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Master of Science / Rubber is a widely used material globally and undergoes significant changes as it ages. However, the specific consequences of rubber aging on tires and vehicle dynamics remain a relatively underexplored domain. This study delves into the effects of rubber aging on tires and motorcycle dynamics. A Dynamical Mechanical Analysis (DMA) test was performed to study the effect of rubber aging combined with computer simulation models to predict how much the rubber wears out over time. It was found that as rubber gets older it doesn't wear out much faster. This might be because the changes in the rubber properties as it ages are very small. The rubber material also gets stiffer as it ages, leading to minimal differences in the wear rate. The Magic Formula (MF) model was used in this study to model motorcycle tires. A 3-4% increase in the longitudinal and lateral tire forces was observed as the tire aged. This was followed by simulations to study the motorcycle behavior during straight-line and turning motion. It was found that the front tires of the motorcycle had an approximately 3% change in the forces experienced, while the forces experienced by the rear tires only changed by 1-2% with respect to aging. These results are similar to the results obtained by other researchers on the effects of rubber aging on car performance. Thus, this study stresses the importance of understanding how tires change over time and how that affects how motorcycles perform.

Hydroplaning is a phenomenon that occurs when a layer of water between the tire and pavement pushes the tire upward. The tire detaches from the pavement, preventing it from providing sufficient forces and moments for the vehicle to respond to driver control inputs such as breaking, accelerating and steering. This work is mainly focused on the tire and its interaction with the pavement to address hydroplaning. Before using a full-scale tire model, interactions of the tread block with a specific surface is studied. To do so, several mechanical tests such as uniaxial, biaxial, planar (shear), and DMA are conducted to predict the hyper-viscoelastic properties of the rubber. Using multi-scale modeling techniques, the friction coefficient between the tire and pavement, for wet conditions, is characterized via developing 2D and 3D model representing the rubber tread interacting with the rough surface. Using a tire model that is validated based on results found in the literature as well as in-house experimental data, fluid-structure interaction (FSI) between the tire-water-road surfaces are investigated through two approaches. In the first approach, the coupled Eulerian-Lagrangian (CEL) formulation was used. The drawback associated with the CEL method is the laminar assumption that the behavior of the fluid at length scales smaller than the smallest element size is not captured. To improve the simulation results, in the second approach, an FSI model incorporating finite-element methods and the Navier-Stokes equations for a two-phase flow of water and air, and the shear stress transport k-ω turbulence model, was developed and validated, improving the prediction of real hydroplaning scenarios. The improved FSI model was applied to hydroplaning speed and cornering force scenarios. In addition, tire contact patch length was calculated using the developed FSI model and was compared to the results obtained from the intelligent tire. / Doctor of Philosophy / Hydroplaning is a phenomenon that occurs when a layer of water between the tire and pavement pushes the tire upward. The tire detaches from the pavement, preventing it from providing sufficient forces and moments for the vehicle to respond to driver control inputs such as breaking, accelerating and steering. Hydroplaning as well as low skid resistance are considered as the main factors leading to traffic accidents. This work is mainly focused on the tire and its interaction with the pavement to address hydroplaning. Different factors involve in the hydroplaning phenomenon such as water film thickness, tire pressure, tire tread pattern, tire tread depth, vehicle speed and pavement texture. Before using a full-scale tire model, interactions of the tire tread with a specific surface is studied. To do so, several mechanical tests are conducted to predict the hyper-viscoelastic properties of the rubber. Using a single scale methodology is not capable to obtain the sufficient information regarding the effect of roughness on the friction. As a result, using multi-scale modeling techniques, the friction coefficient between the tire and pavement, for wet conditions, is characterized via developing 2D and 3D model representing the rubber tread interacting with the rough surface. Since in the hydroplaning problem, a solid structure and a fluid domain are in interaction, such a problem considered as a fluid-structure interaction (FSI) problem. In this work, the FSI between the tire-water-road surfaces are investigated through two approaches. To improve the simulation results, an FSI model incorporating finite-element methods and the Navier-Stokes equations for a two-phase flow of water and air, and the shear stress transport k-ω turbulence model, was developed and validated, improving the prediction of real hydroplaning scenarios. In addition, tire contact patch length was calculated using the developed FSI model and was compared to the results obtained from the intelligent tire.

A significant number of studies address various aspects related to tire modeling; most are dedicated to the development of tire models for on-road conditions. Such models cover a wide range of resolutions and approaches, as required for specific applications. At one end of the spectrum are the very simple tire models, such as those employed in real-time vehicle dynamic simulations. At the other end of the spectrum are the very complex finite element models, such as those used in tire design. In between these extremes, various other models have been developed, at different levels of compromise between accuracy and computational efficiency. Existing tire models for off-road applications lag behind the on-road models. The main reason is the complexity added to the modeling due to the interaction with the soft soil. In such situations, one must account for the soil dynamics and its impact on the tire forces, in addition to those aspects considered for an on-road tire. The goal of this project is to develop an accurate and comprehensive, while also efficient, off-road tire model for soft soil applications. The types of applications we target are traction, handling, and vehicle durability, as needed to support current army mobility goals. Thus, the proposed approach is to develop a detailed semi-analytical tire model for soft soil that utilizes the tire construction details and parallels existing commercially available on-road tire models. The novelty of this project relies in developing a three-dimensional three-layer tire model employing discrete lumped masses and in improving the tire-soil interface model. This will be achieved by enhancing the resolution of the tire model at the contact patch and by accounting for effects and phenomena not considered in existing models. / Master of Science

A major challenge in tire, as well as in road engineering, is to understand the intricate mechanisms of friction. Pavement texture is a feature of the road surface that determines most tire-road interactions, and can be grouped into two classes: macro-texture, resulting mainly in the hysteretic component of friction, and micro-texture, resulting in adhesion. If both textures are maintained at high levels, they can help provide sufficient resistance to skidding. The ultimate objective of this research is to develop a physics-based multiscale rubber-road friction model that can predict the effectiveness of the tire as it interacts with the vehicle and the pavement. The model is developed based on sound physics and contact mechanics theories and uses road profile measurements and data measured on various tire compounds. To be able to predict road surface characteristics, it is proven that road surfaces are of fractal nature on given ranges of scale. It is shown that while global fractal quantities fail to classify pavement profiles, a local fractal parameter and three other texture parameters can separate road profiles that have different friction characteristics. Through the implementation of various contact theories and by conducting simulation studies, a methodical understanding of contact mechanics and of the effect of the diverse factors that influence friction is attained. To predict the viscoelastic friction between any given tire tread compound and road, the Nanovea JR25 portable optical profilometer is used to measure the road profiles. To characterize the road profile, the one-dimensional pavement measurements are used to obtain the two-dimensional power spectrum, followed by testing and characterizing the tread compounds (this is being carried out by Bridgestone). This data is used to develop a comprehensive analytical methodology to predict friction. To validate this model, a Dynamic Friction Test apparatus is designed and built. The friction tester enables measurement of the friction between tread compound samples and arbitrary surfaces, at different slip ratios. The correlations between the simulations and both indoor and outdoor experimental results are investigated. / Ph. D.

The contact patch of the tire is responsible for all of the transmission of a vehicle's motion to the road surface. This small area is responsible for the acceleration, stopping and steering control of the vehicle. Throughout the development of vehicle safety and stability control systems, it is desirable to possess the exact forces and moments at the tire contact patch. The tire is a passive element in the system, supplying no explicit information to vehicle control systems. Current safety and stability algorithms use estimated forces at the tire contact patch to develop these control strategies. An "intelligent" tire that is capable of measuring and transmitting the instantaneous forces and moments at the contact patch to the control algorithms in real-time holds promise to improve vehicle safety and performance. Using the force and friction information measured at the contact patch, an anti-lock braking control strategy is developed using sliding mode control. This strategy is compared to the performance of a current commercial anti-lock braking system that has been optimized by performing a threshold sensitivity analysis. The results show a definite improvement in control system strategy having known information at the tire contact patch. / Master of Science

Vehicle modeling and simulation have fast become the easiest and cheapest method for vehicle testing. No longer do multiple, intensive, physical tests need be performed to analyze the performance parameters that one wishes to validate. One component of the vehicle simulation that is crucial to the correctness of the result is the tire. Simulations that are run by a computer can be run many times faster than a real test could be performed, so the cost and complexity of the testing is reduced. A computer simulation is also less likely to have human errors introduced with the caveat that the data input into the model and simulation is accurate, or as accurate as one would like their results to be. Simulation can lead to real tests, or back up tests already performed. The repeatability of testing is a non-issue as well. Tire models are the groundwork for vehicle simulations and accurate results cannot be conceived without an accurate model. The reason is that all of the forces transmitted to and from the vehicle to the ground must occur at the tire contact patches. This presents the problem of obtaining a tire model. Tire companies do not readily give out tire data since the tire industry is still as much "black art" as it is science. For tire data one must begin with a testing apparatus. The test rig must be accurate and must have been validated before results can be used. This thesis presents the process of the design and construction of a portable tire test rig. It then will discuss tire testing procedures and validation techniques. The resulting data shows good correlation between test data and known tire test data from flat track testing provided by a tire manufacturer. Then, a simple rollover study of a military truck will be compiled in TruckSim. Lastly, a control method for the rollover case will be designed and implemented. The results of the roll control simulation are positive. The study shows an increase in dynamic roll stability due to the implementation of the control algorithm. / Master of Science

The advent of finite element methods has changed the tire industry's design process over the past three decades. Analyses, previously impractical using analytical methods and physically limited by experimental methods, can now be performed using computational methods. This decreases the cost and time associated with bringing a new design to the marketplace; however some physical testing is still required to validate the models. The design, fabrication, installation, and operation of a tire, suspension, and chassis test fixture (TiSCTeF) is detailed as part of this study. This fixture will support the validation of effective, parametric finite element models currently under development, as well as the design and testing of suspension and chassis components for the Virginia Tech Formula SAE team. The fixture is designed to use the Formula SAE race car as the test platform. Initially, the fixture is capable of performing static load-deflection and free-rolling tire tests. Provision has been made in the design for incremental upgrades to support cornering tests and additional instrumentation. An initial load-deflection test has proven that the fixture is capable of creating reproducible data sets. Specific recommendations are made concerning the improvement of data quality for future tests. This study also presents a process for analyzing existing tire cornering data and eliminating anomalies to improve the effectiveness of normalization techniques found in the literature. The process is shown to collapse tire cornering data, which is partially ill- conditioned, onto master curves that consistently display the effect of inclination angle and tire inflation pressure on tire response. / Master of Science

Studying the kinetic and kinematics of the rim-tire combination is very important in full vehicle simulations, as well as for the tire design process. Tire maneuvers are either quasi-static, such as steady-state rolling, or dynamic, such as traction and braking. The rolling of the tire over obstacles and potholes and, more generally, over uneven roads are other examples of dynamic events which are of importance. In the latter case, tire dynamic models are used for durability assessment of the vehicle chassis, and should be studied using high fidelity simulation models. In this study, a threedimensional finite element model (FEM) of the 16 inch TMPT Tire has been developed using the commercial software package ABAQUS. The purpose of this study is to investigate tire transient dynamic behavior for various inputs. The process of running dynamic FE tire simulations starts by statically inflating and loading the tire using an implicit method with refined mesh in the contact patch. Then, by using the "result transfer" option in ABAQUS, final state vectors are used as initial conditions for subsequent simulations. Using this sequence of loading steps helps increase the efficiency of the code. The validation of the model is performed in two stages. First, tire mode shapes and associated natural frequencies and damping values are compared with the experimental data. Second, a series of transient dynamic simulations are performed using an explicit method with a fine mesh around the circumference of the tire. Finally, the FEM model results are filtered to eliminate the numerical noise, and their correlation with the test data is investigated. Moreover, the peak values and time shifts associated with spindle forces as a function of normal load are studied. The results show that the tire dynamic response is autonomous. / Master of Science

The growth of the automobile Industry in the past 50 years is radical. The development of chassis control systems have grown drastically due to the demand for safer, faster and more comfortable vehicles. For example, the invention of Anti-lock Braking System (ABS) has resulted in saving more than a million lives since its adaptation while also allowing the vehicles to commute faster. As we move into the autonomous vehicles era, demand for additional information about tire-road interaction to improve the performance of the onboard chassis control systems, is high. This is due to the fact that the interaction between the tire and the road surface determines the stability boundary limits of the vehicles. In this research, a real-time system to classify the road surface into five major categories was developed. The five surfaces include Dry Asphalt, Wet Asphalt, Snow, and Ice and dry Concrete. tri-axial accelerometers were placed on the inner liner of the tires. An advanced signal processing technique was utilized along with a machine learning model to classify the road surfaces. The instrumented Volkswagen Jetta with intelligent tires was retrofitted with new instrumentation for collecting data and evaluating the performance of the developed real-time system. A comprehensive study on road surface classification was performed in order to determine the features of the classification algorithm. Performance of the real-time system is discussed in details and compared with offline results. / Master of Science / The automobile industry has been improving road transportation safety over the past 50 years. While we enter the autonomous vehicles era, the safety of the vehicle is of primary concern. In order to get the autonomous vehicles to production, we will have to improve the on board vehicle control systems to adapt to all surfaces. Gaining more accurate information about the tire and road interaction will help in improving the control systems. Tires have always been considered a passive element of the vehicle. However, more recently, the idea of “tire as a sensor” has surfaced and has become one of the major research thrusts in tire as well as vehicle companies. The intelligent tire research at the Center for Tire Research (CenTiRe) begun in 2010 and has been going strong. In this work, we have developed a classification algorithm to classify the road surfaces in real-time based on acceleration measured inside the tire. The information regarding the road surface would be highly beneficial for the developing new control strategies, automate service vehicles and aid surface prediction in autonomous vehicles.