Fatigue Strength of Notched Steel Plates Based on Crack Initiation Life

Research Project

Project/Area Number	60550309
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	船舶構造・建造
Research Institution	University of Osaka Prefecture
Principal Investigator	OKAMURA Yoichiro University of Osaka Prefecture, Associated Professor, 工学部, 助教授 (80081397)
Project Period (FY)	1985 – 1986
Project Status	Completed (Fiscal Year 1986)
Budget Amount *help	¥700,000 (Direct Cost: ¥700,000) Fiscal Year 1986: ¥700,000 (Direct Cost: ¥700,000)
Keywords	Notched Steel Plate / Repeated Tensile Loading Fatigue Test / Fatigue Crack Initiation Life / Elastic Stress Concentration Factor / Elastic Stress Gradient / Fatigue Strength Reduction Factor / Empirical Formula of Fatigue Strength / 寸法効果係数
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> .