An experimental study on the effect of damage on the stress-strain behaviour for Al-Si model composites

An experimental study has been conducted to assess the interaction between work-hardening behaviour and damage accumulation for a model Al-Si composite, which contained 20% Si particles. In order to separate the effects of work-hardening from damage accumulation, damage in the form of cracked silicon particles was introduced in the material by cold rolling. After cold rolling, the matrix was returned to its initial state by a recrystallization heat treatment. Tensile tests were then conducted on the material with different levels of damage and with different matrix tempers, i.e. matrix in the supersaturated solid solution or in the T6 condition. The work-hardening behaviour of the samples was then examined by numerically differentiating the experimentally determined stress-strain data. A characteristic change in work-hardening, which served as a signature of damage, could readily be observed. The changes in work-hardening behaviour were rationalized by a model for composite hardening which included a dislocation-based constitutive model for the matrix and a load transfer model for describing the stresses in the particles. Good agreement was observed between the experiments and the model. The key conclusion of the work is to support the supposition of [M.T. Kiser, F.W. Zok, D.S. Wilkinson, Acta Mater. 44 (1996) 3465-3476] that the critical parameter controlling tensile fracture is not the level of damage but the rate of damage evolution.