Fatigue behaviour of metal pin-reinforced composite single-lap joints in a hygrothermal environment

In this study, the fatigue behaviour of stainless steel pin-reinforced cocured composite single-lap joints in a hygrothermal environment was experimentally investigated. Specimens were exposed to a temperature of 71 °C and a relative humidity of 85% until moisture saturation was achieved. Fatigue tests were conducted on the specimens in three different environmental conditions (RTD, room temperature and dry, ETD, elevated temperature and dry; and ETW, elevated temperature and wet). Tension–tension cyclic loads were applied to the specimens with a stress ratio of 0.5 and the maximum stress levels ranging from 50% to 90% of the static strengths of the joints. The results showed that the fatigue strength of a z-pinned joint at a million cycles of repeated loads was improved up to 48.3% compared to that of a joint without z-pins for the ETW condition.