| Fatigue damage of engineering materials involves many different length and time scales, such as instantaneous crack growth and long term structural degradation. The objective of this study is to develop and validate a novel small time scale model for the crack growth and fatigue life prediction under both uniaxial and multiaxial loadings. The developed model is fundamentally different from existing models due to the intrinsic smaller temporal formulation. The methodology is first demonstrated under uniaxial constant and variable amplitude loadings. Following this, a generalized crack growth model under general proportional and non-proportional multiaxial loading is developed. To address the fatigue crack growth uncertainty, the in-house fatigue testing is designed to investigate the crack growth behavior under various loading spectrums including constant amplitude, variable amplitude and multiaxial loadings. Finally, the developed small time scale model is extended to include the interaction of fatigue and creep effect at high temperatures. The developed study will greatly enhance the understanding of fatigue damage of materials and facilitate the structural level fatigue damage prognosis. |
