Numerical modelling and simulations on the mechanical failure of bulk superconductors during magnetization: based on the phase-field method

The high-temperature bulk superconductors with high critical current density are brittle, and can be damaged by large Lorentz forces and thermal stress during magnetization. Several studies have reported the failure of bulk superconductors during flux jumps. In this study, we analyzed the magnetization characteristics and mechanical response of the HTS bulk with inhomogeneous current density along the c-axis. The numerical simulation was consistent with the experimental results presented in the reference. Moreover, a flux jump occurred near the area of the pre-arrangement flux during the second pulsed field magnetization. The maximum temperature is lower than the critical temperature during the flux jump. In the mechanical analysis, the flux jump led to an abrupt change in the maximum stress of the bulk, and the maximum radial stress was significantly higher than the maximum hoop stress during the flux jump. The maximum radial stress increased with decreasing ambient temperature during the flux jump, and the maximum stress area was always near the seeded plane. Subsequently, the magnetization characteristics and mechanical response were studied for different locations of the seeded surface, two concentric superconducting bulks, and non-uniform fields.

Section: Introductionmentioning

confidence: 99%

Flux jump and mechanical response in inhomogeneous high-temperature superconductor under the pulsed-field magnetization

Wang,

Wu,

Yong

2023

“…Thus, thermomagnetic instability is coupled with mechanical failure. In the past few years, many researchers have contributed to the investigation into the mechanical stresses [40,41] and the fracture/damage [42][43][44][45] evolution within bulk superconductorsduring magnetization. However, few works [46][47][48] have been reported that investigate the fully coupled thermomagnetic-mechanical instability behavior in bulk superconductors.…”

Section: Introductionmentioning

confidence: 99%

Coupled multiphysics modeling of the thermal-magnetic-mechanical instability behavior in bulk superconductors during pulsed field magnetization

Jing¹

2022

Self Cite

Magnetization is of great importance for the application of bulk superconductors. Flux jumps are frequently encountered challenges during magnetization, which lead to sharp temperature rises and material failure and eventually affect the field trapping capability of bulk superconductors. Intrinsically, flux jumps and mechanical failure induced by thermomagnetic instability are coupled with each other, which made the numerical simulation of the magnetization of bulk superconductors a challenging task. In this paper, a numerical simulation framework is developed based on my previous work (Jing Z 2020 Supercond. Sci. Technol. 33 075009), which further coupled the H-formulation and the phase-field fracture model with the heat diffusion equation to simulate the flux jump and mechanical failure behaviors of bulk superconductors during magnetization. The experimentally observed features of the flux jumps are reproduced, and the corresponding mechanical failure is evaluated. The magnetic field, temperature, stress/strain, and mechanical failure within the bulk sample are presented. It is found that the varying ramp rate of the pulsed field significantly influences the flux jump behaviors of bulk superconductors. The optimum characteristic time t0 of the pulsed field for the final trapped field is predicted through numerical simulations.

“…We have also investigated the mechanical properties of disk-and ring-shaped REBaCuO bulks with finite height during FCM using the finite element method (FEM) and proposed optimal reinforcement structures made of metal to avoid mechanical fracture [19,[26][27][28][29]. For PFM, FEM analyses of mechanical properties have been performed such as quench and crack propagation in the disk bulk [30][31][32][33][34]. We have also investigated the electromagnetic and thermal properties of REBaCuO ring bulks with an inhomogeneous critical current density, J c , profile during PFM using numerical simulations, and compared these with those of a ring bulk with a homogeneous J c profile [35], in which the electromagnetic and thermal hoop stresses were lower than the fracture strength of the bulk material.…”

Section: Introductionmentioning

confidence: 99%

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

Shinden

Fujishiro

Takahashi

et al. 2022

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.