No abstract

The principle energy exchange of a brake system occurs in the tribological boundary layer between the pad and the disc. The associated phenomena are primarily responsible for the dynamics of brake systems. The wear debris forms flat contact structures, or "patches," which carry the majority of the normal load in the system and are highly influential on the friction behavior of the system. A new simulation tool is presented, which is capable of rapidly performing simulations of the contact between an entire brake pad and disc. The "Abstract Cellular Automaton" simulations accurately model the patch coverage state of a brake pad surface based on the system's load history. This can be used to simulate the complex dissipation phenomena within the tribological contact of the entire pad, including time-dependent local friction coefficients, wear and wear debris transport, and vibrational effects on highly differing scales.

The complex processes involved in the dry friction between two bodies are not yet fully understood. Towards an improved understanding of the associated tribological phenomena, the authors combine their skills and expertise in the respective fields of tribological experimentation, modeling, and simulation, as well as topological and chemical surface analyses. The aim of this research is more accurate predictions of the tribological behavior of minimal friction material mixtures. In order to improve the technical understanding of high-load tribological contacts (in which wear debris significantly influences the contact situation), a great volume and variety of research is necessary. The authors have devised a "vertically integrated" research approach towards addressing the myriad interdependent phenomena associated with such investigations. MethodsThe authors at the Institute of Dynamics and Vibrations have made several contributions towards the understanding of highload tribological contacts. For example, they have advanced the understanding of the influence of "patch dynamics" on the tribological behavior of high-load tribological contacts. They have also developed dynamic models of the coefficient of friction, which are capable of accurately representing complex behavior using simple mathematics [1]. They have developed various cellular automata towards the precise computation of tribological effects in a realistic 3-D model of a friction material mixture, and also towards efficiently simulating the tribological contact between a full-scale brake pad and disc [2].Multiple tribometers have been developed at the Institute of Dynamics and Vibrations which are capable of investigating high-load tribological contacts. These devices precisely measure the input and reaction forces very close to the tribological contact. Many other quantities are also measured, such as the temperatures of the two friction bodies, acoustic signals, and environmental conditions. An example of resulting friction and temperature measurements is shown in Figure 1. Furthermore, one of the tribometers is equipped with a built-in topography measurement station. Using this, quasi in situ photographs and measurements of the friction material's topography can be automatically made throughout the measurement procedure [3].The Institute of Surface Technology has performed various types of investigations into tribological systems, with a focus on surface technology and tribochemistry. They have developed methods for actively adjusting the friction and wear behavior of tribological contacts through the use of various coatings and thermal treatments, and analyzed the results based on the chemical composition of the associated surfaces [4]. By optimizing plasma nitriding treatments, they have improved the wear resistance of mechanical parts under tribological loads [5]. Recently, this institute has developed methods for optimizing chemical analyses of friction materials, particularly at the tribological boundary layer. As shown in Figure 2, this involv...

An acoustic characterization method for directional microphones is presented that does not require an anechoic chamber to provide a controlled plane-wave sound field. Measurements of a directional microphone under test are performed in a nearly arbitrary sound field for several angles of sound incidence, and the corresponding sound pressure and pressure gradients in the vicinity of the test microphone are measured using an automated probe microphone scanning system. From these measurements the total acoustic frequency response of the directional microphone can be decomposed into its sensitivities to sound pressure and pressure gradient using a least squares estimation technique. These component responses can then be combined to predict the directional response of the microphone to a plane-wave sound field. This technique is demonstrated on a commercially available pressure gradient microphone and also on a combination sound pressure-pressure gradient microphone. Comparisons with the plane-wave responses measured in an anechoic environment show that the method gives reasonable results down to 100 hertz.

An acoustic characterization method for directional microphones is presented that does not require an anechoic chamber to provide a controlled plane-wave sound field. Measurements of a directional microphone under test are performed in a nearly arbitrary sound field for several angles of sound incidence, and the corresponding sound pressure and pressure gradients in the vicinity of the test microphone are measured using an automated probe microphone scanning system. From these measurements the total acoustic frequency response of the directional microphone can be decomposed into its sensitivities to sound pressure and pressure gradient using a least squares estimation technique. These component responses can then be combined to predict the directional response of the microphone to a plane-wave sound field. This technique is demonstrated on a commercially available pressure gradient microphone and also on a combination sound pressure-pressure gradient microphone. Comparisons with the plane-wave responses measured in an anechoic environment show that the method gives reasonable results down to 100 hertz.