Plasticity

Evoution of Yield surfaces: Past and Future Trend - Simulation

In continuation of our work on yield surfaces

Part- 1 (http://imechanica.org/node/9016)

Part- 2 (http://imechanica.org/node/9073) and

Part- 3 (http://imechanica.org/node/9103

On the three-dimensional Filon construct for dislocations

(to appear in the Intl. Journal of Engineering Science)

Robin J. Knops and Amit Acharya

The relationship between dislocation theory and the difference of linear elastic solutions for two different sets of elastic moduli, derived by Filon in two-dimensions, is generalised to three-dimensions. Essential features are developed and illustrated by the  examples of the edge and screw dislocations. The inhomogeneity  problem is  discussed within the same context and related to Somigliana dislocations, and  in the limit  to the interstitial atom.

Crack Initiation with UMAT

Dear all,

I want to model crack initiation and propagation for a user defined material, using Abaqus. When I try to model , I get the following error:

A MATERIAL PROPERTY THAT IS NOT ALLOWED WITH A USER MATERIAL HAS BEEN SPECIFIED

when I take out critical damage initiation, the model works fine; which means that it doesnt allow me to couple UMAT with crack initiation. Does anyone know how to handle this problem?

All the best,

Panos

On an equation from the theory of field dislocation mechanics

(Paper to appear in Bollettino della Unione Matematica Italiana - Bulletin of the Italian Mathematical Union)

Luc Tartar and Amit Acharya

Global existence and uniqueness results for a quasilinear system of partial di fferential equations in one space dimension and time representing the transport of dislocation density are obtained. Stationary solutions of the system are also studied, and an in finite dimensional class of equilibria is derived. These time (in)dependent solutions include both periodic and aperiodic spatial distributions of smooth fronts of plastic distortion representing dislocation twist boundary microstructure. Dominated by hyperbolic transport-like features and at the same time containing a large class of equilibria, our system di ffers qualitatively from regularized systems of hyperbolic conservation laws and neither does it fi t into a gradient flow structure.

Controversy: Dynamic Peierls-Nabarro equations

In 2010,  Yves-Patrick Pellegrini published a paper in Physical Review B called

CISM Course: Plasticity and Beyond

Dear all,

please find information about the 5 day - course on Plasticity and Microstructures at CISM Udine, Italy.

Flyer is attached.

Best regards,

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Original post from CISM website:

Plasticity and Beyond: Microstructures, Crystal-Plasticity and Phase Transitions

June 27, 2011 — July 1, 2011

Coordinators:

SES 2011: Minisymposium on Mechanics of Crystalline and Composite Nanostructures

Dear Colleagues:

We would like to invite you to submit an abstract for the upcoming 2011 Annual Technical Meeting of the Society of Engineering Sciences (SES 2011), to be held October 12-14, 2011, at Northwestern University in Evanston, Illinois (http://ses2011.org/).  The area of the minisymposium is "Mechanics of Crystalline and Composite Nanostructures", and we anticipate having a diverse and well-respected group of theoreticians and experimentalists give presentations on this subject.  Abstracts can be submitted by going to the following conference website:

http://ses2011.org/submit_abstracts.php

where our minisymposium is labeled 3.1.  We look forward to seeing you at Northwestern in the fall of 2011!

Plotting the Johnson-Cook strength model

I'm trying to plot the stress-strain curve described by the Johnson-Cook strength (and eventually damage) models. The strength model is defined as:

σ=[A+Bεn][1+C ln(ε_dot*)][1-T*m]

where A, B, C, n, and m are material constants, ε_dot* is the non-dimensionalized strain rate, and T* is the homologous temperature where T*=(T-T0)/(Tmelt-T0)

To calculate the thermal softening (term in the last bracket of the J-C model), I need to determine the increase in temperature related to an increase in stress (and strain). I'm using the following equation:

ΔT=∫ Χ (σ/(ρ*cp)) dε

Variable Elasticity (Young) Modulus

I need to simulate a sheet forming but I must consider the variation of Young modulus with plastic strain.

Has anybody tried this? How can I implement a function for this? I have never worked with UMAT / VUMAT.

Thank you.

Hi everyone!

Large Plastic Deformation in High-Capacity Lithium-ion Batteries

Evidence has accumulated recently that a high-capacity electrode of a lithium-ion battery may not recover its initial shape after a cycle of charge and discharge.  Such a plastic behavior is studied here by formulating a theory that couples large amounts of lithiation and deformation.  The homogeneous lithiation and deformation in a small element of an electrode under stresses is analyzed within nonequilibrium thermodynamics, permitting a discussion of equilibrium with respect to some processes, but not others.  The element is assumed to undergo plastic deformation when the stresses reach a yield condition.  The theory is combined with a diffusion equation to analyze a spherical particle of an electrode being charged and discharged at a constant rate.  When the charging rate is low, the distribution of lithium in the particle is nearly homogeneous, the stress in the particle is low, and no plastic deformation occurs.  When the charging rate is high, the distribution of lithium in the particle is inhomogeneous, and the stress in the particle is high, possibly leading to fracture and cavitation.

Characterization of residual stress fields in nonlinear elasticity; a question posed by Sebastien Turcaud

In the post

http://www.imechanica.org/node/9509

Sebastien Turcaud asks the question (my interpretation) of the characterization of  all possible residual elastic distortion fields on a given configuration (interpreted as the current configuration). If one in addition introduces a reference configuration then the deformation gradient w.r.t. this reference is known and depending upon how one defines 'eigendeformation' in nonlinear elasticity, corresponding eigendformation fields to the residual elastic distortion fields can be determined. Such eigendeformation fields can contain fields arising from plastic deformation, non-uniform thermal expansion etc.

Surface mediated plasticity in sub-10-nm-sized gold crystals

Nature Communications 1, Article number:144 | DOI:10.1038/ncomms1149

Although deformation processes in submicron-sized metallic crystals are
well documented, the direct observation of deformation mechanisms in
crystals with dimensions below the sub-10-nm range is currently lacking.
Here, through in situ high-resolution transmission electron
microscopy (HRTEM) observations, we show that (1) in sharp contrast to
what happens in bulk materials, in which plasticity is mediated by
dislocation emission from Frank-Read sources and multiplication, partial
dislocations emitted from free surfaces dominate the deformation of

Soil Mechanics and Fossil Dinosaur Trackways

My PhD student Peter Falkingham (who graduated 15 December 2010) has published some interesting papers on Dinosaur Trackways. These might be of interest to those teaching Soil Mechanics, to give some examples that might be more stimulating than foundation design or traditional geotechnical engineering.

References below:

Research associate position at University of Sheffield

The successful candidate will work on the EPSRC funded research project 'Ultimate and permissible limit state behaviour of soil-filled masonry arch bridges', which is being undertaken in collaboration with the University of Salford and various industrial partners (Network Rail, ADEPT, the International Union of Railways and Balfour Beatty Rail). This is an exciting opportunity to help develop the next generation of analysis and assessment techniques for masonry arch bridges, thus helping to ensure a sustainable future for structures that continue to form a vitally important part of the rail and regional road networks of the UK and other countries.

Research assistant and PhD position at PoliMi on micro-plasticity models

cyclic plasticity models
, based on the “continuum” approach, have been proposed
in order to account for different mechanical effects (such as ratchetting,
disadvantage of this approach is the elevated number of model parameters
introduced in order to correctly predict the material behaviour. The determination
of these parameters, usually difficult and expensive,
is one of the reasons why the modern
constitutive models are not widely used in finite element simulations of

APS March Meeting Focus session: "Fracture, Friction, and Deformation Across Length Scales"

Abstracts due Friday, Nov. 19, 2010

APS March Meeting Focus session: "Tribophysics: Friction, Fracture and Deformation Across Length Scales"

March 21 - 25, 2011, Dallas, Texas
Details at
http://www.aps.org/meetings/march/scientific/focus2.cfm#12.7.3

Invited speakers: Michael Marder (Univ. of Texas); Julia Greer (Caltech)

Organizers: Robin Selinger (Kent State), Jacqueline Krim (NCSU), Noam Bernstein (NRL)

Microcanonical Entropy and Mesoscale Dislocation Mechanics and Plasticity

(Journal of Elasticity, Carlson memorial Volume)

A methodology is devised to utilize the statistical mechanical entropy of an isolated, constrained atomistic system to define the dissipative driving-force and energetic fields in continuum thermomechanics. A thermodynamic model of dislocation mechanics is discussed. One outcome is a definition for the mesoscale back-stress tensor and the symmetric, polar dislocation density-dependent, Cauchy stress tensor from atomistic ingredients.

Plasticity Data in Vumat

Hello everyone,

I am using a VUMAT with isotropic hardening in my three dimensional model. Can someone tell me how is plasticity data passed into this subroutine? In VUMAT for kinematic hardening we define the yield stress and hardening modulus along with E and poisson's ratio in *User Material. I did not find any isotropic hardening VUMAT examples in manual. Do we define the hardening modulus or the yield stress-plastic strain data in isotropic hardening VUMAT? I will be really thankful if anyone can help me.

Thank you

Swapnil

Disparity in Simple Shear solution in ABAQUS

Dear All,
We tried to simulate simple shear using ABAQUS and compared it with the analytical solution. To our surprise, even though the equivalent stress and strain matched perfectly, the component stress and strain had a large deviation between the semi analytical and ABAQUS methods. The zero components in the analytical model were calculated to be non-zero in the results of ABAQUS. This paradox could not be understood clearly as whether it is a case of software deficiency or conceptual error. A COMPLETE ANALYSIS OF THE PROBLEM IS ATTACHED AS A REPORT.

I have asked for technique support. Their answer was that my strain rate was incorrect for finite deformation. But I do not think so.

A new postdoc position is available

A new postdoctoral position in continuum mechanics is available at the Weizmann Institute of Science. Candidates should have a strong background in physics and/or theoretical mechanics, as well as experience with analytical and computational methods for solving partial differential equations. Possible projects include the mechanics of frictional sliding, the mechanics of biomaterials, the mechanics of glassy materials and dislocation-mediated plasticity. Highly motivated candidates are requested to send their CV, publications list and statement of research interests to Dr. Eran Bouchbinder eran.bouchbinder@weizmann.ac.il

Mechanics of Materials: Textbook Recommendation

I will be teaching a sophomore level class  mechanics of materials class.  The class will cover mechanics of basic strength of materials (e.g. beams, pressure vessels), but I also want to teach basic elements of failure mechanics (fracture, fatigue, plasticity, and wear.)  I'm looking for a recommendation of an undergrad mechanics textbook that covers the fracture, fatigue, plasticity, and wear.  The students will have had a statics and mechanics class and their textbook already covers strength of materials.  Thanks.

plasticity

Good Time to Everybody, I am working on Thermoplasticity, especially thermoviscoplasticity, will be comparing the results of some basic examples problem worked be Simo and Miehe, modelled in Abaqus with the results of a locally developed code. I am new comer in this excellent forum and I am happy to see myself among a nice community of Mechanicians. I regard all those who are conneted in this form and those who helped in connecting this chain of  Mechanics.

Evoution of Yield surfaces: Past and Future Trend - Part 2

Continuing on the work from the previous thread posted on

Results are presented on the evolution of subsequent yield surfaces with
finite deformation in a very high work hardening annealed 1100 aluminum
alloy. In Part I [Khan, A.S., Kazmi, R., Stoughton, T., Pandey, A.,
2009a. Evolution of subsequent yield surfaces and elastic constants with
finite plastic deformation. Part 1: a very low work hardening aluminum
alloy (Al-6061–T6511) 25, 1611–1625.] of this paper, similar results are
presented for a very low work hardening aluminum alloy.

How do ductile materials fail?

This is a review on ductile fracture committed to the Advances in Applied Mechanics (Vol 44). Part of the review has an educational purpose and, as such, is intended for advanced undergraduates and starting graduate students. The other part is an account of recent research conducted in the field.

Though quite long, the review is by no means exhaustive. As noted in the discussion, many valuable contributions to this field have been left out. The focus was laid on micromechanics-based approaches to connect to microstructural aspects in engineering materials.

I will try to post the electronic PDF once I get permission from Elsevier.