High temperature vacuum axial fatigue testing machine

This paper describes fatigue equipment which was developed to test thin-walled refractory metal specimens in a vacuum under repeated axial loading at temperatures up to 2100°F. The machine is of the constant displacement type and incorporates an eccentric and crank mechanism which allows the alternating stress, mean stress, and frequency of cycling to be varied. The stresses in the specimens are easily calculated from σ = P/A, where P is the axial load measured by a ring dynamometer and A is the cross-sectional area of the specimen. The test specimen is uniquely heated by placing a tungsten heating element inside the thin-walled tubular specimens. The evacuated test chamber is completely visible through the use of a pyrex bell jar seated on an O-ring seal. Axial motion is transmitted into the vacuum chamber through a copper alloy bellows. Preliminary results of fatigue tests on commercially pure arc-cast molybdenum specimens subjected to fully reversed stresses at 1700°F and 875 cpm, are included in this paper.Atomic Energy Commission, Contract No. AT (11-1)-67, Project 2