Axial reverse-cycle fatigue tests of high strength pulse magnet conductors at 77 K

High strength conductors, used for the construction of pulsed magnets at NHMFL, must withstand demanding stress, strain and cyclic fatigue requirements. The safe design and operation of pulse magnets requires an understanding of the expected conductor performance as determined from design-specific low-cycle fatigue tests. A test fixture has been developed to perform fatigue stress cycling at 77 K that enables the application of axial tension and compression in a stress or strain control mode. Special wedge grips with low thermal mass were designed that are capable of reverse cycling (tension-compression) of various size specimens. The low cycle fatigue life of Glidcop-AL60, a commercially available high strength/high conductivity conductor, has been characterized and is reported. Stress and strain data acquired for the tests, are evaluated to assess the material's strain hardening or strain softening characteristics and its influence on fatigue life. The influence of test control mode (stress control versus strain control), and r-ratio on the fatigue life, are discussed.