Low cycle fatigue life of Ti–6Al–4V alloy under non-proportional loading

Multiaxial low cycle fatigue life of Ti–6Al–4V under non-proportional loading was studied. Strain-controlled multiaxial fatigue tests at room temperature were carried out using tubular specimens. The strain paths employed were push–pull loading, reversed torsion loading, and two kinds of 90° out-of-phase loadings. The former two loadings are proportional loading tests where the principal directions of stress and strain are fixed in the cycle. The latter two are non-proportional loading tests where there is a 90° phase difference between axial and shear loadings, and the principal directions are cyclically rotated continuously. Failure lives are reduced obviously by non-proportional loadings in comparison with those in proportional loading tests. This paper focuses on determining a suitable fatigue model for evaluating the failure lives of Ti–6Al–4V under multiaxial loading.

► Strain controlled multiaxial low cycle fatigue tests of Ti–6Al–4V were carried out.
► Proportional (P) and non-proportional (NP) loadings were employed.
► A large reduction in failure life with no additional hardening due to NP loading.
► Proposing a suitable fatigue model for evaluating the failure lives.
► Analyzing a mechanism of failure life reduction due to NP loading.