Indigenous Development of Epoxy Resin System for Cryogenic Services and Fusion Application

An epoxy resin system is used in a superconducting tokamak to insulate the conducting components, such as superconducting windings, cooling pipes, metal electrodes, and bonding and sealing of dissimilar material joints at cryogenic temperature. The main aim is to develop and fabricate the dissimilar material joints of metal and glass fiber reinforced plastic (GFRP) polymer in the form of cryogenic components for the superconducting fusion magnet. To bond and fabricate the dissimilar joints, the epoxy resin needs to have low viscosity, good adhesion, resistance to moisture, long usable life, and high toughness at low temperatures.

A two-component-modified diglycidyl ether of bisphenol-A (DGEBA) epoxy resin was formulated with a modified polyamine-based hardener. To increase the toughness and minimize the induced thermal stress at low temperatures, a silane coupling agent, gamma-aminopropyltrithoxysilane, was used for its superior bonding and fast curing process. The tensile strength examination test results were found to 85 MPa, as per the International Organization for Standardization standard ISO 527-2, and an interlaminar shear strength of 12 MPa was found, as per the American Society for Testing and Materials standard ASTM D5868 at 77 K, respectively.

The mechanical performance enhancements at 77 K overcome the issue of cracks and helium leaks that develop at cryogenic temperatures, as reported. The dissimilar material joints fabricated using the epoxy resin in the form of a cryo component have been validated in machine with an acceptable helium leak tightness of 1.0E-08 mbar-l/s. In this work, we report on the development, mechanical, thermal, and electrical performance tests, the testing and failures of various epoxy resins systems used, and the cryo components at 300 and 77 K.