Composite driver desk cleared to EN 12663 for a European Siemens Desiro fleet

The specific project was a composite instrument panel bolted onto a welded steel frame, carrying the full array of LCD displays and control instruments — a structure that had to satisfy EN 12663, the European standard for structural requirements of railway vehicle bodies, together with the OEM's own Technical Base Specification (TBS A6Z00017718837).

Polytec Mering's in-house team owned the design and manufacturing route, but they needed external help for the analytical case.

With the composite material and manufacturing route already fixed, the layup itself was still open — the ply schedule and local thickness distribution had to be established analytically before the driver desk could be released. Polytec Mering engaged eCon to run the EN 12663 verification and to shape the layup through the analysis.

The analysis had to represent this load path faithfully before the layup could be judged.

The composite instrument panel is a short-fibre composite with quasi-isotropic in-plane stiffness, captured through an isotropic material law from customer-supplied tension-test data (E = 7 869 MPa, ν = 0.1, ρ = 1.82×10⁻⁹ t/mm³). The panel and its supporting steel-and-aluminium substructure were modelled with shell elements — 5 mm on the evaluated panel, 10 mm on the frame. Every mounted instrument was represented as a concentrated point mass at its centre of gravity and coupled to the shell via RBE3 constraint equations, summing to 71 kg of added mass distributed across the panel.

The bolted attachments were resolved down to the joint level, because a smeared connection would have hidden the exact mechanism the standard was interested in. A frictional contact with a coefficient of 0.4 was defined between panel flange, composite shell, and metallic frame; the bolt itself was a beam element sized to the physical M5, tied to the hole edges by rigid beams. Bolt pretension was calibrated iteratively against the requirement that all inter-panel contacts remain sticking under 3g longitudinal loading — the governing panel being the one with the worst mass-to-bolt ratio — and settled at 500 N.

With the model in place, ten static and twelve fatigue load cases were run per EN 12663 and TBS A6Z00017718837. Static combinations covered ±3g longitudinal, ±1g transverse, and (1±2)g vertical; fatigue covered acceleration/braking and switch/curve regimes at 10⁷ cycles, with limits derived from a Tsai-Wu failure criterion. Evaluation used signed von Mises and maximum shear stress, referenced against Rp0.2 = 94.1 MPa with a safety factor of two on the static side.

The verification ran across two iterations. Local shell thickness in high-stress regions and the placement of reinforcement ribs were refined in loop with Polytec Mering, and both changes were carried into the physical product.

The result is a verification chain in which the composite layup, the bolted-attachment behaviour, and the full EN 12663 load spectrum sit inside a single traceable analytical package — with two of the layup decisions traceable to a specific eCon recommendation.