Composite ceramic-metal plates tested with flexural waves and holography

A method to determine weak or defective bonding areas within the brazed adj oining contact surfaces of composite ceramic-metal plates is proposed. The plates include voids, as well as hairline cracks in the ceramic layer, caus ed by the high-temperature brazing process. To detect these flaws, transien t flexural waves are generated and transmitted through the plate by means o f an attached piezoelectric transducer. These pulses are a narrow band sign al generated in the time domain. The characteristic wavelengths correspondi ng to the narrow frequency spectrum may be larger than the size of the flaw . Dynamic holographic interferometry using a double-pulsed twin-cavity Nd:Y AG laser, comprising two independent reference beams, was used to measure t he response. The experimental interferograms (phase maps) coincide rather p recisely with analytic results derived from Mindlin's plate equations (incl uding effects of shear and rotary inertia).