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Effective Simulation of the Boundary Layer of an Entire Brake Pad

Tu Braunschweig-Georg Ostermeyer, Joshua Merlis
Published 2015-09-27 by SAE International in United States
The dynamic friction behavior of automotive brakes is generated by the boundary layer dynamics between pad and disk [OST01]. A key component of the Friction Interface is the influence of mesoscopic surface contact structures known as patches, upon which the friction power is concentrated, and whose sizes vary with time. Through this dynamic process, time and load history-dependent effects come about, which cause, for example, the brake moment behavior commonly observed in an AK-Master test.In recent years, several simulation tools have been developed in order to predict the complex friction behavior caused by the patch dynamics in the friction boundary layer. Such simulations are often based on a two or three-dimensional spatial grid, where the explicit physical phenomena at all locations in the boundary layer are modeled by time-consuming calculations of local material dependent balance equations.A new abstract Cellular Automata simulation tool is introduced, which reduces the necessary computation to the patches in the friction boundary layer. Rather than making use of a spatial grid, each patch is considered a single cell, whose size can…
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Investigations on Tribological Memory Effects in Friction Materials

SAE International Journal of Passenger Cars - Mechanical Systems

Tu Braunschweig-Lars Wilkening, Georg Peter Ostermeyer
Federal Mogul-Hans-Guenther Paul
  • Journal Article
  • 2014-01-2481
Published 2014-09-28 by SAE International in United States
Friction materials for automotive brakes are known to exhibit a time-dependent tribological behavior. When examining these dynamic effects special demands are made on the measurement device: The influences of the brake system should be minimized and parameters like velocity, contact pressure and temperature should be controlled closely and independently. Furthermore, special test procedures need to be designed. This can ideally be achieved using a scaled tribometer like the High-Load-Tribometer at the Institute of Dynamics and Vibrations in Braunschweig.Former investigations [1] have shown that a kind of memory effect can occur for a low-met brake pad rubbing on a cast iron disk. A variation of the initial disk temperatures has revealed that a temporary increase of the coefficient of friction can occur at slightly elevated temperatures. This effect is memorized by the material as a certain procedure needs to be performed in order to achieve a regeneration. The scope of the current work is to extend this examination with respect to different materials and also include different load cases. It will be studied if effects, like…
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High Precision Measurements of Topography for Brake Components

Tu Braunschweig-Georg Peter Ostermeyer
Inst Dynamics and Vibrations-Tobias Schramm
Published 2014-09-28 by SAE International in United States
There are few principal excitation mechanisms that brake system NVH simulations are based on, especially the high frequency squeal simulations. These mechanisms can be described by some simple mechanical models that exhibit excitation or self-excitation effects induced by friction [1, 2]. These models use very simple friction laws of Coulomb type, described by a friction coefficient that is either a constant or simple functions of some state variables, taking into account a Stribeck characteristic.Measurements from the AK-Master or SAE J2521, however, show that the friction coefficient is not a simple function of some state variables, describing a steady state behavior of friction. In the past several years, material dependent descriptions of the frictional brake interface have started attracting attention [3]. These aspects are greatly influenced by the tribological effects at the frictional interface, which can be characterized by typical wear patterns.To get a better understanding of the friction mechanisms between the brake pad and the disk, the topography of the disk must be measured using in-situ nondestructive methods, which must be very fast because of…
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On Similarities and Differences of Measurements on Inertia Dynamometer and Scale Testing Tribometer for Friction Coefficient Evaluation

SAE International Journal of Materials and Manufacturing

Tu Braunschweig-Nils Perzborn, Georg Peter Ostermeyer
Link Engineering-Carlos Agudelo
  • Journal Article
  • 2014-01-2523
Published 2014-09-28 by SAE International in United States
Inertia dynamometers are commonly used to determine the friction coefficient of brake assemblies. Dynamometers are a well-established platform, allow testing under controlled conditions, exhibit a good correlation to many situations encountered in real driving, and are comparatively economical and less time-consuming than full vehicle test. On the other side of the spectrum is the use of scaled tribometer. These test systems make possible a test without the entire brake corner. This separation allows the investigation of the frictional-contact only (frictional boundary layer) speedily and independently of a given brake system or vehicle configuration. As the two test systems (inertia dynamometers and tribometers) may have different users with possibly different tasks, the question remains regarding how comparable the two systems are. These issues provide incentives to better define the fields of investigations, correlation, and applicability for the two systems.In order to provide further insights and learning on this topic, this paper focuses on the measurement of the friction coefficient and the wear behavior using inertia dynamometer and scaled pin-on-disc tribometer testing. Thus, friction coefficient levels and…
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Dynamic Friction Measurements, Especially for High Power Applications

Tu Braunschweig-Nils Perzborn
Univ. Of Braunschweig-Georg Peter Ostermeyer
Published 2011-09-18 by SAE International in United States
Dynamic aspects in the understanding of friction are increasingly coming into focus. Therefore, test arrangements are required, which allow dynamic measurements as well, especially with defined and reproducible sliding speeds. In addition, investigations of vehicle brakes require high power. A simple, reliable measurement device, based on the pin-on-disc principle, that meets these requirements was developed and will be presented here.This high load tribometer is based on a specially altered lathe. One key benefit of a lathe as a basic unit is the fact that the main mechanical part is standardized industrial equipment. Additional components and measuring devices can be integrated with little effort and great flexibility. The built-in 15kW AC motor and the embedded gearbox permit speeds and torques to the service areas of vehicle brakes, also of heavy duty vehicles and sports cars. The forces can be measured either with a 3-axes strain gauges sensor or a 3-axes piezoelectric sensor directly at the sample.The high load tribometer is a suitable tool to investigate fundamental questions of tribology. It also allows investigations close to a…
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