Detection of Interfacial Weakness (Kissing Bonds) in Honeycomb Sandwich Structure Using Guided Waves

Abstract

AbstractHoneycomb sandwich structure is a regular and periodically repeated array of hexagonal cells used in automobile, aviation, marine, and construction industries. This structure offers a high strength-to-weight ratio, effective acoustic insulation, high energy absorption, and good thermal properties advantages. Variable load application and hazardous work conditions can lead to bond interface weakness in the honeycomb sandwich structure, leading to sudden failure. The existing non-destructive evaluation techniques cannot detect interfacial weakness effectively. This study aims to develop a shear-horizontal (SH) guided wave-based technique to evaluate the interfacial weakness in an aluminium honeycomb sandwich structure. The particle vibration in SH-guided waves is parallel to the adhesive-adherent interface, thus improving sensitivity in detecting interfacial properties. The interaction of SH-guided waves with different levels of interface shear stiffness is studied using a finite element model. A semi-analytical finite element model is solved in the frequency domain to simulate the wave propagation. The spring stiffness approach is adopted to model the interface stiffness. Different cases of interfacial adhesion, ranging from the perfect bond, intermediate and weak bonds, were modelled by changing the transverse spring stiffness constant. Frequency-wavenumber analysis reveals that the incident SH0 wave mode converts to SH0 and S0 modes. The presence of the S0 mode can be used as an indicator of the bond quality. Experiments were carried out on the aluminium-epoxy-aluminium honeycomb core joint using PPM-EMAT to verify the findings of the finite element simulations. The analysis shows that the proposed technique can detect the different adhesion levels rather than classify them as good or bad bonds.KeywordsHoneycomb structureEMATsSH-guided waves2.5D analysisWeak interfaceKissing bonds