Effects of cracks and notches: collapse

Abstract

In Linear Elastic Fracture Mechanics (LEFM; Chapter 3) as well as in Elastic-Plastic Fracture Mechanics (EPFM; Chapter 4) the analysis of fracture is based on a parameter representing the crack tip stress field; while the quantity used in EPFM is actually the strain energy release rate, this can be shown to be equivalent to a stress field parameter. In neither LEFM nor EPFM the possibility of so-called plastic collapse is implicitly evaluated. Fracture mechanics analysis may provide a fracture stress (residual strength) higher than the stress for plastic collapse; since the maximum load carrying capacity is reached at the time of collapse, the fracture stress calculated with fracture mechanics may be in error (too high). Similarly, in such a situation, the calculated critical crack size would be too large. Fracture parameters measured in a test where fracture occurs due to collapse would be too low.