Comparative Fatigue Crack Growth and Fractographic Investigation of Composite‐Patch–Repaired Al 2024‐T3 and Al 7075‐T6 Aerospace Alloys

Abstract

ABSTRACT This study compares fatigue crack propagation and fracture mechanisms in Al 2024‐T3 and Al 7075‐T6 aerospace alloys repaired with bonded carbon/epoxy composite patches. Single‐edge notched tension specimens were tested under identical constant‐amplitude cyclic loading, and repair efficiency was assessed using fatigue life data, stress intensity factor analysis, and SEM fractography. Composite repair markedly extended fatigue life: Al 2024‐T3 increased from about 1.35 × 10 5 to 4.05 × 10 5 cycles, whereas Al 7075‐T6 increased from about 3.9 × 10 4 to 1.6 × 10 5 cycles. The patch reduced the crack‐driving force by nearly 70% at large crack lengths. Fractography showed ductile crack growth in Al 2024‐T3 and more localized, brittle‐like damage in Al 7075‐T6. Fatigue life improvement was governed by load transfer, crack shielding, and crack closure, confirming the effectiveness of bonded composite repair for aerospace aluminum structures.