Nonlinear local wave-direction estimation for in-sight and out-of-sight damage localization in composite plates

Abstract

In this study, a novel wave processing algorithm: “local wave-direction estimation (LWDE)”, is proposed to localize sources of guided waves using full-field scanning laser Doppler (SLDV) measurements. The LWDE algorithm uses angular bandpass filters in the wavenumber domain to determine the local propagation direction of the guided wave. The obtained local wave-direction map is converted into an error map by the use of a virtual local wave-direction map. The resulting error map reveals the sources of guided waves as local minima. The exploitation of local directional wave information provides the opportunity to scan only a small part of the component for localization of out-of-sight sources of guided waves. The source localization performance of LWDE is illustrated for localization of multiple piezoelectric sources in a quasi-isotropic CFRP plate.LWDE is further coupled to nonlinear vibrations in view of damage localization (NL-LWDE). The second higher harmonic component is extracted from the SLDV measurement and the sources of this higher harmonic component are localized. Damages behave as sources of higher harmonics and are thus localized by this NL-LWDE approach. This is demonstrated for a cross-ply CFRP plate with low velocity impact damage. The proposed combination of (i) nonlinear vibration filtering, (ii) direction estimation using angular bandpass filtering in the wavenumber domain and (iii) error map construction using the virtual wave-direction map results in a robust and baseline-free NDT technique. It can be used for accurate localization of multiple in-sight or out-of-sight damages in composite plates with unknown material properties and layup.