Abstract
The effect of local defect resonance (LDR) on the nonlinear ultrasonic response of defects is studied and applied for enhancement of sensitivity of nonlinear ultrasonic NDT. As the local vibration amplitude increases, the LDR“amplifier” exhibits transition to nonlinear regime with an efficient generation of nonlinear frequency components solely in the defect area. The concept of the defect as a nonlinear oscillator brings about different dynamic and frequency scenarios characteristic of parametric oscillations. The experiments confirm unconventional nonlinear dynamics of simulated and realistic defects subject to LDR. The nonlinear modes observed include sub- and superharmonic resonances with anomalously efficient generation of the higher harmonics and subharmonics. A modified version of the superharmonic resonance (combination frequency resonance) is used to enhance the efficiency of frequency mixing mode of nonlinear NDT. A strong localization of the resonance nonlinearity is applied for high-contrast imaging of defects in composite materials.
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