Stress–strain behavior under static loading in Gd123 high-temperature superconductors at 77K

We have investigated the electromagnetic and thermal properties of a REBaCuO ring bulk with an inhomogeneous critical current density, J c, profile during pulsed field magnetization (PFM) using a numerical simulation and compared those to a bulk with a homogeneous J c profile. A notch was introduced in the bulk periphery, which was assumed as a crack existing in the actual bulk material. A sudden flux penetration (flux jump) took place through the notch area and as a result, a large temperature rise also took place around this notch. Consequently, the final trapped field profile was simulated to be a ‘C-shaped profile’, which qualitatively reproduced our previous experimental results. The size and position dependences of the notch on the flux penetration behaviour were also simulated, in which a larger and outer notch promotes the flux jump phenomenon easily. On the other hand, in the homogeneous model, under the same conditions, no flux jump phenomenon was observed. These results suggest that the imperfection in the bulk can be a possible starting point of the flux jump. The electromagnetic and thermal hoop stresses were also simulated in the ring bulk during PFM, in which the electromagnetic stress and the thermal stress were both observed to be lower than the fracture strength of the bulk material. This provides good evidence that the experimentally observed ‘C-shaped profile’ results from the flux jump rather than the fracture of the bulk.

Section: Electromagnetic and Thermal Hoop Stresses During Pfmsupporting

confidence: 81%

Section: Electromagnetic and Thermal Hoop Stresses During Pfmmentioning

confidence: 94%

Numerical simulation of flux jump behavior in REBaCuO ring bulks with an inhomogeneous J_c profile during pulsed-field magnetization

Hirano

Fujishiro

Naito

et al. 2020

“…The tensile strength is about 30∼70 MPa [17,18,[23][24][25][26] at the liquid nitrogen temperature. The flexural strength is slightly larger than the tensile strength [21,22]. The average compressive strength has been reported by Murakami et al [20], and its value changes from 368 to 466 MPa at the liquid nitrogen temperature.…”

Section: Introductionmentioning

confidence: 69%

“…Bulk superconductors, such as (RE)BCO (where RE stands for a rare earth element, particularly, Y), have intrinsic brittleness due to the perovskite structure, and the strength and fracture toughness of the materials is low [15,16]. The mechanical properties of bulk (RE)BCO are commonly evaluated by the tensile, compressive and bending tests at room and liquid nitrogen temperatures [17][18][19][20][21][22]. The tensile strength is about 30∼70 MPa [17,18,[23][24][25][26] at the liquid nitrogen temperature.…”

Section: Introductionmentioning

confidence: 99%

Viscous flux flow velocity and stress distribution in the Kim model of a long rectangular slab superconductor

Yang

Chai

2018

When a bulk superconductor endures the magnetization process, enormous mechanical stresses are imposed on the bulk, which often leads to cracking. In the present work, we aim to resolve the viscous flux flow velocity υ 0 /w, i.e. υ 0 (because w is a constant) and the stress distribution in a long rectangular slab superconductor for the decreasing external magnetic field (B a ) after zero-field cooling (ZFC) and field cooling (FC) using the Kim model and viscous flux flow equation simultaneously. The viscous flux flow velocity υ 0 /w and the magnetic field B * at which the body forces point away in all of the slab volumes during B a reduction, are determined by both B a and the decreasing rate (db a /dt) of the external magnetic field normalized by the full penetration field B p . In previous studies, υ 0 /w obtained by the Bean model with viscous flux flow is only determined by db a /dt, and the field B * that is derived only from the Kim model is a positive constant when the maximum external magnetic field is chosen. This means that the findings in this paper have more physical contents than the previous results. The field B * <0 can be kept for any value of B a when the rate db a /dt is greater than a certain value. There is an extreme value for any curve of maximum stress changing with decreasing field B a after ZFC if B * 0. The effect of db a /dt on the stress is significant in the cases of both ZFC and FC.

“…Another way to improve the internal mechanical properties is the elimination of voids, which were reduced by increasing the O 2 pressure in the postannealing after the crystal growth [16]. Both the fracture strength and Young's modulus of the REBaCuO bulk were increased with decreasing contents of voids [17][18][19]. For the void-free and crack-free microstructure of YBaCuO bulk superconductors, its mechanical strength was estimated to be higher than 300 MPa, suggesting a possible trapped field of over 30 T without fracture [20].…”

Section: Introductionmentioning

confidence: 99%

Proposal of an effective mechanical reinforcement structure for a REBaCuO disk bulk pair by full metal encapsulation to achieve a higher trapped field over 20 T

Fujishiro

Naito

Awaji

2019

In this paper, we propose an effective mechanical reinforcement of a REBaCuO superconducting disk bulk pair to avoid mechanical fracture due to a large hoop stress during field-cooled magnetization (FCM), and confirm the reinforcement effect using numerical simulation. In this reinforcement, the disk bulk is fully encapsulated by an outer metal ring with upper and lower plates made by stainless steel (SUS316). The trapped field, B z , in the bulk pair with various critical current densities, J c , was numerically simulated during FCM from B app =22 T, and the hoop stress, σ θ , was also estimated during FCM after cooling from 300 to 20 K. As a result, the trapped field of over 20 T can be achieved in the gap center of the bulk pair. A large compressive hoop stress, s q , cool due to the difference of thermal expansion coefficients between the bulk and stainless steel, was effectively applied to the whole bulk during the cooling process, compared to that for the conventional reinforcement using only a SUS316 outer ring. The electromagnetic hoop stress, σ θ FCM , during FCM was also reduced, and the maximum of the total hoop stress, s q total (=σ θ FCM +s q cool), can be reduced below the fracture strength of the REBaCuO bulk. The possibility to achieve a higher trapped field over 20 T is suggested in the gap of the REBaCuO bulk pair without mechanical fracture.