Disbond detection of honeycomb sandwich structure through laser ultrasonics using signal energy map and local cross-correlation

Detecting disbonds in honeycomb sandwich structures using ultrasonics is challenging due to the complex wave propagation. This paper investigates the method for disbond quantification in honeycomb sandwich structures using laser ultrasonics. In the experiments on an aluminum specimen, the detection frequency range was determined by the local defect resonance (LDR) in the disbond regions. The energy maps of bandpass wavefields identified the locations of disbonds. To improve the results, a frequency-wavenumber analysis of the wavefields was performed. The wavenumber spectra were reconstructed by wavenumber filtering to strengthen the outline components for quantifying disbonds. Local cross-correlation (LCC) was proposed to show the outlines of disbonds and honeycomb cells, whose results agreed well with the X-ray imaging. Moreover, LCC could also quantify a disbond in the composite honeycomb sandwich structure. Consequently, combining energy maps and LCC results can effectively detect the locations and sizes of disbonds in honeycomb sandwich structures.