Reversed bending fatigue properties of 25 S-T, 75 S-T, and 76 S-T aluminum alloys
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The problem of this investigation was to determine the effects of surface roughness and surface stressing on the reversed bending fatigue properties of 25 S-T, 75 ST and 76 S-T aluminu...
| Summary: | NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The problem of this investigation was to determine the effects of surface roughness and surface stressing on the reversed bending fatigue properties of 25 S-T, 75 ST and 76 S-T aluminum alloys.
Tests were conducted in a stress range from 37,700 psi, to that stress giving a fatigue life of 500,000,000 cycles.
Surface roughness was varied from five micro-inches to 400 micro-inches. Two different machining tools were used to obtain the various degrees of surface roughness: 1/8" radius tool, and a sharp pointed tool.
Surface stressing was obtained by shot peening with 0[...]028 diameter shot at .010/.012 A-2 intensity, and cold rolling at 100 lbs. and 200 lbs. pressure.
It was determined that fatigue life decreased as surface roughness increased in a similar manner for specimens machined with both types of tool; but that endurance limit was not affected by the sharp tool, whereas it was decreased by the 1/8" radius tool.
Shot peening increased fatigue life of 25 S-T by about 500%; it had but slight effect on 76 S-T.
Cold rolling increased fatigue life of 25 S-T and 76 S T by about 2500%. 75 S-T was neither shot peened nor cold rolled.
This work was carried out by the author at the Guggenheim Aeronautical Laboratory, California Institute of Technology under the supervision of Dr. E. E. Sechler.
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