IMPACT OF LOCAL PLASTIC DEFORMATION ON FATIGUE LIFE AND STRENGTH OF 2024-T3 ALUMINUM ALLOY NOTCHED SPECIMENS

This study investigates the impact of local plastic deformation on the fatigue life and strength of 2024-T3 aluminum notched specimens. Fatigue tests were performed under constant amplitude loading on both undeformed and plastically deformed specimens. The results indicated that significant plastic deformation induces numerous microcracks, reducing crack initiation time and shortening fatigue life, particularly near the fatigue limit. Fractographic analysis revealed a higher density of microcracks in pre-stretched specimens. Finite element analysis showed that residual compressive stresses delay crack initiation under high applied stresses. Additionally, fatigue tests on cold-expanded holes demonstrated improvements in fatigue resistance, with elliptical mandrels outperforming circular ones. The longitudinal orientation exhibited higher fatigue resistance than the transverse orientation for untreated holes. The beneficial effects of cold expansion were consistent regardless of the loading direction. These findings illustrate the influence of plastic deformation on fatigue life by altering crack initiation and propagation mechanisms, providing insights into discrepancies observed with different surface preparation methods.