Estimation of the elastic properties of an adhesive joint of thermoplastic honeycomb sandwich panels through analysis of structural resonant behaviour

In recent years the use of adhesive bonds for structural joints has increased greatly. Currently, many different material types are combined in a sole product. Especially in applications where lightweight materials are used, adhesive bonded joints offer distinct advantages over traditional joining techniques like welding, bolting and riveting. Important features are the possibility to join different types of materials and the ability to smoothen structural stress concentrations. A lot of research work has already been performed in the field of adhesives. However, it mainly focuses on the more fundamental physical-chemical properties of the different adhesive types, substrate adhesion and theoretical models that describe the viscoelastic behaviour of adhesives. There is a high number of environmental parameters that influence the elastic behaviour of an adhesive joint. Therefore, also the vibration behaviour of adhesively bonded structures is a process that is subjected to many uncertainties. This paper focusses on the joining of glass fibre reinforced polypropylene honeycomb sandwich panels by means of an adhesive bond. The simple case of joining two rectangular panels is considered. A first part discusses the adhesive type and bonding application. It thereby focusses on the estimation of elastic properties of the bonded zone. The uncertainty involved is quantified where possible. The second part estimates the impact of the uncertainty on bonding parameters on the resonant behaviour of the two joined honeycomb panels. As reference data, experimentally determined resonance frequencies and mode shapes under free boundary conditions are used. This part fully discusses how finite element modelling is used to estimate the bonding layer's shear modulus. The third part discusses the influence of vibration frequency, temperature and amplitude on the bonding layer's shear modulus. Various validation experiments are considered. Finally, the paper summarizes the research work and prospects to further application driven resear