Sufficient heat dissipation is crucial to the effective operation of friction based braking systems. Such cooling is generally provided by ensuring a sufficient supply of cooling air to the heated components, hence the aerodynamics in the region of the brake components is extremely important. The objective of the research was to develop an understanding of how aerodynamics could be used to improve the cooling of automotive disc brakes. Two separate sets of wind tunnel experiments were developed. Tests were performed on a vented disc (rotor) to measure the internal flow through the vents on a rotating vented disc under various conditions, including an isolated disc in still air, the disc in still air with the wheel on, the disc in moving air with the wheel on, and an on-road simulation using a ¼ car. On vehicle tests were also performed in a wind tunnel using a purpose built brake test rig. These tests measured the thermal performance of different brake discs under various operating parameters; including constant load braking, and cooling from high temperature under various speeds, wheels and disc types. It was found that airflow through vented rotors was significantly reduced during simulated on-road driving, compared to when measured in isolation, but not particularly affected by the vehicles speed. In the situations tested, vented discs offered a 40+% improvement in cooling over an equivalent sized solid rotors. However the research indicates that the greatest benefit of vented rotors over solid will be in vehicles where air entering the wheel cavity is limited, such as low drag vehicles. It was also found that the most significant improvements in brake thermal performance could be achieved by maximising the airflow into the region of the brake components; including increasing the open area of the wheel, and increasing the vehicle velocity. Other improvements can be achieved by using a wheel material with good conductive capability, and increasing the mass of the disc. Evidence of vortex shedding was also discovered in the airflow at the exit of an internal vented rotor, any reduction in this flow disturbance should lead to increased airflow with associated improvements in thermal performance.

During braking, both the disc and pads in disc brakes are worn. Since disc brakes are not sealed,some of the wear particles generated can become airborne. Several studies have found anassociation between adverse health effects and the concentration of particles in the atmosphere,so it is of interest to improve our knowledge of the airborne wear particles generated by discbrakes. This thesis deals with experimental and computational methods focusing on airborne wearparticles from disc brakes. The eight appended papers discuss the possibility to both measure andnumerically determine the concentration and size distribution of airborne wear particles thatoriginate from the pad-to-disc contact. The objective is to increase the scientific knowledge ofairborne wear particles generated from disc brakes. Papers A, B and C describe tests of disc brake materials conducted in a modified pin-on-discmachine. The results show that the test set-up can be used to measure and rank disc brakematerials with respect to the concentration of airborne particles generated. Ultrafine (nanosized),fine and coarse airborne wear particles that contain metals such as iron, copper and tin werefound. Papers D and E describe a novel disc brake assembly test stand and tests of disc brake materialsconducted in it. The results show that the test set-up can be used to measure the concentrationand size distribution of airborne wear particles generated from disc brake materials. The resultsalso indicate an ability to rank different pad/disc combinations with respect to the concentrationof airborne wear particles. Furthermore, the results suggest that this test stand can be used tostudy rust layer removal from the disc and that airborne particles are generated even at low brakepressures, such as used to remove dirt from the disc. Paper F compares measurements made in passenger car field tests with measurements made in adisc brake assembly test stand and in a pin-on-disc machine. A promising correlation between thethree different test methods is found. Paper G presents and discusses a simulation methodology that numerically determines theconcentration and size distribution of airborne wear particles generated from the pad-to-disccontact in disc brakes by using general-purpose finite element software. Paper H discusses a cellular automaton model that describes the microscopic contact situationbetween the pad and disc in disc brakes. This model is used to numerically determine the amountof wear that leaves the contact. The results correlate qualitatively with experimental observationsfound in the literature. / QC 20110317

Hot spotting of automotive disc brakes is an undesired thermal localisation phenomenon, which is a challenge for numerical modelling in terms of both accuracy and efficiency especially for complex disc geometry. In this research, the aim was to develop a computationally efficient finite element (FE) approach for 2-piece pin-mounted ventilated disc hot spot prediction with acceptable accuracy enabling parametric studies to contribute to the knowledge of the complex mechanisms. A time reduction strategy for the simulations was established by incorporating an axisymmetric brake pad assumption with material scaling factor and the friction characteristics were defined by a user-subroutine. The computing accuracy and efficiency of this method were then verified by comparing with traditional FE models. 2D in-plane, 2D out-of-plane, and 3D models were performed to investigate the effects of ventilated disc hot spotting, radial hot spot/band migration, and hot spotting of realistic complex disc geometry respectively. Both 2D and 3D results were validated using experimental results based on a laboratory dynamometer and showed good correlation. The results suggested that adequate modelling of friction pair contact pressure distribution and the subsequent non-uniform heat generation is essential for hot spot simulation; speed was identified as the determinant for the number of hot spots, whereas hot spot temperature was determined by energy level. Furthermore, recommendations for vent design, pins, disc run-out, cooling, material selection, wear rate, pad length and loading distribution were given. Finally, hot spotting and hot band migration cause-effect chains were established based on the results and discussion. / Appendix 1 and Appendix 2 are unavailable online due to copyright restrictions.

This dissertation details the methods and analysis of extensive physical tests and simulation conducted by the Center for Vehicle Systems and Safety (CVeSS) at Virginia Tech on the maneuverability, roll-stability, and brake type performance of 33-ft double trailers. Little literature exists for 33-ft doubles because they are uncommon on the U.S. roads due to current federal restrictions limiting long-combination vehicles to 28-ft doubles. With the continual rise in e-commerce, however, there is a push by package carriers on legislation to permit carriers to introduce 33-ft doubles into their fleets. Three separate studies detailed herein highlight 33-ft double trailers' off-tracking, roll-stability with stability control systems, and brake type influence on braking performance. The first study compares low-speed off-tracking of a 33-ft double to 28-ft double and 53-ft single configurations via simulation and full-scale tests. Novel numerical tractrix models are introduced and compared to existing models commonly used to evaluate low-speed off-tracking of long combination vehicles (LCVs). Unlike pre-existing models, accuracy of one of the proposed models is largely unaffected by input path resolution and regularity—a significant benefit for reducing computational cost and easing implementation for many applications. Full-scale tests are conducted at Virginia Tech and an extensive uncertainty analysis is detailed for the test procedure and measurements. Field tests compare favorably with simulations for all tested maneuvers and trailer configurations and clearly demonstrate the order from least to most off-tracking as 28-ft double, 33-ft double, and 53-ft single. The 33-ft doubles have slightly larger off-tracking than 28-ft doubles, whereas 53-ft singles have substantially larger off-tracking than 28-ft and 33-ft doubles. The second study evaluates 33-ft double straight-rail trailers rollover propensity with different stability control system implementations: stock (none), tractor electronic stability control (ESC), trailer roll-stability control (RSC), and RSC+ESC. Extensive test vehicle instrumentation and structural reinforcement are detailed for the test preparations. Tests are conducted on a test track with either driver or robot steering. On their own, both ESC and RSC clearly reduce the rollover propensity of the trailers for all maneuvers, and the trailers exhibit the highest roll-stability when both RSC and ESC are active. The tested ESC and RSC modules are off-the-shelf products from industry suppliers chosen by the program sponsor. The third study compares trailer drum and disc brake performance in three conditions: straight-line braking distance, brake type influence on RSC performance, and roll dynamics in a combined braking and turning maneuver. A braking robot is designed, fabricated, and implemented to provide precise and repeatable brake pedal application. Test results suggest that disc brakes tend to provide reduced braking distance and are less susceptible to brake fade than drum brakes. Anti-lock braking system (ABS) and suspension dynamics react differently to the two brake types. Small, noticeable differences in RSC performance are evident between the two brake types. Within the test limitations, rollover dynamics were not clearly different between the two brake types for braking-in-turn maneuvers, performed for a large range of entry speeds and brake activation delay relative to the start of steering. / Doctor of Philosophy / Due to their large size, mass, and high center-of-gravity, heavy vehicles, especially long combination vehicles (LCVs) require a substantial amount of space to negotiate turns, long distances to brake from highway speeds to a stop and are susceptible to rollover. Combination vehicles on the U.S. roads are commonly in 53-ft single trailer or 28-ft double trailer configurations. With the continual rise of e-commerce, package carriers are pursuing 33-ft double trailers to increase each vehicle's cargo volume. Before introducing these trailers into a fleet, there is a need to understand (1) if 33-ft doubles can negotiate existing routes traveled by 28-ft double and 53-ft single configurations, (2) if 33-ft doubles can benefit from existing stability control systems, and (3) how trailer brake types perform on 33-ft doubles. Three separate studies are conducted to address these topics. The first study compares off-tracking for the three mentioned trailer configurations through low-speed, real-world maneuvers via physical full-scale tests and simulation. Off-tracking is a metric illustrative of maneuverability and is defined as the relative distance in paths of the rearmost axle to the lead steer axle. New mathematical models are introduced and used to simulate vehicle motion through low-speed maneuvers. The simulation and field tests determine that, for all tested maneuvers, the order from smallest to largest off-tracking is 28-ft double, 33-ft double, and 53-ft single configurations, with the 33-ft doubles having slightly larger off-tracking than 28-ft doubles. This suggests that 33-ft doubles can travel through routes typically traveled by a 53-ft single but need slightly more space on the road than a 28-ft double. The second study tests 33-ft double trailers with and without stability control systems. Tests, conducted at a test track, are designed to replicate real-world maneuvers that induce trailer rollover. It is found that the 33-ft double trailers are clearly less likely to rollover with the tested stability enhancement systems than without. The tests also illustrate that the different tested control systems' effectiveness in reducing rollover propensity is maneuver dependent. The third study tests the braking distance, brake influence on the stability control systems, and rollover dynamics while braking-in-turn for two different types of brakes, drum brakes and disc brakes. Small but evident differences in the performance of the two brake types suggest disc brakes could provide shorter stopping distance and time at highway speeds, compared with drum brakes. The studies detailed in this dissertation provide valuable information on 33-ft doubles dynamics and provide guidance for their safe introduction on the U.S. roadways.

Over the past decade vehicle judder caused by Disc Thickness Variation (DTV) has become of major concern to automobile manufacturers worldwide. Judder is usually perceived by the driver as minor to severe vibrations transferred through the chassis during braking [1-9]. In this research, DTV is investigated via the use of a Smart Brake Pad (SBP). The SBP is a tool that will enable engineers to better understand the processes which occur in the harsh and confined environment that exists between the brake pad and disc whilst braking. It is also a tool that will enable engineers to better understand the causes of DTV and stick-slip the initiators of low and high frequency vibration in motor vehicle brakes. Furthermore, the technology can equally be used to solve many other still remaining mysteries in automotive, aerospace, rail or anywhere where two surfaces may come in contact. The SBP consists of sensors embedded into an automotive brake pad enabling it to measure pressure between the brake pad and disc whilst braking. The two sensor technologies investigated were Thick Film (TF) and Fibre Optic (FO) technologies. Each type was tested individually using a Material Testing System (MTS) at room and elevated temperatures. The chosen SBP was then successfully tested in simulated driving conditions. A preliminary mathematical model was developed and tested for the TF sensor and a novel Finite Element Analysis (FEA) model for the FO sensor. A new method called the Total Expected Error (TEE) method was also developed to simplify the sensor specification process to ensure consistent comparisons are made between sensors. Most importantly, our achievement will lead to improved comfort levels for the motorist.

AN ABSTRACT OF THE DISSERTATION OF TITLE: (OPTIMIZATION PROTECTION OF CARBOB-CARBON COMPOSITES DISC-BRAKES MATERIAL BY COATING WITH ANTI-OXIDANTS) Developing glass enhancer mixture solutions (Ki’s), which promote the formation of a stable glass layer, homogenous clear liquid solution, and low viscosity liquid form, are easy to apply, and penetrating. They are compatible with ceramic liquid glass based anti-oxidants for treating surfaces of carbon/carbon composites material, and significantly increase the rate of protection against oxidation. Ki’s’ are comprised of mixing chemical compositions at standard temperature and pressure conditions from group one and two such as Na, K, Ca, Mg, etc. of 5 to 25 wt. %, deionized water from 95 to 75 % by weight, and adding up to 1 % by weight of surfactants such as DF-16, DF-20, and CF-10 with specific proportions, and followed by thorough stirring to produce a homogeneous blend of mixture solution. The glass enhancers, which are aqueous mixture solutions, are applied to the surfaces of carbon/carbon (C/C) composites by dipping, brushing, spraying, or other painting application techniques, followed by annealing, or a heat-treating range of 80 to 110 ℃ for a minimum of 8 hours, and allowing cooling time of the coated C/C composites of a minimum of 12 hours to room temperature. Preferential compatibility of the glass enhancer mixture solutions (Ki's) is with liquid glass former's, anti-oxidants comprised mostly of borate and phosphate glasses. The glass enhancer solution mixtures (Ki’s) are supplemental additions to ceramics’ liquid anti-oxidants coatings used for carbon-carbon composites protection against oxidation, and it will increase the rate of protection against oxidation for low, and moderate temperature’s range from 400 to 900 ℃. The glass enhancer Ki’s mixture solutions should be used with liquid glass former's’ anti-oxidants, such as SiO₂, GeO₂, B₂O₃, and P₂O₅. A series of glass enhancer’s Ki’s, heat treatment cycle (char-cycle) ranged between 700 to 900 ℃, and application methods, were developed and tested experimentally. Two arbitrary isothermal temperatures of 650 ℃, and 871 ℃ were selected for thermal oxidation testing, and a temperature of 650 ℃ was selected, and tested against catalytic thermal oxidation. Additions of glass enhancer Ki’s improved protection of C/C composites disc-brakes against oxidation by double, and triple amount of time in hours versus the use of anti-oxidant coatings alone.