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Plane stress Abaqus UMAT

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Hello everyone,

I have created a UMAT code for J2 elasto-plasticity with isotropic hardening for 3D solid elements.

At this point I would like to support also plane stress shell elements. What changes in the code are

suggested? The already implemented code, takes as input the strain tensor at time tn and the strain

increment tensor and updates the stress at time tn+1 and calculates the material Jacobian and 

achieve quadratic convergence. The stress and strain tensors are manipulated as 6x1 vectors and the 

plane stress incompressible neo-Hookean hyperelasticity


I was wondering how is it possible to implement incompressible neohookean material in abaqus? 

With the incompressibility assumption c(3,3)=1/(- c(1,2)^2 + c11*c22), with c being the Cauchy-Green strain tensor. It also implies that S33=0 and it is possible to find the pressure directly. In addition, h=sqrt(c(3,3))*h0 with h and h0 being current and initial thickness, respectively. 

my question is that how is it possible to implement the last condition in umat? 






shreeram111's picture

Plane_Stress, Plane_Strain and 3D - Simple doubt..

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Hello everybody,

 UPDATE :   Question can be deemed as closed.. :)

                       I have a very simple doubt in 3D model simplification. I believe plane stress and plane strain conditions are the two extreme states to simplify a 3D model to 2D case.

Mohr-Coulomb Shell in Abaqus. Help!

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I am new to Abaqus and I am trying to use it to model some industrial shells. According to some preliminar studies, the material has a mohr-coulomb plastic behaviour. Thus, I wanted to use shell elements, with a mohr-coulomb plastic material, but it seems that it is not possible in Abaqus.

According to the theoretical manual and the user manual (18.3.3-6):

David J Unger's picture

J-Integral Elliptical Hole (Plane Stress) Perfectly Plastic Material

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The fracture mechanics community may be interested in a new evaluation of a J-Integral for a fundamental geometry:  an elliptical hole in a perfectly plastic material under the Tresca yield condition for plane stress loading conditions. The analysis is exact and involves only elementary functions.  This makes the problem suitable as a classroom example or as a homework problem for a graduate level course in fracture mechanics.  See J. Elasticity (2008) 92:217-226.

Plane stress with thickness

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