In recent years, nondestructive evaluation (NDE) by SQUID has been studied by many investigators. SQUID application has great advantages over conventional NDE, such as high sensitivity, high spatial resolution, wide dynamic range, and noninvasion and noncontact character. The SQUID NDE system detects fatigue failure before flaws appear. This paper describes the system and its components. Each cryostat is different for NDE samples and cryostats for NDE systems are explained. Also some NDE examples using SQUID are described.
Hybrid materials involving epoxies with different numbers of reactive groups have been prepared to determine the molecular design of epoxies with high fracture toughness at cryogenic temperatures. To answer the opponent demands, that is, strong and flexible chains, hybrid materials were proposed. Two types of epoxy resin with different numbers of epoxy groups were mixed and cured by changing the mixing ratio. Fracture toughness, flexural strength, dielectric loss tangent, and thermal contraction of the hybrid epoxy resins were measured down to cryogenic temperatures. A hybrid material with high fracture toughness, even at liquid helium temperature, was successfully developed and hence the molecular design orientation was confirmed to be possible.
In some cases where the direct measurement of temperature and heat flux was given priority, it was found that the installed measuring sensors spatially and temporally disturbed the transient thermal phenomenon of interest. It is now easy to perform extensive numerical analysis using supercomputers and also to obtain accurate data on thermophysical properties. With this situation in mind, a measuring method of rapid transient heat transfer with the aid of numerical analysis is presented in which the utmost effort has been made to exclude disturbances in the transient process. A stainless steel strip, both surfaces of which were coated with a PVF film and a 24-μm-thick carbon-paste film, was used as a test piece to simulate an insulated superconductor in practical use. The test piece was heated stepwise in liquid helium, and the carbon-paste films were utilized as a resistance thermometer. The full numerical analysis of transient heat conduction in the test piece was carried out on a supercomputer using the transient data obtained with a sampling time of 50μm as a boundary condition and the respective empirical formulas derived for thermal conductivity and specific heat of the materials composing the test piece. The present results of rapid trnsient boiling heat transfer were in good agreement with the experimental results of others. According to error analysis of this measuring method, the maximum error in the surface temperature of the test piece was of the order of 15% (3% on average) and the maximum error in the wall heat flux was of the order of 26% (10% on average).