Fatigue Damage Assessment in AL6XN Stainless Steel Based on the Strain-Hardening Exponent n-Value

The fatigue life curve was determined for the AL6XN stainless steel under strain-controlled Low Cycle Fatigue (LCF) tests. Additionally, a specific number of loading cycles were applied to new specimens made from the same AL6XN alloy batch to set an Accumulated Fatigue Damage (AFD) based on the Palmgren–Miner rule. The AFD was 0.25, 0.50 and 0.75; subsequently, these specimens were subjected to tensile tests. It was observed that all AFD specimens exhibited a yield strength increment with respect to the AL6XN material property, thus, it was similar to a strain-hardening mechanism. However, the stress–strain behavior and microstructure characterization showed a microvoid nucleation and growth mechanism that competed against the strain-hardening one. The fracture in the 0.75 AFD specimens was dominated by this microvoid-based mechanism. The experimental results indicated that the strain-hardening exponent (n-value) and electrical resistivity (ρ-value) were consistently modified by the AFD in all the specimens, with an inverse linear relationship for the n-value and a nonlinear increasing behavior for the ρ-value.