Università degli studi di Modena e Reggio Emilia

In the automotive field, piezo-resistive strain sensors have been increasingly integrated into “intelligent tyres”, to monitor the operating parameters, and to transmit them in real-time to the ECU. This work deals with polymer based piezo-resistive strain sensors with Carbon NanoTubes (CNT) embedded. CNTs slightly increase the mechanical strength of the sensor while improve the conductive and piezo-resistive behaviour of the polymer. A numerical methodology based on the Representative Volume Element (RVE) is proposed to predict the mechanical and electrical response of CNT-polymer. Finite Element method has been applied to obtain equivalent properties, which have been compared to experimental data available in the literature. Good estimate of the mechanical (i.e. Young’s Modulus) and electrical (i.e., resistivity) parameters has been achieved. The proposed methodology is thus suitable to identify electrical and mechanical properties of polymers with dispersed nanofibres

In the present paper, the crashworthiness of a thick unidirectional carbon fibre reinforced polymer is investigated. This material is manufactured via compression moulding process. A Low-Velocity Impact (LVI) test is implemented on a quasi-isotropic laminate for the experimental evaluation of the energy absorption due to impact, while the internal failure mechanism is detected using Computerized Tomography (CT). Two different Finite Element (FE) models are applied to model the damage onset and propagation: firstly, a shell-based model and, secondly, a solid-based model using Cohesive Zone Method (CZM). In the CZM, the analytical modelling of the cohesive element properties is adopted, and the critical force evaluated experimentally is related to the energy release rate of mode II, and to the equivalent elastic properties of the laminate. The strength and weakness of the proposed approach in mimicking the impact behaviour and the actual failure mechanism, are discussed, and validated versus numerical simulation. The models are in good agreement with the experimental results; in fact, the relative error of the maximum force is about 4 per cent, and it occurs in the shell-based model.

A honeycomb impact attenuator for a Formula SAE (FSAE) prototype vehicle is examined using both experimental and numerical analyses. Two common FSAE impact attenuators were compared to a new design concept, combining four layers of hexagonal honeycomb. The comparison aimed to obtain the combination of the lowest mass and highest energy absorption. The attenuator must comply with both the FSAE championship rules and further internally-defined design constraints. The work continues addressing the numerical-experimental correlation of the applied materials. Finally, the finite element models for virtual crash testing are presented and were validated through the experimental tests.