Damage mechanisms at room and high temperature in notched specimens of Al6061/Al2O3 particulate composites

The aim of the present study was the investigation of the effects of macroscopic stress triaxiality on the presence and evolution of damage in particulate MMC. Two Al6061/Al2O3/10p and 20p particulate reinforced composites were investigated on smooth and differently notched specimens pulled in tension at 20 and 250 °C. Fractographic analyses and microstructural observations were carried out in order to identify and to map damage mechanisms. Particle fracture was the prominent form of material damage at 20 °C, while debonding was the main damage mechanism at 250 °C. The distribution of the two damage forms within the specimen volume was interpreted on the basis of the results of finite element analyses. At a given level of triaxiality (considered as the hydrostatic to Von Mises stress ratio), particle fracture localized in regions of high maximum principal stress, generally associated to the high hydrostatic stress. It was further observed that matrix/interface debonding concentrated in the same regions, but developed on other particles at higher/lower load level depending on test temperature.