FRACTURE-ANALYSIS OF MULTISITE CRACKING IN FUSELAGE LAP JOINTS

A two-dimensional plane stress elastic fracture mechanics analysis of a cracked lap joint fastened by rigid pins is presented and results ar e applied to the problem of multi-site damage (MSD) in riveted lap joi nts of aircraft fuselage skins. Two problems are addressed, the proble m of equal length MSD cracks and the problem of alternating length MSD cracks. For the problem of equal length cracks, two models of rivet/s kin interactions are studied and the role of residual stresses due to the riveting process is explored. Stress intensity factors are obtaine d as a function of normalized crack length. Also, the load distributio n among rivet rows and the compliance change of the joint due to MSD c racking are obtained. For the problem of alternating length cracks, at tention is focussed on how load is distributed between columns of rive ts and how this load shedding can alter crack tip stress intensity fac tors. The equal and alternating length crack analyses reveal no clear- cut mechanism to explain the relative uniformity of fatigue cracks eme rging from lap joint rivet holes in actual aircraft and in mechanical lap joint tests.