Chapter 16 Flashcards
What is a composite?
Multiphase material that is artificially made
A combination of two or more individual materials
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
What are the two phase types of composites?
Matrix- is continuous
Dispersed- is discontinuous and surrounded by matrix
What is the purpose of the matrix phase?
1) transfer stress to the dispersed phase
2) protect the dispersed phase from the environment
What are three types of matrix/dispersed phase relationships?
MMC (metal)
CMC (ceramic)
PMC (polymer)
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
What are the three types of the dispersed phase?
particle, fiber, and structural
What are the four classifications of composites?
1) particle-reinforced
2) fiber-reinforced
3) structural
4) nanoparticles
What are the two classifications of particle-reinforced composites?
1) large-particle
2) dispersion-strengthened
What are the two classifications of fiber-reinforced composites?
1) continuous (aligned)
2) discontinuous (short)
What are the 2 categories of discontinuous (short) fiber-reinforced composites?
1) aligned
2) randomly oriented
What are the two categories of structural composites?
1) laminates
2) sandwich panels
What are three examples of particle-reinforced composites?
1) spheroidite steel
2) WC/ Co cemented carbide
3) automobile tire rubber
What are the matrix/particle components in spheroidite steel?
matrix: alpha ferrite
particles: cementite Fe3C
What are the matrix/particle components in WC/Co cemented carbide?
matrix: cobalt
particles: WC
What are the matrix/particle components in automobile tire rubber?
matrix: rubber
particles: carbon black
What is concrete’s classification?
particle-reinforced composite
What is concrete made from?
gravel+sand+cement+water
sand fills voids between gravel particles
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
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
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
