Analysis of delamination and heat conductivity of epoxy impregnated pancake coils using a cohesive zone model

• Published in: Engineering fracture mechanics Vol. 245; p. 107555
• Main Authors: Peng, Xubin, Yong, Huadong, Zhang, Xingyi, Zhou, Youhe
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 15.03.2021; Elsevier BV
• Subjects: Cohesion; Conductors; Cooling; Coupled thermal–mechanical cohesive; Critical current (superconductivity); Damage; Degradation; Delamination; Heat conductivity; Heat transfer; Pancake coil; Pancake coils; Room temperature; Temperature distribution; Tensile strength; Thermal conductivity; Thermal resistance; Thickness; Weibull distribution; Pancake coil; Weibull distribution; Delamination; Coupled thermal–mechanical cohesive
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2021.107555

•Delamination is analyzed using a coupled thermal–mechanical cohesive zone model.•Cohesive strength distribution has a remarkable impact on the delamination.•Influences of thermal-conductivity degradation caused by delamination are studied. Epoxy-impregnated pancake coil is observed to delaminate locally when its temperature is cooled from room temperature to 77 K. The delaminations cause the degradation of the critical current of the coil. Besides, the delamination may degrade the thermal conductivity and affect the thermal conductive path. Thus, in this study, the delamination behavior of epoxy-impregnated pancake coil during the cooling process is analyzed through a coupled thermal–mechanical cohesive zone model. The measured transverse tensile strength of coated conductors has shown considerable scatter and Weibull distribution has been adopted to fit the transverse tensile strength. The simulations are able to capture the main characterizations of the observed delaminations with the cohesive strength of the cohesive element following a Weibull distribution. After the cooling process, a heat spot is applied to the degraded positions to analyze the temperature field and the thermal conductive path in the damaged coil. Compared to the original undamaged coil, the delaminations indeed degrade the thermal conductivity and increase the thermal resistance. What’s more, the effects of the variation of the thickness of the epoxy and different interfacial cohesive strength distributions of the coated conductor are considered. The results show that reduction of the thickness of the epoxy can lower the radial stress and release the damage, and the random distribution of the cohesive strength inside the coated conductor dominantly determines the delamination pattern of the coil.