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We present computational thermo-fluid analysis of a disk brake, including thermo-fluid analysis of the flow around the brake and heat conduction analysis of the disk. The computational challenges include proper representation of the small-scale thermo-fluid behavior, high-resolution representation of the thermo-fluid boundary layers near the spinning solid surfaces, and bringing the heat transfer coefficient (HTC) calculated in the thermo-fluid analysis of the flow to the heat conduction analysis of the spinning disk. The disk brake model used in the analysis closely represents the actual configuration, and this adds to the computational challenges. The components of the method we have developed for computational analysis of the class of problems with these types of challenges include the Space-Time Variational Multiscale method for coupled incompressible flow and thermal transport, ST Slip Interface method for high-resolution representation of the thermo-fluid boundary layers near spinning solid surfaces, and a set of projection methods for different parts of the disk to bring the HTC calculated in the thermo-fluid analysis. With the HTC coming from the thermo-fluid analysis of the flow around the brake, we do the heat conduction analysis of the disk, from the start of the breaking until the disk spinning stops, demonstrating how the method developed works in computational analysis of this complex and challenging problem. [ABSTRACT FROM AUTHOR]

Self-excited vibrations are observed in many technical applications. Frictional contacts are often involved in the mechanism which generates vibrations. Reasons for the excitation mechanisms are decreasing friction characteristics depending on the sliding velocity, fluctuating normal loads or different geometrical effects. First, the mechanisms are explained using simple examples. The practical relevance of self-excited, friction-induced vibrations is exemplified with three technical systems: a system with an axial seal; a tread block of a tyre; and a disc brake.The knowledge of the excitation mechanism is necessary to introduce successfully design countermeasures. These measures to avoid self-excited vibrations are important to solve practical problems. They are the main focus of this work. Further, additional passive and active subsystems are described and validated experimentally. Therefore, a large range of design, active and passive solutions are given. [ABSTRACT FROM AUTHOR]

Carbon-carbon composites (CCCs) have extremely high thermal stability and shock resistance and find use in aerospace applications and aircraft disk brakes. The processing of CCCs can be divided into three stages: curing of precursor resin/fiber-reinforced-laminate; carbonization; and densification. During carbonization, the precursor resin (such as phenolic and furfuryl alcohol) develops microcracks and oftentimes delaminations, which reduce the mechanical properties of the material. In this study, we investigated the influence of carbon nanofibers (CNFs) when mixed with phenolic matrix precursor on the microstructure and interlaminar shear strength (ILSS) of the ascured and carbonized composite specimens. CNFs offer low cost benefits, unlike traditional carbon nanotubes (CNTs) that tend to be expensive. Different loadings (0%, 2%, and 5% weight/weight of resin) of CNFs, in conjunction with various percentages of surfactant (0%, 12.5%, and 50% by weight of acetone) treated carbon fabric reinforcement were used for the study. The rationale for treating the fabric with surfactant was to vary interfacial conditions of reinforcing fiber-CNF-matrix. This paper outlines the work done in the processing of CCC-CNF composites, and the influence of surfactant and various percentages of CNFs on the resulting microstructure and ILSS properties. The use of CNFs provided a bridging mechanism for matrix microcracking and reducing matrix shrinkage that occurs during first carbonization. Porosity and delaminations were found to increase with increase in surfactant treatment. An inverse relationship was observed between ILSS and porosity. At the as-cured and carbonized stages, an optimal value of 2% CNFs yielded the highest ILSS values of ∼40 MPa and 6 MPa respectively. [ABSTRACT FROM AUTHOR]

Abstract: Friction-induced vibrations are a major concern in a wide variety of mechanical systems. This is especially the case in aircraft braking systems where the problem of unstable vibrations in disk brakes has been studied by a number of researchers. Solving potential vibration problems requires experimental and theoretical approaches. A non-linear model for the analysis of mode aircraft brake whirl is presented and developed based on experimental observations. The non-linear contact between the rotors and the stators, and mechanisms between components of the brake system are considered. Stability is analyzed by determining the eigenvalues of the Jacobian matrix of the linearized system at the equilibrium point. Linear stability theory is applied in order to determine the effect of system parameters on stability. [Copyright &y& Elsevier]

This paper presents a two degree of freedom model for disk brake systems that makes use of the concept of a friction layer-based coupling stiffness. This model is then used to investigate noise and vibration, especially high-frequency squeal. It is shown that for automotive brake systems, the friction layer plays a significant role in the performance characteristics. Hence, the coupling stiffness between the brake pad and the rotor is modelled as a combination of the elastic stiffness of the friction layer superimposed on the coupling modal stiffness of the brake-pad combination. The elastic properties of the friction layer are obtained from nano-indentor tests and the contact area is approximated using light microscopy and scanning electron microscopy analysis. The coupling modal stiffnesses are obtained from impact tests and finite element studies. Preliminary results from the model are consistent with the actual high squeal data collected from the field. The main objective of this work is to introduce a new way of modelling the coupling stiffness based on the properties of the friction layer, which has not been extensively studied till now. [ABSTRACT FROM AUTHOR]

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A transient analysis for thermoelastic contact problem of disk brakes with frictional heat generation is performed using the finite element method. To analyze the thermoelastic phenomenon occurring in disk brakes, the coupled heat conduction and elastic equations are solved with contact problems. The numerical simulation for the thermoelastic behavior of disk brake is obtained in the repeated brake condition. The computational results are presented for the distributions of pressure and temperature on each friction surface between the contacting bodies. Also, thermoelastic instability (TEI) phenomenon (the unstable growth of contact pressure and temperature) is investigated in the present study, and the influence of the material properties on the thermoelastic behaviors (the maximum temperature and contact ratio on the friction surfaces) is investigated to facilitate the conceptual design of the disk brake system. Based on these numerical results, the thermoelastic behaviors of the carbon–carbon composites with excellent mechanical and thermal properties are also discussed. [Copyright &y& Elsevier]

The geometrical characteristics and morphology of wear particles generated from brake materials are important for environmental and tribological reasons. Low- and high-speed, pin-on-disk friction and wear testing of a commercial truck brake pad material against cast iron was conducted in which wear debris was collected. The sliding speed was held constant either at 0.275 or at 5 m/s, and the nominal contact pressure was varied between 0.125 and 1.25 MPa in room temperature air. In low-speed experiments, some tests were conducted with the pin in continuous sliding contact and others in which the pin specimen was raised and lowered periodically. Laser scattering examination of wear debris revealed two distinct peaks in the plot of frequency versus the mean particle size. The first peak occurs around 350 nm and does not vary with respect to the pressure and the sliding speed. The location of the second peak varies between 2 and 15 μm, depending on the pressure and the sliding speed. Energy dispersive X-ray (EDX) analysis of wear particles revealed particles having a high concentration of carbon, silicon, aluminum, iron, oxygen, molybdenum, and sulfur. It was also found that the continuity or discontinuity of sliding contact affects the size distribution of wear particles. In general, when the motion was discontinuous, as is the case in a repeated braking action, smaller wear particles are generated. [Copyright &y& Elsevier]