Abstract
A new ultrasonic method for measuring closed crack depth is proposed which uses nonlinearity of the leaky Rayleigh wave passing through the crack. For aluminum samples with given fatigue crack depths, only the leaky Rayleigh wave was excited and received by a special surface wave transducer. The second harmonic amplitude caused by clapping and rubbing the crack surfaces was extracted by FFT. The second harmonic amplitude showed good correlation with the crack depth, and therefore the depth of closed cracks can be estimated by the second harmonic amplitude of the leaky Rayleigh wave for simple crack geometry.
