On the temperature dependence of the fatigue and damage behaviour of a particulate-reinforced metal-matrix composite

The fatigue and damage behaviour of the particulate-reinforced aluminum-matrix composite AA6061-Al2O3-20p was investigated at temperatures between T=−100 and 300 °C. Experiments performed at the highest temperature are characterized by pronounced cyclic softening which can clearly be explained by overaging (coarsening) of the precipitate structure in the matrix. A completely different behaviour was found at low and ambient temperature, where, at larger strain amplitudes, initial hardening was observed, followed by cyclic softening until fracture. At small strain amplitudes, a more stable cyclic behaviour was obtained. Damage was characterized by particle fracture at low and intermediate temperatures and debonding at high temperature, respectively. A procedure is proposed to determine the evolution of damage during the fatigue tests on the basis of the decrease of the stiffness determined from the tensile and compressive unloading branches of the stress–strain hysteresis loops. From the separate evaluation of these two branches, the internal damage (fracture of particles) can be distinguished from the growth of the final fatigue crack. This procedure was applied successfully in low and ambient temperature fatigue tests.