Impact damage detection in composite chiral sandwich panels

This paper demonstrates impact damage detection in a composite sandwich panel. The panel is built from a chiral honeycomb and two composite skins. Chiral structures are a subset of auxetic solids exhibiting counterintuitive deformation mechanism and rotative - but not reflective - symmetry. Damage detection is performed using nonlinear acoustics, involves combined vibro-acoustic interaction of high-frequency ultrasonic wave and low-frequency vibration excitation. High- and low-frequency excitations are introduced to the panel using a low-profile piezoceramic transducer and an electromagnetic shaker, respectively. Vibro-acoustic modulated responses are measured using laser vibrometry. The methods used for impact damage detection clearly reveal de-bonding in the composite panel. The high-frequency "weak" ultrasonic wave is also modulated by the low-frequency "strong" vibration wave when nonlinear acoustics is used for damage detection. As a result frequency sidebands can be observed around the main acoustic harmonic in the spectrum of the ultrasonic signal.