EMPIRICAL MODELING OF SUBCRITICAL CRACK-GROWTH SIZE AND PROFILE UNDERCONTINUED LOADING

During continued loading the slow crack growth regions at the crack ti p assume different shapes and sizes. Two different crack front profile s may be identified in practice depending on the extent of crack growt h. They may be approximated as parabolic and semi-circular in shape. C rack fronts tend to be semi-circular for relatively large extent of cr ack growth and parabolic during the early stages of crack growth. Mode lling of crack growth size and profile for each crack growth increment is carried out by two approaches; namely, offset measurement and area consideration. The variation of average crack growth size DELTAaBAR a s well as the convergence of DELTAaBAR as a function of measurement nu mber is studied. The difference in the DELTAaBAR values obtained by th e offset method and area method is also investigated in addition to th e influence of specimen thickness and maximum crack growth on phi. Exp erimental verification of crack growth front profiles and the change i n the DELTAaBAR value with phi is carried out. It suffices to consider eight to ten measurements for modelling crack growth size and profile in commonly used specimen thickness.