Fracture initiation in alumina/aluminium composites: Effect of residual stresses

It has been found that the strength of Al2O3/Al composites with an interpenetrating network structure is essentially independent of the volume fraction of metal. It is proposed that crack initiation in the ceramic phase is hindered by compressive residual stresses. Thermal expansion measurements are used to calculate the residual stresses in the individual phases and it is found that they are relatively constant in the composite as a function of metal content. The inclusion of the metal phase additionally changes the inherent flaw sensitivity of the metal, removing the stress concentrations caused by inherent defects such as pores which are subsequently filled by metal. Fracture is therefore crack initiation controlled with failure coming from microstructurally dependent microcracks.