Multiaxial fatigue life prediction method of notched specimens considering stress gradient effect

Abstract

This paper investigates the effect of stress gradient on the fatigue life of U‐notched specimens under multiaxial proportional loading by studying the shear stress gradient and normal stress gradient on the crack initiation plane separately. First, based on the energy method and critical plane method, an energy‐critical plane method for determining the direction of crack initiation is proposed. Second, with the help of the concept of stress field intensity, the shear stress gradient and normal stress gradient on the critical plane are studied. Finally, a multiaxial fatigue life prediction model is established by combining the equivalent stress field intensity, composed of the shear stress field intensity and normal stress field intensity, with the Manson–Coffin equation. Theoretical analysis is verified by the experiments of Q345 steel notched specimens, and the results show that the predicted accuracy of the proposed method is not conservative and is superior to the local stress–strain method.

Multiaxial fatigue life prediction model with relative stress gradient and size effect

“…In recent years, the study of critical plane has been increasingly improved, and many scholars prefer to combine the concept of energy combined with critical plane theory to explore the evolution of fatigue damage. 28,29 Therefore, in order to accurately and reliably assess fatigue life, the energy-critical plane method 30,31 is applied to determine the critical plane. This method is based on the critical plane perspective, which combines the existing critical plane theory and the concept of energy and introduces the strain energy density as the parameter that determines the critical plane.…”

“…In order to determine the location of the critical plane, the derivative of Equation 7gives the values of θ and φ. For details, see Liu et al, 30,31 and the location of the critical plane is finally determined as…”

“…34 To characterize the stress variation at the notch root, it is shown that the sixth-order multinomial stress function can better characterize the stress distribution and is closer to the actual situation. 31,35,36 Therefore, in this paper, the sixth-order multinomial stress function is used to characterize the stress distribution on critical plane, and its expression is specified as follows:…”

A damage-based method to predict crack initiation lifetime of high-strength steel under proportional bending-torsional loadings

“…Existing experiments show that the fatigue performance under proportional load is consistent with that under uniaxial load. 24 Therefore, the equivalent stress amplitude can be used to replace the stress amplitude when the specimen is subjected to multiaxial proportional load. Meanwhile, the strain hardening law is expressed as:…”

Multiaxial fatigue evaluation of type 316L stainless steel based on critical plane and energy dissipation

“…In recent years, the CPA has made some new progress in dealing with multiaxial fatigue issues. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Susmel and Lazzarin 22 proposed a novel method for multiaxial fatigue life prediction based on a combined use of the CPA and a non-conventional bi-parametric Wöhler curve. Gates and Fatemi 33,34 improved the classic FS model by considering additional factors related to variable amplitude loading conditions and successfully applied it to both un-notched and notched specimens.…”