Local defect resonance and nonlinearity of porosity air bubbles in solids.

Acoustics of bubbles is quite developed field mainly due to multiple cavitation-related ultrasonic applications in liquids. New applications, which require detailed studies of ultrasound encounter with bubble in solid materials, have become apparent recently and are concerned with detectability of porosity in advanced solid materials based on layered technology, like composite and additive manufactured structures. To elucidate the transition from liquids to solids the present paper starts from theoretical similarity between both and proceeds to experimental study of the resonance acoustic effects of air bubbles in epoxy resin.

Linear vs nonlinear ultrasonic testing of kissing bonds in adhesive joints.

Kissing bonds in adhesive joints are precursors to damage and failure in materials and components used in safety-critical industries. They are zero-volume, low-contrast contact defects widely regarded as "invisible" in conventional ultrasonic testing. In this study, the recognition of the kissing bonds is examined in automotive industry-relevant aluminum lap-joints with standard bonding procedures using epoxy- and silicone-based adhesives.

Ultrasonic frequency mixing via local defect resonance for defect imaging in composites.

A new approach to nonlinear frequency mixing based on local damage resonance is proposed, analysed and tested experimentally for flexural waves in composites. The method is free from stringent requirements on the mode types and frequencies for interacting waves. The resonance of damage enhances strongly its higher-order nonlinear response and boosts the efficiency of generation for numerous-order combination frequencies.

Thermosonic Chladni figures for defect-selective imaging.

Thermosonic patterns produced by resonant vibrations of simulated and realistic defects are experimentally observed and compared with conventional vibration Chladni figures. The patterns are interpreted on the basis of hysteretic damping model that accounts for in-plane polarization component of vibrations. The analysis and simulation results show that thermosonic Chladni figures are the patterns of dissipation of vibration energy determined by a square of the in-plane strain developed in the resonant vibrations.

Air-coupled laser vibrometry: analysis and applications.

Acousto-optic interaction between a narrow laser beam and acoustic waves in air is analyzed theoretically. The photoelastic relation in air is used to derive the phase modulation of laser light in air-coupled reflection vibrometry induced by angular spatial spectral components comprising the acoustic beam. Maximum interaction was found for the zero spatial acoustic component propagating normal to the laser beam.

Instability, chaos, and "memory" in acoustic-wave-crack interaction.

A new class of nonlinear acoustic phenomena has been observed for acoustic wave interactions with cracked defects in solids. Parametric modulation of crack stiffness results in fractional acoustic subharmonics, wave instability, and generation of chaotic noiselike acoustic excitations. Acoustic-wave impact on a crack is shown to exhibit amplitude hysteresis and storage for parametric and nonlinear acoustic effects.