Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 Paper Reference ID: RTC 011 SURFACE TEMPERATURE DISTRIBUTION IN A COMPOSITE BRAKE ROTOR A.A. Adebisi1, M. A. Maleque1 and Q. H Shah2 1Department of Manufacturing and Materials Engineering, 2Department of Mechanical Engineering International Islamic University Malaysia 53100 IIUM Gombak, Kuala Lumpur, Malaysia e-mail: [email protected], [email protected], [email protected] ABSTRACT brake rotor play an important role by influencing the thermal conductivity and heat dissipation during The prediction of surface temperature for brake rotor is braking. Recent studies have shown that advanced regarded as an important step in studying the brake composite such as aluminium matrix reinforced with system performance. The frictional heat generated on silicon carbide particle is a potential material for brake the rotor surface can influence excessive temperature rotor development due to its thermo-physical rise which in turn leads to undesirable effects such as properties (Qi, et al., 2001). In a study by Gao and Lin thermal elastic instability (TEI), premature wear, brake (2002), they observed that considerable evidence has fluid vaporization (BFV) and thermally excited shown that the contact temperature distribution is an vibrations (TEV). The purpose of this study is to integral factor influencing the combined effect of load, investigate the temperature distribution profile for speed, friction coefficient and the thermo-physical and brake caliper pressure application of 0.5, 1.0 MPa with durability properties of the materials. In another study a speed of 60km/h braking condition on the disc rotor Lee and Yeo (2000) stated that the uneven distribution surface. The brake rotor assembly is built by using a 3 of temperature at the surfaces of the rotor could bring dimensional finite element model of a real car brake about thermal distortion which causes thermal judder rotor. To verify the simulation results, an experimental and excited vibration. investigation is carried out. It is believed from the study that composite brake rotor influences the Finite element (FE) method for brake rotor analysis has temperature distribution and heat dissipation rate become a preferred method in studying the thermal which could prevent excessive temperature rise and distribution performance because of its flexibility and subsequently prolong the service life of the rotor. The diversity in providing solutions to problems involving finite element method is cost effective and also assists advanced material properties. Chandrupatla and the automotive industry in producing optimised and Belegundu (2002) stated that temperature distribution effective brake rotor for thermal distribution analysis. analysis is mostly performed using FE method due to its powerful tool for numerical solutions for a wide Keyword: brake rotor, temperature distribution, finite range of engineering problems. Day (1988) conducted element model, frictional heat a study using FE to predict temperature, wear, pressure distribution and thermal distortion of a brake drum 1.0 INTRODUCTION which is generated during high pressure brake application from two different road speed and friction Brake system is an essential component in the materials. Valvano and Lee (2000) proposed a thermal automotive industry due to its safety concern to reduce analysis on disc brake based on a combination of or stop a vehicle on high speed. The braking computer based thermal model and FE based performance is significantly affected by the techniques to provide reliable method to calculate the temperature rise in the process of halting the vehicle. temperature rise and distortion under a given brake Each moment (time step) during the continuous schedule. braking process gives a different value of temperature distribution as a result of the frictional heat generated In this paper, the FE model of a real brake rotor on the rotor surface which can cause high temperature assembly is developed and simulated using the rise (Qi and Day, 2007; Hwang and Wu, 2010). When commercially available FE software packages, ANSYS the temperature rise exceeds the critical value for a and LS-prepost respectively. The model is simulated given material, it leads to undesirable effects in the using a 3D thermo-mechanical coupling model in order operation of the rotor such as thermal elastic instability to observe the surface temperature distributions profile (TEI), premature wear, brake fluid vaporization (BFV) for different applied braking condition. and thermally excited vibrations (TEV) (Gao and Lin, 2002; Kao, et al., 2000). The material properties of the 145 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 2.0 FINITE ELEMENT MODEL as shown in Figure 1. The FE model is developed based on the actual Proton Wira 1.3 solid brake rotor The finite element model of a real brake rotor consists assembly. of the composite rotor disc and two friction materials (a) Finite element model (b) Proton Wira brake assembly Figure 1: Brake rotor assembly The brake rotor model assembly utilizes up to 9053 degrees of freedom at each node: translations, solid elements with the rotor element comprising of velocities, and accelerations in the nodal x, y, and z 8787 and the pads 133 elements. The SOLID 164 directions. It gives a reduced one point integration element type is used for the three-dimensional which saves computer time and robustness in cases of modeling of the brake rotor solid structures. The large deformations. The description of the brake rotor element is defined by eight nodes having the following model is given in Table 1. Table 1: Description of the brake rotor assembly components Components Number of Type of Elements Number of nodes Elements Rotor Solid 164 8787 7638 Pads Solid 164 133 640 The FE model structure is imported into the LS-prepost the thermal contact conductance as a function of software in preparation for the implicit dynamic temperature, pressure parameters and contact stiffness. solution. The contact type is defined as automatic This is to ensure that the temperature distributions on surface to surface thermal friction for the model which the rotor/pad interface is more significant compared to defined the mechanical static and dynamic friction other contact interfaces. The rotor is chosen as the coefficient as a function of temperature. It also defined 146 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 master surface due to its stiffness, while the friction materials were chosen as the slave surface. 3.0 THERMAL DISTRIBUTION ANALYSIS 2.1 Boundary Conditions The dissipated energy converted into heat is specified as all the mechanical energy is converted into thermal For structural and thermal analysis of the brake rotor energy. Energy dissipated as heat between the surfaces model, boundary condition is specified; and the distributions are equal between the two interacting surfaces. Heat is generated on the surfaces 2.1.1 Structural boundary condition between the rotor and pad when the rotor rotates. This It is specified by imposing nodal motion on the set of could be expressed as (Al-Bahkali and Barber, 2006). nodes and the motion is prescribed with respect to the local coordinate system of the brake rotor. The degree q Vp .............................. (1) of freedom (DOF) for the boundary prescribed motion specifies that x/y DOF for node rotating about the z axis is at a location specified in the x-y plane. The SPC where  is the friction coefficient, V is the sliding set specifies the constraints at the nodal single points. velocity of the rotor and pis the contact pressure at the interface, qis the amount of heat generated by 2.1.2 Thermal boundary condition friction. For other regions on the rotor and pad exposed Boundary temperature condition for the set of nodes is to the environment, it is assumed that the heat specified for coupled thermal/ structural analysis of the exchange is transferred through convection process. brake rotor by the load curve ID for temperature versus Therefore, convection surface boundary condition is time interval. applied. This can be expressed as: T k hTT0,t x .............. (2) where h is convection heat transfer coefficient, Tis atmosphere temperature and T0,tis the current temperature of the node. 4.0 SIMULATION AND EXPERIMENTATION Figure 2: Thermal boundary condition In the present study, a proton wira with vehicle curb 2.2 Load Application weight of 1250kg is utilised, the friction and drag coefficient of the contact pair is 0.35 and 0.30 Load is applied to the rotor model structure in respectively with an initial temperature of 35C. The preparation for explicit dynamic solution. The pressure rotor material for the study is 20 wt% MPS-SiC AMC. is defined using load segment keyword which is The dimension and material properties of the brake applied to the faces of the model, on top of the rotor and pads are listed in Table 2. appropriate solid elements (as rigid body). The faces are defined with segments and the load is defined with Table 2 the load curve number. The load curve is specified Material property and dimension of brake rotor and pad with a well defined load direction before it is then Rotor Pad applied on the brake rotor model as Inner radius (mm) 135 155 shown in the Figure 3. Outer radius (mm) 230 221 Thickness (mm) 15 10 Density (kg/m3) 2.903 2.595 Specific heat (Nm/kgK) 845 1465 Thermal conductivity (Nm/s°Cm) 170 1.212 Young`s modulus (GPa) 113 22 Poisson`s ratio 0.24 0.25 Tensile strength (MPa) 178 - The vehicle speed is 60km/h during the static running test carried out in the automotive laboratory for varied brake pressure application. Brake pressure of 0.5, 1.0 Figure 3: Load application on brake rotor and pad MPa is applied on the pad through the caliper piston to generate the pressure which is monitored with a 147 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 pressure gauge from the caliper valve (nipple). The rotor where it becomes constant. The rotational speed model is symmetrical about the work surface of the of the rotor during contact with the pad develops friction contact pair which is defined to carry out frictional heat until the temperature gradually simulation for the temperature distribution profile. increases. After which the rotation of the rotor Based on the 3D thermo-mechanical coupling becomes constant and the thermal analysis continue technique, the analysis generated for the braking until the end of the simulation. The mid distance region process was presented for temperature versus time of contact between the rotor and pad is analysed for interval. To verify the simulation results, an temperature distribution profile on the rotor surface. experimental investigation was carried out for the AMC brake rotor temperature distribution and also Figure 4 shows a temperature profile for pressure compared with the conventional cast iron brake disc application of 0.5MPa and figure 5 gives the rotor. corresponding mid radial temperature distribution plot, the temperature gradually increases to 78°C for a time 5.0 RESULTS AND DISCUSSION period of 20 ms. Figure 6 shows the temperature profile for pressure of 1MPa with a temperature rise of Several assumptions were taken into consideration 147.7°C for 20 ms and figure 7 gives the mid radial when performing the thermal analysis. The applied temperature distribution plot respectively. From the brake pressure is assumed to be uniformly distributed surface temperature profile plots, it shows that the on the brake pads during operation. The coefficient of temperature increases and decreases at certain region at friction is assumed to remain constant throughout the the same time interval. The increase in temperature analysis. The material and thermal properties are results from the rotor contact with the pad, and when homogeneous and invariant with the temperature. The the rotor slides away from the pad the temperature will wear affect is also neglected. slightly drop. The reason for this is as a result of the cooling effect through heat transfer process Brake pressure is applied directly on the pads through (conduction) which also depends on the material the caliper piston until it makes contact with the brake properties of the rotor. Figure 4: Surface temperature distribution profile for 0.5MPa Figure 5: Mid radial temperature distribution plot for 0.5MPa 148 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 Figure 6: Surface temperature distribution profile for 1.0MPa Figure 7: Mid radial temperature distribution plot for 1.0MPa From the result, the time history curve for the rotor surface shows that temperature increases linearly before dropping which indicates that increase in brake pressure increases the surface temperature of the rotor. Cast Iron Rotor The study also found that higher temperature occurs at the center of the rotor surface and it spreads to the circumferential direction. The inner portion of the rotor remains the warmest section. The AMC brake rotor Figure 8: Thermograph analysis for average surface properties exhibited better distribution of temperature temperature profile for AMC and cast iron brake rotor. which reduced the localization of heat generation thereby influencing the hot spot and thermal elastic At a pressure of 0.5MPa the average surface instability (Khai, et al., 2007). Experimental test was temperature for both rotors is slightly different, but as conducted for both AMC and cast iron brake rotors. the pressure applied is increased to 1 MPa the Figure 8 shows the profile analysis for both rotors. temperature gap increases, this is due to the material P = 0.5MPa P = 1MPa properties application. The surface temperature profile T = 20 secs T = 20 secs of the rotor measured in the experimentation test for 0.5 and 1MPa is shown in Figure 8. This shows that the simulation results for the AMC brake rotor are in good agreement with the experimental values. AMC Rotor CONCLUSIONS 149 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 The present study investigated the surface temperature Chandrupatla, T.R. and Belegundu, A. D. (2002) distribution analysis of the AMC brake rotor. The LS- Introduction to finite elements in engineering. prepost (LS-Dyna) finite element software package is 3rd edition Prentice Hall. utilized to predict the temperature distribution on the Day, A. (1988). An analysis of speed, temperature and rotor surface. Long duration investigation is limited performance characteristics of automotive due to hardware limitation and time constraint, drum brakes. Journal of tribology, 110: 298. although results generated from the investigation is Gao, C. and Lin, X. (2002). Transient temperature field adequate to observe some relevant characteristics of analysis of a brake in a non-axisymmetric temperature distribution profile. Moreover, the three-dimensional model. Journal of materials following conclusions can be made from the study; processing technology, 129 (1-3): 513-517. 1. Successful development of AMC brake rotor Hwang, P. and Wu, X. (2010) Investigation of through experimental and FE model analysis. temperature and thermal stress in ventilated 2. The AMC brake rotor exhibited better disc brake based on 3D thermo-mechanical distribution of temperature which reduces the coupling model. Journal of mechanical localization of heat generation thereby science and technology, 24(1): 81-84. influences thermoelastic instability TEI, Kao, T., Richmond, J. and Douarre, A. (2000) Brake premature wear and thermally excited disc hot spotting and thermal judder: an vibrations TEV. experimental and finite element study. 3. Properties of the AMC rotor shows improved International Journal of Vehicle Design, cooling effect due to its high thermal 23(3): 276-296. conductivity when compared to conventional Khai, L. C., and Abu Bakar, A. and Abdullah, M. cast iron properties. S. (2007). Prediction of temperature 4. Both the experimental and simulated results distributions in a disc assembly using the for the AMC rotor are in good agreement. finite element method. 5th Malaysian Friction ACKNOWLEDGEMENT Materials. The authors acknowledge the support of the Qi, H.S. and Day, A. J. (2007). Investigation of department of Manufacturing and Materials disc/pad interface temperatures in friction Engineering, International Islamic University Malaysia braking. Wear, 262 (5-6): 505-513. and also grateful to the Research Management Centre, Qi, H., Fan, Y. and Ding, Z. (2001). Application of the International Islamic University Malaysia (IIUM), for particular reinforced aluminum composite to financial support to conduct this research work under automobile brake rotors. Journal of the Hebei project EDW B 0906-332. Academy of Sciences, 2. Sangkook, L. and Taein, Y. (2000). Temperature and REFERENCES coning analysis of brake rotor using an Al-Bahkali, E. A. and Barber, J. R. (2006). Nonlinear axisymmetric finite element technique. Steady State Solution for a Thermoelastic Science and Technology, 17-22. Sliding System Using Finite Element Method. Valvano, T., Lee, K. and Systems, D. A. (2000). An Journal of Thermal Stresses, 29 (2): 153-168 analytical method to predict thermal distortion of a brake rotor. SAE transactions, 109(6): 566-571. 150 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 Paper Reference ID: RTC 011 SURFACE TEMPERATURE DISTRIBUTION IN A COMPOSITE BRAKE ROTOR A.A. Adebisi1, M. A. Maleque1 and Q. H Shah2 1Department of Manufacturing and Materials Engineering, 2Department of Mechanical Engineering International Islamic University Malaysia 53100 IIUM Gombak, Kuala Lumpur, Malaysia e-mail: [email protected], [email protected], [email protected] ABSTRACT brake rotor play an important role by influencing the thermal conductivity and heat dissipation during The prediction of surface temperature for brake rotor is braking. Recent studies have shown that advanced regarded as an important step in studying the brake composite such as aluminium matrix reinforced with system performance. The frictional heat generated on silicon carbide particle is a potential material for brake the rotor surface can influence excessive temperature rotor development due to its thermo-physical rise which in turn leads to undesirable effects such as properties (Qi, et al., 2001). In a study by Gao and Lin thermal elastic instability (TEI), premature wear, brake (2002), they observed that considerable evidence has fluid vaporization (BFV) and thermally excited shown that the contact temperature distribution is an vibrations (TEV). The purpose of this study is to integral factor influencing the combined effect of load, investigate the temperature distribution profile for speed, friction coefficient and the thermo-physical and brake caliper pressure application of 0.5, 1.0 MPa with durability properties of the materials. In another study a speed of 60km/h braking condition on the disc rotor Lee and Yeo (2000) stated that the uneven distribution surface. The brake rotor assembly is built by using a 3 of temperature at the surfaces of the rotor could bring dimensional finite element model of a real car brake about thermal distortion which causes thermal judder rotor. To verify the simulation results, an experimental and excited vibration. investigation is carried out. It is believed from the study that composite brake rotor influences the Finite element (FE) method for brake rotor analysis has temperature distribution and heat dissipation rate become a preferred method in studying the thermal which could prevent excessive temperature rise and distribution performance because of its flexibility and subsequently prolong the service life of the rotor. The diversity in providing solutions to problems involving finite element method is cost effective and also assists advanced material properties. Chandrupatla and the automotive industry in producing optimised and Belegundu (2002) stated that temperature distribution effective brake rotor for thermal distribution analysis. analysis is mostly performed using FE method due to its powerful tool for numerical solutions for a wide Keyword: brake rotor, temperature distribution, finite range of engineering problems. Day (1988) conducted element model, frictional heat a study using FE to predict temperature, wear, pressure distribution and thermal distortion of a brake drum 1.0 INTRODUCTION which is generated during high pressure brake application from two different road speed and friction Brake system is an essential component in the materials. Valvano and Lee (2000) proposed a thermal automotive industry due to its safety concern to reduce analysis on disc brake based on a combination of or stop a vehicle on high speed. The braking computer based thermal model and FE based performance is significantly affected by the techniques to provide reliable method to calculate the temperature rise in the process of halting the vehicle. temperature rise and distortion under a given brake Each moment (time step) during the continuous schedule. braking process gives a different value of temperature distribution as a result of the frictional heat generated In this paper, the FE model of a real brake rotor on the rotor surface which can cause high temperature assembly is developed and simulated using the rise (Qi and Day, 2007; Hwang and Wu, 2010). When commercially available FE software packages, ANSYS the temperature rise exceeds the critical value for a and LS-prepost respectively. The model is simulated given material, it leads to undesirable effects in the using a 3D thermo-mechanical coupling model in order operation of the rotor such as thermal elastic instability to observe the surface temperature distributions profile (TEI), premature wear, brake fluid vaporization (BFV) for different applied braking condition. and thermally excited vibrations (TEV) (Gao and Lin, 2002; Kao, et al., 2000). The material properties of the 145 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 2.0 FINITE ELEMENT MODEL as shown in Figure 1. The FE model is developed based on the actual Proton Wira 1.3 solid brake rotor The finite element model of a real brake rotor consists assembly. of the composite rotor disc and two friction materials (a) Finite element model (b) Proton Wira brake assembly Figure 1: Brake rotor assembly The brake rotor model assembly utilizes up to 9053 degrees of freedom at each node: translations, solid elements with the rotor element comprising of velocities, and accelerations in the nodal x, y, and z 8787 and the pads 133 elements. The SOLID 164 directions. It gives a reduced one point integration element type is used for the three-dimensional which saves computer time and robustness in cases of modeling of the brake rotor solid structures. The large deformations. The description of the brake rotor element is defined by eight nodes having the following model is given in Table 1. Table 1: Description of the brake rotor assembly components Components Number of Type of Elements Number of nodes Elements Rotor Solid 164 8787 7638 Pads Solid 164 133 640 The FE model structure is imported into the LS-prepost the thermal contact conductance as a function of software in preparation for the implicit dynamic temperature, pressure parameters and contact stiffness. solution. The contact type is defined as automatic This is to ensure that the temperature distributions on surface to surface thermal friction for the model which the rotor/pad interface is more significant compared to defined the mechanical static and dynamic friction other contact interfaces. The rotor is chosen as the coefficient as a function of temperature. It also defined 146 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 master surface due to its stiffness, while the friction materials were chosen as the slave surface. 3.0 THERMAL DISTRIBUTION ANALYSIS 2.1 Boundary Conditions The dissipated energy converted into heat is specified as all the mechanical energy is converted into thermal For structural and thermal analysis of the brake rotor energy. Energy dissipated as heat between the surfaces model, boundary condition is specified; and the distributions are equal between the two interacting surfaces. Heat is generated on the surfaces 2.1.1 Structural boundary condition between the rotor and pad when the rotor rotates. This It is specified by imposing nodal motion on the set of could be expressed as (Al-Bahkali and Barber, 2006). nodes and the motion is prescribed with respect to the local coordinate system of the brake rotor. The degree q Vp .............................. (1) of freedom (DOF) for the boundary prescribed motion specifies that x/y DOF for node rotating about the z axis is at a location specified in the x-y plane. The SPC where  is the friction coefficient, V is the sliding set specifies the constraints at the nodal single points. velocity of the rotor and pis the contact pressure at the interface, qis the amount of heat generated by 2.1.2 Thermal boundary condition friction. For other regions on the rotor and pad exposed Boundary temperature condition for the set of nodes is to the environment, it is assumed that the heat specified for coupled thermal/ structural analysis of the exchange is transferred through convection process. brake rotor by the load curve ID for temperature versus Therefore, convection surface boundary condition is time interval. applied. This can be expressed as: T k hTT0,t x .............. (2) where h is convection heat transfer coefficient, Tis atmosphere temperature and T0,tis the current temperature of the node. 4.0 SIMULATION AND EXPERIMENTATION Figure 2: Thermal boundary condition In the present study, a proton wira with vehicle curb 2.2 Load Application weight of 1250kg is utilised, the friction and drag coefficient of the contact pair is 0.35 and 0.30 Load is applied to the rotor model structure in respectively with an initial temperature of 35C. The preparation for explicit dynamic solution. The pressure rotor material for the study is 20 wt% MPS-SiC AMC. is defined using load segment keyword which is The dimension and material properties of the brake applied to the faces of the model, on top of the rotor and pads are listed in Table 2. appropriate solid elements (as rigid body). The faces are defined with segments and the load is defined with Table 2 the load curve number. The load curve is specified Material property and dimension of brake rotor and pad with a well defined load direction before it is then Rotor Pad applied on the brake rotor model as Inner radius (mm) 135 155 shown in the Figure 3. Outer radius (mm) 230 221 Thickness (mm) 15 10 Density (kg/m3) 2.903 2.595 Specific heat (Nm/kgK) 845 1465 Thermal conductivity (Nm/s°Cm) 170 1.212 Young`s modulus (GPa) 113 22 Poisson`s ratio 0.24 0.25 Tensile strength (MPa) 178 - The vehicle speed is 60km/h during the static running test carried out in the automotive laboratory for varied brake pressure application. Brake pressure of 0.5, 1.0 Figure 3: Load application on brake rotor and pad MPa is applied on the pad through the caliper piston to generate the pressure which is monitored with a 147 Regional Tribology Conference Bayview Hotel, Langkawi Island, Malaysia, 22-24 November 2011 pressure gauge from the caliper valve (nipple). The rotor where it becomes constant. The rotational speed model is symmetrical about the work surface of the of the rotor during contact with the pad develops friction contact pair which is defined to carry out frictional heat until the temperature gradually simulation for the temperature distribution profile. increases. After which the rotation of the rotor Based on the 3D thermo-mechanical coupling becomes constant and the thermal analysis continue technique, the analysis generated for the braking until the end of the simulation. The mid distance region process was presented for temperature versus time of contact between the rotor and pad is analysed for interval. To verify the simulation results, an temperature distribution profile on the rotor surface. experimental investigation was carried out for the AMC brake rotor temperature distribution and also Figure 4 shows a temperature profile for pressure compared with the conventional cast iron brake disc application of 0.5MPa and figure 5 gives the rotor. corresponding mid radial temperature distribution plot, the temperature gradually increases to 78°C for a time 5.0 RESULTS AND DISCUSSION period of 20 ms. Figure 6 shows the temperature profile for pressure of 1MPa with a temperature rise of Several assumptions were taken into consideration 147.7°C for 20 ms and figure 7 gives the mid radial when performing the thermal analysis. The applied temperature distribution plot respectively. From the brake pressure is assumed to be uniformly distributed surface temperature profile plots, it shows that the on the brake pads during operation. The coefficient of temperature increases and decreases at certain region at friction is assumed to remain constant throughout the the same time interval. The increase in temperature analysis. The material and thermal properties are results from the rotor contact with the pad, and when homogeneous and invariant with the temperature. The the rotor slides away from the pad the temperature will wear affect is also neglected. slightly drop. The reason for this is as a result of the cooling effect through heat transfer process Brake pressure is applied directly on the pads through (conduction) which also depends on the material the caliper piston until it makes contact with the brake properties of the rotor. Figure 4: Surface temperature distribution profile for 0.5MPa Figure 5: Mid radial temperature distribution plot for 0.5MPa 148