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Mat E 202 > Week 4 > Flashcards

Week 4 Flashcards

1
Q

What happens at a flaw: stress is concentrated at _____ _____

A

Crack tips

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2
Q

What are these arrows points to

A

Region of high local stress

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3
Q

Uniform applied stress= number of ______ per unit _____

A

Lines

Width

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4
Q

What variable equation answers the question of “how much is the stress multiplied at a crack tip”

(Variable)

A

Kt

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5
Q

Stress concentration:

A

Sharp crack

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6
Q

Formula for sharp crack

(Small Row sub t)

A
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7
Q

What’s the difference in critical flaw size in ceramics vs. metals

A

Ceramics: microns to tens of microns

Metals: millimetres to cm

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8
Q

Why do metals perform better in tension than ceramics?

A

Metals have a smaller critical flaw size (mm to cm)

(While ceramics are microns to tens of microns)

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9
Q

What are the 3 loading modes for cracks

(and their corresponding numbers)

A

Opening (I)

Shearing (II)

Tearing (III)

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10
Q

Cracks: what loading mode is this?

A

Opening

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11
Q

Cracks: what loading mode is this

A

Shearing

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12
Q

Cracks: what loading mode is this?

A

Tearing

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13
Q

What variable answers the question of

“plane strain fracture toughness”

A

Kc

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14
Q

Critical stress intensity factor: what does picture mean

A

K in mode 1 fracture

(Where K= critical stress intensity factor)

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15
Q

When does a crack fail instantaneously

A
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16
Q

Plane strain fracture toughness: refers to ________ samples

A

Thick

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17
Q

What does DBBT stand for

A

Ductile to brittle transition temperature

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18
Q

BCC: metals get ______ at low temps

A

Brittle

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19
Q

What graph relates to temp dependence

(Axis titles)

A

Y: impact energy

X: temperature

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20
Q

Temperature dependence graph: describes the 3 lines and what they represent

A
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21
Q

BBC: low strength _____

A

Steels

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22
Q

FCP and HCP: low strength ______

A

Metals

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23
Q

More carbon = stronger _____

A

Steel

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24
Q

Describe the composition dependence graph for carbon steels

(Described general trend)

(And what do the decimals mean)

A

More carbon = stronger steel

Decimal= carbon content in weight percent (wt%)

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25
Q

Define fracture toughness

A

Resistance to crack propagation

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26
Q

Define impact toughness

A

Abilities to deform without breaking under rapid loading

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27
Q

What type of toughness does this picture show

A

Impact toughness

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28
Q

What the of toughness does this picture show

A

Fracture toughness

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29
Q

What are the 3 types of toughnesses

A

Tensile

Fracture

Impact

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30
Q

Define cyclic loading

A

Loading at low stresses (below yield strength)

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31
Q

Can cyclic loading still cause failure

A

Yes

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32
Q

What type of testing does this show

A

Fatigue testing

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33
Q

Where are these on a stress vs. time graph

A
34
Q

Do cracks grow in compression

A

Compression

35
Q

What are the axis for an S-N curve

A

Y: stress amplitude
X: cycles to failure, N

36
Q

Describe the 3 mean stress lines

(And greatest to least)

A
37
Q

Do BCC metals have a fatigue limit

A

YES

38
Q

Where is the fatigue limit for BCC’s on an S-N curve

A

Extend horizontal line to y axis

39
Q

Do FCC’s have a fatigue limit

(And why)

A

NO

(No horizontal line to extrapolate)

40
Q

What does the S-N graph for FCC’s look like

A
41
Q

What fatigue fracture is this

A

Beach marks

42
Q

What fatigue fracture is this

A

Striations

43
Q

Fatigue failure are ALWAYS from what type of stress?

A

Cyclic stresses

44
Q

What type of failure is this

A

Fatigue

45
Q

Define crack initiation

A

A crack forms, or already exists in the material

46
Q

Fatigue crack growth: define propagation

A

The crack advances a small amount each loading cycle

47
Q

Define fast fracture

A

Part can no longer handle the applied load

48
Q

Name the three parts of fatigue crack growth here

A

Crack initiation (top)

Crack propagation (middle)

Reputed to failure (squiggly lines)

49
Q

List the 3 stages of fatigue crack growth in order

A

1) crack initiation

2) propagation

3) fast fracture

50
Q

Fatigue fracture surfaces : define origin

A

Origin: at a stress concentration

51
Q

Fatigue fracture: define beach marks (how wide are they usually)

A

A discrete period of crack growth

(A few mm wide)

52
Q

Striations: 1 Striation = _______ loading _____

A

One loading cycle

53
Q

What equipment do you need to be able to see striations

A

An electron microscopy

(Or else way to small)

54
Q

Striations are NOT tree ______, they shouldn’t not be _______

A

Rings

Counted

55
Q

Say if they have a fatigue limit or not

BCC metals
FCC metals

A

BCC metals: has a fatigue limit
FCC metals: no fatigue limit

56
Q

What question does the “Paris Law” answer

A

How quickly will a crack grow

57
Q

What question does the “critical stress intensity factor” answer?

A

How SENSITIVE is a material to sudden, uncontrollable crack growth

58
Q

List the four ways to avoid fatigue

A

Lower the mean stress

Surface treatments

Reduce exposure to corrosive environments

Reduce thermal gradients, especially for insulating materials

59
Q

Avoiding fatigue: explain lowering the mean stress

A
60
Q

Avoiding fatigue: explain surface treatments

A

Place the surface into compression (shot owen or carburize)

61
Q

The stress at a crack tip APPROACHES ________

A

Infinite

62
Q

Name the 3 things in this picture

A
63
Q

Describe the local stress vs. r graph for this picture

A
64
Q

Creep happens above……

(And simple formula for this)

A
65
Q

Creep happens below ………

A

The yield strength of the material

66
Q

Creep: failure is often at _____ ______

A

Low strains

67
Q

List the 3 requirements for creep

A

Time, temp, stress

68
Q

When does lead experience creep

A

Room temperature

69
Q

Is creep testing the same as tension testing?

A

NO

70
Q

Describe tension testing

A
71
Q

Describe creep testing

A
72
Q

List the 5 stages of creep

A

Elastic deformation

Primary creep

Secondary creep

Tertiary creep

Final failure

73
Q

Stages of creep: describe elastic deformation

A

Bonds stretch

74
Q

Stages of creep: describe primary creep

A

Slope decreases, work hardening happens

75
Q

Stages of creep: describe secondary creep

(What is constant)

(And what is it also called)

A

Work hardening cancelled out by recovery

(Constant strain rate)

(Also called steady state creep)

76
Q

Stages of creep: describe tertiary creep

A

Increases fast, sample fails

77
Q

What variable represent strain RATE

A
78
Q

Stages of creep: describe final failure

A

Voids are a vacuum, there is nothing in them

79
Q

Creep: what type of final failure is this

A

Intergranular

80
Q

Creep: what type of final failure is this

A

Transgranular

81
Q

Define critical flaw

A

Max size of a flaw that can exist under loading before immediate failure occurs

82
Q

Define work hardening

A

Increase in hardness of a metal

Mat E 202 (10 decks)

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