Fatigue crack growth rate base-curve involving thickness and stress ratio in 2024-T3 &T351 aluminium alloys.

Abstract

The availability of reliable fatigue crack growth (FCG) prediction tools is essential to the design of structures subjected to fatigue loading. Constant amplitude (CA) test provides ∆k vs. da/dN data, but CA test data applicability is limited because of the strong influence of stress ratio (R) and thickness on the FCG. To develop crack growth rate base-curves involving thickness and R, available CA test data from litera-ture have been analysed according to PIFCC fundamentals and considering the transition from plane strain state to plane stress state at the crack tip. This tool is able to estimate ∆k vs. da/dN data under CA loading for thicknesses and stress ratios of which there is no information available, especially for thin components (1 to 5 mm) in which the stress state transitions hinder the estimations. Applied to 2024 and 7075 aluminium alloys it provides an expression of FCG rate along 4 decades.