Analysis of Partial Fatigue Crack Surface Contact in Residual Stress Fields

Abstract

Fatigue crack growth rate in a residual stress field has been predicted by using the superposition technique. In this method, a residual SIF (stress intensity factor) is computed and, by taking into account a real stress ratio of the summation of applied and residual (real) SIFs, a fatigue crack growth rate is predicted. When a crack grows from a compressive residual stress field, however, it is necessary to compute a SIF due to partial crack surface contact. In our previous paper, this effect was discussed and simple method of computing the SIF was shown. In this paper, by using this method, we stdudied the effect more precisely for some specimen geometries and loading types. Results obtained are as follows; (1) When the specimen completely unloaded, the real SIF is not affected by specimen geometries. (2) Partial crack surface partial contact is affected by loading types. (3) The bending loading reduces the loading when the crack surfaces contact compared with the tensile stress. Moreover, the partial crack contact does not occur at a crack in the residual tensile stress field. (4) A notch induced in the specimens reduces the SIF of partial crack surface contact.