Three-Dimensional Effects on Fatigue Crack Closure in the Small-Scale Yielding Regime

Robert H. Dodds, Jr.
M.T. Geoffrey Yeh Chair
Department of Civil & Environmental Engineering
University of Illinois, Urbana, IL 61801, U.S.A.

Date:  Friday, March 7, 2003
Time:  3:30 p.m.
Place:  W183 Nebraska Hall


Plasticity induced closure often influences strongly the behavior of fatigue cracks at engineering scales in metallic materials. Current predictive models generally adopt the effective stress-intensity factor ( ) in a Paris law type relationship to quantify crack growth rates. This work describes a 3-D finite element study of mode I fatigue crack growth in the small-scale yielding (SSY) regime under a constant amplitude cyclic loading with zero T-stress and a ratio . Dimensional analysis suggests, and the computational results confirm, that the normalized remote opening load value, , at each location along the crack front remains unchanged when the peak load ( ), thickness (B) and material flow stress ( ) all vary to maintain a fixed value of . Through parametric computations at various levels, the results illustrate the effects of normalized peak loads on the through-thickness, opening-closing behavior and the effects of , where E denotes material elastic modulus. This new scaling relationship and the computational results provide the needed framework to rationalize and extend existing simplified models of the crack closure process.