Exploiting bulk residual stresses to improve fatigue crack growth performance of structures

Bulk residual stress, normally viewed as a nuisance, requires additional safety margin and reduces structural performance. However, by carefully considering residual stress during the design and manufacturing processes, it should be possible to remove the uncertainty associated with residual stress and optimize the residual stress in a part for maximum performance. This analysis, design, and test program clearly demonstrates the potential for such improvement and a method to achieve it. An aluminum–lithium extrusion was selected, and its residual stress and crack growth properties were measured. A design study for center-cracked fatigue crack growth specimens was conducted with the specimen excise location within the extrusion cross-section as the design variable. The stress intensity factors due to residual stress were predicted with finite element analysis and incorporated into crack growth predictions by superposition. For validation, several specimens were produced and tested. Test results confirmed the analytical predictions, and the longest crack growth life was 3.7 times the shortest.