Nondestructive detection of flaw in carbon-fiber-reinforced plastics usinghigh-T-c superconducting quantum interference device

The nondestructive detection of small cracks and deep-lying flaws in struct ures is important for safety inspection. Carbon-fiber-reinforced plastics ( CFRP) are complex materials for use in aircrafts and structures. We investi gated the possibility of detecting flaws in CFRP using a nondestructive eva luation system using high-T-c superconducting quantum interference device ( SQUID). A SQUID system for the nondestructive evaluation was developed usin g a SQUID magnetometer and a SQUID gradiometer fabricated based on a YBa2Cu 3O7-delta thin film. Holes, the diameters of which were equal to or larger than 0.4 mm, were made in CFRP plates and all holes except the smallest one were detected by a current-injection method using this system. The results show that the location and the diameter of the holes can be estimated from the distribution of the magnetic flux density, B-z, measured by the magnet ometer or the distribution of the first-order gradient of B-z, dB(z)/dx, me asured by the gradiometer. The effect of texture of the carbon fiber in CFR P on the magnetic signal strength was discussed.