EBB 220/3 POLYMER COMPOSITE

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EBB 220/3POLYMER COMPOSITE
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What is Composites?

• Combination of 2 or more materials
• Each of the materials must exist more than 5
• Presence of interphase
• The properties shown by the composite materials
  are differed from the initial materials
• Can be produced by various processing techniques

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Constituents of composite materials

• Matrix phase
• Continuous phase, the primary phase.
• It holds the dispersed phase and shares a load
  with it.
• 2. Dispersed (reinforcing) phase
• The second phase (or phases) is imbedded in the
  matrix in a
• continuous/discontinuous form.
• Dispersed phase is usually stronger than the
  matrix, therefore it is sometimes
• called reinforcing phase.
• 3. Interface
• Zone across which matrix and reinforcing phases
  interact (chemical, physical,
• mechanical)

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Matrix Function
however the distribution of loads depends on the
interfacial bondings
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Reinforcement Function
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Reinforcement can be in the form of

• Continuous fiber
• Organic fiber- i.e. Kevlar, polyethylene
• Inorganic fiber- i.e. glass, alumina, carbon
• Natural fiber- i.e. asbestos, jute, silk
• Short fiber
• whiskers
• Particle
• Wire

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Interface Function

• To transfer the stress from matrix to
  reinforcement
• Sometimes surface treatment is carried out to
  achieve the required bonding to the matrix

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Characteristics of dispersed phase that might
influence the properties of composites
a) Concentration (b) size (c) shape (d)
distribution (e) orientation
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Classification of composites
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Examples of composites

1. Particulate random
2. Discontinuous fibers unidirectional
3. Discontinuous fibers random
4. Continuous fibers unidirectional

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Classification based on Matrices
Composite materials
Matrices
Polymer Matrix Composites (PMC)
Metal Matrix Composites MMC)
Ceramic Matrix Composites (CMC)
Thermoset
Thermoplastic
Rubber
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What is Hybrid composites?What are the
advantages of hybrid composites?
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• Widely used- ease of processing lightweight

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Properties of composites depend on

• Amount of phase
• - Amount/proportion (can be expressed in weight
  fraction (Wf) or volume fraction (Vf))of phases
  strongly influence the properties of composite
  materials.
• Xc Xf Vf Xm (1 - Vf ) - Rule of Mixture
• Xc Properties of composites
• Xf Properties of fiber
• Xm Properties of matrix

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Voids

• Free volume
• Gas emission leads to voids in the final product
• In composites- Voids exist in the matrix,
  interface and in between fiber fiber
• Voids create stress concentration points-
  influence the properties of the composites

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Geometry of dispersed phase (particle size,
distribution, orientation)

• Shape of dispersed phase (particle- spherical or
  irregular, flaky, whiskers, etc)
• Particle/fiber size ( fiber- short, long,
  continuous) particle (nano or micron size)
• Orientation of fiber/particle (unidirection,
  bi-directions, many directions)- influence
  isotropic dan an-isotropic properties
• Dictribution of dispersed phase
  (homogenus/uniform, inhomogenus)

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Processing technique and parameters

• Influence final product, selection of correct raw
  materials, void content, etc

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Glass Fiber

• The types of glass used are as follows
• E-Glass the most popular and inexpensive glass
  fibers. The designation letter E means
  electrical (E-Glass is excellent insulator).
  The composition of E-glass ranges from 52-56
  SiO2, 12-16 A1203, 16-25 CaO, and 8-13 B203
• S-Glass stronger than E-Glass fibers (the
  letter S means strength). High-strength glass
  is generally known as S-type glass in the United
  States, R-glass in Europe and T-glass in Japan.
  S-Glass is used in military applications and in
  aerospace. S-Glass consists of silica (SiO2),
  magnesia (MgO), alumina (Al2O3).
• C-Glass corrosion and chemical resistant glass
  fibers. To protect against water erosion, a
  moisture-resistant coating such as a silane
  compound is coated onto the fibers during
  manufacturing. Adding resin during composite
  formation provides additional protection. C-Glass
  fibers are used for manufacturing storage tanks,
  pipes and other chemical resistant equipment.

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Glass Fiber

• Fiberglasses (Glass fibers reinforced polymer
  matrix composites) are characterized by the
  following properties
• High strength-to-weight ratio
• High modulus of elasticity-to-weight ratio
• Good corrosion resistance
• Good insulating properties
• Low thermal resistance (as compared to metals and
  ceramics).
• Fiberglass materials are used for manufacturing
  boat hulls and marine structures, automobile and
  truck body panels, pressure vessels, aircraft
  wings and fuselage sections, housings for radar
  systems, swimming pools, welding helmets, roofs,
  pipes.

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Carbon Fiber

• The types of carbon fibers are as follows
• UHM (ultra high modulus). Modulus of elasticity gt
  65400 ksi (450GPa).
• HM (high modulus). Modulus of elasticity is in
  the range 51000-65400 ksi (350-450GPa).
• IM (intermediate modulus). Modulus of elasticity
  is in the range 29000-51000 ksi (200-350GPa).
• HT (high tensile, low modulus). Tensile strength
  gt 436 ksi (3 GPa), modulus of elasticity lt 14500
  ksi (100 GPa).
• SHT (super high tensile). Tensile strength gt 650
  ksi (4.5GPa).

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Carbon Fiber

• Carbon Fiber Reinforced Polymers (CFRP) are
  characterized by the following properties
• Light weight
• High strength-to-weight ratio
• Very High modulus elasticity-to-weight ratio
• High Fatigue strength
• Good corrosion resistance
• Very low coefficient of thermal expansion
• Low impact resistance
• High electric conductivity
• High cost.
• Carbon Fiber Reinforced Polymers (CFRP) are used
  for manufacturing automotive marine and
  aerospace parts, sport goods (golf clubs, skis,
  tennis racquets, fishing rods), bicycle frames.

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Kevlar Fiber

• Kevlar is the trade name (registered by DuPont
  Co.) of aramid (poly-para-phenylene
  terephthalamide) fibers.
• Kevlar fibers were originally developed as a
  replacement of steel in automotive tires.
• Kevlar filaments are produced by extrusion of the
  precursor through a spinnert. Extrusion imparts
  anisotropy (increased strength in the lengthwise
  direction) to the filaments.
• Kevlar may protect carbon fibers and improve
  their properties hybrid fabric (Kevlar Carbon
  fibers) combines very high tensile strength with
  high impact and abrasion resistance.

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Kevlar Fiber

• Kevlar fibers possess the following properties
• High tensile strength (five times stronger per
  weight unite than steel)
• High modulus of elasticity
• Very low elongation up to breaking point
• Low weight
• High chemical inertness
• Very low coefficient of thermal expansion
• High Fracture Toughness (impact resistance)
• High cut resistance
• Textile processibility
• Flame resistance.
• The disadvantages of Kevlar are ability to
  absorb moisture, difficulties in cutting, low
  compressive strength.

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Kevlar Fiber

• There are several modifications of Kevlar,
  developed for various applications
• Kevlar 29 high strength (520000 psi/3600 MPa),
  low density (90 lb/ft³/1440 kg/m³) fibers used
  for manufacturing bullet-proof vests, composite
  armor reinforcement, helmets, ropes, cables,
  asbestos replacing parts.
• Kevlar 49 high modulus (19000 ksi/131 GPa),
  high strength (550000 psi/3800 MPa), low density
  (90 lb/ft³/1440 kg/m³) fibers used in aerospace,
  automotive and marine applications.
• Kevlar 149 ultra high modulus (27000 ksi/186
  GPa), high strength (490000 psi/3400 MPa), low
  density (92 lb/ft³/1470 kg/m³) highly crystalline
  fibers used as reinforcing dispersed phase for
  composite aircraft components.

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Reasons for the use of polymeric materials as
matrices in composites

• i. The mechanical properties of polymers are
  inadequate for structural purposes, hence
  benefits are gained by reinforcing the polymers
• Processing of PMCs need not involve high pressure
  and high temperature
• The equipment required for PMCs are much simpler

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Disadvantages of PMC

• Low maximum working temperature
• High coefficient of thermal expansion-
  dimensional instability
• Sensitivity to radiation and moisture

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Classification of Polymer Matrices

• 1. Thermoset
• 2. Thermoplastic- crystalline amorphous
• 3. Rubber

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Thermoset

• Thermoset materials are usually liquid or
  malleable prior to curing, and designed to be
  molded into their final form
• has the property of undergoing a chemical
  reaction by the action of heat, catalyst,
  ultraviolet light, etc., to become a relatively
  insoluble and infusible substance.
• They develop a well-bonded three-dimensional
  structure upon curing. Once hardened or
  cross-linked, they will decompose rather than
  melt.
• A thermoset material cannot be melted and
  re-shaped after it is cured.
• Thermoset materials are generally stronger than
  thermoplastic materials due to this 3-D network
  of bonds, and are also better suited to
  high-temperature applications up to the
  decomposition temperature of the material.

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Thermoplastic

• is a plastic that melts to a liquid when heated
  and freezes to a brittle, very glassy state when
  cooled sufficiently.
• Most thermoplastics are high molecular weight
  polymers whose chains associate through weak van
  der Waals forces (polyethylene) stronger
  dipole-dipole interactions and hydrogen bonding
  (nylon) or even stacking of aromatic rings
  (polystyrene).
• The bondings are easily broken by the cobined
  action of thermal activation and applied stress,
  thats why thermoplastics flow at elevated
  temperature
• unlike thermosetting polymers, thermoplastic can
  be remelted and remolded.

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• Thermoplastics can go through melting/freezing
  cycles repeatedly and the fact that they can be
  reshaped upon reheating gives them their name
• Some thermoplastics normally do not crystallize
  they are termed "amorphous" plastics and are
  useful at temperatures below the Tg. They are
  frequently used in applications where clarity is
  important. Some typical examples of amorphous
  thermoplastics are PMMA, PS and PC.
• Generally, amorphous thermoplastics are less
  chemically resistant

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• Depends on the structure of the thermoplastics,
  some of the polymeric structure can be folded to
  form crystalline regions, will crystallize to a
  certain extent and are called "semi-crystalline"
  for this reason.
• Typical semi-crystalline thermoplastics are PE,
  PP, PBT and PET.
• Semi-crystalline thermoplastics are more
  resistant to solvents and other chemicals. If the
  crystallites are larger than the wavelength of
  light, the thermoplastic is hazy or opaque.
• Why HDPE exhibits higher cystallinity than LDPE?

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Comparison of typical ranges of property values
for thermoset and thermoplastics

• Properties t/set t/plastic
• Youngs Modulus (GPa)1.3-6.0 1.0-4.8
• Tensile strength(MPa) 20-180 40-190
• Max service temp.(ºC) 50-450 25-230
• Fracture toughness,KIc 0.5-1.0 1.5-6.0
• (MPa1/2)

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Thermoplastics are expected to receive attention
compared to thermoset due to

• Ease of processing
• Can be recycled
• No specific storage
• Good fracture modulus

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Rubber

• Common characteristics
• Large elastic elongation (i.e. 200)
• Can be stretched and then immediately return to
  their original length when the load was released
• Elastomers are sometimes called rubber or rubbery
  materials
• The term elastomer is often used interchangeably
  with the term rubber
• Natural rubber is obtained from latex from Hevea
  Brasiliensis tree which consists of 98
  poliisoprena
• Synthetic rubber is commonly produced from
  butadiene, spt styrene-butadiene (SBR) dan
  nitrile-butadiene (NBR)

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• To achieve properties suitable for structural
  purposed, most rubbers have to be vulcanized the
  long chain rubber have to be crosslinked
• The crosslinking agent in vulcanization is
  commonly sulphur, and the stiffness and strength
  increases with the number of crosslinks

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