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The Factors Governing Corrosion Stiction of Brake Friction Materials to a Gray Cast Iron Disc

Hyundai Mobis-Wangyu Lee, Dooyeon Kim, Keeyang Lee
Korea Univ.-Jaehyun Gweon, Sanghee Shin, Ho Jang
Published 2018-10-05 by SAE International in United States
Corrosion stiction at the contact interface between a brake friction material and a gray iron disc under the parking brake condition was investigated by evaluating the possible parameters that affect the shear force to detach the corroded interface. Using production brake friction materials, comprising non-steel and low-steel types, corrosion tests were carried out by pressing the brake pad onto the gray iron disc using a clamp at various conditions. Results showed that the shear force to detach the corroded interface tended to increase with applied pressure and corrosion time. On the other hand, porosity, acidity, and hydrophobicity of the friction material did not show a reliable correlation to the stiction force. The poor correlation of the stiction force with the friction material properties indicated that the stiction force was not determined by a single factor but governed by multiple parameters including surface contact areas and inhomogeneity of the ingredients. Microscopic observation of the detached disc surface showed adhered fragments that were removed from the friction material surface, thus shedding light on the possible estimation of…
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Incorporation of Friction Material Surface Inhomogeneity in Complex Eigenvalue Analysis to Improve the Accuracy of Brake Squeal Analysis

Hyundai Motor Co.-Yoon Cheol Kim, Jaeyoung Lee
Korea Univ.-Byung Soo Joo, Ho Jang
Published 2018-10-05 by SAE International in United States
The sliding surface of the brake friction material is not uniform but composed of random contact plateaus with a broad pressure distribution, which are known to closely related to the triggering mechanism of friction induced noise and vibrations. The non-uniform contact plateaus are attributed to the various ingredients in the friction material with a broad range of physical properties and morphology and the size and stiffness of the plateau play crucial roles in determining the friction instability. The incorporation of friction surface inhomogeneity is, therefore, crucial and has to be counted to improve the accuracy of the numerical calculation to simulate brake noise. In this study, the heterogeneous nature of the friction material surface was employed in the simulation to improve the correlation between numerical simulations and experimental results. The distributions of contact stiffness and roughness on the friction material surface were used to represent the surface inhomogeneity in the complex eigenvalue analysis (CEA). The results from the noise simulation with uneven surface contacts minimized the difference between experiments and simulations and shed light on…
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Development of Noise Propensity Index (NPI) for Robust Brake Friction

SAE International Journal of Commercial Vehicles

Hyundai Motor Company-Jae Seol Cho, JongYun Jeong, Hyoung Woo Kim, Hwa Sun Lee, Yang Woo Park, Junghwan Lim, Yoonjae Kim
Korea University-Jinwoo Kim, Byung Soo Joo, Ho Jang
  • Journal Article
  • 2017-01-2529
Published 2017-09-17 by SAE International in United States
A semi-empirical index to evaluate the noise propensity of brake friction materials is introduced. The noise propensity index (NPI) is based on the ratio of surface and matrix stiffness of the friction material, fraction of high-pressure contact plateaus on the sliding surface, and standard deviation of the surface stiffness of the friction material that affect the amplitude and frequency of the stick-slip oscillation. The correlation between noise occurrence and NPI was examined using various brake linings for commercial vehicles. The results obtained from reduced-scale noise dynamometer and vehicle tests indicated that NPI is well correlated with noise propensity. The analysis of the stick-slip profiles also indicated that the surface property affects the amplitude of friction oscillation, while the mechanical property of the friction material influences the propagation of friction oscillation after the onset of vibration. An additional case study for noise reduction was carried out using commercial brake friction materials before and after the modification of NPI. The results of the case study based on in-vehicle noise tests indicate that a robust friction material can…
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The Role of Copper on the Friction and Wear Performance of Automotive Brake Friction Materials

SAE International Journal of Materials and Manufacturing

Hyundai Motor Company-Seong Jin Kim, Jae Young Lee, Jai Min Han, Yoon Cheol Kim, Hyun Dal Park
Korea University-Ho Jang
  • Journal Article
  • 2011-01-2367
Published 2011-09-18 by SAE International in United States
Copper has been regarded as one of the indispensable ingredients in the brake friction materials since it provides high thermal diffusivity at the sliding interface. However, the recent regulations against environmentally hazardous ingredients limit the use of copper in the commercial friction material and much effort has been made for the alternatives. In this work, the role of the cuprous ingredients such as copper fiber, copper powder, cupric oxide (CuO), and copper sulfide (CuS) are studied using the friction materials based on commercial formulations. The investigation was performed using a full inertial brake dynamometer and 1/5 scale dynamometer for brake performance and wear test. Results showed that the cuprous ingredients played a crucial role in maintaining the stable friction film at the friction interface, resulting in improved friction stability and reduced aggressiveness against counter disk. In particular, the addition of copper fiber or copper sulfide contributed to improved friction stability during effectiveness test. The test result also showed that the friction material containing 10 wt.% of cupric oxide exhibited better fade resistance without showing an…
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Corrosion Induced Brake Torque Variation: The Effect from Gray Iron Microstructure and Friction Materials

Hyundai Motor Company-Seong Jin Kim, Jae Young Lee, Hyun Dal Park, Jung Seok Oh, Jong Dae Lim
Korea University-Keun Hyung Cho, Jae Min Han, Ho Jang
Published 2005-10-09 by SAE International in United States
Brake judder caused by corrosion of gray iron disks was investigated. In this study, the microstructure of the gray iron disks and the friction film developed on the disk surface by commercial friction materials were examined to find the root cause of the corrosion induced brake torque variation. Corrosion of the disk was carried out in an environmental chamber, simulating in-vehicle disk corrosion. Moisture content and acidity of the friction materials were also taken into account for this investigation and brake tests to examine torque variation during brake applications were performed using a single-end brake dynamometer. Results showed that the friction film developed on the disk surface strongly affected the amount of corrosion, while graphite morphology of the gray iron had little effect on the corrosion. Dynamometer test results also confirmed that the composition of the friction film affects brake torque variation and the oxides on the disk surface persisted for an extended period of time during the dynamometer tests. This suggested that the friction material composition, which was directly related to the composition of…
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The Effect of the Composition and Microstructure of Gray Cast Iron on Preferential Wear During Parasitic Drag and on Intrinsic Damping Capacity

Department of Materials Science and Engineering, Korea University-Ho Jang, Jang Hyuk Yoon, Seong Jin Kim
R&D Division for Hyundai Motor Company and Kia Motors Corporation-Jae Young Lee, Hyun Dahl Park
Published 2003-10-19 by SAE International in United States
Propensity of cold judder was studied by investigating the correlation between the microstructure of gray iron brake disks and friction properties of commercial brake linings. Based on a brake disk for a mid-size passenger car, gray iron disks with 6 different microstructures were manufactured by changing the carbon equivalent (C.E.) and cooling speed in a commercial manufacturing facility. Graphite morphology of the gray iron changed proportionally according to the C.E. and cooling speeds, exhibiting longer graphite flakes with high C.E. at slow cooling speeds. After screening tests of 23 commercial brake linings, 4 different brake linings (two non-steel and two low-steel linings with high μ and low μ) were selected for parasitic drag tests. Results showed that the preferential disk wear was pronounced in the case of using low steel linings and the trend was marked with the disks containing short graphite flakes. Examination of the disks after the drag tests revealed that the initial DTV (disk thickness variation) pattern was preserved during the wear tests while the intensity of the DTV pattern was increased.…
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The role of raw material ingredients of brake linings on the formation of transfer film and friction characteristics

Advanced Material Research Team, R&D Center, Hankook Tire Co.-Geunjoong Jeong, Daehwan Kim, Chunrak Choi
Department of Materials Science and Engineering, Korea University-Min Hyung Cho, Eun Gap Bae, Ho Jang
Published 2001-10-28 by SAE International in United States
An NAO friction material (low-steel type) containing 15 ingredients was investigated to study the role of transfer film on the coefficient of friction, friction oscillation, and fade resistance. The friction material specimens containing extra 100% of each ingredient were tested using a pad-on-disk type tribotester. A non-destructive method of measuring the transfer film was developed by considering the electrical resistance of the transfer film. Results showed that solid lubricants and iron powder assisted transfer film formation on the rotor surface and abrasive ingredients tended to remove the film. No apparent relationship between transfer film thickness and the average friction coefficient was found in this experiment. Fade resistance was also found to be independent of the transfer film thickness when the stable film was formed on the rotor surface at elevated temperatures. On the other hand, the transfer film on the rotor surface reduced the amplitude of friction oscillation.
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The Effect of Solid Lubricants on Friction Characteristics

Korea University-Ho Jang, Jung Joo Lee, Sung Jin Kim, Kee Young Jung
Published 1998-09-20 by SAE International in United States
Friction materials with three different formulations containing different solid lubricants were investigated to study the role of lubricants on the friction performance. The three friction materials contained 10 vol.% graphite, 7 vol.% graphite + 3 vol.% Sb2S3, and 7 vol.% graphite + 3 vol.% MoS2, respectively, with the same amount of other ingredients. Results of this work showed that each formulation had advantages and disadvantages. The friction materials containing two lubricants (graphite + MoS2 or Sb2S3) showed better resistance to fading and improved friction stability than the friction material containing only graphite. However, the friction materials with two lubricants showed disadvantages on anti-fading, wear resistance, and DTV generation.
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