極低温引張試験装置の試作

Abstract

With the development of cryogenic equipments such as superconducting magnets in recent years, there has been an increased requirement for knowledge of mechanical properties of structural materials at cryogenic temperatures. Taking these circumstances into consideration, the authors designed and constructed an apparatus for tensile tests to perform in the temperature range from room temperature to −271°C. The apparatus consists of a universal testing machine,a cryostat, an automatic temperature controller, a supply system for the coolant (liquid helium), a recovery system for the helium gas and a vacuum system. Temperatures down to −269°C can be controlled by the power inputs both to the heater in the coolant and the heater wound around specimens. Temperatures below −269°C can be obtained by pumping the cryostat with a mechanical pump. The cryostat, the most important part of the apparatus, consists of a dewar and a testing device inserted into the dewar. Specimens are fastened between the lower ends of pull rods and the bottom plate of a cylinder. Padding of copper scraps was provided around the specimens to keep uniform temperature distribution in the specimen. After measuring the natural evaporation rate of liquid helium in the cryostat and examining uniformity of the temperature distribution in the specimens, actual tensile tests were performed at cryogenic temperatures with 18-8 stainless steel and copper specimens. Then the reproducibility of test results were studied. The variation in the values of ultimate tensile strength and yield strength were within ±6 kg/mm2 and those of elongation were within ±5%.The work was performed as part of a national project and supported by the Agency of Industrial Science and Technology.