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Brake pad, position of the thermocouple elements and leading/trailing edges according to the disc sliding direction.
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This paper presents a methodology for the modelling of the variability of brake linings. The impact of the contact surface topography on thermal and braking noise issues is well known but the behaviour of its variability is still barely studied. We propose to introduce it in finite element models using stochastic processes (e.g. random variables an...
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... the first part of the experimental investigation, the to- pographical and structural aspects of 40 semi-metallic linings under four different wear states are studied (i.e. 10 linings per wear state). Series production linings fitted out with frictional under-layer and damping shim are used (see figure 1). The lin- ing material is a complex composite formed by hot compaction of coarse powders, fibres and a binder. ...
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... pro- grams are run after a bedding phase corresponding to the first section of the SAE norm [39]. The temperature is measured inside the lining using thermocouple elements (located 5 mm under the contact surface and positioned as shown on the figure 1). The mass of the vehicle considered to run the programs is 1950 kg. ...
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... figure 2 presents four observations of different pads corresponding to the four programs described in the table 1. All the observations are made at the centre of the contact surface (see figure 1). The first observations using the SEM method show strong modifications of the micro-structures of the lining contact surfaces according to their different wear states. ...
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... the shims are removed from the pads before the measurements. The measurements are made on a conven- tional compression testing machine ( figure 17) fitted with spe- cial flat circular dies (1 mm 2 of nominal contact surface). The nominal surface of the dies is related to the mesh refinement. ...
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... curves are used to determine regularized contact law made of the nonlinear part of the indentation curves. The figure 18 shows an example of indentation curves of a pad subjected to the program-4 and illustrates the methodol- ogy used to extract the force-penetration curve. The nonlinear part of the measurement is extracted from the indentation curve by subtracting the linear (i.e. ...
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... the first instance, we will study the topographical properties of brake linings after different braking conditions. These measurements will enable to determine the main geometrical parameters of the contact interfaces and then to generate artificially numerical surfaces. Secondly, the structural properties are measured by indentation tests and pad-to-disc contact laws are defined. The topographical and structural properties of the pad surfaces will then allow to compute realistic contact pressure distributions. So as to complete this study, a friction law depending on local pressure, velocity and temperature is finally defined. These three points permit to model brake sliding surfaces in a realistic way and to solve efficiently thermal or braking noises issues. For the first part of the experimental investigation, the topographical and structural aspects of 40 semi-metallic linings under four different wear states are studied (i.e. 10 linings per wear state). Series production linings fitted out with frictional under-layer and damping shim are used (see Fig. 1). The lining material is a complex composite formed by hot compaction of coarse powders, fibres and a binder. Moreover, the investigated parts come from the same charge in order to limit production deviation. Table 1 presents the extrema of the wear-programs: number of braking cycles n braking , maximal velocity of the car v max car , maximal brake line pressure p max calliper and maximal temperature of the linings t max . Excepted for program 1, the linings are worn on an industrial flywheel dynamometer simulating real braking conditions, i.e. slowdowns and stop brakings. The programs are run after a bedding phase corresponding to the first section of the SAE norm [39]. The temperature is measured inside the lining using thermocouple elements (located 5 mm under the contact surface and positioned as shown in Fig. 1). The mass of the vehicle considered to run the programs is 1950 kg. Moreover, the ratio between the car velocity (in km/h) and the nominal sliding velocity at the contact interface (in m/s) is 6.8 and the ratio between the brake line pressure (in bar) and the nominal contact pressure (in MPa) is 29.1. Hence, a car velocity of 50 km/h and a brake line pressure of 30 bar correspond to 7.3 m/s and 1.03 MPa at the sliding interface. The four braking programs are equivalent to: program 1, new linings; program 2, normal customers’ brake linings; program 3, sporty braking conditions; program 4, temperature faded linings. The program 2 is made up of 80 km/h down to 30 km/h, 80 km/h down to 10 km/h and 50 km/h down to standstill brakings. The brake pressure fluctuates between 0 bar and 50 bar and the temperature between 50 1 C and 250 1 C. The program 3 is a complex series of brakings, whose initial velocity fluctuates between 50 km/h and 220 km/h and final velocity between 80 km/h and standstill. The brake pressure and temperature evolve within the 0–50 bar and 50–300 1 C ranges. The program 4 is made of 80 km/h down to 30 km/h and 100 km/h down to standstill brakings. The temperature is increased up to 500 1 C and the pressure is maintained under 30 bar. The topographical analysis of the new and worn linings was made by means of scanning electron microscopy (SEM) and white light interferometry. These observations allow a comparative investigation of the microscopical and macroscopical aspects of the contact surfaces after different braking conditions. Before the measurements, the linings and discs are cleaned from third body and the acquisitions are made at room temperature. The pads were prepared by means of ethanol and ultrasonic cleaning. Fig. 2 presents four observations of different pads corresponding to the four programs described in Table 1. All the observations are made at the centre of the contact surface (see Fig. 1). The first observations using the SEM method show strong modifications of the micro-structures of the lining contact surfaces according to their different wear states. Regarding the pad of the program 1 (upper left corner of Fig. 2), the structure of the material is apparent and the distinction between the different main components is possible, e.g. fibres, binder and some metallic particles (in order to make the observation more effective, the scale of the observation of the program 1 is different than the ones of the three other programs). Looking at the lining of the program 2 (upper right corner of Fig. 2), the contact surface is clearly worn and contact plateaus are formed. The plateaus diameters are 50 2 500 m m and they constitute about 30–40% of the nominal pad surface, which is twice the surface observed by Eriksson and Jacobson [33]. Contact plateaus are on the surfaces of the program 3 (lower left corner of Fig. 2) still apparent but the main structure is degraded and the outlines of the plateaus are blurred. Moreover, wrenching areas (i.e. tear in the surface material) and microscopical grooves can be observed. Thus, the increase of the initial braking velocity by 220 km/h sustains the phenomena of contact plateaus deterioration. The figure on the lower right corner of Fig. 2 presents the structure of a lining surface after temperature fading loads (i.e. successive warm-ups over 500 1 C). The surface is subjected to a strong smoothing. Neither the material components nor the contact plateaus are visible and a thin metallic layer covers almost completely the pad surface. Moreover, an energy dispersive spectrometry (EDS) analysis of the layer composition (Fig. 3) shows, in comparison to program 2 linings, a rise of iron and oxygen levels. The other values remain constant. Thus, during the temperature-fading the lining and disc surfaces meet with high degradations that lead to the formation of a homogeneous third-body layer (sintering of wear debris of both pads and disc) which settles on the disc and pad contact surfaces. The observations of the surfaces by means of SEM confirm the presence of contact plateaus for the brake linings under normal braking conditions. But after high speed and high temperature brakings we observe a disappearance of these local contact areas through a global deterioration of the pad surface for high speed and through the formation of an oxide film after high temperature conditions. Using a white light interferometer, large areas of the brake linings are observed. These measurements allow to determine and to compare the spectral and spatial properties of the sliding interfaces at a macroscopical scale. The surfaces are measured along three radial and two tangential strips (Fig. 4). The measurements are performed using a Nikon objective lens 5 Â /0.13 TI and by means of stitch sequences (i.e. 1.41 Â 1.06 mm patches with 10% overlap). The vertical and lateral resolutions are respectively lower than 1 nm and 5 m m. During the measurements, fringes are removed and a post-process of the raw signal is performed in order to complete the missing data. This stage is achieved by means of Voronoi natural neighbours interpolations of the scattered data [40]. Moreover, the concentric profiles are obtained using step-pattern stitchings, whose scattered data are projected on a concentric mesh grid by means of two-dimensional data interpolation method [40]. The strips consist of about 230 lines made of 10,200 points. The profiles are then considered as roughnesses, superimposed on more general curvatures called wavinesses, and long-range deviations called forms. The transition from roughness to waviness or from waviness to form is determined by user-defined cut- offs. In order to make the analysis easier and judicious, a second post-process is made so as to break the profiles down into forms F , wavinesses W and roughnesses R . The form is extracted using fourth degree polynoms and the waviness is isolated from the roughness using a finite impulse response filter defined ...
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... the first instance, we will study the topographical properties of brake linings after different braking conditions. These measurements will enable to determine the main geometrical parameters of the contact interfaces and then to generate artificially numerical surfaces. Secondly, the structural properties are measured by indentation tests and pad-to-disc contact laws are defined. The topographical and structural properties of the pad surfaces will then allow to compute realistic contact pressure distributions. So as to complete this study, a friction law depending on local pressure, velocity and temperature is finally defined. These three points permit to model brake sliding surfaces in a realistic way and to solve efficiently thermal or braking noises issues. For the first part of the experimental investigation, the topographical and structural aspects of 40 semi-metallic linings under four different wear states are studied (i.e. 10 linings per wear state). Series production linings fitted out with frictional under-layer and damping shim are used (see Fig. 1). The lining material is a complex composite formed by hot compaction of coarse powders, fibres and a binder. Moreover, the investigated parts come from the same charge in order to limit production deviation. Table 1 presents the extrema of the wear-programs: number of braking cycles n braking , maximal velocity of the car v max car , maximal brake line pressure p max calliper and maximal temperature of the linings t max . Excepted for program 1, the linings are worn on an industrial flywheel dynamometer simulating real braking conditions, i.e. slowdowns and stop brakings. The programs are run after a bedding phase corresponding to the first section of the SAE norm [39]. The temperature is measured inside the lining using thermocouple elements (located 5 mm under the contact surface and positioned as shown in Fig. 1). The mass of the vehicle considered to run the programs is 1950 kg. Moreover, the ratio between the car velocity (in km/h) and the nominal sliding velocity at the contact interface (in m/s) is 6.8 and the ratio between the brake line pressure (in bar) and the nominal contact pressure (in MPa) is 29.1. Hence, a car velocity of 50 km/h and a brake line pressure of 30 bar correspond to 7.3 m/s and 1.03 MPa at the sliding interface. The four braking programs are equivalent to: program 1, new linings; program 2, normal customers’ brake linings; program 3, sporty braking conditions; program 4, temperature faded linings. The program 2 is made up of 80 km/h down to 30 km/h, 80 km/h down to 10 km/h and 50 km/h down to standstill brakings. The brake pressure fluctuates between 0 bar and 50 bar and the temperature between 50 1 C and 250 1 C. The program 3 is a complex series of brakings, whose initial velocity fluctuates between 50 km/h and 220 km/h and final velocity between 80 km/h and standstill. The brake pressure and temperature evolve within the 0–50 bar and 50–300 1 C ranges. The program 4 is made of 80 km/h down to 30 km/h and 100 km/h down to standstill brakings. The temperature is increased up to 500 1 C and the pressure is maintained under 30 bar. The topographical analysis of the new and worn linings was made by means of scanning electron microscopy (SEM) and white light interferometry. These observations allow a comparative investigation of the microscopical and macroscopical aspects of the contact surfaces after different braking conditions. Before the measurements, the linings and discs are cleaned from third body and the acquisitions are made at room temperature. The pads were prepared by means of ethanol and ultrasonic cleaning. Fig. 2 presents four observations of different pads corresponding to the four programs described in Table 1. All the observations are made at the centre of the contact surface (see Fig. 1). The first observations using the SEM method show strong modifications of the micro-structures of the lining contact surfaces according to their different wear states. Regarding the pad of the program 1 (upper left corner of Fig. 2), the structure of the material is apparent and the distinction between the different main components is possible, e.g. fibres, binder and some metallic particles (in order to make the observation more effective, the scale of the observation of the program 1 is different than the ones of the three other programs). Looking at the lining of the program 2 (upper right corner of Fig. 2), the contact surface is clearly worn and contact plateaus are formed. The plateaus diameters are 50 2 500 m m and they constitute about 30–40% of the nominal pad surface, which is twice the surface observed by Eriksson and Jacobson [33]. Contact plateaus are on the surfaces of the program 3 (lower left corner of Fig. 2) still apparent but the main structure is degraded and the outlines of the plateaus are blurred. Moreover, wrenching areas (i.e. tear in the surface material) and microscopical grooves can be observed. Thus, the increase of the initial braking velocity by 220 km/h sustains the phenomena of contact plateaus deterioration. The figure on the lower right corner of Fig. 2 presents the structure of a lining surface after temperature fading loads (i.e. successive warm-ups over 500 1 C). The surface is subjected to a strong smoothing. Neither the material components nor the contact plateaus are visible and a thin metallic layer covers almost completely the pad surface. Moreover, an energy dispersive spectrometry (EDS) analysis of the layer composition (Fig. 3) shows, in comparison to program 2 linings, a rise of iron and oxygen levels. The other values remain constant. Thus, during the temperature-fading the lining and disc surfaces meet with high degradations that lead to the formation of a homogeneous third-body layer (sintering of wear debris of both pads and disc) which settles on the disc and pad contact surfaces. The observations of the surfaces by means of SEM confirm the presence of contact plateaus for the brake linings under normal braking conditions. But after high speed and high temperature brakings we observe a disappearance of these local contact areas through a global deterioration of the pad surface for high speed and through the formation of an oxide film after high temperature conditions. Using a white light interferometer, large areas of the brake linings are observed. These measurements allow to determine and to compare the spectral and spatial properties of the sliding interfaces at a macroscopical scale. The surfaces are measured along three radial and two tangential strips (Fig. 4). The measurements are performed using a Nikon objective lens 5 Â /0.13 TI and by means of stitch sequences (i.e. 1.41 Â 1.06 mm patches with 10% overlap). The vertical and lateral resolutions are respectively lower than 1 nm and 5 m m. During the measurements, fringes are removed and a post-process of the raw signal is performed in order to complete the missing data. This stage is achieved by means of Voronoi natural neighbours interpolations of the scattered data [40]. Moreover, the concentric profiles are obtained using step-pattern stitchings, whose scattered data are projected on a concentric mesh grid by means of two-dimensional data interpolation method [40]. The strips consist of about 230 lines made of 10,200 points. The profiles are then considered as roughnesses, superimposed on more general curvatures called wavinesses, and long-range deviations called forms. The transition from roughness to waviness or from waviness to form is determined by user-defined cut- offs. In order to make the analysis easier and judicious, a second post-process is made so as to break the profiles down into forms F , wavinesses W and roughnesses R . The form is extracted using fourth degree polynoms and the waviness is isolated from the roughness using a finite impulse response filter defined ...
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... the first instance, we will study the topographical properties of brake linings after different braking conditions. These measurements will enable to determine the main geometrical parameters of the contact interfaces and then to generate artificially numerical surfaces. Secondly, the structural properties are measured by indentation tests and pad-to-disc contact laws are defined. The topographical and structural properties of the pad surfaces will then allow to compute realistic contact pressure distributions. So as to complete this study, a friction law depending on local pressure, velocity and temperature is finally defined. These three points permit to model brake sliding surfaces in a realistic way and to solve efficiently thermal or braking noises issues. For the first part of the experimental investigation, the topographical and structural aspects of 40 semi-metallic linings under four different wear states are studied (i.e. 10 linings per wear state). Series production linings fitted out with frictional under-layer and damping shim are used (see Fig. 1). The lining material is a complex composite formed by hot compaction of coarse powders, fibres and a binder. Moreover, the investigated parts come from the same charge in order to limit production deviation. Table 1 presents the extrema of the wear-programs: number of braking cycles n braking , maximal velocity of the car v max car , maximal brake line pressure p max calliper and maximal temperature of the linings t max . Excepted for program 1, the linings are worn on an industrial flywheel dynamometer simulating real braking conditions, i.e. slowdowns and stop brakings. The programs are run after a bedding phase corresponding to the first section of the SAE norm [39]. The temperature is measured inside the lining using thermocouple elements (located 5 mm under the contact surface and positioned as shown in Fig. 1). The mass of the vehicle considered to run the programs is 1950 kg. Moreover, the ratio between the car velocity (in km/h) and the nominal sliding velocity at the contact interface (in m/s) is 6.8 and the ratio between the brake line pressure (in bar) and the nominal contact pressure (in MPa) is 29.1. Hence, a car velocity of 50 km/h and a brake line pressure of 30 bar correspond to 7.3 m/s and 1.03 MPa at the sliding interface. The four braking programs are equivalent to: program 1, new linings; program 2, normal customers’ brake linings; program 3, sporty braking conditions; program 4, temperature faded linings. The program 2 is made up of 80 km/h down to 30 km/h, 80 km/h down to 10 km/h and 50 km/h down to standstill brakings. The brake pressure fluctuates between 0 bar and 50 bar and the temperature between 50 1 C and 250 1 C. The program 3 is a complex series of brakings, whose initial velocity fluctuates between 50 km/h and 220 km/h and final velocity between 80 km/h and standstill. The brake pressure and temperature evolve within the 0–50 bar and 50–300 1 C ranges. The program 4 is made of 80 km/h down to 30 km/h and 100 km/h down to standstill brakings. The temperature is increased up to 500 1 C and the pressure is maintained under 30 bar. The topographical analysis of the new and worn linings was made by means of scanning electron microscopy (SEM) and white light interferometry. These observations allow a comparative investigation of the microscopical and macroscopical aspects of the contact surfaces after different braking conditions. Before the measurements, the linings and discs are cleaned from third body and the acquisitions are made at room temperature. The pads were prepared by means of ethanol and ultrasonic cleaning. Fig. 2 presents four observations of different pads corresponding to the four programs described in Table 1. All the observations are made at the centre of the contact surface (see Fig. 1). The first observations using the SEM method show strong modifications of the micro-structures of the lining contact surfaces according to their different wear states. Regarding the pad of the program 1 (upper left corner of Fig. 2), the structure of the material is apparent and the distinction between the different main components is possible, e.g. fibres, binder and some metallic particles (in order to make the observation more effective, the scale of the observation of the program 1 is different than the ones of the three other programs). Looking at the lining of the program 2 (upper right corner of Fig. 2), the contact surface is clearly worn and contact plateaus are formed. The plateaus diameters are 50 2 500 m m and they constitute about 30–40% of the nominal pad surface, which is twice the surface observed by Eriksson and Jacobson [33]. Contact plateaus are on the surfaces of the program 3 (lower left corner of Fig. 2) still apparent but the main structure is degraded and the outlines of the plateaus are blurred. Moreover, wrenching areas (i.e. tear in the surface material) and microscopical grooves can be observed. Thus, the increase of the initial braking velocity by 220 km/h sustains the phenomena of contact plateaus deterioration. The figure on the lower right corner of Fig. 2 presents the structure of a lining surface after temperature fading loads (i.e. successive warm-ups over 500 1 C). The surface is subjected to a strong smoothing. Neither the material components nor the contact plateaus are visible and a thin metallic layer covers almost completely the pad surface. Moreover, an energy dispersive spectrometry (EDS) analysis of the layer composition (Fig. 3) shows, in comparison to program 2 linings, a rise of iron and oxygen levels. The other values remain constant. Thus, during the temperature-fading the lining and disc surfaces meet with high degradations that lead to the formation of a homogeneous third-body layer (sintering of wear debris of both pads and disc) which settles on the disc and pad contact surfaces. The observations of the surfaces by means of SEM confirm the presence of contact plateaus for the brake linings under normal braking conditions. But after high speed and high temperature brakings we observe a disappearance of these local contact areas through a global deterioration of the pad surface for high speed and through the formation of an oxide film after high temperature conditions. Using a white light interferometer, large areas of the brake linings are observed. These measurements allow to determine and to compare the spectral and spatial properties of the sliding interfaces at a macroscopical scale. The surfaces are measured along three radial and two tangential strips (Fig. 4). The measurements are performed using a Nikon objective lens 5 Â /0.13 TI and by means of stitch sequences (i.e. 1.41 Â 1.06 mm patches with 10% overlap). The vertical and lateral resolutions are respectively lower than 1 nm and 5 m m. During the measurements, fringes are removed and a post-process of the raw signal is performed in order to complete the missing data. This stage is achieved by means of Voronoi natural neighbours interpolations of the scattered data [40]. Moreover, the concentric profiles are obtained using step-pattern stitchings, whose scattered data are projected on a concentric mesh grid by means of two-dimensional data interpolation method [40]. The strips consist of about 230 lines made of 10,200 points. The profiles are then considered as roughnesses, superimposed on more general curvatures called wavinesses, and long-range deviations called forms. The transition from roughness to waviness or from waviness to form is determined by user-defined cut- offs. In order to make the analysis easier and judicious, a second post-process is made so as to break the profiles down into forms F , wavinesses W and roughnesses R . The form is extracted using fourth degree polynoms and the waviness is isolated from the roughness using a finite impulse response filter defined ...
Citations
... Nonetheless, iron-copper matrix pads have passed the control tests and have been used on both cars and train braking systems for some years now. It is clear, from the few previous studies, that the mechanical properties of the break-pad strongly influence its durability [29,30]. In some cases, early degradation of the pad has been observed [31], with massive weight losses. ...
The industrial sintering process used to produce metallic matrix pads has been altered to diminish the amount of copper used. Unfortunately, replacing a large part of the copper with iron seems to have reached a limit. In the high-energy, emergency-type rail braking used in this study, the materials are put to the very limit of their usage capacity, allowing us to observe the evolution of the microstructure and mechanical properties of sintered, metallic matrix pads. After the braking test, their compressive behaviour was assessed using digital image correlation (DIC), and their microstructure with scanning electron microscopy (SEM). The worn material has three flat layers with different microstructures and compressive behaviours. The bottom layer seems unmodified. Macroscopic and microscopic cracks run through the intermediate layer (2–15 mm depth). The top layer has stiffened thanks to resolidification of copper. The temperature reaches 1000 °C during the braking test, which also explains the carbon diffusion into iron that result in the weakening of iron–graphite interfaces in the pad. Finally, submicronic particles are detected at many open interfaces of the worn and compressed pad. Associated with the predominant role of graphite particles, this explains the weak compressive behaviour of the pads.
... Also, this approach is particularly suited to study the existing relationships between wear and friction mechanisms and parameters like rotational speed, contact pressure and environmental conditions [1,2]. Studies of investigations on materials for brake systems, particularly for road vehicles [3][4][5][6][7] and trains [8][9], report the pin-on-disc results. The pin-on-disc is ideal for product certification of automotive friction pads and mainly to obtain design-oriented information. ...
... According to friction theories, the friction coefficient between two surfaces is an intrinsic constant of the material, but also this is only for a particular speed line, contact pressure, lubrication state, etc. [6][7][8]. The analysis of the tribological behaviour of coupling materials (composite/iron cast materials) follows the evaluation of friction coefficient, depending on different loading parameters such as pressure and sliding speed. ...
Contact between the automotive brake pad and the disc is mathematically modelled to estimate the coefficient of friction (COF). The mathematical model is proposed for the prognosis of the COF of brake pad material, by considering the contact mechanics between the interfacing surface and their material properties. The Greenwood-Williamson contact model is applied for rough contact surfaces for the estimation of the real contact radius. A MATLAB program has been formulated for generating the surface of brake pad material by considering its material properties which aid in the analytical evaluation of the COF. The proposed model is further validated with experimentation on pin-on-disc apparatus, as it is considered suitable for friction pad product testing according to previous research. The 25 pins were fabricated as per the ASTM G99 test for testing under varying loads and speeds. The obtained results showed that the range of COF has been between 0.2 and 0.4. The investigation presents an analytical approach for estimating COF and contact radius for brake disc and brake pad, which can be used to design an efficient automotive brake disc-brake pad system under the given load and rotational speed. The artificial neural network (ANN) is modelled for predicting the values of the COF for brake disc-brake pad systems, which can be further used for determining the tribological properties of new friction materials and their compatibility for efficient brake systems.
... The pressure exertion over brake pads is an indication of reducing the volume of pad by the impact of pressures varying from minimum to maximum levels [32,33], Fig. 3. represents the uncoated braking system with applied pressure of 0.5 mpa. The total deformation found during the analysis was 2 mm as shown in Fig. 3a; the directional deformation (x axis) found in this analysis was found to be 2 mm as shown in Fig. 3b; maximum shear strain developed during this analysis was found to be 0.12 as shown in Fig. 3c and the maximum shear stress developed during this analysis was found to be 12 mpa as shown in Fig. 3d. ...
This paper focuses on heat dissipation analysis of brake pads uncoated and coated with a layer of Al 2 O 3 , TiO 2 and ZrO 2 with in the time intervals when a pressure of 0.5 subjected to 35 o C (Load case 1) and 1 mpa subjected to 55 o C (Load case II). The plasma arc coating process was done for brake pads to estimate the analysis within the atmospheric temperature. The coating is done in the range of 300 lm to perform the analysis; In addition to that salt spraying technique is employeed to estimate the corrosion resistance for these materials. The coated braking pads are dipped in the sodium based solution for 2 h with the presence of 6 % as chloride agents to identify the possibilities of corrosion. The model was drawn using CATIA, and heat dissipation analysis was performed on the model by ansys workbench by multiphysics software. The parameters such as Total deformation, directional deformation,max shear strain and max shear stress also calculated in ansys multiphysics. However it was noted that Al 2 O 3 coatings posess better performance as compared to uncoated materials. The other parameters investigated in this analysis were heat dissipation, total heat flux, total directional heat flux and error analysis. From this analysis it was observed that the pressure exertion for load case I, it was observed that the maximum heat dissipation rate for Al 2 O 3 coated braking systems was found to 22 o C, maximum heat dissipation 2.5 w/m 2 , directional heat flux 2.1w/m 2 and 3 % error. which is as compared to uncoated materials, For load case II, it was observed that the maximum heat dissipation rate for Al 2 O 3 coated braking systems was found to 40 o C, total heat flux was found to be 2.5 w/m 2 , directional heat flux of 4.9 w/m 2 .;with error of 2.2 % compared to uncoated materials. For all the load cases, Al 2 O 3 coated braking materials possses better performance as compared to uncoated materials. Hence it was suggested to use Al 2 O 3 coated materials to improve the brake pad efficiency and life span in the field of automobile sector. By implementing the Al 2 O 3 coated materials the entire automotive industry has numerous benefits in terms of preventing breakdown main-tanence and saving the maintanence costs.
... Les auteurs prennent en compte les effets du coefficient de frottement et de Introduction 9 évidence son évolution après une sollicitation sévère en pression et en température (fading) et développent un modèle analytique pour étudier la dynamique à l'interface de contact. Heussaff et al. [66], Tison et al. [16] et Renault et al. [2] ont montré l'intérêt de substituer la surface de contact traditionnellement lisse par une famille de surfaces générées aléatoirement représentant plus fidèlement les surfaces réelles observées expérimentalement. La méthode proposée repose sur quelques mesures discrètes de la surface de contact [66] en utilisant un interféromètre à lumière blanche dans le but d'acquérir les fonctions de corrélations 1D dans les directions radiale et tangentielle de la plaquette [66]. ...
... Heussaff et al. [66], Tison et al. [16] et Renault et al. [2] ont montré l'intérêt de substituer la surface de contact traditionnellement lisse par une famille de surfaces générées aléatoirement représentant plus fidèlement les surfaces réelles observées expérimentalement. La méthode proposée repose sur quelques mesures discrètes de la surface de contact [66] en utilisant un interféromètre à lumière blanche dans le but d'acquérir les fonctions de corrélations 1D dans les directions radiale et tangentielle de la plaquette [66]. Ces données sont ensuite utilisées pour construire des champs aléatoires homogènes par l'intermédiaire de la décomposition de Karhunen Loève. ...
... Heussaff et al. [66], Tison et al. [16] et Renault et al. [2] ont montré l'intérêt de substituer la surface de contact traditionnellement lisse par une famille de surfaces générées aléatoirement représentant plus fidèlement les surfaces réelles observées expérimentalement. La méthode proposée repose sur quelques mesures discrètes de la surface de contact [66] en utilisant un interféromètre à lumière blanche dans le but d'acquérir les fonctions de corrélations 1D dans les directions radiale et tangentielle de la plaquette [66]. Ces données sont ensuite utilisées pour construire des champs aléatoires homogènes par l'intermédiaire de la décomposition de Karhunen Loève. ...
Le crissement de frein est une nuisance sonore qui affecte le bien-être collectif et rend le système mécanique non conforme aux exigences du client. Sa réduction, voire sa suppression, représente depuis quelques décennies un enjeu majeur pour les industriels du secteur des transports ainsi que la communauté scientifique. Ce phénomène, de nature non déterministe, est difficile à reproduire et trouve son origine à l’interface de contact entre les plaquettes de frein et le disque. Afin de développer des jumeaux numériques plus prédictifs, une voie prometteuse consiste à prendre en compte les surfaces réelles des plaquettes. L’objectif de la thèse est de poursuivre dans cette voie de recherche dans le but d’établir un lien entre les paramètres topographiques et la propension au crissement. Les travaux proposés balayent à la fois un cadre expérimental et numérique. Dans un premier temps, une campagne combinant des essais dynamiques et des analyses topographiques de plaquettes issues de différents fabricants est menée pour identifier les évolutions topographiques en fonction de l’usure des plaquettes. En parallèle, des essais interrompus sont mis en place de manière à disposer des topographies de plaquettes suite à un crissement ou non. Dans un second temps, la variabilité des paramètres de surfaces issus d’une décomposition multi-échelles des topographies est quantifiée et exploitée afin de reproduire numériquement des familles de surfaces représentatives des essais. Ces dernières sont ensuite implémentées au sein d’un modèle élément fini pour quantifier leur impact sur les instabilités issues d’analyses de stabilité et de simulations transitoires non-linéaires. Dans un dernier temps, une modélisation mixte éléments finis/éléments discrets est mise en place puis calibrée pour investiguer l’évolution du spectre fréquentiel associé à l’évolution des surfaces au cours de la simulation temporelle.
... To numerically simulate the behavior of brakes is realistic, it is essential to accurately represent the frictional behavior at the contact interface. The complexity of the interactions between the different parameters determines the difficulty of reliable and exact frictional laws [8]. Unfortunately, many researchers use classic laws of friction in their sophisticated finite element analysis, which is insufficient. ...
Different brake pad materials are produced, each with their unique composition in the recent past, yet performing the same task and claiming to be better than others. The article provides references for different automotive brake pads subjected to various operating conditions. The present investigation develops an analytical approach for estimating COF and contact radius for different disc-brake pads, which can be used to design an efficient automotive brake pad-disc system under the given load and rotational speed. The coefficient of friction at the pad-disc interface is investigated considering Greenwood Williamson (GW) model and developed novel friction test rig. A MATLAB program along with FFT was developed to simulate the surface topography of the contact interface during the braking process aiding the estimation of contact radius. Surface topography of tested brake pads has been analyzed using an infinite-focus-microscope to verify contact radius. At last, the reference is verified by an experimental investigation using a developed test rig and considering operating parameters.
... At this speed, the friction block exhibited higher friction and severe localized wear, and a rough wear surface. In parallel with these phenomenological observations, several numerical works have tried to quantify the influence of contact surface heterogeneity (in terms of profilometry or local mechanical properties) [31][32][33] on squeal occurrence. The quantitative properties may be added in numerical modeling at a macroscopic scale. ...
Brake squeal is an important issue in the automotive and railway industry with high frequencies and acoustic pressure (above 1 kHz and 80 dB). For the comfort of passengers, the generation mechanism of this noise needs to be investigated to propose mitigation solutions. Recent works show that the state of the rubbing surface has a strong influence on the occurrences. In this paper, we propose to consider the effect of contact localization on the occurrence of squeal through experiments on a pin-on-disc system close to the braking application. An in-operando and in-situ monitoring of the contact surface during tests is carried out with thermal tracking of the friction body through thermocouples inserted in the pin near the rubbing surface. Based on the thermal measurements, an inverse method is used to identify the heat dissipation zone. Assuming that this zone is equivalent to the macroscopic load-bearing area, a stability analysis is performed to determine the unstable frequencies from contact area. Correlations between numerical results with experiments show that the change of squeal frequencies agrees with the evolution of the contact localization at a macroscopic scale. This localization can then be considered as one of the key parameters linking the surface state and the occurrence of squeal.
... Heussaff (Heussaff et al. 2012) worked with semi-metallic brake linings experimentally and with the use of FEM. They developed a methodology for finite element model by introducing the variability of brake lining surfaces in terms of contact pressure, velocity and temperature. ...
... A global decrease in equivalent bulk Young Modulus is observed that depends on the friction history of the materials. The history effect, also, has an impact on the roughness that changes the local stiffness (Heussaff et al. 2012). ...
Friction brakes can induce vibrations and noise, including squealing, which is a major public health concern. Squeal results from dynamic instabilities, leading to high amplitude vibrations and intense noise emissions. Although the phenomenon is well known, the origin of squealing occurrences remains poorly understood. It is recognized that squealing is related to many factors, including the wear of the friction parts. However, the multi-scale nature of physical couplings, the complexity of friction materials and the closed nature of contact are all obstacles to understanding its appearance.This experimental work is based on the third-body approach and the notion of a tribological circuit to explore the mechanisms originating squeal, considering that flows of third body at the interface continuously change the friction surfaces and thus the load-bearing area during the slip.The objective of the work is to examine the link between the change of the third body, that of the tribological triplet and the appearance of noise in dry friction conditions. For this purpose, an elementary tribometer dedicated to the analysis of contact vibrations is used, the experiment allowing a monitoring of the interface through a transparent disc and a control of the tribological circuit by the use of an artificial third body and an appropriate contact configuration. The results show in particular that the appearance of squealing is strongly related to the densification and redistribution of the third-body layer in the contact during sliding
... The usefulness of thermomechanical modelling is shown, for example, in Refs. [17][18][19][20][21][22][23]. These studies used numerical simulations to investigate the influence of brake-pad design on the development of contact pressure localisations and subsequent formation of hot spots. ...
Due to the complexity of friction materials, the characterization of the tribological properties is prioritised over the bulk material properties even though the tribology is expected to be influenced by the material behaviour. The extent of this relationship is still unknown and further knowledge is required to account for the load history and evolution of the bulk properties. With this view, the compression behaviour and microstructure of a semi-metallic friction material with reduced formulation were investigated before and after a braking program. The thermal loading was monitored with inserted thermocouples. Uniaxial compression tests coupled with Digital Image Correlation (DIC) show significant changes in the worn material, which develops a compression behaviour similar to that of a tri-layered material. The microstructural analysis indicates microcracking of the metallic matrix and carbon diffusion in the Fe-phase. The thermal loading was found to be the key parameter controlling both the friction behaviour and evolution of the material properties. The expected effects of material evolution on the contact uniformity, durability and tribology are discussed.
... Information about mechanical properties of brake pads is essential, because they are involved on contact pressure, temperature distribution, tribological performance, and fatigue behavior that allow to estimate lifetime of any material [4,5]. For automotive and railway industries, crucial problems are vibrations and noise during squeal occurrence. ...
... Hence, it is crucial to consider these heterogeneities, which is often done in models by introducing discontinuous contact surface, or heterogeneous contact stiffness that could be identified from experimental tests [9,11,13]. These investigations are done with compression [14] or indentation tests at the pad surface, giving a map of rigidity that is introduced in the numerical models [5,12]. Even if the results are hopeful, as they show an influence of stiffness distribution in squeal propensity, the heterogeneity of properties is introduced at one scale, macroscopic or mesoscopic, but the relevance of this scale remains unclear. ...
This work is focused on the mechanical characterization by multiscale indentation (nano and macro) of a brake pad material, with multiple phases and complex microstructure for applications in the railway industry. Grid nanoindentation tests allowed to identify the mechanical properties of the components in the formulation. The significant difference between constituent’s properties gives a quickly composite response. In parallel, multicyclic macroindentation tests were performed to obtain a composite mechanical response. The properties change according to test locations and configurations of staking phases, due to the high heterogeneity of the brake pad material. The results demonstrated that multiscale indentation tests give a consistent response, which approximates the mechanical properties at different scales. Considering such a very heterogeneous material (broad distribution of properties and particle sizes), the used methodology is appropriate for other heterogeneous complex materials. A multiscale characterization of the mechanical properties is necessary to deal with the problematic of vibrations induced by friction, particularly for brake squeal prediction.
... They all take into account the dynamic and physical transformation of materials. An interesting approach is the work achieved in [13]. By measuring the brake lining, the authors proposed to investigate the micro-mechanical properties of the surfaces using indentation tests. ...
... There is almost any real complete multi-scale approach from the system to the contact interface. These are mostly simple approaches and only a few finite elements approaches except for example Heussaff work [13], which is only focused on the surface interface. The goal would be to take also into account the near-contact volumic 2 properties including surface and material heterogeneous properties. ...
... Identification of material behavior model shows that the heterogeneity is very strong at different friction states with a global decrease of the equivalent bulk Young Modulus depending on the history effect. This history effect has an impact on the roughness too which changes the local stiffness as shown by [13]. A complete model considering the floating caliper and vented disc as in real test application, coupled with data acquired with indentation have been studied in a complex eigenvalue analysis. ...
Friction pads are made by a recipe of numerous components leading to a heterogeneous material. The originality of this paper is firstly to propose a method leading to identify local mechanical properties of friction a pad, performed at different locations, via an indentation test. Secondly, the mechanical properties obtained for each location are introduced in a modeling to perform a complex modal analysis. A comparison with an equivalent homogeneous friction pad is performed to highlight the difference. Finally, the previous approach is extended to other friction pads which have been submitted to the same test sequence but interrupted at different times to investigate the history effect.
