Influence of yielding behaviour and stress-strain law on the failure analysis

The yielding behaviour and its influence on failure have been investigated for different structural steels. The yield strength and the flow stress of bcc steels as a function of temperature and strain rate was described quantitativly with the mechanism of thermally activated flow. A description of strain hardening behaviour of materials has to distinguish between a purely mathematical approximation of the stress-strain curve (Ramberg-Osgood, Ludwik's equation) and the real strain hardening of the material (dσtdϵt). The estimation technique according to Shih and Kumar and the Two-Criteria-Approach, which take into consideration the strain hardening of the material with increasing plastic deformation, was used to estimate the critical loads of center cracked wide plate specimens.