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The fatigue life of type 1100-H14 commercial aluminum in reverse bending at 125 to 140 cps is about seven times longer in high vacuum than in wet air and about four times longer in high vacuum than in dry air. Life is independent of pressure in the range 760 to 10−2 torr, increases rapidly in the range 10−2 to 10−4 torr, and is again independent of pressure in the range 10−4 to 7 × 10−9 torr. There is some indication that life is longer under argon bombardment than in high vacuum. The cyclic strain causes more surface roughening in vacuum than in air.
A hypothesis based on adsorption equilibria is proposed to explain the step change in life with pressure as well as the improved life in vacuum.
Ham, John L.
Research Associate, National Research Corp., Cambridge, Mass.
Reichenbach, George S.
Associate Professor, Massachusetts Institute of Technology, Cambridge, Mass.