Abstract:
In the aviation industry, sandwich structures are widely used for interior furnishings such as galleys, monuments and stowages. There are various techniques of joining these structures, though the most common way of attaching to the aircraft interface is the use of an embedded metallic structure. In recent times, there has been an increased acceptance by regulators and OEMs allowing stress analysis reports for aircraft interior products to use stress output from finite element modelling (FEM) to validate stresses in panels and joints. It is not currently considered acceptable by regulators and OEMs to use FEM output to validate stresses around discontinuous structures such as embedded blocks and bonded doublers. Regions around the discontinuous structure, therefore, require additional hand analysis which is time-consuming and incorporates high levels of conservatism. The action of a bonded doubler on a long beam bending scenario was investigated. FE models using Altitude Aerospace Interiors’ modelling approach were found to adequaelty predict the flexural stiffness. The study highlights the importance of considering constraints applied to rigid elements. Modelling results are approximately 13% lower in stiffness than the experimental values. It is generally considered acceptable to be conservative in the approach and 13% is considered adequate. Digital image correlation (DIC) was used to investigate the core shear distribution on discontinuities subject to an out-of-plane load. DIC revealed that the shear strain in the core, for a beam with symmetric doublers, rapidly decreases at the boundary of the doubler and then increases upon passing the doubler edge. For an asymmetric doubler arrangement, there is a local maximum and minimum present at the doubler edge, the distribution varies through the thickness, and the change in shear strain magnitude is at an angle to the beam normal. Modelling methods used by Altitude Aerospace Interiors were shown to significantly overestimate the deflection, and fail to capture the core shear distribution in a shear dominated problem. A solid model was shown to form a good agreement with experimental data in terms of deflected shape and magnitude, and adequately captures the shear strain distribution at the doubler peripheral.