Maiorano, Antonio (2021) Innovative approaches fot tyre characterization aimed at road contact modelling for automotive applications. [Tesi di dottorato]

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In Automotive the role of the tyre mechanics and physics is crucial for the optimization of vehicle stability, performance and safety. Most engineers usually face the analysis of tyres' mechanical and viscoelastic properties with the aim to comprehend the interaction phenomena between the tread and the road. In the last decades, compound-substrate modelling has been discussed a lot in the scientific literature. Many theories have been developed to determine the frictional behaviour of rubber sliding on a texture in a wide working range in terms of temperature, contact pressure, profile roughness, etc. The most common and recent theories, such as Klüppel's and Persson's [1, 2], are widely employed because they try to explain the contact modelling problem following different approaches and hypothesis. However, the analysis of the contact problem requires full knowledge of the roughness profile and the rubber viscoelastic properties. The identification of the macro-roughness scales and especially of the micro-scales is an enigma yet to be unequivocally solved for the optimization of the multiscale theories [3]. On the other side, the properties of the rubber compound are complex to determine, unless the tyre tread can be destroyed to obtain a specimen and then perform the Dynamic Mechanical Analysis (DMA), which usually requires expensive machines and a long time for a full time-temperature characterization of the material according to William-Landel-Ferry theory [4, 5]. Nonetheless, in most applications, as well as Motorsport ones, the tyres are linked to restrictions and they cannot be analysed by the standard and laboratory procedures. In this scenario, the main activities described in the present PhD thesis deal with the tyre tread compound characterization through innovative methodologies and devices in order to overcome the limits that Motorsport racing teams or tyre manufacturers are used to face with. The non-destructive viscoelastic analysis through the device developed thanks to the precious support of the skilled and motivating research team of the Industrial Engineering Department of the University of Naples Federico II, which is called VESevo (Viscoelasticity Evaluation System evolved), is an advantageous testing procedure proving indication of the tyre viscoelastic properties variations with respect to the temperature, wear phenomena, ageing, etc. Ergonomics, portability and smart analysis are key features of this device, allowing it to be widely used by engineers of racing teams on tracks during Motorsport races and events and further by operators in tyre 26 manufacturers facilities, that also need a fast and reliable analysis of the trustworthiness of their final product series. Once introduced the innovative approaches for tyres characterization, the contact mechanics models have been analysed in-depth highlighting their features and limits for automotive applications. Particularly, the GrETA (Grip Estimation for Tyre Analyses) tool, developed by the Applied Mechanics group of the Industrial Engineering Department of the University of Naples Federico II and improved during the PhD research period, is proposed as a multi-contact simplified physical model for the analysis of adhesive and hysteretic contributions to the overall friction between the rubber and the substrate macro and micro asperities. The main parameters of the GrETA have been identified thanks to specific experimental friction benches, which have involved the last part of the PhD program. The results achieved can be considered as a baseline for innovative approaches in terms of tyre characterization and contact modelling for friction prediction. Actually, some limits concerning the experimental friction analysis have been faced during the research program, which will be overcome thanks to the realization of the new proposed friction test bench allowing to strengthen the identification of the contact mechanics models and focus on new research scenarios, as well as the analysis of rubber wear phenomena.

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