Mechanisms of isothermal relaxation
Isothermal relaxation tests

Only a brief description of the relaxation mechanisms will be given in the case of a relaxation test with the initial relaxation stress above the yield stress, σ₀ > σ_E[2]. During loading, dislocations are created and propagate. How do these dislocations evolve during relaxation?

Plastic strain ε_p is related to the density of mobile dislocations ρ_m by the Bailey-Orowan relation :

where α is a geometric factor, b the modulus of the Burgers vector and L the mean free path of dislocations.

Deriving this equation, we then have :