Abstract:

The paper gives an overview of a recent advancement in the development and implementation of an innovative nonlinear modulation technique for nondestructive testing. The theoretical and experimental investigations discovered that a weakly or incompletely bonded interface or contact-type defect causes the modulation of a probing high-frequency ultrasonic wave by low-frequency vibration. The vibration varies the contact area modulating the phase and amplitude of a higher-frequency probing wave passing through the interface. In the frequency domain the result of this modulation manifests itself as sideband spectral components with respect to the frequency of the probing wave. Such a modulation effect was observed experimentally for various materials (metals, composites, concrete, sandstones, glass) with various types of defects such as cracks, debondings, delaminations, and microstructural changes. Two modifications of the technique have been developed: vibromodulation (VM) and impact modulation (IM), employing cw and impact-induced vibrations, respectively. The examples of applications of these methods include crack detection in Boeing 767 steel fuse pins, combustion engine cylinder heads, sandstone, and glass. These methods also proved their effectiveness in evaluating bonding conditions in titanium and composite plates, as well as corrosion in reinforced concrete.