Basic Research On Bond Quality Inspection Of Aluminum Skin Honeycomb Core Sandwich Structure With Ultrasonic Guided Waves

In order to increase inspection speed of bond quality of Aluminum-skin honeycomb core sandwich structure, research works on the theories and methods relating to ultrasonic guided waves have been made and a set of ultrasonic guided waves inspection system for bond quality testing of Alumininum-skin honeycomb core sandwich structure has been designed.Firstly, the theories of guided waves propagated in single-layered plates and two-layered plates were researched. The mathmetical models of guided waves in both single-layered plates and two-layered plates were built, their dispersion curves were calculated, the wave structures were analyzed, and mathematical simulations of guided waves had been finished through finite element method(FEM). Furthermore, as far as the thin adhesive layer was concered, its effect on the guided waves was considered.Secondly, the guided waves inspection system of Aluminum-skin honeycomb core structure was designed. On the one hand, the harware system was set up including of the probe frequency, mode selection, and the excitation and reception method; on the other hand, the software was programmed. During mode selection, the first characterize value named as signal volitage amplitude was got.Thirdly, the signal post-processing methods were studied for the nonstable characteristic and dispersion of guided waves. After denoise methods such as average and wavelet were applied, the time-frequency analyses including short time Fourier transform and wavelet transform were then researched. The mode conversion during the progation was studied. The multi-resolution analysis with Mallat algorithom was used to decompose the guided waves and the second characterize value named as d3 was extracted.At last, the bond quality of hongeycomb core sandwich specimen was inspected respectively with A0 and S0 modes. In order to overcome the disadvantage of through transmission method, the X-Y two dimensions line scan cross-product adding menthod was presented. The experiment results indicated that A0 mode whose center frequency was 1.5MHz can inspect the debond defects in Aluminum-skin of 0.5mm thickness honeycomb core sandwich structure. The X-Y two dimensions line scan cross-product adding method can be applied effectively to image the guided waves signal under the condition of through transmission method. After the inspection result was compared with traditional thorough transmission method, it can be concluded that the guided waves method is less time-consuming 27.5 times than the traditional ultrasonic through transmission method.