Elastic constants of dense, textured

137

The development of bulk high-temperature superconductors (HTSs) and their applications has today come to a point where the mechanical response to high magnetic fields may be more important than their critical-current density and large-grain property. Reviewed in this article are the recent studies of the magneto-elastic effects which are caused by flux pinning in the superconductors. This includes the work on the giant irreversible magnetostriction and internal stress, which often cause fatal cracking of the HTS bulks as they become magnetized. The cracking is a problem that today accompanies the quest for the highest trapped field values, and the latest development in this area is also presented. While the first part is an overview of experimental efforts, the second summarizes the work done to model the pinning-induced stress and strain under various magnetic and geometrical conditions.

Section: Elastic Constantsmentioning

confidence: 99%

Flux-pinning-induced stress and magnetostriction in bulk superconductors

Johansen¹

2000

137

“…Experimental data on the temperature dependence of the filament Young's modulus are scarce, especially at high temperatures. Therefore, it was simply approximated to follow a first-order polynomial whose slope was determined based on the measurements at 293 and 1033 K [17]. For the matrix metals, the temperature dependence of Young's modulus and yield strength were estimated with second-order and first-order polynomials, respectively, as in [18].…”

Section: General Issuesmentioning

confidence: 99%

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

Ahoranta¹,

Lehtonen²,

Tarhasaari³

2008

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.

“…The next step is the consolidation of the Bi-Sr-Ca-Cu-O (BSCCO) superconducting powders. This has been achieved by various methods such as hot pressing [12][13][14], hot forging [15,16], explosion sintering [17], a combination of magnetic pulsed compaction and hot pressing [18], isostatic pressing [19] and plasma-activated-sintering (PAS) [20]. Usually the consolidation was performed on initial powders with the majority 2223-phase.…”

Section: Introductionmentioning

confidence: 99%

Reactive-field-assisted-sintering of freeze-dried powders in the BSCCO system

Badica

Aldica

Groza

et al. 2001

The reactive-field-assisted-sintering technique (RFAST) has been applied to freeze-dried decomposed precursor powders with a starting cation composition of Bi:Pb:Sr:Ca:Cu = 1.7:0.3:2.0:2.5:3.5. A short time (<15 min) RFAST treatment at 800-900 • C did not lead to the formation of Bi 2 Sr 2 Ca 2 Cu 3 O 10+x (2223-phase). But RFAST was favourable to Bi 2 Sr 2 CaCu 2 O 8+y (2212-phase) formation particularly in samples with a low content of the 2212-phase in the precursor powder. Heat treatment (HT) after RFAST showed that the 2223 phase could form more rapidly than in freeze-dried pressed and sintered pellets produced by the traditional technique. The resultant ceramics after 70 h of annealing contain 75% 2223-phase and have T c(R=0) = 100.7 K, T c = 109.5 K and T c = 22.4 K.