Evaluating safety margins in structures using elasto–plastic fracture mechanics methods

In many cases fracture–related accidents have a serious economic impact as well as a large influence on public acceptance of industries with higher potential of risk. On the other hand, there is a tendency in some industries to increase the demand on the material and structure or to extend the lifetime and to avoid unnecessary safety margins. The design and analyses of structures like pressure vessels, pipes, housings, etc. is normally based on the assumption that the structure is free from defects. In special cases the behaviour of postulated or detected cracks are investigated. The analysis method applied in the past was based on linear elastic fracture mechanics (LEFM). The developments in elasto–plastic fracture mechanics (EPFM) have advanced to a state where the description of the whole process – crack initiation, stable crack growth and instability – is feasible. The post–instability and crack–arrest behaviour is a major topic in future R&D work. Together with the increased capabilities of present non–destructive testing methods, an adequate analysis method exists to evaluate defects in ductile structures and to determine the margins of safety.