A Consideration on Fatigue Strength of Notched Steel Plates Based on Crack Initiation Life (Continued Report)

Abstract

In the previous paper, the relation between the fatigue strength based on crack initiation life N_c and the stress concentration factor K_t and the elastic stress gradient G was clarified in the case of large values of K_t. In this paper, to investigate the effect of K_t and G on the fatigue strength of N_c-basis in the case of small values of K_t, the repeated tensile fatigue tests for SS41 steel plates are carried out in intermediate cycle range. From the test results, the following conclusions are obtained. (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. (2) From above results, the empirical formula giving K_f, for relatively small values of K_t, is obtained in the following form: [numerical formula] 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.