Relation of strength distribution of Nb3Al filaments to strength of multifilamentary superconducting composite wire

Ochiai, Shojiro; Sawada, T.; Nishino, Sayaka; Hojo, Masaki; Takahashi, Kenichi; Yamada, Yuichi

doi:10.1016/0011-2275(96)88782-0

Cited by 10 publications

(10 citation statements)

References 10 publications

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“…The scatter increases with decreasing m. For instance, the values m = 3, 5 and 10 correspond to the coefficient of variation (= standard deviation/average) 0.36, 0.23 and 0.12, respectively. The m values estimated in our previous work for Bi2223, Nb 3 Sn and Nb 3 Al were 4.7 [18], 7-12 (depending on heat-treatment temperature and time) [7,8] and 6-7 [9,19,20], respectively. This means that the strengths of the filaments are different from each other and also the strength of a given filament is different from position to position.…”

Section: Introductionmentioning

confidence: 99%

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Ochiai

Nagai

Okuda

et al. 2003

Supercond. Sci. Technol.

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We have studied the tensile behaviour of Bi2223 superconducting composite tapes at room temperature, and the influence of the tensile damages introduced at room temperature on the critical current Ic and the n values at 77 K. In the measurement of the Ic and n values, the overall composite with a gauge length 60 mm was divided into six elements with a gauge length of 10 mm in order to find the correlation of the Ic and n values of the overall composite to those of the local elements which constitute the composite. From the measured stress–strain curve of the composite and the calculated residual strain of the Bi2223 filaments, the intrinsic fracture strain of Bi2223 filaments was estimated to be 0.09–0.12%. When the applied strain was lower than the onset strain of the filament damage, the original Ic and n values were retained both in the overall composite and the elements. In this situation, while the overall voltage at the transition from superconductivity to normal conductivity of the composite was the sum of the voltages of the constituent elements, among all elements the overall voltage was affected more by the element with the lower Ic (higher voltage). The damage of the filaments arose first locally, resulting in a reduction of the Ic and n values in the corresponding local element, even though the other elements retained the original Ic and n values. In this situation, the voltage of the overall composite stemmed dominantly from that of the firstly damaged weakest element, and the overall Ic and n values were almost determined by the values of such an element. After the local element was fully damaged, the damage arose also in other elements, resulting in segmentation of the filaments. Thus, the Ic and n values were reduced in all elements. The correlation of Ic between the overall composite and the elements could be described comprehensively for non-damaged and damaged states from the voltage–current relation.

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Section: Introductionmentioning

confidence: 99%

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Ochiai

Nagai

Okuda

et al. 2003

Supercond. Sci. Technol.

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“…As mechanical and electromagnetic stresses acting during fabrication and/or service of superconducting composite wires affect the superconductivity, it is necessary to clarify the mechanical behaviour and its relation to the superconductivity. Recently the present authors [1,2] have studied the static and fatigue behaviours at room temperature and their influences on critical current at 4.2 K of an Nb 3 Al composite wire which has been developed for wide engineering application owing to the high critical current densities at high magnetic field and high strain endurance and low strain sensitivity of the critical current [3][4][5][6][7][8][9]. Concerning the static behaviour at room temperature, it was found that (a) the scatter of tensile strength of the multifilamentary composite is very small in spite of the large scatter of strength of the Nb 3 Al filaments and (b) the strength of the composite wire has a very slight dependence on length, although the strength of the Nb 3 Al filaments decreases markedly with increasing length.…”

Section: Introductionmentioning

confidence: 83%

“…Concerning the static behaviour at room temperature, it was found that (a) the scatter of tensile strength of the multifilamentary composite is very small in spite of the large scatter of strength of the Nb 3 Al filaments and (b) the strength of the composite wire has a very slight dependence on length, although the strength of the Nb 3 Al filaments decreases markedly with increasing length. These features were explained and simulated well by combining the Monte Carlo simulation method with shear lag analysis to calculate the loss of stress-carrying capacity of the broken filaments, stress concentrations near the broken filaments and mechanical interactions among the broken filaments [1]. Also it was shown that (c) the critical current decreases at high applied stress owing to the breakage of Nb 3 Al filaments.…”

Section: Introductionmentioning

confidence: 93%

Progress of fatigue damages and its influence on the critical current of multifilamentary Nb₃Al superconducting composite

Ochiai

Ohno

Sekino

et al. 1999

Supercond. Sci. Technol.

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Progress of the fatigue damage with increasing number of stress cycles at room temperature and its influence on the critical current at 4.2 K of Nb3Al multifilamentary composite wire were studied. The main results are summarized as follows. (i) With increasing number of stress cycles, the damage progressed in the order of the following three stages: stage I, formation of cracks in the clad copper; stage II, stable propagation of the cracks in the clad copper into the inner core portion, causing fracture of the Nb3Al filaments; stage III, unstable propagation of the main crack, causing overall fracture of the composite. (ii) The critical current remained nearly constant in stage I but was reduced in stage II, while the residual strength was reduced slightly in stage I and substantially in stage II. The reduction in residual strength and critical current in stage II arose from the fracture of the stress-carryable and superconducting-current-transportable Nb3Al filaments. Stage II occurred in the late stage of fatigue life. (iii) The extent of the damage and therefore the reduction in residual strength and critical current in stage II was dependent on the maximum stress level. At the high maximum stress level, where the damage was mainly cracking in the clad copper and partially a small number of breakages of the filaments, the reduction in residual strength and critical current was minor. With decreasing maximum stress, the damage accumulated more, resulting in larger reduction in residual strength and critical current, while the accumulation process varied with the stress level; at the intermediate stress level, many cracks in the clad copper grew into the core region but, at the low stress level, one of the many cracks in the clad copper grew into the inner core region.

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“…Nb 3 Al strands have excellent strain tolerance and critical current properties in a practical metal superconductor [1]. So far, the effects of mechanical strain on their superconducting properties have been investigated for nuclear fusion magnets [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…Previous investigation of strain effects considered coil fabrication only. In addition, cyclic strain loading on the superconducting wires was generally performed at room temperature using a mechanical testing machine [4,5].…”

Section: Introductionmentioning

confidence: 99%

Critical Current and Fracture Behavior of Nb3Al Superconducting Strands under Cyclic Electromagnetic Force

Wadayama¹,

Natsume²,

Mito³

et al. 2011

JMSE-A

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Abstract:To obtain basic information on fracture behavior and its critical current properties in superconducting strands with long-term periodic excitation, a unique experiment of cyclic strain loading was carried out. The strain was applied to a superconducting filament directly at 4.2 K using an electromagnetic (Lorenz) force instead of the usual mechanical load. The sample strands were Jelly-roll process Nb 3 Al with a copper ratio of 2.1. A new magnet system to evaluate long-term cyclic strain loading was set up. It was able to generate external fields up to 14 T with 58 mm bore. Cyclic strain was applied by the sample current control: 500 A, 0.1 Hz. In the experiment, critical current measurements and applied cyclic strain were carried out in alternation and the variation of critical current was obtained during the cyclic test. In this paper, the experimental results of cyclic strain loading on the critical current of Nb 3 Al strand and mirostructural observation of fracture surface of the filaments is described. Our results show that degradation of critical current properties was not observed at cycle number n = 1500 under the applied axial strain of 0.17%. A noxious sample, from which the outside copper stabilizer was deliberately removed, broke after n = 10, and crack propagation was observed at the fracture surface of the Nb 3 Al filaments. Under a microstructural observation of the break sample, the fracture points of the filaments were seen to be different in a longitudinal direction. A striped pattern like a beach mark due to crack propagation was also observed at the Nb 3 Al fracture surface. It was found that the cross-sectional homogeneity of the strand is important to avoid the damage and breaking from cyclic loading.

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Relation of strength distribution of Nb3Al filaments to strength of multifilamentary superconducting composite wire

Cited by 10 publications

References 10 publications

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Progress of fatigue damages and its influence on the critical current of multifilamentary Nb₃Al superconducting composite

Critical Current and Fracture Behavior of Nb3Al Superconducting Strands under Cyclic Electromagnetic Force

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Relation of strength distribution of Nb3Al filaments to strength of multifilamentary superconducting composite wire

Cited by 10 publications

References 10 publications

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

Progress of fatigue damages and its influence on the critical current of multifilamentary Nb3Al superconducting composite

Critical Current and Fracture Behavior of Nb3Al Superconducting Strands under Cyclic Electromagnetic Force

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Progress of fatigue damages and its influence on the critical current of multifilamentary Nb₃Al superconducting composite