Hello Everyone, 

I am curious as to how Abaqus increments strains in a VUMAT subroutine. I am performing a uniaxial tension test with a single element test case using a fractional viscoelastic material model and a displacement boundary condition.

When I plot the stress and the strain for the model, The stress in the axial direction matches the analytical results. However, the lateral strains are zero and the lateral stresses are nonzero. I am unable to explain why this occurs with the subroutine.