HIGH-STRAIN CYCLIC FATIGUE AND FRACTURE-BEHAVIOR OF A SIC REINFORCED CAST-ALUMINUM ALLOY COMPOSITE

The high strain cyclic fatigue characteristics of a cast aluminum alloy A356 discontinuously reinforced with 20 vol% silicon carbide particulates strained to failure over a range of strain amplitudes giving lives of less than 10(4) cycles to failure were studied. The specimens were cycled using tension-compression loading under total strain control. The as-cast material displayed cyclic hardening and eventual softening to failure at the higher cyclic strain amplitudes, and progressive cyclic softening at low strain amplitudes. The observed cyclic hardening and softening behavior are a mechanical effect and attributed to concurrent and competing effects of an increase in dislocation-dislocation interaction, dislocation multiplication and dislocation-particle (SiC) interactions. The cyclic fracture behavior of the alloy is discussed in light of composite microstructural effects, plastic strain amplitude and concomitant response stress.