Crack closure and retardation effects – experiments and modelling

Abstract

The design of cyclically loaded components is in many cases carried out on the basis of experiments on small-scale laboratory specimens. In this approach, many effects such as load ratio, residual stresses and short crack growth are taken into account and described in a computational crack growth model. However, it can be seen that the prediction of the actual component lifetime with such models often is clearly too conservative. The reason for this behaviour can be found in occurring load sequence effects during operation, which are often not dealt with in the context of small-scale experiments.This paper attempts to examine such variations of applied load stresses as they may occur during operation. On the basis of cyclically loaded single edge bending (SEB) specimens, crack retardation effects are investigated in detail. It will be shown that residual stresses and overloads as well as extended operation times under small loads can lead to a significant extension of the lifetime of a component.