Advanced volumetric method for fatigue life prediction using stress gradient effects at notch roots

In the present study, the role of relative stress gradient for fatigue life assessment using volumetric method is highlighted. The polynomial volumetric method point of view has been proposed which satisfies weight function conditions, removes numerical derivation errors, elucidates effective stress terms as subtraction of average stress and relative stress gradient based phrase. According to the elastic-plastic finite element outcomes for considered notched specimens, Peak Stress Trajectory Path “PSTP” and Effective Stress Trajectory Path “ESTP” have been proposed. The “PSTP” represents linear characteristics in logarithmic diagram and it can be applied to avoid more excessive mesh density generation refinement around notch roots for low applied loading magnitudes. The “ESTP” yields the effective distance-effective stress curve and effective stress-applied loading magnitude curves which can facilitate the calculation of effective stress and effective distance due to the parabolic shape configuration of mentioned curves. The volumetric method and Stress Field Intensity method are compared using the weight functions and corresponding stresses at notch roots. The comparisons exhibit that polynomial volumetric weight function completely satisfies all necessary requirements and the volumetric effective stress is slightly greater than Stress Field Intensity stress. The current phenomenon concludes less number of cycles to failure relative to the Stress Field Intensity method which overestimates it.