Abstract
High Power Ultrasonics has been a useful tool in studying fatigue and internal friction in metals since a large number of cycles can be obtained in a short time. It was first used by the speaker at Bell Laboratories in 1956. Further work was done at Columbia using an improved arrangement. Brass, copper, iron and titanium were studied. The first three fatigued plastically, whereas titanium fatigued elastically by slipless cracks. A correlation between internal friction and breakaway of dislocations and with two stages of plastic deformation has been found. Optical and electron microscope pictures show the various mechanisms up to the fatigue region. Electron microscope pictures show that fatigue cracks progress much faster for ultrasonic vibrations than for the slower fatigue tests. While the structure changes are somewhat different for ultrasonic vibrations than for low frequency testing, the number of cycles to fatigue is slightly larger for ultrasonic testing than for low frequency testing except for steel.
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