Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Mat > Mechanical 2 > Flashcards

Mechanical 2 Flashcards

1
Q

Strength of paper

A

about 60MPa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

suffixes like mega, milli, pico, etc

A

learn off

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

why easier to rip paper with crack

A

stress is concentrated at tip of crack, material fails there, allowing crack to grow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

relationship between fracture stress and crack length

A

σf ∝ 1/√a

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

fracture toughness in tough vs brittle materials

A
  • tough: value of constant high, good at tolerating cracks

- brittle: low, even small cracks weaken them

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Fracture Toughness equation

A

Kc = Qσf√(πa)

Q = a constant
σf = fracture stress
a = crack length
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Values of Q

A

taking a crack in a flat sheet,
if
a < W and a < H, then Q = 1.0

other values shown on graph on lecture slides 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Total length of crack in a flat sheet

A

Length of crack = 2a

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Brittle fracture

A

a material containing a crack will break at a stress σf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Ductile fracture

A

Failure by yielding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Sizes of cracks

A
  • Those having large cracks will fail by brittle fracture

- Those with small cracks (a < a*) will fail by ductile fracture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Cracks and strength of material

A

cracks only affect strength if they are larger than a* (see diagram on lecture slides 4)

smaller cracks are harmless

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Unit of fracture toughness

A

MPa√m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what a* means

A

Materials can have cracks up to this length without any loss of strength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Static properties of a material

A

Stiffness
Strength
Toughness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Long-Term Failure

A

Creep
Fatigue
Wear

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Creep

A

Plastic strain which takes time

  • Sometimes if you apply stress and hold it constant, strain will gradually increase over time
  • can happen for stresses above and below σy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

stages of creep test

A

primary, secondary, tertiart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Time to failure formula

A

t(subscript f) = C/σᵐ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what time to failure depends on

A

stress

temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Fatigue

A

A stress which was not sufficient to cause failure when applied once, can, if repeated enough times, eventually cause failure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Cyclic Loading

A
  • tests carried out with given stress range △σ and mean stress σₛₜᵣₑₛₛ
  • number of cycles to failure, N(subscript f) counted for each specimen tested
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Stress-Life curve

A

-straight line except at high cycles, where line may become horizontal at “fatigue limit”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Wear

A

-Happens when two surfaces rub together

  • you need a compressive force F and a shear movement d
  • material removed from one or both surfaces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Wear testing

A

-Volume of material lost △V found by measuring/weighing test piece

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Wear formula

A

△V = kFd

k = constant, tells you how easily material will wear away
d = shear movement
F = compressive force
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

four classes of materials

A

Metals
Polymers
Ceramics
Composites

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Alloys

A

made by combining elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Metals

A

strong and tough, but heavy and expensive

30
Q

Polymers

A
  • Light and cheap, can be strong

- fracture toughness poor but have high impact resistance

31
Q

Ceramics

A

Includes cement, glass, diamond, rocks, alumina and silicon carbide

32
Q

Glass

A
  • Stiff and strong

- Low toughness

33
Q

Composites

A

Made by combining materials from the other three classes

eg. fibre glass, carbon fibre, reinforced polymers

34
Q

Three levels of structure

A

Nanostructure
Microstructure
Macrostructure

35
Q

Nanostructure

A
  • Also called atomic structure as atoms and molecules are around this size
  • 1 nm = 10⁻⁹ m
36
Q

Microstructure

A

1 μm = 1 micron = 10⁻⁶ m

37
Q

Macrostructure

A

things greater than 1mm eg. aggregate particles and reinforcing bars in concrete

38
Q

Levels of structure and properties

A

-Different properties come from diff levels of structure

39
Q

Young’s Modulus and Atomic Structure

A

E, the elastic stiffness, comes from stiffness of atomic bonds of material

40
Q

Atomic Lattices

A

In most metals & ceramics, atoms arranged in regular, three-dimensional lattices

41
Q

3 types of lattices we studied

A

Body Centred Cubic (bcc)
Face Centred Cubic (fcc)
Hexagonal Close Packed (hcp)

42
Q

Unit cel

A

smallest group of atoms which can be repeated to make the whole lattice

43
Q

Simple Cubic

A
  • atoms at cube corners
  • 1 atom per unit cell (8 atoms x 1/8 volume/atom)
  • atomst ouch along sides of cube
  • cube side L = 2r
44
Q

Body Centred Cubic

A
  • atoms at centre and at corners
  • 2 atoms per cube
  • atoms touch along body diagonal
45
Q

Face Centred Cubic

A

-atoms at corners and c centres of each face

-

46
Q

Hexagonal Close Packed

A

-unit cell is hexagonal prism
-7 atoms on top face, 3 in middle, 7 on bottom face
-

47
Q

Stacking sequences

A

a, b, c stacking sequence

a b a b stacking sequence

48
Q

Amorphous structure

A

In some materials there’s no pattern: atoms packed together in random way eg. glass

49
Q

Types of atomic bonds

A
  • Strong bonds

- Weak Bonds

50
Q

Strong Bonds

A

Ionic bonds
Covalent bonds
Metallic bonds

51
Q

Weak Bonds

A

Hydrogen bonds

Van der Waals bonds

52
Q

Metallic bond

A

involves non-specific sharing of outer electrons, bond is non-directional

53
Q

ceramic materials bonds

A

-both ionic and covalent

54
Q

Ionic bonds

A
  • involve attraction of oppositely charged ions

- non-directional

55
Q

Covalent bonds

A
  • directional

- occur only at specific angles

56
Q

Polymer chain molecule bonds

A
  • covalent

- between chains are often weak bonds

57
Q

Distance between atom centres

A

Normally equal to 2r

58
Q

Potential energy

A

of the bond is energy needed to bring atoms to a separation a, starting at a = infinity

59
Q

Force vs Separation graph

A
  • Max force is strength of bond (not material)

- Slope near a₀ determins Young’s Modulus

60
Q

Total potential energy formula

A

W = A/aⁿ - B/aᵐ

F = dW/da

61
Q

a₀

A

when F=0

62
Q

Fₘₐₓ

A

breaking strength of bond

63
Q

Young’s modulus

A

proportional to slope of line dF/da at a = a₀

64
Q

Converting dF/Da to dσ/dε

A

Divide force by area over which it acts to get stress, divide da by bond length a₀ to get strain

65
Q

E at atomic level

A

fixed, as it is determined at atomic level

66
Q

changing stiffness, strength, toughness

A
  • stiffness: change to diff material

- strength & toughness: can be changed within given type of material

67
Q

Strength and diff materials

A
  • Metals and composites have good strength
  • Ceramics are strongest materials
  • Polymers weakest
68
Q

Plastic deformation and atoms

A
  • plastic deformation permanent
  • atoms must move to make new shape, but lattice pattern and bond separation will not change
  • Deformation by shear is easier
69
Q

what do we need to cause plastic strain?

A

shear stress

plastic strain always happens by shearing

70
Q

Greatest shear stress on a plane

A

at 45°

where yielding usually occurs

71
Q

Dislocations

A

-Error or mistake in atomic lattice, exists in form of line in meterial

  • Can move under applied stress if shear stress
  • When it moves, causes plastic strain
72
Q

Summary about yielding in metals

A
  • Plastic strain happens n shear
  • Shear strain much easier when you have dislocations
  • Yield strength actually stress needed to make dislocations move

Mat (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions