From scribe to crack through the

Crack propagation in a stump seam (experimental)
Crack propagation in a stump seam (experimental)
Crack propagation in a stump seam (simulation)
Crack propagation in a stump seam (simulation)

When crack propagation concept (RFK), it is assumed that the component has already occurred a crack initiation. In this fracture mechanical approach crack shape and crack size are assumed to be known and the service life up to crack initiation is not included in the rule. In contrast to the concepts previously described not the scribe line, but the crack growth is analyzed up to a critical crack length, where it comes to rest, due to the fracture cross-sectional weakening.

Since the stresses can reach very high, theoretically infinite values at the crack tip, local stress and strain as a characteristic stress values are unsuitable. Instead, the crack length is dependent on the stress level and the stress intensity factor K in the linear-elastic fracture mechanics (LEFM) is negligible with small plastic zones used at the crack tip. Large plastic crack tip stresses can be detected by the elastic-plastic fracture mechanics (EPBM).

The main field of application in steel construction is less in the replacement of the stress based fatigue calculation rather than in the evaluation of cracks and crack-like imperfections. In particular, to estimate the remaining service life of the crack propagation concept can be used to define the necessary inspection intervals or material toughness to avoid brittle fracture.

How to crack propagation concept

The individual calculation steps in the crack growth concept
The individual calculation steps in the crack growth concept