Aging aircraft may develop multiple-site damage (MSD) that can reduce the structural integrity of fuselage structures. The existence of small cracks emanating from adjacent rivet holes in a fuselage lap-splice joint is of major concern. The residual strength of a panel with a lead crack is greatly reduced by the presence of smaller collinear cracks compared to that of only a lead crack. Recent studies in predicting the residual strength of flat and curvilinear panels with riveted lap-splice joints gave quite encouraging results, but some difficulties arose in modeling small cracks at rivet-loaded holes. Thus, there was a need to conduct detailed fracture analyses of the crack-linkup phenomenon in lap-splice joints with rivet-loaded fasteners.
The objective of this paper was to analyze the crack-linkup behavior in riveted-stiffened lap-splice joint panels with small MSD cracks at several adjacent rivet holes. Analyses were based on the STAGS (STructural Analysis of General Shells) code with the critical crack-tip-opening angle (CTOA, Ψc) fracture criterion. To account for high constraint around a crack front, the “plane strain” core option in STAGS was used. The importance of modeling rivet flexibility with fastener elements that accurately model load transfer across the joint was discussed. Fastener holes were not modeled, but rivet connectivity was accounted for by attaching rivets to the sheet on one side of the cracks that simulated both the rivet diameter and MSD cracks. Residual strength analyses made on 2024-T3 alloy (1.6-mm thick) riveted-lap-splice joints with a lead crack and various-size MSD cracks were compared with test data from Boeing. Analyses were conducted for both restrained and unrestrained against buckling conditions. Comparison of these analyses with lap-splice-joint test panels, which were partially restrained against buckling, was generally bounded by the restrained and unrestrained failure loads.