Issue 50

J. Papuga et alii, Frattura ed Integrità Strutturale, 50 (2019) 163-183; DOI: 10.3221/IGF-ESIS.50.15

Figure 6 : Results of the sensitivity analysis on critical plane criteria of the maximum damage type.

Figure 7 : Results of the sensitivity analysis on critical plane criteria of the maximum shear stress range (MSSR) type.

The maximum damage critical plane criteria presented in Fig. 6 show that a non-zero phase shift increases the fatigue life. Both methods are quite insensitive to the phase shift effect if the torsion load channel is prevalent. The only exception in both cases is for a brittle material, where a decrease of approx. 5% can be observed. The most radical increase in fatigue strength is for extra-ductile materials, if axial stress is dominant. The criteria that look first for the critical plane related to the maximum shear stress range (see Fig. 7) provide a radically different response, above all for brittle materials. The response of the Susmel criterion to a stress ratio of 1.73 is not encountered by any other criterion in the tested set – the phase shift effect predicted by the Susmel method for this setup is so high that it should be obviously measurable. The response to the phase shift effect by a ductile material is not so pronounced, and a loading with dominant axial stress would be the most effective for confirming the effect. Both criteria show more visible phase shift dependency for an extra-ductile material than for a ductile material, as do other prediction methods. The Dang Van method in the original version (DVO) shows higher phase shift dependency (to increase the admissible stresses for a non-zero phase shift) than most other methods – see Fig. 8. The most sensitive response of the method is to a stress ratio of 1.73, but the values for brittle materials and for a stress ratio of 1.00 are also quite extreme. The modified Dang Van method presents reduced dependency, there is almost no phase shift effect for the dominant torsion channel, and the results also predict a relatively mild effect for a stress ratio of 1.00. The use of ductile or extra-ductile materials with

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