過小応力による疲労被害に関する研究 (プログラム周期の影響と過小応力のみによる破壊)

概要

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One of the purposes of the present study was to investigate the effect of the program period on the fatigue life under programmed load. The load programs of two-stress repeated-block type were adopted in the experiment, in which the lower stress was set at a level below the endurance limit. The ratio of the number of cycles at the lower stress level to that at the higher stress level was fixed, and only the program period was varied in a wide range. Another purpose of the study was to investigate the possibility of fatigue failure by only the stresses below the ordinary endurance limit. Similar load programs were used in this experiment, but both of the stress levels were set at suitable values below the endurance limit. Carbon steel S50C was used and the tests were conducted under cantilever type rotating bending stress. The following conclusions were obtained from the present investigation. (1) The fatigue life under the program load composed of stresses above and below the endurance limit was influenced remarkably by the program period and the fatigue life showed a rapid decrease with the decrease of program period. Moreover, the effect of the program period became larger as the lower stress level became closer to the endurance limit. (2) Occurrences of the fatigue failure caused by the stresses below the endurance limit were observed when the applied load was altered rather rapidly.
1973-02-15