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The normal operation of various superconducting magnets is greatly influenced by the thermal stress of the insulating system, commonly made of epoxy resins with vacuum pressure impregnation (VPI) technology, throughout the curing and cooling processes. In this work, we developed a Fiber Bragg Grating (FBG) strain measurement method to monitor the real-time strain responses of an epoxy resin IR-3 and its glass fiber-reinforced composite during both curing and cooling processes. Then, we also monitored the same process of a Nb–Ti superconducting magnet coil prepared by VPI technology. With the help of FBG strain sensors, the residual strains of the coil at various positions and directions were investigated. The results show that the large residual strain occurred near the end of the coil in the axial direction. In addition, the interlaminar shear stress properties were measured at both room temperature and liquid nitrogen temperature. The strain characteristics of the epoxy resin IR-3 and the insulating system can provide useful guidance for the design and construction of high-field Nb–Ti superconducting magnets. [ABSTRACT FROM AUTHOR]

The database of thermal expansion behavior of closed-cell polyurethane rigid foam at very low temperatures is required for designing and manufacturing thermal insulation components of various cryogenic systems. In the present work, thermal expansion behaviors of closed-cell polyurethane rigid foams with different densities were investigated in the 20 K–270 K temperature range by means of a high-resolution extensometer technique, which has been verified through comparison with standard values of an AISI 304 stainless steel rod. The comparison result demonstrates that the maximum deviation from the standard coefficient of thermal expansion of the AISI 304 in cryogenic temperatures is less than 6.6%. Testing results indicate that the cryogenic thermal expansions of closed-cell polyurethane rigid foams depend reversely on density. Moreover, the thermal expansion behavior of closed-celled polyurethane rigid foams exhibits difference from that of bulky amorphous isotropic polymers, which have been attributed to several factors such as enclosed air and cellular structure. [ABSTRACT FROM AUTHOR]