The tire-ice interaction is a highly complex phenomenon, which has a direct influence on the overall performance of the pneumatic tire. From tire-terrain interaction dynamics, it is evident that icy road conditions and tire operational parameters play a vital role in determining the overall performance of the vehicle. With the reduction of traction available at the surface in icy conditions, the dynamics of the vehicle becomes more unpredictable, as the system can become unstable. In order to design an appropriate safety system, the tire-ice interaction must be closely investigated. Since the tire is the part of the vehicle that is in direct contact with the terrain during operation, it is critical to have an in-depth understanding of the contact mechanics at the contact patch. This study has led to the development and validation of an existing tire-ice model to further improve the understanding of the contact phenomena at the tire-ice interface. Experimental investigations led to a novel measurement technique in order to validate the semi-empirical based tire-ice contact model. The Advanced Tire-Ice Interface Model serves to simulate the temperature rise at the contact patch based on the pressure distribution in the contact patch, thermal properties of the tread compound and of the ice surface. Since its initial development, the advanced model is now capable of simulating the thin water film created from the melted ice, the prediction of tractive performance, the estimation of the viscous friction due to the water layer, and the influence of braking operations including the locked wheel condition. Experimental studies, carried out at the Terramechanics, Multibody, and Vehicle Systems (TMVS) Laboratory, were performed on the Terramechanics Rig. The investigation included measuring the bulk temperature distribution at the contact patch in order to validate the temperature rise simulations of the original Tire-Ice Model. The tractive performance of a P225/60R16 97S Standard Reference Test Tire and a 235/55R-19 Pirelli Scorpion Verde All-Season Plus XL were also investigated during this study. A design of experiment was prepared to capture the tire tractive performance under various controlled operating conditions. / Ph. D.

Viscoelastic materials have been used widely in different applications, such as constructing tires, artificial joints, shoe heels, and soles. A study on the different characteristics of viscoelastic materials has always been a matter of interest in order to improve their properties for various applications. In the automotive industry, rubber, as a viscoelastic material, has been used in several subsystems, such as vehicle interior, suspension, steering joints, and tires. The tire and terrain's contact characteristics are among the essential factors for assessing the performance of the tire and the vehicle in general. Friction and tread wear are two of these contact characteristics. Considering the tire's functionality, for most applications, it is desired to have higher friction to have better traction and a lower wear rate to minimize the material loss of the tread. The friction coefficient and the rubber's wear rate depend on various parameters such as rubber material properties, terrain characteristics, temperature (tread and the environment), and the load. To obtain the wear rate and friction of a viscoelastic material, three approaches have been used for this study: Experimental, Analytical, and Numerical. The results obtained using these approaches have been compared and validated. Several test setups have been designed and implemented to study the wear and friction of the rubber experimentally. Also, a new linear friction tester has been designed and manufactured by the author to achieve this project's objectives. The new test setup has several advantages over existing test setups in this field, such as covering a higher range of velocities while maintaining high precision. The designed Linear Friction tester and the modified dynamic friction tester at the CenTiRe laboratory at Virginia Tech were used to measure the rubber's friction and wear for different testing conditions such as different normal loads, different velocities, and various surfaces such asphalt and sandpaper. The data collected by the experiment will later be used for the validation of the developed models. In order to obtain the wear rate of the rubber using the analytical approach, the real contact area and friction of the rubber were calculated using Persson's model. The simulation has created the surface to obtain the friction coefficient and the real contact area. After obtaining the friction coefficient and the real contact area, the rubber's wear rate was calculated using a novel approach by combining the Persson Powdery Rubber Wear model with the Crack Propagation model. The results from the improved model compare well with the results from the original model. For the last step of this project, a Finite Element approach was used for modeling a tread block and round rubber sample. A new semi-empirical model for wear was developed by improving the Archard wear model. The novel approach was implemented to Abaqus by using the Umeshmotion subroutine and adaptive mesh motion (ALE) and subroutine UFric and UFric_Coef in two categories: The Node base method and the Ribbon base method. For finite element modeling, the visco-hyper elastic material model has been used to define the rubber's material properties. / Doctor of Philosophy / Viscoelastic materials have been used widely in different applications, such as constructing tires, artificial joints, shoe heels, and soles. Therefore, studying the different characteristics of viscoelastic materials has always been a matter of interest in improving their properties for various applications. In the automotive industry, rubber, as a viscoelastic material, has been used in several subsystems, such as vehicle interior, suspension, steering joints, and tires. The tire and terrain's contact characteristics are among the essential factors for assessing the performance of the tire and the vehicle in general. Friction and tread wear are two of these contact characteristics. Considering the tire's functionality, for most applications, it is desired to have higher friction to have better traction and a lower wear rate to minimize the material loss of the tread. This study used different approaches such as experimental, analytical, and numerical methods to predict the friction and wear of the rubber sample in contact with different surfaces. For the experimental parts, the author designed and manufactured a linear friction test setup. For the numerical parts, a new semi-empirical model was created to predict rubber samples' wear accurately.

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Obtaining the modal parameters of a deflected and rolling tire represents a challenge due to the complex vibration characteristics that cause the tire's symmetry distortion and the natural frequencies' bifurcation phenomena. The modal parameters are usually extracted using a detailed finite element model. The main issue with full modal models (FEA, for example) is the inability to integrate the tire modal model with the vehicle models to tune the suspension system for optimal ride comfort. An in-plane rigid–elastic-coupled tire model was used to examine the 200 DOF finite difference method (FDM) modal analysis accuracy under non-ground contact and non-rotating conditions. The discrete in-plane rigid–elastic-coupled tire model was modified to include the contact patch restriction, centrifugal force, Doppler, and Coriolis effects, covering a range of 0-300 Hz. As a result, the influence of the contact patch and the rotating tire conditions on the natural frequencies and modes were obtained through modal analysis. The in-plane rigid–elastic-coupled modal model with varying conditions was created that connects any two DOFs around the tire's tread or sidewall as inputs or outputs. The vertical movement of the wheel was incorporated into the in-plane rigid–elastic-coupled tire modal model to extract the transfer function (TF) that connects road irregularities as an input to the wheel's vertical movement as an output. The TF was utilized in a quasi-static manner to obtain the tire's enveloping characteristics rolling over short wavelength obstacles as a direct function of vertical wheel displacement under varying contact patch length constraints. The tire modal model was implemented with the quarter car model to obtain the vehicle response rolling over short wavelength obstacles. Finally, a sensitivity analysis was performed to examine the influence of tire parameters and pretension forces on natural frequencies. / Doctor of Philosophy / The goal of vehicle manufacturers is to predict the vehicle's behavior under various driving conditions using mathematical models and simulation. Automotive companies rely heavily on computational simulation tools instead of real-time tests to shorten the product development cycle and reduce costs. However, the interaction between the tire and the road is one of the most critical aspects to consider when evaluating automobile stability and performance. The tires are responsible for generating the forces and moments that drive and maneuver the vehicle. Tires are complex products due to their intricate design, and their characteristics are affected by many factors such as vertical load, inflation pressure, speed, and a road with an uneven surface profile. Consequently, this project aims to describe the influence of various driving circumstances and load conditions on tire properties, as well as to develop a model that can represent the vertical tire and vehicle behavior while traveling over a cleat under different vehicle loads.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Rubber is the main component of the pneumatic tire. When rubber is put under cyclic loading, like when a tire is rolled, heat is generated and stored in the rubber, due to hysteresis. Heat stored in the tire is increased by factors like under-inflation, overloading, speeding and defects in the tire. The heat causes high temperatures in the tire due to the poor thermal conductivity of rubber. When the temperature in the rubber increases to 185 °C, pyrolysis and thermo-oxidation starts and can cause the tire to eventually explode. A numerical model of a rolling passenger vehicle tire was developed to calculate the temperature distribution inside the tire and analyse the effect of different operating conditions on the temperature. Operating conditions include loading, inflation pressure, rolling velocity and ambient temperature. The tire was modelled by a single rubber type, using the Mooney-Rivlin material model. The bead wire was modelled using an isotropic material model, while the body and steel cord plies were modelled as rebars. The cavity, used to inflate the tire, included the pressure increase due to the volume change, when the tire is loaded. The numerical model was validated using experimental data from tests done on an actual tire. These tests included deformation and contact stress analysis, as well as surface temperature measurements. Numerical results showed an increase in temperature when the load, rolling velocity and the ambient temperature were increased, as well as when the inflation pressure was decreased. The trends of the numerical data matched the trends of the experimental data. However, the values of the numerical model were not consistent with the experimental data due to material properties from literature being used to model the tire. / AFRIKAANSE OPSOMMING: Rubber is die hoofkomponent in die pneumatiese band. As rubber onder ’n sikliese las geplaas word, soos wanneer ’n band rol, word hitte gegenereer en in die rubber gestoor as gevolg van histerese. Die hitte wat in die band gestoor word, word verhoog deur faktore soos lae inflasiedruk, hoë las, hoë rol snelhede en gebreke in die band. Die hitte veroorsaak hoë temperature in die band weens die swak termiese geleiding van rubber. As die temperatuur in die band hoër as 185 °C raak, vind piroliese en termo-oksidasie plaas en die band kan uiteindelik ontplof. ’n Numeriese model van ’n passasiersmotorband is ontwikkel om die temperatuurverspreiding te bepaal, asook om die effek van verskillende werkstoestande op die temperatuur te analiseer. Die band is gemodelleer met een tipe rubber en die Mooney-Rivlin materiaal-model is gebruik om die rubber te beskryf. Die spanrand van die band is deur ’n isotropiese materiaalmodel gemodelleer, terwyl die hoof- en staalkoordlae as bewapening gemodelleer is. Die holte wat gebruik word om die band op te blaas, neem die druk toename as gevolg van die verandering in volume in ag wanneer die band belas word. Die numeriese model was bekragtig met eksperimentele data wat deur toetse op ’n werklike band onttrek is. Die toetse sluit die volgende in: vervormingen kontakspanninganalises, asook temperature wat op die oppervlak van die band gemeet is. Die numeriese resultate toon ’n toename in temperatuur wanneer die las, rolsnelheid en omgewingstemperatuur verhoog word, asook waneer die inflasiedruk verlaag word. Die numeriese model se tendense stem ooreen met die eksperimentele data, maar die waardes van die numeriese model is nie in ooreenstemmig met die eksperimentele data nie. Die verskil is as gevolg van die materiaaleienskappe wat uit die literatuur geneem is.

Orientador: Jorge Luís Akasaki / Banca: Jefferson Sidney Camacho / Banca: Armando Lopes Moreno Júnior / Resumo: O presente trabalho tem como objetivo estudar algumas propriedades de concretos e argamassas, com substituição parcial do agregado miúdo por resíduos de borracha de pneus provenientes do processo de recauchutagem. Para todas as misturas foi utilizado o cimento CP V - ARI PLUS, areia e, para os concretos, brita basáltica. As substituições foram de 12% em volume do agregado miúdo por borracha para argamassa e 10% em volume para concreto. Em argamassa procurou-se verificar a influência do tratamento do resíduo de borracha com solução saturada de hidróxido de sódio. As propriedades estudadas foram: resistência à compressão, resistência à tração, absorção de água e índice de consistência. As propriedades analisadas em concreto à temperatura ambiente foram: resistência à compressão, absorção de água, resistência à tração, resistência à abrasão, módulo de elasticidade e resistência à flexão. Em concreto aquecido a 600ºC, avaliaram-se as propriedades de resistência à compressão e módulo de elasticidade. Os resultados obtidos em argamassas, após o tratamento do resíduo, mostram que este não influencia nas propriedades estudadas. Também é observado, após a substituição de parte do agregado pelo resíduo, queda na trabalhabilidade e nos resultados referentes à resistência mecânica. Os resultados de resistência à abrasão em concreto mostram-se interessantes para o uso da mistura em pavimentação. Após o aquecimento do concreto, observa-se redução na resistência à compressão e módulo de elasticidade para as misturas com e sem borracha. Também é observado que as relações de perda de resistência entre o concreto com e sem borracha são mantidas após o aquecimento. / Abstract: The aim of this work is to study some properties of mortars and concretes, whose fine aggregate was partially replaced by tire rubber from retreading process. It was used in all mixes CPV - ARI PLUS cement, river sand, and basaltic coarse aggregate. The replacement was made in volume of fine aggregate by tire rubber and it was 12% in mortars and 10% in concrete. The influence of the residue's treatment with a sodium hydroxide saturated solution was analyzed through tests in mortar. The studied properties were: compressive strength, splitting tensile strength, water absorption, and consistence index. The properties analyzed in concrete at room temperature were: compressive strength, splitting tensile strength, modulus of elasticity, and flexural tensile strength. The tests made at 600ºC heated concrete were compressive strength and modulus of elasticity. The results from mortars tests, after the rubber's treatment, show that it doesn't influence considerably the studied properties. It is also observed that after the replacement of part of the aggregate by tire rubber; there is a decrease in workability and mechanical tests results. The abrasion resistance tests results show that an interesting use to tire rubber concrete is in precast-concrete paving brick. It can be noted from the heated concrete results that compressive strength and modulus of elasticity decrease in mixes with and without tire rubber. It could be also seen that the relationship between concrete strength losses are kept after heating. / Mestre

The objective of this study is to integrate a continuum-based deformable tire and terrain interaction model into a general-use physics-based simulation environment capable of off-road vehicle mobility analysis and high-performance computing potential. Specifically, the physics-based deformable tire and terrain models which were recently proposed and validated by Yamashita, et al. will be implemented into the structure of the multi-physics simulation engine Chrono. In off-road vehicle mobility analysis, empirical and analytical models have been commonly used for vehicle-terrain interaction. While these models utilize experimental data or terramechanics theories to create quick predictive mobility models, they are unable to capture the highly nonlinear behavior of soft soil deformation, which can lead to inaccurate or unreliable results. In order to resolve these limitations, the use of physics-based numerical approaches have been proposed. These methods make use of finite element and discrete element simulations to describe the interaction between the vehicle and deformable terrain. Continuum-based finite element models transfer tire forces to the terrain and model the deformation with elasto-plastic constitutive models. Discrete element soil uses a large number of small rigid body particles to describe the microscale behavior of granular terrain, with the deformation of the soil represented by the motion and contact of the particles. While these physics-based models offer a more accurate vehicle-terrain interaction model, the solution procedure can become complex and computationally expensive since co-simulation techniques are often used. To address these issues, the analysis of physics-based full vehicle dynamics simulations utilizing high-fidelity deformable tire and terrain models in a multi-physics engine with high-performance computing capability is desired. To this end, a continuum mechanics based shear deformable laminated composite shell element proposed by Yamashita, et al. was integrated into the flexible body dynamics simulation framework of Chrono. This element was based on the absolute nodal coordinate formulation and is defined by the global position coordinates and the transverse gradient coordinates of its four nodes. Element lockings are eliminated with the incorporation of the enhanced assumed strain (EAS) and assumed natural strain approaches (ANS). The element formulation includes an extension to model laminated composite materials. Additionally, a locking-free 9-node brick element was integrated into the Chrono framework that makes use of the curvature coordinates at the center of the element. This element is formulated with the Hencky strain measure such that multiplicative finite strain plasticity theory can be used to incorporate soil plasticity models, such as the capped Drucker-Prager failed criterion. With the shear deformable laminated composite shell element and plastic soil brick element integrated into the Chrono multi-physics simulation engine, an off-road deformable tire and terrain interaction model was developed using the vehicle dynamics simulation module Chrono::Vehicle. An off-road deformable tire model was parameterized based on commercial tire properties and generated as an interchangeable tire model option in the full vehicle dynamics system. Benchmark verification tests were performed to ensure the accuracy of tire deformation and tire force characteristics. Further tests were performed to validate a deformable tire model with a deformable tread pattern constructed from shear deformable shell elements and co-rotational tetrahedral elements. The deformable soil model was also integrated as a terrain option in Chrono::Vehicle and numerical tests were carried out to demonstrate its interaction with rigid and deformable tire models. To make use of the computational performance enhancements available in Chrono, Open Multi-Processing (OpenMP) and Advanced Vector Extensions (AVX) were applied to the evaluation of the elastic force/Jacobian matrix and large matrix operations of flexible bodies, respectively, in order to reduce the computation time by nearly 60%.

<p>Vehicle simulators are becoming more common in vehicle industries. Company earns lot of money on simulations instead of real tests. Real tests are necessary but not made so extensively as before.</p><p>In this thesis the building of an vehice simulator will be described and a comparison between three different cruise controls. The three cruise controls are PI-regulator, a regulator who regulates after positions in the terrain and a MPC-regulator. The reason for choosing this three is to see the difference between simple regulation and more complex regulation with respect to fuel consumption, travel time and complexity.</p><p>The vehicle simulator is made in Matlab/Simulink, Visual Studio and Open Scene Graph. The facilities needed for runnning the simulator is a relative good computer with a grapics card on at least 128 MB RAM plus a steering wheel and pedals for brake and gas to achieve best feeling. A keyboard can be used but it reduces almost all feeling.</p><p>After several simulations a conclusion was made. The MPC-regulator was the regulator who consumed least fuel and travel time. The regulator who regulates after positions in the terrain was not too far away. It would be interesting to do more research about it. In fact it is only a PI-regulator who makes ``clever'' decisions when a hill with enough slope appears. With enough slope means a downhill where the vehicle can accelerate without the use of fuel and an uphill where the vehicle can not keep its speed with maximum use of fuel.</p><p>A conclusion was stated that the friction and height profile influenced on settings for the PI-regulator and with some adjustments on this settings, fuel could be saved.</p>

Tire bales have become an innovative and cost effective fill material that can be used for the construction of geotechnical structures, like embankments for highway projects. The mechanical and physical properties they present allow them to be suitable for this type of structures, as long as they are provided with an appropriate drainage system. Stability of these structures is controlled by the interface shear strength existing in the contact surfaces between the bales. However, the tire bale has a jagged, uneven and highly variable surface and it presents a number of irregular tire ridges with random dimensions that are difficult to quantify. Due to the flexibility of these ridges, deformation of the interface occurs when a horizontal shear load is applied, and following this deformation the actual displacement of the interface takes place. Freilich (2009) performed large scale tests in the field and in the laboratory to observe the behavior of the whole tire bale structure, which is composed of the tire bale mass and the tire bale interface. Due to the irregular and highly variable surface of the tire bale, the deformations that occur on the ridges along the interface cannot be directly measured and quantified. Following similar concepts of some rock mechanic models, Freilich characterized the tire ridge interface using three parameters and came up with a model. Using these parameters, an ideal interface was constructed where the variability was reduced by incorporating a known geometry, and it can still be characterized in the same manner as that for the tire bale interface. Loads, deformations and displacements occurring along the interface were measured and recorded. From this data, shear strength parameters are defined and incorporated into Freilich’s tire ridge interface model that is used to predict the geometric and mechanical behavior of the irregular ridges controlling the interface shear strength. The behavior predicted from the model is then compared to the recorded data representing the actual geometric and mechanical behavior of the interface with known geometry, where the deformations on the asperities are approximated. This comparison verifies that the consideration of the flexibility from the tire ridges is not entirely described by the tire ridge interface model. Therefore a possible modification, based on the observations recorded, could be found. / text

The first essay examines the relation between fund performance and stock selection process. I classify mutual funds into two groups according to their distinctive stock selection approaches: tire kickers who rely on fund managers' personal judgment and fundamental analysis to pick stocks, and quant jocks who use computer-based models to select stocks. I examine how the stock selection approach affects mutual fund performance and economies of scale. I document an increasing trend of quantitative techniques used by mutual funds, in addition to some unique characteristics of quant jocks. Quant jocks and tire kickers have similar factor-adjusted alphas, but quant jocks have higher Sharpe ratios. Quant jocks tend to be much smaller than tire kickers. I explore possible explanations for the size difference. I find that although quant jocks can cheaply screen a large universe of stocks, the stocks that quant jocks invest in are smaller and less liquid, which results in higher transaction costs and limited scalability of quantitative investment strategies. The second essay investigates mutual fund managers' private information about future stock returns as revealed in their portfolio holdings. Specifically, we develop three different stock alpha estimators to predict stock returns based on portfolio compositions and past performance of mutual funds. We find that investment strategies based on our stock alpha estimators perform well, when using information on recent fund holdings and fund purchases. This evidence suggests that fund managers' stock selection skills are quite persistent, and vary widely in the cross-section. We also compare our strategies with 12 quantitative investment signals based on market anomalies, and find that our strategies are not subsumed by these quantitative signals. Thus, our stock alpha estimators reflect private skills of active fund managers that are unrelated to known anomalies. Finally, we develop a conditional stock alpha estimator using information on stock characteristics and fund characteristics. Investment strategies based on the conditional stock alphas deliver further improved performance.