Numerical Studies of Thermally Induced Residual Strain/Stress in Bi2Sr2Ca2Cu3O x /Ag/Ag Alloy Composite Tapes and the Dependence of Material Properties on the Temperature

Abstract

Thermally induced residual strain/stress in Bi2Sr2Ca2Cu3Ox (Bi2223)/Ag/Ag alloy composite tapes and the dependence of material properties on the temperature have been studied numerically. Based on both the straight and bending 3D tape models, and with the temperature dependence on material properties (especially the coefficient of thermal expansion) among the constituents (Bi2223, Ag and Ag alloy sheath) of Bi2223 multifilament composite tapes, the residual strain accumulation and the distribution of the residual stress have been obtained. We found that by taking account of the temperature dependence on material properties of Bi2223 composite tapes the residual strain in the current transportation direction is up to 15 % larger than that without taking temperature dependence into account. Furthermore, by considering the distribution of the stress induced from the changing temperature, we analyzed the mechanical strength of Bi2223 composite tapes and concluded that the initial mechanical failure due to large temperature circle (intrinsically induced from the mismatch of the coefficient of thermal expansion of each constituent in composite tapes) comes from the following aspects: (i) the tensile fracture in the Bi2223 filaments occurring at the center of the tape and (ii) the delamination most likely arising at the interface between the Bi2223 filaments and Ag matrix near both edges of the cross-section of the tape, which originates at the Bi2223 side of the interface.