Elastic-Softening Model with Stiffness and Strength Degradation

We consider the same model as before, but consider now that, upon unloading, some permanent strain £v remains at zero stress, as depicted in Fig. 8.4.2d. We can simply write that, on the unloading-reloading
branch,

*’-f + Wer ‘ (8A7)

The only extra information required is the evolution of єр. The simplest assumption is that it is a unique function of єЛ For example, Ortiz (1985) assumed (in a much more complex framework) that the permanent strain is a fixed fraction of the (maximum) inelastic strain, i. c.,

єр = ає! ■ ■ (8.4.8)

where о is a constant between 0 (for pure damage) and 1 (for pure plasticity).