Fatigue Fracture Behavior of SiC Whisker/Aluminum Matrix Composite under In-Phase and Out-of-Phase Tension/Torsion Loading.

Abstract

We describe an investigation on the fatigue fracture behavior of an SiC whisker reinforced A6061 aluminum alloy fabricated by a squeeze casting process under combined tension/torsion loading at room temperature. Attention was focused on in-phase and out-of-phase tension/torsion loading. The tests were conducted under a load-controlled condition keeping a constant value of the combined stress ratio, α=τmax/σmax. Irrespective of loading condition, the mechanical properties of the composite including fatigue strength were superior to those of an unreinforced A6061 alloy, not only under uniaxial loading, but also under combined in-phase and out-of-phase tension/torsion loading. In the case of the unreinforced matrix material, the fatigue strength under out-of-phase combined loading was smaller than that under in-phase loading. However, for the composite, the fatigue strength under out-of-phase combined loading was higher than that under in-phase combined loading. The crack initiation and propagation behavior was closely examined using a surface replication technique, and the fracture mechanisms under in-phase and out-of-phase combined loading were discussed.