Failure Theory (material) - Ductile Material Failure Criteria

Ductile Material Failure Criteria

Criteria used to predict the failure of ductile materials are usually called yield criteria. Commonly used failure criteria for ductile materials are:

• the Tresca or maximum shear stress criterion.
• the von Mises yield criterion or distortional strain energy density criterion.
• the Gurson yield criterion for pressure-dependent metals.
• the Hosford yield criterion for metals.
• the Hill yield criteria.
• various criteria based on the invariants of the Cauchy stress tensor.

The yield surface of a ductile material usually changes as the material experiences increased deformation. Models for the evolution of the yield surface with increasing strain, temperature, and strain rate are used in conjunction with the above failure criteria for isotropic hardening, kinematic hardening, and viscoplasticity. Some such models are:

• the Johnson-Cook model
• the Steinberg-Guinan model
• the Zerilli-Armstrong model
• the Mechanical threshold stress model
• the Preston-Tonks-Wallace model

There is another important aspect to ductile materials - the prediction of the ultimate failure strength of a ductile material. Several models for predicting the ultimate strength have been used by the engineering community with varying levels of success. For metals, such failure criteria are usually expressed in terms of a combination of porosity and strain to failure or in terms of a damage parameter.