Bonded composite repair of cracked load-bearing holes

Externally bonded composite repairs have recently been shown to be an effective technique for repairing a range of structural problems associated with cracked or damaged aircraft components, including multi-site damage in cracked fuselage lap-joints. This paper attempts to further clarify the mechanisms by which these repairs work. The results are presented of a combined numerical and experimental investigation into the use of bonded repairs for a load-bearing hole containing a single "through-thickness" crack. The specimen was repaired with bonded boron/epoxy doublers and a steel sleeve insert. Constant amplitude fatigue tests were performed, on both the repaired and unrepaired specimens, and the resultant fatigue-crack-growth data are presented. This crack-growth data is then correlated with the stress intensity factors obtained from a three-dimensional finite element analysis.