Preliminary Engineering Studies Notes

Topic 1: Engineering Fundamentals

Areas of Engineering Practice Nature and range of the work of engineers • Engineers have been responsible for the built and technological world we

have today Historical and Societal Influences Historical developments of engineering • Wheel- 4th millennium BC • Bronze- 4th millennium BC • Iron- 1st millennium BC • Steam engine- 1698 • Cast iron- 1707 • Steel- 1856 • AC electricity- 1886 • Human flight- 1903 • Helicopter- 1920s • Pacemaker- 1958

Effect of engineering innovation on people’s lives

• Woken up by alarm, electric toothbrush to brush teeth, toaster for bread and bicycle to get to school- all of these created by ‘engineers’

• Engineers make things happen and we reap the benefits

Engineering Mechanics Mass and Force Newtons laws of Motion 1st Law : A body will remain at rest or at constant velocity unless acted upon by an unbalanced external force. 2nd Law: A body acted upon by an external unbalanced force will accelerate in proportion to the magnitude of this force in the direction in which it acts. Newton’s second law is often written in formula form as shown below. F= ma F-Force (N) M=mass (kg) A= acceleration (ms2)

3rd law: To every action there is an equal and opposite reaction Mass: the amount of matter that a body contains with the SI unit being the kilogram (kg) Force: Push or pull on body in Newtons (N) Gravity: Earth exerts a gravitational force on all bodies. The gravitational force accelerates at 9.8ms2 gravity (g) or also known as 10 ms2 gravity (g) Weight is a force that is created by gravity. Weight is the effect that the Earths gravitational force has on a body. W= mg W=Weight (N) M= mass (kg) G= acceleration due to gravity (ms2) So if you have a mass of 60kg, then your weight will be 600N Example 1.1 A power drill has a mass if 1.5kg, what is its weight? Solution: W = mg W = 1.5 x 10 W = 15N Answer: the drill weighs 15N Scalars and Vectors Scalar quantities are those that are defined by their magnitude only e.g. distance (20M), time (30s), mass (22.8kg). These quantities are represented by a number and the relevant units. Vector quantities are those that are defined by their magnitude and their direction e.g. displacement (1 km north), force (67 N vertically down), velocity (27ms-1 west) Vectors may be represented by a heavy dark line with an arrowhead which shows the following four features;

1. Magnitude 2. Direction 3. Sense 4. Point of application

Simple Mechanisms Lever

− The simplest ‘machine’ using force acting over a distance to magnify the effort (mechanical advantage providing leverage)

Inclined Plane − A basic ramp allows the load to be progressively raised in height − E.g. wheel chair ramps, car ramps

Screws

− A specific kind of spiral inclined plane − Screws magnify effort (mechanical advantage) − Used for fine adjustments

Wheel and Axle

− The invention of the wheel in 3500bc Mesopotamia changed the world forever

Pulley − Allows forces to be applied in different locations or directions − Pulleys can be joined together to produce a block and tackle − Pulleys can also be used to transfer torque from one shaft to another

Gears

− Like pulleys they can transfer torque from one shaft to another − They have the advantage of allowing drive ratios to be changed

Chain Drives

− Chains are a hybrid of characteristics from gears and belt drive systems Engineering Materials Classification of Materials

− Elements are building blocks of nature, can’t be broken down − Solutions occur where one substance dissolves in another − Compounds are a combination of two or more elements combined

chemically − Mixtures are the result of two or more pure substances (elements or

compounds) which are mechanically mixed together Polymer Structures − Thermoplastics − Thermosets

− Thermoplastics

• Are also known as thermosoftening polymers cause they can be resoftened and reformed

• With covalent bonds and weak secondary bonds between the chains

− Thermosets • Cannot be resoftened by heating. Once they are formed, heat cannot

reshape them Properties of Materials Mechanical Properties

− Strength: withstand applied loads without failure − Hardness: the ability of material to resist scratching, abrasion or

indentation − Elasticity: to return to its original shape and dimension − Stiffness: to resist elastic deformation under load − Plasticity: to undergo some degree of permanent deformation without

rupture − Malleability: to be hammered and rolled into thin sheets − Ductility: to be drawn out into thin wire

Electrical Properties

− Electrical conductivity is the ability to conduct electricity. Metals and carbon are good conductors; pure water & timber are poor conductors. And air, glass, most polymers and ceramics are good insulators.

− Semi-conductors are materials that are manufactured to be poor conductors

Structure of Materials − Each atom is made up of three components: protons, neutrons and electrons.

− Protons and neutrons are located at the centre of the atom called the nucleus, while the electrons orbit the nucleus.

o Neutrons- − Have no charge − Are located in the nucleus o Protons − Have a single positive charge − Located in the nucleus o Electrons − Have an equal value negative charge − Electrons In the outer shell are called valence electrons as they are used in

bonding Bonding

− Noble (inert (not reactive)) gases do not react at normal temperatures and pressures

− They have a full outer shell making them stable and not needing to bond − They are useful for welding applications (MIG) where it is desirable to

exclude oxygen and other reactive gases Crystal Structure

− When a material is in its liquid form there is little or no order to the structure. As the material solidifies, however, the atoms arrange themselves into regular crystal structure.

− Three most important structures are: ● Body centred cubic (BCC) ● Face centred cubic (FCC) ● Hexagonal close packed (HCP)

Atomic Structure: Primary Bonds- Atoms form three types of primary bonds: ionic, covalent & metallic. Primary bonds are the strong bonds between the tightly clustered atoms that give any pure substance its characteristic properties. Secondary Bonds- these are van der Waals and hydrogen bonds and are relatively weak Predominant bonds: Metals- metallic Polymers- covalent Ceramics- ionic and/or covalent bonding Ionic Bond

− Large differences in valance electrons usually metals and non-metals (such as NaCI) and involves the transfer of one or more electrons

− Donor atom loses its valance electrons − Recipient fills its outer shell − The imbalance (electron: proton: ratio) creates an ionic charge of

attraction

Covalent Bond − Generally occur between non-metal elements − The strong attraction results in a sharing of valance electrons − Covalent bonding is important in polymers

Secondary Bonds

− Molecular or van der Waals bonds − The weak bond is produced by the concentration of –ve electrons on one

side of an atom at one particular time which leaves the rest of the atom with a +ve charge

− The change can vary with time and can be easily be broken down but heat, candle wax, graphite and polymers

Polymorphism

− Polymorphism or allotropy is the ability of a single substance to exist in multiple forms or crystal structures

Crystal Structure

− Liquids have little or no ordered structure − A crystal is a homogenous solid of definite chemical composition, with

internal order, bounded by plane faces ● BCC ● FCC ● HCP

Non-crystalline materials (amorphous)

● Amorphous means without form ● Eg are all liquids and gases, glass, which is technically a liquid

Crystalline

● Regular ordered patterns ● All metals, majority of ceramics, some polymers and most minerals are

crystalline Metals Ferrous metals

● Iron is the primary constituent in ferrous metals

● Mild steels contain low carbon and magnesium ● MS can easily be formed (i.e ductility) machined and welded. ● Issues are corrosion

● Stainless steel ● The chromium reacts with oxygen to forma chromium oxide layer that

prevents further corrosion Non-ferrous metals

● Iron is not the primary constituent metal ● Copper and Aluminium are the most commercial non-ferrous metals

Copper

● The main electrical conductor used due to high electrical conductivity ● High ductility, malleable and good corrosion resistance ● Used in electrical wiring, electrical contacts, motor windings

Brass

● Alloy of Copper & Zinc ● Can contain up to 40% zinc, but beyond that is too brittle ● All brasses are corrosion-resistant and harder then pure copper ● Good wear, conduction and corrosion resistance makes them useful for

switchgear and contacts ● Outdoor taps are cast using 60/40 brass.

Bronze

● An alloy of copper and tin ● By pressing and sintering bronze powder, a porous sleeve may be

produced ● The porous article is then impregnated with oil, graphite or

polytertrafluroethylene (PTFE or Teflon) Aluminium

● Is a highly used metal, which has low density and excellent corrosion resistance; low strength and as such is usually used in alloyed form.

● Aluminium foil is almost pure aluminium ● Usually aluminium is alloyed with materials like copper, zinc, magnesium,

lithium and other metals to gain excellent strength ● Is lightweight, offers strength to weight ratios better than most ferrous

alloys Basic forming processes suitable for materials Casting

● Casting Is a forming process that involves heating up a material, such as a metal alloy and then placing it in a mould

● Moulds may be permanent moulds made of metal or they may be disposable moulds made of sand

● Die casting uses permanent moulds and is extensively used for non- ferrous alloy casting. Sand casting is used for a lot of ferrous alloy casting.

Rolling ● Many metals can be cast in the form of ingots or bars ● For example circular or square bar ● Rolling may be done at a high temperature (Hot rolling)- easier ● Slightly elevated temperature (cold rolling)

● Cold rolling is harder to do and the final metals structure will be stressed and deformed, but it will have a better surface finish and be more dimensionally accurate.

Extruding

● Extruding may be likened to squeezing toothpaste from a tube ● Aluminium alloy window frames are generally made up of extruded

sections. Cutting

● Removal of unwanted material ● Most familiar with cutting with a hacksaw ● Turning, grinding, sawing, drilling, etc

Joining

o Various methods dependant on the material and the use of the metal o Metallurgical:

• Electric arc welding ● Method: metal is melted by an electrode, which doubles as the filter metal

covered by flux to prevent oxidation of molten metal. ● Applications: joining thick steel sections and small runs

• Oxy-acetylene welding ● Method: metal is melted by flame and filler metal added ● Applications: joining steel fan cages

• Bronze welding ● Method: a flame heats the parent metal and bronze filler metal which is

added to the joint. There is little or no metal of the parent metal. ● Applications: low strength uses

• MIG welding ● Method: metal inert gas uses a continuous feed wire (electrode) and inert

gas (eg argon) preventing rapid oxidisation ● Applications: suited for automation and can be set up for aluminium using

a suitable feed wire and special gas mixture • TIG welding

● Method: Tungsten Inert Gas uses a tungsten electrode (that doesn’t melt) and a manually fed filler rod or wire

● Applications: joining aluminium and stainless steel, especially thick sections

o Mechanical Joining ● Bolts, nuts and screws used to fasten materials together ● Hole drilling and corrosion pose issues for this form Fabricating ● Is the process of assembling an item from various components ● Eg mild steel welded together Polymers

− Polymers are generally solid materials made up of long molecular chains that are created by adding or connecting smaller molecules together.

− Polymers are often termed organic, due to carbon being the primary constituent.

− Although most polymers are synthetic, there are some natural polymers, such as natural rubber and cellulose fibres.

− The term polymer is a very broad term; the field has a wide group of materials, each having distinct structures and properties.

− They are used for a wide range of applications − Synthetic polymers make up the remainder, known as “plastics”

e.g PET, HDPE, PVC, LDPE, PP, PS − They tend to exhibit good strength-to-weight ratios − They are generally formed into shape by moulding, rolling, extruding or

other heat forming processes − Derived from crude oil

Ceramics

− Engineers use ceramics for high temperature applications and situations where abrasion resistance or thermal stability is required

− Ceramics are hard and brittle, high compressive strength, low tensile strength, low electrical & thermal conductivities.

− Ceramics have been used for centuries and are now finding new uses due to their hardness and good thermal properties.

− Any ceramic material that requires some form of purification, mixing or

firing is a synthetic ceramic, e.g. clay-body ceramics, glass, refractories and cement.

− Clay body ceramics

• Made from a combination of different clay materials • Classified as earthenware, china, stoneware and porcelain

● Porcelain and china are two most common seen in homes Porcelain has low porosity (1%)- this is important for plates and cups that hold beverages and food. Good electrical and thermal insulator. Glazed to improve aesthetics and reduce surface porosity to zero. However brittle & heavier than polymers. Glass:

● Transparent, brittle, most used glass is soda lime ● No atomic order- represent liquids in their atomic structure ● Maximum theoretical strength of glass is 30,000 MPs ● Ceramic glass cooktops also use special glass tops which prevent the

saucepan from directly contacting the heating element. Gorilla Glass:

● Modern smartphones use a capacitive touchscreen that must be strong and resistant to cracking yet be exposed so a finger can contact it.

● By an ion exchange a compression stress is a set-up in the surface, which makes it more difficult to introduce tensile failure in the glass.

● Higher density Composite materials

− Are made of different materials combined together to capitalise on the desirable properties in each.

− Fibreglass as an example uses fine glass fibre with high tensile strength in a thermosetting resin matrix. The glass fibre provides good tensile strength while the resin provides toughness usually absent in glass.

− Concrete & timber are examples of composites. − Properties include specific strength (strength- to weight-ratio) − Concrete is sand, cement, aggregate (acts as a binder/glue)

Timber is a natural composite that is composed of cellulose fibres, the tracheids, are held together by the lignin. Advantages-

● High specific strength (strength-mass ratio) ● Wood is a regenerative and if managed professionally can be a permanent

resource ● Easily handled, worked and joined

Disadvantages: ● Wood is combustible ● Strength of wood varies with the species and direction of the applied

force Communication Freehand sketching in three-dimensional and third angle orthogonal projection ● Freehand sketching is a style of drawing made without the use of guiding or

measuring instruments, as distinguished from mechanical or geometrical drawing; also, a drawing thus executed.

● Orthogonal drawings use multiple two-dimensional views to represent an

object

Engineering Reports • Title page Title of the report, identifies the writer or writers, their company or organisation and publication date • Abstract A clear, concise summary of the report, giving the readers a brief explanation on the purpose of the report, too see if it is relevant for their needs • Introduction Introduction to the report and background information • Main section/ procedure • Results • Conclusions • Acknowledgements • References • Appendix

Topic 2: Engineered Products

Skills of the professional Engineer Engineers as problem solvers

● Develop solutions to problems ● Evaluate all possible solutions ● Engineers generally test the final design prior to production ● Use a factor of safety in their design

Engineers as designers

● Responsible for the original design of projects ● Are designers ● Generally design in collaboration with a team of engineers ● Research/collaboration with other professionals/people to develop ideas

and concept sketches Engineers as communicators

● Communication is the only means by which ideas are shared ● Such as oral, written, aural, visual, intercultural ● Collaboration with others is essential ● For effective communication, engineers must have

o Oral skills o Written skills o Listening skills o Visual skills

Engineers as project managers

● Project management- is a temporary endeavour with unique goals and objectives

● Resources: o Hardware o Software o Essential ware- time, finances, energy o Wetware-ideas and thought

● Project managers are responsible for planning, execution and closing of any project

Historical and Societal Influences Historical development of various engineered products

Lawnmowers developed over time Scythe & animals

− Machete with a handle First lawn mower- Edward budding 1832

− Made from cast iron and very heavy to push − Had a grass catcher − Cast gear system to drive cutting cylinder

Horse-Drawn lawn mower 1840

− Horse pulling action alleviated the blades digging into the grass The first side wheel lawn mower 1869

− Roller behind cutting cylinder − Cutting cylinder driven by side wheels

The greens lawn mower 1859

− Use of chain drive: was simpler and quieter − Used machine gears for first time

The steam (1892), electric & petrol (1896) powered lawn mowers

− First powered lawn mowers − Steam powered were heavy (1.5 tonnes) − Made from cast iron and still very heavy

The Webb deluxe lawn mower

− First use of pressed steel for side frame − Steel used for handle and most other parts rather than cast iron

Australian Victar rotary lawn mower 1952

− First commercially successful rotary lawn mower − All steel construction with dangerously exposed blades − Used small 2 stroke petrol engine and peach tin to hold fuel − Steel wheels

Air cushion lawn mower 1963

− First model had a sheet metal cowling The effects of engineered products on peoples’ lives and living standards • Engineered products such as lawnmowers, cars, etc. mean that people can

complete an activity as efficiently as possible

Environmental implications of the engineered product • Products such as engines may pollute the environment with toxic gases

Engineering Mechanics Forces Nature and type of forces • Forces are a push or a pull on a body and can be found acting in many

different ways. • Many force systems are three dimensional, however for simplicity only

co-planar or two-dimensional force systems will be dealt with here. • Co-planar forces can be:

● Concurrent: these forces that all pass through the same point

● Non-current: this is a system of forces that are not concurrent. They may intersect at various points or be parallel.

● Co-linear: this is a system of forces where the forces all act along the same line

Addition of Vectors

• Unlike scalar, vector quantities must be added in a way that include their magnitude and direction

• Up= positive. Down= Negative. Left= Negative. Right= Positive Addition of Vectors Couples and Force/Couples A couple may be defined as two parallel, co-planar forces of the same magnitude and direction but opposite sense, that produce or tend to produce rotation but not translation.

Equilibrium of concurrent force systems Equilibrium is a condition when the force system is balanced, that is, there is no resultant The conditions for equilibrium are:

● That there is no resultant force ● That the sum of all force components (vertical and horizontal) and all

moments equals zero i.e. − Sum of forces in vertical direction = 0 − Sum of forces in horizontal direction= 0 − Sum of moments= 0

Moments of a force

● A force causes actual or potential rotation ● Moments are clockwise (positive) and anti- clockwise (negative) ● SI unites are Nm (newton metres)

● A moment is calculated by multiplying the force’s magnitude by the

perpendicular distance from the pivot point M=Fd M=moment of force F=force D=perpendiculars distance

Equilibrants − The force that will balance all other combined forces is called the equilibrant

Equilibrium of concurrent co-planar forces (three force rule)

− When concurrent, co-planar forces are in equilibrium (i.e. all forces balance and there is no movement) the resultant and equilibrant is zero, which means that, the force polygon for a system of forces, which is in equilibrium, must close. Method 2- mathematical

− Convert all forces at point A into horizontal and vertical rectangular components − Sum of forces in x direction= 0 (right +)

Transmissibility of a force

− A force may be relocated at ANY position along its line of action providing it has the same magnitude and direction

Engineering Materials Modification of materials Through the use of various techniques, some materials may be modified in such a way that their properties improve compared to their original state. What is work hardening? (also called cold working)

• If a material is worked (shaped, beaten, bent, etc) at a temperature below its recrystallization temperature, the metal reforms by atoms slipping along shear planes. Therefore it can be toughened and shaped when it’s cold.

• Work hardening is accompanied by reduced ductility Heat Treatment

• Steels − When heated until red hot, then quenched in water, the steel will become hard

but brittle − As the carbon content increases this quenched steel will become even harder and

more brittle, this is due to a change in the structure that produces high stress- called martensite

− Heat treatment processes for steels include: ● Annealing- Annealing is a heat process whereby a metal is heated to a specific

temperature (900o) /colour and then allowed to cool slowly. This softens the metal, which means it can be cut and shaped more easily.

● Quenching- a type of heat-treating, is the rapid cooling of a work piece to obtain certain material properties.

● Process Annealing- is used to counteract the hardening effects of a cold-working operation on a metal. After significant cold work, a piece may become too brittle to safely continue the working process. The piece may then be heated to a temperature anywhere below its austenitizing (above 900o) temperature until

stresses have been removed from the lattice structure, and then slowly cooled to avoid introducing new stresses. Alloying Materials

• Done to improve desired properties • Eg steel is alloy or carbon and iron- carbon improves strength • Alloying can improve a materials usability in certain applications • Alloying forms solid solutions with one metal dissolved within another

Engineering applications of materials There are a variety of reasons why certain materials are used to manufacture an item:

• Material suitability- is it right for the application • Availability- some materials are harder to obtain than others • Processing- how the material is manufactured is a deciding factor • Cost- expensive materials cannot be used for everything

Recyclability of materials Implications

• Many materials an engineer uses are not renewable • Iron is readily available whilst iron ore isn’t • Thus it’s highly important that humanity understands the importance of

recycling these materials Costs and benefits of recycling materials

• Steel, aluminium, brass, polymers and rubber all can be effectively recycled • Recycling means less of an impact towards the environment

Engineering electricity/electronics Basic principles

● Electricity definition- is the flow of electrons through a system. ● Current (I) definition- the quantity of elections flowing per second likened to

water flowing through a pipe. ● Current is measured in amperes (A or amp) ● Direct current (DC) is where the current flows in one direction. Example includes

a battery. ● Alternating Current (AC) is where the current is changing direction and often

magnitude as well, at a frequency of typically 50 Hz (times per second) Example includes domestic power supply in Australia of 240V AC V=IR Voltage= Current resistance

● Potential different (E) definition- the potential difference between the point where the electrons enter a system and the point at which they exit it. An example includes a pressure to a pipe.

● Electrical potential difference is measured in volts (V) ● Resistance (R) definition = “the resistance to current flow” where low resistance

means good conduction. Resistance is measured in Ohms

● Resistance is affected greatly by length, and the cross sectional area of he conductor.

● The longer the wire, the greater the difference

Magnetic Induction The process by which a substance, such as iron or steel, becomes magnetized by a magnetic field. The induced magnetism is produced by the force of the field radiating from the poles of a magnet. Electrical Safety

● Electricity is ‘lazy’ and will travel through the path with the least resistance ● Electrical systems are now being designed to remove the chance of human

contact with live wires ● A lot of domestic appliances are double insulated- prevents the user coming into

contact with anything live Fundamentals of AC and DC currents

DC = direct current ● Charge moves in one direction ● Direct positive to negative movement

AC = alternating current ● Charge moves back and forth periodically. ● Directions changes 50 times per second.

Electric Motors and Generators ● Electric motors convert electrical energy into mechanical energy ● Generators do the opposite of the above ● Some electric motors run AC, some run DC ● Electric motor passes current through a rotating coil; the coil has a magnetic field

induced around it, which will react with the magnetic field surrounding it and tends to produce a force that rotates the coil.

Communication

Orthogonal and Pictorial Drawings • Two types of pictorial drawings: isometric and oblique • Isometric: constructed on a set of three axes at 1200 to one another (300) • Oblique drawings constructed on a set of three axes: one horizontal, one

vertical and one receding at 450

Australian Standard • For all orthogonal drawings there are standards on how various parts should

be presented • These include: line type used, placement of dimensions and special ways of

representing some features eg threads, welds, springs, etc.

Dimensioning

Material lists • Often is necessary for drawings to use material lists • Situated at the bottom right corner and are a list of the parts used, the

amount required and the material it’s made of • Important to orthogonal drawings Computer Graphics eg computer aided drawing (CAD) • Is the use of computer systems to assist in the creation, modification,

analysis, or optimization of a design/drawing. • CAD software is used to increase the productivity of the designer, improve

the quality of design, improve communications through documentation, and to create a database for manufacturing

Collaborative work practices • Collaborative practice involves community service organisations working

together to achieve shared goals. • In the community services delivery system, collaboration is achieved when

organisations develop mechanisms - structures, processes and skills - for bridging organisational and interpersonal differences, and together arrive at outcomes that they value.

Developing an engineering report • Creating an engineering report on software, presenting it to the class as an

oral presentation, then hand in as a report to the teacher • Report should be word processed

Topic 3: Braking Systems

Historical and Societal Influences Historical developments of braking systems including band, drum, disc, ABS, regenerative brake systems and automotive hand brake Contracting band brake: • Carryover from the horse drawn cart- friction block acting against the iron

tyre of the wooden wagon wheel • After the invention of Pneumatic rubber tyres for cars in 1895, works by

holding attaching a band to the outside of the drum, the band is tightened to produce a stopping force

• 1902 found new, superior contracting band brake

Drum Brake • 1902- Works with an internally expanding drum brake • Initially drum brake shoes were opened by lever systems and a cam but as

car speeds increased, hydraulically operated pistons operated the shoes Disc Brake • 1902- rotating disc is connected to axle. Connected to the suspensions is a

backing plate with a caliper attached. This caliper wraps over the disc and houses two pads that are forced laterally against the disc by a hydraulically operated piston

ABS • 1929- Anti-lock braking system (ABS) is an automobile safety system that

allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding.

Regenerative Braking systems • A regenerative brake is an energy recovery mechanism, which slows a vehicle

or object by converting its kinetic energy into a form, which can be either used immediately or stored until needed.

Automotive Hand Brake • In cars, the automotive hand/parking brake is usually used to keep the

vehicle stationary. It is sometimes also used to prevent a vehicle from rolling when the operator needs both feet to operate the clutch and throttle pedals.

Engineering innovations in braking systems and their effect on people’s lives Drum Brakes • Improved stopping power- car can travel faster whilst stopping safely

• Increased speed means potentially less safe; cars need to adapt their safety features to these changes

• Four wheel brakes mean safer cars • Drum brakes handle better in contrast to contracting band brakes in poor

weather conditions

Disc brakes • Cars more effective at stopping at higher speeds • Improved heat dissipation over the drum brakes means safer continual

braking effort (eg going down a hill) • Easily adapted to computer controls (eg ABS) Environmental implications from the use of materials in braking systems • Prior to 1902, brake linings were leather or woven cotton with poor thermal

stability and low coefficient of friction • 1902 found asbestos lining introduced; greater stability at higher

temperatures (when brakes become hot, the frictional force is reduced) • Although major health problems were associated with asbestos- potentially

causes lung cancer through inhalation of broken fibres • Care should now be taken when acting with this material Engineering Mechanics and Hydraulics Static friction (with simple calculations) • Is used to stop/slow down a moving vehicle – it is essential • Definition: resistance to motion of two bodies in contact • The amount of friction produced is the coefficient of friction • Equation:

• Frictional force is dependant on the coefficient of friction between the mating surfaces and the normal reaction force

• The lower the coefficient of friction, the higher the normal reaction must be to gain the same level of frictional resistance or vice versa

o Loads and Extension o Stress and Strain o Work, power and energy, principle of the conservation of energy o Fluid mechanics Forces & Strength (Stress Strain) • Tensile stresses are those produced by forces trying to pull apart or lengthen

a material • Compressive stresses are those produced by forces trying to compress or

reduce the length of a material • Shear stresses are those produced by forces trying to slide one part of the

material over the other. Stress and strain ● These terms relate to what happens to a material when subject to a load ● Eg when a material is subject to an axial load in tension will stretch ● Stress is how the load relates to its original cross sectional area (P/A) )

tensile or compressive stress) ● Strain is the proportional change in length under axial load. Stress σ is the relationship between an applied load and a material’s cross-sectional area and is measured in N/mm2 or Mega Pascals (MPa)

Stress = Load / area Stress therefore has the units of N/m2 or N/mm2 1N/m2 = 1Pascal (Pa) σ= Stress (Pa) P= Load (N) A= cross sectional area (M2) 

Definition Formula Units Work When a force causes

motion W=F x S Joules

Energy An objects ability to do work

KE Energy an object possesses due to its motion.

KE=1/2 mv2 Joules

PE Energy due to its position

PE=MGH Joules

Heat Braking converts KE to heat energy via frictional forces

Joules

Electrical Electrical regeneration brakes such as those used in hybrid cars capture a percentage of braking energy as electrical energy via a motor /generator

Joules

Power Power is the rate at which work is done

Watts (1 joule per second)

Power The principle of conservation of energy Energy is neither created nor destroyed but converted from one form to another ● Energy ● Has the same SI units as work ie the joule ● Definition: an objects ability to do work ● Exists as mechanical, chemical, electrical heat and atomic Solving Work/Energy Problems- The work-Energy principle Any PE present plus any KE present will equal the final KE and PE unless there is work done PE1 + KE1 +_W= PEf + KEf

● The deeper something is under a fluid the greater the pressure ● It is possible for us to determine the hydrostatic pressure at a specified depth

of a container if we know the pressure at the top (or the surface) Formula: P=P0 + pgh P =pressure at depth Po = Pressure at the top P= density of the fluid (kgm-3)

G= acceleration due to gravity (ms-2) h= depth below top (m)

Blaise Pascal ‘pressure applied to a confined liquid is transmitted equally throughout the liquid’ P=f/a P=pressure F=force (N) A= area Hydraulic systems- advantages o Equal forces are applied to each output cylinder o Higher efficiency than other systems o Less maintenance and more reliable o One disadvantage of hydraulic braking systems using foot operated disc

brakes is that the force required to effectively operate the brakes is generally in excess of what a person can apply at the brake pedal. Brake boosters are used to magnify the brake pedal force.

Advantages of hydraulics when compared to pneumatics: o Hydraulic fluid is basically incompressible and results in less spring o Hydraulic systems can exert much higher forces as a result of the

incompressibility of the hydraulic fluid. By pressing the pedal, the piston is forced into the cylinder so increasing the pressure in the master cylinder. This increase in the master cylinder creates an increase in pressure in all brake callipers, forcing the pads against the discs and so applying the brakes.

Hydrostatic Pressure

Engineering Materials Materials for braking systems

Steels- What is steel?

o An important alloy. It is a binary alloy of iron and carbon, with no more than 2% carbon. Steels are classified according to their carbon content

What is the maximum carbon content? o 2% o As steel cools it changes its structure. o The amount of carbon present determines at what temperature these

changes occur. What is Austenite?

o When a steel is heated to 1000oc it becomes austenite in structure. It is a constituent of some forms of steel. Obtains an FCC structure.

What is Ferrite and what are its properties?

o A form of pure iron with a body-centered cubic crystal structure, occurring in low-carbon steel. When steel cools, some of the austenite will form into ferrite. It is soft and ductile, containing a maximum of 0.025% carbon dissolved in it.

What is Cementite and what are its properties?

o A hard, brittle iron carbide present in cast iron and most steels. What is Pearlite and what are its properties?

o A finely laminated mixture of ferrite and cementite present in cast iron and steel formed by the cooling of austenite.

What is Eutectoid steel?

o Any steel with a composition of 0.83% carbon

Cast Irons- The primary difference between steel and cast iron is what?

o Carbon content. Steel never contains more than 2%, whilst cast iron contains 2.5-5%.

What are some desirable properties of cast iron? o Heat resistance, relatively cheap, compressive strength and rigidity, easily

machined, good fluidity How can a metal with such high carbon content be made to not be so extremely hard and brittle?

o Varying the amounts of alloying elements present or through heat treatment processes can alter the structure.

White Cast iron o What is it and where might it be used? o Hard and brittle iron is a hard and brittle iron formed due to fast cooling

or low silicon. The structure is pearlite or cementite. Used for wear resistance

Grey cast iron o What is Grey cast iron? o Is the result of high silicon content and is ‘grey’ due to its colour of its

structure. What is the ingredient and what does it do?

o It has graphite in the form of flakes. These flakes are essentially voids in the structure, which makes grey cast iron weak in tension, although strong in compression

The graphite forms what shape? o Flakes

What properties do grey cast irons have in regards to the following properties: o Tension -Weak o Compression -Strong o Machinability –Easily machined o Vibration characteristics –Excellent vibration dampening characteristics

Composites- Composite materials are most often formed by the combination of two or more materials to achieve properties that are superior to those of its individual constituents. Their specific benefits include:

o High strength to weight ratio o Desirable corrosion resistance o Thermal resistance

Examples of composites include

o Asbestos o Wood o Sintered metal composites

Testing of materials Tensile and compression test- o Standardised samples of materials are tested both in tension and

compression on a tensometer and the results are plotted on a load-extension diagram.

− Hooke’s law states that stress is proportional to strain (producing a straight

line) up to the elastic limit. • Below the elastic limit, if the load is removed, the material will return to

its original shape- like a car spring. • Above the elastic limit, plastic deformation occurs which is permanent

deformation of the test sample- like bending fence wire − Yield point occurs when there is a marked increase in extension without an

increase in load o The compression test is used to determine how well a material behaves

under compressive forces. It is essentially a tensile test in reverse. Malleable materials will tend to deform while brittle materials will display characteristic breakage

Hardness tests-

o Used to determine hardness of material o Most tests work on the principle of forcing a specially shaped indentor into the

surface of an object o There are numerous tests:

− Brinell: hardened steel ball forced into an object under specified load conditions

− Vickers: small square pyramid is forced into a test piece under specified load conditions

− Rockwell: diamond cone is forced into an object under specified load conditions and a reading is displayed on a dial (number from 100-500)

Communication Graphical mechanics; graphical solutions to simple mechanical problems Pointers:

o Make drawings large; the larger the more accurate o Be accurate in transferring angles to force diagram o Ensure all vectors are drawn to correct scale

Pictorial, orthogonal and exploded drawings o Pictorial: − Oblique − Isometric o Orthogonal: − Dimension it fully − Not too many dimensions on one view − Don’t place redundant dimensions − Front view is drawn in the direction of the arrow given on the pictorial o Exploded: − Used to illustrate various parts that constitute an assembly − Usually labelled

Topic 4: Biomedical Engineering

Scope of the profession Nature and range of the work of biomedical engineers o Responsible for the development of useful devices to replace human tissue

and bone o E.g. artificial limbs, joints, replacement heart valves, bionic ear, etc. o Designs surgical equipment for use during replacement surgery Current projects and innovations o Three key biomedical projects: − Artificial hearts: offers better chance for people who cannot obtain a donor

heart − Bionic ear: offers hearing to those who have lost their hearing or born deaf − Artificial limbs: the replacement of diseased or damaged limbs Health and safety Matters o Health and safety prime concern o May conduct work in laboratory conditions o May be risks to the biomedical engineer that involve infection by disease, and

great care must be taken when working with diseased tissue o Health and safety of the recipient of the item is of great importance o Safety checks to be completed to ensure engineered item is without defect or

problem/flaw. Eg. If an artificial heart is at fault, may result in potential death Training for the Profession o Universities – high level qualifications o Competent in understanding of materials technology o Do not need to complete a medical degree- their courses are extensions on

more traditional engineering areas Career Prospects o Biomedical industry (field) does not offer the same amount of jobs as such as

civil engineering o Although, job prospects do exist (technologies develop- field expands)

Relations with the Community o Improve the quality of most peoples lives- earn great respect and praise o In contrast, religious or cultural groups do not support the replacement of

limbs with artificial items – dilemma with patient and engineer Technologies unique to the profession

o Many of the technologies developed by biomedical engineers are exclusive o Most of the technologies are adapted or modified from existing developments o Technologies from mechanical and electrical fields turned into biomedical

technology o Eg. Artificial hips use metals that are chemically resistant, fatigue resistant

and durable (eg stainless steel/titanium) alongside polymer and ceramics Ethics and engineering o Relates to the ‘morality’ of the subject- impacts people in society o Implications will be positive and/or negative o E.g. introduction of steam engine to society means efficient power source but

loss of non-renewable resources (timber) and environmental pollution

o Engineers must be aware of ethical implications of their developments o E.g. testing a new product on machines may be viable although when actual

testing on a patient (artificial heart) comes as a necessity. Should ‘brain dead’ people/volunteers be used? And the result of this (e.g. injury/death)

Engineers as managers o May be managers in two senses of the word 1. Managers of the design process, overseeing the development of the project.

An engineer in such a position will have other engineers working on the project, coordinating the teams and overseeing all development

2. Some companies believe experienced engineers should be in company management- improving their income and autonomy.

Historical and Societal Influences Historical Background to biomedical engineering o Was created as early as the 1500s (articulated limbs) o Initially most products were wooden, then metal was used o It wasn’t until WW1 that biomedical engineering grew o WW2 stage found expansion of use of prosthetic limbs (metal and rubber) o Then creation of prosthetic hands- utilisation of plastic o 1960- first internal body joint (hip joint) o 1978- first human fitted with cochlear implant

o Artificial heart received bad publicity in 1980s although has returned with vast improvements

Historical Development of Products   Although the cochlear implant is specifically produced to enable the hearing of deaf individuals; historic methods of enabling amplification of sound were created. Such were made through non-electronic ways and have gradually become extremely efficient in comparison to today   Simple Ear Trumpet (1700’s)

o This model was commonly used in the 1700s. This product amplified minimal sound and was uncomfortable and awkward to utilize

  London Dome (1850’s) o A bit spiffier than the simple ear trumpet, this device was made of thin metal,

and could be acquired in a variety of sizes, depending on hearing loss.   Ear Tube (1887)

  o This ear tube allowed the user to get sound straight from the source: the speaker held one end, while the user placed the other over the ear.

o Later on in this year and subsequently 1966 found the implantation of electrode units into the patients ears

  Carbon Microphone Aids/Hearing Aids (1930’s)

o Hearing aids were developed in the 1930 and 40s. Dependent on the requirements of the user, greater amplification meant an increase in size due to a larger microphone. Gradually, smaller designs were created and batteries were made to last longer than just one day.

  Cochlear implants (1970s)

o 1970s marked the stage in which research had led to technological advancement. The Cochlear implant is implanted into the head behind the ear of a deaf person, when used with a microphone and an additional speech processor, by electrically stimulating the auditory nerve this allows the person being able to hear sound. Cochlear implants were the new way of finally allowing a deaf person to hear sound, rather than solely just the amplification of it. The effect of biomedical engineering on people’s lives

o Immense impact on peoples lives; prior to 1960 a failed heart meant death/a failed hip meant individuals confined to a wheelchair

o Biomedical engineering opens new options- enables people to hear, feel, see and move again. These are of immeasurable value to individuals

o Responsible for the precision design of equipment used in surgical procedures and medical surveillance and imagery

o Development of heart monitors, various scanners (CAT, MRI, nuclear cameras) and surgical equipment is of paramount importance Engineering Mechanics and Hydraulics Orders of levers Levers are one of the simplest machines used by engineers, yet they are the basis for many more complex machines. The operation of levers can be divided into three forms or orders of levers. These include: o First order levers: These levers have the load and the effort placed either side of the pivot point. An example of this includes a crowbar used to lift, pliers, surgical retractions and a hammer pulling out a nail. The ratio of effort to load is called mechanical advantage, and is dependent on their respective distances from the pivot point.

o Second-Order levers: These levers have the load between the pivot point and the effort (force coming up). Examples include a wheelbarrow, a brake pedal, a bottle opener and a foot pump. With this type of lever the effort is always less than the load. • mechanical advantage, velocity ratio and efficiency

o Third Order levers: The third order lever, places the effort between the load and the pivot point. Examples include a fishing rod, tongs and many linkages on hydraulic

earthmoving machinery. The third order lever will always have an effort larger than the load.

Medical Advantage and velocity ratio o Mechanical Advantage (MA): The mechanical advantage of a machine is a measure of how it helps the user. Mechanical advantage in a mechanical machine is the ratio of load to effort and is founded by the formula:

The higher the medical advantage, the lower the effort must be for a given load. If mechanical advantage is below one, than we have a mechanical disadvantage. A large mechanical advantage would seem like the best option but there are times when a low mechanical advantaged is a better choice. A good example of this includes a brake lever on a bike. o Velocity Ratio (VR) The velocity ratio is the ratio of the distance the effort moves, to that distance that the load moves in a mechanical system. VR is represented by the formula:

The higher the VR the greater the distance that the user must move. Unlike the Mechanical advantage, the velocity ratio is not affected by friction and system losses. If a machine is perfectly efficient, then MA will equal VR. The lower the velocity ratio the greater the effort that is required. In the example on bike brake levers, we can say that the operating the lever at the end gives a high velocity ration, while operating near the pivot point gives a low velocity ratio. o Efficiency: An ideal machine is one that is 100% efficient. This means all energy put into the machine is used. However this never occurs. There is always some type of

energy loss (usually a result of friction) that results in the efficiency being below the ideal 100%. In the case of levers there may be friction in the pivots or the lever may bend slightly. VR is always the same irrespective of efficiency, since there is no change in the distances of the effort and the load. But Mechanical Advantage is affected, by a less than ideal efficiency; thus the Mechanical Advantage will always be less than the VR for machines with efficiencies below 100%. The percentage efficiency I found by the following formula: o MA, VR and Levers: The three orders of levers each have characteristics of MA and VR relationships:

First Order lever: − MA and VR may be greater than, or less, one depending on the distances of

the effort and load from the pivot.

Second Order Lever: − MA and VR are always greater than one. Thus the effort is lower than the load

but a greater distance is moved by the effect compared to the load.

Third Order Lever: − MA and VR are always less than one. Thus a high effort is required but a small

distance is moved by the effort, as compared to the load. Engineering Materials o Forming methods – Forging • Forging is the process of shaping a metal with forceful blows. It may be done

with the metal hot (hot forging) or cold (cold forging or pressing). • Hot forging is carried out above the recrystallization temperature. The

simplest type of forging is that which a blacksmith does against an anvil. • Forging may draw out a metal while reducing its cross sectional area

(drawing), reduce its length while increasing its cross sectional area (upsetting) or it may force the metal into dies to take the required shape, as in drop forging.

• One advantage of forging is the grain flow within the metal will conform to the shape of the article, thus increasing strength in the direction of the axis item.

– Casting (done previously) – Cutting (done previously) – Joining (done previously)

Structure and properties of appropriate materials Biomedical engineering makes use of some wide and varied materials for manufacturing various items. The properties of these materials are often decided by the materials structure. Structures may be referred to on different levels. The three discussed here are crystal, micro and macro: − Crystal Structure: − The crystal structure refers to how the atoms are arranged in a solid material. If the material is amorphous, there will be no regular structure, but if it is a crystalline then the way those atoms are structured has an effect on the materials properties. Amorphous materials tend to be brittle, but also display good strength and stiffness along with unique physical properties. If the structure is crystalline, it may be one of many structures. Metal crystals may be faced centred cubic (FCC), body centred cubic (BCC), hexagonal close packed (HCP). − Microstructure: When a material is viewed under a microscope its microstructure is revealed. Many features may be shown under such examinations. Phases are chemically stable single homogenous areas in an alloy. They may even be seen; for example in steel; ferrite and cementite are two phases that will be seen. Inclusions and impurities are shown in that structure also. − Macrostructure: The macrostructure of a material is that which is seen with the naked eye, or under a magnifying glass. The macro structure of a material is highly dependent on the way it is manufactured. Cast items may display features such as inclusions, shrinkage, stress raisers and columnar grain growth (elongated parallel grains) while forged items may display grain flow, grain growth or grain refinement, and a welded item may show grain growth, gas porosity or inclusions. Some of these features are desirable such as grain glow, but stress raisers and inclusions are not. Alloy steels such as stainless steel, titanium o Ferrous alloys: − Because of the criteria previously listed plain carbon steels see relative little

use in biomedical applications. Ferrous alloys with elevated contents of such elements as nickel and chromium are generally required creating what are generally known as stainless steel.

o Stainless steels: − Stainless steels are probably the best-known high alloy steels, yet most

students are probably unaware that there are five different types. The primary stainless steels for biomedical engineering are austenitic stainless steels.

o Ferritic Stainless Steels: − Good strength and moderate ductility − In automotive exhaust systems and for some drainage sinks. o Martensitic Stainless Steels: − Have both chromium (11.5-18) and carbon (0.15-1.2). Martensitic stainless

steels are used where corrosion resistance is needed as well as high hardness. Knife blades and stainless tools with a c cutting edge also ball bearings.

o Austenitic Stainless steels: − The largest family of stainless steel − Notably some grades − Not able to be hardened Titanium Alloys − Relatively lightweight metal − Provides excellent corrosion resistance − High strength to weight ratio − Good high temperature properties − It is used extensively in biomedical applications such as, investment cast knee

and hip implants, tibial nails, screws, LVAD housings and pacemaker housings

− Their usage is favourable due to a durable passive layer forming which prevents detrimental corrosion when in contact with bodily fluids.

− One of the challenges of titanium alloys is that they can be difficult to hot work above 525 C due to reactivity above tis temperature; moreover they can be a challenging material to weld

o Polymers (done previously) o Ceramics (done previously)

Electricity/electronics

Ohms Law

o Ohms Law relates voltage (v), current (I) and resistance (R) is included, then I= V/R. Using the Ohm’s law triangle: to find the equation for any term, cover the term with your finger- the equation will be the other two terms.

o For example if you cover the letter V, you are left with I x R so V= I x R and so on.

Series and parallel circuits Series:

● There is only one current pathway. ● Current is the same throughout the whole circuit ● If a series circuit is broken at any point then the electricity cannot flow through

it. ● Current remains constant (IT = I1 = I2 = I3) and voltage varies (VT=V1+V2+V3). ● RT = R1 + R2 + R3 …

Parallel:

● There is more then one current pathway ● All components have the same potential difference across them ● If a parallel circuit is broken, electricity can still flow through it ● In parallel, voltage remains constant (VT = V1 = V2 = V3) and current varies

(IT=I1+I2+I3). ● 1/RT = 1/R1 + 1/R2 + 1/R3

Power Source Cells and batteries in series and parallel ● Many torches feature 1 1.5-volt D cells connected in series. By connecting the

cells in series the voltages of each cell are combined, but the current remains the same

● The 12V lead acid battery used in most cards is a set of six 2.1 V cells connected together in series, this gives a total voltage of 12.6V

Microcircuits/integrated circuits Integrated circuits (ICs) are a whole miniaturised circuit manufactured onto a single chip silicon. The chip is made into a circuit consisting of resistors, capacitors, transistors and diodes all in one very small piece of silicon. Most ICs are only about 0.1-0.3 mm square

Parallel Series VT= V1 = V2 = V3 VT= V1 + V2 + V3

IT=I1 + I2 + I3 IT=I1 = I2 = I3

● A recent development has been programmable ICs or PICs. Eg PICAXE ● The PICAXE allows the operator to upload a small BASIC program onto the

chip ● An IC is a microscopic array of electronic circuits and components that are

diffused or implanted onto the surface of a single crystal (‘chip’ or wafer) of semiconductor

● ICs have the advantages of low mass, microscopic in size, low power consumption, very durable (solid state), high processing speeds, low cost, easily replaced

Digital Technology o Systems that operate around binary numbers o Simply combinations of on or off o 0 is off, 1 is on o Because we can only interpret analogue signals, analogue signals are

converted to digital signals for processing and sending, and then converted back to analogue for output

Logic Gates

• Considered as electronic circuits that respond to the logic state of the inputs

• They are fundamental to the operation of many digital circuits • Most logic gates are packed as integrated circuits with some ICs

containing a number of gates in the one package • The logic state of the inputs can either be 1 (high) or 0 (low)