Laser vibration measurements and data processing for structural diagnostic on composite material

In recent years, the identification and characterization of defects in mechanical and civil structures have been widely investigated by processing of vibration measurement results. In this field laser Doppler vibrometry (LDV) offers large potentials in terms of spatial resolution and reduced intrusivity. In this work LDV technique has been applied to measure delamination extension, depth, and location in composite materials. A lumped parameter model has been developed to describe the dynamic behavior of a delaminated composite panel with the aim of determining which kind of measurement data must be extracted for damage monitoring and to design efficient postprocessing algorithms for experimental LDV data. It is shown that the root-mean-square (rms) values computed in different frequency bands are indicators of the delamination depth. In fact, the vibration exhibits a higher rms value in higher frequency bands, if the defect is deeper. Following the model results, an experimental investigation by LDV has b...