Plasticity

Heip to get second order effect in reinforced concrete column

Hello all,


Modellilng Deep and shallow foundations in Abaqus

Dear All,

I decided to put this post since I am trying to model piles on granular materials with Abaqus and I am having LOADS of problems, some of them due to my lack of understanding in the subject and others becasue there is not enough information around. Some of my problems are:

1- convergence problems: I am using Mohr coulomb for the soil and elasticity for the pile. If the difference between Young's modulus for both materials is to big it does not converge on Abaqus Static. If I do not put a bit of cohesion in my soil it also does not converge.

2- Different failure mode or smaller than it should be.


Robertt Valente's picture

PhD positions in Computational Mechanics

We are looking for suitable candidates for a PhD research work in Computational Mechanics and numerical simulation, to be carried out at the Department of Mechanical Engineering, University of Aveiro, Portugal, in one of the following areas:

- development of new finite elements for metal forming applications;

- numerical simulation of metal forming (sheet and bulk forming);

- tubular hydroforming numerical simulation;

- structural stability and buckling analysis of reinforced aircraft panels;

- integrated design, modelling and reliability assessment (iDMR) by computational tools.

 Candidates are free to contact me using the email: robertt AT ua DOT pt


Survey on XFEM: is XFEM good at characterizing Failure rather than Fracture?

Would like to hear your expertise/user/non-expert/sceptic comments on XFEM. Here are some of the challenges. Would like to hear your relections.

1. Can XFEM be utilized in characterizing Failure rather than Fracture?

2. What sort of challenges XFEM still have with respect to Fracture Mechanics?

3. How the Fracture mechanics benefit the industry, from the perspective of strcutural integrity?

4. Failue investigations vs. Fracture investigations: benefit to industry?

5. Academist vs Engineer: Perspective on XFEM

If possible, please vindicate your justifications with any relevant literature. Would like to see where and how XFEM is evolving.


notch tip radius

Hello everyone,

 

I am looking for a way to measure notch tip radius experimentally. Would you give me some ideas about that? is there any relationship between  morphology of notched cracked body surface and notch tip radius?

 Thank you and Regards, 


Dynamic simulations with nonlinear material into Explicit

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?


ABAQUS (6.8, 6.9 EF) - Effect of the number of back stresses

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)?


ABAQUS (6.8, 6.9 EF) - Effect of the number of back stresses

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)?


Robert Gracie's picture

Postdoctoral Fellowship for Research into the Mechanics of Magnesium Alloys

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. .


Hirschberger's picture

Position for Research staff member at Leibniz Universität Hannover, Germany

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 Effec
ts” and is initially limited to 1 year.


Ahmad Rafsanjani's picture

Writing User Subroutines with ABAQUS

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


Eran Bouchbinder's picture

Nonequilibrium Thermodynamics in Solid Mechanics

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.


Amit Acharya's picture

Case Studies in Mesoscale Field Dislocation Mechanics

 (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


How to deal with negetive plastic strain increment in FEA in an elasto - plastic problem

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 


Shape memory alloy material models including plasticity implemented in ABAQUS

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:


hiader k. mahbes's picture

Plasticity and elasticity questions

 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?


Help!!! How to calculate the consistency parameter by consistency condition (potential function) of plasitc flow

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?


Mike lee's picture

How to build a contact model involved the plastic defoemation?

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.

Smile 


Jidong Zhao's picture

Postdoc position at HKUST on computational mechanics/geomechanics

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.


Amit Acharya's picture

New inroads in an old subject: plasticity, from around the atomic to the macroscopic scale

(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.


Deformation gradients and atomistic simulations

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


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