Isotropic Material Failure Surface

Introduction

This damage initiation law predicts that failure initiates when maximum principal stress exceeds tensile strength of the material or when maximum shear stress exceeds shear strength of the material. It can also model pressure-dependent initiation stresses. Because it deals with principal stresses and tensile failure is the same regardless of direction, this law is only appropriate for isotropic materials such as an IsoSoftening material.

Failure Surface

Three possible failure stress failure surfaces are shown in the figure. Which surface to use for initiation is determined by the tractionFailureSurface property of the parent isotropic softening material. The calculations for initiation transpose these surface to principle stress space and find critical stress by Mohr's circle calculations. The details are given in Ref. .

These initiation calculations allow the properties, in general, to depend on external parameters such as pressure, strain rate, or more. The only external dependence currently modeled is to allow shear strength to depend on pressure.

Damage Law Properties

The following table lists the input properties for maximum principal stress failure surface:

Property	Description	Units	Default
sigmac	Critical tensile stress for failure	pressure units	infinite
tauc	Critical shear stress for failure	pressure units	infinite