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Elements > Chapter 16 > Flashcards

Chapter 16 Flashcards

1
Q

What is a composite?

A

Multiphase material that is artificially made

A combination of two or more individual materials

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2
Q

What is the primary design goal of composites (ex)? What is this principle called?

A

Obtaining a more desirable combination of properties. For instance, low density and high strength

Principle of combined action

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3
Q

What are the two phase types of composites?

A

Matrix- is continuous
Dispersed- is discontinuous and surrounded by matrix

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4
Q

What is the purpose of the matrix phase?

A

1) transfer stress to the dispersed phase
2) protect the dispersed phase from the environment

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5
Q

What are three types of matrix/dispersed phase relationships?

A

MMC (metal)
CMC (ceramic)
PMC (polymer)

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6
Q

What is the purpose of MMC, CMC, or PMC dispersed phase?

A

MMC: increase σy (yield strength), TS, and creep resistance
CMC: increase K sub IC (fracture toughness)
PMC: increase E (mod. of elasticity), TS, σy (yield strength), and creep resistance

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7
Q

What are the three types of the dispersed phase?

A

particle, fiber, and structural

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8
Q

What are the four classifications of composites?

A

1) particle-reinforced
2) fiber-reinforced
3) structural
4) nanoparticles

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9
Q

What are the two classifications of particle-reinforced composites?

A

1) large-particle
2) dispersion-strengthened

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10
Q

What are the two classifications of fiber-reinforced composites?

A

1) continuous (aligned)
2) discontinuous (short)

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11
Q

What are the 2 categories of discontinuous (short) fiber-reinforced composites?

A

1) aligned
2) randomly oriented

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12
Q

What are the two categories of structural composites?

A

1) laminates
2) sandwich panels

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13
Q

What are three examples of particle-reinforced composites?

A

1) spheroidite steel
2) WC/ Co cemented carbide
3) automobile tire rubber

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14
Q

What are the matrix/particle components in spheroidite steel?

A

matrix: alpha ferrite
particles: cementite Fe3C

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15
Q

What are the matrix/particle components in WC/Co cemented carbide?

A

matrix: cobalt
particles: WC

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16
Q

What are the matrix/particle components in automobile tire rubber?

A

matrix: rubber
particles: carbon black

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17
Q

What is concrete’s classification?

A

particle-reinforced composite

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18
Q

What is concrete made from?

A

gravel+sand+cement+water

sand fills voids between gravel particles

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19
Q

What is reinforced concrete? Why do we do it?

A

concrete reinforced with steel rebar or remesh

it increases strength- even if cement matrix is cracked

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20
Q

How is prestated concrete formed?

A

1) rebar/remesh placed under tension during setting of concrete
2) tension is released by setting places concrete in a state of compression

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21
Q

How do you fracture concrete?

A

applied tensile stress must exceed compressive stress

22
Q

What is posttensioning?

A

tightening nuts to place concrete under compression

23
Q

What are the properties of the Elastic modulus of composites?

A

Elastic modulus: Ec

two “rule of mixture” extremes:
upper limit: Ec= VmEm + VpEp
lower limit: 1/Ec = Vm/Em + Vp/Ep

24
Q

What is a composite’s Elastic modulus, Ec, also applied to?

A

Electrical conductivity, σe: replace E’s in equations with σe’s

Thermal conductivity, k: replace E’s in equations with k’s

25
Q

Describe fiber-reinforced composites

A

Fibers very strong in tension that provide significant strength improvement to the composite

26
Q

What is an example of a fiber-reinforced composite? What are its components?

A

Fiber-glass: continuous glass filaments in a polymer matrix

Glass fibers: strength and stiffness
Polymer matrix: holds fibers in place, protects fiber surfaces, transfers load to fibers

27
Q

What are the three fiber types of fiber-reinforced composites?

A

Whiskers, fibers, and wires

28
Q

What is the whiskers fiber type of fiber-reinforced composites? What are three things to note?

A

thin single crystals- large length to diameter ratios

1) graphite, silicon nitride SiN, silicon carbide SiC
2) high crystal perfection- extremely strong, strongest known
3) very expensive and difficult to disperse

29
Q

What are two properties of fibers (fiber type of fiber-reinforced composites)?

A

1) polycrystalline and amorphous
2) generally polymers or ceramics

30
Q

What are three examples of a wire fiber type of fiber-reinforced composites?

A

1) steel
2) molybdenum
3) tungsten

31
Q

What are the two categories of fiber alignment? Subcategories of those?

A

Continuous
1) aligned continuous
- transverse direction
- longitudinal direction

Discontinuous
1) aligned
2) random

32
Q

What are two examples of aligned continuous fibers?

A

Metal: γ’(Ni3Al)-α(Mo) by eutectic solidification

Ceramic: Glass with SiC fibers formed by glass slurry

33
Q

In how many dimensions are discontinuous fibers discontinuous?

A

2 dimensions

34
Q

What is an example of a discontinuous fiber? It’s fabrication process? Uses?

A

Carbon-carbon

Fabrication: carbon fibers embedded in polymer resin matrix, resin up to 2500 C

Uses: disk brakes, gas turbine exhaust flaps, missile nose cones

35
Q

What is a property that is calculated for fiber-reinforced composites?

A

Critical fiber length for effective stiffening and strengthening

σf- fiber ultimate tensile strength
d- fiber diameter
Tc- shear strength of fiber-matrix interface

36
Q

What is the common fiber length for fiberglass?

A

> 15 mm

37
Q

Is stress transference more efficient from a matrix with longer or shorter fibers?

A

longer fibers- “high fiber efficiency”

38
Q

What is composite stiffness called?

A

Longitudinal loading

39
Q

What are the two composite production methods?

A

1) Pultrusion
2) Filament Winding

40
Q

What is pultrusion?

A

A composite production method where continuous fibers are pulled through a resin tank to impregnate fibers with thermosetting resin

41
Q

What are the steps of pultrusion?

A

1) Fibers pulled through a resin impregnation tank with thermosetting resin
2) Impregnated fibers pass through steel die that preforms the desired shape
3) The preformed stock passes through a curing die that is
a) precision machined to impact final shape
b) heated to initiate curing of the resin matrix

42
Q

What is filament winding?

A

A composite production method where fibers are positioned in a predetermined pattern to form a hollow (usually cylindrical) shape

43
Q

What are the steps of filament winding?

A

1) Fibers are fed through a resin bath to impregnate the thermosetting resin
2) Impregnated fibers are wound (automatically) onto a mandrel
3) After sufficient layers are added, it’s cured in an oven or at room temperature
4) Mandrel is removed to give the final product

44
Q

What are the two structural composite classifications?

A

1) Laminates
2) Sandwich panels

45
Q

What are laminates? What are their benefits?

A

Structural classification of composites

1) stacked and bonded fiber-reinforced sheets
2) stacking sequence: eg 0º/90º
3) Benefit: balanced in-plane stiffness

46
Q

What are sandwich panels?

A

Structural classification of composites

1) Honeycomb core between two facing sheets
2) Benefits: low density and large bending stiffness

47
Q

What is the benefit of CMCs?

A

Increased toughness

48
Q

What is the benefit of PMC’s?

A

Increased elongation per density

49
Q

What is the benefit of MMCs?

A

Increased creep resistance

50
Q
A

Elements (15 decks)

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