Determination of the stress intensity factor for parallel and symmetric edge cracks under pure bending

Abstract

An experimental and semi-theoretical investigation concerning thin plates having “Parallel and Symmetric” (P.A.S.) † † This terminology is used throughout this paper to represent equal parallel edge cracks along one of the longer edges of the specimen with an additional edge crack along the other long edge. This additional edge crack is opposite to and symmetric with the middle crack of the equal parallel edge cracks, see Fig. 1. edge cracks and subjected to pure bending will be discussed in this paper. Experiments were performed extensively on plates with P.A.S. equal edge cracks in order to study the effect of the variation of the length of the cracks and crack spacing seperately. Observations show that when crack spacing becomes larger than crack length, the diameter of the caustic for the equal P.A.S. edge cracks approaches the diameter of the caustic of the double edge cracks. Based on this fact, the equation that expresses the semi-theoretical and experimental stress intensity factor for the double edge cracks was first modified and then utilized in order to express the strese intensity factor of P.A.S. edge cracks. Moreover, an alternative formula for the stress intensity factor was established which is based on a cubic interpolating polynomial. For large crack spacing the cubic interpolating polynomial converges to unity and as a result, the diameter of the caustic and the stress intensity factor approach those of a double edge crack. For the case of unequal P.A.S. edge cracks, a crack closure phenonmenon under the pure bending condition was investigated. Experimental measurements showed that the relative position of the shorter crack with respect to the longer cracks for which the crack closure phenomenon happens is related not only to the crack spacing of the parallel edge cracks in the tension region, but also strongly related to the variation of the existing symmetric edge crack in the compression region.