Study of heat transfer on front and back-vented brake discs. PhraNakhon, Bangsue, Bangkok 10800, Thailand

Transcription

1 Study of heat transfer on front and back-vented brake discs Supachai Lakkam 1*, Kullayot Suwantaroj 1, Phupoom Puangcharoenchai 1, Songwut Mongkonlerdmanee 1 and Saiprasit. Koetniyom 2 1 Department of Mechanical Engineering, Rajamangala University of Technology PhraNakhon, Bangsue, Bangkok 10800, Thailand 2 The Sirindhorn International Thai-German Graduate School of Engineering, King Mongkut s University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand * Corresponding author. address: supachai.l@rmutp.ac.th Abstract Admittedly, a brake disc plays an important role in the auto industry since it concerns directly with safety. Therefore, a wide range of brake discs has been designed in order to develop its heat ventilation such as front- and back-vented brake discs. Such different types of physical brake disc geometries affect directly to the heat ventilation which is a vital factor of the brake s capability. Therefore, the research team recognized its importance and attempted to create the test to investigate the temperature gradient of the brake disc with the hope to evaluate the coefficients of heat convection varied by the change of temperature distribution in both brake discs under the forced heat convection

2 in the steady condition. However, the heat radiation value does not take into account because heat convection is dominated by physical brake disc geometry. The JASO C406 Standard is adopted as a guideline to set up the experimental test for investigation of heat transfer by convection. The experimental results in term of heat convection coefficients are used in the numerical simulation via the Finite Element Method (FEM) in order to study the temperature diffusion and heat ventilation of front and back-vented brake discs. Consequently, the experimental results reveal that the overall heat convection coefficients of the front-vented brake disc are higher than that of the backvented one. From the simulation, the front-vented type of brake disc can ventilate the heat better than another one. It can be summarized that the front-vented type of brake disc has more temperature differences between outboard and inboard rotors than the back-vented type. Hence, the front-vented type is likely subjected to more thermal stress from the temperature difference than the back-vented type and might be damaged during the operation more than another type. Keywords: brake disc temperature, front-vented brake disc, back-vented brake disc, heat conduction, heat convection 1. Introduction While the auto industry nowadays is growing and plays a major role in Thailand, a brake disc is one of automotive products that is crucial for safety of vehicle. Normally, numbers of brake discs are imported or locally produced with high competition in design and efficient developments and variety of physical designs including the usage of local materials in production. In Thailand, brake discs are concerned as safety parts in vehicles and some of manufacturers only duplicate Original Equipment Manufacturer

3 (OEM) parts or change their designs without evaluation of their products due to the reduction of production cost. In addition, an unclear process of specific testing method and high cost of test equipment causes the shortage of full size test equipment for local auto part industry resulting in insufficient development of auto part products. Therefore, it is necessary to conduct research to investigate an effect of products that have been designed and manufactured from local material. And the full size test equipment can be used to design and evaluate the new design of brake disc in the future. In theory, the basic breaking system is to retard or reduce speed when a driver desires (vehicle deceleration). The kinetic energy of vehicle in term of wheel speed is changed into heat energy due to the brake application from the friction force between pad and brake disc which applies friction torque to wheel in opposite travel direction. Therefore, vehicle speed is reduced and heat energy occurring in the brake disc causes temperature increment of brake disc during the brake application. This physical action of brake disc causes heat conduction transferring to the adjacent components in the braking system. If there is an inconsistent dissipation of heat inside the brake disc, deformation of brake disc occurs (Lee, 2004). This problem can normally be found during operation. In addition to such problem, the friction loss by brake disc deformation causes the brake fade (Cueva et al., 2003). The wearing of components results in shorter life time (Hunter et al., 1998). The deformation of brake fluid from liquid to vapor due to high temperature brake disc results in decreasing brake efficiency. Such high temperature of brake disc affects the bearing damages, and causes cracking in brake disc material due to high thermal stress. If cycle of brake application and cooling period occurs in normal operation (repeated cycle), thermal fatigue mechanism due to temperatures different under the repeated cycle, the brake disc is subjected to crack as shown in Figure 1

4 (Bagnoli et al., 2009). Furthermore, these factors also cause vibration (Bergman et al., 1999 and Papinniemia et al., 2002). Hence, the characteristics of brake disc should be able to be absorbed and dissipated the heat effectively in any repeated cycle of operating condition. The effects described above are all undesired performance in braking system. However, these problems are unavoidable in daily life meanwhile, study of heat collection characteristics of brake disc is necessary to solve this problem and as a guideline to design suitable disc break in each condition. Figure 1. Crack on brake disc caused be thermal stress and fatigue (Bagnoli et al., 2009) From above problems, variety of brake discs are researched and developed. This research project is to study heat dissipation characteristics of each type of brake disc during its operation. There are very important factors that affect the braking efficiency and directly relate to safety and mainly to study brake disc characteristics. Additionally, front- and back-vented brake discs that are modified by using materials of typical brake disc available in Thailand are conducted in these experimental tests in order to determine the convection coefficients from those brake discs. Those experimental results are used as thermal property in the computer simulation in order to determine the temperature responses and temperature distribution of such brake discs together with brake disc distortion due to various temperature gradients. 2. Literature survey

5 Finite Element Analysis is a method that is normally used to study heat characteristics. There is temperature analysis (Koetniyom, 2003) on brake disc made from cast iron under heavy operating conditions using Finite Element Method with two different attachments, front and back attachments to the finned disc neck. The results from temperature test indicated that automotive brake disc type plays a role in determining direction and temperature characteristics of brake disc including overall efficiency of brake disc. And maximum temperatures of both brake disc types were at approximately 380 C. Besides, the temperature dissipation of automotive brake disc by adapting kinetic energy in Finite Element Method was analyzed (Kamnerdtong et al., 2005) to determine mechanical and thermal effects together with disc movements and heat caused by frictions. From this study, they found that temperatures on rotor surface at each point changed over the period, inconsistent dissipation and difference in each side of rotor. Temperature differences are tended to increase when applying more brake applications due to the heat accumulation caused by friction energy. Furthermore, inconsistent contact between disc pad and brake disc affects material deformation caused by imbalance of temperatures. And this is a factor to cause vibration during the brake application. In addition, the heat convection coefficient is one of a key interest and was studied by invention of dynamometer for brake disc with electric heater on surface of brake disc (Koetniyom, 2006). Test result showed that heat convection coefficient was high on inboard surface of rotor because its surface had poorer ventilation than outboard rotor. This characteristic was also studied with vehicle speed dependence which was related to wind speed.

6 Furthermore, thermal stress on brake disc using Finite Element Method was studied (Wonchai, 2008) with the brake disc design in holes drilled in many forms to protect the brake disc from squeezing caused by thermal expansion. On the other hand, the drilled holes affect increment of stress on brake disc. From such analysis, the motorcycle brake disc with ventilation (drill) holes in form of spiral was investigated with the number of curls and circles together with various rotating speeds and constraints on the brake disc. It was found that maximum stress were unstable with dependence on number of curls and drill holes. Likewise, the damaged mechanism and thermodynamics burden of brake disc were examined from the heat transfer phenomena on brake disc including heat transmission and transformation equations to solve the problem after being in contact (Dufrénoy et al., 2012). By using numerical calculation, it was found that pressure dissipation and surface temperature on brake disc and pad are subjected to material characteristics. And carbon is the best durable material that can withstand the heat transformation. Although, the electrically controlled brake modulator was studied to investigate heat dissipation (Qi et al., 2007). A proposed process was introduced using brake pad temperatures to control operation and data for adjusting specific parameters for the calculation of the contact force during the brake application. Hence, installation of two temperature sensors is sufficient for electrically controlled the braking system. Moreover, study of temperatures (Saric et al., 2009) at the contact points between the pad and brake disc during the brake application, revealed that maintaining of temperature is important for efficient modern brake systems and is important for safety, measurement and dissipation forecast. The research carried out using thermo coupling drilled into brake pad at contact point to examine temperature dissipation which consists

7 of many parameters such as brake frequency, flow speed, brake burden and materials. Later, it was found that the most important factor is the brake frequency, while actual contact area between the pad and brake disc is related to kinetic energy dissipated by friction which affected to the contact temperatures. While effect of actual surface area on specific contact temperatures and coefficient of friction were analyzed by Finite Element Method and found that maximum temperatures at contact point were not linearly increased while contact area ratio decreased. While, investigation of surface temperatures (Thevenet et al., 2010) on brake disc and measured radiation with two-color pyrometer which was developed by using pyrometer technique to transmit two light colors that can measure from brake disc at temperatures between 200 to 800 C with sensitivity response at 8 µs per round and calibrated temperature with black surface material. The results of temperature measurement with such technique provided very accurate data. When tested with equipment, it was found that radiation varies with quality of surface materials on the brake disc. Additionally, an optimization study for brake squeals aims to minimize the strain energy of vibrating pads with constrained layer damping (Lakkam et al., 2012). By finite element method and experiments were represented to specify the position of the constrained layer damping patch under the pressure condition. 3. Conceptual study 3.1 Test kit for the brake disc temperature To examine heat dissipation on brake disc, tools and test kits are proposed and implemented. It is necessary to make a Single Dynamometer Test Kit that complies to

8 JASO C406:2000 standard for simulating heat transfer under the wind flow condition on the tested brake disc. Test kits and tools have 4 components as shown in Figure 2 and 3: Wind Tunnel (Number 1) To achieve the actual coefficient of heat convection, the air flow is forced by the wind tunnel with 11 m/s of constant speed according to JASO C406: Disc Drive (Number 2) To simulate the virtual rotation of wheel, there are two major parts: a motor and a variable speed controller (Inverter), both of which are related to this work as shown in Figure 2. The motor is used to drive the brake disc from 90 to 140 km/hr of car speeds depending on the inverter. Disc Heater (Number 3) Under temperature control, a set of initial temperature conditions on the surface disc at 100, 200, and 300 C are generated by the disc heater installing in the middle of disc. However, its operation is restrained by surface temperature of disc. Data Collector (Number 4) In experiment, to keep the temperatures there are three points of the measured temperature: the neck, inboard and outboard side of disc surface temperature. To sum up, these data will be sent to the data acquisition via cables and slip ring as shown in Figure 3. Figure 2. Single Dynamometer Test Kit

9 Figure 3. Assembly of disc heater 3.2 Experimental testing for the heat convection coefficient on both types of brake disc There are two methods to verify heat convection coefficient of front- vented and back-vented discs. The same test conditions by the heat input application to both discs to obtain a set of initial temperature conditions on the surface disc at 100, 200, and 300 C. In addition the rotation of the disc are set at the same vehicle speed of 90, 110, and 140 km/hr under the constant wind speed at 11 m/s. Conditions and test patterns are shown in Table 1. In this case the control surface is considered as the surface energy balance because of no longer relevant and only necessary to deal with surface phenomena (shown in Figure 4). Thus, generation and storage terms are neglected as radiation for this temperature range. Therefore, Q is under the forced heat convection in the steady condition, thus the heat quantity is Q = Q (1) conduction convection As mentioned, the heat convection coefficient can be calculated by dt ka = ha( Tout T ) dx x= l (2) Figure 4. The surface energy balance

10 Table 1. Test Pattern Front-vented disc To verify heat convection coefficient of the front-vented disc requires temperature values from each point such as heater temperature ( ), room temperature (T ), disc neck temperature ( ), outboard side of disc surface temperature ( ), the inboard T neck side of disc surface temperature( ), average temperatures of outboard and inboard sides of disc surface ( T ), as shown in Figure 5. Therefore, heat quantity ( Q ) in term ave T in T heater of conduction can be determined by the different temperature between average T out temperatures of disc surface ( T ave ) and heater temperature. Consequently, aforementioned Q served in term as the forced heat convection in the steady condition combined with average temperatures of disc surface ( ) and room temperature (T were used to calculated the heat convection coefficient. T ave ) Figure 5. Temperature sensor positions on the front-vented disc Table 2. Application of heat input to initial surface temperature at 100 C for the front-vented disc

11 Table 3. Application of heat input to initial surface temperature at 200 C for the front-vented disc Table 4. Application of heat input to initial surface temperature at 300 C for the front-vented disc From Table 2, 3 and 4, it was found that temperature at each sensor position is not much different when applying the initial disc surface temperature at 100, 200 and 300 C under different vehicle speeds. These results reveals that the disc speeds have less effect on heat transfer of the disc. Therefore, average temperature data from each position at different speeds will be used to determine heat convection coefficient Back-vented disc To verify heat convection coefficient of the back-vented disc the requirements for temperature values from each point such as heater temperature ( T heater ), room temperature ( ), disc neck temperature ( ), outboard side of disc surface T temperature(t ), inboard side of disc surface temperature ( ), average temperature of out outboard and inboard sides of disc surface (T ) are shown in Figure 6. Therefore, heat quantity ( Q ) and heat convection coefficient value can be calculated by uniform technique in topic ave T neck T in

12 Figure 6. Temperature sensor positions on the back-vented disc Table 5. Application of heat input to initial surface temperature at 100 C for the back-vented disc Table 6. Application of heat input to initial surface temperature at 200 C for the back-vented disc Table 7. Application of heat input to initial surface temperature at 300 C for the back-vented disc From Table 5, 6 and 7, it was found that temperature at each sensor position is not much different as soon as disc surface temperature initiates to transfer heat at 100, 200 and 300 C under different vehicle speeds. This outcome reveals that disc speeds have less effect to the heat transfer of the disc. Therefore, average temperature data from each position at different speeds are used to determine heat convection coefficient. 4. Result and discussion 4.1 Heat convection coefficient

13 Heat quality (Q) is used to calculate heat convection coefficient at each position such as heat convection coefficient at inboard disc surface ( ), heat convection coefficient at outboard disc surface ( ), average heat convection coefficient from both side disc ( h ave ) h out. However, since disc speeds or vehicle speeds have no effect to the heat transfer, average values of these three data ( illustrated in Table 8 and 9. h ave, total h in ) represent heat convection coefficient as Table 8. Heat convection coefficient of the front-vented disc Table 9. Heat convection coefficient of the back-vented disc Figure 7. Heat convection coefficient comparison between two type discs From Figure 7, heat convection coefficients of two disc types have similar values while the heat convection coefficient of front-vented disc is 825 W/m 2.K at 300 C. At the same time the heat convection coefficient of back-vented disc is 789 W/m 2.K or equal to 4.4% difference. In conclusion, heat convection coefficients of both discs tend to be in the same direction and are lower when brake disc temperature increases. Alternatively, the heat convection coefficient increases when temperature decreases simultaneously.

14 4.2 Two brake disc models Two brake disc models with different physical looks namely front-vented disc model and back-vented disc model are created by SolidWorks software and exported to Abaqus software. These models are created as actual workpiece to get the most identical size of brake disc as shown in Figure 8. Figure 8. Front-vented brake disc (Left) and back-vented brake disc (Right) 4.3 Simulate with Finite Element Method To analyze brake disc problems with Finite Element Method using commercial software, it is very convenient and with low cost. Therefore, it is popular and widely used but needed to have accurate data. To obtain accurate results, the exact values of conditions such as models, brake disc materials, environment, etc. should be identified. The process is as follow: Identify conditions and scope To simulate with Finite Element Method with Abaqus software it is necessary to identify conditions and scope under realistic circumstances. Important factors for Finite Element Method are material characteristics of brake disc such as heat conduction coefficient, specific heat and density which are standard value of disc metal as shown in Table 10 while heat convection coefficient should be obtained from actual test or experimental test under different temperatures.

15 Table 10. Material characteristics to simulate with Finite Element Method (Koetniyom, 2006) To analyze temperatures behavior of front-vented disc and back-vented disc, sizes and dimensions of brake discs are changeless. For 360 degrees disc consists of 728,469 nodes and 346,890 elements while 12 degrees disc consists of 33,879 nodes and 14,730 elements. To reduce calculation process, model is built by only one sector or 12 degrees of full size disc as shown in Figure 9. Simulation sequences of this Finite Element Method are as follow: verify test environment reliability, simulate to investigate heat transfer behavior and compare heat transfer behavior between front and back-vented discs at heat transfer temperatures start from 100, 200 and 300 C during 120 seconds. Figure 9. Simulated 12 degrees brake disc with Mesh Verify test environment reliability Verification by heat application to brake disc model in the same quantity as test environment and simulation with same heat convection coefficients, scope and condition is shown in Figure 10 and determine the temperature responses after 120 seconds as shown in Figure 11. Then temperature responses from heat transfer from test with and simulation are compared through initial ( T Initial ) and final temperature responses ( ) as shown in Table 11. T Final

16 Figure 10.Heating to brake disc Figure 11.Cooling on brake disc Table 11. Temperature response between experimental and simulation results in back-vented disc After verified reliability under unchanged conditions and scope, it was instituted that temperature response in the test case is reduced from C to C after 120 seconds or equal to 34.0% while temperature response is reduced from C to C or equal to 27.5% in the simulation case. Hence, difference between test and simulation cases is 7% as shown in Table 11 which is acceptable. This difference is not only dependent on inefficiency of test equipment but also the conditions and scope because of conducted heat by a connected solid shaft and uncontrollable air temperature Heat transfer simulation Heat transfer simulation for both types of disc is carried out at three temperature points of 100, 200 and 300 C with same 120 seconds each as shown in Table 12. Table 12. Finite Element Simulation

17 There are three points on both front-vented and back-vented discs that are used to measure temperatures to examine heat transfer characteristics as follow: inboard disc surface (A), outboard disc surface (B) and disc neck (C) as shown in Figure 12. Figure 12. Temperature points on front-vented and back-vented disc The process starts from heating up both surface sides of both discs until they reach stable temperature at 300 C then stop and wait for 120 seconds for the heat transfer period in case of 300 C. Then, the heat transfer coefficient can be determined as shown in Figure 13. Besides, the simulation at heat transfer temperature of 100 C and 200 C is similarly behavior. Therefore, the temperatures at each point and percent of heat transfer at any cases as shown in Table 13. Figure 13. Heat transfer characteristics at 300 C of the front-vented and backvented disc Table 13.Temperatures at each point and percent of heat transfer 4.4 Comparison of temperature difference at disc surfaces

18 Comparison from temperature responses at both sides of both discs collected from simulation results are shown in Table 14. If there are significant differences of temperature responses, thermal stress occurs because of disc temperatures. Table 14. Temperature differences at disc surfaces From Table 14, it was found that inside and outside temperatures of front-vented and back-vented discs are different around 3.9 C and 1.5 C respectively. This outcome represents that temperatures changed from the front-vented disc is higher than the backvented disc. Therefore, the front-vented brake disc causes more thermal stresses and tends to be deformed. 4.5 Comparison of heat transfer performance Heat transfer performance from simulation for both types of discs at the initiate temperature of 100, 200 and 300 C is compared to examine the heat transfer performance as shown in Table 15. Table 15. Heat transfer performance at different temperatures From Table 15, it was found that the temperature responses started at 100, 200 and 300 C have the heat transfer performance at 25.8%, 31.2% and 33% respectively.

19 Therefore, the heat transfer performance increases at higher temperatures and decreases at lower temperatures. 5. Conclusions 5.1 Experimental analysis According to the experimental works, the heat convection coefficient tests of frontand back-vented brake discs with reference to JASO C406 : 2000, a Passenger Car - Braking Device - Dynamometer Test Procedures to identify heat transfer efficient can only be performed at maximum temperatures of 200 C due to the limitation of test equipment. Unfortunately, the tested brake discs cannot be heated up to more than 200 C of surface temperature under test speed conditions. Furthermore, it was found that the heat transfer performances of both disc types have the same direction. As a result, the heat convection coefficient of front-vented disc at temperature of 100, 200 and 300 C is 2,143, 1,218 and 828 W/m 2.K respectively and the heat convection coefficients of back-vented disc at temperature of 100, 200 and 300 C is 2,040, 1,119 and 789 W/m 2.K respectively. It was found that the heat convection coefficient is low when the brake disc is operated under high temperatures and vice versa the front-vented disc has higher heat convection coefficient than back-vented disc around 4.4%. 5.2 Simulation analysis The simulation results were found that the front-vented brake disc has better heat transfer performance than back-vented brake disc when it is simulated using Finite Element Method with initial temperatures at 100, 200 and 300 C within 120 seconds

20 for heat transfer differences of those brake discs at 2.55, 3.15 and 3.37% respectively. Hence, the front-vented brake disc has better heat transfer performance than the backvented brake disc at average initiate temperature around 3.02%. In addition, both brake discs have different heat transfer behaviors. It means the inboard surface of front-vented brake disc provides higher temperature response than outboard surface. This is because the heat from the outboard surface can transfer to the brake neck and dissipate into the air while the heat from the inboard surface can only dissipate heat into the air resulting in the different temperatures from those surfaces by around 3.9 C. For the back-vented brake disc, the outboard surface temperature is higher than the inboard surface because the heat from inboard surface can transfer heat to the brake neck and dissipate into the air while the heat from the outboard surface can only dissipate heat into the air. Therefore, the inboard and outboard surfaces have different temperatures around 1.5 C. On the whole, the experimental method was utilized to find the actually thermal properties in case of finely different discs. There is to 1,066.6 Watt of average heat transfer for front-vented disc in 100 to 300 C of temperature while to 1,035.8 Watt for back-vented disc in the same case. However, it did not indicate heat transfer in some of the areas. To handle, the simulation method was applied to elucidate in term of the heat transfer. Thereby, the result shows that the front-vented brake disc has temperature difference more than the back-vented brake disc due to the difference in temperatures dissipation. Therefore, the front-vented brake disc has more potential to create stress due to higher temperature than the back-vented brake disc. And the frontvented brake disc has high potential to deform during the operation more than the backvented brake disc.

21 Acknowledgments The authors are grateful for the financially sustaining in experimental works from Rajamangala University of Technology Phra Nakhon and appreciative for instrument support from King Mongkut s University of Technology North Bangkok. Also, the authors would like to thank the organizing committee of Songklanakarin J Sci Technol for providing the opportunity to present this work. REFERENCES Bagnoli, F. Dolce, F. and Bernabei, M Thermal Fatigue Cracks of Fire Fighting Vehicles Gray Iron Brake Discs. Engineering Failure Analysis. 16, Bergman, F. Eriksson, M. and Jacobson, S Influence of Disc Topography on Generation of Brake Squeal. Wear , Cueva, G. Sinatora, A. Guesser, W.L. and Tschiptschin, A.P Wear Resistance of Cast Irons Used in Brake Disc rotors. Wear. 255, Dufrénoy, P. Bodovillé, G. and Degallaix, G Damage Mechanisms and Thermomechanical Loading of Brake Discs. European Structural Integrity Society. 29, Hunter, J. E. Cartier, S. S. Temple, D. J. and Mason, R. C Brake Fluid Vaporization as a Contributing Factor in Motor Vehicle Collisions. SAE Technical Paper , Kamnerdtong, T. Chutima, S. and Siriwattanpolkul, A Analysis of Temperature Distribution on Brake Disc. Proceeding of The 19 th ME-NETT, Phuket, Thailand. October 19-21, 2005.

22 Koetniyom, S Temperature Analysis of Automotive Brake Discs. The Journal of King Mongkut's University of Technology North Bangkok. 13, Koetniyom, S Study of Heat Convection Coefficient in Automotive Brake Disc. Proceeding of The 20 th ME-NETT, Nakhonratchasima, Thailand, October 18-20, Lakkam S. and Koetniyom S., Optimization of Constrained Layer Damping for Strain Energy Minimization of Vibrating Pads, Songklanakarin Journal of Science and Technology. 34(2), Lee, K Numerical Prediction of Brake Fluid Temperature Rise During Braking and Heat Soaking. SAE Technical Paper , 1-9. Papinniemia, A. Laia Joseph, C.S. Zhaob, J. and Loader, L Brake squeal: a literature review, Applied Acoustics. 63, Qi H.S. and Day A.J., Investigation of Disc/Pad Interface Temperatures in Friction Braking, Wear. 262, Saric S., Bab-Hadiashar A. and Van Der Walt J., Estimating clamp force for brake-by-wire systems: Thermal considerations, Mechatronics. 19, Thevenet J., Siroux M. and Desmet B., Measurements of brake disc surface temperature and emissivity by two-color pyrometry, Applied Thermal Engineering, 30, Wonchai, B Stress Analysis in Disc Brake by Finite Element Method. Proceeding of The 22th ME-NETT, Thammasat University, Patumthani, Thailand, October 15-17, 2008,

23 Table 1. Test Pattern Types of brake disc Temperature ( C) Vehicle speed(km/hr) Wind speed(m/s) 100 Front-vented disc / , 110, Back-vented disc 300 Table 2. Application of heat input to initial surface temperature at 100 C for the front-vented disc Vehicle Temperature ( C) Q speed(km/hr) Theater T Tneck Tout Tin Tave (Watt) Average Table 3. Application of heat input to initial surface temperature at 200 C for the front-vented disc Temperature ( C)( Q Theater T Tneck Tout Tin Tave (Watt) Vehicle speed(km/hr) Average Table 4. Application of heat input to initial surface temperature at 300 C for the front-vented disc Vehicle Temperature ( C) Q speed(km/hr) Theater T Tneck Tout Tin Tave (Watt) , ,104.5 Average ,066.6

24 Table 5. Application of heat input to initial surface temperature at 100 C for the back-vented disc Vehicle Temperature ( C) Q speed(km/hr) Theater T Tneck Tout Tin Tave (Watt) Average Table 6. Application of heat input to initial surface temperature at 200 C for the back-vented disc Vehicle Temperature ( C) Q speed(km/hr) Theater T Tneck Tout Tin Tave (Watt) Average Table 7. Application of heat input to initial surface temperature at 300 C for the back-vented disc Vehicle Temperature ( C) Q speed(km/hr) Theater T Tneck Tout Tin Tave (Watt) , , ,090.5 Average ,035.8

25 Table 8. Heat convection coefficient of the front-vented disc Initial temperature of disc( C) hin h (W/m 2.K) 90 (km/hr) 110 (km/hr) 140 (km/hr) h h h h h h h h out ave in out ave in out ave h ave, total 100 2,220 2,127 2,173 2,340 2,209 2,274 2,019 1,950 1,984 2, ,247 1,188 1,217 1,251 1,191 1,221 1,241 1,193 1,217 1, Table 9. Heat convection coefficient of the back-vented disc Initial temperature of disc( C) hin h (W/m 2.K) 90 (km/hr) 110 (km/hr) 140 (km/hr) h h h h h h h h out ave in out ave in out ave h ave, total 100 2,066 2,066 2,066 2,040 1,937 1,989 2,044 2,088 2,066 2, ,108 1,099 1,104 1,097 1,035 1,066 1,229 1,147 1,188 1, Table 10. Material characteristics to simulate with Finite Element Method (Koetniyom, 2006) Temperature ( C) Heat conduction (W/mm C) Material properties Specific heat(j/kg C) Density (kg/m 3 ) Heat convection (W/m 2 K) ,950 from actually test ,950 from actually test ,950 from actually test Table 11. Temperature response between experimental and simulation results in back-vented disc Heating Cooling Time Temperature ( C) Time Temperature ( C) Heat transfer (s) TInitial TFinal (sec) TInitial TFinal (%) Experiment NA Simulation NA

26 Table 12. Finite Element Simulation Types of brake disc Temperature( C) Heat transfer time(s) 100 Front-vented disc / Back-vented disc Table 13.Temperatures at each point and percent of heat transfer Types of brake disc TA Temperature( C) T T B C T aver,a-b Heat transfer C Front-vented disc Back-vented disc C Front-vented disc Back-vented disc C Front-vented disc Back-vented disc Table 14. Temperature differences at disc surfaces Temperature( C) Front-vented disc( C) Back-vented disc( C) T in T out Δ T T in T out Δ T Average Table 15. Heat transfer performance at different temperatures Heat transfer performance (%) Temperature100( C) Temperature200( C) Temperature300( C) Frontventevented Average Front- Back- Backventevented Average Frontventevented Back- Average

27 Figure 1. Crack on brake disc caused be thermal stress and fatigue (Bagnoli et al., 2009) Figure 2. Single Dynamometer Test Kit

28 Data cables Wind Tunnel Brake disc Slip ring Heater Figure 3. Assembly of disc heater Figure 4. The energy balance

29 T T out T in T neck T heater Figure 5. Temperature sensor positions on the front-vented disc T T out T in T neck T heater Figure 6. Temperature sensor positions on the back-vented disc

30 Heat convection coeficient (W/m 2 K) 2,500 2,000 1,500 1, Temperature ( C) 1 : Front-vented disc 2 : Back-vented disc Figure 7. Heat convection coefficient comparison between two type discs Figure 8. Front-vented brake disc (Left) and back-vented brake disc (Right) Heating area 12 Figure 9. Simulated 12 degrees brake disc with Mesh

31 B C A Temperature ( C) Heat transfer time (s) A : Disc neck B : Disc fin C : Disc surface Figure 10.Heating to brake disc B C A Temperature ( C) Heat transfer time (s) A : Disc neck B : Disc fin C : Disc surface Figure 11.Cooling on brake disc

32 A B A B C C Figure 12. Temperature points on front-vented and back-vented disc 300 Temperature ( C) Heat transfer time (s) Front-vented disc Inside disc (A) Outside disc (B) Disc neck (C) Back-vented disc Inside disc (A) Outside disc (B) Disc neck (C) Figure 13. Heat transfer characteristics at 300 C of the front-vented and backvented disc