Low temperature irradiation effects on mechanical properties of epoxy used in superconducting magnets

Superconducting magnets for fusion devices are greatly influenced by the radiation environment and the principal radiation-induced troubles arise from changes in the mechanical fracture behaviour of organic materials used as insulating and/or potting materials. Small compression test specimens of epoxy resin were tested after gamma and reactor irradiation at low temperatures. Three kinds of mechanical properties; breaking stress, breaking strain and elastic moduli were investigated. A statistical analysis of the data from a large number of small specimens revealed different effects due to gamma and neutron irradiation on the fracture behaviour suggesting that a simulation study by gamma irradiation is not valid for neutron irradiation. In the case of reactor irradiation overall softening was induced accompanied by local hardening and embrittlement. A qualitative explanation of the above results is presented and their relationship to the performance of the magnets is given. (author)