ヒステリシスエネルギに基づいた疲労強度減少係数の一考察

概要

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Fatigue strength of a notched plate subjected to the repeated tensile load in intermediate cycle range was analyzed theoretically by using a rule proposed by Hardrath and Ohman. On a hypothesis that a fatigue crack will initiate at a same life from a notch of any shape factor, when the accumulated hysteresis energy at the notch reaches a certain value related to material properties, the relation between the nominal net section stress range for a geometrically notched plate and crack initiation life N_c was expressed by a equation with the elastic stress concentration factor of a notch, K_t as a parameter. Also the fatigue strength reduction factor of N_c-basis, K_f, was obtained as a function of K_t and work hardening constants in the cyclic hysteresis loop. Experimental investigation was made on notched specimens, of which K_t value was varied from 1.08 to 10.84 in order to verify the theoretical analysis. Results of zero-to-tension axial loading fatigue test showed excellent agreement with theoretical values. The K_f, which is always lower than the K_t value, shows linear relation against K_t value. The propagation life in an unnotched and notched specimen was expressed as a function of stress range irrespectively of K_t value. The K_f value shows the increasing tendency with increasing N_c value, and the increasing amount is larger for the higher K_t value.
社団法人日本船舶海洋工学会の論文