1
Q
what are structure insensitive properties
A
- properties that do not change despite changes in microstructure due to different working/heat treatment during manufacturing
2
Q
what are the most important structure insensitive properties
A
- density
- elastic modulus
- some electrical and thermal characteristics
3
Q
what type of properties are most affected by changes in microstructure
A
- mechanical properties called structure sensitive properties
4
Q
what are the most important structure sensitive properties
A
- yield strength
- fracture strength
- ductility
5
Q
what is a metallic bond
A
- the attraction between the positive metal ions and the cloud of negative electrons resulting in a stable structure
6
Q
what are interatomic bonds
A
- bonds between atoms that act like springs
7
Q
what is the equation for bond energy
A
8
Q
why is the bond energy curve asymmetrical
A
- the repulsive part inreaster faster with atom distance than the attractive so the resulting bond energy curve is asymmetrical
9
Q
how to find the equilibrium point on a bond energy curve
A
- the lowest energy
10
Q
what does the stable separation between atoms correspond to
A
- stable separation between atoms corresponds to an energy minimum
11
Q
how to find the bond strength on a bond energy-atom distance curve
A
- it is the depth of the minimum in the bond energy-atom distance curve as it is the energy needed to separate the atoms completely
12
Q
why do materials expand when heated
A
- as energy is added to a material, the thermal vibration of the atoms causes them to oscillate around the equilibrium distance, the average distance between the atoms increases as temperature increases
13
Q
what is the relationship between the bond energy-atom distance curve and the thermal expansion coefficient
A
- the narrower the curve, the lower the coefficient
14
Q
what causes materials to melt
A
- if the heating process is continued, the atoms reach a degree of vibration that causes them to separate, breaking the bond
15
Q
what are the forces that act on atoms
A
- an attractive force that pulls the atoms together and increase as they get closer together
- a repulsive force that increases faster with distance
16
Q
what is the net force between atoms (F)
A
- the sum of the attractive and repulsive forces acting on the atoms
17
Q
what is true when the net force between the atoms is zero
A
- the distance between the atoms = the equilibrium distance
18
Q
how to find the bond force from a bond energy-atom distance curve
A
- it is the derivative of the bond energy-atom distance curve
19
Q
where is the maximum on the bond force curve
A
- at the point of inflection
20
Q
what is true at the equilibrium distance
A
- the sum of the two forces is 0
21
Q
what happens to the forces when the atoms are brought closer together
A
- both the repulsive and attractive forces increase, but the repulsive increases quicker than the attractive
22
Q
how can atoms be moved from their equilibrium positions
A
- by tensile or compressive loading
23
Q
what happens when atoms are stretched/compressed
A
- a force appears that resists the stretching or compression
24
Q
what is true about the force that resists stretching for small extensions
A
- the force is closely proportional to the extension for all materials in tension and compression
25
what is the stiffness of the bond, S, and the equation for it
- the gradient of the bond force atom distance curve
- the second derivative of the bond energy atom distance curve
- dF/dr = d²U/dr²
26
what is the elastic modulus (Young’s modulus) E
- the gradient of the bond force-atom distance curve at the equilibrium distance
27
what is the equation for the elastic modulus
- S (stiffness)/r⁰(equilibrium distance)
28
what is a tensile test used for
- to determine the strength of a material when it is stretched
29
describe how to perform the tensile test
- test specimens have standard dimensions
- the specimens are stretched slowly at a constant rate
- the applied force and elongation of the specimen are recorded
30
what is the initial gauge length
- the part of the test specimen over which the length increase is measured at any point during the test
31
what are the important dimensions in the tensile test
- initial gauge length
- initial cross-sectional area
32
what two parts does the elongation of the test specimen consist of
- elastic deformation - the initial deformation which is reversible upon unloading
- plastic deformation- not reversible upon unloading and is permanent
33
what type of test specimens are usually used in the tensile test
- thin pieces cut from sheet metal (rectangular cross section)
- machined from bulk metal (circular cross section)
34
describe elastic deformation
- it is often linear with the elongation produced under load being directly proportional to the load
35
describe plastic deformation
- it involves a region of uniform deformation in which all the parts of the gauge length elongate to the same amount
- involves a non-uniform region in which localised deformation occurs which is called necking
36
how is deformation stopped
- the deformation process is terminated by fracture in the necked region
37
when is a metal described as ductile
- when considerable plastic deformation occurs before fracture
38
when is a metal described as brittle
- fracture occurs in the elastic (or after only a small amount of plastic deformation)
39
what are load-elongation curves normally converted to
- stress-strain curves
40
how is load converted to true stress
- load/instantaneous cross sectional area
- (𝜎ₜ=𝐹/𝐴)
40
how is load converted to the normal/engineering stress
- load/original cross-sectional area
- (𝜎ₙ=𝐹/𝐴₀)
41
how to calculate normal/engineering strain
42
how to calculate true strain
43
what is the equation for Young’s Modulus when in the elastic region (where stress is proportional to strain)
- E = 𝜎ₙ/ εₙ
44
what measurements can be taken from the engineering stress-strain diagram
- modulus of elasticity,E - initial slope of the curve
- yield strength - the value of normal stress at the onset of plastic flow
- tensile strength - maximum normal stress that is applied to the specimen (onset of necking)
- failure strength - the normal stress at failure
- ductility - the total elongation of the specimen that is due to plastic deformation
- tensile toughness - total area under the curve, it is the energy absorbed by the specimen during the whole test
