Issue 38

M. Leitner et alii, Frattura ed Integrità Strutturale, 38 (2016) 47-53; DOI: 10.3221/IGF-ESIS.38.06 51 v n 2    (4) Fig. 6 presents the stress-time distribution for the three tested load-cases and the corresponding characteristic of the equivalent stress amplitude by Huber-Mises-Hencky depending on the actual load time t and cutting plane angle  . The values are normalized to the experimentally evaluated bending fatigue strength  B,R in accordance to Fig. 4. Figure 6 : Normalized equivalent stress  v1 for (a.)  T /  B =0 (bending only), (b.)  T /  B =0.5 (bending and torsion) and ( c.)  T /  B =∞ (torsion only). On the basis of the two presented equivalent stress criteria, the maximum allowable normal (bending  B =  xx ) and shear (torsion  T =  xy ) stress amplitudes are determined as summarized in Tab. 1. In case of only bending loading (  T /  B = 0 ),  v1 reveals an almost comparable bending fatigue strength  B as the experiments indicate, whereas the calculated value is slightly conservative. An application of the maximum normal stress criteria  v2 also agrees well to the test results. For the combined loading state (  T /  B = 0.5 ) both concepts lead to a slightly overestimation of the corresponding fatigue strength values. Torsion loading without bending (  T /  B = ∞ ) again overrates the experimental values, but however, in case of  v1 by just 7 % compared to 49 % on the basis of  v2 . The accordant critical plane angles  also differ significantly, whereas for  v1 the values match acceptably well to the failure modes of the tested specimens.