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Description
If a structure is loaded or deformed, the atoms within the material are displaced and the material responds with a deformation. This deformation determines the mechanical behaviour of the material. Different types of deformation exist. In particular, it can be possible to distinguish reversible deformations, with the deformation disappearing after unloading, and irreversible deformations that preserve the deformation after unloading. Generally, reversible deformations are called elastic, irreversible deformations are called plastic. The complete analysis of the structure requires first of all the definition of the states of stress and deformation induced inside the material and then the development of specific tools to complete the analysis. The attention is focused on the yield criteria to distinguish between elastic and plastic regime, the flow rule to govern the correlation between stresses and strain increment and the hardening evolution equation to describe how the yielding surface modifies during the deformation.