Design and Development of Fatigue Testing Machine for Cryogenic Temperatures
Prior knowledge of fatigue strength properties of materials is very crucial in design and development of a mechanical system failing which the entire system can fail prematurely without any indication. Reliable data of strength properties of many engineering materials are not available at cryogenic temperatures. Available room temperature data cannot be extrapolated down to cryogenic temperature zone since many of the mechanical properties change abruptly e.g. ductile to brittle transition of carbon steels. With this background, a rotating beam fatigue testing machine suitable for both room and cryogenic temperatures has been designed and developed to determine fatigue properties of various materials commonly used for cryogenic temperature applications. The test specimens of the selected material are fabricated as per the specifications of DIN 50113. Tests are conducted within an insulated cryogenic chamber. Desired cryogenic temperatures down to 77K are maintained by circulation of pressurised liquid nitrogen with the help a solenoid valve which is activated by a PID controller. In this experimental work, fatigue strength properties of aluminium alloy (Al7075) are determined using the developed machine both at room and cryogenic temperature. The test results are compared and analysed.
Keywords - Cryogenics, Liquid nitrogen, Fatigue strength, cyclical stress and Cryogenic chamber