A compact cryogenic test chamber can be cooled to approximately 5 to 6 Kelvin for materials testing. The system includes a temperature controller and multiple sensors to measure specimen temperature at different locations. The testing chamber provides a fast and easy method to perform materials testing at lower than liquid nitrogen temperature (77 K). The advantage of this chamber is that lower than 77 K temperatures are achievable, and the temperature can be controlled and stabilized during a test.
The purpose of the chamber is to cool a composite lap shear specimen to approximately 20 K so that tensile test force and displacement data may be acquired at this cryogenic temperature range. Other specimens of similar size and possibly different geometry can also be tested using the same technique with minimal chamber modification.
The chamber is constructed from commercially available supplies and materials. A copper pipe is capped at the ends, allowing a segment of the specimen to pass through each side and attach to a tension-testing machine. A coil of tubing wraps around the outside to allow cooling with cold gas from the end of a transfer line that is inserted into liquid-helium supply dewar. The transfer line feeds liquid helium into the tube coil of the chamber through a gas-tight quick-connect fitting. The cold helium gas cools the chamber and flows inside the chamber to cool and exchange heat before venting through the outlet. The inlet and outlet lines are thin-walled stainless-steel tubing that traverses a thick layer of high-performance insulation. Stainless-steel wire is adhered with epoxy to the outer chamber wall and functions as a heater for temperature control. The temperature of the chamber and specimen are monitored, and a standard PID (proportional–integral–derivative) control is applied to the heater circuit to regulate temperature.
This work was done by John J. Francis and James Tuttle of Goddard Space Flight Center. For further information, contact the Goddard Innovative Partnerships Office at (301) 286- 5810. GSC-15694-1