The following laws and criteria can describe the plastic behaviour of materials: yield criteria, yielding law and work hardening law. The yield criterion defines the general level of stresses from which a solid passes in a plastic forming state. The constitutive equations describe the changes in the law of variation of the yielding stresses during the deformation of the material. The present paper analyses the main aspects concerning the mathematical formulation and field of application of the main yield criteria and constitutive equations
