Modeling of cracked thick metallic structure with bonded composite patch repair using three-layer technique

A finite element analysis involving three-layers of two-dimensional Mindlin plate elements, to model cracked plate, adhesive, and composite patch, was developed to characterize fatigue crack growth behavior of a thick metallic panel repaired with an adhesively bonded composite patch. Also, fatigue experiments were conducted with 6.35 mm thick specimens with a pre-crack repaired asymmetrically with adhesively bonded unidirectional boron/epoxy patch. Fatigue crack growth rates on the unpatched and patched faces (PF) were measured along with debond of the composite patch. Stress intensity factors obtained from the analysis were combined with the fatigue crack growth relationship for the unrepaired cracked material to obtain the analytical fatigue crack growth rates. The experimental and analytical fatigue crack growth rates on the unpatched face (UPF) were in a good agreement with each other when the proper consideration of the effective crack length and debond were incorporated in the analysis. Thus, the three-layer technique was found to be capable of characterizing the fatigue crack growth behavior of the repaired thick panels as in the case of repaired thin panels shown in the previous studies. (C) 1999 Elsevier Science Ltd. All rights reserved.