Summary of the Effect of Multiple Site Damage on the Linkup Strength of 2024-T3 Aluminum Panels

An aging aircraft accumulates fatigue cracks commonly referred to as multiple site damage (MSD). A simplified engineering fracture mechanics model, generally referred to as the linkup model (or plastic zone touch model), has been used with some success to describe the MSD fracture phenomenon in 2024-T3 aluminum panels. A disadvantage of the linkup model is that it gives excessively inaccurate results for some configurations. A modified linkup model has been developed through empirical analysis of test data taken from unstiffened panels with MSD cracks at open holes. The modified linkup model was then validated with test data from stiffened panels including single-bay panels with the lead crack centered between stiffeners and two-bay panels with the lead crack centered beneath a severed stiffener. Further validation of the modified linkup model was done with test data from panels with bolted lap joints. Test results were obtained from 112 different panels. The modified linkup model is a significant improvement over the linkup model based on a comparison of predicted values with test values. Portions of this project have been previously published. However, the purpose of this paper is to present a summary of the results including details of the panel geometry, crack configurations, test results, and results from both the linkup model and the modified linkup model for the 112 panels.