Thermo-Structural disc brake rotor of a car

Thermo-Structural
Analysis of Slotted and Drilled Disc Brake

 

Ch.Indira
Priyadarsini

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Assistant Professor

Chaitanya Bharathi Institute of Technology

Gandipet, Hyderabad, India

[email protected]

 

Abstract

 

The current tendencies in automotive industry need
intensive investigation in problems of interaction of safety systems with brake
system equipments. At the same time, the opportunities to decrease the power
take-off of single components, disc brakes systems. Disc brakes sometimes
spelled as “disk” brakes, use a flat, disk-shaped metal rotor that spins with
the wheel. When the brakes are applied, a calliper squeezes the brake pads
against the disc, slowing down the wheel.The disc brake is a device for slowing
or stopping the rotation of a wheel. Repetitive braking of the vehicle leads to
heat generation during each braking event. Transient Thermal Analysis of the
Rotor Disc of Disk Brake is aimed at evaluating the performance of disc brake
rotor of a car under severe braking conditions and there by assist in disc
rotor design and analysis. Disc brake model and analysis is done using ANSYS
workbench 16.0. The main purpose of this study is to analysis the thermo
mechanical behaviour of the dry contact of the brake disc during the braking
phase. The coupled thermal-structural analysis is used to determine the thermal
stresses and to calculate the Heat fluxes in x-y-z planes. This is established
with two discs they are, Drilled type and Slotted type and analysis is done by
taking two different components such as Cast Iron and Stainless Steel and
comparing which material is best suited for making of a disc brake.

 

Keywords: Thermal
analysis, Slotted brake, Drilled
brake, Disc brake.

 

 

1.     
Introduction

The disc brake
is a device for slowing or stopping the rotation of a wheel. A brake disc
usually made of cast iron or ceramic composites (including carbon, Kevlar and
silica), is connected to the wheel and/or the axle. To stop the wheel, friction
material in the form of brake pads (mounted on a device called a brake caliper)
is forced mechanically, hydraulically, pneumatically or electromagnetically
against both sides of the disc. Friction causes the disc and attached wheel to
slow or stop. Most modern cars have disc brakes on the front wheels, and some
have disc brakes on all four wheels. This is the part of the brake system that
does the actual work of stopping of the car. The purpose of friction brakes is
to decelerate a vehicle by transforming the kinetic energy of the vehicle to
heat, via friction, and dissipating that heat to the surroundings. So friction
based braking systems are still the common device to convert kinetic energy
into thermal energy, through friction between the brake pads and the rotor
faces. Braking system is performed by combination of different components of
disc brake assembly such as caliper, piston and cylinder, pads, and rotor. Disk
brake types: 1. Drilled type 2. Drilled and slotted. 3. Disk with internally
slotted. 

Nevertheless,
they are certain issues arising in the disc brakes while braking. Some of the
issues which generally occur while braking are:

 

NVH ISSUES

Noise, vibration
and harshness are complex issues that involve the entire system of components
from the brake system. Ongoing investigations in the industry have identified
several initiating factors relating to the brake elements themselves which can
be grouped into the following sections: 1. Brake disc hot spots which typically
result in thermal judder.

2. Uneven rotor
thickness wear and rotor thickness variation.

3. Rotor
deflection and oscillation.

 

THERMAL
MANAGEMENT ISSUES

1. Uneven
heating of brake rotors can temporarily cause, or increase, thickness
variation, and sometimes can produce a primary thermal buckling that warps the
rotor.

2. Uneven rotor
cooling in the case of a vehicle parked immediately following strenuous braking
activity can cause the area of rotor under the brake pads to cool more slowly
than the portion of the rotor open to the atmosphere, resulting in uneven
thermal stresses in the rotor and leading to pad imprinting, residual
internal  stresses and material failure.

 

2.     
Literature Review

T Piotr
GRZE? 1 investigated the temperature fields of the solid disc brake during
short, emergency braking. Transient thermal analysis of disc brakes in single
brake application was performed. To obtain the numerical simulation parabolic
heat conduction equation for twodimensional model was used. The results show
that both evolution of rotating speed of disc and contact pressure with specific
material properties intensely. In basic working operation, a disc or drum brake
system has to reduce wheel speed when a driver desires vehicle deceleration.
The kinetic energy generated by a vehicle in terms of wheel speed is converted
into heat energy due to the application of the brake system. The friction force
between disc/drum and brake pad/brake shoe applies friction torque to the wheel
in the opposite direction of the car’s movement. This result in the reduction
of vehicle speed and heat energy occurring in the brake disc/drum causes a
temperature increment in the disc/drum swept area during the brake application.
This physical action of the brake disc/drum causes heat conduction to the
adjacent braking system components 1. Lee 2 stated that inconsistent
dissipation of heat inside the brake disc could cause deformation of the disc.
Even worst, the disc deformation could also cause friction loss and
consequently led to brake fade 3. Furthermore, high temperatures of the brake
disc could cause cracking in the brake disc material due to high thermal
stresses. On top of that these factors also cause vibration 4, 5. It is
become common in the brake research community to fully utilize finite element
approach in order to identify and predict disc/drum brake structural
performance. For instance, Koetniyom 6 performed temperature analysis on
brake discs under heavy operating conditions. He found that the physical shape
of vehicle brake discs play a significant role in determining the temperature
characteristics including the overall brake efficiency. Kamnerdtong et al. 7
attempted to link the interaction between mechanical and thermal effects with
disc movements and heat caused by frictions. They concluded that, from finite
element analysis, temperatures on the disc surface changed at each point over
the period, which indicates inconsistent dissipation and temperature
differences in each side of the disc. Hence, inconsistent contact between disc
and pad could affect material deformation. Belhocine et al. 8 used the finite
element Sofware ANSYS to study the thermal behaviour of the dry contact between
the discs of brake pads at the time of braking phase. Temperature distribution
obtained by the transient thermal analysis was used in the calculations of the
stresses on disc surface. Abdullah and Schlattmann 9 used finite element
method to calculate the heat generated on the surfaces of friction clutch and
temperature distribution for case of bands contact between flywheel and clutch
disc, and between the clutch disc and pressure plate (one bad central and two
bands) and compared with case of full contact between surfaces for single
engagement and repeated engagements. In other work, Abdullah et al. 10 used
the finite element method used to study the contact pressure and stresses
during the full engagement period of the clutches using different contact
algorithms. Moreover, sensitivity study for the contact pressure was presented
to indicate the importance of the contact stiffness between contact surfaces.
Akhtar et al. 11 employed finite element (FE) method to explain the transient
thermo elastic phenomenon of a dry clutch system. The effect of sliding speed
on contact pressure distribution, temperature and heat flux generated along the
frictional surfaces was analyzed. Sowjanya and Suresh 12 conducted a static
structural analysis of the disc brake whose some composite materials were
selected to compare the results obtained such as deflection and stresses. In
the research developed by Reddy et al. 13, thermal and structural coupled
analysis was carried out to find the strength of the disc brake.

 

3.      Material
for disc brake

3.1 CAST IRON

Cast iron
usually refers to grey cast iron, but identifies a large group of ferrous
alloys, which solidify with a eutectic. Iron accounts for more than 95%, while
the main alloying elements are carbon and silicon. The amount of carbon in cast
iron is the range 2.1-4%, as ferrous alloys with less are denoted carbon steel
by definition. Cast irons contain appreciable amounts of silicon, normally
1-3%, and consequently these alloys should be considered ternary Fe-C-Si
alloys. Here graphite is present in the form of flakes. Disc brake discs are
commonly manufactured out of a material called grey cast iron.

 

3.2 STAINLESS STEEL

Stainless steel
is a steel alloy with minimum of 10.5% chromium content by mass. Stainless
steel is notable for its corrosion resistance, and it is widely used for food
handling and cutlery and many other applications. Due to its corrosion resistance
properties it is used in the manufacture of disc brake. They are many types of
stainless steel available but depending upon the requirements of the design its
properties and corrosion resistance is chosen.

Material properties

 

NOTE: The
specific heat of the material used is constant throughout and does not change
with the temperature.

Material: Cast iron

Table.1 Cast iron Properties

S.NO

PROPERTY

VALUE

UNITS

1

Density

7200

Kgm^-3

2

Youngs Modulus

1.1E+11

Pa

3

Poissions
Ratio

0.28

 

4

Bulk Modulus

8.3333E+10

Pa

5

Shear Modulus

4.2969E+10

Pa

6

Ultimate
tensile strength

2.4E+08

Pa

7

Ultimate
compressive strength

8.2E+08

Pa

8

Isotopic
thermal conductivity

52

Wm^-1C^-1

 

Material: Stainless Steel

Table.2 Stainless Steel Properties

S.NO

PROPERTY

VALUE

UNITS

1

Density

7750

Kgm^-3

2

Youngs Modulus

1.93E+11

Pa

3

Poissions
Ratio

0.31

 

4

Bulk Modulus

1.693E+11

Pa

5

Shear Modulus

7.3664E+10

Pa

6

Tensile Yield
strength

2.07E+08

Pa

7

Compressive
Yield strength

2.07E+08

Pa

8

Tensile
Ultimate strength

5.86E+08

Pa

9

Isotropic
Thermal conductivity

15.1

Wm^-1C^-1

 

 

 

4.     
Modelling and meshing

4.1
MODELLING

With The disc brakes created using Solid works 2016 in
which main modules are:

SKETCHERPARTASSEMBLY

Sketcher is used
to create design and part is used to apply extrude and material to see the
model in Three- Dimensional as shown in Fig.1 and 2

Fig.1 Slotted
Disc Brake

 

Fig.2 Drilled
Disc Brake

After Modelling
of the disc brakes, the thermal analysis of the disc brakes are done in Ansys
workbench 16.0.

 

4.2 MESHING

The goal of
meshing in Workbench is to provide robust, easy to use meshing tools that will
simplify the mesh generation process. The model using must be divided into a
number of small pieces known as finite elements. Since the model is divided into
a number of discrete parts, in simple terms, a mathematical net or
“mesh” is required to carry out a finite element analysis. A finite
element mesh model generated is shown below with elements of 18768 and nodes of
33534

Fig.4 Mesh of
Slotted Brake

 

Fig.5 Mesh of
Drilled Disc Brake

 

 

5.     
RESULTS OF THERMAL ANALYSIS

5.1 RESULTS OF SLOTTED AND DRILLED DISC BRAKE

 

5.1.1Stainless
steel

 

Fig.6 Nodal
temperature of SS material

Max=798.58,Min=31.48

Fig.7 Total deformation of SS material Max=0.0033817,Min=0

 

 

Fig.8 von –Mises Stress of SS material

Max=1.1612e9,Min=6.1972e6

 

5.1.2 Cast iron

 

Fig.9 Nodal
temperature of CI material

Max=524.32,
Min=103.88

 

Fig.10
Deformation  of CI material

Max = 0.0012333, Min =0

Fig.11 Von-mises
stress of CI material

Max =5.1073e8,
Min= 1.4904e6

 

5.2 RESULTS OF SLOTTED DISC BRAKE

 

5.2.1Stainless steel

 

Fig.12 Nodal
temperature of SS material

Max= 947.4, Min
= 36.155

Fig.14
Deformation of SS material

Max = 0.0040041,
Min = 0

Fig.15 Von-mises
stress of SS material

Max = 1.295e9,
Min= 9.0283e6

 

 

5.2.2 Cast Iron

Fig.16
Nodal temperature of CI material

Max
=630.18, Min = 129.71

Fig.17
Deformation of CI material

Max= 0.0014691,
Min = 0

Fig.18 Von-mises
stress of CI material

 

 

5.3 Comparison of Slotted and Drilled , Slotted Discs
Results

 

Table.3
Comparisons of  Slotted disc brake with
SS and CI materials

 

Type Of
Material

Thermal
Temperature(?C)

Thermal
Deformation(m)

Max.

Min.

Max.

Min.

Caste Iron

630.18

129.17

0.0014691

0

Stainless
Steel

947.4

36.155

0.0040041

0

 

33.4%

 

75%

 

 

Table42
Comparisons of  Slotted and Drilled disc
brake with SS and CI materials

 

Type Of
Material

Thermal
Temperature(?C)

Thermal
Deformation(m)

Max.

Min.

Max.

Min.

Caste Iron

524.32

103.88

0.00123

0

Stainless
Steel

798.58

31.48

0.0033817

0

 

34%

 

64%

 

 

6. CONCLUSIONS

 

The following
conclusions are drawn from the presentwork.

1. Static
structural analysis is carried out by couplingthe Thermal solution to the
structural analysis andthe maximum Von Mises stress was observed to be

6.8e8
Pa for CI,1.295e9 Pa for slotted and slotted and drilled disc brake

2. The
deformation due to thermal loading was observed 0.0012333 for CI and0.0033817
for SS for slotted drilled disc brake

3.The
deformation due to thermal loading was observed 0.0014691 for CI and
0.0040041for SS for slotted disc brake

4. CI Slotted
drilled disk showed 63.53% better than the SS slotted disk brake.

5. CI Slotted
drilled disk showed 63.31% better than the SS slotted disk brake.

6.From analysis
it is observed that the CI slotted and drilled disc brake showed 16.05 % better
than the CI slotted disc brake

7. The Brake
disc design is safe based on the Strengthand Rigidity Criteria.

Comparing the
different results obtained from theanalysis, it is concluded that Cast Iron is
the best material for both slotted disc, because the thermal temperature and
thermal stresses obtained for this material is lesser than compared to the
stainless steel material.

CI disc showed 33% reduction in temperature Deformation was less in CI by 75% compared to SS

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