Numerical-experimental procedure for predicting fatigue life in SAE AMS 7475-T7351 aluminum alloy considering the effect of stress ratio

Abstract

This study addresses the prediction of fatigue life in SAE AMS 7475-T7351 aluminum alloys under variable loads, commonly used in the construction of aircraft fuselages. The main objective of the research was to develop a numerical-experimental procedure to analyze crack growth, using the Walker’s approach which considers the effects of the stress ratio $R$ on the fatigue crack growth rate $da/dN$, combined with the Finite Element Method and Linear Regression of the Stress Intensity Factor. Observations showed that Walker’s model effectively consolidated fatigue crack propagation data for various stress ratios when applied longitudinally to L-T rolling orientation, due to low dependence of exponent $m$ on $R$-value in $da/dN$ equation. Simple averaging of $m$ values effectively calculated Walker’s exponent. The methodology employed experimental tests following ASTM standards for tension, fracture toughness, and fatigue, complemented by Finite Element Method (FEM) simulations. The Walker’s model proved more effective, while the Paris-Erdogan model, which ignores the $R$ effect, resulted in overly conservative service life estimates. The principle of similitude suggests that this methodology could be effective in predicting fatigue life in cases with complex geometries, where calculating the Stress Intensity Factor Fracture parameter is challenging and the Finite Element Method shows efficiency.

Key words
Aluminum alloys; crack growth; fatigue failure; load ratio; numerical simulation