FATIGUE FRACTURE-BEHAVIOR OF SIC WHISKER ALUMINUM MATRIX COMPOSITE UNDER IN-PHASE AND OUT-OF-PHASE TENSION/TORSION LOADING/

We describe an investigation on the fatigue fracture behavior of an Si C whisker reinforced A6061 aluminum alloy fabricated by a squeeze cast ing process under combined tension/torsion loading at room temperature . Attention was focused on in-phase and out-of-phase tension/torsion l oading. The tests were conducted under a load-controlled condition kee ping a constant value of the combined stress ratio, alpha= tau max/sig ma max. Irrespective of loading condition, the mechanical properties o f the composite including fatigue strength were superior to those of a n 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 und er 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 l oading. The crack initiation and propagation behavior was closely exam ined using a surface replication technique, and the fracture mechanism s under in-phase and out-of-phase combined loading were discussed.