Abstract
Composite materials are widely used in many engineering applications and fields of technology. One of the main defects, which occur in fiber-reinforced composite materials, is delamination. It manifests itself in the separation of layers of material and the damaged structure once subjected to mechanical loads degrades further. Delamination results in lower stiffness and the decrease of structure’s carry load capability. Its early detection is one of the tasks of non-invasive structural health monitoring of layered composite materials. This publication discusses a new method for delamination detection in fiber-reinforced composite materials. The approach is based on analysis of energy signal, calculated with Teager–Kaiser energy operator, and comparison of change of the weighted instantaneous frequency for measurement points located in- and outside of delamination area. First, applicability of the developed method was tested using simple models of vibration signals, reflecting considered phenomena. Next, the authors’ weighted instantaneous frequency was applied for detection of deamination using signals obtained from FEM simulated response of the cantilever beam. Finally, the methods effectiveness were tested involving real experimental signals collected by the laser Doppler vibrometer (LVD) sensor measuring vibrations of the delaminated glass-epoxy specimens.
Highlights
time synchronously averaged (TSA) displacement signals from measurement points M1 and M2 of the successive specimens as well as reference signal, measured by the sensor located on mounting clamp, were processed with the use of the DESA-2 algorithm to obtain f w
The paper discussed the application of the original Teager–Kaiser weighted instantaneous frequency f w dedicated for analysis of vibrational response of the beams with breathing delamination
Numerical models were created, reflecting breathing delamination phenomena in vibration signal; the conducted experimental tests confirmed half-period variation of instantaneous frequency resulting from breathing delamination; the weighted instantaneous frequency f w, a new approach for estimation of instantaneous frequency, has been developed and its effectiveness was tested; a failure indicator and a diagnostic method were proposed for detection of breathing delamination type failure
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Nonlinear dynamics of breathing deformation, observed in the finite element model of the vibrating specimen as well as in experimental tests, points to the need of selecting proper signal processing and analysis methods allowing to detect this phenomena. The analysis of the time domain signal using the Teager–Kaiser energy operator enables observation of transient disturbances of the signal’s instantaneous frequency (IF) [32] Such disturbances can result from a failure, e.g., crack or delamination of a composite structure. In the considered case of breathing delamination, comparison of instantaneous frequency of vibration signals recorded in measurement points located within and outside delamination allows to create a useful failure indicator.
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