G. Cook, C. Timbrell, M. Wiehahn

Abaqus UK Users Group Conference, Warrington, England, Nov 12-13 2002

Abstract:
Many analysts are keen to investigate cracks in components under static or cyclic external loading. In the latter case fatigue crack growth prediction is also of importance. It is known that surface treatment effects such as shot peening have a beneficial effect on component life due to the compressive residual stresses introduced in the vicinity of the surface. Such treatments are used in maintenance programmes to extend the life of components in service. The effect on crack growth rate can be dramatic with significant changes in the crack growth profiles and increase in fatigue life to failure. The approach discussed in this paper applies fracture mechanics techniques to establish crack growth rates based on detectable defect sizes above the crack initiation stage established by non-destructive inspection. Thereby, extended fatigue life can be predicted, extended inspection periods calculated and the retirement of some components may be avoided.
This paper demonstrates how the Abaqus DLOAD user subroutine can be used to include the effect of residual stresses from shot peening in the analysis of crack growth in 3D finite element models. The inclusion of these effects may be so beneficial that a crack will change from a "growing" state without residual stress to a "non-growing" i.e. below threshold state, if residual stress is included.
Initially the effect of residual stresses are presented using a linear fracture mechanics approach for a single edge notched specimen and a corner crack specimen. Subsequently, the non-linear effects of contact at the crack surfaces are modelled and the effects on the cyclic energy release rates are presented.