VHCF test and life distribution of aluminum alloy LC4CS

Very high cycle fatigue (VHCF) test of 82 aluminum alloy LC4CS specimens was done by piezo-electric fatigue testing machine and fatigue life data were obtained. The obtained fatigue life data showed that the fatigue life distribution of the alloy under VHCF has a characteristic of duplex peak, which is related to the locations of fatigue crack initiation. The crack initiation site was found near the specimen surface in each fracture surface, but some defects such as inclusions and voids were found at the crack initiation site for the specimens with shorter life, whereas no defect was found at the crack initiation origin for the ones with longer life. This characteristic makes staircase method measuring the fatigue limit inconsequential, and the fatigue life scatter of the VHCF is far larger than those of low cycle fatigue (LCF) and high cycle fatigue (HCF). The fatigue life data were statistically analyzed and a mixed probability distribution function of two lognormal distribution functions was proposed in the present paper, and results showed that the mixed function is suitable to describe the fatigue life distribution of aluminum alloy LC4CS in the VHCF region.