PSI - Issue 23

Krzysztof Kluger et al. / Procedia Structural Integrity 23 (2019) 89–94 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 5 experimental lifetime. The obtained inconsistency is the effect of the ratio of shear to axial stress amplitudes = ⁄ variable as a function of the number of cycles to failure for the given fatigue characteristics of the tested steel. This results from different slope values of the fatigue curves (for bending 9.79 and for torsion 16.62, Fig. 2). Taking into consideration the variability of the ( ) parameter as the function of a number of cycles to failure being present in the coefficients of the validated models substantially improved the conformity of experimental and computed fatigue lives. For instance, for the Matake model, the global fatigue scatter band (0.95) decreased from 24.1 down to 3.2 (see Fig. 3b). The lowest scatter band of fatigue lives was obtained for the Carpinteri-Spagnoli model with a value equal to 2.1 that is slightly higher than the experimental value equal to 1.99 obtained for fatigue characteristic under cyclic torsion. 93

Fig. 3. Comparison of the experimental and computed fatigue lives on the basis of the Matake criterion for: (a) constant material parameters, (b) life dependent material parameters

Fig. 4. Comparison of the experimental and computed fatigue lives on the basis of the Carpinteri-Spagnoli criterion for: (a) constant material parameters, (b) life dependent material parameters