Possibility of mechanical fracture of superconducting ring bulks due to thermal stress induced by local heat generation during pulsed-field magnetization

TY - JOUR

T1 - Possibility of mechanical fracture of superconducting ring bulks due to thermal stress induced by local heat generation during pulsed-field magnetization

AU - Shinden, Motoki

AU - Fujishiro, Hiroyuki

AU - Takahashi, Keita

AU - Ainslie, Mark D.

N1 - Funding Information: This new concept of thermal stress origin started from discussion for the mechanical fracture of the disk bulk during FCM between the author (H.F.) and Prtof. Tomoyuki Naito (T.N.) of Iwate University in 2018. H.F. thanks T.N. for valuable suggestions. The authors thank Mr Michael Beck of the University of Cambridge for valuable discussions. This research is supported by JSPS KAKENHI Grant No. 19K05240, and by Adaptable and Seamless Technology transfer Program through Target-driven R&D (A-STEP) from Japan Science and Technology Agency (JST), Grant Nos. VP30218088419 and JPMJTM20AK. M D Ainslie would like to acknowledge financial support from an Engineering and Physical Sciences Research Council (EPSRC) Early Career Fellowship, EP/P020313/1. All data are provided in full in the results section of this paper. Publisher Copyright: © 2022 IOP Publishing Ltd.

PY - 2022/3/4

Y1 - 2022/3/4

N2 - During quasi-static magnetization of bulk superconductors using field-cooled magnetization (FCM) from high fields at low temperatures, such bulks are sometimes broken, which is believed to be mainly due to an electromagnetic force - and subsequent stress - larger than the fracture strength. However, a ring bulk can break, even during pulsed field magnetization (PFM), from relatively lower pulsed fields and at relatively higher temperatures. Previous simulation results suggest that the ring bulk should not break due to the electromagnetic force during PFM. In this paper, taking experimental and numerical results into consideration, we propose the possibility of mechanical fracture of a ring bulk during PFM due to thermal stress induced by local heat generation, which has not been considered and investigated to date. Two numerical models with different sizes of heat-generating region were constructed for the ring bulk with a relatively large inner diameter (60 mm outer diameter, 36 mm inner diameter, 17 mm height). For Model-1, with a large heat region, the bulk fracture due to the thermal stress results from the tensile stress along the radial direction in the neighboring heat region. The risk of bulk fracture is enhanced at the inner or outer edges of the bulk surface, compared with that inside the bulk. For Model-2, with a small heat region inside the bulk, the bulk fracture due to the thermal stress results from the compressive stress along the radial direction in the neighboring heat region. These results strongly suggest the possibility of mechanical fracture of an actual ring bulk due to thermal stress induced by local heat generation. This idea is also applicable more generally to the fracture mechanism during FCM of superconducting bulks.

AB - During quasi-static magnetization of bulk superconductors using field-cooled magnetization (FCM) from high fields at low temperatures, such bulks are sometimes broken, which is believed to be mainly due to an electromagnetic force - and subsequent stress - larger than the fracture strength. However, a ring bulk can break, even during pulsed field magnetization (PFM), from relatively lower pulsed fields and at relatively higher temperatures. Previous simulation results suggest that the ring bulk should not break due to the electromagnetic force during PFM. In this paper, taking experimental and numerical results into consideration, we propose the possibility of mechanical fracture of a ring bulk during PFM due to thermal stress induced by local heat generation, which has not been considered and investigated to date. Two numerical models with different sizes of heat-generating region were constructed for the ring bulk with a relatively large inner diameter (60 mm outer diameter, 36 mm inner diameter, 17 mm height). For Model-1, with a large heat region, the bulk fracture due to the thermal stress results from the tensile stress along the radial direction in the neighboring heat region. The risk of bulk fracture is enhanced at the inner or outer edges of the bulk surface, compared with that inside the bulk. For Model-2, with a small heat region inside the bulk, the bulk fracture due to the thermal stress results from the compressive stress along the radial direction in the neighboring heat region. These results strongly suggest the possibility of mechanical fracture of an actual ring bulk due to thermal stress induced by local heat generation. This idea is also applicable more generally to the fracture mechanism during FCM of superconducting bulks.

KW - flux jump

KW - local heat generation

KW - mechanical fracture

KW - numerical simulation

KW - pulsed field magnetization

KW - superconducting ring bulk

KW - thermal stress

UR - http://www.scopus.com/inward/record.url?scp=85126791923&partnerID=8YFLogxK

U2 - 10.1088/1361-6668/ac5785

DO - 10.1088/1361-6668/ac5785

M3 - Article

AN - SCOPUS:85126791923

SN - 0953-2048

VL - 35

JO - Superconductor Science and Technology

JF - Superconductor Science and Technology

IS - 4

M1 - 045015

ER -