Multi-axis test of the toroidal field coil material for CIT

One TF conductor option being considered for the Compact Ignition Tokamak (CIT) is an explosively welded laminated plate constructed of a C10700 copper core with a high-strength UNS7718 sheet on both sides. The feasibility of this approach is dependent on the explosion bonding process and the strength of the composite conductor to carry the applied loads. The purpose of the tests performed was to determine the strength of the metallic laminate under a state of biaxial fatigue loading. Two materials of different copper-to-718 thickness ratios were tested. In each test, two machined lap-shear-type specimens were tested simultaneously in a symmetrical back-to-back configuration. The test apparatus consisted of a 1,500,000-lb MTS machine which applied transverse compression (perpendicular to the lamination), and a floating load frame which applied axial tension. Shear stress was developed by the specimen design. The test specimens were subjected to a programmed constant-amplitude loading schedule for up to 6000 cycles at combined stress levels which reached 71000-psi compression, 42000-psi tension, and 12000-psi shear