Transversal load introduction on sandwich RailwayCarbodies

Abstract: Sandwich structures made up by foam core and carbon fiber face-sheets are now seen as a promising technical solution for the design of railway carbodies by many railway manufacturers. Despite their numerous advantages over the classical metallic structures, transversal load introduction usually result in high stresses in the core of a sandwich structure. Hence, the fastening of equipment on a sandwich carbody must be studied carefully. The focus of this thesis has been put on the seat fastenings. Several technical solutions were compared. A metallic part, called a C-rail, adhesively bonded on the top of the sandwich panel represents the best solution according to the requirements. The aim of the C-rail is to spread the load and therefore lower the stress concentration in the core. The reaction loads at the seat fastenings, when the seats are loaded according to the European norms, where calculated using finite element (FE) analysis. Guidelines for the design of the C-rail were developed, based on 2D FE models. The focus was put on the reduction of stress concentration in the core. It was shown that an optimal C-rail cross section can be found for a specific sandwich panel. An analytical solution of the residual shear stresses induced by thermal expansion was developed to facilitate the choice of adhesive. It was shown that thick adhesive layers with low shear stiffness have the best strength with respect to temperature changes. Based on the 2D FE model, efficient techniques were derived for the modeling of adhesive layers. The influence of the face-sheet and adhesive modelisation on the stress distribution in the adhesive was studied. For that purpose, several combinations of material properties for the face-sheet and adhesive were investigated. In particular a spring based model of the adhesive was derived in order to include the face-sheet out of plane stiffness. It was shown that the stiffness of the adhesive have a high influence on the stress distribution in the adhesive layer. A 3D model was built up in order to investigate the load cases derived at the fastenings and to validate the qualitative studies based on the 2D models. The choice of the final sandwich panel depends on numerous issues such as sound insulation, dynamic properties or weight.Various sandwich configurations were investigated in order to determine the influence of issues related to equipment fastening on the final choice of sandwich panel. The face-sheet bending stiffness as well as the core stiffness were identified as the key parameters regarding the sandwich panel out of plane strength. The panel configuration obtained by weight optimization of the carbody represents the weakest configuration with respect to out of plane load introduction. Note that the solution proposed fulfilled the requirements for that configuration.