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Few studies have focused on effect of nanoparticles on mechanical properties of PI film at low temperature. In this paper, one king of POSS namely polyphenylsilsesquioxane (PPSQ) was added to PI molecules, and the mechanical property of PI-POSS composites were studied by molecular dynamics. The variation of bulk modulus and shear modulus of the composites at low temperature was analyzed. Bulk modulus and shear modulus of Polyimide-POSS composite model would decrease as the temperature rose. Compared with the pristine PI model, the bulk and shear modulus of composite model was smaller.

Superconducting magnet is an important portion in international thermonuclear experimental reactor (ITER). The reliability of superconducting magnet is of great significance for the stable operation of ITER. Due to its excellent cryogenic electrical properties, low thermal shrinkage stress and strong radiation resistance, polyimide (PI) is often used as the insulating material for superconducting magnet. Since a pulse power is used to drive ITER device, PI faces the dual challenge of low temperature and pulse voltage. It is easy to cause charge accumulation and lead to insulation breakdown. This article studied the surface charge and discharge features of PI irradiated by electron beam of various doses under repetitive pulse voltage. The irradiation doses are 0, 300, 500 and 700 kGy. The surface charging was finished with a 40% relative humidity under pulse voltage. The electrostatic voltmeter was employed to collect surface potential data. The results show that moderate irradiation can promote the surface charge decay, reduce the charge accumulation, and make the trap level of PI shallower. Nevertheless, excessive irradiation can weaken the effect.