Material Damage Modeling and Detection in a Homogeneous Thin Metallic Sheet and Sandwich Panel using Passive Acoustic Transmission

A passive acoustic method is developed for material damage detection and location in homogeneous thin metallic sheets and sandwich panels using non-contact acoustic transmission measurements. Theoretical models of a flat sheet and sandwich panel are developed to describe the effects of global material damage due to density, modulus, or thickness changes on backplane radiated sound pressure level distributions. To describe the effects of local material damage, a two-dimensional, three-segment stepped beam model is developed. It is shown that increases in transmitted sound energy at high frequencies occur behind a damaged material component that exhibits changes in thickness or other geometric or material property. Experiments on a baffled homogeneous sheet subjected to broadband acoustic energy show that transmitted intensity measurements with non-contact probes can be used to identify and locate material defects in the sheet. Material damage is most readily identified where transmitted sound intensity is highest in the resonant frequency range of the panel.