Use of an energy‐based/critical plane model to assess fatigue life under low‐cycle multiaxial cycles

Abstract

For engineering components subjected to multiaxial loading, fatigue life prediction is crucial for guaranteeing their structural security and economic feasibility. In this respect, energy‐based models, integrating the stress and strain components, are widely used because of their availability in fatigue prediction. Through employing the plastic strain energy concept and critical plane approach, a new energy‐based model is proposed in this paper to evaluate the low‐cycle fatigue life, in which the critical plane is defined as the maximum damage plane. In the proposed model, a newly defined NP factor κ* is used to quantify the nonproportional (NP) effect so that the damage parameter can be conveniently calculated. Moreover, a simple estimation method of weight coefficient is developed, which can reflect different contributions of shear and normal plastic strain energy on total fatigue damage. Experimental data of 10 kinds of materials are employed to assess the effectiveness of this model as well as three other energy‐based models.

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

“…As can be seen from Figure 10, the results of the proposed method and the local stress–strain method are both within a factor of two error bands. However, in order to evaluate the advantages and disadvantages of the proposed method and the local stress–strain method, a statistical method is employed to investigate the errors of the two methods 25,50 : In Equation (26), P error represents the life error and N f and N e are the predicted life and the experimental life, respectively. According to the prediction error of each different loading mode, the expression of probability density function (EPDF) curve based on normal distribution can be drawn in Figure 11, and the EPDF is as follows: where δ is the standard deviation and μ is the mean of the error.…”

“…However, for multiaxial nonproportional loading, the prediction results are inclined to danger because the nonproportional additional hardening effect is not considered. The energy method 24 considers the fatigue damage to be an irreversible process, and the fatigue failure of the material will occur once fatigue damage reaches a critical level 25,26 . In addition, the greater the strain energy absorbed on the material plane is, the greater the probability of crack initiation in that direction is 27 .…”

Path‐dependent multiaxial fatigue prediction of welded joints using structural strain method

“…σ’ f , ε’ f , τ’ f , and γ’ f are the fatigue strength coefficient, fatigue ductility coefficient, shear fatigue strength coefficient, and shear fatigue ductility coefficient, respectively. The above four material parameters of the S460N steel are set as 834 MPa, 0.1572, 529 MPa, and 0.213 for analysis 59 …”

“…The energy-based models are the Smith-Watson-Topper (SWT) model, 57 the Varvani-Farahani (VF) model, 58 and the Gan-Wu-Zhong (GWZ) model. 59 F I G U R E 1 1 Equivalent FP w,eq versus the experiment life [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The above four material parameters of the S460N steel are set as 834 MPa, 0.1572, 529 MPa, and 0.213 for analysis. 59 Note that the SWT and VF models do not contain the nonproportional factor, and the proposed path factor (Equations 3 and 4) is consequently used to make life prediction for fatigue data of OP loading paths.…”