WEIBULL MODELING OF PARTICLE CRACKING IN METAL-MATRIX COMPOSITES

An investigation into the occurrence of reinforcement cracking within a particulate ZrO2/2618 Al alloy metal matrix composite under tensile plastic straining has been carried out, special attention being paid t o the dependence of fracture on particle size and shape. The probabili ty of particle cracking has been modelled using a Weibull approach, gi ving good agreement with the experimental data. Values for the Weibull modulus and the stress required to crack the particles were found to be within the range expected for the cracking of ceramic particles. Ad ditional information regarding the fracture behaviour of the particles was provided by in -situ neutron diffraction monitoring of the intern al strains, measurement of the variation in the composite Young's modu lus with straining and by direct observation of the cracked particles. The values of the particle stress required for the initiation of part icle cracking deduced from these supplementary experiments were found to be in good agreement with each other and with the results from the Weibull analysis. Further, it is shown that while both the current exp eriments, as well as the previous work of others, can be well describe d by the Weibull approach, the exact values of the Weibull parameters so deduced are very sensitive to the approximations and the assumption s made in constructing the model.