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Mat E 202 > Week 4 > Flashcards

Week 4 Flashcards

(82 cards)

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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
Define fracture toughness
Resistance to crack propagation
26
Define impact toughness
Abilities to deform without breaking under rapid loading
27
What type of toughness does this picture show
Impact toughness
28
What the of toughness does this picture show
Fracture toughness
29
What are the 3 types of toughnesses
Tensile Fracture Impact
30
Define cyclic loading
Loading at low stresses (below yield strength)
31
Can cyclic loading still cause failure
Yes
32
What type of testing does this show
Fatigue testing
33
Where are these on a stress vs. time graph
34
Do cracks grow in compression
Compression
35
What are the axis for an S-N curve
Y: stress amplitude X: cycles to failure, N
36
Describe the 3 mean stress lines (And greatest to least)
37
Do BCC metals have a fatigue limit
YES
38
Where is the fatigue limit for BCC’s on an S-N curve
Extend horizontal line to y axis
39
Do FCC’s have a fatigue limit (And why)
NO (No horizontal line to extrapolate)
40
What does the S-N graph for FCC’s look like
41
What fatigue fracture is this
Beach marks
42
What fatigue fracture is this
Striations
43
Fatigue failure are ALWAYS from what type of stress?
Cyclic stresses
44
What type of failure is this
Fatigue
45
Define crack initiation
A crack forms, or already exists in the material
46
Fatigue crack growth: define propagation
The crack advances a small amount each loading cycle
47
Define fast fracture
Part can no longer handle the applied load
48
Name the three parts of fatigue crack growth here
Crack initiation (top) Crack propagation (middle) Reputed to failure (squiggly lines)
49
List the 3 stages of fatigue crack growth in order
1) crack initiation 2) propagation 3) fast fracture
50
Fatigue fracture surfaces : define origin
Origin: at a stress concentration
51
Fatigue fracture: define beach marks (how wide are they usually)
A discrete period of crack growth (A few mm wide)
52
Striations: 1 Striation = _______ loading _____
One loading cycle
53
What equipment do you need to be able to see striations
An electron microscopy (Or else way to small)
54
Striations are NOT tree ______, they shouldn’t not be _______
Rings Counted
55
Say if they have a fatigue limit or not BCC metals FCC metals
BCC metals: has a fatigue limit FCC metals: no fatigue limit
56
What question does the “Paris Law” answer
How quickly will a crack grow
57
What question does the “critical stress intensity factor” answer?
How SENSITIVE is a material to sudden, uncontrollable crack growth
58
List the four ways to avoid fatigue
Lower the mean stress Surface treatments Reduce exposure to corrosive environments Reduce thermal gradients, especially for insulating materials
59
Avoiding fatigue: explain lowering the mean stress
60
Avoiding fatigue: explain surface treatments
Place the surface into compression (shot owen or carburize)
61
The stress at a crack tip APPROACHES ________
Infinite
62
Name the 3 things in this picture
63
Describe the local stress vs. r graph for this picture
64
Creep happens above…… (And simple formula for this)
65
Creep happens below ………
The yield strength of the material
66
Creep: failure is often at _____ ______
Low strains
67
List the 3 requirements for creep
Time, temp, stress
68
When does lead experience creep
Room temperature
69
Is creep testing the same as tension testing?
NO
70
Describe tension testing
71
Describe creep testing
72
List the 5 stages of creep
Elastic deformation Primary creep Secondary creep Tertiary creep Final failure
73
Stages of creep: describe elastic deformation
Bonds stretch
74
Stages of creep: describe primary creep
Slope decreases, work hardening happens
75
Stages of creep: describe secondary creep (What is constant) (And what is it also called)
Work hardening cancelled out by recovery (Constant strain rate) (Also called steady state creep)
76
Stages of creep: describe tertiary creep
Increases fast, sample fails
77
What variable represent strain RATE
78
Stages of creep: describe final failure
Voids are a vacuum, there is nothing in them
79
Creep: what type of final failure is this
Intergranular
80
Creep: what type of final failure is this
Transgranular
81
Define critical flaw
Max size of a flaw that can exist under loading before immediate failure occurs
82
Define work hardening
Increase in hardness of a metal

Mat E 202 (10 decks)

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