Mechanical Properties and Strain Effects in Bi₂Sr₂CaCu₂O_x/Ag Composite Conductors

Abstract

With the development and testing of powder-in-tube and surface-coated Bi₂Sr₂CaCu₂O_x (Bi2212) prototype systems to demonstrate engineering feasibility there is a need for accurate engineering data on the superconducting materials. Another important issue is the effect of mechanical strain on the superconducting properties. While it is evident that large strains induce irreversible damage, applications may be limited by fatigue at low strain values due to crack propagation. Here we report on the mechanical properties at room temperature and both the mechanical and superconducting properties at liquid helium temperature of IGC surface-coated Bi2212 conductor. Results of the effects of cyclic fatigue on J_c of the Bi2212 as measured by electrical transport are also shown. The conductor’s critical current exhibited little sensitivity to strain below a critical strain of 0.165% in room temperature axial strain tests. Above the critical strain little critical current remained. The effect on I_c was the same regardless of the number of times the conductor was cycled at a given strain. Tests performed at 4.2K in a Lorentz-force axial strain device showed a gradual degradation in I_c above a critical strain of 0.18%. Room temperature bend strain results can be explained by a simple application of the axial room temperature I_c versus s result.