Interpretation of Different Low‐Cycle Fatigue Failure Modes for a Near Alpha Titanium Alloy via Crystal Plasticity Finite Element Method

Ti6321 alloy exhibits excellent weldability and toughness, yet its low‐cycle fatigue (LCF) behavior under stress‐controlled loading remains insufficiently studied. This work investigates the LCF properties under stress ratios of R = 0 and R = −1. Results show that compressive stress markedly reduces fatigue strength, inducing ductile failure at lower maximum stresses compared to R = 0. Failure modes are classified as ductile, mixed, and brittle. Crystal plasticity finite element simulations reveal that accumulated plastic strain in individual grains drives the difference in LCF performance under varying stress ratios. The mixed failure mode is governed by competition between micro‐void coalescence and crack initiation.