Orthotropic elastoplastic model with isotropic damage - TrabBone3d

This model combines orthotropic elastoplasticity with isotropic damage. Material orthotropy is described by the fabric tensor, i.e., a symmetric second-order tensor with principal directions aligned with the axes of orthotropy and principal values normalized such that their sum is 3. Elastic constants as well as coefficients that appear in the yield condition are linked to the principal values of the fabric tensor and to porosity. The yield condition is piecewise quadratic, with different parameters in the regions of positive and negative volumetric strain.