STUDY OF THE DAMAGE MECHANISMS IN AN OSPREY(TM) AL-ALLOY SICP COMPOSITE BY SCANNING ELECTRON-MICROSCOPE IN-SITU TENSILE TESTS

Damage mechanisms in a 7049 Al alloy + 15% SiCp metal matrix composite were studied qualitatively and quantitatively by in situ tensile tests in a scanning electron microscope with gold microgrids deposited onto the surface of the specimen. The first damage mechanisms were found to be rupture of the most elongated particles and, in smaller proportion, decohesion of the particle-matrix interface. A high aspect ratio, large size and low local volume fraction of particles appeared to increase the cracking probability. An Eshelby iterative method modified to account for the elastoplastic behaviour of the matrix was used to calculate the stress field induced by the thermomechanical treatment and mechanical loading of the composite. Knowledge of the statistical characteristics of the damaged particles permitted estimation of the critical stress for the two observed damage initiation mechansims. In the case of particle cracking this stress depends on the particle size.