Influence of residual stress redistribution on fatigue crack growth and damage tolerant design

The safe operation of many structures and components is ensured through the operation of damage tolerant design and evaluation. Substantial residual stresses can exist in many systems and it is important that these are incorporated in damage tolerance calculations of fatigue crack growth. Recent improvements in non-destructive measurement techniques and in the application of weight or Green's functions methods of including residual stress fields into stress intensity factor (SIF) calculations have enabled predictions of the effects of residual stresses on fatigue crack propagation to be made more readily. Two examples from the aerospace industry, structures containing (i) cold expanded holes and (ii) fusion welds are used to show that presently, although final crack growth lives can be accurately predicted, the details of crack growth are not well represented with initial growth typically being underestimated and later growth being over estimated. It is shown that this is most likely to be due to residual stress redistribution. and that this must be built into fatigue life prediction models if accurate damage tolerance based procedures are to be developed for components and systems containing substantial residual stresses.