A scalar quantity called the equivalent strain, or the von Mises equivalent strain, is often used to describe the state of strain in solids. Several definitions of equivalent strain can be found in the literature. A definition that is commonly used in the literature on plasticity is ε ε e q = 2 3 ε ε d e v : ε ε d e v = 2 3 ε ε i j d e v ε ε i j d e v ; ε ε d e v = ε ε − − 1 3 t r ( ε ε ) I This quantity is work conjugate to the equivalent stress defined as σ σ e q = 3 2 σ σ d e v : σ σ d e v