Rolling stock manufacturers are finding structural solutions to reduce power required by the vehicles, and the lightweight design of the car body represents a possible solution. Optimization processes and innovative materials can be combined in order to achieve this goal. In this framework, we propose the redesign and optimization process of the car body roof for a light rail vehicle, introducing a sandwich structure. Bonded joint was used as a fastening system. The project was carried out on a single car of a modern tram platform. This preliminary numerical work was developed in two main steps: redesign of the car body structure and optimization of the innovated system. Objective of the process was the mass reduction of the whole metallic structure, while the constraint condition was imposed on the first frequency of vibration of the system. The effect of introducing a sandwich panel within the roof assembly was evaluated, focusing on the mechanical and dynamic performances of the whole car body. A mass saving of 63% on the optimized components was achieved, corresponding to a 7.6% if compared to the complete car body shell. In addition, a positive increasing of 17.7% on the first frequency of vibration was observed. Encouraging results have been achieved in terms of weight reduction and mechanical behaviour of the innovated car body.

The transition to a globalised electrical power supply pushes rolling stock manufacturers to find structural solutions for reducing the power required by the vehicles. Within a market where details can make the difference in economic terms, the concept of design optimization is becoming established. However, current industrial procedure for the evaluation of carbody structural strength, in static field and according to EN 12663-1:2015 standard, does not include any optimization process. More in general, optimization processes, and especially dynamic optimization, are not widely used for designing of railway vehicles. In this framework, the present paper proposes a new dynamic optimization approach to support the design of railway vehicle carbodies subjected to static loads. Proposed methodology aims to minimize the mass of the metallic structure, working on the thicknesses of the optimized components, maintaining the baseline geometry. The constraint function was imposed on the first natural vibration frequency of the system. The optimization strategy is based on a dynamic size optimization process in conjunction with modal analysis techniques, applied on the single carbody shell. The procedure has involved the roof assembly of a single tram vehicle body. The proposed approach is resulted numerically efficient in terms of calculation times. Encouraging results have been achieved in terms of mass saving and mechanical behaviour of the carbody shell. Optimized components were 21% lighter than the original, that corresponds to 3% if evaluated on the total mass of the single carbody metallic structure. The methodology turns out to be a useful tool for supporting designers to reduce the mass of the carbody structures, reducing overdimensioning condition that could affect the carbody structure.

Nowadays, due to environmental pollution caused by CO2-emissions, a global transition to electricity is taking place within railway industry. Lightweight design of railway vehicles could allow to reduce the power required during their operation conditions. Optimization processes, especially dynamic optimization approaches, are not widely used for designing of railway vehicles. In addition, in recent years, with the aim to increase weight reduction, sandwich structures were commonly introduced in the carbody structure. However, almost always they did not have any structural functionality. The present paper proposes the modelling and dynamic size optimization of a new roof assembly of a tramway vehicle including a sandwich structure. A new optimization procedure has been defined to support the traditional design approach. Subsequently, the roof assembly of the tram vehicle has been redesigned to allow the correct installation of the sandwich panel, fastened through a bonding joint. Encouraging results have been achieved in terms of mass saving and mechanical behaviour of the carbody shell. The developed methodology turns out to be a useful tool for supporting designers for obtaining a lightweight design. The innovative configuration of the roof assembly has shown promising performance in terms of mass saving, increasing of frequencies of vibration and costs.

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