A new distortion energy-based equivalent stress for multiaxial fatigue life prediction

A new equivalent stress amplitude expression has been developed for the assessment of fatigue life in components under multiaxial loading. The expression was generated by incorporating non-linear/plastic stress–strain relation into a mechanical energy calculation, and then applying the calculation to the distortion energy theory for a cyclic loading case. Therefore, the new uniaxial equivalent stress expression determines an appropriate stress amplitude value for multiaxial cyclic loading. The purpose of the equivalent stress value is to determine multiaxial fatigue failure using an energy-based fatigue life prediction criterion. The governing understanding behind the criterion states that the physical damage quantity for failure is equal to the accumulated strain energy in a monotonic fracture, which is also equal to the accumulated strain energy during fatigue failure. Using the new equivalent stress amplitude expression and the energy-based life prediction method, a comparison is made between prediction results and multiaxial empirical data. The multiaxial data was acquired by a vibration-based biaxial bending fatigue test and a torsion fatigue test with an assumed axial misalignment. The results of the comparison provide encouragement regarding the capability of the newly developed equivalent stress amplitude expression for fatigue life prediction.

► Energy-based life prediction method has been validated for axial fatigue R>or=−1.
► Energy-based life prediction method has been validated for uniaxial-bending fatigue R>or=−1.
► Energy-based life prediction method has been validated for in-phase multiaxial loading.
► Distortion energy equivalent stress would simplify energy-based multiaxial life prediction.
► Equivalent stress prediction results compare well to multiaxial prediction and empirical data.