1
Q
What are the physical properties of materials?
A
- Density
- Melting point
- Conductivity
- Coefficient of expansion
2
Q
Define thermal conductivity.
A
Measure of the quantity of heat that flows through a material
3
Q
Materials with low thermal conductivity are typically used as _______.
A
insulators
4
Q
What does corrosion resistance describe?
A
Ability to prevent natural chemical or electrochemical attack
5
Q
How is density defined?
A
Mass of the material per unit volume
6
Q
What is the formula for calculating density?
A
ρ = m / V
Where m = mass and V = volume.
7
Q
An object has a mass of 570g and a volume of 2,280cm³. What is its density?
A
0.25g/cm³
8
Q
The melting point of a substance is defined as the temperature at which _______.
A
phase change occurs from solid to liquid
9
Q
What is specific heat capacity?
A
Amount of heat energy required to raise the temperature of a substance per unit of mass
10
Q
Define hardenability.
A
How far into the metal the hardness can travel when the steel is heated and then cooled
11
Q
What does weldability refer to?
A
Ability of materials to weld/join with similar materials
12
Q
What is permittivity?
A
How well a material can store electrical energy when an electric field is applied
13
Q
Define recyclability.
A
Ability of a material to be recycled into a similar or other form
14
Q
What does thermal expansion refer to?
A
Fractional change in size of a material in response to temperature change
15
Q
What is permeability?
A
How easily a material can become magnetised
16
Q
What are the two types of properties that materials have?
A
- Physical properties
- Mechanical properties
17
Q
Define fatigue strength.
A
Maximum stress a material can withstand after many repeated cycles of load
18
Q
What is shear strength?
A
The ability of a material to resist forces that causes layers of the material to slide over each other
19
Q
What is tensile strength?
A
Maximum pulling force a material can take before it snaps
20
Q
What is the yield strength?
A
Amount of force needed for a material to permanently deform
21
Q
How is toughness measured?
A
Using the Charpy impact test
22
Q
Define hardness.
A
Material’s ability to resist permanent indentation
23
Q
What is ductility?
A
Ability of a material to deform without fracturing and retain the new shape
24
Q
What does malleability describe?
A
Material’s ability to be formed without breaking
25
Define **elasticity**.
The ability of a material to return to its original size and shape when a force is removed
26
What is **plasticity**?
A material's ability to permanently change shape when a force is applied
27
Define **brittleness**.
Failure without deformation upon application of stress
28
What are the **three groups** of metals?
* Ferrous
* Non-ferrous
* Alloys
29
The term **ferrous** relates to any material that contains ______ in its composition.
iron
30
What is **pig iron**?
Rough form of iron containing lots of impurities, cast into small ingots called "pigs"
31
What is **cast iron**?
Pig iron that has been re=melted and poured into moulds to form shapes
32
What is the carbon content of **mild steel**?
Up to 0.3% carbon
33
What is **wrought iron**?
Purified iron that contains strands of slag
34
What is the carbon content range for **carbon steel**?
0.6–1.4% carbon
## Footnote
Carbon steel can be hardened and tempered.
35
What is **ingot iron?**
Purest form of commerical iron
36
What are the properties of **stainless steel**?
Tough, resistant to rust, subject to stains
37
What is the **carbon content** of **high carbon steels**?
More than 0.6% carbon
38
What are common **impurities** in carbon steels?
* Sulphur
* Phosphorus
39
What is the purpose of adding **manganese** to steel?
To counteract the effects of impurities
40
What forms can metals be supplied in? List at least three.
* Square bar
* Round bar
* Sheet steel
41
What is the **blast furnace** used for?
To melt iron ores and produce pig iron
42
What are non ferrous metals?
Metals that don't contain iron.
43
What are the common properties of non-ferrous metals?
Corrosion-resistant, malleable, good conductors of heat and electricity
44
Key properties of aluminium?
Malleable, corrosion-resistant, lightweight and conductive
45
Uses for aluminium?
Aerospace, automotive and lightweight components
46
How can aluminium's strength be improved?
By combining it with copper, silicon, iron or manganese
47
Key properties of copper?
Malleable, corrosion-resistant, conductive, moderate tensile strength
48
Uses for copper?
Pipes, electrical wiring, cookware
49
What alloys can be made from copper?
Bronze (copper + tin) and Brass (copper + zinc)
50
Key properties of zinc?
Soft, brittle, ductile, moderately conductive, corrosion-resistant
51
Uses for zinc?
Galvanising steel, alkaline batteries
52
What is brass made of?
Alloy of copper and zinc
53
Key properties of brass?
Highly malleable, low melting point (900 C), flows when melted, corrosion-resistant
54
Uses of brass?
Decorative items, instruments, fittings
55
What is bronze made of?
Hard, brittle, melts (950 C), high corrosion resistance, fatigue-resistant, very good conductor
56
What is phosphor bronze?
Bronze with 8% tin + 0.3% phosphorus, high strength
57
What is gunmetal?
Tin + bronze + zinc alloy with moderate strength and very high corrosion resistance
58
Uses of copper-nickel alloys?
British silver coins due to their hardness and ductility
59
What are nickel silvers?
Copper + nickel + zinc alloy
60
What are silver bronzes?
Copper alloys with higher zinc content, suitable for hot working
61
Uses for silicon bronze?
Areas with high volumes of sulphur (e.g. chimneys)
62
Key properties of copper-aluminium alloys?
Golden colour, strong, can be annealed to become soft and ductile
63
What are thermoplastics?
Plastic that melts under heat after curing
64
What are thermosets?
Plastic that retains its form and stays solid under heat
65
Why do thermoset plastics retain their shape?
Strong covalent bonds in their polymer structure
66
What is the polymer structure of a thermoplastic?
Weak intermolecular forces, no cross-links
67
How does a thermoplastic work?
They take shape of mould when they are poured as they melt, cools to a solid
68
Common examples of thermoplastics?
Polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC)
69
Examples of processes that use thermoplastics?
Extrusion, injection moulding, thermoforming
70
Examples of thermoset plastics?
Polyester resin, polyurethanes, polyurea/polyurethane hybrids Bakelite,
71
Other examples of thermoset plastics?
Urea-formaldehyde foam, melamine resin, diallyl-phthalate (DAP), epoxy resin, silicone resins
72
What's the difference between thermoplastics' and thermosets' melting point?
Thermoplastic = lower then degradation temp, thermoset = higher then degradation temp
73
What are elastomers?
Loosely crosslinked polymers
74
Examples of elastomers?
Rubber and neoprene
75
What are composites?
Fibre-reinforced polymers (FRPs), made from a polymer matrix that is reinforced with a man-made or natural fibre
76
What does the matrix do?
Protects fibres from external damage, fibres also provide strength and stiffness to help resist cracks and fractures
77
Composites are **anisotropic**, what does this mean?
Means that the material properties change depending on placement and number of layers of fibres.
78
Why does this give engineers flexibility?
Allows designers to tailor properties when it comes to tensile, shear and compressive strength
79
What is tensile strength?
Refers to amount of stress a material can handle before it fails
80
What is flexural strength?
Material's ability to withstand bending forces
81
What is tensile strength measured in?
Megapascals (MPa)
82
How can you control shear properties?
Sequencing of layers, type and volume of fibres, type and density of core materials
83
What is compressive strength?
How a material performs when it's compressed or flattened
84
Examples of composite materials?
MDF (Medium Density Fibreboard), Plywood, Glass reinforced plastic (GRP), Carbon fibre reinforced plastic (CRP)
85
Ceramic products can be categorised as _________, __________ or ___________ products.
Whiteware, refractory or engineering products.
86
What are engineering ceramics?
Advanced, structural or fine ceramics that are extremely pure
87
What are the three types of wood?
Softwoods, hardwoods, engineered/composite woods
88
Where do softwoods come from?
Conifer trees (gymnosperms)
89
Where do hardwoods come from?
Deciduous trees (angiosperms)
90
What makes engineered woods different from natural woods?
They are made from waste wood or manufactured from wooden material
91
What are smart materials?
Materials that respond to external stimuli by changing their properties
92
Examples of smart materials and what they do?
Shape memory alloy (SMA) - deforms from heat or forces, Quantum tunnelling composite (QTC) - acts as insulator normally, electrical conductor when compressed
93
What are piezoelectric crystals?
Crystals that when force is applied - causes voltage to set up, in reverse causes material to twist or bend in a controlled manner
94
What is the structure of an atom?
Protons - positive particle, neutron - no charge, electron - negative particle in orbit around nucleus
95
What are the three types of atomic bonding?
Covalent bonding, ionic bonding, metallic bonding
96
What happens in a covalent bond?
Sharing of electrons between two non-metal atoms (e.g. H - O - H)
97
What happens in an ionic bond?
Electrons transferred to non-metal atom, each atom ends up with a noble gas configuration (e.g. Na - F)
98
What happens in a metallic bond?
Electrons are shared in outer shell along with metal ions in a bond with two metal atoms (e.g. Cu - Ca)
99
What are Van der Waals bonds?
Materials made up of long string molecules consisting of carbon atoms covalently bonded with other atoms
100
What are Van der Waals forces?
Short forces in liquid and gas phases due to increase in electron clouds surrounding nucleus
101
Depending on the process, what do atoms arrange themselves into?
Regular pattern or a lattice structure
102
What is a polymer?
A chain of monomers which are simple molecules
103
What are copolymers?
Polymers that contain two or more different types of monomers
104
What atomic bonds are in a ceramic structure?
Ionic and covalent bonds, as they are much stronger then metallic bonds
105
What is a crystalline solid?
Particles that are arranged in a 3D pattern, with uniform intermolecular forces, called a crystal lattice.
106
What is the difference between a crystalline structure and an amorphous structure?
Amorphous is shapeless, disordered and irregular. Crystalline is uniform with atoms held firmly in place.
107
What is the structure of a composite?
Dispersed phase (fibres) are embedded in the continuous phase (matrix). Material is distributed through matrix (reinforcing phase)
108
What are the three categories of FRPs?
CFRPs, GFRPs, AFRPs
109
What are the two categories of particule reinforced composites?
Large particle reinforced and small particle reinforced
110
What is the difference between small particle reinforced material and large particle reinforced material?
Small particle is on a molecular level, large particle involves larger particles and distribution of load between phases.
111
What is a composite laminate?
An assembly of layers of fibrous composite materials which can be joined together.
112
What is metal forming?
Processes that reshape a raw metal into a finished component
113
What happens in plastic deformation?
A force greater then yield strength of material is applied, this changes material's physical shape permanently
114
What occurs in bending?
Metal sheet is placed over a die block that punch presses material using a brake press.
115
What is rolling?
A metal forming process that reduces thickness of metal to make it uniform.
116
What is the difference between hot rolling and cold rolling?
Hot rolling - Steel is heated above recrystallisation temperature then cooled at room temperature (normalisation) Cold rolling - Steel is below recrystallisation temperature
117
What properties are improved when hot rolling and why does hot rolling improve a metal's properties?
Toughness and ductility, steel's microstructure undergoes permanent changes
118
Limitations of hot rolling?
Susceptible to shrinkage, giving less control over the size and shape of product.
119
What is hot working?
Where deformed grains are replaced by defect-free grains in the metal, used to remove cracks and faults
120
What is the difference between hot working and cold working?
Hot working - above recrystallisation temperature, Cold working - below recrystallisation temperature
121
What occurs in the cold working process?
Strength is built by dislocation (crystallographic defect) movements of the metal structure, internal stresses build up and cracks may appear.
122
What is stretching?
Where a material is deformed through radial strain
123
What is a deep drawing?
Where metal is clamped in place over a cavity shaped die to form hollow-shaped components.
124
What is sintering?
Sintering (frittage) is where a solid mass of material is formed through heat and pressure without melting to a liquid.
125
What are some of the key properties that are improved during sintering?
Thermal and electrical conductivity, material strength and translucency
126
What is thermoplastic powder coating?
A finish that becomes liquid and very soft when heated which eliminates chemical bonding
127
What is thermoset powder coating?
Thermoset powder forms chemical bonds, hard to recycle
128
What are the three types of casting?
Expendable moulds, permanent moulds and composite moulds
129
What is sand casting?
Expendable mould casting that uses permanent patterns to create mould, molten metal is poured into sand mould which solidifies to form part
130
What is shell moulding?
A thin shell mould that is very small that is sand bounded together using thermoset resin binders
131
Is plaster mould casting similar to sand casting?
Yes, except you use a plaster mould instead of sand.
132
What is injection moulding?
Process of melting plastic pellets that are injected at pressure into a mould cavity which fills and solidifies to produce final product.
133
What plastics can you use to injection mould?
Acrylic, Acrylonitrile butadiene styrene (ABS), Polycarbonate (PC), Polyethylene (PE) (HDPE or LDPE)
134
What is metal hardening?
Where alloys are heated above critical transformation temperature for material then cooled rapidly to transform soft material to harder material.
135
What is case hardening?
A metal with a low carbon content gets combined with a higher carbon content metal to make a material harder and ductile
136
What are the three stages of precipitation hardening?
Solution annealing, quenching and ageing
137
What is solution annealing?
A metal is treated with a solution at high temperatures to transform inhomogeneities into homogeneities
138
What is quenching?
Rapid cooling that takes place until solubility limit is exceeded to prevent alloys from discharging
139
What is used in quenching?
Water, oil and gas
140
What is ageing?
Solution is heated to a temperature and is held in a constant heat.
141
What does the exact ageing temperature depend on?
Composition of material
142
What is tempering?
Reheating steel at a low temperature leading to precipitation and spheroidization of carbides in microstructure
143
What can tempering fix?
Relieving stresses caused by quenching
144
What is annealing?
Where a metal is made softer and more workable which reduces material fracture.
145
What is annealing commonly used for?
Removing stresses caused by welding and to improve conductivity of a metal
146
How does painting improve the material?
Protects the material from oxidation and corrosion
147
What is plastic coating?
A preheated part is immersed into liquid plastisol to form a plastic coating which improves aesthetics and protection.
148
Special purpose _________ can be used in coating to provide specific properties such as ______ __________, __________ ________ and _____ __________.
Special purpose additives can be used in the coating to provide specific characteristics such as fungal resistance, dielectric strength and flame retardancy.
149
What is galvanising?
Refers to the application of a zinc coating to surface of a metal to prevent corrosion
150
What are the two types of protection from galvanising?
Barrier protection and galvanic protection
151
What happens during barrier protection?
Zinc coating hardens to form zinc oxide layer that is impervious to air and moisture.
152
What happens during galvanic protection?
Galvanic protection (cathodic protection) protects steel by corroding preferentially
153
Why does zinc corrode to protect the steel from corrosion?
Because zinc is an electronegative metal, it corrodes first when the steel is unprotected, which provides protection until coating is consumed fully.
154
What is corrosion?
A refined metal naturally converts to its oxide, hydroxide or sulphide state, which leads to deterioration of the material.
155
What is rust caused by?
Exposure to oxygen and water
156
What is uniform corrosion and how does it work?
Where corrosion takes place evenly over large surface areas of a material
157
What is pitting corrosion?
Where a local anodic or cathodic point forms a corrosion cell in the surface of a material.
158
Why is pitting corrosion the most aggressive form of corrosion?
Penetrates material and can be hard to predict, detect or categorise.
159
What is pitting corrosion caused by?
Its caused by damage in the oxide film and can also be due to non-uniformities in structure of a metal
160
What is crevice corrosion?
Forms in areas where oxygen is restricted
161
What causes crevice corrosion?
Difference in ion concentration between two areas of metal, usually under washers or bolt heads.
162
What is stress corrosion?
Where a material corrodes due to applied stress.
163
What is galvanic corrosion?
Where two different metals with physical/electrical contact are immersed in an electrolyte (e.g. salt or water)
164
What is intergranular corrosion?
Where impurities are present at grain boundaries which are formed during solidification of an alloy.
165
What name is given to two metals immersed in an electrolyte?
Galvanic couple
166
Where does intergranular corrosion happen?
Next to or along the grain which affects mechanical properties
167
What is chemical corrosion?
Gradual destruction of a metal's surface due to reaction of surface with chemicals in its external environment
168
What is stress corrosion cracking (SCC)?
Growth of cracks due to a corrosive environment which can lead to failure in ductile metals when subjected to tensile stress at high temperatures.
169
What is erosion corrosion?
Caused by rapid flow of fluid on a metal surface combined with corrosion of moving fluid
170
What is the first step for corrosion prevention?
Determining material's position in the galvanic series, alongside studying environmental conditions
171
What methods can be used for corrosion prevention?
Protective coating, metal alloys, corrosion inhibitors, use of sacrificial anode
172
What forces cause deformation?
Tensile, compressive, shear, bending, torsion
173
What are the types of deformation?
Elastic deformation, plastic deformation, metal fatigue and compressive failure
174
What are the key differences between elastic and plastic deformation?
**Elastic** - reversible, elastomers have huge elastic deformation ranges, **Plastic** - irreversible, soft thermoplastics have large deformation variance
175
What is the difference between metal fatigue and compressive failure?
Metal fatigue - happens mainly in ductile metals, Compressive failure - applied to bars and columns which leads to shortening, loads can increase compressive stress until max compressive strength is reached
176
What is fracture?
Caused by separation of material into two or more pieces under stress
177
What is the key difference between ductile fracture and brittle fracture?
Ductile fracture - first experience plastic deformation, material resists self from stretching, Brittle fracture - material breaks without warning
178
What happens in cup-and-cone formation?
Ductile material starts necking -> cavities start to form perpendicular to stress direction -> cavities merge to form crack -> crack expands -> material fractures (cup and cone forms at top and bottom)
179
How does crack formation affect the two types of fractures?
Ductile - crack is stable, only propagating when more stress is applied, Brittle - propagate across material instantly, meaning no warning before failure
180
What is fatigue?
Weakening of a material
181
What is necking?
Type of plastic deformation in ductile materials where there is reduction in cross-sectional area of a material, giving it a 'neck' shape
182
Where do cracks form when fatigue occurs?
Surface, persistent slip bands (PSBs) and grain interfaces
183
What are the three stages of the creep curve?
1. Primary creep region - increases in strain hardening 2. Steady state creep - creep is constant and has longest duration 3. Tertiary creep - where material approaches failure
184
What is creep failure?
A timely and permanent deformation of a material when subjected to constant load or stress
185
What is visual testing (VT)?
Non-destructive inspection carried out by the naked eye
186
What are the different types of destructive testing?
Tensile, impact, fatigue and hardness tests
187
How does tensile testing work?
Investigates how much a material can be stretched before it breaks
188
What is the process of a tensile test and what is the outcome?
Performed by gripping ends of a prepared material and applying a continually increasing load until failure occurs, provides information that can be used in calculations
189
What measures yield strength?
Extensometers
190
What is the Charpy impact test?
Measures amount of energy absorbed by specimen during fracture
191
What is the Birnell test?
A type of hardness test composing of a hard steel ball indenting the surface of a sample material using a standard load
192
What is the Vickers test?
A type of hardness test where a square based pyramidal diamond indents the surface of very hard materials
193
What is the Rockwell test?
A type of hardness test that focuses on an inverse relationship between major and minor loads
194
What is the Wohler test?
A type of fatigue test that simulates a fatigue cycle by applying compressive and tensile stresses onto a metal
195
What is immersion testing?
A corrosion test that examines how a material responds to particular conditions
196
What is the hot wall test?
Where elevated temperatures in a metal vessel indicate high levels of corrosion
197
What is the salt spray test?
Where a coated sample's resistance to corrosion is tested, measures suitability of protective coating
198
What is the Taber abrasion test?
A method used to determine ability of a material to withstand wear, mainly performed on coated materials
199
What is the formula for electrical conductivity?
p=RA/I p is resistivity, R is resistance, A is area and I is length
200
What is the conductivity measured in?
Siemens (S), s=1/p
201
What is defined as the act of applying a force?
Loading
202
What is Hooke's law?
Law of elasticity, states that small deformations of an object are directly proportional to deforming force or load
203
What is the formula for Hooke's law?
F=-kX, F=force applied to the spring, X=elongation of spring (negative value), k=spring constant (stiffness)
204
What is Young's modulus?
Measure of the ability of a material to withstand changes in its length under tension or compression
205
The stress is the ________ __ ___ _______ _____ _______ __ ___ _____-_________ ____, or _/_
quotient of the tensile force divided by the cross-sectional area, or F/A.
206
What is the formula for Young's modulus?
Stress/strain = FLo / A (Ln - Lo), F=force, A=area, Lo/Ln=original/new length
207
What are the two units for Young's modulus?
Pounds per square inch (psi) and Newtons per square metre (N/m^2)
208
What is the formula for stress?
Stress=Force/Area
209
What is strain?
The ratio of change in dimension to the initial dimension of a metal
210
What are the three types of strain?
Normal, volumetric and shear
211
What is the formula for stress?
ε=(l-lo)/lo io=inital length (mm) I=stretched length
212
What are stress-strain curves?
Obtained by observing deformation in a material when load is applied gradually to it.
213
A _____ _______ ______ where the material undergoes elastic deformation
Linear elastic region
214
A ______ _________ ______ that occurs when the material is subjected to its ultimate tensile strength.
Strain hardening region
215
The _______ ______ where the ____ forms. At this point, the material's ability to sustain stress _________ rapidly as it approaches fracture.
necking region, neck, decreases
216
How do you plot a stress-strain curve?
Complete a tensile test, plot parameters onto an X-Y graph.
217
To interpret a stress-strain graph, when does a material exhibit elastic behaviour?
Up until the yield strength point
218
To interpret a stress-strain graph, when does a material exhibit plasticity?
Beyond the elastic limit and proportional limit of yield strength
219
To interpret a stress-strain graph, how do you determine the ultimate strength of a material?
Based on its maximum ordinate value from origin to rupture. The value provides rupture with strength at the point of rupture.
Decks in class (17)
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