Ratcheting phenomenon and post-ratcheting tensile behaviour of an aluminum alloy

The aim of this investigation is to examine ratcheting phenomenon and post-ratcheting tensile properties of an aluminum alloy in as-received and annealed conditions. Stress-controlled fatigue tests were carried out at room temperature up to 100 cycles under different combinations of mean stress (σm) and stress amplitude (σa), apart from characterization of the microstructural features and assessment of conventional mechanical properties of the material. A few tensile tests were also carried out on specimens ratcheted for 100 cycles. The results highlight that accumulation of ratcheting strain may increase or decrease with increasing σa (at constant σm) for annealed and as-received conditions respectively. Post-ratcheting tensile strength increases while ductility decreases with increasing σa for as-received samples. The increase in strain accumulation during ratcheting is explained using the phenomenon of increased cyclic damage parameters as well as increased dislocation density. The increase in tensile strength and decrease in ductility have been attributed to cyclic hardening.