An experimental study on the fatigue performance of CFRP and BFRP repaired aluminium plates

Cracked aluminium plates were repaired with multidirectional carbon/epoxy and boron/epoxy reinforcements. Aircraft repair conditions were simulated by using a steel bonding rig that constrained the effective thermal expansion to the level measured from real locally heated aircraft structures. Residual thermal stresses were varied using the rig and by varying the curing and testing temperatures. The repairs were tested using a variable amplitude loading (R = −0.14) with anti-buckling edge supports. The residual thermal stresses had a rectilinear and distinct effect on the crack growth rate. The structural support against bending had a significant effect on the fatigue life of the repairs. The fatigue life improvement factor with the centre-cracked single-sided repairs was greatest with the wet-laminated carbon/epoxy repairs having a stiffness ratio of 1.04. With edge-cracked specimens the longest life was achieved with the double-sided boron/epoxy repairs having a stiffness ratio of 0.65. The cracked aluminium plate 2024-T3 clad had the longest fatigue life, followed by the S07-1020 and 7075-T6 clad aluminium grades.