Effects of mounting and exciter coupling on vibrothermographic NDE

Vibrothermography, also known as Sonic IR and Thermosonics, is notoriously sensitive to extrinsic parameters such as specimen mounting and transducer coupling. This is a result of the complicated resonances which deliver vibrational energy and allow the crack to heat up. We present an approximate theory which explains how the mechanical mounting and transducer coupling affect the resonances of the specimen, and compare this theory with simulation and experiment. Based on these explanations we suggest guidelines to assist practitioners in minimizing the sensitivity of their vibrothermography tests to specimen mounting and transducer coupling.