Abstract
It was expected by the authors that the existence of the ‘knee’ on the S-N curve would be related to the instability of the structure of metals and the sudden bend of the P-N curve would correspond to this knee. With this expectation in mind, the effects of the age hardening ability of materials on the S-N diagram and on the P-N diagram were studied by fatigue testing.
Two kinds of rimmed steel were prepared for testing; specimens A, in which the age hardening ability was attained through heat treatment, and specimens B, in which the ageing process in specimens A was completed by leaving them in room temperature. The S-N diagram and the P-N diagram were made from rotating fatigue testing (the test speed of 1500 cycles per minute).
As a result, for the test on specimens B, the knee did not appear on the S-N diagram and the P-N diagram showed a logarithmic normal distribution. On the other hand for the specimens A, the knee appeared in the S-N diagram near N=106 and also the bending point in the P-N diagram near N=5.8×105. It was concluded that these effects were due to the ageing ability of the material.
