Chapter 16 Flashcards by Marisol Morse

What is a composite?

Multiphase material that is artificially made

A combination of two or more individual materials

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

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

Principle of combined action

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What are the two phase types of composites?

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

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What is the purpose of the matrix phase?

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

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What are three types of matrix/dispersed phase relationships?

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

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

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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What are the three types of the dispersed phase?

particle, fiber, and structural

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What are the four classifications of composites?

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

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What are the two classifications of particle-reinforced composites?

1) large-particle
2) dispersion-strengthened

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What are the two classifications of fiber-reinforced composites?

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

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

1) aligned
2) randomly oriented

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What are the two categories of structural composites?

1) laminates
2) sandwich panels

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What are three examples of particle-reinforced composites?

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

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What are the matrix/particle components in spheroidite steel?

matrix: alpha ferrite
particles: cementite Fe3C

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

matrix: cobalt
particles: WC

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

matrix: rubber
particles: carbon black

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What is concrete’s classification?

particle-reinforced composite

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What is concrete made from?

gravel+sand+cement+water

sand fills voids between gravel particles

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What is reinforced concrete? Why do we do it?

concrete reinforced with steel rebar or remesh

it increases strength- even if cement matrix is cracked

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How is prestated concrete formed?

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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How do you fracture concrete?

applied tensile stress must exceed compressive stress

What is posttensioning?

tightening nuts to place concrete under compression

What are the properties of the Elastic modulus of composites?

Elastic modulus: Ec

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

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

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

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

Describe fiber-reinforced composites

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

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

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

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

Whiskers, fibers, and wires

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

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

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

1) polycrystalline and amorphous 2) generally polymers or ceramics

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

1) steel 2) molybdenum 3) tungsten

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

Continuous 1) aligned continuous - transverse direction - longitudinal direction Discontinuous 1) aligned 2) random

What are two examples of aligned continuous fibers?

Metal: γ’(Ni3Al)-α(Mo) by eutectic solidification Ceramic: Glass with SiC fibers formed by glass slurry

In how many dimensions are discontinuous fibers discontinuous?

2 dimensions

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

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

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

Critical fiber length for effective stiffening and strengthening σf- fiber ultimate tensile strength d- fiber diameter Tc- shear strength of fiber-matrix interface

What is the common fiber length for fiberglass?

> 15 mm

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

longer fibers- "high fiber efficiency"

What is composite stiffness called?

Longitudinal loading

What are the two composite production methods?

1) Pultrusion 2) Filament Winding

What is pultrusion?

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

What are the steps of pultrusion?

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

What is filament winding?

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

What are the steps of filament winding?

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

What are the two structural composite classifications?

1) Laminates 2) Sandwich panels

What are laminates? What are their benefits?

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

What are sandwich panels?

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

What is the benefit of CMCs?

Increased toughness

What is the benefit of PMC's?

Increased elongation per density

What is the benefit of MMCs?

Increased creep resistance