Braking Systems Notes (T3)

11ES Braking Systems Notes

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Brakes

- Mechanical devices used to restrict movement, thus slowing down a vehicle

- Convert forward kinetic energy into another form:

o Heat (friction)

o Electricity (regenerative, eddy current braking systems)

o Potential energy (pressurised air/oil)

o Kinetic energy within another component

- Applications of brakes:

o Usage on the ground:

Rotating axles or wheels

o Usage in a moving fluid (e.g. air, water):

Aircraft/ship flaps

Parachutes (aircraft, drag racing cars)

o Some vehicles obviously use a combination of brakes to meet a variety of purposes.

History of Brakes:

Date Description

Early 1890s

Wooden block (spoon brake): a lever controls a wooden block that adds friction on a wheel. Prevented the movement of a horse-drawn or steam powered vehicle in the Roman era.

1902 Drum based braking system is invented by French manufacturer Louis Renault (wood blocks were changed to external cast iron brake shoes)

Disc braking system patented by William Lanchester

? Internal expanding shoe brake is invented/ The brake shoes are placed inside the drum brake to protect them from dust/heat/water that affected their performance

1918 End of mechanically-activated brakes

(Four-wheel) Hydraulic brake system is invented by Malcolm Loughead. Fluids transferred the force on the pedal to the pistons and then to the brake shoes.

1950s Disc braking system becomes popular, due to faster and heavier cars and the ineffectiveness of the hydraulic system to distribute heat

Types of Brakes (3):

Type of Brake Description

Frictional Well-defined wear surface - 'Shoe' brakes: (band brake, drum brake) - 'Pad' brakes: (disc brake)

Some can use a working fluid as friction - Hydrodynamic brakes: (parachute)

Pumping Used when a pump is part of the machinery Pumping losses from the engine can be converted into useful braking

Electromagnetic Used when an electric motor is part of the machinery Used as a generator to charge electric batteries, etc.

- Regenerative brake Used to apply resistance via electromagnetic induction/force:

- Eddy current brakes - Electro-mechanical brakes


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Example Brakes

Band Brake:

- Primary/secondary brake

- A band of friction material tightens around a cylindrical piece of equipment (as opposed to

drum brakes that expand)

- Properties:

o Simple, compact and rugged

o Little input force generates high braking force

o Prone to brake grabbing (malfunctions) and brake chatter (grabbing and vibrations)

o Prone to brake fade (a loss of brake force when hot)

- Uses: winch drums (i.e. the rotating handle), chain saws, (some) bicycle brakes

Drum Brake:

- Brake shoes contained inside the drum expand when pressure is applied

- The expansion of brake shoes presses against the drum to slow down the wheel

- Uses: cars typically used in the rear wheels due to (as compared to a disc brake):

o Less expensive in manufacturing

o Less precise

o Ability to also incorporate a parking brake mechanism

Disc Brake:

- Callipers push together when pressure is applied

- Brake pads with friction material on the heads of the callipers slow down a disc and

subsequently the wheel

- Uses: bicycle (via chains), car (via hydraulics fluid, pistons)

- Car configurations:

o Front-disc/rear-drum brake setup

o On all four wheels (only necessary today within high performance cars)

- Usage in a car (as compared to a drum brake):

o Slimmer and smaller design

o Exposure to open air reduces chances of overheating and oversaturation thus

reducing chances of brake fade

Greater reliability particularly in racing


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ABS (Anti-lock Braking System):

- History:

o 1929: ABS developed for aircraft usage pilots could immediately apply full brakes

and automatically adjust instead of slowing increasing pressure to find the skid point

of the brakes. Also meant fewer burned/burst tires

o 1958: scientific acknowledgement of the value of ABS in motorcycles

o 1970s: incorporation of ABS in many major car companies leading to improvements

in ABS technology cheaper and more reliable.

- Principle: traction (frictional force) is necessary within braking systems. ABS continually

adjusts to deliver maximum frictional force between surfaces without the wheels slipping.

o Slipping wheels provide less traction than non-slipping wheels

- Advantages: shorter stopping distances, better control of the vehicle (potentially steering

away from a crash)

- ABS system and how it works:

1. A controller (typically located in the centre of the car) analyses speed sensors

located on wheels.

The number of speed sensors in a car is dependent on the ABS configuration:

a. Four-channel, four-sensor: best scheme one set of speed sensor and valve

for each wheel (most cars)

b. Four-channel, three-sensor: one set for each front wheel, one set for both

rear wheels (used in pickup trucks)

c. One-channel, one-sensor: one set for both rear wheels (pickup trucks)

2. Unexpected decelerations in a wheel in proportion to the movement of a car signal

the wheel is about to lock up. The wheel stops moving at a faster rate than the

movement of the car, causing skidding.

3. If the controller detects this, ABS activates at the corresponding area. Pressure is

decreased using a valve to accelerate the wheel because this process is then

reversed using a pump generates a pulsing action of acceleration and

deceleration (up to 15Hz).

4. The tire now moves at the same rate as the car. Automatic controlling means ABS

provides maximum braking power.

Regenerative Braking:

- Energy recovery conversion technique: converts kinetic energy into another useable form

(immediately used or stored)

o Differs from conventional braking systems using friction (brake linings): conversion

of KE to heat is wasteful and intrusive

- Conversion techniques:

o Electrical energy: via a generator

o Mechanical energy: via kinetic energy recovery systems (KERS)

- Some limitations of regenerative braking: because of this it is often used alongside

traditional friction-based braking

o Only useable on wheels linked to the drive motor (issues within two-wheel drives)

o Cannot be used if other components on the same supply system are drawing power,

or if the battery/capacitors are fully charged


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o Ineffective at:

Low speeds: low amounts of KE

High speeds: inability for the battery to cope with the extra load

o Physical necessities:

Physical locking still required (parking brakes)

Necessity of friction brakes in the instance of failure

Automotive Hand Brake (parking/emergency brake):

- A latching brake to keep vehicles stationary

- Exist in a variety of forms, all of which bypass normal braking: see below

- Mechanical system:

o Hand brake -> brake cable -> lever -> equalizer -> rear wheels

Note: the cable passes via a lever to amplify the user's pull

Note: the cable passes an equalizer that splits the cable in two and

distributes the force equally over the rear wheels

o Rear drum brake: cable runs directly to the brake shoes

Bypasses the hydraulic system and requires no extra parts

o Rear disc brake: requires a redesign of the brake

Exclusive parking brake / Auxiliary drum brake: a drum brake system is

mounted inside the rear motor

Calliper-actuated parking brake system: addition of a lever and corkscrew in

the calliper pistons of the disc braking system

- Electric e-brake system:

o Replacement of a lever with a small button (on the dash)

o Button signals an electric motor to pull the brake cable or engage the brake callipers

Overall Braking Systems Process


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1. User presses on the brake pedal

2. Force generated by the user is 'boosted' by the vacuum booster

3. Boosted force compresses brake fluid, via the brake master cylinder

o Brake fluid: a hydraulic fluid stable in volume under a variety of temperatures it

does not expand with heat

4. Distribution of brake fluid into all the brakes

o Disc brakes, drum brakes, and parking brakes are all examples of the braking

systems available on the vehicle

Car Features

Engine Strokes: completed over two cycles

Induction A pin opens; oil comes in from one side (introduction of oil)

Compression The pin closes; oil is compressed

Power Oil combusts; the engine is compelled to turn again

Exhaust A second pin opens; oil exhaust is released from the other side

V6, V8, V10, V12: describes the number of cylinders an engine has. More cylinders -> more engine

strokes -> more power generated

- Horsepower: equivalent to 745.7 watts

Powertrain: the group of components in a motor vehicle that generate and deliver power (in a

sequence). Includes the engine and transmission + drive shafts and differentials, etc.

- Driveline/Drivetrain: consists of parts of the powertrain excluding the main components of

an engine and transmission (i.e. drive shaft onwards)

Engine to Drive Shaft:

1. Engine: fuel is burnt to generate power

2. Transmission/Gearbox (manual/automatic): gears control the ratio of

speed between the engine and the wheels

3. Drive Shaft: Uses torque to transfer engine power to the opposite

end of the car. Delivers to front or rear wheels depending on the

location of the engine.

Two-wheel drives:

- 4x2 means there are four wheels, and two are powered by the engine

Four-wheel drives (4x4): all four wheels receive torque from the engine simultaneously


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Gearbox:

- Neutral position: no gears engaged

- 1st Gear: largest gear is engaged (i.e. the last gear of the top line / output shaft)

o Used when the car starts moving or climbs a steep incline/slope

- Subsequent gears (2nd, 3rd) allow for faster speeds by using smaller differences in a smaller-

to-larger gear ratio

- 4th gear: bypasses all gears (i.e. no gears in the bottom line / layshaft are used) this means

the wheels are directly connected to the engine

o Used when the car moves along a level road

- Reverse gear: in a pseudo-1st-gear position, a reverse cog is activated that spins the output

shaft in the opposite direction reversing wheel movement.

Gear Box to Wheels:

- Drive Shaft: placed in the middle of the car, alongside the car's

length a spinning metal pipe that delivers torque power from

the gearbox to the differential

- Differential: supplies power to the rear wheels 'pipes' placed

alongside the car's width.

o Note: gears within the differential (the final drive) are

used to change the torque's rotation

o Power to each wheel can be separately controlled to allow for turning and to

prevent skidding

- Together the gearbox and differential control the torque output / power delivered to the rear

wheels (that is, if they are opposite the front engine).

Car steering:

- Steering wheel: accept user input

- Manual: the driver's actions/force applied directly cause the

turning of the front wheels

- Power: the driver's actions are directed to a motor

Suspension System:

- A system placed above the wheels to absorb vibrations.

- Uses springs that encase shock absorbers. Shock absorbers are

pipes filled with hydraulic fluid fluid is forced up to absorb the

shocks of bumps.


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Electrical System: other electrical components/appliances in the car, such as:

- Lights: headlights, tail-lights, turn signals

- Sound (and television): car-horn, radio system, etc.

- Windshield wipers

Engineering Mechanics

Friction

- Definition: the resistance to motion, of two bodies/surfaces in contact

- Essential to starting or stopping a vehicle

Static Friction:

- Equation: measured in N

= FF / RN

where = coefficient of friction, FF = frictional force, RN = normal reaction

o Coefficient of friction: describes the 'amount' of friction

between the two materials it is a ratio of the frictional

force to the normal reaction between the two surfaces

o Frictional force: opposes the force that tends to cause the

motion of the object. In static friction, FF = opposing force.

o Normal force: opposes the force of weight that causes the

two surfaces to touch and rub against one another

- Therefore the coefficient of friction can be a useful measurement of the amount of friction a

material produces:

FF = *RN

- Note RN (normal reaction) refers to the force opposing gravity (i.e. RN = W = mg)

- Braking systems require materials of different coefficients of friction depending on their

usage. Higher coefficients of friction lead to higher amounts of heat energy produced:

o Thus, bicycle braking systems use a higher coefficient of friction than in a car

o In response, automotive braking systems with lower coefficients of friction need to

generate more force (RN)

Stress:

- A measure of the internal reaction to an externally applied load

- Measured in Pascals (Pa); equivalent to N/m2

- Equation:

f = P / A

where f = stress (Pa), P = load (N), A = cross-sectional area (m2)

- Stress: denoted by sigma () in the past; today practises use 'f', with a subscript for if the

stress in tensile, compressive, shear or torsional.

o Tensile and compressive: the load acts perpendicular to the surface

o Shear: the load acts parallel to the surface [?]


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Strain:

- Proportional change in length under the an axial load

- Dimensionless number it is ratio/fraction/percentage

- Equation:

e = x / l

where e = strain, x = extension, l = original length

- Strain: denoted by epsilon () in the past; today practises use 'e'

Hooke's Law:

- Stress is directly proportional to strain within its proportional limit (seen on stress-strain

graph). This is a linear function.

Stress Strain

Stress = k * Strain

- The constant 'k' is known as Young's Modulus of Elasticity a measure of the stiffness of an

elastic material. Often also represented by the symbol E.

o The constant 'k' is a constant of proportionality, measured in Pa.

o Young's Modulus is the gradient of the stress-strain graph (rise/run)

k = Stress / Strain

Stress and Strain Continuum

- Load/Extension diagram: plotted by testing sample pieces of a material in compressive and

tensile strength

- Stress-strain diagram: translated data from a load/extension diagram

o Produces similar-or-near-identical curve pattern to load/extension diagrams


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Graphs notations:

- Proportional Limit: Hooke's Law proportional relationship of stress and strain

- Elastic Limit: point where strain changes from elastic to permanent (plastic) deformation

(elastic and plastic regions)

- Yield Points: points of increased strain without increased stress the material momentarily

'giving up' to slip and dislocation movement

- Ultimate Tensile Strength: maximum stress obtainable by a material

o Unimportant in structures never go past the elastic limit

o Important in press forming operations to prevent material fracturing

Uniform Extension: material stretches evenly along its length

Necking: uneven and localised deformation

Work Hardening: increased material strength and hardness due to congestion of slip planes.

Compressive strength increases in a material while tensile strength further weakens (tensile

strength of an alloy results from weak bonding of foreign atoms)

True stress vs. engineering stress

- Both apply the normal stress formula (f = P/A)

- Engineering stress: ratio of applied load to the undeformed (original) cross-sectional area

- True stress: ratio of applied load to the instantaneous cross-sectional area

Fluid Mechanics

Hydrostatic Pressure (pressure at a depth)

- Fluid pressure: acts upon the entire surface of an object, at right angles to the surface

o Equation: pressure = force/unit area

P = F/A

- Not affected by (independent of) the cross-sectional size or shape of container

- Affected by depth (i.e. pressure is greater at lower depths)

o Equation: [similar to potential energy?]

Ph = P0 + gh

where pressure (rho) at depth h = pressure at the top + density * gravity * height

Pascals Principle (force-distance trade-off; pistons)

- Definition: pressure applied to an enclosed static liquid is

transmitted undiminished to every point in the fluid and

to the walls of the container

o I.e. increasing the pressure at the surface P0 (i.e. by

forcing a piston into the fluid) causes a uniform

increase throughout the liquid

- Equation: P = F/A, therefore via substitution,

F1/A1 = F2/A2

- Pistons: a multiplication of force (see right), as long as it is

implied that P1 = P2.

o Another force-distance trade-off


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Archimedes Principle (the gravity of an object in a fluid)

- Explains buoyancy provides an upwards force on an object, partially balances weight force

o Objects buoyancy greater than the weight force on the object (due to lower density)

-> the object floats

- Buoyancy: force exerted by a fluid on an object this is dependent upon:

o Density of the fluid

o Volume of the object submerged

o Buoyant force = weight of fluid displaced by the objects submergence

- Definition of buoyancy via Archimedes Principle: a body wholly or partially submerged in a

fluid is buoyed up by a force equal to the weight of the fluid displaced by the body

- Definition of Archimedes Principle: determines the specific gravity of objects independent

of an objects shape

o Equation:

Specific gravity = (weight of object in air) / (weight loss when submerged in water)

g specific = weight air / weight loss in water (i.e. buoyancy)

Equation for specific weight (used to calculate specific gravity):

Work, Energy and Power

Work:

- Definition: energy transferred by a force causing either,

o Motion (travelling a distance)

o Distortion (via a tensile/compressive load)

W = Fs

where W = work (J), F = force (N), s = displacement (m)

- Unit: in joules. 1 J = 1N * 1m = 1 Nm

- Displacement is a vector therefore positive and negative work can be done (direction)

- Example forces of work:

o Applied forces:

Acceleration/deceleration

Tensile, compressive or shear forces

o Gravitational (weight) forces: acts from the centre of a body

Does positive work; lifting forces do negative work

o Frictional forces:

Does negative work opposes motion (deceleration)


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Energy

- An objects ability to do work (i.e. ability to move or deform an object)

- Many forms of energy; all obeying the Law of Conservation of Energy

- Mechanical energy: examples below

o Potential energy (PE):

Energy/ability to do work due to a certain position

E.g. gravitational potential energy (PE = mgh)

o Kinetic energy (KE):

Energy an possesses due to motion

KE = mv2 mu2 (final initial KE)

- Heat energy:

o E.g. seen in friction brakes kinetic energy is converted to heat and sound

- Electrical energy:

o E.g. electrical/regenerative braking, where generators cause kinetic -> electrical ->

chemical energy (battery)

o Note electrical potential energy: its potential difference between points = voltage

Engineering Materials for Braking Systems (Excel)

History:

Time Brake Material

Early- Spoon brakes Wooden blocks Leather lining (optional)

Late 19th

century Herbert Frood Woven cotton brakes (for wagons and early automobiles)

Woven cotton impregnated (saturated) with a bitumen solution

1908 Herbert Frood Harder wearing and heavier duty brakes for motorised vehicles

Resin-impregnated woven asbestos, reinforced with brass wire

1920s Improved brake lining materials Moulded materials containing chrysotile asbestos fibres

? Early drum braking systems Iron shoes against steel Variety of strange materials (e.g. walrus hide lining)

Today- Modern drum braking systems

Continue to contain many organic-based materials (polymers, plant fibres) Thousands of different brake material additives Composite friction materials (out of 5-20 different material ingredients)

Today- High technology carbon composite brakes

Carbon composites

Roles of Additives:

- Create property enhancements in:

o Friction stability under a variety of braking speeds or in hot/cold-wet/dry conditions

Refers to the ability of the brake pad's friction coefficient to remain high

o Wear control

o Durability

o Noise and vibration minimisation

- Functional properties are determined by composition


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o Individual constituent form, distribution and particle size -> affects -> friction,

performance and wear behaviour

- Brake materials and additives are grouped according to function:

o Abrasives:

Maintain cleanliness of mating surfaces

Control the build-up of friction films (generated by surfaces in contact)

E.g. aluminium oxide, iron oxides, quartz, silica, zirconium silicate

o Friction modifiers:

Help to raise friction, lubricate, or react with oxygen and help control

friction films

E.g. brass, graphite, ceramic 'microspheres', copper, 'friction dust', lead

oxide, magnetite, various metal sulphides (Cu2S, Sb2S3, PbS)

o Fillers or reinforcements

o Binding materials (matrixes holding constituents together)

E.g. commonly a phenolic matrix (thermoset polymer matrix)

Steel and cast irons

- Both are primarily iron with carbon (main alloying element)

- Steel: less than 2% carbon; typically less than 1%

o 2% is the greatest concentration of carbon at while iron can solidify as a single-phase

alloy, with all carbon in solution in austenite

- Cast iron: more than 2% carbon

o Solidify as heterogeneous alloys they always contain more than one constituent in

their microstructure

o Must also contain silicon (1-3%) -> in reality they are iron-carbon-silicon alloys

- Classification of carbon steels: by its properties/procedures:

o Chemical composition

o Mechanical properties

o Method of de-oxidation

o Thermal treatment (and resultant microstructure)

Use of steel and cast iron in brake drums and discs:

- Early models:

o Cast iron: flake graphite in a ferritic matrix

o Good thermal conductivity; but soft and poor wear resistance

- Subsequent models:

o Cast iron: flake graphite in a pearlitic matrix

o Improved properties moderate hardness

- Modern models:

o Grey cast iron: graphite (flakes in uniform distribution and random orientation) in a

pearlitic matrix

o Wear problems in grey cast iron mostly occur from abrasion and oxidisation this is

however only problematic in certain vehicles:

Motorcycle disc brakes: now usually stainless steel


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Racing component disc brakes: continue to use cast iron for improved

friction properties

- Advantages of grey cast iron: result due to their high-carbon and silicon content

o Excellent castability

o Melting temperatures (lower than steel)

o More fluidity (than molten steel)

o Less reactivity with moulding materials

o Excellent machinability even at wear-resistant hardness levels

o Dampening of vibration due to graphite (lubrication on wearing surfaces)

o High compressive strength

o Good resistance to fatigue

o Good thermal conductivity

- Disadvantages of grey cast iron: noticeably less due to its usefulness today

o Low ductility no rolling or forging applicable [?]

- To increase the hardness of cast iron for abrasive-wear applications:

o Addition of alloying elements -> promotes formation of carbides

o Iron is heat-treated -> martensitic matrix

o Hardened by flame or induction methods

Composites

- Composite: formed by combining two or more materials superior properties as compared

to those of the individual constituents. Examples:

o Porcelain enamel products (glass coated metal)

o Polymer / metal laminated corrugated paper

o Fibreglass strengthened cement

o Fibre reinforced plastics

o Steel reinforced rubber (tyres)

Categorised into one of four engineering categories:

- Polymer matrix composite

o E.g. (glass-fibre) reinforced (in thermosetting resin) plastic in 90% of domestic

appliances

o E.g. Fibre reinforced polymer (FRP) replaced traditional materials (wood,

aluminium, steel)

o Advantages over traditional materials:

Higher strength to weight ratio

Lighter weight

Greater corrosion resistance

Dimensional stability

Higher dielectric strength

Increased design flexibility

- Metal matrix composite

- Ceramic matrix composite

o E.g. extensive use in civil engineering structures roads, bridges, buildings

- Carbon matrix composite


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Brake materials: most materials are composites due to their:

- Range of engineering properties

- Service conditions

- Environmental conditions

Friction brake materials

- Mainly classified as:

o Organics o Semi-metallics

- Both categories may contain copper due to its ability to dissipate heat during braking

- Materials can occur within/between these categories due factors including:

o Wear rate

o Braking properties

o Noise levels

o Appearance

Asbestos (organic)

- Early hydraulic brakes: lining materials of any brake were the same -> 30-70% asbestos, and

a variety of binder materials

- Hydrated magnesium silicate Mg3 Si2O5 (OH)4

o Most common type: white asbestos (fibrous chrysotile)

- Asbestos fibres are variable in length; straight or curled

- Advantages:

o Resistance to heat and chemical attack

o Thermal stability to 500C (produces silicates above this temperature)

o Silicates produced by asbestos are harder and more abrasive than asbestos

o Excellent wear characteristics

o Regeneration of the friction surface during use

o Thermal insulation

o Ease of processing

o Stability in the environment

o Kinetic coefficient of friction of ~0.8 against clean iron

- Disadvantages: engineering perspective as compared to alternatives

o Increased wear at high temperatures

o Reduced coefficient of friction at as low as 121C, from formation of a surface glaze

o Reduced coefficient of friction (up to 65%) when wet

o Insulation properties preventing heat transfer

Extremely important in smaller brakes

- Disadvantages: social perspective

o Fibres act as a health hazard:

Lung problems/cancer

Toxicity

Potential of cancer

Chance of death

- Possible replacements for asbestos in brakes: performing similar/improved characteristics as

compared to asbestos please note that many are also composites (no contradictions)


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o Wollastonite (calcium silicate)

o Vermiculite (hydrated calcium aluminium silicate)

o Mica (aluminium silicate)

o Basalt fibre

o Rock wool

o Ceramic fibre

o Polyacrylonitrile (PAN)

o Polyester

o Chopped glass fibre

o Aramid fibres (Kevlar)

Non-asbestos organic materials

- Organic brake pads: light grey appearance, smooth surface texture. May contain fibreglass,

Kevlar, ceramics, carbon, copper, etc.

o Softer materials: better coefficients of friction, but fast wearing

o Harder organics/man-made materials: improved service life

- Fibreglass

o Most common due to its properties (i.e. hardness)

o Properties: strength, temperature resistance, friction qualities, relatively low cost

- Aramid fibres (Kevlar)

- Ceramics

o Can withstand extreme temperatures (up to 1,650C)

o Often used as part of a mixture with hard metals (via sintering heating to the point

of flowing together into a mixture)

- Carbon

o Carbon-carbon composites

Carbon matrix reinforced by long carbon fibres

Withstands high temperature (e.g. space shuttle caps)

o Necessary only in racing conditions

Very resistant to wear

More reliable

Reduces vehicle vibration

Causes less pollution than traditional brakes

A variety of different properties to carbon-carbon can be formed from

adjusting the composition of fibres (changing the form and binding matrices)

Other important carbon-carbon properties:

Density

Thermal conductivity

Tensile strength

Flexural strength

Compressive strength

Shear strength

Impact strength

o Carbon fibre composite discs with carbon fibre pads

Once common in racing

Now outlawed in racing due to unexpected and catastrophic failure

o Aircraft brakes: resin/steel, metallic linings, or carbon-carbon (C-C) combinations

- Copper (optional, used only in small amounts)


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Semi-metallics:

o 1950s: introduction of resin-bonded metallic linings

o 1960s: development of semi-metallics

- A mixture of chopped, powdered or sintered (mixture via heating) metal, bound together

with phenolic resins (thermoset polymer matrix) and other binder or filler materials

- Semi-metallic brake pads: darker in colour, visible metallic fibres, rough surface texture.

o Generally composed of ferrous metals (in the form of chopped steel-wool fibre and

finely powdered iron)

o Can also contain copper, graphite, or lesser amounts of inorganic fillers and friction

modifiers

- Lead: rarely used health concerns (poisoning)

Future semi-metallics:

- Aluminium-based Metal matrix composite (Al-MMC):

o Properties:

Reduction in component weights

Increased service life

Reduced system maintenance

- Aluminium-based composites containing 20-30% silicon carbide (SiC):

o Potential substitute for grey cast iron in fabrication of vehicle brake drums/discs

o Advantages in braking systems:

Weight reduction (40-50%)

Increased wear resistance

Thermal conductivity three times that of cast iron

Lower brake disc operating temperatures (better heat dissipation)

- Al-MMC continuum:

o Processing can occur through forging or casting

o Recycling of foundry scrap important in casting both in terms of fabrication,

production and environmental costs

o Other properties:

Not as resistant to high temperatures thus used on rear axles (similar to

the usage of drum brakes -> less energy dissipation requirements)

Expensive production as compared to conventional grey cast iron (i.e. is this

worth the reduction in weight?)


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Braking Systems Notes (T3)

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