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MAT SCI > TEST 3 > Flashcards

TEST 3 Flashcards

1
Q

What is normal Stress and its formula

A

F/A
Force per unit area where force is perpendicular to the cross section of the item

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2
Q

What is shear stress and its formula

A

F/A
Force per unit area where force is parallel to the cross section

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3
Q

What are the types of normal stress

A

Tensile and Compression

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4
Q

What is engineering strain

A

delta (L)/L

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5
Q

What is poisson’s ratio

A

coaxial strain/ perpendicular strain
v= -ℨx/ℨz = -ℨy/ℨz

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6
Q

Poisson’s ratio for metals

A

~.33

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7
Q

Poisson’s ratio for ceramics

A

~.25

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8
Q

Poisson’s ratio for polymers

A

~.40

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9
Q

What is Young’s Modulus E

A

sigma= Eℨ

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10
Q

What is shear modulus? G

A

tau= Gy

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11
Q

What is ultimate tensile stress

A

The maximum stress in a stress vs strain graph

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12
Q

What is the difference between elastic and plastic deformation

A

Plastic deformation can not be reversed

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13
Q

What separates elastic and plastic deformation

A

yield stress

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14
Q

How to calculate Young’s modulus E from stress vs strain graph

A

Slope in linear elastic regime

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15
Q

How to calculate resilience from stress vs strain graph

A

area under elastic area

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16
Q

How to calculate yield stress

A

.2% offset of elastic region

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17
Q

What is tensile stress

A

maximum stress

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18
Q

What is max strain

A

strain right before failure

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19
Q

what is toughness

A

area underneath the s-s curve

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20
Q

area reduction formula

A

delta area/ initial area

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21
Q

Formula for true stress

A

sigmaT= sigma(1+ strain)

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22
Q

True strain

A

strain (t)= ln(1+ strain)

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23
Q

Is dislocation easier in metals or ceramics/glass

A

Metals

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24
Q

What will an s-s curve look like for brittle materials

A

curve is mostly linear before failure

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25
Q

What will an s-s curve look like for elastomers

A

Elastomers will have much greater max strain

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26
Q

Why do some materials deform plastically?

A

Materials deform plastically because the internal energy is lower than elastic deformation

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27
Q

Dislocation with burgers vector in close packed plane will give what kind of surface and what sized vector

A

smooth surface
small burgers vector

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28
Q

Dislocation motion occurs along __ and in ____

A

Close packed planes, close packed directions
WHERE THE ATOMS TOUCH EACH OTHER

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29
Q

Slip plane, direction, system number for FCC

A

Plane (111)
Direction <1(-1)0>
4*3=12

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30
Q

Slip plane, direction, system number for BCC

A

{110}
<-111>
6*2=12

31
Q

What is the slip system

A

Slip plane+ slip direction

32
Q

What is the schmid factor

A

cos θ cos λ
θ: angle to slip plane normal from axis
λ: angle to slip direction from axis

33
Q

Formula for resolved shear stress

A

σR= σcosθcosλ
σR= σ*schmid factor

34
Q

How would you find θ and λ given the vector directions of Slip plane normal, slip direction, and force

A

Dot product the two vectors to find the angle

35
Q

What is resolved shear stress

A

tau=σ*schmid factor

36
Q

When will slip occur

A

When criticial resolved shear stress is reached
σ*schmid factor >_ tau criticial

37
Q

Compare toughness before fracture for brittle and ductile materials

A

Ductile materials exhibit large toughness before fracture
Brittle materials exhibit low toughness before fracture

38
Q

Compare fracture profiles of
soft metals
ductile typical metals
brittle materials

A

soft metals will have a small large change in area with the cross section being basically 0

typical ductile materials will have a some change in area of cross section

brittle materials will have ~0 change in area of cross section

39
Q

What are the 5 stages of ductile fracture

A
  1. Necking
  2. Cavity Formation
  3. Cavity Coalescence
  4. Crack propagation
  5. Fracture
40
Q

What is a transgranular fracture

A

When fracture occurs within grain of crystal; along crystal planes

41
Q

What is intergranular fracture

A

when fracture occurs on grain boundaryu

42
Q

Formula for max stress

A

σm= 2σ* sqrt(a/pt)
σm: max stress
σ: applied stress
a: half length of crack
pt: radius of curvature of crack

43
Q

What is K= Yσ sqrt( pi * a)

A

K is stress intensity factor
σ:
Y: geometry factor ; ~1
σ: normal stress external

44
Q

What is K(IC) = sqrt( 2 * E* y)

A

Fracture Toughness for brittle materials
E: Young’s modulus
y: specific surface energy

45
Q

What is failure criterion

A

K >_ K(IC)

46
Q

What can the griffith criterion predict

A

expected fracture stress

47
Q

What formula is this: σc= sqrt[(2Ey/(pi*a)]

A

Griffith criterion formula

48
Q

Why are ceramics stronger in compression

A

Ceramics are so weak in tension because tensile fractures are a result of fracture propagation and fractures result from defects. there are a lot of defects in ceramics

49
Q

What will increase with cold work?

A

dislocation density

50
Q

What does this formula mean
%CW= [(Ao-Ad)/Ao]*100

A

%CW and how it realtes to % change in cross sectional area

51
Q

What are four ways to strengthen metal

A

Grain size
solid solution
cold work
precipatates

52
Q

How does change in grain size affect strength

A

Grain boundaries resist dislocation motion

53
Q

What formula is this and what trend does it tell us

A

σy= σ1 + ky /sqrt(d)
where
σy: yield stress
d: average grain diameter
σ1: CONSTANT
ky: constant

grain size decreases –> yield stress increases

54
Q

What are the two types of solid solution strengthening?

A

Interstitial impurity
substitutional impurtiy

55
Q

How does solid solution strengthening work?

A

Creates stress field that restricts dislocation movement

56
Q

What trend is seen in increasing percentage of impurity?

A

strength increases
ductility decreases

57
Q

How does cold work affect dislocations

A

After cold work, rolling affects grain orientation and shape
Dislocations become more entangled with one another -> dislocation movement becomes more difficult

58
Q

How does precipitation strengthening work

A

A precipitate of an impurity forms on metal which restricts movement of dislocations

59
Q

What is aging

A

Holding a rapidly quenched solid solution at a given temperature for some time

60
Q

What are the three stages of heating after cold work

A

recovery
recrystallization
grain growth

61
Q

What does recovery do to a metal

A

allows metals to decrease their internal energy by rearranging or decreasing dislocations

62
Q

What equation is this:
d^n - do^n =Kt

A

do: initial grain diameter
n,K: constants
t: time
d: new grain diameter

63
Q

Basic trend for metals and impurities

A

ANYTHING added to a metal that restricts motion of dislocations will increase yield stress and decrease ductility

64
Q

Two major glass strengthening methods?

A

Tempering: Rapid cooling from softening temps.
Ion exchange: smaller alkali ions are replaced by larger ions, restricting motion of dislocations

65
Q

What does a phase diagram show

A

shows all equilibrium states under a range of given conditions

66
Q

What are metastable structures

A

A system that may not be at equilibrium but the rate of approach to equilibrium is so slow that the system can exist for a finite or indefinite time.

67
Q

What equation is F=C +2-P

A

Gibbs Phase Rule
P: Number of phases
C: Number of components at point
F: # of variables that can be changed independently without changing the number of phases present

68
Q

What is solubility limit

A

maximum concentration of solute thatmay dissolve in solvent as solid solution

69
Q

What is a binary isomorphous system

A

two components are totally soluble in one another at all proportions

70
Q

How to determine phase composition from a T vs composition graph?

A

draw a horizontal line and the corresponding values give the concentration of each phase

71
Q

What is homogenous nucleation

A

nuclei form in the bulk of the liquid metal

72
Q

what is heterogenous nucleation

A

impurity of daughter phase already exists so easier to form; does not require supercooling or undercooling

73
Q
A

MAT SCI (5 decks)

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