AN ANALYSIS OF DUCTILE FAILURE BY GRAIN-BOUNDARY VOID GROWTH
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Crack growth along grain boundaries, by nucleation and growth of microvoids initiating from grain boundary particles, is studied experimentally and numerically using an elastic-viscoplastic constitutive model of a ductile porous solid to characterize the evolution of room temperature damage along the grain boundary. The material modelled is an AlLi alloy with coarse grain boundary particles. Crack tip loading conditions are obtained by modelling the complete tensile specimen geometry used in the experiments. The material is characterized by a phenomenological porous plastic constitutive relation in which the voids are represented in terms of a single parameter, the void volume fraction. The distribution of grain boundary voids is modelled by allowing void nucleation in a band, the width of which is the grain boundary particle spacing. The grains are modelled as roughly circular regions free of void nucleating particles. The grain size and width of the grain boundary void nucleating band are varied to determine their influence on fracture initiation and toughness predictions. The predicted values of KIC and tearing modulus, based on calculated J-resistance curves, are found to be in reasonable agreement with experimentally determined values. The calculations show a strong dependence of the fracture toughness on the width of the grain boundary void nucleating band and a mild dependence on the grain size. 1989.