses.

Is the number of 1 back stress is equivalen to the case of linear
kinematic hardening (Ziegler's)?

Since ABAQUS 6.8, a new feature has been added to the combined hardening material input.

Let's assume a combined Kinematic and Isotropic hardening case, such as those happen in metals.

"Half cycle" uni-axial test results has been utilized to model the yield stress-plastic strain behavior as well as the Kinematic behavior of the metals.

In the same user interface,  there is an option to choose the number of back stresses.

Is the number of 1 back stress is equivalen to the case of linear kinematic hardening (Ziegler's)?

A postdoctoral fellow is sought to study the mechanics of magnesium alloys at the University of Waterloo, Canada, under the guidance of Dr. Worswick and Dr. Gracie. The qualified applicant will have a proven background in computational mechanics, substantiated by publications in international journals.  Preference will be given to candidates with experience coding large deformation plasticity models, coding the finite element method and with using fracture mechanics.  In addition, experience with high strain rate testing of materials is desirable.

Applications must include: a cover letter, a curriculum vitae and a list of references. .

The Graduate School MUSIC ("Multiscale Methods for Interface Coupling") and the
Institute of Continuum Mechanics at Leibniz Universität Hannover invites
applications for a position as a

Research Staff Member in Computational Mechanics

(Salary scale E13 TV-L)

to be appointed on 1 April 2010.

The position is embedded into the Junior Research Group on „Multiscale Modelling of
Materials and Interfaces with Size Effects” and is initially limited to 1 year.

International Journal of Structural Changes in Solids

Mechanics and Applications

 An open access journal

Volume 1 No.1, 2009

Inaugural Issue :: in honor of Prof.Alan Wineman

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

Solids that are driven beyond their elastic limit exhibit strongly disspative and irreversible dynamical behaviors. Such behaviors call for the development of nonequilibrium approaches that go beyond standard equilibrium thermodynamics. In a recent work we have developed an internal-variable, effective-temperature non-equilibrium thermodynamics for glass-forming and polycrystalline materials driven away from thermodynamic equilibrium by external forces [1, 2]. The basic idea is that the slow configurational (structural) degrees of freedom of such materials are weakly coupled to the fast kinetic-vibrational degrees of freedom and therefore these two subsystems can be described by different temperatures during deformation. The configurational subsystem is defined by the mechanically stable positions of the constituent atoms, i.e. the "inherent structures", and is characterized by an effective temperature. The kinetic-vibrational subsystem is defined by the momenta and the displacements of the atoms at small distances away from their stable positions, and is characterized by the bath temperature.

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

In case of elasto-plastic problem it is mentioned that unloading of an integration point should be started along the elastic moduli when the solution gives a negetive increment of the plastic strain at the integration point. If anyone could elaborate it a little more, it will be really helpful.

Thanks 

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:

 Dear AllI has question about these stresses.1.Are deviatoric stress generate plastic deformation?2. Are hydrostatic stress generate plastic deformation?3.What is the advantage of transferring strain tenser orientation to the principle coordinate axes? 4. What is the difference between rupture and fracture stress?

hi, there!

I have read a "Manual for LS-DYNA Wood Material Model 143"(website: http://www.tfhrc.gov/safety/pubs/04097/sec150.htm#toc_1_5_1 and http://www.tfhrc.gov/safety/pubs/04097/append_e.htm).

I have two question:

1. how to calculate the consistency parameter (formula (180)) by potential function, I'm quite not understant how the formula (19), (20), (25), and (26) came out. Could anyone explain it to me or tell me what material I should get and read?

Hello, everyone.

Recently, I am trying to build a plastic contact model to describe teh relationship between the plastic deformation and the contact force, which is a crucial point in my work that dealing with the grasp force in robotics. So, anybody has some ideas about this? Actually, I am attempting to find a analytic model.

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)

Nonsingular, stressed, dislocation (wall) profiles are shown to be 1-d equilibria of a non-equilibrium theory of Field Dislocation Mechanics (FDM). It is also shown that such equilibrium profiles corresponding to a given level of load cannot generally serve as a traveling wave profile of the governing equation for other values of nearby constant load; however, one case of soft loading with a special form of the dislocation velocity law is demonstrated to have no ‘Peierls barrier’ in this sense. The analysis is facilitated by the formulation of a 1-d, scalar, time-dependent, Hamilton-Jacobi equation as an exact special case of the full 3-d FDM theory accounting for non-convex elastic energy, small, Nye-tensor dependent core energy, and possibly an energy contribution based on incompatible slip. Relevant nonlinear stability questions, including that of nucleation, are formulated in a non-equilibrium setting. Elementary averaging ideas show a singular perturbation structure in the evolution of the (unsymmetric) macroscopic plastic distortion, thus pointing to the possibility of predicting generally rate-insensitive slow response constrained to a tensorial ‘yield’ surface, while allowing fast excursions off it, even though only simple kinetic assumptions are employed in the microscopic FDM theory. The emergent small viscosity on averaging that serves as the small parameter for the perturbation structure is a robust, almost-geometric consequence of large gradients of slip in the dislocation core and the persistent presence of a large number of dislocations in the averaging volume. In the simplest approximation, the macroscopic yield criterion displays anisotropy based on the microscopic dislocation line and Burgers vector distribution, a dependence on the Laplacian of the incompatible slip tensor and a nonlocal term related to a Stokes-Helmholtz-curl projection of an ‘internal stress’ derived from the incompatible slip energy.

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

Hello,

I am doing numerical simulation using ABAQUS 6.7. I faced some problem to apply load that will be used as the forced displacement in one face of our model.I used user subroutine for appling load.But, i don't know how to apply forced displacement means the command of forced displacement.

Could you please help me regarding this problem.

Regards,

Arefin

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. Any kind of help in this sense would be very useful!

Thank you. 

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

INELASTICITY OF MATERIALS- An Engineering Approach and a Practical Guide

by 

Arun R Srinivasa (Texas A&M University, USA) &

Sivakumar M Srinivasan (Indian Institute of Technology, Madras, India)

With the advent of a host of new materials ranging from shape memory alloys to biomaterials to multiphase alloys, acquiring the capacity to model inelastic behavior and to choose the right model in a commercial analysis software has become a pressing need for practicing engineers. Even with the traditional materials, there is a continued emphasis on optimizing and extending their full range of capability in the applications. This textbook builds upon the existing knowledge of elasticity and thermodynamics, and allows the reader to gain confidence in extending one's skills in understanding and analyzing problems in inelasticity. By reading this textbook and working through the assigned exercises, the reader will gain a level of comfort and competence in developing and using inelasticity models. Thus, the book serves as a valuable book for practicing engineers and senior-level undergraduate/graduate-level students in the mechanical, civil, aeronautical, metallurgical and other disciplines.

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. Abaqus uses a non-associative plastic flow rule definition in the shear yield space but doesn't provide any valid explanation for the equation of the flow potential used.

Nano Letters 9, 2295 (2009), 10.1021/nl9004805, http://www.rsc.org/chemistryworld/News/2009/May/26050903.asp, http://www.nytimes.com/2009/07/07/science/07obsalt.html, http://www.sciencenews.org/view/generic/id/45132/title/Salt_stretches_in..., http://www.sandia.gov/LabNews/090605.html, http://www.newscientist.com/article/dn17374-salt-crystals-reveal-surpris..., http://www.youtube.com/watch?v=OGcFCD8E7o8