THE SENSITIVITY OF J-INTEGRALS TO MATERIAL LAW VARIATIONS FOR SEMIELLIPTIC SURFACE CRACKS

In finite element analysis of cracked bodies, it is quite common to re present the material law (stress-strain curve) in a simplified form e. g. bilinear approximation. Many steels, however, have a more complex m aterial law, which includes a perfectly plastic region before work har dening. Two dimensional finite element analyses have shown that fractu re parameters, such as the J-integral, are very sensitive to variation in material law for shallow cracks, and the writers have now commence d three dimensional analyses for surface semi-elliptical cracks in pla tes. Some computations have been made for specimens tested experimenta lly by Dodds and Read [1], and the results show that what appears to b e a reasonable approximation of the material law is inadequate in mode lling the deformation behaviour, and that more accurate modelling of t he material law, especially the plastic part immediately after yield, which may include perfectly plastic behaviour, is required for reliabl e results.