Vibro-acoustic-modulation pseudo-force spectrum: A new concept for localizing “breathing” debondings in laminated beams

Laminated beams, although extensively utilized in engineering structures, are vulnerable to local debondings. When subjected to a vibro-acoustic excitation, the opening-closing motion of a “breathing” debonding generates contact-induced nonlinearity. Such nonlinearity allows for manifesting the presence and evaluating the extent of debonding by sideband harmonics, known as the vibro-acoustic modulation (VAM) technique. To further sharpen the capability of the VAM technique in localizing debondings, this study incorporates the emerging concept of nonlinear pseudo-force (NPF) into the VAM technique, producing a new concept of VAM pseudo-force spectrum (VAM-PFS). As NPFs exist exclusively within debonding regions, the VAM-PFS built on a group of NPFs linked to the neighboring sideband harmonics can serve as an ideal indicator for localizing debondings. Notably, the NPFs are reconstructed directly from operating deflection shapes (ODSs) associated with the sideband harmonics, eliminating the need for prior knowledge of material and structural parameters. Additionally, to suppress interference in the VAM-PFS from measurement noise, multiscale analysis is applied to the measured sideband ODSs. The VAM-PFS is numerically proven using the finite element method, and its applicability is experimentally validated on steel laminated beams with through-width debondings, whose sideband ODSs are measured via laser scanning using a scanning laser vibrometer. The results demonstrate that VAM-PFSs are ideal indicators to manifest the presence of “breathing” debondings and characterize their locations and sizes.