Prediction of the fatigue-damaged behaviour of Al/Al2O3 composites by a micro–macro approach

The use of very heterogeneous materials in structural components submitted to cyclic loadings, leads us to present an elastoplastic micromechanical model. After some revision of the homogenisation principle based on a mean field theory, a non-linear kinematic and isotropic strain hardening is introduced in the matrix. Validation is made on a Al–3.5% Cu/SiC particles and the case of an A356/Al2O3 fibres is treated as a first application. Damage is introduced in the model by using a fibre failure criterion. It is based on the increase in the volume fraction of broken fibres as a function of the maximum principal stress in the fibre family. The damage law is identified with in situ tensile test performed inside the scanning electronic microscope. The number of broken fibres is determined with the applied load and the number of cycles. The model predicts the fatigue behaviour, the lost of stiffness, the volume fraction of broken fibres for different volume fraction, aspect ratio, distribution of orientation, distribution of strength of the fibres. The effect of the mechanical fatigue properties of the matrix is also studied.