Satya Deo Sharan Nirala Dept. of Mechanical Engineering Maulana Azad National Institute of Technology Bhopal, India

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1 Design and Analysis of Brake Rotors of Three Materials Satya Deo Sharan Nirala Dept. of Mechanical Engineering Maulana Azad National Institute of Technology Bhopal, India Abstract- Suppose you are driving a car at the speed of 80km/hr, and suddenly you see a pothole in the road then the only thing comes in your mind is to push the brake pedal as hard as you can. But at the same time the chances of deformation of the brake components become too high so designing the brake components accurately is highly required. In case of disc brakes the main component on which the braking rely is the brake disc, if the brake rotor are designed accurately, the braking of the vehicle improves. Here, in the following study we are going to design and analyze brake rotor of three different materials: Stainless Steel, Grey Cast Iron, and Aluminum Alloy. We will design the brake rotor in the Solidworks15, and will analyze it on the Ansys workbench 15. On the basis of this conceptual approach I designed the brake rotor for the student formula car Supra. KEYWORDS:- Material, Heat transfer, Heat flux, Thermal Analysis, Structural Analysis, Solidworks15.0, Ansys INTRODUCTION Most of us only think about brakes when a panic stop occurs in the traffic sand we press the brake pedal with all our effort to stop the vehicle. These emergencies illustrate how important the brakes are to our safety. If racing is your game then you need to know more about brakes than the casual driver. Especially in case of street racing, brake performance is vital. Most of modern cars are equipped with disc brakes because the demand of more efficient braking system is increased at the cost of less maintenance and the disc braking system provides both. Brake rotor plays vital role in the disc braking system and the performance of braking system depends on the type of brake rotor you used. So to simplify this problem we are going to analyze brake rotor of three different types of materials which are Grey CI, Stainless Steel, and Aluminum alloy and on the basis of the result we will set criteria for their selection. MATERIAL SELECTION To select the best appropriate material for brake rotors, we decided some parameters and on the basis of these parameters we ll rectify the materials available. The parameters are cost, availability, weight, resistant to corrosion as our material is exposed directly to the 23 environment, and machinability of the material. On the basis of these parameters, we have selected Stainless Steel, Grey Cast Iron, and Aluminum Alloy. Aluminum alloy has better strength then the aluminum so we use the alloy of aluminum instead of pure aluminum. Ceramics and Aluminum alloys are used on the vehicles where high efficiency is required and the focus is on weight reduction and so the cost is not that important factor as in general vehicles. The grade of Aluminum Alloy is Al6061-T6 and grade of stainless steel is AISI410. To analyze the brake rotors we need the mechanical and thermal properties, and those are listed below for each material- Property Stainless Steel Aluminum Alloy Grey Cast Iron AISI410 Al6061-T6 Density (Kg/m^3) Coefficient of Thermal Expansion (µm/m*. o C) Reference Temperature ( o C) Young s modulus (GPa) Poisson Ratio Bulk Modulus (GPa) Shear Modulus (GPa) Tensile Yield Compressive Yield Tensile Ultimate CALCULATIONS As we are analyzing rotors of different material, we consider that we are using all three rotors on a same vehicle and so pre-requisites of a vehicle are same for all three rotors and as per their result of analysis, we will conclude that which one was most appropriate among three. Pre-requisites:

2 Gross Weight of Vehicle 300g N Braking Force distribution in front and rear axle -58:42 Average vehicle velocity 60KMPH or M/Sec Radius of Tire meter Diameter of Rotor 9.8 inches Friction Coefficient between Road and Tires- 0.8 When we apply brakes to a vehicle, its kinetic energy gets converted into the heat and that heat is further dissipated to the surroundings. Calculation of heat flux has been shown below- Total kinetic Energy of the vehicle = 1/2mv 2 = 1/2x 300 x = Joules Now, as the braking ratio from the front to rear is 58:42. So, total Heat generated on front discs = 0.58x total KE generated = x.58 = joules Total Heat generated on rear discs = 0.42 x Total KE generated = x 0.4 = joules Now, to calculate heat generated per area which is termed as heat flux: Heat flux =Change in kinetic Energy per unit time per unit area = (dk.e./dt)/area pad =[d(½mv 2 )/dt]/a pad since{a = dv/dt} = (mva/a pad) Where A p is the area of brake pads is = 0.02 m 2 Acceleration of the vehicle is a = µ rt x g = 0.8 x 9.8 = 7.84 m/s 2 To calculate the heat flux after the t sec. of applying brakes, we need to just put the velocity after t sec. Velocity after t sec v = u - at = t So the heat flux becomes = m(u-at)a/a p Now, as we know that never 100% of the K.E. converted into the heat lost to the environment and some losses are always there due to friction between the pads and rotor and we consider that the loss is total 5% of the total heat generated and so 95% of K.E. will be converted into total heat. So, the total heat flux generated on a single front rotor 24 will be half of total heat generated on total front rotor so, Total heat on a single front rotor = [0.95 x m x ( t) x a x ( 0.66/2)]/0.02 Flux after t sec of applying brakes:- Time(sec) Velocity after t sec.(m/s) Heat Flux (w/m 2 ) DESIGNING THE BRAKE ROTOR:- We are keeping the design of the all three rotors same so there will be no change due to difference in design and it will simplify the comparison of the rotors. The CAD model has been prepared in Solidworks15.0. The outer diameter of the rotor is 200mm and the thickness has been kept 3mm. I am using a very simple type of brake rotor to analyze; you can modify the design later. The dimensions are taken on the basis of the availability. Figure 1 : CAD MODEL OF ROTOR To use the CAD file for analyze in the ansys, we need to change the file format. For this just go to save as and choose the file format.xt or IGES. Now it can be used to analyze in the ansys. Determination of Coefficient of Heat Transfer:- When we apply the brakes the kinetic energy of the vehicle

3 gets converted into the heat and it is further dissipated to the environment. This phenomenon results in raising the temperature of the brake rotor. To calculate the raised temperature, we need to calculate the exact value of coefficient of heat transfer. That depends on the various variable like types of braking system used, thermal properties of rotor material, vehicle speed, and the speed of rotor. But the calculation of h is very tiresome so we use CFD ansys to calculate the value of the h. The ansys was carried in CFD fluent and the value. STRUCTURAL ANALYSIS OF THE ROTORS:- When we push the brake pedal, this force is transmitted to the calipers through master cylinder and the calipers clamp the brake rotors with the help of brake pads. This force causes a physical stress on the rotor that result in the deformation of the rotor so the rotors require higher strength and should not deform. Deformation of the brake rotor causes the failure of the braking system of the vehicle. To avoid this, structural analysis is necessary and that is performed in the ANSYS WORKBENCH MESH GENERATION- First we import the cad file into ansys workbench. The ansys automatically generates the mesh from the geometry. The automatic mesh has been generated for coarse size of the elements and this mesh is further refined by using higher relevance and sizing to fine. Mesh quality is further improved by using proximity function. Average size of the element in the generated mesh was mm. The mesh consists of total nodes and total numbers of elements. CONSTRAINTS:- The brake rotor is bolted to the rim surface and this one is the only constrain in this analysis. Here we apply fixed support. This fixes the rotor bolts and so unaffected from the forces acting over the rotor. LOADING CONDITIONS:- During the braking of the vehicle, the rotor is subjected to two loads, one the clamping force from the calipers and other one frictional force due to contact of tires and road. The caliper applies forces from both sides, and the average of the force acting on one rotor is: F = µ.mg N. There is a moment that also works on the rotor whose magnitude is equal to = F x R eff. Now using all these inputs I did the analysis of all three rotors and the results are shown below in the images:- A) STRUCTURAL ANALYSIS OF BRAKE ROTOR OF STAINLESS STEEL- 25

4 B) STRUCTURAL ANALYSIS OF BRAKE ROTOR OF GREY CAST IRON C) STRUCTURAL ANALYSIS OF BRAKE ROTOR OF ALUMINUM ALLOY THERMAL ANALYSIS OF BRAKE ROTOR:- As we have already discussed that when we apply the brakes, the kinetic energy of the vehicle gets converted into the heat that results in the raising the temperature of the vehicle. To find the rise in the temperature of the rotor, we need to do thermal analysis of the brake rotor. As the temperature is not stay for a considerable time limit so the steady state is not achieved and hence we need to do transient thermal analysis of the brake rotor. Energy input for the transient thermal analysis is in the form of heat flux. The heat flux has been calculated already. The thermal conductivity of the brake pads is very small as compared to that of rotor and so it is neglected. Mode of heat transfer is convection and so we require coefficient of heat transfer to be calculated before. If the speed of your vehicle is not sufficiently high, the heat transfer by radiation can been neglected. Initial temperature has been taken 22 0 C. After calculating heat flux and coefficient of heat transfer we have done the transient thermal analysis of all the rotors in the ansys workbench 15. The result has been shown below:- A) Transient thermal Analysis of Brake Rotor:- 26 Stainless Steel

5 modern cars because modern cars focus on weight reduction. The cost is higher for the Aluminum Alloy and so it cannot be used in general vehicles as it will increase the total cost of the vehicle. The stainless steel is the perfect material for the brake rotor as it has medium cost and medium weight and it is also rustproof. The aluminum is very light in weight but it can sustain temperature max of 660 o C and then it will convert into liquid whereas the cast iron can withstand at temperature even more than C and steel rotors can take even higher than the C temperature. Grey Cast Iron Aluminum Alloy CRITERIA OF SELECTION In the following table we are tabulating important results that are key points for the selection of a rotor:- Material Stainless Steel Grey Cast Iron Aluminum Alloy Equivalent Stress(MPa) Max Temp( 0 C) Weight Cost Medium Medium Highest Lowest Lowest Highest From the above table you can conclude that the max stress is present in grey cast iron and has maximum durability among the three rotors. Cast Iron was highly used in old cars because it is highly durable and because iron has maximum weight and so cannot be used in CONCLUSION:- In the above study we studied various parameter and factors on which the selection of a brake rotor depends. We did calculation to calculate heat, heat flux which was used later in different analysis. We selected rotor s size from the various size and designs available in market and designed its cad model into solidworks15.0. We did various analysis in ansys 15.0 and concluded that the cast iron rotors are fit where the weight factor is not considered and durability is preferred and it is cheap so also reduces overall cost of the vehicle. Aluminum rotors are used to reduce weight of the vehicle and these rotors are used in supercars where the cost is not an important factor. The stainless steel rotors are highly used in modern road as well as race cars where the proper balance of weight and cost is maintained. The following approach was used for the selection of Supra 18 car. REFERENCES:- 1) Fred Puhn Brake handbook. 2) Pranay Tiwari, Pranjal Agrawal & Devanjan Mishra, Designing An Automotive Disk 3) Harshal Nikam, Prem Mishra & Sayali Bharambe, Design and Analysis of Brake Rotor with Parameter Optimization. 4) Thomas D Gillespie (1992), Fundamentals of Vehicle Dynamics. 5) Belhocine,, C.-D. Cho, M. Nouby, Y. B. Yi, A. R. Abu Bakar, Thermal Analysis of both Ventilated and Full Disc Brake Rotors with Frictional Heat Generation 6) SAE Design and Analysis Project with SolidWorks Software.. 27