An improved small-time-scale crack growth rate model considering overloading and load-sustaining effects for deep-sea pressure hulls

Abstract

The fatigue life assessment of deep-sea pressure hulls needs to consider its load characteristics reasonably, including short-term overloading and load-sustaining at a certain depth in a load cycle lasting several hours. In this case, the traditional reversal-based crack growth rate model is no longer applicable while the small-time-scale model which can consider the crack growth process in any small interval highlights its advantages. This paper presents an improved small-time-scale crack growth rate model with consideration of overloading and load-sustaining effects as well as the stress/strain constraints. The formula for crack tip opening angle is modified to more accurately demonstrate its changing tendency from crack opening to final fracture. A concept of plastic zone influence range is proposed to express the effect of the plastic zone size and the overload ratio. Creep effects at load-sustaining period at high stress level are included into calculation. Finally, model validation and parametric analysis are conducted. The improved model can be reasonably applied for fatigue life prediction of deep-sea pressure hulls.