### 5.3.6. Isotropic Material Failure

The failure criteria for isotropic materials is based on the von Mises stress (or equivalent stress in Mechanical):

| (5–122)

or on the von Mises strain (or equivalent strain in Mechanical):

| (5–123)

where and are the first and second principal strains. For isotropic material, the stress failure function is defined as:

| (5–124)

and the strain failure function is defined as:

| (5–125)

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