Temperature effect on the failure behavior of adhesively strap joints

This study experimentally investigated the effects of temperature exposure on the mechanical behavior of single-strap joints (SSJs) and double-strap joints (DSJs) fabricated from GFRP composites. Specimens were exposed to temperatures of 25, 80, 120, and 160 °C for 4 h, while additional specimens were exposed to 80 °C for 2, 4, and 6 h to evaluate the effect of exposure time. The influence of thermal conditions was evaluated based on the failure loads obtained from tensile tests. The results showed that the failure loads increased at intermediate temperatures (80–120 °C) due to the post-curing effect of the epoxy matrix. However, a reduction in strength was observed at 160 °C because of matrix softening and possible weakening of the adhesive–composite interface. In the time-dependent tests conducted at 80 °C, the highest failure load was obtained after 2 h of exposure, whereas longer exposure times resulted in a gradual decrease in mechanical performance. Under all test conditions, DSJ specimens exhibited higher failure loads than SSJ specimens because of their more uniform load distribution. Analysis of variance (ANOVA) confirmed that both temperature and exposure time significantly affected the failure loads (p < 0.05).