Stainless Steel Fatigue Cryogenic Tests

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Stainless Steel Fatigue Cryogenic Tests

Testing the fatigue characteristics of materials used with liquid nitrogen requires a special test machine that includes a LN2 cryostat. The machine consists of a dual column servo hydraulic test machine with the actuator placed in the adjustable height crosshead. A large LN2 cryogenic dewar is located under the actuator. Prior to submersion, a test sample is gripped and a special low temperature extensometer mounted. The frame includes a sub frame located below the actuator so that the loads are reacted against inside the test environment. During setup, the crosshead is lowered, with actuator extended until the subframe is submerged in the media. The cryostat is modular and can be removed with a conventional low temperature chamber (rated -185C) replacing it. 820 test systems feature high resolution (24 bit) digital servo control of an all electric fatigue rated actuator capable of testing at speeds of 1 micron per minute to 125 mm per sec. The actuator features a digital position encoder with resolution of 0.25 micron. The system is rated to 55 kN.