Thank you for your responses. I defined the damage criterion in the UMAT and once the damage occurred the stiffness of reduced to a nearly zero value. It seems that due to the small stiffness the damage element will have large distortion and causing problem of the calculation. DO you guys know...
dear abaqus users,
I was modelling a model with contact parts (cohesive surface). Previous I've defined the material property in my model to be elastic and it works. Then I've incorporated UMAT just to define the material damage (once damage criterion has met, reduce the stress to 0.01 original...