Performance evaluation of boron/epoxy and carbon/epoxy composite patches for extending service life of damaged AA7075-T6 aircraft components

Abstract

Despite extensive theoretical predictions, no systematic experimental comparison between boron/epoxy and carbon/epoxy patch repairs has been conducted under standardised conditions, creating a critical knowledge gap in aerospace structural maintenance. This study provides the first rigorous experimental validation of these competing repair technologies under identical ASTM E647 protocols. AA7075-T6 specimens (400 × 160 × 2 mm3) with 6 mm rivet holes and 1 mm starter cracks were repaired using single-sided composite patches and subjected to constant amplitude fatigue loading (22 kN, 10 Hz, R = 0.1). Crack propagation monitoring revealed boron/epoxy patches achieved 96,000 cycles versus 78,000 cycles for carbon/epoxy systems, a quantified 23% performance advantage. Stress intensity factor analysis demonstrated up to threefold reductions compared to unrepaired specimens, with boron/epoxy exhibiting superior crack growth retardation (da/dN rates 40% lower at equivalent ΔK values). Post-fatigue residual strength testing confirmed enhanced load-bearing capacity in both repair configurations. These benchmark experimental data validate two decades of theoretical predictions whilst establishing the first standardised comparative database for evidence-based material selection in aircraft repair programmes. The quantified performance metrics provide essential validation data for regulatory compliance and structural integrity assessments in aerospace maintenance applications.