To investigate the synergistic effects of radiation and stress on mechanical properties, we performed three kinds of creep tests on epoxy resin (before, after, and during high-energy electron-beam irradiation) and two kinds of creep tests on polyethylene (before and during γ-ray irradiation). The simultaneous application of radiation and stress enhanced creep. To clarify the mechanisms of this enhanced creep, we measured the electron spin resonance of three kinds of specimens: (1) stressed, nonirradiated specimens, (2) irradiated specimens, and (3) specimens that were stressed during irradiation. Spins for the specimens stressed during irradiation were about 10 to 30% more than those of the irradiated specimens. In this paper, we discuss the mechanism of creep deformation during irradiation on basis of the experimental results and the molecular dynamics method for a simple molecular model.
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