Tensile testing methods of Cu/Nb₃Sn superconducting wires at room temperature

Preliminary tests for determining the procedure of round robin test on tensile testing methods of Cu/Nb₃Sn composite wires at room temperature have been conducted. Two kinds of bronze processed wires were used. The following results were obtained. (1) The initial part of the stress-strain curve was liable to be varied. Beyond the stress level of about 80 MPa, stress-strain behaviors were basically identical regardless of the gripping method and the inter-grip distance although shifts in strain axis were inevitable. Pre-loading of about 40 MPa was fairly effective for obtaining a consistent stress-strain behavior for a wire. (2) A reliable modulus of elasticity could be determined using unloading curve regardless of the unloading stress level. (3) The stress-strain curves could be expressed as a simple exponential function, which fitted the experimental data fairly well excepting initial part and was useful to determine the zero strain position of the curves. (4) The 0.2% proof stresses with a coefficient of variance of less than 5% could be obtained using the zero strain position and the modulus of elasticity.