Empirical modelling of subcritical crack growth size and profile under continued loading

Abstract

During continued loading the slow crack growth regions at the crack tip assume different shapes and sizes. Two different crack front profiles may be identified in practice depending on the extent of crack growth. They may be approximated as parabolic and semi-circular in shape. Crack fronts tend to be semi-circular for relatively large extent of crack growth and parabolic during the early stages of crack growth. Modelling 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 Δ a as well as the convergence of Δ a as a function of measurement number is studied. The difference in the Δ a values obtained by the offset method and area method is also investigated in addition to the influence of specimen thickness and maximum crack growth on ø. Experimental verification of crack growth front profiles and the change in the Δ a value with ø is carried out. It suffices to consider eight to ten measurements for modelling crack growth size and profile in commonly used specimen thickness.