Influence of parameter variations on the fatigue behavior of magnet insulation systems

The application of glass-fiber-reinforced plastics (GFRP's) as insulation materials for fusion magnet coils (e.g. of ITER) requires the full characterization of their mechanical performance under ITER relevant conditions. Tension-tension fatigue is a useful procedure to simulate the pulsed tokamak operation of the ITER coils in the relevant range of 104-105 cycles. The fatigue parameters, such as the R-ratio and the load frequency, may influence the material behavior under cyclic load. Therefore, investigations were made under load control and at 77 K on an industrial glass-fiber-reinforced/epoxy compound. Stress-lifetime diagrams were generated with R-values between 0.1 and 0.5 and frequencies between 5 and 20 Hz. The results are discussed with respect to the lifetime performance of ITER.