Fatigue Crack Growth Retardation Due to Compressive Overloads

Fatigue crack growth retardation and complete arresting were experimentally observed in the CT specimens of grade A ship steel after compressive overloads were applied on the upper and lower sides of the ligament instead of loading at the pin positions. The degree of retardation depended on the magnitude of the compression and the crack arrested immediately after the compressive overload, KOL/ΔKbase < -2(σc < -100 MPa), contrasting to the tensile overload case, KOL/ΔKbase > 3, where the crack arrested after growing by a small amount. The current crack closure model admits of compressive yielding near the crack tip even when the load is suppressed. Additional compressive loads, hence, proceed to the compressive yielding and increase the compressive yield strength there, which causes the slower crack growth associated with less reversed plastic zone size ahead of the crack. Compressive pre-strain also raised the compressive yield strength in the material : slower growth rates, about 1/5 of the original rates were measured on the pre-strained specimen for -485 MPa.