I am trying in implement an invariant-based hyperelastic model (Holzapfel-Ogden 2009) in Abaqus using VUMAT. The constitutive model is modified to a slightly compressible form.
The subroutine with single element under biaxial testing and triaxial shear give expected results comparing to analytical solution. However, under compression test, the model start to have weird deformation (zig-zag) which happens in both single element and larger models. I have tried both C3D8 and C3D8R elements. In single element case, C3D8R with hourglass control and distortion control solved the issue. However, in larger models, both element types behave similarly with the zig-zag shape as shown below. I wonder if anyone can give any insight on how this could be solved? Thank you!