Fatigue crack propagation in oil environments— II. A model for crack closure induced by viscous fluids

Several mechanisms have recently been identified for fatigue crack closure. The current work examines the concept of crack closure induced by the hydrodynamic wedging action of a viscous fluid within an advancing crack during cyclic loading. Unlike previous analyses, the model considers both the hydrodynamics of the pressure distribution within the crack and the kinetics of the penetration of the fluid into the crack. In addition, the results are presented in fracture mechanics terminology, and expressed as an effective (near tip) stress intensity range. Analyses involving both “full-” and “partial-penetration” of the viscous fluid inside the crack are utilized to rationalize the influence of viscosity on fatigue crack propagation in dehumidified oil environments, described in Part I of this paper. The roles of stress intensity range, crack size and frequency on the development of such fluid-induced crack closure are also examined.