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MEC132 JD > Lecture 1 and 2 > Flashcards

Lecture 1 and 2 Flashcards

1
Q

Materials made of

A

atoms bonded together

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2
Q

stress and strain related by

A

mechanical properties

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3
Q

altering the properties of a material can be done by

A

altering the method of processing the raw material

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4
Q

Present day dependant on what type of materials

A

none renewable

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5
Q

binary alloy

A

two atomic species together

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6
Q

ternary alloy

A

two different atomic species together

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7
Q

Material science atm focuses on

A

nano materials - altering materials at the atomic scale

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8
Q

over how many engineering materials

A

100,000

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9
Q

Issues with new materials

A

have to alter manufacturing processes to use - economics
environmental issues
is it legally allowed

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10
Q

what percentage of inovations comes from materials

A

70%

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11
Q

hard materials are

A

quite brittle - small crack likely to break but keep an edge

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12
Q

choose a material based on

A

properties
performance
processing
structure

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13
Q

microstructurally insensitive

A 
arise from bonding energy arrangements and the packing of atoms
density
elasticity/YMS
melting point
thermal conductivity
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14
Q

microstructurally sensitive

A

imperfections within crystal structure
hardness
ductility

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15
Q

hardness and how is it related to yield strength

A

how difficult is it is to scratch a material related to yield strength as permanently deforming the material

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16
Q

density is

A

mass over volume kg/m3

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17
Q

approximate density of water

A

1000

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18
Q

Metals density of most metals

A

8000

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19
Q

requirements to float on water

A

density should be lower than water

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20
Q

properties change with

A

temperature therefore need to specify temperature at which the mechanical property is measured

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21
Q

a ductile fracture

A

will require a lot of energy - will have a higher impact fracture toughness

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22
Q

brittle fracture

A

clean brake one crack - ductile many cracks form before break

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23
Q

Different processing methods will

A

change the material properties of a material

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24
Q

why is it important to process a material correctly

A

to make sure the product at the ends properties at the ones we desire - are not poor

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25
all materials (solids liquid gasses) are made of
atoms
26
when breaking a material what are you actually breaking
chemical bonds between the atoms to form two separate surfaces
27
material properties determined by
how atoms are arranged strength and nature of bonds between them
28
outside shell of an atom called
valence shell
29
atoms want to have
full outer shell - shell goes 2 8 8 8
30
outer electrons responsible for
chemical bonding - can be shared or transferred - how it does this determines mechanical properties
31
metallic bond
valence electrons shared between all atoms - inner shell kept, generates sea of electrons that can move freely good thermal and electrical properties easy to rearrange material - ductile and malleable generally materials
32
covalent bond
sharing of electrons - carbon has 4 valence electrons hydrogen has 1 therefore 4 hydrogen to one carbon, charge interaction generates strong and directional bonds - not easy to rearrange therefore stiff and hard material diamond
33
ionic bond
complete transfer of electrons between atoms to form positive and negative ions atoms give up or take in valence electrons chemical reaction donating atoms or taking in to fill or get rid of outer shell
34
method of measuring atomic densities
RDF - radial distribution function
35
how does rdf work
choose an atom draw round set of concentric atoms count number of atoms inside ring divide by average density move ring outwards repeat seeing how close its nearest neighboring atom is
36
RDF of gas
no regular arrangement no long range order none near it as you go outwards rises to density of gas
37
RDF of liquid
no regular arrangement vibrate and move about each other sticky- viscosity no nearest neighbour nearby then large spike short range order but no long range order
38
RDF of solid
atoms and molecules tightly packed usually regular pattern can vibrate around fixed position have a number of atoms at fixed distance - spike then none until get to next nearest neighbour -spike atoms on regular crystal array have to go so far to see next nearest atom vibration of atom leads to a slight cone shape crystalline solid
39
RDF of solid in glassy state
same as liquid - when you process material dont have time to get to crystal state freezes in liquid state rapidly remove energy - cool quickly
40
RDFs of materials
not fixed to described RDFs, these RDFs tell you about the structure of the material no whether it is solid liquid or gas
41
how do solids liquids and gasses act in a container
gas fills container - lots of space between atoms easy to compress liquid fills bottom of container - difficult to compress solids retain their shape no easy to compress
42
solid to liquid
melting reverse freeze
43
liquid to gas
vaporise reverse condense
44
solid to gas
sublimation
45
gas to solid
deposition
46
which state has highest energy
gas
47
pressure temperature diagram
can vary pressure to change state (with constant temperature)
48
given mass of liquid has
fixed volume - varies slightly with temperature and pressure - similar to solid
49
given mass of gas has
variable volume very dependent on temperature and pressure
50
solids strong interactions between atoms mean
it can support stresses - has moduli and a given strength
51
liquids atomic molecules in what type of state
atomic molecules in high energy state as move past each other sticky - visocscity
52
method to think about bonds
like springs - although different in detail force energy curves are similar for all types of bonds
53
lennord jones potential equation, which part is repulsive which is attractive when does it apply
order of 12 term = repulsive order of 6 term = attrative when thinking about bonds as springs - ionic case for simplicity electrons repel each other ions attract each other describes potential energy of two atoms seperated by distance r
54
what are the material constants in the lennord jones equation
epsilon and sigma
55
where does atom want to sit on energy distance curve
lowest point the well lowest energy state distance known as ro
56
diagram of lennord jones curve
``` potential energy vs distance potential energy well epsilon sigma ro ```
57
energy required to break bond lennord jones curve
energy to push out of well distance from ro to xaxis
58
lennord jones curve it atom is to the right of well
atom attracted falls into well
59
lennord jones curve if atoms left of well
atoms really close together | repel each other
60
epsilon lennord jones
depth of well in joules in J minium point on lennord jones curve
61
sigma lennord jones
distance away from atom (m) where lennord jones curve crosses x axis potential energy = 0
62
what happens when ro distance apart
atoms happy | lowest energy
63
what happens when you compress spring - ie push atoms closer together
spring wants to force atom back atoms repel each other due to electronic charge repelling high energy state - requires a lot of energy to do difficult repulsive term dominates
64
what happens when you expand the spring ie pull atoms apart
spring wants to bring atoms back together atoms attracted to each other attractive term dominates eventually pull so far apart break bond
65
How do you convert energy to temperature
boltzman constant kb E= KbT
66
Temperature energy can change the
bond energy - make well shallower as atoms vibrate up side of well if temperature energy increases mean inter atomic distance increases as atoms vibrating bond stiffness decreases - easier to melt material
67
low melting point metals
have a shallower well - their epsilon value is lower
68
Relating bond energy to melting point
high bond energy = high melting point
69
highest melting point
covalent and metallic bonds | ionic slightly lower but have higher bond energy
70
secondary type of bonds
van der waals and hydrogen - not the exchange of atoms much lower bond energy and melting point
71
Extensive properties
linearly dependent on the amount of substance. Examples: mass, volume
72
Intensive Properties
independent of the amount of substance. Examples: | temperature, pressure, density

MEC132 JD (9 decks)

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