Multiple site fatigue damage in fuselage skin splices - experimental simulation and theoretical prediction

The results of experimental and theoretical research into multiple site fatigue damage (MSD) in the skin splices of pressurized fuselages are described. First, a special coupon-type splice test specimen has been designed that approximates on-aircraft conditions and enables realistic MSD to be created and studied in a laboratory environment. The coupon specimens usually used in industry and research are not suitable for studying MSD crack growth because the net section stress increases atypically as the cracks progress and because the specimens tend to fail before MSD has developed adequately. The specimen concept described in this paper is intended to overcome these problems. Second, an efficient computer program for predicting MSD crack growth within a frame-bay has been developed. Rooke's technique of compounding stress intensity factors is applied in a new way, and graphical output of multiple crack growth curves can be produced in a few minutes on a SUN computer workstation. In an initial evaluation, the program agreed well with experimental results.