eCon Engineering performed the strength analysis with layer optimisation of a polymer composite railway instrument panel, while supporting the design team with different simulation solutions during the development phase.
The loads and boundary conditions were based on the railway standard EN 12663 (Railway applications. Structural requirements of railway vehicle bodies) that describes the relevant load cases that represent different operating conditions of the structure. The loads can be separated into two main groups: exceptional and operational loads. The instrument panel is made of a glass fibre-reinforced polymer composite. The main aim of the simulation task is to define the proper layer number and layer orientation of the composite structure, or, if a glass mat is used as a reinforcing layer or if the base structure is a quasi-isotropic short-fibre composite, then the areas with the need of additional unidirectional layers can be determined.
Finite Element Model (FE-Model) and Boundary Conditions
The mechanical behaviour of the instrument panel was investigated using a finite element model. A finite element model was built with layered shell elements representing the composite structure. Each layer has an orthotropic material model, the material parameters come from specimen tests. The instruments and displays were modelled as concentrated mass-points with proper mass and inertia values. Bolted connections were modelled as beam elements with pre-tension forces and contact surfaces at the bolt-head and the nut. Quasi-static load cases with acceleration loads in the different directions were calculated with commercial FEM software.
Composite Material Tests
When simulating composite structures, it is very important to determine the direction-dependent mechanical parameters of the material accurately. The materials testing lab of eCon Engineering has a 50 kN tensile testing machine and a 100 kN fatigue testing machine with additional equipment such as flexure fixtures, compression platens and optical and thermal cameras. We can determine stiffness and strength values of composites in different fibre directions as well as in-plane shear stiffness values with high precision by measuring strains with strain-gauges or in an optical way.
Deformations at different load-cases were evaluated; for the composite parts different composite failure criteria were also evaluated. As we have the ability to accurately determine strength values in different fibre directions, we can fit material constants to any second-order failure criteria like Tsai-Hill, Tsai-Wu and Hoffmann, after which we can calculate material utilisations and safety factors. If needed, we can use more sophisticated failure criteria like Hashin and Puck for the evaluation and we can even calculate safety against delamination.
The presented simulation approach can be applied to all different types of instrument panels and is an important method for the development of instrument panels or any polymer composite parts, especially in the early design phase.