Analysis procedures for the assessment of the damage tolerance of aircraft attachment lugs are developed and presented. Stress and fracture analyses are conducted for simple male straight shank lugs subjected to symmetric loading and tapered lugs subjected to symmetric and off-axis lodings. Solutions of stress distributions and stress intensity factors are obtained for various parameters. The parametric variations include lug outer-to-inner radius ratios corner and through-the-thickness cracks, crack lengths and aspect ratios, with and without interference-fit bushing and loads above and below yield of the lugs. Methods of varying degree of sophistication are considered in the development of stress intensity factor solutions for cracks in attachment lugs. For through-the-thickness crack problems, simple compounding method, two- dimensional cracked finite element method, and the weight function mthod are used. In the case of corner cracks, solutions are obtained using simple compounding method, weight function method and rigorous three-dimensional hybrid displacement cracked finite element method. The stress distributions and the stress intensity factors are consolidated into a crack growth analysis procedure including several crack growth models and spectrum retardation models to predict the fracture and crack growth behaviors in attachment lugs.

This volume covers the results of experimental evaluation of crack growth analysis methods for attachment lugs which were reported in Vol. II of the final report. These experiments were conducted to assess the damage tolerance of aircraft attachment lugs. The experimental test program included baseline material characterization, crack initiation, residual strength and crack propagation tests. Several loading and geometric complexities were considered in the test program. The types of loading complexities included were constant-amplitude, block spectrum and flight-by-flight spectrum, symmetric and off-axis loadings. Peak stress levels in the lug which were below and above the yield strength of the materials were also included in the test program. The types of geometric complexities considered were straight, tapered, dogbone, clevis and real aircraft lug configurations. Additional geometric complexities considered include lugs with lower thickness and lugs with interference-fit bushings. The experimental results were correlated with the analytical predictions made using methods described in Vol. II of the final report and are presented in this volume. Excellent correlation results were obtained for most of the test cases. In some cases, the developed analytical methods needed some improvements or some new solutions had to be generated. Such efforts were conducted and the refined correlation results are also included in the present volume.

This volume covers the results of experimental evaluation of crack growth analysis methods for attachment lugs which were reported in Vol. II of the final report. These experiments were conducted to assess the damage tolerance of aircraft attachment lugs. The experimental test program included baseline material characterization, crack initiation, residual strength and crack propagation tests. Several loading and geometric complexities were considered in the test program. The types of loading complexities included were constant-amplitude, block spectrum and flight-by-flight spectrum, symmetric and off-axis loadings. Peak stress levels in the lug which were below and above the yield strength of the materials were also included in the test program. The types of geometric complexities considered were straight, tapered, dogbone, clevis and real aircraft lug configurations. Additional geometric complexities considered include lugs with lower thickness and lugs with interference-fit bushings. The experimental results were correlated with the analytical predictions made using methods described in Vol. II of the final report and are presented in this volume. Excellent correlation results were obtained for most of the test cases. In some cases, the developed analytical methods needed some improvements or some new solutions had to be generated. Such efforts were conducted and the refined correlation results are also included in the present volume.