| Research Abstract |
In this study , the repeated tensile loading fatigue tests for SS41 and HT50 notched plates are carried out. And from the results on the fatigue strength based on crack initiation life <N_c> in intermediate cycle range , the relation between the fatigue strength and the stress concentration factor <K_t> and the stress gradient G , is discussed in the case of small values of <K_t> .
The results obtained in this study are summarized as follows:
(1) The relation between the fatigue strength reduction factor of <N_c> -basis , <K_f> and <K_t> for relatively small values of <K_t> is approximately expressed as the linear function under constant values of <N_c> and G , which satisfies <K_f> =1 for <K_t> =1. The relation between <K_f> and <K_t> for SS41 is almost the same as that for HT50.
(2) From above results , the empirical formula giving <K_f> , for relatively small values of <K_t> , is obtained in the following form for the both materials:
Kf=1+[(Kt-1)/(1+ <d_1> <G^(h_1)> )] <N^(d_2G^(h_2))_C)> where <d_1> , <d_2> =constants , <h_1> , <h_2> =exponents. This formula is applied in the extent where G value is not very large. This formula shows good agreement with the results of other researchers in comparatively high cycle range.
(3) The size effect factor showing degree of the size effect of notched plates , <K_s> , for relatively small values of <K_t> is obtained as a function of G and <K_t> ,i.e., <K_s> = <K_t> / <K_f> .
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