抄録
Electromagnetic acoustic transducers (EMATs) are applied to detection of delamination in glass fiber reinforced plastic (GFRP) laminates. Since the delamination lowers the strength of the FRP, it should be detected nondestructively to assure the structural safety. Lamb wave may be useful in detecting the thickness reduction due to delamination, because its velocity depends on the plate thickness. In this study, while delaminating uniaxial GFRP laminate stepwise, we measure the Lamb wave velocity at each level of delamination. The Lamb wave of the lowest symmetric mode is used to avoid the interference with the other modes. The EMATs are used to transmit and receive the Lamb wave. Since the GFRP is nonconductive, coils are embedded in the laminates. When magnets are put on the coils in order to compose the EMATs, the Lorentz force acting on the current in coil wire launches the Lamb wave. Scan of the measuring point can be achieved by sliding the magnet. Both the group velocity and the phase velocity are measured using broadband pulse and burst wave, respectively. The delamination can be evaluated as the area of elevated velocity. Accuracy of evaluation of delamination front is discussed.
