Single-sided access remote imaging via resonant airborne activation of damage

摘要

The feasibility of remote imaging of damage by using resonant airborne acoustic activation combined with laser vibrometry is studied experimentally. Two-step optimization to stimulate the damage vibration comprised resonant oblique incidence followed by frequency selective local resonance in the damaged area (LDR). The methodology is applied to a wide variety of flaws from artificial planar defects to real damages in composite parts. Various types of damage are shown to manifest LDR in two different ways depending on the structure of the damage. The resonance is activated either as in-phase vibration over a total damaged area at a single frequency (normal LDR) or includes weakly coupled resonant vibrations of its parts at different frequencies. In the latter case, LDR is a combination of multiple so-called fractional resonances. Both kinds of the resonances enhance the sensitivity of remote defect-selective imaging and are applicable to a wide range of flaws from clearly visible to barely visible and even virtually invisible damage in composites.