実働荷重疲労試験装置と累積ひん度曲線による二, 三の実験

抄録

An electro-dynamic type fatigue testing equipment has been developed for the study of the fatigue strength under random and program loads. The equipment consists of four basic parts; the signal generator, the power amplifier, the power transducer, and the measuring instruments. The available range of the test frequency is from 2cps to 2kc, the maximum power being 360VA, and the maximum oscillating force which naturally depends on the test frequency and the flexibility of the specimen, being approximately 45kg at 60cps.
The program load fatigue tests were made on notched specimens of 7075-T6 aluminum alloy, in which the amplitude of the alternating stress was controlled along the curve that was similar to the gust load on transport aircrafts. It was observed that the linear damage rule held good when the root-mean-square value of peak stress was higher than the conventional endurance limit, but that the fatigue life became shorter than that of the linear estimate when the root-mean-square value was near or lower than the endurance limit. This fact seems to indicate that the alternating stress whose magnitude is less than the endurance limit contributes to the progress of the fatigue damage.