Effect of single tensile overload on fatigue crack growth behavior in DP780 dual phase steel

Abstract

The purpose of this study was to analyze the effect of single tensile overload on fatigue crack growth (FCG) behavior in DP780 dual phase steel. The compact tension samples were tested under constant amplitude load and overload condition. The results showed that all the material conditions responded favorably to the single tensile overloads; the magnitude and extent of crack retardation was amplified due to an increase in overload ratio (OLR) and a longer crack length at overload application. The error between the overload affected crack growth increment and the magnitude of overload monotonic plastic zone size decreased about 30% after introducing the factor (n−1)/(n+1) into Irwin model. A plastic zone size factor was used to modify the Wheeler model to calculate the FCG rate during retardation period after an overload, the predicted results were in good agreement with the experimental data. During the application of an overload, a crescent moon shaped damage zone was formed ahead of the crack tip characterized by cleavage surfaces, tearing ridges, dimples and voids. The fracture morphology after crack front reformation was severely damaged due to the premature contact of the crack flanks. Crack branching was not significant interaction effect for the crack growth retardation under overload.