NOTE ON FATIGUE MECHANISM IN FCC METALS AT ULTRASONIC FREQUENCIES.
COLUMBIA UNIV NEW YORK DEPT OF CIVIL ENGINEERING AND ENGINEERING MECHANICS
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A comparison is made of microstructural changes leading to fatigue of copper and alpha-brass at small strain-amplitudes imposed at the normal test frequency of 1700 cpm and at the ultra-sonic frequency of 1700 cps. A striking difference appears in the distribution of slip. At normal frequency the slip spreads densely over a grain, with no slip-band cracking stage S of the SN curve. At ultrasonic frequency the slip concentrates in single isolated bands in only occasional grains and reduces these to microcracks before any general spread of slip can be observed. However, as might be expected, the ultra-sonic slip did spread in specimens tested at elevated temperatures which expedited dislocation climb and diffusion processes then this spreading of slip prevented the slip-band microcracking at ultra-sonic frequency also. Author
- Properties of Metals and Alloys