Compression-Fatigue, Elastic Modulus, and Thermal Contraction of Insulated Conduit Arrays of ITER CS Modules

Compression-fatigue tests at ~ 77 K were conducted to compare two insulation systems (epoxy resin impregnated glass/Kapton) for use in the ITER central solenoid modules. Test samples consisted of insulated conduits that were stacked in 4 × 4 arrays. The thermal contraction (295-77 K) prior to fatigue, elastic modulus during fatigue, and the structural integrity of the insulation were measured and assessed at the National Institute of Standards and Technology large-scale test facilities. The maximum cyclic stress of 72 MPa, minimum stress of 25 MPa, and 1.2 × 10⁶ cycles were used to comply with ITER design objectives. Thermal contraction between 295 and 77 K and the elastic modulus were measured using strain gages and strain-gage extensometers. Calibration of the strain was obtained through the use of an equivalent-size block of 6061-T6 aluminum alloy with known thermal contraction and elastic moduli. Following fatigue, the arrays were cross-sectioned and optically examined for resin-impregnation quality and fatigue cracking tendencies of the insulation systems. The thermal contraction and elastic modulus of cross-sectioned samples were remeasured at the National High Magnetic Field Laboratory for property confirmation, using different techniques.