Instrumented indentation measurements of residual stresses around a crack tip under single tensile overloads

• Using indentation technique to study residual-stress fields around the crack tip after overload.
• FEM was used to verify the results obtained by indentation.
• The probable mechanisms for overload retardation were re-evaluated by indentation results.

In this study, the residual-stress fields around crack tip of M(T) specimens under three single tensile overload ratios (Rol) during fatigue crack growth of aluminum alloy 2524-T3 were investigated using the instrumented indentation tests (IIT). The results showed that both the magnitude and region of the compressive residual stress around the crack tip increase with the increase of Rol. Finite element method was also used to simulate the residual stress distributions near the crack tip at the same loading conditions as experiments, which confirmed that the estimation of the crack-tip residual stress using Suresh et al.'s model based on IIT was feasible. The profiles of the crack tip under constant-amplitude loading and three overload ratios were examined using optical microscopy. It was found that the geometry of crack tip changes significantly from the sharp crack to the blunt crack with increasing Rol after applying a tensile overload. The probable mechanisms resulting in the change of the crack-growth behavior due to tensile overloads were also discussed. It was suggested that the combined effects of the residual stress, crack tip profile and the crack tip hardening may be responsible for the observed overload retardation effect of the present M(T) specimens during fatigue crack growth.