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Fiber Reinforced Composites > Midterm 1 > Flashcards

Midterm 1 Flashcards

1
Q

Precursor of carbon fiber

A

PAN (polyacrylonitrile)

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2
Q

Carbon fiber manufacture steps

A

Precursor, oxidize, carbonize, graphitize, hot stretch, etch

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3
Q

Oxidization of carbon fiber temperature

A

200-300 C

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4
Q

Carbonization of carbon fiber temp

A

1000-2000 C

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5
Q

Carbonization of carbon fiber

A

Removal of oxygen and nitrogen from polyacrylonitrile precursor to form aromatic carbon

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6
Q

Graphitization of carbon fiber temp

A

> 2000C

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7
Q

Graphitization of carbon fiber

A

Converts aromatic carbon structure into graphitic structure with high modulus and low strength

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8
Q

Role of CF hot stretching

A

Increased strength by aligning graphitic planes

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9
Q

Role of CF etching

A

Preparation for bonding to resin in composites

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10
Q

Four modulus categories

A

Ultra-high modulus, high modulus, intermediate modulus, high tensile

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11
Q

UHM

A

> 450 GPa

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12
Q

HM

A

350-450 GPa

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13
Q

IM

A

200-350 GPa

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14
Q

HT

A

<100 GPa, ST > 3.0 GPa

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15
Q

Weave - UD

A

Unidirectional (no weave; plastic stitching).

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16
Q

Use of UD weave

A

Where principal loading predictable

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17
Q

Weave - plain

A

Checkerboard weave.

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18
Q

Weave - twill

A

Skipping weave.

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19
Q

Example: 2x2 twill weave

A

Each fiber passes over 2 fibers and under 2 fibers

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20
Q

Weave - harness satin

A

Each fiber passes over n and under 1

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21
Q

Example: 4HS weave

A

Each fiber passes over 4 and under 1 fiber

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22
Q

Tow

A

Larger strip of carbon fiber consisting of many individual filaments

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23
Q

Tow notation

A

nk, denoting n thousands of fibers per tow

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24
Q

Significance of tow counts

A

Low tow counts are difficult to manufacture and more expensive

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25
Q

Significance of bulk factor

A

Large bulk factors lead to wrinkling

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26
Q

Factors that contribute to bulk factor

A

Vacuum compaction, curing shrinkage, resin infiltration into fibers

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27
Q

Autoclave vs. OOA, cost

A

Autoclave is higher

28
Q

Autoclave vs. OOA, time

A

Autoclave is shorter

29
Q

Autoclave vs. OOA, atmospheric pressure

A

Autoclave 3-8 atm (higher pressure); OOA ambient

30
Q

Autoclave vs. OOA, atmospheric composition

A

Autoclave N2, OOA air

31
Q

Autoclave vs. OOA, bulk factor

A

Autoclave can have higher bulk factor

32
Q

Autoclave vs. OOA, void content

A

Autoclave lower

33
Q

Autoclave vs. OOA, void reduction mechanisms

A

Autoclave governed by pressure resulting in air evacuation and resin infiltration; OOA depends on availability of evacuation channels and resin flow.

34
Q

Autoclave vs. OOA vacuum bag considerations

A

OOA vacuum bag requires an edge dam

35
Q

Autoclave vs. OOA, DOI

A

Autoclave uses DOI ~ 100%; OOA uses lower DOI

36
Q

Autoclave vs. OOA, strength of resin

A

Autoclave stronger

37
Q

Autoclave vs. OOA, viscosity

A

Autoclave higher viscosity

38
Q

Autoclave vs. OOA, fiber-matrix ratio

A

Autoclave higher fiber-matrix ratio

39
Q

Autoclave vs. OOA, end use

A

Autoclave for primary structural parts; OOA for secondary

40
Q

Autoclave vs. OOA, temperature

A

Autoclave 177 C; OOA 93/121 C.

41
Q

Resin transfer molding, binder

A

Binder additive is used to stabilize fibers and maintain a better shape.

42
Q

Resin transfer molding steps

A

Binder-stabilized fabric, lay up, preforming, resin injection, curing

43
Q

Gelation

A

Beginning of polymer cross-linking and formation of viscoelastic solid

44
Q

Gelation wrt rate of cure

A

Does not affect rate of cure.

45
Q

Relevance of gelation for work life

A

Gelation point is upper limit of work life (i.e. no more working should be performed on polymer)

46
Q

Vitrification

A

Glass transition temperature is increased to cure temperature, causing formation of glassy elastic solid

47
Q

Vitrification wrt rate of cure

A

Vitrification does result in a rapid decrease in the rate of cure

48
Q

Effect of temperature of cure on glass transition temperature

A

Increased overall temperature of cure raises glass transition temperature

49
Q

Viscous response to stress wrt time

A

Linear strain response

50
Q

Elastic response to stress wrt time

A

Near instant strain response; returns to initial state after strain removal

51
Q

Viscoelastic response to stress wrt time

A

Time-dependent strain

52
Q

1-2 vs. x-y

A

1 is fiber, 2 is transverse, x and y are loading directions

53
Q

theta in 1-2 vs. x-y drawings

A

Angle between x and 1.

54
Q

Orthotropic

A

Orthogonal planes of property symmetry

55
Q

Example of isotropic material

A

Glass, plastic (amorphous)

56
Q

Example of anisotropic material

A

Diamond, crystals

57
Q

Example of orthotropic material

A

CF lamina

58
Q

Isotropic response to tensile normal stress

A

Elongation in direction of tensile stress, contraction in other direction

59
Q

Anisotropic response to tensile normal stress

A

Extensional-shear coupling; both extensional and shear deformation

60
Q

Orthotropic response to tensile normal stress

A

If in principal direction, behaves as isotropic material. Else behaves as anisotropic material.

61
Q

[0/45/90]

A

0 followed by 45 followed by 90

62
Q

Subscript S in layup code

A

Symmetrical about a midplane

63
Q

+- sign in layup code

A

Fabric repeated twice, positive then negative

64
Q

[0/(+-45)_2]

A

[0/45/-45/45/-45]

65
Q

[0/90/0bar]_s

A

Odd layup with 0 at center: [0/90/0/90/0]

Fiber Reinforced Composites (2 decks)

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