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| Keywords: MetalFatigue 001.jpg The two newly-developed automatic stopping devices installed on a fatigue-testing machine at the National Bureau of Standards Note the motor in the foreground is not part of the set-up The metal specimen under test is held in place between the two bearing boxes right The bearing boxes are supported at the ends away from the specimen and weighted at the ends near the specimen so that the weighted ends tend to sag more when a crack begins to form in the specimen If the crack is on only one side of the specimen vibration as well as sagging will result The deflection-responsive stopping device consists of the microswitch center actuated by the lever rigidly fastened to the right-hand bearing box The vibration-responsive device just behind and to the right of the specimen consists of a steel ball poised on a pedestal; when vibration shakes the ball from the pedestal it closes a circuit Both devices are used simultaneously at NBS with their circuits in parallel; either may be actuated first depending on the nature of the incipient crack National Institute of Standards and Technology National Institute of Standards and Technology PD-USGov-NIST PD-USGov National Bureau of Standards National Institute of Standards and Technology | ||||
