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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:


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,



Amit Acharya's picture

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

CISM Course: Plasticity and Beyond

Dear all,

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

The link is:

Flyer is attached.

Best regards,



Original post from CISM website:

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

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:

Variable Elasticity (Young) Modulus

Free Tags: 

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. 

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:

Falkingham P.L., Bates K.T., Margetts L. and Manning P.L. (2011) "The 'Goldilocks' effect: Presevational bias in vertebrate track assemblages", Journal of the Royal Society Interface, accepted for publication. Impact factor 4.241.

CanhLe's picture

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.

S. Beretta's picture

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

In the last decade, different
cyclic plasticity models
, based on the “continuum” approach, have been proposed
in order to account for different mechanical effects (such as ratchetting,
strain range dependence, non-proportional loading and memory effect), [1, 2]. A
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

Robin Selinger's picture

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

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

Amit Acharya's picture

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


Disparity in Simple Shear solution in ABAQUS

Choose a channel featured in the header of iMechanica: 

Dear All,

Eran Bouchbinder's picture

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.

vicky.nguyen's picture

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.

Shabeer Khan's picture


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.


benzerga's picture

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.

johnsmart1987's picture

plasticity induced fatigue crack closure

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hi friends am doin my my project on" FEA of plasticity induced crack closure". my specimen size is 80*80 mm. by using symmetry condition i modelled 1/4th of model in ANSYS. therfore i created 40*40 mm plate. with initial crack length of 4mm.means its MT specimen of 80*80mm with 8 mm crack length, by symmetry condition i modelled 40*40 with 4mm crack lenth.


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