Analyzing the modal behavior of adhesive bonded thermoplastic honeycomb sandwich panels to estimate the elastic properties of the joint

In recent years adhesive bonds are more and more used in structural joints where mechanical performance is crucial. Currently, many different material types are combined in a sole product. Especially in applications where lightweight materials are used, adhesive bonded joints can offer distinct advantages over traditional joining techniques like welding, bolting and riveting. The possibility to join different material types and the ability to smoothen structural stress concentrations are very attractive from a mechanical-elastic point of view. A lot of research work has already been carried out in the field of adhesives. However, much of the documented work mainly focuses on the more fundamental physical-chemical properties of the different adhesive types, the substrate adhesion and theoretical models that describe the viscoelastic behaviour of adhesives. There are not many publications that discuss application driven research on elastic properties of adhesive joints, certainly not in the area of structural dynamics. 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 a hotmelt adhesive bond. The simple case of lap-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 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 complex shear modulus. Various validation experiments are considered. Finally, the paper summarizes the research work and prospects to further application driven research.status: publishe