Cold Work Simulation of Hole Expansion Process and Its Effect on Crack Closure

Using cold working fastener holes is a simple life enhancement procedure thatstrengthens metallic components by retarding crack growth around a hole. In the present paper, theresidual stress field that is induced by the hole expansion process is obtained based on differentmaterial models, namely elastic perfect plastic, isotropic hardening and kinematic hardening usingthe three-dimensional finite element method. Moreover, crack closure analysis was performedfollowing introduction of residual stress. The effect of modeling parameters such as the percent ofcold work, remote tensile stress and crack length was also considered. Crack closure analysisindicates that the material model would affects normalized crack opening loads, especially at lowlevel of remote tensile stress where small scale yielding is dominant. Cold work simulation resultsindicate that the residual stress variation through the thickness is considerable. At low stress level,the effect of material behavior model is considerable and at high stress levels the crack openingload is dropped. Moreover, increasing the cold work interference percent results in a higher anddeeper compressive residual stress.

Keywords:

material behavior , cold work , residual stress , finite elements