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 metalli c panel repaired with an adhesively bonded composite patch. Also, fatigue e xperiments were conducted with 6.35 mm thick specimens with a pre-crack rep aired asymmetrically with adhesively bonded unidirectional boron/epoxy patc h. 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 rel ationship for the unrepaired cracked material to obtain the analytical fati gue crack growth rates. The experimental and analytical fatigue crack growt h rates on the unpatched face (UPF) were in a good agreement with each othe r when the proper consideration of the effective crack length and debond we re incorporated in the analysis. Thus, the three-layer technique was found to be capable of characterizing the fatigue crack growth behavior of the re paired thick panels as in the case of repaired thin panels shown in the pre vious studies. (C) 1999 Elsevier Science Ltd. All rights reserved.