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The Normal-Load and Sliding-Speed Dependence of the Coefficient of Friction, and Wear Particle Generation Contributing to Friction: High-Copper and Copper-Free Formulations

Compact International (1994) Co., Ltd.-Meechai Sriwiboon, Nipon Tiempan, Kritsana Kaewlob
SKR Consulting Inc.-Seong K. Rhee
Published 2019-09-15 by SAE International in United States
Automotive brakes operate under varying conditions of speed and deceleration. In other words, the friction material is subjected to a wide range of normal loads and sliding speeds. One widely accepted test procedure to evaluate, compare and screen friction materials is the SAE J2522 Brake Effectiveness test, which requires full-size production brakes to be tested on an inertia brake dynamometer. For the current investigation, disc pads of two types of 10 different formulations (5 high-copper and 5 copper-free formulations) were prepared for testing on a front disc brake suitable for a pickup truck of GVW 3,200 kg. Each pad had 2 vertical slots, and one chamfer on the leading edge and also on the trailing edge of the pad. One segment of the test procedure looks at the coefficient of friction (Mu) under different brake line pressures and different sliding speeds to determine its stability or variability. In all cases, the Mu is found to be dependent on the normal load and sliding speed, contrary to the commonly called “Amontons-Coulomb’s Laws of Friction”. According to…
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Aging Effect on Disc Pad Properties

Compact International (1994) Co., Ltd.-Meechai Sriwiboon, Kritsana Kaewlob, Nipon Tiempan
SKR Consulting Inc.-Seong K. Rhee
Published 2019-09-15 by SAE International in United States
One low-copper formulation and one copper-free formulation were made into disc pads, and both of them were cured under 4 different conditions. These pads had no backing layer and no scorched layer. Pad thickness, dynamic modulus and natural frequencies were continuously monitored over a period of 12 months. After 12 months at room temperature, pad thickness, dynamic modulus and natural frequencies all increased to higher values. The low-copper formulation increased relatively rapidly during the first 60 days and the copper-free formulation increased relatively rapidly for the first 90 days, and then slowly thereafter. Two competing processes are found to be taking place simultaneously; internal stress relief leading to pad expansion and cross-linking of the resin leading to pad shrinkage. As the pad properties are changing continuously, the timing of property measurement becomes an important issue for quality assurance. Implications of these changing properties are discussed for friction, wear, brake squeal and squeal modeling/simulation, and simple non-destructive test methods are recommended for checking pad quality consistency.
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Effect of Slot and Chamfer Shape of Brake Pad on Mode Coupling

Compact International (1994) Co., Ltd.-Meechai Sriwiboon
Chulalongkorn University-Sirapath Yeamdee, Thiti Bovornratanaraks, Chanat Ratanasumawong
Published 2019-03-25 by SAE International in United States
In the present, one of the essential quality concerns in the automotive industry is brake squeal. Brake pad shape is one of the factors affecting to brake vibration and squeal noise. This research aims to study the effect of slot and chamfer shape on mode coupling through the Finite Element Analysis (FEA), impact hammer testing and performance test from dynamometer. The results can be used to develop geometry of the brake pad surface that leads to brake squeal reduction in the design stage. The natural frequencies and mode shape of brake components calculated by FEA are compared with the impact hammer testing to ensure the accuracy of the results. The FE results are also verified through the standard test with a dynamometer.
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Disc Pad Physical Properties vs. Porosity: The Question of Compressibility as an Intrinsic Physical Property

SAE International Journal of Materials and Manufacturing

Compact International (1994) Co., Ltd.-Meechai Sriwiboon, Nipon Tiempan, Kritsana Kaewlob
Industrial Measurement Systems Inc.-Donald Yuhas
  • Journal Article
  • 05-11-01-0007
Published 2017-09-17 by SAE International in United States
Disc pad physical properties are believed to be important in controlling brake friction, wear and squeal. Thus these properties are carefully measured during and after manufacturing for quality assurance. For a given formulation, disc pad porosity is reported to affect friction, wear and squeal. This investigation was undertaken to find out how porosity changes affect pad natural frequencies, dynamic modulus, hardness and compressibility for a low-copper formulation and a copper-free formulation, both without underlayer, without scorching and without noise shims. Pad natural frequencies, modulus and hardness all continuously decrease with increasing porosity. When pad compressibility is measured by compressing several times as recommended and practiced, the pad surface hardness is found to increase while pad natural frequencies and modulus remain essentially unchanged. However, there is no consistent pattern in compressibility change with increasing porosity, and thus a question arises on the validity of compressibility measurement as an intrinsic physical property measurement. Also after 12-months of ageing at room temperature, all the properties are found to change significantly, but property change trends with increasing porosity remain…
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