Basic Research on Electro-Magnetic Failure and Quench of High Tc oxide Superconductor by Means of SQUID

为了建立像YBCO这样的高T_c超导体的可靠使用，必须从机理上了解这些陶瓷超导体的脆性破坏，以便将这些材料应用于工程零部件，这些部件可能受到大电流引起大电磁力。在微观上，裂纹的萌生和扩展可能是破坏过程，与其他陶瓷材料一样。在本研究中，超导量子干涉仪已成功应用于超前条件下YBCO形成和扩展的微裂纹探测。还进行了磁场分析，以确定微裂纹的位置，从而确定试件的裂纹位置。结果表明：1)在机械载荷作用下，YBCO中观察到了微裂纹萌生和稳定的裂纹扩展，并利用Kaiser效应进行了验证。2)SQUID无损地检测到了这些稳定的微裂纹的形成。3)SQUID可以在非常早期的阶段检测到猝灭现象。

In order to establish a reliable use of high Tc uxide superconductor such as YBCO, mechanistic understanding of brittle failure of these ceramics superconductors have to be achieved to apply these materials for engineering parts and / or component which can be subjected a large current causing large electromagnetic force. In micro crack initiation and propagation can be failure processes as well as other ceramics materials. In this research, SQUID (Superconducting Quantum Interference Device) has been successfully applied to detect micro crack for formation and growth of YBCO under leading condition. Magnetic field analysis was also performed for determination of location of micro cracking and result in identify the cracking site of specimens. Results can be summarized as follows,1) Micro crack initiation and stable crack growth were observed in YBCO under mechanical loading and confirmed by use of Kaiser effect.2) These stable micro crack formation was detected nondestructively by means of SQUID.3) Quench phenomenon can be detected at a very early stage by SQUID.