The experiments on high-frequency fatigue in copper, Armco iron, and mild steel described in the following paper were carried out in the Engineering Laboratory, Oxford, for the Fatigue Panel of the Aeronautical Research Committee. The cost of the apparatus was defrayed by a grant from the Engineering Research Board of the Department of Scientific and Industrial Research. In 1911 Prof. B. Hopkinson called attention to the importance of ascertaining whether the fatigue limit of metals was dependent on the rate of alternation of stress. He designed and made an electric alternating directstress machine, and published the results of tests on mild steel carried out at about 7,000 periods per minute (116 per second), which was more than three times as fast as any tests made up to that time. The results at this speed were compared with those made by Dr. Stanton at the National Physical Laboratory on the same material at 2,000 periods per minute (33 per second). Prof. Hopkinson considered that the results showed that speed had a marked effect, but he did not consider that his tests were conclusive. In the light of the knowledge gained on fatigue testing since that date neither set of tests can be considered satisfactory. The question is of importance to the users of high-speed machinery. It is also of importance when comparisons are made between tests carried out at different speeds, and, finally, it has a bearing on the causes of fatigue failure. For these reasons it appeared to be desirable to make a more thorough investigation, and, if possible, to extend the tests to very much higher speeds.
In Situ and Post-Mortem Characterizations of Ultrasonic Spot Welded AZ31B and Coated Dual Phase 590 Steel Joints
