Short fatigue crack growth in cast iron described using P−a curves

Abstract

Abstract A new approach to the description of short crack growth — the P − a curve — has been tested using extensive data on submillimetre cracks in a grey cast iron. It is shown that this approach, in which the probability of growth is plotted as a function of crack length, is valid in that it produces a plot that is consistent from specimen to specimen and is a function of both crack length and stress level. The growth probability, P g , can be defined systematically in terms of the average amount of crack growth, Δc mean within a given interval of cycles, ΔN ; this leads to the concept that P g characterizes growth at a particular rate: Δc mean / ΔN . Predictions were made of the endurance, N f , using a numerical model that simulates the growth of a large number of cracks. Crack coalescence was found to be a critical feature, both of the model and of the experimental findings. The great majority of crack growth was found to occur by coalescence; a simple model of coalescence, based on fracture mechanics, was successfully incorporated into the predictions.