Fatigue tests on edge cracked four-point bend steel specimens repaired by CFRP

Abstract An experimental study has been performed to investigate the fatigue behavior of edge cracked four-point bend (FPB) specimens repaired by carbon fiber-reinforced polymer (CFRP). A total of 12 specimens, including bare specimens and CFRP-repaired specimens, have been tested under loading conditions of different K II / K I ratios. This study aims to assess CFRP strengthening effects in terms of various mode-mixities, which are evaluated by a comparative analysis of unrepaired and repaired specimens’ failure modes, crack mouth opening displacement (CMOD), fatigue crack growth curves and lives. Different CFRP layer number is also taken into consideration. The results indicate that CFRP strengthening efficiency varies with loading modes. For specimens with single CFRP layer, the most remarkable strengthening efficiency is observed for mode I loading, enhancing fatigue life by more than 6 times. In contrast, the improvement ratios for mixed loading conditions are lower, ranging from 141% to 189% as the K II / K I ratio decreased. The CFRP-repaired specimens subjected to pure mode II loading see the least fatigue improvement, with fatigue life increasing only by 18% over that of the unrepaired counterparts. A significantly higher repair effectiveness is attained when two or three CFRP layers are applied. It is also found that patching multiple CFRP layers have some impact on mixed mode I/II crack trajectories.