Representative stress–strain curves of brittle (A and B), brittle-ductile (C), and ductile behavior (D–F). A shows elastic behavior followed immediately by failure, which represents brittle behavior. In B, a small viscous component (permanent strain) is present before brittle failure. In C, a considerable amount of permanent strain accumulates before the material fails, which represents transitional behavior between brittle and ductile. D displays no elastic component and work softening. E represents ideal elastic-plastic behavior, in which permanent strain accumulates at constant stress above the yield stress. F shows the typical behavior seen in many of the experiments, which displays a component of elastic strain followed by permanent strain that requires increasingly higher stresses to accumulate (work hardening). The yield stress marks the stress at the change from elastic (recoverable or non-permanent strain) to viscous (nonrecoverable or permanent strain) behavior; failure stress is the stress at fracturing.
Pic Courtessy: Earth Structure- An introduction to structural geology and tectonics.
