UMAT Problem with multiple Element Meshes - Finite Element Modeling
https://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/
PolymerFEM.com Discussion Boarden-USTue, 16 Apr 2024 14:58:14 +0000wpForo60
https://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7216
Wed, 03 Jun 2009 20:03:58 +0000Finite Element ModelingJorgenhttps://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7216
https://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7205
Wed, 03 Jun 2009 03:20:09 +0000thanks for your reply.I know that my UMAT works with sigma, epsilon even though there are strains up to 40%. Do you think that this might be the Problem?I tried to vary the way to calculate the UMAT with forward, backward, analytical, using the elastoplastic Tangent Modulus, the consisten Jacobian and so on. Although the only one that worked was the one Im using right now (see my last post). Does anyone have tips/literature on how to create a more precise DDSDDE?Greetings, ixfem]]>Finite Element ModelingThygemahttps://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7205
https://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7195
Tue, 02 Jun 2009 21:10:16 +0000Finite Element ModelingJorgenhttps://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-7195UMAT Problem with multiple Element Meshes
https://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-27278
Thu, 28 May 2009 10:25:32 +0000I have written a UMAT to simulate metal-foams with the constitutive modelof Deshpande & Fleck. #### Constitutive Model & ImplementationIt has an oval like yield criterion in the J2/I1 plane. (I1 meaning the first Invariant of sigma, J2 meaning the second Invariant of the deviatoric part of sigma)This yield criterion is used to calculate the new stresses with the help of the Closest-Point-Projection Algorithm (CPP). All of the aforementioned works fine.#### Calculation of Jacobian-MatrixTo calculate DDSDDE I use kind of a forward differential approach because its the only DDSDDE that let ABAQUS/Standard converge.I start from sigma_n1(stress at the end of the increment) and use 6 different pertubations to calculate each row of DDSDDE.With the use of (1) deltaEpsilon = (a,0,0,0,0,0)for the Iteration of the pertubated stress, I calculate sigma_n1* (the perturbated stress) with my Implementatino of the CPP-AlgorithmThen I use the forward differential scheme,(2) df(x) / dx = ( f(x+h) - f(x) ) / hto calculate the Jacobian-matrix.In this case I calculate the first row,(3) DDSDDE(1,i) = ( sigma_n1*(i) - sigma_n1(i) ) / epsilon(i)(epsilon(i) is always a) #### Verifying/testing the UMAT My testing refers to a simple compression test with a cube: I tested the UMAT using a cube with a single-element mesh and it worked fine.It works for given stresses or strains.All the ouput (sigma/eps curves...) is and the wallclock time it takes is ok.Then I created a multiple-element mesh cube and tried to analyse it. The Analysis smoothly runs through the purely elastic region, enters the elastoplastic region and continues quite a while. Then it suddenly stops at a Point and ABAQUS tells me the equilibrium conditions do not converge any more. The strain and strains ABAQUS stops increase with lesser elements. It works completely for 2x2x2 elements, but not for 3x3x3 and more.I have tried to mess around with DDSDDE and calculate it explicitely but it did not work out. The only one that worked is the aforementioned.I would be very thankful if anybody has an idea on how to find and fix this problem.Greetings, ixfem(I have to excuse for my poor english, but its not my first language.)]]>Finite Element ModelingThygemahttps://polymerfem.com/community/finite-element-modeling-aa/umat-problem-with-multiple-element-meshes/#post-27278