Study of Fatigue Crack Growth Rate for X52 Pipeline Steel Under Overload Application

The effect of overload on fatigue crack growth rate for X52 pipeline steel was studied under different stress ratio and overload ratio. The results show that tensile overload causes a delayed retardation to fatigue crack growth. The crack propagation curve after overloading includes three processes: accelerated growth, retardation growth and recovery growth. Under a constant stress ratio, plasticity induced crack closure is more significant with the increase of overload ratio; the crack growth rate is decreased as a result. However, crack growth retardation is more significant at a lower stress ratio. SEM analysis of the fracture surface shows that the overload plastic strain suffered more erosion at a higher overload ratio and the fracture surface morphology is more different after a higher overload ratio.