Issue 41

J.V. Sahadi et alii, Frattura ed Integrità Strutturale, 41 (2017) 106-113; DOI: 10.3221/IGF-ESIS.41.15 111             f f f N N E ' 2 2b b+c ' ' 1 n, max f f 2 2 2 , (7) where, Δε 1 /2 represents the maximum normal stress, and accordingly σ n,max is calculated on the plane where Δε 1 /2 occurs. Fig. 3 (b) illustrates the evolution of this parameter with respect to θ, along with Δε n /2 and σ n . The critical planes predicted with this formulation are orientated at 0 and 180º from the y-axis, as oriented in Fig. 1 (b). Fig. 5 presents the fully reversed normal strain-life curve used to calibrate the models. Since no shear strain-life curves were available at the time of this analysis, the additional material parameters needed for the Fatemi-Socie criterion were estimated based on the relationships presented in Tab. 2. Moreover, the results and material parameters presented in the work of Lopez-Crespo et al [17] were used as a benchmark for verifying the implementation of both parameters. Parameter Axial Shear Fatigue Strength Coefficient  f '     f f ' '   / 3 Fatigue Strength Exponent b  γ b b Fatigue Ductility Coefficient  f '    f ' ' f γ 3 Fatigue Ductility Exponent c  γ c c Modulus E      E G 2 1 Table 2: Correlation between material fatigue parameters. Figure 4: Strain-life curve used for model calibration. Fatigue Life Prediction After calibrating both models, their performances were assessed using the biaxial test data presented in Tab. (1) (for this analysis, the runout (CX06) was not considered). Fatigue lives were calculated using Eqs. (4), (5) and (7) at the material plane where each of the parameters (FS and SWT) reached their maximum. The results were plotted against the experimental fatigue lives in Fig. 5 and summarized in Tab. (3). The solid black line in the plot represents perfect correlation between predicted and experimental life. In contrast, predictions lying above this line represent non-conservative predictions, and data points below the line represents conservative predictions. Further, the dashed lines represent the bounds of twice and half of the fatigue life. It is observed that the Fatemi-Socie parameter presented conservative predictions, with all its results in the safe area of the plot. As σ 2,peak magnitude decreases towards the uniaxial loading and uniaxial stress conditions(CX1, CX4 and CX07), the prediction error increased proportionally. The farthest point to the solid black line corresponds to CX07 under uniaxial stress state condition. Nevertheless, the parameter presented good correlation with the equi-biaxial loading cases (CX02 and 10 2 10 3 10 4 10 5 10 -2 10 -1 10 0 10 1 10 2