Finite element models for thermal stress, axial tension, bending, and transversal compression of filamentary Bi-2223 tapes

Abstract

Most filamentary superconductors have soft matrix metal and brittle filaments, which make them very vulnerable during mechanical loading. Therefore, estimating the impacts of loading in the conductors is important in designing applications. Finite element models provide a way to study the stress and strain distributions in a tape, taking into account the details of the tape cross section. This paper presents finite element models for some basic loading conditions met, for example, in magnets. The cases investigated include thermal stresses, axial tension, transversal compression, and bending of a tape. The focus is on Bi-2223 tapes, although similar models could also be applied to other conductor types. To evaluate the validity of the models, the results are compared to experimental data. The results of the models showed the same trends as the experiments, but some inaccurately known properties of the modelled tapes caused uncertainty in the models. For example, the stiffness and fracture strength of the filament material are essential parameters to pay attention to when the initiation of critical current is predicted.

Homogeneous performance and strain tolerance of long Bi-2223 HTS conductors under hoop stress

“…The more recent conductors show higher strain tolerances, and with metallic lamination, either by copper alloy (DI-BSCCO type HT-CA) or by stainless steel (type HT-SS), can withstand tensile stress up to 250 MPa and 270 MPa at 77 K, respectively [2,18]. There have been numerous works on the strain effect of Bi-2223 conductors in straight short sample stress-strain tests and hoop stress tests, as well as modeling the effect of filament breakage on critical current (I c ) and n-value [19][20][21][22]. Although these studies provide crucial information on the magnet design, the voltage criterion used in determining I c is typically 1 µV cm −1 , which is at least an order of magnitude greater than the voltage level acceptable in safe operating conditions of the magnet.…”