P 5. Solids under stress Revamp Flashcards
(117 cards)
1
Q
Almost there
A
u right
2
Q
Experiment to learn?
A
When the case calls
3
Q
Define limit of proportionality
A
- When the proportional behaviour
- of forces and extension stops
4
Q
Define elastic limit
A
- Point at which deformation
- ceases to be elastic
5
Q
Define permanent extension
A
When it’s permanent, irreversible deformation
6
Q
Define elastic behaviour
A
- When extension disappears when force is removed
- returns to its original size and shape
7
Q
Define plastic behaviour
A
- When extension decreases
- only slightly when stress is removed
- Doesn’t return to its original size and shape
8
Q
Define Hooke’s law?
(4-way)
A
- The tension in a spring or ware
- is proportional to its extension
- from its natural length
- within the limit of proportionality
9
Q
Hooke’s law formula?
A
F = kx
10
Q
Define F
(Hooke’s law)
A
Force applied/tension
(N)
11
Q
Define k
(Hooke’s law)
A
The spring constant
(force per unit extension)
12
Q
Define x
(Hooke’s law)
A
The extension from the spring’s natural length
(mm, cm, m)
13
Q
What do springs look like in parallel?
A
1 hanging each side
14
Q
What do springs look like in series?
A
Hanging on top of each other
15
Q
If springs are in parallel, what happens to the k?
(2-way… + 1 thing)
A
- x = doubled
- k = halved
- k1 + k2 = ktotal
16
Q
If springs are in series, what happens to the k?
(2-way… + 1 thing)
A
- x = halved
- k = doubled
- 1/k1 + 1/k2 = 1/ktotal
17
Q
How is the energy stored in stretched spring equation formed?
A
- Area under line on force-distance graph = wd
- Likewise to Hooke’s law thing
- E = ½ Fx
- Sub in F = kx
- E = ½ kx2
18
Q
Therefore, what’s the equation to find energy stored in a stretched spring?
(in data booklet)
A
E = ½ kx2
19
Q
Define stress
A
Force per unit cross-sectional area
20
Q
Formula for tensile stress (σ)?
A
σ = N/m2
21
Q
Formula for tensile stress expressed in words?
A
Tensile stress = Force/Area
22
Q
Define σ
(Tensile stress formula)
A
Tensile stress…
(Nm-2 or Pa)
23
Q
Define N
(Tensile stress formula)
A
Force
(Newtons)
24
Q
Define m2
(Tensile stress formula)
A
Area
(x2)
25
Define strain
Extension per unit length
26
Formula for tensile strain (ε)?
ε = m/m
27
Formula for tensile strain expressed in words?
Tensile strain = extension/length
28
Define ε
(Tensile strain formula)
... tensile strain
(A ratio, no units)
29
Define the m's
(Tensile strain formula)
(2-way)
- Extension above
- Length below
30
For any material, if we work within the limit of proportionality, what happens to the ratio for stress/strain?
What's it called?
- Becomes a constant value
- YOUNG MODULUS
31
Formula for young modulus (E)?
E = σ/ε
32
What's an easier equation for young modulus?
E = Fl/Ax
33
How is the easy young modulus equation developed?
(3 steps)
1. E = (F/A)/(x/l)
2. = F/A x l/x
3. = Fl/Ax
34
Define elastic?
(2-way)
- Material that regains its shape
- after stresses are removed
35
Define ductile?
(2-way)
- Material that can be easily stretched
- or drawn into a wire
36
Define malleable?
(2-way)
- Material able to be hammered or pressed
- into a shape without breaking/cracking
37
Define brittle?
(2-way + e.g.)
- Material that'll snap
- without yield
- ... without any give
38
Define stiff?
(1-1-way)
- Small strains for large stresses
- ;Not stretch or bendy
39
Define plastic?
(2-way)
- Material that undergoes permanent deformation
- under large stress rather than cracking
40
Define strong?
(in terms of this topic)
Large stress needed to break it
41
Define hard?
(in terms of this topic)
Resists indentation on impact
42
Topics left...?
- Stress-strain graph for ductile metals
- Brittle material
- Polymeric materials
Finish in time o7.... it seems we have an alternate path
43
What are the 3 categories used to classify solid materials?
- Crystalline solids
- Amorphous solids
- Polymeric solids
44
What type of materials are crystalline solids?
(psh remember 1/4)
- Metals
- Diamond
- Graphite
- Salt
45
Define crystalline solids
(2 things)
- Atoms arranged into a crystal lattice
- Consists of regularly repeating unit cells
46
What do crystalline solids exhibit?
Long-range order and symmetry
47
What's the jig with poly-crystalline structures?
(3 things)
- Structure split up into many small crystallites/grains
- Randomly arranged
- Forms different grain boundaries
48
What type of materials are amorphous solids?
(remember 1/3)
- Glass
- Ice
- Ceramics
49
Define amorphous solids?
(2-way + 2-way)
- Atoms have no long-range order
- ... Or symmetry
- Considered to be super cooled liquids:
- atoms randomly arranged, no overall pattern
50
What do amorphous solids tend to be more?
(2-way)
- Brittle
- with little elasticity
51
What type of materials are polymeric solids?
(remember 1/4)
- Rubber
- Cellulose
- Polyethylene (ploythene)
- PVC
52
Define polymeric solids?
(1 thing + 3-way)
- Compromised of long molecular chains
- Consists of basic units:
- monomers repeatedly linked together
- w/ strong covalent bonds
53
If the polymeric solid is randomly tangled up, what can be said bout' it?
(2 things)
- Amorphous
- No long-range order
54
How can a polymeric solid display semi-crystalline properties?
- Stretched rubber
- When chains are untangled
55
Crystalline solid in molecular terms?
(2-way)
- Long range order
- Lattice arrangement
56
Amorphous solid in molecular terms?
(2-way)
- Short/no range order
- Random arrangement
57
Polymeric solid in molecular terms?
Long chain molecule arrangement
58
Define elastic strain
(1 thing, 2-way + 2 features)
- Force applied to a material
- Atoms stretched apart
- ... by a very small distance
- Strain measures = relatively small forces
- Small strains = no bonds broken
59
Define plastic strain
(2-way-aparts + 1 main)
- Imperfections within a lattice:
- **Edge dislocations**
- ... causing bonds to break
60
Explain the theory suggesting lattices contain imperfections
(1 thing + 2-way)
- Mistakes within structure
- Incomplete plane of atoms creating
- "an **edge dislocation**"
61
What are edge dislocations?
(2-way + 2-way)
- Creates a point of weakness within material...
- where large stresses occur
- These points = material start to fail if.....
- Larger forces applied here
62
Movement of edge dislocation = ?
Plastic deformation
63
What's the symbol representing edge dislocation?
⊥
(wowow)
64
How the edge dislocation move within a material?
(2-way + 2-way)
- If **shear stress** applied
- dislocation migrates throughout material
- New bonds made to the left....
- edge dislocation moves to the right
65
What causes permanent deformation within material?
(2-way + 2-way + 1 thing)
- Not applying force....
- to move the dislocation
- Plastic strain occurred
- has gone beyond elastic limit
- Edge dislocation stays permanently to right
66
Define work hardening?
(3-way + 2 features)
- When lots of dislocation meet
- Impedes each other
- to stop dislocation propagation
- Material = gets stronger
- Larger stress to cause further strain
67
Define grain boundaries?
(2 things + 2-way + 2 things)
- Polycrystalline materials have this
- Forms barriers to edge dislocation movement
- Smaller grains = short distance travelled
- ... by the dislocation
- Can make the material stronger
- Dislocation can't jump to next grain
68
Define necking
(2-way)
* The thinning of the cross-sectional area
* of a material at the weakest point
69
When does necking occur?
(2-way + 1 thing)
- When material continues to be stretched
- .... after reaching its ultimate tensile stress
- Rapidly leads to materials failing
70
Define ductile fracture?
(2-way)
- Process of **large strains** and **necking**
- leading up to the material failing
71
What are the 3 ways to strengthen metals?
- Grain size reduction
- Work hardening
- Foreign atoms
72
Explain grain size reduction?
(Strengthening metals)
(3-way)
- Smaller grains produce
- more barriers
- to dislocation movement
73
Explain work hardening?
(Strengthening metals)
(3-way)
- Plastically deforming metal
- by creating a greater dislocation density
- makes metal stronger
74
Explain foreign atoms?
(Strengthening metals)
(2-way + 2-way)
- Making metal alloys by....
- introducing new elements into molten metal
- Has effect of causing changes to lattice
- impedes the movement of dislocation
75
How is steel made through foreign atoms?
(2-way + 1 things' definition)
- Since adding similar sizes but different element atoms
- to lattice distorts the lattice slightly
- **Interstitial** takes place
- (fitting in between the lattice atoms)
76
Describe through labelled diagrams of the behaviour of ductile materials?
When the time calls...
77
Show & draw me the stress-strain graph for ductile metals?
(4 stages w/ 2 having 1/3 things)
1. Limit of proportionality
2. Elastic limit
^^^ Yield strength
3. Plastic region
^ first half = work hardening
^ second half = necking
^ peak = ultimate strength
4. Fracture
When the time calls.
78
What does it mean if brittle materials don't undergo ductile fracture?
No plastic deformation within material
79
What do brittle materials undergo?
(2 things + 2-way)
- Elastic deformation
- Usually failing within their elastic limit
- They obey Hooke's law....
- up to their fracture point
80
We're at a considerably good spot
Lock in for A levels first. But it doesn't hurt to be diligent
81
Welcome back?
I wish there was a date here but meh it was definitely last year, few months ago
82
A material(s) that's brittle and "amorphous"?
- Glass
- Concrete
83
Why doesn't glass yield?
(2 things)
- The way fracture occurs within material
- They break suddenly
84
Why doesn't glass have any "failures"?
Doesn't have slippages of atomic planes (ductile materials)
85
What happens if a bond breaks for a brittle material?
(2-way)
- Crack in atomic planes
- propagates rapidly
86
In depth of surface imperfections on brittle materials?
(1-2-way)
- Failure of material
- Crack rapidly at right angles
- to the stress forming a flat surface
87
How the the cracks of a brittle material often propagate?
(2 things)
- By cleavage
- e.g. atomic bonds break along specific crystal planes
88
Example of how a crack moves through a brittle material?
Like a zip undoing O_o
89
Major difference between brittle materials w/ bonds and a ductile material?
Bonds don't reform like the dislocation movement
90
The 1 way to bend glass then?
Freshly made glass fibre
91
Explain compressive stress of a brittle material?
(3-way + 1 thing)
- Inside of bend is touched...
- nothing happens
- due to surface under compression
- Surface cracks are closed
92
Explain tensile stress of a brittle material?
(2-way + 2-way)
- When touched on outside of curve
- ... immediately shatters
- Surface cracks are opened
- and rail rapidly
93
Hence, in what way is brittle materials stronger?
Under **compressive forces** than tensile forces
94
What are 2 types of glass you can get for if u increase their breaking stress?
- Fibre glass (thin fibres)
- Toughened glass
95
How are thin fibres stronger than **thick** glass rods
(2 things)
- Smaller surface area
- Fewer cracks & surface imperfections
96
Hence, how are fibre glass created?
(3-way)
- Placing thin fibres into
- resin glue
- Very mouldable
97
How is toughened glass achieved?
(6-way)
(Understanding problem)
- Rapidly cooling outside of
- molten glass (jets of air)
- Outside cools and contracts
- Inside is soft and able to give
- Once inside hardens and contracts,
- outside cant give and thus placed under compressive stresses
98
How are toughened glass much harder to form cracks?
(2-way)
- Close up due to
- internal compressive forces
99
What happens when toughened glass (pre-stressed glass) completely breaks?
(3-way)
- Shatters into tiny pieces
- w/ rounded edges than
- jagged sharp edges
100
How is pre-stressed concrete achieved?
(3-way)
- Use of steel reinforcing bars/rods
- compensates for concrete's weakness
- when placed under tension
101
How is pre-stressed concrete made?
(5-way)
(Understanding problem)
- Steel rods placed under tension + st retched
- Wet concrete placed around steel
- allow to set causing to bond
- Tension removed from steel rods allowing it to contract
- Concrete now under permanent compressive forces
102
How about how larger structures of pre-stressed concrete is made?
(2-way + 1 thing)
- Fit together sections of
- pre-stressed concrete
- Strong under both compressive & tensile stresses
103
Explain concrete without metal rods?
(3-way)
- Lower surface under tension
- Force causes cracks in surface
- rapidly opens leading to failure
104
Explain concrete w/ metal rods?
(2-way + 2-way)
- Lower surface under compression
- due to rods
- Force will cause cracks
- in surface to close
105
Stress-strain graph for brittle materials?
(Lil situation)
Maybe I'll find one online and try implement
106
Define polymeric materials?
(2-way)
- Consists of long chain molecules
- which're held together by cross bonds
107
2 examples of polymeric materials?
- Rubber
- Polythene
108
What does it mean if rubber is an elastic material?
Can go back to original shape after deformation
109
Stress-strain graph of rubber?
(lil situation)
Well, its in the booklet but...
- Loading and unloading
- Looks like a skewered flame
110
What is observed during microscopic analysis of a rubber material?
(3 things + 2-way)
- Like monomers together creating polymers
- Bonding = covalent and strong
- Longer chain = weak VDW bonds to form between adjacent lengths of the coils
- Weaker bonds easily broken HENCE
- can stretch exhibiting large strains
111
In-depth reason how rubber is elastic?
(2 things + 2-way + 2-way)
- After removal of stress and chains curling back up,
- Thermal energy causes atoms & molecules to vibrate
- Thermal agitation makes chain want to become more
- randomly arranged
- Often referred to stretching polymers
- against thermal opposition
112
In stress-strain graph of rubber, what's the phenomena called of the contracting curve not coinciding with the expanding curve?
Hysteresis
113
In stress-strain graph of rubber, what's the area enclosed known as?
Hysteresis loop
114
How to gain energy transferred per unit volume from stress-strain graph of rubber?
The area.... the hysteresis loop...
115
Hence, the 3 behaviours of rubber
(Left - right = loading,
Right - left = unloading)
- Tangled
- Straightening
- Straight
116
.... DRAW, the 3 behaviours of rubber B|
Okay aight stage yours lol
117
Brother I pray u consistently nail this
Hm.
