A 2nd Generation Crack-Growth Prediction Methodology for Cold-Worked Fastener Holes

"The objective of this project is to develop and validate a 2nd generation crack-growth prediction methodology for cold-worked fastener holes. The methodology will be based on a three-dimensional weight function, and will handle cracks growing from theedge of the hole, as well as cracks initiating in the residual tension zone away from the hole. A predictive capability, based on probabilistic fatigue analysis, will be used to determine the most probable failure mode for the hole. For cracks initiatingin the residual tension zone, the methodology will account for the multi-stage crack growth. It will track the relaxation of the residual stresses as the crack grows through the residual stress in Stage I. In Stage II, the methodology will predict theinitiation and the growth of a secondary crack at the hole edge, resulting from the relaxation of the compressive residual stresses. The methodology will track the coalescence of this secondary crack and the primary crack into a single macro-crack inStage III. To predict the net section stress contour for the probabilistic fatigue analysis, the methodology will be combined with a CAD-based multi-layer joint analysis program to enable the cold-worked hole to be treated as part of a complex structuralsystem, rather than as an isolated hole. the 2nd generation crack-growth prediction methodology will lead to an improved ability to predict the fatigue and crack growth lives for multi-layer