Composites

1
Composites

• Chapter 15

Composite technology with T-800 Carbon Fiber
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Overview

• Composites types are designated by
• the matrix material (Ceramic Matrix Composite,
  Metal MC, Polymer MC)
• the reinforcement (particles, fibers,
  structural)
• Composite property benefits
• MMC improved E, sy, creep performance, Tensile
  Strength
• CMC improved KIc
• PMC improved E, sy, TS, creep resistance
• Particulate-reinforced
• Types large-particle and dispersion-strengthened
  
• Properties are isotropic
• Fiber-reinforced
• Types continuous (aligned) and discontinuous
  (aligned or random)
• Properties can be isotropic or anisotropic
• Structural
• Laminates and sandwich panels

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Classification of Composites
Composite materials, a mix of fibers and resins
designed to provide great strength yet remain
very light weight, have been synonymous with all
aerospace applications from airplanes to NASA
spacecraft and have advanced into lightweight,
strong materials for helmets, tennis rackets and
other sporting goods.
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Composite

• A composite material is basically a combination
  of two or more materials that are mechanically
  bonded together.
• The resulting material has characteristics that
  are different than the components in isolation.
• The concept of composite materials is ancient. An
  example is adding straw to mud for building
  stronger mud walls. Most commonly, composite
  materials have a bulk phase or matrix and a
  dispersed, non-continuous, phase called the
  reinforcement.
• Some other examples of basic composites include
  concrete (cement mixed with sand and aggregate),
  reinforced concrete (steel rebar in concrete),
  and fiberglass (glass strands in a resin matrix).

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Older Technology
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Aerospace
The Lockheed F-22 uses composites for at least a
third of its structure.
Grumman X-29

• Making composite structures is more complex than
  manufacturing most metal structures.
• To make a composite structure, the composite
  material is put in a mold under heat and
  pressure. The resin matrix material flows and
  when the heat is removed, it solidifies. It can
  be formed into various shapes.
• Composites can be layered with fibers in each
  layer running in a different direction.
• This allows materials engineers to design
  structures with specific behavior. They can
  design a structure like the Grumman X-29
  experimental plane that has forward-swept wings
  that do not bend up at the tips like typical
  metal wings do during flight.
• The greatest value of composite materials is that
  they can be both lightweight and strong. The
  heavier an aircraft weighs, the more fuel it
  burns.
• Modern military aircraft, like the F-22, use
  composites for at least a 1/3 of their
  structures, and some experts have predicted that
  future military aircraft will be more than 2/3
  composite materials.

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Why use composites ?
8
Boeing 787 All Composite Fuselage

• The Boeing 787 Dreamliner is a mid-sized,
  wide-body, twin-engine jet airliner still being
  tested.
• Rationale for the new design more fuel-efficient
  than predecessors and the first major airliner to
  use composite materials for most of its
  construction. The 787 has involved a large-scale
  collaboration with numerous suppliers.
• The 787's has an all-composite fuselage (main
  body). The Boeing 777 contains 50 aluminum and
  12 composites, the new airplane uses 50
  composite (mostly carbon fiber reinforced
  plastic), 15 aluminum, and other materials.
• The 787 fuselage is made up of composite barrel
  sections joined end to end. Each fuselage barrel
  will be manufactured in one piece. This will
  eliminate the need for some 50,000 fasteners used
  in conventional airplane assembly.
• It was stated that carbon fiber, unlike metal,
  does not visibly show cracks and fatigue. Boeing
  has dismissed such notions, insisting that
  composites have been used on wings and other
  passenger aircraft parts for many years and they
  have not been an issue.
• The 787 features lighter-weight construction. Its
  materials (by weight) are 50 composite, 20
  aluminum, 15 titanium, 10 steel, 5 other. The
  787 will be 80 composite by volume. Each 787
  contains approximately 35 tons of carbon fiber
  reinforced plastic, made with 23 tons of carbon
  fiber.
• Composites are used on fuselage, wings, tail,
  doors and interior.
• Aluminum is used on wing and tail leading edges,
  titanium used mainly on engines with steel used
  in various places.

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Disassembled fuselage section of the Boeing 787
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CFRP

• Carbon fiber-reinforced polymer or carbon
  fiber-reinforced plastic (CFRP or CRP), is a very
  strong, light and expensive composite material or
  fiber-reinforced polymer. Similar to fiberglass
  (glass reinforced polymer), the composite
  material is commonly referred to by the name of
  its reinforcing fibers (carbon fiber). The
  polymer is most often epoxy, but other polymers,
  such as polyester, vinyl ester or nylon can be
  used.
• Some composites contain both carbon fiber and
  other fibers such as kevlar, aluminum and
  fiberglass reinforcement.
• It has many applications in aerospace and
  automotive fields, as well as in sailboats, and
  notably in modern bicycles and motorcycles.
• CFRPs has a higher strength-to-weight ratio than
  traditional aircraft materials, and helped make
  the Boeing 787 a lighter aircraft.
• Improved manufacturing techniques are reducing
  the costs and time to manufacture, making it
  increasingly common in small consumer goods as
  well, such as laptops, tripods, fishing rods,
  paintball equipment, archery equipment, racquet
  frames, stringed instrument bodies, classical
  guitar strings, drum shells, golf clubs and
  pool/billiards/snooker cues.

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Shortcomings

• Despite their strength and low weight, composites
  have not been a miracle solution for aircraft
  structures. Composites are hard to inspect for
  flaws. Some of them absorb moisture. Most
  importantly, they can be expensive, primarily
  because they are labor intensive and often
  require complex and expensive fabrication
  machines.
• Aluminum, by contrast, is easy to manufacture and
  repair. Anyone who has ever gotten into a minor
  car accident has learned that dented metal can be
  hammered back into shape, but a crunched
  fiberglass bumper has to be completely replaced.
  The same is true for many composite materials
  used in aviation.

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Composite Phases

• Phase types
• -- Matrix phase is continuous
• -- Dispersed phase is discontinuous
  surrounded by a matrix
• Dispersed phase can have various shapes and
  arrangements.

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Dispersion Strengthened Composites

• In dispersion strengthened composites, small
  particles on the order of 10-5 mm to 2.5 x 10-4
  mm in diameter are added to the matrix material.
• These particles help the matrix resist
  deformation to make the material harder and
  stronger.
• In a metal matrix composite with a fine
  distribution of very hard and small secondary
  particles, the matrix material will carrying most
  of the load and deformation will be done by slip
  and dislocation movement. The secondary particles
  impede slip and dislocation and, thereby,
  strengthen the material.
• The mechanism is the same as precipitation
  hardening, but the effect is not as strong.
• However, particles like oxides do not react with
  the matrix or go into solution at high
  temperatures so the strengthening action is
  retained at elevated temperatures.

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Particle Reinforced Composites

• The particles in these composites are larger than
  in dispersion strengthened composites. The
  particle diameter is typically a few microns. So,
  the particles carry a major portion of the load.
• The particles are used to increase the modulus
  and decrease the ductility of the matrix.
• An example of particle reinforced composites is
  an automobile tire that has carbon black
  particles (nanoparticles) in a matrix of
  polyisobutylene elastomeric polymer.
• Particle reinforced composites are much easier to
  make and less costly than fiber reinforced
  composites. With polymeric matrices, the
  particles are added to the melt in an extruder or
  injection molder during polymer processing.
• Similarly, reinforcing particles are added to a
  molten metal before it is cast.

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Isotropy and Anisotropy in Composites

• Fiber reinforced composite materials typically
  exhibit anisotropy. That is, some properties vary
  depending upon the geometric axis or plane they
  are measured along.
• For a composite to be isotropic in a specific
  property, such as CTE or Youngs modulus, all
  reinforcing elements, whether fibers or
  particles, have to be randomly oriented. This is
  not easily achieved for discontinuous fibers,
  since most processing methods tend to impart a
  certain orientation to the fibers.
• Continuous fibers in the form of sheets are
  usually used to deliberately make the composite
  anisotropic in a particular direction that is
  known to be the principally loaded axis or plane.

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Fiber Alignment
Longitudinal direction
Transverse direction
aligned continuous
aligned random discontinuous
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Matrix Properties

• The role of the matrix is to support the fibers
  and bond them together in the composite material.
  
• It transfers any applied loads to the fibers,
  helps to maintain fiber position and orientation.
  
• The matrix also gives the composite environmental
  protection.

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What are the main factors affecting the choice of
reinforcement ?
19
What is a prepreg?
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Prepregs

• When selecting prepregs the maximum service
  temperature is one of the key selection criteria
  for choosing the prepreg matrix.
• The cure can be simply represented by
  pre-polymers whose reactive sites join together
  forming chains and cross linking. Once this
  process has taken place the polymer is fully
  cured.
• The thermoset cure essentially joins the reactive
  sites together with the help of added components
  (filler, accelerator, hardener, thermoplastic
  resins).

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What are the properties of different thermoset
matrices ?

• There are three main matrix types
• epoxy
• phenolic
• bismaleimide
• The table indicates the advantages of each type
  and typical applications.

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Sports

• Over the years, in many different sports,
  material science has brought great performance
  advancements. Let's take a brief look back at the
  history of several different sports.
• GOLFBen Hogan used to play with wooden shafted
  golf clubs. Then, in the 1940's, golf shafts
  became steel. It was not until the late 1980's
  that we started to see Carbon Fiber used in golf
  shafts. Today, Tiger Woods and all PGA golfers
  are using clubs that are made with Carbon Fiber.
• TENNISBjorn Borg and Chris Evert played at
  Wimbledon with wooden rackets. Then, in the
  1980's, Jimmy Connors started to win using a
  metal Wilson T-2000 racquet. Today, all tennis
  racquets are made of Carbon Fiber. To the right,
  Roger Federer is seen winning Wimbledon with his
  Carbon Fiber tennis racquet.

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More Sports

• WATER SKISWhen water skiing began in 1922, skis
  were made of wood. It was not until the early
  1970's that EP Water Skis developed a
  fiberglass/foam core water ski. In 1994, GOODE
  Skis developed the world's first Carbon Fiber
  water ski. Carbon Fiber skis are now used by all
  World Champions and World Record Holders.
• SKI POLESSki poles were constructed of bamboo.
  Then, during World War II, ski poles were made
  of steel. In 1958, Ed Scott invented the aluminum
  ski pole. It took another 31 years before Dave
  Goode invented the World's first Carbon Fiber ski
  pole.
• OTHER SPORTSThere are many, many other sports
  that have benefited from the use of Carbon Fiber
  (hockey, cycling, archery, etc.).

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SNOW SKIING

• So what has happened to snow skiing?
• Why is Carbon Fiber not being used, even at the
  most elite competition levels? The answers are
  not completely clear, however, some reasons are
  as follows
• Possible lack of innovation within the ski
  industry.
• Higher cost of raw materials (Carbon typically
  costs 30x that of fiberglass).
• Long molding cycles (3 hours for Carbon vs. 12
  minutes for conventional fiberglass skis).
• Difficult to design and engineer.
• In 1988, GOODE was the first company to introduce
  a Carbon Fiber ski pole. In 1994, GOODE was the
  first company in the world to introduce an all
  Carbon Fiber water ski.

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c15cof01

• Carbon Fiber, weighs about 1/2 of a traditional
  wood core/fiberglass ski (typical 175cm GOODE ski
  weighs only 2.1lbs).
• The layered Carbon Fiber used in all GOODE Skis
  has twice the strength of fiberglass (3.5 times
  the strength of aluminum) while weighing half as
  much. That is a four times (4X) Strength to
  Weight Ratio. 

• Cross section of a high performance ski.
• The function and material of each component is
  listed.

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Snow Boards
handmade honeycomb core.
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Classification Structural
Laminates - -- stacked and bonded
fiber-reinforced sheets - stacking
sequence e.g., 0º/90º - benefit
balanced in-plane stiffness
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Sandwich Construction
ANALOGY BETWEEN AN I-BEAM AND A HONEYCOMB
SANDWICH CONSTRUCTION
Advantages very low weight, high stiffness,
durable, design freedom, reduced production
costs. Tensile and compression stresses are
supported by the skins Shearing stress is
supported by the honeycomb The skins are stable
across their whole length Rigidity in several
directions Excellent weight saving
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Helicopters
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Classification Particle-Reinforced (i)
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Classification Particle-Reinforced (ii)
Concrete gravel sand cement water -
Why sand and gravel? Sand fills voids between
gravel particles
Reinforced concrete Reinforce with steel rebar
- increases strength - even if cement
matrix is cracked
Prestressed concrete - Rebar placed
under tension during setting of concrete
- Release of tension after setting places
concrete in a state of compression - To
fracture concrete, applied tensile stress must
exceed this compressive stress
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Classification Particle-Reinforced (iii)
Elastic modulus, Ec, of composites -- two
rule of mixture extremes
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Problem 15.1

• The mechanical properties of cobalt may be
  improved by incorporating fine particles of
  tungsten carbide (WC) in the matrix.

Cermet (refractory carbide) Ceramic imbedded
in a Metal matrix Composite
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Classification Fiber-Reinforced

• Fibers very strong in tension
• Provide significant strength improvement
• Ex 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

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Fiberglass

• Fiberglass is the most common composite material,
  and consists of glass fibers embedded in a resin
  matrix.
• Fiberglass was first used widely in the 1950s for
  boats and automobiles, and today most cars have
  fiberglass bumpers covering a steel frame.
• Fiberglass was first used in the Boeing 707
  passenger jet in the 1950s, where it comprised
  about 2 of the structure.
• By the 1960s, other composite materials became
  available, in particular boron fiber and
  graphite, embedded in epoxy resins. The U.S. Air
  Force and U.S. Navy began research into using
  these materials for aircraft control surfaces
  like ailerons and rudders. The first major
  military production use of boron fiber was for
  the horizontal stabilizers on the Navy's F-14
  Tomcat interceptor. By 1981, the British
  Aerospace-McDonnell Douglas AV-8B Harrier flew
  with over 25 of its structure made of composite
  materials.

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• Reinforcement Types
• Whiskers - thin single crystals - large length to
  diameter ratios
• graphite, silicon nitride, silicon carbide
• high crystal perfection extremely strong
• very expensive and difficult to disperse

nanowires

• Fibers
• polycrystalline or amorphous
• generally polymers or ceramics
• Ex alumina, aramid, E-glass, boron

• Wires
• metals steel, molybdenum, tungsten

SiC whiskers
boron
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Fiber materials

• Glass is the most common and inexpensive fiber
  used for the reinforcement of polymer matrices.
  Glass has a high tensile strength and fairly low
  density (2.5 g/cc).
• Carbon-graphite is a very light element, with a
  density of about 2.3 g/cc and its stiffness is
  considerably higher than glass. Carbon fibers can
  have up to 3 times the stiffness of steel and up
  to 15 times the strength of construction steel.
  The graphitic structure is preferred over the
  diamond-like crystalline forms for making carbon
  fiber because the graphitic structure is made of
  densely packed hexagonal layers, stacked in a
  lamellar style.
• Polymer has strong covalent bonds that lead to
  impressive properties when aligned along the
  fiber axis of high molecular weight chains.
  Kevlar is composed of rigidly oriented aromatic
  chains. Its stiffness can be as high as 125 GPa
  and although very strong in tension, it has very
  poor compression properties.
• Ceramic fibers made from materials such as
  Alumina and SiC are advantageous in very high
  temperature applications, and also where
  environmental attack is an issue. Ceramics have
  poor properties in tension and shear, so most
  applications are as reinforcement in the
  particulate form.
• Metallic fibers have high strengths but since
  their density is very high they are of little use
  in weight critical applications. Drawing very
  thin metallic fibers (less than 100 micron) is
  also very expensive.

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Reinforcement fibers and particulates
Carbon
Thermoplastic weaves

• Glass
• Carbon
• Kevlar
• Silicon Carbide
• Boron
• Ceramic
• Metallic
• Aggregate

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Scaled Composites

• carbon composite materials technology
• Extensive use of composite materials allows the
  fastest possible prototype fabrication -
  prototypes that are very light, strong, simple
  and cost effective.
• They use many fabrication techniques (filament
  winding and large scale, integrated co-cured
  components to generate very efficient structure).
  

http//www.scaled.com/about/
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What are the fiber properties ?

• Reinforcement materials provide composites with
  mechanical performance excellent stiffness and
  strength, as well as good thermal, electric and
  chemical properties, while offering significant
  weight savings over metals.
• The range of fibers is extensive. The graphs
  highlight the main criteria for fiber selection.

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Classification Fiber-Reinforced
Aligned Continuous fibers
Examples
-- Metal g'(Ni3Al)-a(Mo) by eutectic
solidification.
matrix
(Mo) (ductile)
a
2 mm
g
fibers
(Ni3Al) (brittle)
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Less Weight, More Challenging

• The electronics housing of a Proba 2
  micro-satellite,
• currently made of aluminum, was used in a
  comparative
• study using ANSYS software to evaluate the
  properties
• of composite materials for a lighter-weight
  design.
• Componeering, an analysis company in Helsinki,
  Finland, used the advanced analysis capabilities
  of ANSYS software to create a laminated composite
  housing material that would give them the
  comparable thermal and mechanical behavior of the
  original aluminum while cutting back on overall
  mass.
• The project involved a low-orbiting
  microsatellite, generally much smaller than a
  telecommunications satellite. They determined the
  thermal balance, structural integrity and
  resonant frequencies throughout the tight spaces,
  without applying extreme simplifications. The
  designers evaluated material selection, number of
  layers, layer orientations, and stacking sequence
  for a design that embedded a layer of tungsten
  foil inside a carbon-fiber-reinforced plastic
  (CFRP) laminate.

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REINFORCED CARBON-CARBON (RCC)
44
REINFORCED CARBON-CARBON (RCC)

• RCC is a hard structural material, with
  reasonable strength across its operational
  temperature range (minus 250 degrees Fahrenheit
  to 3,000 degrees). Its low thermal expansion
  coefficient minimizes thermal shock and
  thermoelastic stress.
• The basic RCC composite is a laminate of
  graphite-impregnated rayon fabric, further
  impregnated with phenolic resin and layered, one
  ply at a time, in a unique mold for each part,
  then cured, rough-trimmed, drilled, and
  inspected. The part is then packed in calcined
  coke and fired in a furnace to convert it to
  carbon and is made more dense by three cycles of
  furfuryl alcohol vacuum impregnation and firing.
• To prevent oxidation, the outer layers of the
  carbon substrate are converted into a
  0.02-to-0.04-inch-thick layer of silicon carbide
  in a chamber filled with argon at temperatures up
  to 3,000 degrees Fahrenheit. As the silicon
  carbide cools, craze cracks form because the
  thermal expansion rates of the silicon carbide
  and the carbon substrate differ. The part is then
  repeatedly vacuum-impregnated with tetraethyl
  orthosilicate to fill the pores in the substrate,
  and the craze cracks are filled with a sealant.

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Columbia damage report
46
Classification Fiber-Reinforced
Discontinuous fibers, random in 2 dimensions
Example Carbon-Carbon -- fabrication
process - carbon fibers embedded
in polymer resin matrix, -
polymer resin pyrolyzed at up to
2500ºC. -- uses disk brakes, gas
turbine exhaust flaps, missile nose
cones.
500 ?m
Other possibilities -- Discontinuous,
random 3D -- Discontinuous, aligned
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Onset of composite failure begins as the brittle
fibers start to fracture (ef). Not all fibers
fail at the same time, and the ductile matrix
remains intact. Matrix will continue to
plastically deform at a lower capacity.
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48
Classification Fiber-Reinforced
Critical fiber length for effective stiffening
strengthening
fiber ultimate tensile strength
fiber diameter
shear strength of fiber-matrix interface
Ex For fiberglass, common fiber length gt 15
mm needed
For longer fibers, stress transference from
matrix is more efficient
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c15tf05
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Composite StiffnessLongitudinal Loading

• Continuous fibers - Estimate fiber-reinforced
  composite modulus of elasticity for continuous
  fibers
• Longitudinal deformation
• ?c ?mVm ?fVf and ?c ?m
  ?f
• volume fraction
  isostrain

• Ecl EmVm Ef Vf Ecl
  longitudinal modulus

c compositef fiber m matrix
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Composite StiffnessTransverse Loading

• In transverse loading the fibers carry less of
  the load
• ?c ?mVm ?fVf and ?c ?m ?f ?

isostress
?
Ect transverse modulus
c compositef fiber m matrix
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manufacturing process

• Making an object from a composite material
  usually involves some form of mold.
• The reinforcing material is first placed in the
  mold and then semi-liquid matrix material is
  sprayed or pumped in to form the object. Pressure
  may be applied to force out any air bubbles, and
  the mold is then heated to make the matrix set
  solid.
• The molding process is often done by hand, but
  automatic processing by machines is becoming more
  common.
• One of the new methods is called pultrusion (a
  term derived from the words 'pull' and
  'extrusion'). This process is ideal for
  manufacturing products that are straight and have
  a constant cross section, such as bridge beams.

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Composite Production Methods (i)

• Pultrusion
• Continuous fibers pulled through resin tank, then
  to preforming and curing dies

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Composite Production Methods (ii)

• Filament Winding
• Ex pressure tanks
• Continuous filaments wound onto mandrel

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Orientation

• The fiber directions can be arranged to meet
  specific mechanical performance requirements of
  the composite by varying the orientation.

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Composite Benefits