PSI - Issue 39

Daniele Amato et al. / Procedia Structural Integrity 39 (2022) 582–598 Author name / Structural Integrity Procedia 00 (2019) 000–000 • Given a fixed axial load ratio, , and a fixed phase shift, , the higher the mode-mixity, the larger the deflection angle, as expected theoretically. Furthermore, the angle deviation is in general higher when the load magnitudes are comparable i.e., / = 1 . Moreover, the correlations with a ratio / = 0.76 are always better than the others in terms of both (%) and Δφ . • The experimental deflection angle shows a decrease passing from a higher to a lower one. This could be explained by the fact that with an = − 1 loading condition, during half of the cycle, the crack faces rubber on each other, creating a counter frictional torque which reduces the effects of the applied torsional moment , as well as the kink angle. Changing from zero to − 1 leads also to a reduction of the angle deviation, especially in the case of a shift phase of 0° ; this consideration is not generically applicable to the case of a shift phase of 40° . • The numerical simulation predictions are in all cases acceptably accurate, demonstrating that the algorithms used in this study works fine for the crack growth propagation predictions in non proportional mixed mode missions. In fact, the deviation is generally quite low, proving that the way the missions are analysed covers the physical phenomena involved in a non-proportional loading condition well. Figure 10 and Figure 11 show the comparison between the experimental fracture surface (in red) and the numerical crack propagation (in green) for the loading condition 1_1_00_1 (proportional) and 0_1_40_1 (non-proportional). In these two figures, the fractured specimens’ models are shown in red: the bottom part of the figures, represents half of the V-shaped notch, whereas the middle and upper parts depict the initial rectangular crack (in the experiments a 0.3 mode-I crack was initiated before applying the tension/torsion loading, cfr. [19]) and the experimental fractured surface, respectively. These pictures also represent graphically the volume in between the two surfaces, approximated with a group of triangular prisms built taking as reference the numerical triangulation. By looking at the filling volume, it is possible to appreciate how the predicted crack propagation is more accurate in the case of proportional loading than in the other one.

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Figure 10 Specimen No. 10, proportional loading condition: 1_1_00_1.