This research consists of a three-year period study of the mechanism(s) of fatigue crack growth during plane stress and plane strain cyclic loading in the near-threshold range. This investigation examines experimentally the fatigue behavior of four materials (ferrous and non-ferrous, low alloy and high alloy) using state-of-the-art mechanical testing and microstructural characterization techniques (including transmission electron microscopy analyses of dislocation structures at fracture surfaces). The experimental data are used to test and develop models to describe fatigue behavior as a function of stress state, environment, and material properties.
