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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
Q

all materials (solids liquid gasses) are made of

A

atoms

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26
Q

when breaking a material what are you actually breaking

A

chemical bonds between the atoms to form two separate surfaces

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27
Q

material properties determined by

A

how atoms are arranged strength and nature of bonds between them

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28
Q

outside shell of an atom called

A

valence shell

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29
Q

atoms want to have

A

full outer shell - shell goes 2 8 8 8

30
Q

outer electrons responsible for

A

chemical bonding - can be shared or transferred - how it does this determines mechanical properties

31
Q

metallic bond

A

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
Q

covalent bond

A

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
Q

ionic bond

A

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
Q

method of measuring atomic densities

A

RDF - radial distribution function

35
Q

how does rdf work

A

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
Q

RDF of gas

A

no regular arrangement
no long range order
none near it
as you go outwards rises to density of gas

37
Q

RDF of liquid

A

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
Q

RDF of solid

A

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
Q

RDF of solid in glassy state

A

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
Q

RDFs of materials

A

not fixed to described RDFs, these RDFs tell you about the structure of the material no whether it is solid liquid or gas

41
Q

how do solids liquids and gasses act in a container

A

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
Q

solid to liquid

A

melting reverse freeze

43
Q

liquid to gas

A

vaporise reverse condense

44
Q

solid to gas

A

sublimation

45
Q

gas to solid

A

deposition

46
Q

which state has highest energy

A

gas

47
Q

pressure temperature diagram

A

can vary pressure to change state (with constant temperature)

48
Q

given mass of liquid has

A

fixed volume - varies slightly with temperature and pressure - similar to solid

49
Q

given mass of gas has

A

variable volume very dependent on temperature and pressure

50
Q

solids strong interactions between atoms mean

A

it can support stresses - has moduli and a given strength

51
Q

liquids atomic molecules in what type of state

A

atomic molecules in high energy state as move past each other sticky - visocscity

52
Q

method to think about bonds

A

like springs - although different in detail force energy curves are similar for all types of bonds

53
Q

lennord jones potential equation, which part is repulsive which is attractive when does it apply

A

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
Q

what are the material constants in the lennord jones equation

A

epsilon and sigma

55
Q

where does atom want to sit on energy distance curve

A

lowest point the well lowest energy state distance known as ro

56
Q

diagram of lennord jones curve

A 
potential energy vs distance
potential energy well
epsilon
sigma
ro
57
Q

energy required to break bond lennord jones curve

A

energy to push out of well distance from ro to xaxis

58
Q

lennord jones curve it atom is to the right of well

A

atom attracted falls into well

59
Q

lennord jones curve if atoms left of well

A

atoms really close together

repel each other

60
Q

epsilon lennord jones

A

depth of well in joules in J minium point on lennord jones curve

61
Q

sigma lennord jones

A

distance away from atom (m) where lennord jones curve crosses x axis potential energy = 0

62
Q

what happens when ro distance apart

A

atoms happy

lowest energy

63
Q

what happens when you compress spring - ie push atoms closer together

A

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
Q

what happens when you expand the spring ie pull atoms apart

A

spring wants to bring atoms back together
atoms attracted to each other
attractive term dominates
eventually pull so far apart break bond

65
Q

How do you convert energy to temperature

A

boltzman constant kb E= KbT

66
Q

Temperature energy can change the

A

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
Q

low melting point metals

A

have a shallower well - their epsilon value is lower

68
Q

Relating bond energy to melting point

A

high bond energy = high melting point

69
Q

highest melting point

A

covalent and metallic bonds

ionic slightly lower but have higher bond energy

70
Q

secondary type of bonds

A

van der waals and hydrogen - not the exchange of atoms much lower bond energy and melting point

71
Q

Extensive properties

A

linearly dependent on the amount of substance. Examples: mass, volume

72
Q

Intensive Properties

A

independent of the amount of substance. Examples:

temperature, pressure, density

MEC132 JD (9 decks)

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