EFFECT OF TEST CONDITIONS ON CAVITATION AND FAILURE DURING TENSILE LOADING OF DISCONTINUOUS METAL-MATRIX COMPOSITES

The effect of test temperature and reinforcement shape on cavitation is investigated for commercial purity Al-Al2O3 composite produced via either a powder route or squeeze infiltration followed by extrusion. At room temperature, voids form at the reinforcement/matrix interface. Voids are favoured by reinforcement elongation and planar surfaces normal to the applied stress. Angularities themselves are not favoured sites for cavitation. Increasing the test temperature delays the onset of cavitation and angularities become favoured void nucleation sites. At higher temperature, necking begins to occur at much lower plastic strains, resulting in lower strains to failure, suggesting that void stability is reduced by increasing the temperature. Finite element calculations have been performed to investigate the component of the matrix stress which is responsible for the onset of cavitation in these materials. Results suggest that cavitation is stimulated by the attainment of a critical value of the hydrostatic stress at the interface, rather than of the interfacial normal stress. (C) 1994 The Institute of Materials.