Issue 41

M. Kurek et alii, Frattura ed Integrità Strutturale, 41 (2017) 24-30; DOI: 10.3221/IGF-ESIS.41.04 26 A graphical interpretation of formula (8) is presented in Fig. 1, whereas the broken line marks the proposition developed by Carpintieri (10). 2 2 2 2 3 1 3 1 1 45 ( ) 1 45 2 2 ( ) fi fi B N B B N                                       (10) Figure 1 : The relationship between the angle β and the parameter B 2 according to different models. The final step is the calculation of the fatigue strength. For constant amplitude cyclic loading, the fatigue strength is evaluated by using Basquin’s fatigue characteristics ( A and m ) in compliance with the relevant ASTM standard [14]. The formula for strength calculation under cyclic loading is expressed as follows: , lg 10 eq a cal A m N    (11) where , eq a  is the amplitude of the equivalent stress related to the critical plane (Eq.(1)) , A, m - coefficients of regression equation for oscillatory bending. F ATIGUE STRENGTH SCATTER ANALYSYS he proposition in Eq. (8) presented in Fig. 1 was developed on the basis of the results of a study involving several materials and requires verification. An analysis of the scatter of the results of fatigue life depending on the proposed angle and value of the ratio of the normal to shear stress was undertaken for this purpose. The analysis applied the values of the scatter bands for the particular materials just as it was calculated in [8] for angle β in the range <0°, 45°>. Fig. 2 presents the methodology followed during the analysis of the proposed expression (8) with regard to the relation of angle β and scatter T. The values of angles β were calculated so that the scatter T is in the range <T min , 1.1T min >. On this basis, β opt ϵ <β min , β max >. Fig. 3 illustrates relationship between scatter values T and the angle β for D30 [15]. T