An engineering methodology for predicting crack growth of 2024-T3 aluminium alloys under variable amplitude loading

The propagation of fatigue cracks can significantly reduce the lifespan of components, potentially leading to failures. This study presents an engineering approach that accounts for variable-amplitude loading while incorporating residual stresses at the crack tip. The objective is to evaluate the fatigue life of 2024-T3 aluminum alloys under variable loading by transforming the problem into an equivalent one with constant loading, eliminating complex cycle-by-cycle calculations. The proposed strategy is integrated into the two-parameter fatigue crack growth model, which considers both the total maximum stress intensity factor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mrow> <mml:mo form="prefix" movablelimits="true">max</mml:mo> <mml:mo>_</mml:mo> <mml:mi mathvariant="normal">tot</mml:mi> </mml:mrow> </mml:msub> </mml:math> and the total stress intensity factor range <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msub> <mml:mi>K</mml:mi> <mml:mi mathvariant="normal">tot</mml:mi> </mml:msub> </mml:mrow> </mml:math> . Initially, plastic zone interaction effects are neglected to establish an equivalence relationship between variable and constant loading. The Willenborg model is then used to determine the equivalent stress, ensuring a comparable crack growth rate. To refine the approach, a finite element (FE) elasto-plastic analysis based on the Chaboche model is conducted. This analysis estimates the residual stress distribution at the crack tip, converted into a residual stress intensity factor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mi mathvariant="normal">r</mml:mi> </mml:msub> </mml:math> . This factor is integrated into a correction coefficient equation to account for plastic zone interaction effects. Three loading spectra were examined. Predicted results were compared with experimental data, showing that the proposed model improves crack growth life in 2024-T3 aluminum alloy structures subjected to variable-amplitude loading.