Issue 33

M.Kurek et alii, Frattura ed Integrità Strutturale, 33 (2015) 302-308; DOI: 10.3221/IGF-ESIS.33.34 306 V ERIFICATIONS OF PROPOSED CRITERIA AND ANALYSIS OF OBTAINED RESULTS n order to perform the correct analysis of the fatigue life scatter, the logarithmic dependence of the ratios of experimental and calculation strength should be used. A new method of determination the fatigue life scatter has been proposed by [12], defined as the root mean square error: exp 2 1 log n i cal N N E n    (18) Therefore, the scatter can be determined as: T = 10 E (19) Tab. 2 compares plane rotation angles according to the Carpinteri et al. method. Moreover, the angle β was found for minimum scatter according to the formula (19). Fig. 3 shows the relationship between scatter value (19) and the angle β for the selected PA4 aluminum angle. For this alloy, the least scatter (global minimum) was achieved for β=42 0 (T=2.366). Additionally, local minimum was obtained for β =19 0 (T=2.391). 0 5 10 15 20 25 30 35 40 45 2 3 4 5 6 7 8 9 10 X: 42 Y: 2.366  , o T Figure 3 : Relationship between scatter values T (19) and the angle β. Material β C (3) T min β (T min ) β (21) PA6 44 1.9972 44 42 GGG40 13 2.583 1 16 10HNAP * 1.932 43 44 PA4 44 2.366 42 42 30CrNiMo8 38 1.992 40 39 CuZn40Pb2 ** 4.335 11 →0 Table 2 : The values of rotation angles β and minimum scatters of fatigue life (*out of range > 3 ; ** out of range <1 The Carpinteri et al. method concerning determination of the angle β is based on the assumption that we deal with materials ranging from resilient-brittle to resilient-plastic state. Considering this, the Author assumes that in the first case coefficient B 2 is 1, and in the second extreme case its value is 3 . Therefore, it has been assumed that the plasticization criterion according to the Heber-Mises-Hencke hypothesis is right in the boundary case for materials in resilient-plastic state. As we see, this ratio (Tab. 1) for the 10HNAP steel exceeds that value. Considering this, it has been proposed to I