Maglione, Raffaele (2025) Physically-based framework for viscoelastic modeling and tire performance correlation. [Tesi di dottorato]

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Abstract

Tires are complex multi-physical systems in which structural dynamics, material rheology, and surface interactions jointly determine overall performance. Among the various factors involved, the viscoelastic behavior of rubber compounds plays a central role, governing key tire functions such as grip, rolling resistance, and wear through temperature-, frequency-, and strain-dependent mechanisms. Although numerous studies have investigated these phenomena, often combining experimental, analytical, and numerical approaches, the intrinsic coupling among thermal, mechanical, and surface effects makes the establishment of a unified, quantitatively predictive methodology particularly challenging. This thesis aims to address this challenge by developing an integrated methodological framework that bridges laboratory-scale viscoelastic characterization and full-tire performance evaluation. The approach combines experimental, theoretical, and data-driven components within a physically consistent and traceable workflow, ensuring that each modeling step can be validated against measurable quantities. At the material scale, viscoelastic moduli are obtained through conventional Dynamic Mechanical Analysis (DMA) and through the Viscoelastic Evaluation System Evolution (VESevo), a non-destructive, impact-based testing device capable of acquiring viscoelastic information directly from tread slabs or mounted tires. An advanced indentation-based model was developed to interpret VESevo signals, incorporating amplitude-dependent softening via a Payne-type formulation and enabling the direct estimation of relaxation parameters, storage modulus, and loss tangent under realistic excitation conditions. Building upon this foundation, the thesis introduces the Nonlinear Generalized Fractional Maxwell–Wiechert (NLGFMW) model, a compact yet comprehensive fractional framework that unifies nonlinear and fractional viscoelasticity within a single constitutive representation. This model reproduces the double-slope behavior of the storage modulus near the glass transition and provides smooth, physically consistent trends across broad frequency and temperature domains. At the tire scale, the identified viscoelastic descriptors are integrated with experimental data from indoor (Flat Trac, friction, wear, and thermal characterization) and outdoor (proving-ground braking) campaigns, complemented by detailed surface metrology. The resulting correlations demonstrate that measurable viscoelastic parameters, particularly $E'$ and $\tan\delta$, govern stiffness, grip, and wear evolution, enabling the quantitative prediction of tire performance under realistic boundary conditions. Overall, the thesis establishes a physically grounded and operational methodology that connects viscoelastic material behavior to tire-level dynamics. The framework provides both scientific insight into the mechanisms linking rubber rheology and tire performance, and a practical foundation for predictive, data-informed, and simulation-ready tire development.

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