抄録
As part of the program of the cooperative researches sponsored by the Society of Materials Science, Japan, we have carried out the test in our laboratories in which the different heat treatments were performed for carbon steel and chrome-molybdenum steel, and the variation of residual stress and half-value breadth in the fatigue process was estimated. Among them, the test results on induction quenched materials are mentioned in this report. As for the variation of residual stress and half-value breadth, various test results had hitherto been reported from several laboratories. The final object of those researches as production makers is to grasp the fatigue process of real production parts, that is to say, to predict the break-down. Therefore we have continued for several years the basic tests for putting the X-ray residual stress measurement to practical use. As a result, it was found that it was difficult to predict the break-down of real production parts. Accordingly the other test method (Sonic test) was utilized jointly with the above mentioned method. Consequently we have attained to the following conclusions.
(1) Residual stress, when repeated stress is over the fatigue limit, varies rapidly at an early stage of fatigue, and, after that, does not vary remarkably until break-down. When the repeated stress is under the fatigue limit, nothing but variation of tolerance is observed.
(2) In the diffraction pattern photographed at the measurement of residual stress, obvious change of repeated stress, when it is over the fatigue limit, is observed before and after the fatigue test.
(3) The result of sonic test does not vary so remarkably at the early stage of fatigue, when the repeated stress is over the fatigue limit, that is different from the above mentioned residual stress. But when it approaches the fracture point, it varies suddenly. Also, when the repeated stress is under the fatigue limit, little variation is observed.
(4) The expected object of the present tests was achieved by the above mentioned results; As for the early stage of fatigue, the variation of residual stress and half-value breadth are measured by X-ray method. As for the final stage of fatigue, it will be concluded that it is possible to grasp the fatigue process and predict the fracture.
(5) Although the real production parts were not utilized for the basic test this time, it is expected that X-ray method and sonic test will be jointly used to observe the fatigue process of real production parts for the future plan.
