Scaling Tests on Smooth and Notched Specimens of Polyimide (SINTIMID) at Cryogenic Temperatures

Abstract

Because of applications in space and in cryogenic equipment, such as superconducting magnets, the mechanical properties and in some cases the radiation tolerance of various types of plastics have to be assessed. In the present contribution, we report on tensile strength experiments on a polyimide (SINTIMID) carried out at room temperature, 77 K and 4.2 K. Special attention was paid to “scaling” experiments, where the influence of sample size (scaled down from DIN and ASTM standards) on the elastic modulus, the ultimate tensile strength (UTS) and the failure strain was investigated. In addition, the influence of sample size on the mechanical properties in mode I have been investigated on cylindrical pre-cracked samples with a circumferential notch. The results of the tensile tests show that a variation of the sample size does not affect the UTS. Concerning the test temperature, the results show an increase of both the elastic modulus and the UTS by 40% and 60%, respectively, when decreasing the temperature to 77 K, but no further change at 4.2 K, while the failure strain decreases continuously (by about 25%) when cooling down to 4.2 K. Regarding the fracture tests no sample size dependence of the fracture properties could be detected. The fracture toughness increases continuously by about 10% with decreasing test temperature down to 4.2 K. The results will be discussed and compared with data on other materials. Additional fractographic investigations show no significant dependence of the fracture surfaces on the sample size for both the tensile and the fracture test samples.

Work supported in SubPart by the Federal Ministry of Science and Research, Vienna.