This paper describes the calibration of a metal-fatigue tester (Baldwin-Lima-Hamilton model number SF-1-U) which employs a rotating eccentric mass element located in a cage that can oscillate in the vertical direction only. The vertical motion imparts a periodic force to a metal test specimen. This force is superimposed on a static force which is due to heavy springs that couple the cage to a massive platform that can be raised or lowered to give a desired compression or tension. The task was to determine the peak force that was imparted to a test specimen by the rotating eccentric. We analyzed the operation of the tester and derived a formula for the force in terms of mass, length and time. Measurements of the needed quantities with our corresponding standards led to a traceable calibration. The paper gives the derivation of the formula and describes the measurements. A more complete analysis was done by treating the vertical, spring-induced force as a perturbation on the centripetal force acting on the eccentric mass as it rotated. An estimate of the error made by neglecting the effect of this perturbation is given.
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