Characteristics Of Friction Materials Research Articles

Study of the Judder Characteristics of Friction Material for an Automobile Clutch and Test Verification

The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline. In this research, the judder characteristics of automobile clutch friction materials and experimental verification are studied. First, considering the stick-slip phenomenon in the clutch engagement process, a detailed 9-degrees-of-freedom (DOF) model including the body, each cylinder of the engine, clutch and friction lining, torsional damper, transmission and other driveline parts is established, and the calculation formula of friction torque in the clutch engagement process is determined. Second, the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed, and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software. Finally, judder bench test equipment and a corresponding damping test program are developed, and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed. After a large number of tests, the evaluation basis of the test is determined. The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal. When the friction gradient value is less than −0.005 s/m, the judder signal of the measured clutch cannot be completely attenuated, and the judder phenomenon occurs. When the friction gradient is greater than − 0.005 s/m, the judder signal can be significantly suppressed and the system connection tends to be stable.

Thermophysical characteristics of friction materials based on bronze with 12% tin with the addition of GK-1 graphite powder and foundry coke

The results of measurements of thermal properties in the temperature range from 20 °C to 100 °C of bronze with 12% tin obtained by powder metallurgy and 30 vol. % carbon-containing additive in the form of powders of graphite grade GK-1 (7-10 microns), foundry coke (less than 63 microns). The specific heat capacity of the samples was measured using the differential scanning calorimetry method. Thermal diffusivity and thermal conductivity were studied by two different methods. In the first case, the thermal diffusivity is determined by the laser flash method and the thermal conductivity by the calculation method. In the second case, the coefficients of thermal diffusivity and thermal conductivity were measured by the flat heat source method. It has been established that 30 vol.% of graphite powder GK-1 in the composition of bronze with 12% tin makes it possible to obtain the value of the thermal conductivity coefficient equal to 23,97 W/(m·K) at 20 °C with its further increase to 25,65 W/(m·K) at 100 °C. The specific heat capacity is 376,71 J/(kg·K) at 20°C and 399,26 J/(kg·K) at 100 °C. The addition of 30 vol.% coke powder makes it possible to obtain a thermal conductivity coefficient equal to 9,03 W/(m·K) at 20 ° C and 10,76 W/(m·K) at 100 °C. The specific heat capacity ranges from 391,80 J/(kg·K) at 20 °C to 413,57 J/(kg·K) at 100 °C

Frictional Characterization Of Grey Cast Iron Train Brake Block Using A Reduced Scale Dynamometer

The brake block is an important component that serves to slow down and stop the train. The safety of this transportation is very dependent on the reliability of this component. One of the important features of the brake block material is the coefficient of friction. The coefficient of friction of the brake block material must meet and match the requirements. The coefficient of friction of a material is measured using a friction test. Previous studies have shown that the friction coefficient of a material is influenced by braking conditions, namely contact pressure and friction speed. Many friction testing methods have been developed to study the characteristics of friction materials. In contrast to previous studies, in this study, the frictional characteristics of gray cast iron brake blocks were evaluated using a reduced scale dynamometer. The friction test is carried out by pressing the brake block specimen to the surface of the rotating wheel. The specimen size of the brake block and carriage wheels is reduced to 1/4 of the original size. The friction test is carried out at a contact pressure of 0.15, 0.20, 0.25, and 0.30 (MPa) and the friction speeds of 3, 6, 9, and 12 (m/s). The results of this study indicate that the coefficient of friction of the gray cast iron brake block decreases with increasing friction speed and contact pressure.

Effect of Silicon Carbide Nanoparticles on the Friction-Wear Properties of Copper-Based Friction Discs.

To study the influence of nano-additives on the friction-wear characteristics of friction materials, the nano-sized silicon carbide particles which have excellent chemical and physical properties are considered to add in composite to form the modified friction material. The influence of the silicon carbide nanoparticles (SCN) on the friction-wear characteristics of copper-based friction materials (CBFM) is investigated via the SAE#2 (made in Hangzhou, China) clutch bench test with the applied pressure, rotating speed, and automatic transmission fluid (ATF) temperature taken into account. Moreover, the variations of friction torque and temperature are considered to evaluate the friction performance, and the variable coefficient is employed to describe the friction stability. The wear characteristics of friction materials are investigated by the disc changes in thickness and micro-morphology. The results show that the CBFM with SCN can provide a higher friction torque, which increased by 30% to 50% compared with CBFM. The variable coefficient of CBFM with SCN changes from 674 to 52 with the rotating speed raised from 600 rpm to 3000 rpm, which shows that the friction stability is relatively worse. Furthermore, the micromorphology shows that the CBFM with SCN has lower porosity and surface roughness, which increases the microscopic contact area and the coefficient of friction (COF). Simultaneously, the reduction in porosity also leads to a decrease in the cooling quality, bringing about a rapid temperature rise. Thus, the wear amount of CBFM with SCN increases significantly, especially for the friction disc in the axial middle position.

Physico-mechanical and tribological characteristics of composites used for brake pads

Brake pads are a crucial component of the braking system in an automotive vehicle. It is a primary factor in ensuring the normal driving of motor vehicles and the safety of passengers. Therefore, the research and study of the brake pads are extremely important. The materials which used in the manufacturing of brake pads should be environmentally friendly as harmful substances releases during operations by asbestos containing brake pads, which pollute the environment and thus harmful for human so becomes a primary reason of acceleration for research and development of new materials for brake pads. Composite materials have required excellent properties, so it is gaining an important position in this field. In this research, composite materials with coconut fibre are produced in the laboratory which can be used to produce brake pads for braking systems of the medium-performance small car. This research aims primarily towards producing the composite material which consists of the best proportion of organic fibre to have superior physical-mechanical and tribological characteristics. To achieve these goals, the following steps have been taken, the laboratory manufacturing of organic composite materials, technological analysis of the samples, improving the qualitative characteristics of friction materials, determination of the physical-mechanical and tribological characteristics of the materials according to the standards in force. This paper provides a detailed investigation on the characteristics of composite materials made with coconut fibre for brake pads.

도시철도차량 제동시스템 설계를 위한 제동마찰재의 특성 분석

도시철도차량 제동시스템 설계를 위한 제동마찰재의 특성 분석

Experimental Analysis of Tribological Behaviour of Organic Composites Materials

The friction material plays an important role in ensuring the quality of the brake pads. Friction and wear characteristics of friction material are the decision makers in new formulations of composites materials developed for the brake systems. In this work, it was developed four recipes of frictional materials using coconut fibres reinforcement in aluminium matrix, using powder metallurgy technique. For these new materials developed are presented the physico-mechanical characteristics in accordance with various relevant international standards. These materials for brake pads are tested to determine their tribological behaviour in a standard pin on disc equipment. In this sense, the wear resistance and the evolution of friction coefficient of these composites materials were determined. The comparative study reveals that proposed composites have acceptable level of physic-mechanical and tribological characteristics. The study allows selecting the best formulation of frictional materials for use in manufacturing of brake pads for vehicles.

A preliminary investigation on the use of the pin-on-disc test to simulate off-brake friction and wear characteristics of friction materials

During off-brake driving, some unwanted contact between the brake pads and the rotating discs may occur, thus inducing inefficient fuel usage and additional environmental pollution. This paper addresses the frictional behavior of 5 commercial low-met and NAO friction materials dry sliding against a cast iron counterface disc, under low contact pressures, typical of off-brake driving. In the investigated conditions, kinetic and static coefficient of frictions (COFs) were found to be independent from the contact pressure. The static COFs were all found to be around 0.2, whereas the kinetic COFs were found to be higher in the low-met materials with respect to the NAO materials and they were found to be roughly independent from the contact pressure. The results were explained with reference to the adhesive theory of friction, highlighting the paramount role of the Fe-oxides embedded in the friction layer.

Effect of aspect ratios of aramid fiber on mechanical and tribological behaviors of friction materials

In this study, the effect of aspect ratios of aramid fiber on the mechanical and tribological characteristics of friction materials was studied. It was found that with increased aspect ratio of fiber, flexural strength of the composites generally increased and compressive strength decreased, while μ and wear rate of composites increased first and then decreased at selected load and speed. With the addition of fibers, μ and wear of composites increased. 10vol% of aramid pulp was an optimal volume fraction for improved friction and wear behaviors. The wear mechanisms were discussed under the support of worn surface morphologies.

Analysis of Thermal-Mechanical Coupling of Automotive Disc Brake Based on Numerical Simulation Method

The background and necessity of application of numerical simulation method in research on friction materials of automotive brake are analyzed. The numerical analysis methods of conversion of braking energy, distribution of friction heat, transfer of friction heat and thermal mechanical coupling, are discussed. The dynamic temperature field and thermal stress field of the same brake disc and two kinds of friction plates of different materials, which are the composite materials based on resin and the powder metallurgy based on copper, are simulated and analyzed respectively under emergency braking. The effect of friction materials’ performance on friction temperature and thermal stress distribution is obtained. The results show that the friction performance of composite materials based on resin is better than the powder metallurgy based on copper. The results are consistent with the experimental results. The numerical simulation methods proposed have a good predictive effect on the typical characteristics of friction materials in the process of braking, which provides effective references for preparation and optimization design of friction materials of brake.

Distinguishing the effects of adhesive wear and thermal degradation on the tribological characteristics of paper-based friction materials under dry environment: A theoretical study

Adhesive wear and thermal degradation are the main aging mechanisms of paper-based friction materials. However, how these aging mechanisms affect the tribological characteristics of such materials is not fully understood. In this paper, the respective influences of the two aging mechanisms on the tribological characteristics of the friction materials are investigated through simulation. It is assumed that adhesive wear pre-dominantly affects the surface topography, while thermal degradation significantly affects the mechanical properties of the friction material. The simulation results show that the static friction coefficient and both normal and tangential contact stiffnesses increase due to adhesive wear, but decrease due to thermal degradation. These trends are qualitatively in agreement with experimental observations reported in the literature and our previous work.

Effects of glass-to-rubber transition of thermosetting resin matrix on the friction and wear properties of friction materials

The present study is to examine the effects of glass-to-rubber transition of resin matrix on the friction and wear characteristics of friction materials, in relation to different types of thermosetting resins. Dynamic mechanical thermal analysis and friction test results revealed that glass-to-rubber transition of thermosetting resins influenced significantly the friction and wear behavior of the composite materials. There was a significant increasing tendency in friction coefficient and wear rate values for all composites when braking temperatures increased to 200 or 250°C, accompanying the resin matrix converted from glassy state to rubbery state.

Relationship between wear of friction materials and dissipated power density

Specific tribometric tests showed both the effect and relevance of the power dissipated by friction upon the transition from mild wear to severe wear for friction materials. The dissipated power density could be viewed as an important variable either to identify the critical wear characteristics of friction materials or to make comparisons among different types of friction materials. The scanning electron microscopy analysis showed some correspondence between the sliding surface morphology after the friction tests and the wear rate obtained. Moreover, the phenomena observed are related to known mechanochemical wear mechanisms.

Hot wear properties of ceramic and basalt fiber reinforced hybrid friction materials

In the present study, hybrid friction materials were manufactured using ceramic and basalt fibers. Ceramic fiber content was kept constant at 10 vol% and basalt fiber content was changed between 0 to 40 vol%. Mechanical properties and friction and wear characteristics of friction materials were determined using a pin-on-disc type apparatus against a cast iron counterface in the sliding speeds of 3.2–12.8 m/s, disc temperature of 100–350 °C and applied loads of 312.5–625 N. The worn surfaces of the specimens were examined by SEM. Experiments show that fiber content has a significant influence on the mechanical and tribological properties of the composites. The friction coefficient of the hybrid friction materials was increased with increasing additional basalt fiber content. But the specific wear rates of the composites decreased up to 30 vol% fiber content and then increased again above this value. The wear tests showed that the coefficient of friction decreases with increasing load and speed but increases with increasing disc temperature up to 300 °C. The most important factor effecting wear rate was the disc temperature followed by sliding speed. The materials showing higher specific wear rates gave relatively coarser wear particles. XRD studies showed that Fe and Fe 2O 3 were present in wear debris at severe wear conditions which is indicating the disc wear.

D-17 Friction and Wear Characteristics of Fe-based Friction Pads for Heavy Duty Brake Applications(Session: Wear)

An experimental study of different friction materials namely GCI, Sintered Fe based brake pad employed in MIG-21 fighter aircraft, and newly developed brake pads by a novel P/M technique other than compacting and sintering based on hot powder forging are studied. The friction and wear characteristics of these friction materials were analyzed by using pin-on-disc wear testing machine. The parameters for wear test are two loads (low and high) at constant sliding speed; these are fixed for all friction materials. The experimental results include measurement of COF and wear loss. Average values of COF and specific wear for these friction materials are compared. The temperature rise in the pin near to wearing surface and the noise level are measured. The results of wear test show that the developed brake pad is much better than GCI and sintered pad. The COF of the sintered pad and developed pad are in same range. But the developed pads offer high wear resistance and low temperature rise for long period of time than the sintered pad and GCI. Thus, these properties of the developed friction pads show a bright scope as an initial step to further work on this technique. The characteristics of friction materials are also monitored by hardness, and density measurements.

Prediction of automotive friction material characteristics using artificial neural networks-cold performance

In this study, an artificial neural network technique was used to predict the cold performance of the automotive friction material. Cold performance was predicted for two cases: (i) before and (ii) after fading and recovery tests. Predictions were related to the brake factor C values versus 26 input parameters. The input parameters are defined by the friction material formulation (18 parameters), manufacturing conditions (5 parameters), and testing conditions (3 parameters). For these predictions, the five types of the friction materials were produced and tested. The quality of prediction has been evaluated by comparison of the real results obtained during testing on the single-end full-scale inertia dynamometer and predicted ones. The 15 different architectures of the artificial neural networks have been investigated. The five training algorithms have been employed for the artificial neural networks training.

Influence of Aluminum on the Mechanical and Tribotechnical Properties of Sintered Copper-Based Friction Material

The principal physicomechanical and tribotechnical characteristics of friction materials based on tin bronze and aluminum-tin bronze have been studied over a wide range of velocities and friction loads. Aluminum-tin bronze which has slightly higher strength characteristics, is significantly harder than a similar tin bronze. This in turn affects the friction characteristics of the material, increasing the friction coefficient and wear resistance.

INVESTIGATION OF AUTOMOTIVE CREEP GROAN NOISE WITH A DISTRIBUTED-SOURCE EXCITATION TECHNIQUE

Creep groan is a high-intensity, low-frequency noise and vibration problem that affects road vehicles at very low speeds. It usually persists for short periods of time, but a “skilled” driver can deliberately make it last several seconds by tuning the force exerted on the brake pedal. The original cause is considered to be a self-induced vibration of the brake components, due to the friction material characteristics that make the system prone to a stick–slip behaviour. No clear evidence upon the creep groan and how it is perceived inside the passenger cockpit has yet been analyzed in the literature and no formal methods are yet available for its analysis. The present study focuses on the transmission of the vibration from the brake component regions to the ears of the vehicle occupants. Characterization of the calliper acceleration and noise inside the cockpit are described for a test vehicle. Distributed-source noise excitation via the standard vehicle hi-fi system is proposed as a practical but less rigorous particular application of the exact reciprocity method. Virtual groan (in which sound power is delivered by means of a loudspeaker) dismisses the airbone path and shows that the phenomenon is structure-borne. On the examined vehicle, front brakes contribute more strongly than rear. Groan frequency close to cavity acoustic resonance constitutes the worst case scenario, and has to be avoided.

Comparison of Chase and inertial brake Dynamometer testing of automotive friction materials

For effective and safe automotive brake system applications, friction materials must meet certain minimum requirements for performance, noise and durability. To ensure this, friction materials are subjected to a series of vehicle tests on a test track or on the road before they are released as commercial products. While vehicle tests are expensive, time consuming and subject to road conditions and weather variability, brake dynamometer testing in the laboratory is faster and less costly to screen or verify friction material characteristics. Furthermore, because of the capability to control test conditions precisely, a brake dynamometer serves as an excellent tool for the research and development of friction materials. In the U.S.A. two major types of brake dynamometers are commonly used: the inertial dynamometer which evaluates a full size brake or a brake system and simulates vehicle braking well, but is time consuming and expensive, or a smaller Chase dynamometer that features low capital expenditure and shorter test time using a small friction material sample against a large drum. The Chase dynamometer does not simulate brake conditions as well as the inertial dynamometer, and therefore is used primarily for rapid screening and/or for quality control only. The correlation, or the lack of it, between these two brake dynamometers is discussed in this paper. Friction and wear data from both test systems on several friction pairs under various temperature, sliding speed and load conditions are compared and discussed. The materials used were (a) non-asbestos organic disc pads against cast iron rotors, (b) semimetallic disc pads against cast iron rotors and (c) non-asbestos organic disc pads against copper rotors.

Disk brake noise in rail transit vehicles

A critical parameter in the mechanism of disk brake squeal is the manner in which the coefficient of friction changes as a function of the instantaneous relative velocity between the friction material and the brake rotor. Substitution of alternative materials for asbestos as a friction material constituent has produced squeal in some brake designs but not in others, leading to the conclusion that one or more parameters not associated with friction material characteristics operates to control the squeal mechanism. The probable nature of these parameters is reviewed along with a description of experimental work carried out to investigate the cause of squeal. [Work Supported by US‐DOT‐TSC and Washington Metropolitan Area Transit Authority (WMATA).]