Multi-axial fatigue properties and life prediction under proportional and non-proportional loading at high temperature

The multiaxial fatigue behavior of the notched specimens and thin wall tube specimens of GH4169 super alloy was investigated. Symmetric axial-torsional strain was controlled in fatigue tests at a high temperature of 650°C by using a MTS 809 tension-torsional servo-controlled electro-hydraulic testing machine with proportional and non-proportional loading. The phases between axial strain and torsional strain were 0° in-phase (proportional) and 45°, 90° out-of-phase (non-proportional) respectively. Based on the critical approach, a model for multiaxial fatigue life prediction was established by combining maximum shear strain and normal strain on the critical plane, and the effect of stress state under the multiaxial cyclic loading condition on the fatigue life was taken into account. The results of life prediction show that the new fatigue life prediction model is validated with the experimental.