Tensile properties of superconducting composite conductors and Nb--Ti alloys at 4.20K

Anelastic stress-strain behavior at 4.20K has been found in composites, consisting of a Cu matrix and Nb--Ti filaments, and Nb--Ti alloy samples. If the sample were strained past certain values, deformation proceeded by discontinuous slip. The mechanisms for these phenomena were not determined; however, their presence reveals a source of thermal energy that can be important in the design of large superconducting devices. The effect in large superconducting magnets may be related to the heat produced by hysteretic stress-strain cycles and/or discontinuous slip. It is proposed that micro-yielding may occur with the application of very small stresses. This microplasticity cannot be seen on tensile curves but can be detected by the presence of audible clicks. During the unloading portion of a stress-strain cycle serrations are sometimes evident at very low stress levels