A Microscopic Study of Metals Fatigued at Ultrasonic Frequency

Abstract

This paper is devoted to the microscopic observation and hardness tests on the surface of metals fatigued at ultrasonic frequency (17.8 kc/sec). It was found that, in iron and steel, microcracks were initiated at the boundaries of pearlite and ferrite without any accompanying slipbands. This is in marked contrast with the surface structure seen in those metals fatigued at conventional frequency. In copper, however, no marked difference between both was observed. Micro-hardness of iron failed by fatigue at such a high frequency remained almost equal to that of the annealed state, while that of copper increased as seen in the specimens fatigued at conventional frequency. Results observed above are discussed from a point of view of the strain rate dependence of unidirectional deformation behavior of b.c.c. and f.c.c. metals.