Detection and characterization of defects with vibro-acoustic modulation technique

Various defects such as cracks, debonding, fatigue, etc. lead to anomalous high level of nonlinearity as compared with flawless structures. One of the acoustic manifestations of such nonlinearity is the modulation of ultrasound by low frequency vibration. Two methods employing such interaction, namely vibro-modulation (VM) and impact-modulation (IM) methods, have been developed. The feasibility tests were carried out for different objects and demonstrated high sensitivity of the methods for detection of cracks in steel pipes and engines, adhesion flaws in bonded composite structures, and cracks and corrosion in reinforced concrete. Recent development of this emerging technique has also opened possibilities for quantitative characterization of flaws: determination of a crack position, its size and stress condition. Another example of the quantitative capabilities is an assessment of the bonding quality of composites. The developed modulation technique demonstrated high sensitivity to various flaws and applicability to highly inhomogeneous structures.