Influence of mechanical properties on load sequence effect and fatigue life of aluminium alloy

Most of the structural components in real applications are subjected to variable amplitude loading. The load sequence may have a significant effect on the number of cycles to failure. However, the relationship between the mechanical behaviour of material and the load sequence effects has scarcely been reported. Therefore, this paper discusses the influence of mechanical properties on the load sequence effect and fatigue life behaviour of aluminium alloys AA6061 and AA7075. Tensile and fatigue tests were performed according to ASTM E8 and ASTM E466, respectively. The variable amplitude loading signal was obtained from the engine mount bracket of an automobile in normal driving conditions. Constant amplitude loading, and high-to-low and low-tohigh spectrum loadings were derived from the variable amplitude loading to assess the effects of load sequence on fatigue life. The results showed that AA7075 has better fatigue life properties compared to AA6061. Both alloys were significantly influenced by load sequences. The number of cycles to failure for low-to-high spectrum loading is about 56 % higher than the CAL for AA6061 compared to about 82 % higher than the CAL for AA7075. Thus, it can be concluded that the load sequence effect was more pronounced on AA7075 compared to AA6061