THERMAL ANALYSIS OF DISC BRAKE FOR GREY CAST IRON USING ANSYS

Mr. SATISH LEKKALA*, Mr. ANIL KUMAR GODEA**, Mr.RAJASEKHAR NAVIRI ***.
Cyient LTD, Hyderabad Cyient LTD, Hyderabad Cyient LTD, Hyderabad

ABSTRACT: Brakes are most important safety parts in the vehicles. APPLICATIONS
A disc brake is a wheel brake which slows rotation of the
Generally, all of the vehicles have their own safety devices to stop their
wheel by the friction caused by pushing brake pads against a brake disc
car. Brakes function to slow and stop the rotation of the wheel. To stop
with a set of calipers. The brake disc (or rotor in American English) is
the wheel, braking pads are forced mechanically against the rotor or disc
usually made of cast iron, but may in some cases be made of
on both surfaces. They are compulsory for all of the modern vehicles and
composites such as reinforced carbon–carbon or ceramic matrix
the safe operation of vehicles. In short, brakes transform the kinetic
composites. This is connected to the wheel and/or the axle.
energy of the car into heat energy, thus slowing its speed. Existing
To stop the wheel, friction material in the form of brake pads, mounted
literature revealed some of the gaps in works on the analysis of disc
on a device called a brake caliper, is forced mechanically,
brakes to know the effect of friction, thermal stresses and their
hydraulically, or electromagnetically against both sides of the disc.
distribution with different materials. Work done particularly in the area
Friction causes the disc and attached wheel to slow or stop. Brakes
of structural and thermal analysis of different shapes of ventilated disc
convert motion to heat, and if the brakes get too hot, they become less
brake in view of weight reduction without affecting the life of disc
effective, a phenomenon known as brake fade.
brake. Chosen different materials for analysis of thermal and structural
C CONSTRUCTION
analysis of disk brakes and also planned to study the influence of
different shapes of ventilated holes for the disc brakes to know the effect
of cooling rate and stress distributions.
INTRODUCTION
Brakes are most important safety parts in the vehicles. Generally all of
the vehicles have their own safety devices to stop their car. Brakes
function to slow and stop the rotation of the wheel. To stop the wheel,
braking pads are forced mechanically against the rotor or disc on both
surfaces. They are compulsory for all of the modern vehicles and the
safe operation of vehicles. In short, brakes transform the kinetic energy
of the car into heat energy, thus slowing its speed.
CLASSIFICATION OF BRAKES

1) Purpose: TYPES:Drilled discs: The faces of these discs are drilled all the way
- Primary brakes through mainly to increase surface area so that they can get rid of heat
- Secondary brakes quickly. The holes also go a little way to stopping the gas build up that
2) Construction: causes brake fade. They also speed the clearance of water in wet
- Drum brakes conditions. The problem with drilled discs is that the holes can have a
- Disc brakes tendency to start cracking and collect dust and debris.
3) Method of Actuation: Grooved discs: The faces of these discs have diagonal lines cut into
- Mechanical brakes - Vacuum brakes them, there are two reasons for this. Firstly they allow the venting of
- Hydraulic brakes - Air brakes brake pad gases, thus eliminating brake fade. They also eject brake pad
- Electric brakes - By-wire brakes dust to stop glazing of the pad. This keeps the pad face fresh allowing
4) Extra braking effort: better braking. The problem is that grooved discs have a tendency to be
- Power assisted brakes louder when the brakes are applied due to the scrubbing of the pads.
- Power operated brakes
 torque capacity of the brake. At high temperature, there is rapid wear of
the friction lining, which reduce the life of the lining. Therefore, the
temperature rise should be kept within permissible range.
It is very difficult to precisely calculate temperature rise. In
preliminary design analysis, very often the product (pv) is considered
in place of temperature rise. When the coefficient of friction is
constant, the rate of heat generated is proportional to the product (pv)
where p is the intensity of normal pressure (N/mm2) and v is the
rubbing speed (m/min).
The temperature rise depends upon the mass of the brake drum
assembly, the ratio of the braking period to the rest period and the
Drilled disc brake Grooved disc brake specific heat of the material. For peak short-time requirements, it is
OPERATION OF DISC PAD assumed that all the heat generated during the braking period is
Brake pads are designed for high friction with brake pad material
absorbed by the brake drum assembly. In that case, the temperature rise
embedded in the disc in the process of bedding while wearing evenly.
is given by
Friction can be divided into two parts: Adhesive and abrasive.
∆t = E/mc
Depending on the properties of the material of both the pad and the disc
Where,
and the usage, pad and disc wear rates will vary considerably.
∆t = temperature rise of the brake drum assembly (°C)
E = total energy absorbed by the brake
m = mass of the brake drum assembly (kg)
c = specific heat of the brake drum material (J/kg°C)
The actual temperature rise will be less than that calculated from
above equation. Some heat will be radiated to the atmosphere and some
carried away by the air flow. The equation gives approximate value and
the actual temperature rise is obtained by experiments.

Existing disc model

The below figures 3.1, 3.2, 3.3, 3.4 shows the geometry, padding,
creating holes and final model of the existing disc model which are
Operation of a Disc Brake designed in CATIA part modeling and further imported to ANSYS
When hydraulic pressure is applied to the caliper piston, it forces the workbench.
inside pad to contact the disc. As pressure increases the caliper moves to
the right and causes the outside pad to contact the disc. Braking force is
generated by friction between the disc pads as they are squeezed against
the disc rotor. Since disc brakes do not use friction between the lining
and rotor to increase braking power as drum brakes do, they are less
likely to cause a pull. The friction surface is constantly exposed to the
air, ensuring good heat dissipation, minimizing brake fade. It also allows
for self- cleaning as dust and water are thrown off, reducing friction
differences.
THERMAL CONSIDERATIONS

The energy absorbed by brake is converted into heat, which

increases the temperature at the rubbing surfaces. When the temperature Geometry Padding
increases, the coefficient of friction decreases, adversely affecting the
 Coupled-field analysis depends on which fields are being coupled, but
two distinct methods can be identified: sequential and direct.

Creating Holes Final model

Modified disc model
Flowchart of sequential analysis
The below figures 3.5, 3.6, 3.7, 3.8 shows the geometry, padding,
rotation and final model of the Modified disc model which are designed
in CATIA part modeling and further imported to ANSYS workbench.

Flowchart of Direct analysis

Fig 3.5 Geometry Fig 3.6 Padding

Thermal-Structural Coupling
Thermal-stress analysis involves two sequential analyses. Fig. 4.4
shows a Thermal-Structural Coupling in ANSYS Workbench.

Fig 3.7 Rotation

Fig 3.8 Final model
After creating the final model we have to convert the part into STP
format to import the Model into ANSYS workbench. Thermal-Structural Coupling in ANSYS Workbench
MODELING AND ANALYSIS Kerb weight (kg) : 144
Front : 240mm Disc
It is very difficult to exactly model the brake disc, in which Rear : 130mm Drum
there are still researches are going on to find out transient thermo elastic ii) Calculations
behavior of disc brake during braking applications. There is always a 5
Speed of the vehicle=60kmph = 60× = 16.67m/sec
18
need of some assumptions to model any complex geometry. These
Stopping time = u/4.6 = 16.67/4.6 = 3.62
assumptions are made, keeping in mind the difficulties involved in the
Velocity V= u+at (Final velocity = 0) 0 =16.67+a (4)
theoretical calculation and the importance of the parameters that are
a = -4.16 m/s2;
taken and those which are ignored. In modeling we always ignore the 1
Distance x= ut+ 2 𝑎𝑡 2
things that are of less importance and have little impact on the analysis.
1
The assumptions are always made depending upon the details and Distance x= 16.67×4+ × (-4.16) ×42
2
accuracy required in modeling. The Fig. 4.5 shows a Thermal-Structural Distance x= 33.4m;
Coupling and Inputting properties of the required material in workbench. 1 1
Kinetic energy =2 𝑚𝑣 2 = 2×145×16.672 = 20139 J

Rubbing area = 2𝜋𝑟 2 = 2×3.14× (1152 − 892 ) = 0.0333𝑚 2

The assumptions which are made while modeling the disc brake are
Heat Generated at disc brake = Kinetic energy – ((Drag) + (Friction))
given below:-
For calculating energy carried out by disc brake, the energy carried out
1. The disc material is considered as homogenous and isotropic. by Drag, Friction and rear brake is taken as about 85 percentage.
Thus, Heat generated = 20139×0.15 = 3020.8 w
2. Inertia and body force effects are negligible during the analysis.
Heat Generated
Heat flux Ø =
time×rubbing area
3. The disc is stress free before the application of brake.
3020.8
= = 25031w/m2 = 0.025031 w/mm2
3.6×0.0333
4. Only ambient air-cooling is taken into account and no forced
convection is taken.
Thermal Analysis
5. The kinetic energy of the vehicle is lost through the brake discs i.e.,
no heat loss between the tyre and the road surface and deceleration is
uniform.

6. The thermal conductivity and specific heat of the material used for the
analysis is uniform throughout.

MATERIALS USED FOR DISC BREAK

 Stainless steel
 Grey cast iron

THEORETICAL CALCULATIONS
Geometry model
i) Specifications of engine 150cc pulsar
Engine type : 4-stroke, DTS-i, air cooled single cylinder

Displacement : 149cc
Maximum power : 15.06 @ 9000 (Ps @ RPM)
Maximum torque : 12.5 @ 6500 (Nm @ RPM)
Length (mm) : 2055
Width (mm) : 755
Height (mm) : 1060
Ground clearance (mm) : 165
Wheelbase (mm) : 1320 Meshing model
the input boundary conditions i.e we are giving Convection, Radiation Stress Analysis
and Heat Flux as input conditions for thermal analysis.
the boundary condition of Stress analysis. I.e. imported load from
thermal analysis, Fixed Support and pressure as input boundary
conditions for Stress analysisanalysis.

Convection model

Imported Load Fixed Support

Radiation model

Applying Pressure
the Total deformation and Equivalent (von-Mises) stress of Stainless
Steel Existing Model. As it is evident from the figures, the maximum
total deformation and equivalent (von-Mises) stress are represented by
red colour.

Heat Flux model

the Temperature and Total heat flux of Stainless Steel Existing Model.
The maximum temperature and the maximum total heat flux are
represented by red colour.

TotalDeformation Equivalent Stress

Temperature Heat Flux

Stainless steel Existing model results at different speeds Modified Design results for Grey Cast Iron HT250

Heat Equivalent
speed( Temperatu Deformatio Heat
Flux(W/ Stress(Mpa speed( Temperat Deformat Equivalent
m/s) re(C) n(mm) Flux(W/
m2) ) m/s) ure(C) ion(mm) Stress(Mpa)
m2)
0 30.000 0 0 0.00
5 37.575 8975 0.010 84.82 0 30.000 0 0 0.00
10 45.146 15472 0.027 106.53 5 36.233 16600 0.012 29.45
15 52.719 23208 0.035 129.13 10 42.466 33200 0.017 36.68
15 48.699 49800 0.022 43.97
20 60.174 30854 0.042 151.45
20 54.933 66400 0.026 51.29
25 67.674 38535 0.049 182.48
25 61.040 82762 0.031 58.47
30 75.162 46207 0.057 213.86
30 67.217 99256 0.035 65.76
35 82.631 53866 0.064 245.18
35 73.382 115730 0.04 73.11
40 90.083 61512 0.072 276.45
40 79.537 132180 0.044 82.31
45 97.516 69144 0.079 307.62
45 85.679 148610 0.049 91.50
50 104.93 76761 0.086 338.73 50 91.809 165020 0.054 100.67
55 112.32 84364 0.094 368.78 55 97.927 181400 0.058 109.82
60 119.70 91952 0.101 400.70 60 104.03 197750 0.063 118.95
65 127.08 115530 0.109 432.50 65 110.120 214080 0.067 128.06
70 134.41 124300 0.116 463.37 70 116.200 230380 0.072 137.15

Grey cast iron Existing model results at different speeds Modified Design results with Grey Cast Iron HT300

Heat Heat
speed(m Temperature Deformation Equivalent speed( Temperat Deformat Equivalent
Flux(W/m Flux(W/
/s) (C) (mm) Stress(Mpa) m/s) ure(C) ion(mm) Stress(Mpa)
2) m2)

0 30 0 0 0 0 30.000 0 0.000 0.00

5 36.489 14733 0.012 34.60 5 36.233 16600 0.017 5.35
10 42.977 29466 0.017 47.90 10 42.466 33200 0.024 10.70
15 49.466 44200 0.022 58.90 15 48.699 49800 0.030 16.07
20 55.955 58933 0.027 69.97 20 54.933 66400 0.037 21.40
25 62.307 73485 0.032 80.70 25 61.040 82762 0.044 26.70
30 68.735 88138 0.037 91.65 30 67.210 99256 0.050 32.02
35 75.151 102770 0.041 102.55 35 73.380 115730 0.057 37.34
40 81.555 117390 0.047 113.43 40 79.530 132180 0.064 42.60
45 87.945 132000 0.051 124.28 45 85.670 148610 0.070 47.90
50 94.322 146580 0.056 135.11 50 91.800 165020 0.077 53.20
55 100.690 161140 0.061 145.91 55 94.920 181400 0.083 58.50
60 107.040 175690 0.065 156.69 60 104.030 197750 0.090 63.70
65 113.370 190210 0.070 167.45 65 110.120 214080 0.097 69.03
70 119.690 204710 0.075 178.17 70 116.200 230380 0.100 74.20
GRAPHS

Equivalent Stress vs Speed for (HT250 vs HT300)

Temperature (Stainless Steel vs Grey Cast Iron)
CONCLUSION
The Conclusions drawn about material and Design Modification:
i) Grey cast iron gives better results when compared to Stainless steel
for Existing model.
ii) The Modified Design gives better results in comparison to Existing
Design with Grey Cast iron.
The Conclusions Drawn with Reference to Coupled field Analysis:
i) The disc brake made up of grey cast iron exhibited more heat flux
and capacity to with stand high thermal stresses.
Equivalent Stress (Stainless Steel vs Grey Cast Iron) ii) The couple field analysis of different materials shows that the grey
cast iron gives reliable results as it has good cooling rate efficiency
when compared to stainless steel.
FUTURE SCOPE
In the present investigation of Thermal analysis of disc brake,
a simplified model of the disc brake without any vents with only
ambient air cooling is analyzed by FEM package ANSYS. As a future
work, a complicated model of Ventilated disc brake can be taken and
there by forced convection is to be considered in the analysis. The
analysis still becomes complicated by considering variable thermal
Temperature (Existing Design vs Modified Design) conductivity, variable specific heat and non-uniform deceleration of the
vehicle. This can be considered for the future work.
A full 3D analysis of the brake disc including the pads should
be considered in order to investigate the effects of rotating heat source
and the non-uniform heat flux over the rubbing surfaces due to non-
uniform pressure distributions.
A programe of experimental work needs to be undertaken using a
full size dynamometer since it can subject the brake to the same
sequence of high energy stops that has been modeled in the numerical
situation. This will provide the necessary data to validate the model and
provide an indication of the location of possible fracture sites.

Equivalent Stress (Existing Design vs Modified Design)

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