For brittle materials, three orthotropic failure initiation models are available in Autodyn-2D and 3D, as follows:

These models allow different tensile and shear failure stresses and/or strains for each of the principal (material) directions. The models are intended to enable modeling of orthotropic failure.

Importantly, the orthotropic failure models can be used together with the orthotropic equation of state, which before failure uses the incremental elastic stress-strain relations detailed in Orthotropic Constitutive Models. With any of the above Material failure models, failure is initiated in a principal direction when the stress or strain reaches a user-specified limiting value.