Deformation and damage in Al/Al2O3

Al/Al2O3-composites as an example of light weight materials are very interesting for many industrial applications because of a favourable combination of low density and improved mechanical properties. The prediction of the macroscopic mechanical behaviour of these materials related to their microstructure requires the knowledge of damage initiation and crack development under external loading conditions and, if present, residual stresses have to be taken into consideration. Different types of material degradation like particle/matrix-debonding, particle failure and matrix cracking can be observed in these types of metal matrix composites. The aim of the present work is to introduce damage criteria into a FE-microstructural model in order to foresee the degradation process in an Al2O3-particle reinforced Al(6061) composite during mechanical loading. Presently, the conventional fabrication route of the Al/Al2O3-composite is a metallurgical method with extrusion for homogenisation of the microstructure and final heat treatment to achieve a defined precipitation state. The influence of thermal residual stresses due to cooling down from annealing temperature on the deformation and damage initiation of Al(6061)/10vol%Al2O3-composites is investigated through finite element analyses using the experimentally mapped real microstructure as binary data. Especially, the stresses in the ceramic particles which are responsible for particle cracking and the hydrostatic stresses in the Al-matrix making the particle–matrix interface prone to debonding were analysed. The results show the importance of the thermal residual stresses with respect to damage criteria as obtained by micromechanical FE-calculations.