Determination of residual stresses and the resulting stress intensity factors in the ligament of pre-cracked plates

In general, the ligament of cracked components contains residual stresses, resulting either from the crack forming process or from a prior overload. The crack compliance method allows not only to determine their distribution in the ligament but also offers the possibility to obtain quite easily the stress intensity factor that is produced when the original crack is growing. The latter affect particularly the subsequent sub-critical growth behaviour and, thereby, the safety and residual life of the considered component. Residual stress fields in pre-loaded cracked components exhibit some peculiarities regarding the high level and the local concentration of the residual stresses, which give rise to local plastic yielding in the vicinity of the crack tip that affects the stress measurement. An approximate correction for this effect is suggested. Furthermore, a simple influence function for deeply cracked plates is developed. As demonstrated by examples the crack compliance method is a promising tool to analyse the residual stresses near stress concentrations and their effect on the crack behaviour.