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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
Significance of bulk factor
Large bulk factors lead to wrinkling
26
Factors that contribute to bulk factor
Vacuum compaction, curing shrinkage, resin infiltration into fibers
27
Autoclave vs. OOA, cost
Autoclave is higher
28
Autoclave vs. OOA, time
Autoclave is shorter
29
Autoclave vs. OOA, atmospheric pressure
Autoclave 3-8 atm (higher pressure); OOA ambient
30
Autoclave vs. OOA, atmospheric composition
Autoclave N2, OOA air
31
Autoclave vs. OOA, bulk factor
Autoclave can have higher bulk factor
32
Autoclave vs. OOA, void content
Autoclave lower
33
Autoclave vs. OOA, void reduction mechanisms
Autoclave governed by pressure resulting in air evacuation and resin infiltration; OOA depends on availability of evacuation channels and resin flow.
34
Autoclave vs. OOA vacuum bag considerations
OOA vacuum bag requires an edge dam
35
Autoclave vs. OOA, DOI
Autoclave uses DOI ~ 100%; OOA uses lower DOI
36
Autoclave vs. OOA, strength of resin
Autoclave stronger
37
Autoclave vs. OOA, viscosity
Autoclave higher viscosity
38
Autoclave vs. OOA, fiber-matrix ratio
Autoclave higher fiber-matrix ratio
39
Autoclave vs. OOA, end use
Autoclave for primary structural parts; OOA for secondary
40
Autoclave vs. OOA, temperature
Autoclave 177 C; OOA 93/121 C.
41
Resin transfer molding, binder
Binder additive is used to stabilize fibers and maintain a better shape.
42
Resin transfer molding steps
Binder-stabilized fabric, lay up, preforming, resin injection, curing
43
Gelation
Beginning of polymer cross-linking and formation of viscoelastic solid
44
Gelation wrt rate of cure
Does not affect rate of cure.
45
Relevance of gelation for work life
Gelation point is upper limit of work life (i.e. no more working should be performed on polymer)
46
Vitrification
Glass transition temperature is increased to cure temperature, causing formation of glassy elastic solid
47
Vitrification wrt rate of cure
Vitrification does result in a rapid decrease in the rate of cure
48
Effect of temperature of cure on glass transition temperature
Increased overall temperature of cure raises glass transition temperature
49
Viscous response to stress wrt time
Linear strain response
50
Elastic response to stress wrt time
Near instant strain response; returns to initial state after strain removal
51
Viscoelastic response to stress wrt time
Time-dependent strain
52
1-2 vs. x-y
1 is fiber, 2 is transverse, x and y are loading directions
53
theta in 1-2 vs. x-y drawings
Angle between x and 1.
54
Orthotropic
Orthogonal planes of property symmetry
55
Example of isotropic material
Glass, plastic (amorphous)
56
Example of anisotropic material
Diamond, crystals
57
Example of orthotropic material
CF lamina
58
Isotropic response to tensile normal stress
Elongation in direction of tensile stress, contraction in other direction
59
Anisotropic response to tensile normal stress
Extensional-shear coupling; both extensional and shear deformation
60
Orthotropic response to tensile normal stress
If in principal direction, behaves as isotropic material. Else behaves as anisotropic material.
61
[0/45/90]
0 followed by 45 followed by 90
62
Subscript S in layup code
Symmetrical about a midplane
63
+- sign in layup code
Fabric repeated twice, positive then negative
64
[0/(+-45)_2]
[0/45/-45/45/-45]
65
[0/90/0bar]_s
Odd layup with 0 at center: [0/90/0/90/0]

Fiber Reinforced Composites (2 decks)

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