Effects of Strain Rate on Low Cycle Fatigue Behaviors of High-Strength Structural Steel

The low cycle fatigue (LCF) behavior of a high-strength structural steel was investigated in the strain rate range of 4×10−5- 0. 12 s−1 (0. 001 - 3 Hz) under constant total strain (±1%) control. The cyclic stress response at all strain rates exhibited behavior of rapid softening in the early stage of fatigue life and subsequent saturation up to failure. It was found that the stress amplitude, the plastic strain amplitude, the plastic strain energy density and the fatigue life depend mainly on the strain rate. The strain rate of 0. 012 s−1 was found as a transition point where the LCF of the steel showed different behavior from low strain rate to high strain rate. The relationship between the time to failure and strain rate was expressed well by a power law relation. The fracture surfaces of the fatigue samples were characterized by using a scanning electron microscope (SEM) and the fracture mechanisms were discussed in terms of time-dependent deformation of the steel.