Residual stress affecting environmental damage in 7075-T651 alloy

The role of tensile overload superimposed on a constant amplitude cycling results in compressive residual stresses at the crack tip that cause crack growth retardation. The degree to which this effect manifests depends on whether the tests are done at a constant driving force (Kmax) or at a constant crack growth rate (da/dN). It is observed that depending on the magnitude of the overload at a given applied base stress intensity, these residual stresses can have significant effect on the crack growth in both the inert (vacuum) and the chemical (NaCl) environments. In general, cracks will grow only if the total crack tip driving force Ktotal exceeds the long crack intrinsic threshold ${\rm{K*}}_{{\rm{max,th}}}^{}.$ The crack growth retardation results can be attributed to the combined effects of the crack tip chemical reaction rates and the overload compressive residual stresses.