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Composites

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Title: Composites


1
Composites
  • Chapter 15

Composite technology with T-800 Carbon Fiber
2
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

3
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.
4
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).

5
Older Technology
6
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.

7
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.

9
Disassembled fuselage section of the Boeing 787
10
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.

11
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.

12
Composite Phases
  • Phase types
  • -- Matrix phase is continuous
  • -- Dispersed phase is discontinuous
    surrounded by a matrix
  • Dispersed phase can have various shapes and
    arrangements.

13
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.

14
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.

15
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.

16
Fiber Alignment
Longitudinal direction
Transverse direction
aligned continuous
aligned random discontinuous
17
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.

18
What are the main factors affecting the choice of
reinforcement ?
19
What is a prepreg?
20
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).

21
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.

22
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.

23
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.).

24
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.

25
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.

26
Snow Boards
handmade honeycomb core.
27
Classification Structural
Laminates - -- stacked and bonded
fiber-reinforced sheets - stacking
sequence e.g., 0º/90º - benefit
balanced in-plane stiffness
27
28
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
28
29
Helicopters
30
Classification Particle-Reinforced (i)
31
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
32
Classification Particle-Reinforced (iii)
Elastic modulus, Ec, of composites -- two
rule of mixture extremes
33
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
34
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

35
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.

36
  • 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
37
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.

38
Reinforcement fibers and particulates
Carbon
Thermoplastic weaves
  • Glass
  • Carbon
  • Kevlar
  • Silicon Carbide
  • Boron
  • Ceramic
  • Metallic
  • Aggregate

39
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/
40
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.

41
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)
42
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.

43
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.

45
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
47
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.
47
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
49
c15tf05
50
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
51
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
52
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.

53
Composite Production Methods (i)
  • Pultrusion
  • Continuous fibers pulled through resin tank, then
    to preforming and curing dies

54
Composite Production Methods (ii)
  • Filament Winding
  • Ex pressure tanks
  • Continuous filaments wound onto mandrel

55
Orientation
  • The fiber directions can be arranged to meet
    specific mechanical performance requirements of
    the composite by varying the orientation.

56
Composite Benefits
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