Low-cycle fatigue life of SiC-particulate-reinforced Al-Si cast alloy composites with tensile mean strain effects

The low-cycle fatigue behaviour of a SiC-particulate-reinforced Al-Si cast alloy with two different volume fractions has been investigated under strai n-controlled conditions with and without tensile mean strains. The composit es and the unreinforced matrix alloy showed cyclic hardening behaviour. The composite having a higher volume fraction of the SiC particles exhibited a more pronounced strain-hardening rate. For the tensile mean strain tests, the initial high tensile mean stress relaxed to zero for the ductile Al-Si alloy, resulting in no influence of the tensile mean strain on the fatigue life of the matrix alloy. However, tensile mean strain for the composite ca used tensile mean stresses and reduced the fatigue life. The pronounced eff ects of mean strain on the low-cycle fatigue life of the composite compared to the unreinforced matrix alloy were attributed to the initial large pres train causing non-relaxing high tensile mean stress in the composite with l imited ductility and cyclic plasticity. Fatigue damage parameter using stra in energy density accounted for the mean stress effects quite satisfactoril y. Predicted fatigue life using this damage parameter correlated fairly wel l with the experimental life within a factor of 3. Moreover, the fatigue da mage parameter indicated the inferior life in the low-cycle regime and supe rior life in the high-cycle regime for the composite, compared to the unrei nforced matrix alloy. (C) 1999 Elsevier Science Ltd. All rights reserved.