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The braking system is the most essential part of any automobile. The utmost common means of braking is disk brakes. Every brake system currently used is effective, however the performance during braking differs with different manufacturers and different materials. Due to the customer’s need for more performance in everyday riding, researchers are looking for various alternative materials to increase the efficiency and durability in day-to-day life. In this paper we have reviewed the different materials used in brake disc and compared their properties. To understand the practical problems in current materials, damaged broken rotors have been studied and analyzed.

In this paper we have reviewed the different materials used in brake disc and compared their properties. To understand the practical problems in current materials, damaged broken rotors have been studied and analyzed.

1 The objective of the paper is to perform the structural analysis of disc brake. For the analysis, a disc brake was designed using solid works and further the Static Structural Analysis and Steady State Thermal Analysis was performed in Ansys, between two materials, Martensitic Stainless Steel and Grey Cast Iron. The results show that the maximum strain and total deformation in less in grey cast iron than in stainless steel while the total heat flux in greater in the first. Hence, both materials have similar price range but grey cast iron has better thermal stability hence, it can be considered as a better material.[12] 2 In this paper, the process of design and analysis is explained and the same is done for a carbon fiber brake rotor with different thickness. The break disc with 240mm diameter and 12mm thickness shows a very less deformation. The temperature is also less and hence the heat dissipation takes place faster.[11] 3 Disc plate inspired from TVS Apache RTR 160 is modelled and analyzed for carbon-ceramic material. This materials disc brake when modelled in petal design shows better results in strength and rigidity than compared to the constants recently in use.[13] In the review article of Hemant Kumar, he focuses on various brake rotor materials from 1992 to 2021. In this paper author covered the thermal and mechanical properties of cast iron, steel, aluminium, titanium alloys, and ceramic matrix composites.He concluded that the cast Iron has fast cooling rate while steel has much more corrosion resistance and is lighter than steel. Aluminium has high strength to density ratio with a low operating temperature. CMC is light weight with good mechanical properties while titanium metal matrix composites have high rate of heat dissipation than all the other materials.[16]

Disc Brake

The disc brake is a device to slow up the rotation of a wheel. Due to friction, the disc and attached wheel tend to slow down or stop. Most modern vehicles have disc brakes on the front wheels, and some have disc brakes on all rear wheels. This is the part of the braking system that does the actual work of stopping the vehicles. Hence, vehicle braking is considered to be the most concentrated area of study.

There are two main types of automotive brakes that has been in use till now are-

1] Drum brake

2] Disc brake

Drum brakes operate by pressing shoes (stator) radially outwards against a rotating drum (rotor), while disc brakes operate by axially compressing pads (stator) against a rotating disc (rotor).

Ventilated Disc Brake

A more advanced form of the disc brake is the ventilated or internal cooling disc brake, where air flowing through radial passages or vanes in the disc.

On the application of vehicles brakes, low frequency vibrations may occur, and these vibrations can be felt by the driver in the body, in the form of steering shaking and, in some cases, an audible drone which is known as ‘judder’.

Two types of juddersexist:

1      Hot (or thermal judder)

2      Cold judder.

Cold judder is caused by uneven thickness of the rotor, known as disc thickness variation, this leads to deviations in contact pressure as the pads connect with the rotor. This results in uneven brake torque variation.

Thermal judder, occurs at elevated temperatures, and is caused by thermal deformation of the rotor.

Braking System

Disc brakes are commonly used in automobile applications and it uses calipers to apply pressure against a disc or rotor to create friction.

In the disc brake system, the friction pads apply grip on the external surface of the disc to perform braking. The braking system must decelerate a vehicle in a controlled and repeatable fashion and when appropriate force applied causes the vehicle to stop. The braking should permit the vehicle at a constant speed when traveling downhill. The brake system holds the vehicle stationary when flat or on the gradient.

The brake rotor is the rotating part of wheel's disc brake assembly and must serve as an efficient energy dissipation and storage device. In order to achieve this purpose, air must be circulated through the rotor to provide adequate cooling. The passages, formed by the radical fins between the braking surfaces, acts as a centrifugal fan, facilitating the required air flow for cooling.

Materials In Use

Brake rotors are usually constructed from cast iron. This is an adequate material, but it's also the heaviest. Another material used is steel or layered steel. Steel rotors are lighter and dissipate heat better than cast iron. Aluminum is another material used for rotors, which is favored by motorcycles because it’s lightweight. Additionally, some rotors are constructed from carbon. Carbon rotors offer excellent heat dissipation and performance. Lastly, ceramic (and carbon-ceramic) rotors promise unbeatable cooling capacity and heat dissipation.

Review of Different Rotors In Use

Thermal effects - In different literature, it is clear that the maximum temperature rise of cast iron disc is much small with compared to stainless steel and therefore on the basic of thermal investigation, cast iron is the best desirable substantial for manufacturing disc brake.

From steady state thermal analysis, Avinash et all. says that the temperature distribution remains same in case of both stainless steel and grey cast iron whereas the heat distribution is more in case of grey cast iron as compared to stainless steel. It is observed that minimum temperature in case of grey cast iron is 10.9% higher as compared to stainless steel.[1]

Heat flux-Anil Babu Seelem et al., the total heat flux is 9.02% higher in case of grey cast iron as compared to stainless steel.

Fig- Comparison of temperature and Heat flux for SS and CGI

Deformation due to stress- In another study it observed that the stainless steel can provide better brake performance than others from deformation point of view whereas cast iron provides better performance from stress point of view. [2]

Fig- Deformation of SS and CGI

Corrosion- Though, cast iron disc brake have some drawback of getting corroded when it comes in contact with wetness and hence it cannot be used in two wheelers and thus, we prefer stainless steel. Cast iron have better heat dissipation rate but the tendency of the cast iron is that it gets corroded when comes in contact with water or moisture. Hence it is not suitable for production purpose.

For better weight strength carbon fiber epoxy resin disc is found 50% lighter than the conventional brake disc rotor. So, it is trying to use carbon-carbon or carbon, carbon graphite composites, for better performance. Due to high speed, excess heat is generated and causes damages like cracking, thermal expansion etc.

It is found that to avoid the huge problem arises in the individual field, different materials are used for the solutions and with all these carbon-carbon is still showing better performance for high-speed bike.

Practical Problems In Brake Rotor

When the rotor is subjected to high level of friction by the fluid by capilers and the pressure of rotor pad, its temperature rises to a very high level, later on cooling down to normal.

Fig- The figure shows 2-D drawing of disc brake rotor in Auto-Cad

This further leads to wrapping, scarring or cracking due to high friction and expansion process.

Common indications of a damaged brake rotors include:

1.     A grinding noise when braking

2.     Pulsating or shaking while stopping

3.     Grooves or ridges that you can feel on the surface of the rotor

4.     Visibility rusted or thinned out rotors

5.     Decreased brake performance

Fig- Corroded and broken brake disc rotor

Thermal resistance between the pad and the disk prevents the disk from absorbing the generated heat at the contact surface of the pad, so that temperature of the pad increases and consequently heat soaking to brake fluid increases and this may cause brake fluid vaporization. Therefore, another provision that should be taken into account is to use a brake fluid with an appropriate DOT rating regarding to minimum dry and wet boiling points.

On application of the vehicle brakes, low frequency vibrations may occur, these vibrations can be felt by the driver as body shake, steering shake and in some cases an audible drone, this phenomenon is known as ‘judder’.

Cold judder is caused by uneven thickness of the rotor, known as disc thickness variation, this leads to deviations in contact pressure as the pads connect with the rotor. This results in uneven braking or brake torque variation.

The second type, thermal judder, occurs at elevated temperatures, and is caused by thermal deformation of the rotor.

From this study, it is very clear that an efficient brake system is very important for proper functioning of high-speed vehicles. So, for the future it is required to modify the disc plate and reduce the problems currently faced in the disc as much as possible. Here in this paper, it is observed that the most common factor affecting the performance of the disc plate is corrosion and the high level of heat it is subjected to.Carbon-carbon fiber shows better performance than traditional cast iron and all other materials, on the basis of rusting and other mechanical properties.It works great high temperature but it is not that efficient with the effects after cooling and contraction. On the upper side, carbon -carbon solves the issue of friction to a greater extent. Still, more research is required for high-speed vehicles to ensure maximum safety and best performance.

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