Effect of load amplitude change on the fatigue life of cracked Al plate repaired with composite patch

• An increase of the maximum fatigue load after repair overcomes most of its crack retardation.
• A decrease of the maximum fatigue load after the repair induces a lower crack growth than the unpatched case for Al 7075.
• A crack generated in Al 2014 T3 material under a given fatigue load amplitude has grown faster.

In this study, the fatigue behavior of aluminum alloy 2024T3 v-notched specimens repaired with composite patch under block loading was analyzed experimentally. Two loading blocks were applied: increasing and decreasing at two stress ratio: R = 0 and R = 0.1. Failed samples were examined under scanning electron microscope at different magnifications to analyze their fractured surfaces. The obtained results show that under increasing blocks, the crack growth is accelerated for both repaired and unrepaired specimens. This is attributed to the increase of the loading amplitude in the second block. A retardation effect was observed for decreasing blocks loading in unrepaired specimens. However, this retardation effect is attenuated by the presence of the patch which lead to lower fatigue life for repaired specimens.