Tire parameters play a very important role in tire performance. Depending on the driving conditions for which a given tire is designed, its parameters must be chosen appropriately (e.g., the radius of the tire, the width of the tire, material properties of different sections). Among tire characteristics, the material properties of the rubber compounds have a vital role in tire behavior. Previous studies show that the material properties of the rubber are highly dependent on temperature. Thus, a comprehensive study on the effect of the material properties of the rubber on tire performance for different temperatures as well as different road conditions is required. In this study, a theoretical model has been developed for tire-ice interaction. The temperature changes obtained from the model are used to calculate the height of the water film created by the heat generated due to the friction force. Next, the viscous friction coefficient at the contact patch is obtained. By using the thermal balance equation at the contact patch, dry friction is obtained. Knowing the friction coefficients for the dry and wet regions, the equivalent friction coefficient is calculated. The model has been validated using experimental results for three similar tires with different rubber compounds properties. For the experimental part of this study, four tires have been selected for testing. Three of them have identical tire geometry and structure but different rubber tread compounds. Several tests were conducted for the chosen tires in three modes: free-rolling, braking, and traction. The tests were performed for two different normal loads (4 kN and 5.6 kN), two different inflation pressures (21 psi (144.8 kPa) and 28 psi (193 kPa)), and three tire temperatures levels (-10°C, -5°C, and -1 °C). The Terramechanics Rig at TMVS at Virginia Tech has been used for conducting the tests. The results from this study show the sensitivity of the magnitude of the tractive force with respect to parameters such as tire temperature, normal load, etc. The results also indicate that the tire with the lowest value of the Young modulus has the highest traction among all four tires used in this study. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal loads, etc. The results from this study coincide with the obtained results from the experiments. According to the data available, tire B with the smallest value of Young modulus and the smallest value of the specific heat parameter was shown to have the highest friction coefficient in both simulation and experiment. After validating the results using experimentally collected data, the model was used to perform a sensitivity analysis on the tire performance with respect to six material properties of the tread rubber: thermal conductivity, rubber density, Young's modulus, specific heat, roughness parameter of the rubber, and radii of spherical asperities of the rubber. The results from this study show the sensitivity of the magnitude of the friction coefficient to the rubber material properties. The friction coefficient has a direct relationship with the density of the rubber and has an inverse relationship with Young's modulus, specific heat, and roughness parameter. / Doctor of Philosophy / In order to decrease the number of deaths and injuries caused by driving on icy roads and increase the safety of the vehicle, it is important to improve the tire performance on ice. To this, understanding the effects of different tire and road parameters such as material properties of the rubber, loading condition, and temperature on the tire-ice performance is required. Tire parameters play a very important role in tire performance. Depending on the driving conditions for which a given tire is designed, its parameters must be chosen appropriately In this project, the effects of different tire and terrain parameters such as rubber material properties on tire performance on ice using an experimental and modeling approach have been studied. For the experimental part of this study, several tests were conducted for more than 30 tires with different material properties. The results of this study show what are the most important material properties of the rubber for designing a tire with the best performance on ice. For the modeling part of this study, a semi-analytical model was developed. The model was validated using collected experimental data and was used to predict the performance of the tire by having information about its material and physical properties. The developed model called ATIIM2.0 has several advantages. First, it is a unique model for a complete tire (not a rubber block) that can be used to predict the performance of the tire by using its material properties. In addition, this model can be connected to vehicle models to improve the performance of the vehicle in general. The model developed can be used to predict the temperature changes at the contact patch, the tire friction force, the areas of wet and dry regions, the height of the water film for different ice temperatures, different normal loads, etc. The results from this study coincide with the obtained results from the experiments.

Tire performance over soft soil influences the performance of off-road vehicles on soft soil, as the tire is the only force transmitting element between the off-road vehicles and soil during the vehicle operation. One aspect of the tire performance over soft soil is the tire tractive performance on soft soil, and it attracts the attention of vehicle and geotechnical engineers. The vehicle engineer is interested in the tire tractive performance on soft soil because it is related to vehicle mobility and energy efficiency; the geotechnical engineer is concerned about the soil compaction, brought about by the tire traffic, which accompanies the tire tractive performance on soft soil. In order to improve the vehicle mobility and energy efficiency over soft soil and mitigate the soil compaction, it's essential to develop an in-depth understanding of tire tractive performance on soft soil. This study has enhanced the understanding of tire tractive performance on soft soil and promoted the development of terramechanics and tire model parameterization method through experimental tests. The experimental tests consisted of static tire deflection tests, static tire-soil tests, soil properties tests, and dynamic tire-soil tests. The series of tests (test program) presented herein produced parameterization and validation data that can be used in tire off-road traction dynamics modeling and terramechanics modeling. The 225/60R16 97S Uniroyal (Michelin) Standard Reference Test Tire (SRTT) and loamy sand were chosen to be studied in the test program. The tests included the quantification or/and measurement of soil properties of the test soil, pre-traffic soil condition, the pressure distribution in the tire contact patch, tire off-road tractive performance, and post-traffic soil compaction. The influence of operational parameters, e.g., tire inflation pressure, tire normal load, tire slip ratio, initial soil compaction, or the number of passes, on the measurement data of tire performance parameters or soil response parameters was also analyzed. New methods of the rolling radius estimation for a tire on soft soil and of the 3-D rut reconstruction were developed. A multi-pass effect phenomenon, different from any previously observed phenomenon in the available existing literature, was discovered. The test data was fed into optimization programs for the parameterization of the Bekker's model, a modified Bekker's model, the Magic Formula tire model, and a bulk density estimation model. The modified Bekker's model accounts for the slip sinkage effect which the original Bekker's pressure-sinkage model doesn't. The Magic Formula tire model was adapted to account for the combined influence of tire inflation pressure and initial soil compaction on the tire tractive performance and validated by the test data. The parameterization methods presented herein are new effective terramechanics model parameterization methods, can capture tire-soil interaction which the conventional parameterization methods such as the plate-sinkage test and shear test (not using a tire as the shear tool) cannot sufficiently, and hence can be used to develop tire off-road dynamics models that are heavily based on terramechanics models. This study has been partially supported by the U.S. Army Engineer Research and Development Center (ERDC) and by the Terramechanics, Multibody, and Vehicle (TMVS) Laboratory at Virginia Tech. / Doctor of Philosophy / Big differences exist between a tire moving in on-road conditions, such as asphalt lanes, and a tire moving in off-road conditions, such as soft soil. For example, for passenger cars commonly driven on asphalt lanes, normally, the tire inflation pressure is suggested to be between 30 and 35 psi; very low inflation pressure is also not suggested. By contrast, for off-road vehicles operated on soft soil, low inflation pressure is recommended for their tires; the inflation pressure of a tractor tire can be as low as 12 psi, for the sake of low post-traffic soil compaction and better tire traction. Besides, unlike the research on tire on-road dynamics, the research on off-road dynamics is still immature, while the physics behind the off-road dynamics could be more complex than the on-road dynamics. In this dissertation, experimental tests were completed to study the factors influencing tire tractive performance and soil behavior, and model parameterization methods were developed for a better prediction of tire off-road dynamics models. Tire or vehicle manufacturers can use the research results or methods presented in this dissertation to offer suggestions for the tire or vehicle operation on soft soil in order to maximize the tractive performance and minimize the post-traffic soil compaction.

Noise and vibration transmitted through the tire and suspension system are strong indicators of overall vehicle ride quality. Often, during the tire design process, target specifications are used to achieve the desired ride performance. To validate the design, subjective evaluations are performed by expert drivers. These evaluations are usually done on a test track and are both quite expensive and time consuming due to the several experimental sets of tires that must be manufactured, installed, and then tested on the target vehicle. In order to evaluate the performance, expert drivers tune themselves to the frequency response of the tire/vehicle combination. Provided the right models exist, this evaluation can also be achieved in a laboratory. The research presented here is a method which utilizes the principles of frequency based substructuring (FBS) to separate or combine frequency response data for the tire and suspension. This method allows for the possibility of combining high fidelity tire models with analytical or experimental suspension data in order to obtain an overall response of the combined system without requiring an experimental setup or comprehensive simulations. Though high fidelity models are not combined with experimental data in the present work, these coupling/decoupling techniques are applied independently to several quarter car models of varying complexity and to experimental data. These models range from a simplified spring-mass model to a generalized 3D model including rotation. Further, decoupling techniques were applied to simulations of a rigid ring tire model, which allows for inclusion of nonlinearities present in the tire subsystem and provides meaningful information for a loaded tire. By reducing the need for time consuming simulations and experiments, this research has the potential to significantly reduce the time and cost associated with tire design for ride performance. In order to validate the process experimentally, a small-scale quarter car test rig was developed. This novel setup was specifically designed for the challenges associated with the testing necessary to apply FBS techniques to the tire and suspension systems. The small-scale quarter car system was then used to validate both the models and the testing processes unique to this application. By validating the coupling/decoupling process for the first time on the tire/vehicle system with experimental data, this research can potentially improve the current process of tire design for ride performance. / Ph. D. / Noise and vibration transmitted through the tire and suspension system of a vehicle strongly influence the comfort of passengers. Often, during the tire design process, target specifications are used to achieve the desired vibrational characteristics. Subjective evaluations are then performed by expert drivers in order to validate the tire design. These evaluations are usually done on a test track and are both quite expensive and time consuming due to the several experimental sets of tires that must be manufactured, installed, then tested on the target vehicle. The research presented here utilizes techniques from the field of Dynamic Substructuring which allow frequency data for the tire and suspension systems to be separated or combined. This method allows for the possibility of combining high fidelity tire models with analytical or experimental suspension data in order to obtain an overall response of the combined system without requiring an experimental setup or comprehensive simulations. Several analytical tire and suspension models were developed for this work and the process of separating/combining the frequency data was performed. Then, a small scale test system was developed and used to establish experimental procedures to collect the data necessary to carry out the Dynamic Substructuring techniques. Finally, the process was validated by repeating the process of separating/combing the frequency properties of the experimental data.

A thermal catalytic decomposition process has been developed to recycle used tire rubber. This process enables the recovery of useful products, such as hydrocarbons and carbon blacks. During the catalytic decomposition process, the tire rubber is decomposed into smaller hydrocarbons, which are collected in the process. The solid reaction residue, which normally consists of carbon black, catalysts, other inorganic rubber compound components, and organic carbonaceous deposits, was subjected to a series of treatments with the intention to recover the valuable carbon black and catalyst. The process economics depend strongly on the commercial value of the recovered carbon black and the ability to recover and recycle the catalysts used in the process. Some of the important properties of the recovered carbon black product have been characterized and compared with that of commercial-grade carbon blacks. The composition of the recovered carbon black was analyzed by TGA and EDX, the structure and morphology were studied through transmission electron microscopy (TEM), and the specific surface area was measured by BET nitrogen adsorption. The recovered products possess qualities at least comparable to (or even better than) that of the commercial-grade carbon black N660. Methods for increasing the market value of this recovered carbon black product are discussed. Anhydrous aluminum chloride (AlCl3) was used as the primary catalyst in the process. A catalyst recovery method based on the AlCl3 sublimation and recondensation was studied and found to be non-feasible. It is believed that the catalyst forms an organometallic complex with the decomposed hydrocarbons, such that it becomes chemically bonded to the residue material and hence not removable by evaporation. A scheme for the further study of the catalyst recovery is suggested.

This thesis investigates the stress inside Retroreflective Raised Pavement Markers (RRPMs) under tire-marker impact and laboratory testing scenarios. Many RRPMs have poor durability although they meet certain standards of the existing laboratory tests. It has been suspected that the current testing procedures might not be adequate to decide the field performance of RRPMs. Thus, it is necessary to evaluate the existing laboratory testing procedures and develop additional ones that could simulate the field performance of RRPMs more accurately. The tire-marker impact on rigid and flexible pavement will be investigated to identify the critical locations and magnitudes of stress inside markers during the impact. Various external factors, such as tire loading, tire speed, contact angle and contact location, might have effects on the stress inside markers during the impact and be considered as critical factors when developing a laboratory test. On the other hand, RRPMs have different profiles in terms of height, lens slope, and size etc, which affect the structure and field performance as well. The study explores the stress inside markers during the impact by varying the external factors and marker profile. In addition, the interface forces between RRPMs and pavement surface will be studied. Furthermore, the tire-marker impact simulation on rigid and flexible pavement will be compared so that specific testing procedures can be distinguished based on pavement type. Finally, the existing laboratory tests will be examined and additional tests be recommended based on the tire-marker impact analysis. The researcher found that the critical compressive stress is produced at the top edges of the markers on both types of pavement, while the patterns of critical tensile stress can be different between the two types of pavement. In addition, tire loading and contact location were determined to have effect on the stress inside the markers. Furthermore, different loading rates should be used in laboratory test based on pavement type. Finally, the researcher evaluated four laboratory tests and found that each test has its merit but none of them can test RRPMs comprehensively, so it is recommended that the four tests are used together to test RRPMs.

A thermal catalytic decomposition process has been developed to recycle used tire rubber. This process enables the recovery of useful products, such as hydrocarbons and carbon blacks. During the catalytic decomposition process, the tire rubber is decomposed into smaller hydrocarbons, which are collected in the process. The solid reaction residue, which normally consists of carbon black, catalysts, other inorganic rubber compound components, and organic carbonaceous deposits, was subjected to a series of treatments with the intention to recover the valuable carbon black and catalyst. The process economics depend strongly on the commercial value of the recovered carbon black and the ability to recover and recycle the catalysts used in the process. Some of the important properties of the recovered carbon black product have been characterized and compared with that of commercial-grade carbon blacks. The composition of the recovered carbon black was analyzed by TGA and EDX, the structure and morphology were studied through transmission electron microscopy (TEM), and the specific surface area was measured by BET nitrogen adsorption. The recovered products possess qualities at least comparable to (or even better than) that of the commercial-grade carbon black N660. Methods for increasing the market value of this recovered carbon black product are discussed. Anhydrous aluminum chloride (AlCl3) was used as the primary catalyst in the process. A catalyst recovery method based on the AlCl3 sublimation and recondensation was studied and found to be non-feasible. It is believed that the catalyst forms an organometallic complex with the decomposed hydrocarbons, such that it becomes chemically bonded to the residue material and hence not removable by evaporation. A scheme for the further study of the catalyst recovery is suggested.

Roads in many northern climates like Saskatchewan can undergo structural failure caused by frost action and substructure moisture problems. Frost action can be efficiently controlled by eliminating at least one of the following conditions: moisture; freezing temperatures; and frost susceptible soils. However, effective use of shredded tire material could provide an environmentally sustainable solution for waste tires and could relieve pressure on limited quality aggregate resources. The City of Saskatoon has successfully incorporated crushed rock and crushed recycled concrete as a subsurface road drainage layer to mitigate substructure drainage and frost issues. However, the price of crushed high value aggregates can be cost prohibitive and at times these materials are not available in quantities required. Previous research has documented that shredded tires are efficient in controlling frost action by providing thermal insulation and free drainage, but shredded tires performed poorly as a structural support layer with low mechanical stiffness and high compressibility properties. The goal of this research was to provide improved pavement performance with respect to road substructure moisture drainage and frost mitigation. The specific objectives of this research were to: • Quantify the mechanical properties of shredded tires and investigate the mechanical behavior of mixes of shredded tires with and without sand blended into the tire matrix as compared to conventional subbase and base coarse materials; • Determine the permeability of shredded tires and investigate the effect of sand on the permeability of shredded tire/sand mixes as compared to conventional granular base and subbase materials, and; • Compare the structural primary response behavior and capital cost of alternate road structures constructed with shredded tires and mixes of shredded tire and sand as a free draining subbase material compared to conventional drainage layers and road structures. The hypothesis of this research was that the mechanical behavior of shredded tire material, used as a road substructure layer, can be improved by blending it with free draining sand. It was also hypothesized that blending shredded tire with free draining sand will have improved drainage compared to conventional granular subbase and base course materials. Volumetric and mechanistic material properties and structural performance behavior of shredded tires and shredded tire/sand mixes in the mix ratios (by volume) of 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand were evaluated and compared to City of Saskatoon subbase materials: crushed rock and granular base; as well as Saskatchewan Ministry of Highways and Infrastructure (SMHI) Type 6 subbase. Laboratory characterization showed that 100% shredded tire materials were uniformly graded indicating high amounts of voids. The addition of sand resulted in a reduction of interparticle air voids. Results from strength and stiffness characterization tests indicated that 100% shredded tires exhibited low structural stiffness, but this behavior was improved as the quantity of sand in the shredded tire was increased. The 100% shredded tire material was determined to have a dynamic modulus value of 5MPa, whereas shredded tires/sand blends at the ratios of 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand gave dynamic moduli values of 30MPa, 110 MPa and 158MPa, respectively. For comparison, SMHI Type 6 subbase, City of Saskatoon crushed rock and granular base exhibited dynamic moduli values of 94MPa, 174MPa and 471MPa, respectively. Permeability characterization indicated that the 100% shredded tire materials were free draining at 1.42cm/s. Permeability decreased from 1.42cm/s with 100% shredded tire to 0.0026cm/s with 1Tire:3Sand. However, the shredded tire/sand mixes maintained permeability values higher than sand (0.0013cm/s). SMHI Type 6 subbase and granular materials were found to have a permeability of 0.0018cm/s and 0.000025cm/s, respectively, while crushed rock was free draining with a permeability of 1.12cm/s. Structural behavior of 100% shredded tire, shredded tire/sand mixes and City of Saskatoon subbase materials were studied in road models using a 3-D numerical road modeling software that encoded triaxial material constitutive relationships determined in this research. A typical City of Saskatoon road structure was assumed for all road structures considered in this study with varying subbase material so as to directly compare the structural effect of the shredded tire with conventional road materials under primary load limits. Modeled results of the 100% shredded tire and crushed rock roads showed peak surface deflections of 2.19mm and 0.73mm, respectively. Peak surface deflection under primary load limits was found to decrease with an increase in sand quantity within the shredded tire layer. Based on the modeling results, 1Tire:2Sand and 1Tire:3Sand yielded peak surface deflections of 1.01mm and 0.96mm, respectively. For comparative purposes, road structures with SMHI Type 6 subbase deflected at 1.14mm. Field test sections were constructed at Adolph Way in Saskatoon to compare the structural performance of shredded tire to crushed rock (currently specified by City of Saskatoon for drainage layers) in a typical residential road in Saskatoon. Unfortunately, both crushed rock (control) and shredded tire sections were found to deflect above acceptable limits due to high moisture conditions within the deep subgrade. Therefore, deeper excavation was required and the test sections were not constructed. The Adolph Way field experimentation of shredded tire showed that shredded tire road systems can be effectively constructed in the field, but showed the same sensitivity to poor subgrade conditions as crushed rock. Capital cost analysis showed the 100% shredded tire and shredded tire/sand subbase layers to be less expensive than City of Saskatoon specified crushed rock drainage layers. The 100% shredded tire layer was estimated at a total cost of $2.93/m2 while 1Tire:1Sand, 1Tire:2Sand and 1Tire:3Sand were estimated at $4.39/m2, $4.88/m2 and $5.12/m2, respectively. SMHI Type 6 subbase, crushed rock and granular base layers were estimated at a total cost of $5.85/m2, $13.95/m2 and $9.00/m2, respectively for equivalent thickness. From the structural, permeability and economic perspective of this research, the 1Tire:2Sand and 1Tire:3Sand materials proved to be cost efficient as well as technically viable options for mitigating frost action as compared with City of Saskatoon crushed rock materials evaluated. The use of shredded tire/sand mixes of 1Tire:2Sand and 1Tire:3Sand in urban local road structures with low traffic volumes are therefore recommended as a cost effective subbase drainage layer material.

The vertical force generated from terrain-tire interaction has long been of interest for vehicle dynamic simulations and chassis development. As the terrain serves as the main excitation to the suspension system through pneumatic tire, proper terrain and tire models are required to produce reliable vehicle response. Due to the high complexity of the tire structure and the immense size of a high fidelity terrain profile, it is not efficient to calculate the terrain-tire interaction at every location. The use of a simpler tire model (e.g. point follower tire model) and a pre-filtered terrain profile as equivalent input will considerably reduce the simulation time. The desired produced responses would be nearly identical to the ones using a complex tire model and unfiltered terrain, with a significant computational efficiency improvement. In this work, a terrain pre-filtering technique is developed to improve simulation efficiency while still providing reliable load prediction. The work is divided into three parts. First a stochastic gridding method is developed to include the measurement uncertainties in the gridded terrain profile used as input to the vehicle simulation. The obtained uniformly spaced terrain is considered probabilistic, with a series of gridding nodes with heights represented by random variables. Next, a constraint mode tire model is proposed to emulate the tire radial displacement and the corresponding force given the terrain excitation. Finally, based on the constraint mode tire model, the pre-filtering technique is developed. At each location along the tire's path, the tire center height is adjusted until the spindle load reaches a pre-designated constant load. The resultant tire center trajectory is the pre-filtered terrain profile and serves as an equivalent input to the simple tire model. The vehicle response produced by using the pre-filtered terrain profile and the simple tire model is analyzed for accuracy assessment. The computational efficiency improvement is also examined. The effectiveness of the pre-filtering technique is validated on probabilistic terrain by using different realizations of terrain profiles. It is shown through multiple profiles that the computational efficiency can be improved by three orders of magnitude with no statistically significant change in resulting loading. / Ph. D.

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