Hey Jørgen and fellow members,
I'm working on implementing a path dependent linear viscoelastic UMAT subroutine which accounts for relaxation behaviour during the curing of a thermoset polymer (as implemented by Svanberg et. al 2002). To accompany the UMAT subroutine, UEXPAN is also used to calculate thermal expansion and chemical shrinkage strains.
When carrying out a simple tensile test modelling example with thermal effects, i have a problem with excessive distortions once the bar is stressed by a load. In the model i'm changing between two stiffness matrices (for the polymer in rubber and glassy state depending on T_g).
Is there something i might be overlooking? All my expansion strains passed on from UEXPAN are correct.
Any comments etc. are welcome )