ME 1014 Composite Materials

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ME 1014 Composite Materials
Prof.V.Alfred Franklin., St.Xaviers Catholic
College of EngineeringNagercoil, India.
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Composite Material ?

• Two inherently different materials that when
  combined together produce a material with
  properties that exceed the constituent materials.
• Any combination of two or more different
  materials at the macroscopic level..
• The constituents retain their identities, i.e..,
  they do not dissolve or merge into each other,
  although they act in concert.
• Composites Artificially produced multiphase
  materials.

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Composite Material ?

• Composites A judicious combination of two or
  more materials that produces a synergistic
  effect.
• A material system composed of two or more
  physically distinct phases whose combination
  produces aggregate properties that are different
  from those of its constituents.

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Phases of Composites
Matrix Phase continuous phase, surrounds other
phase (e.g. metal (Cu, Al, Ti, Ni) ,
ceramic (SiC), or polymer (Thermosets,
thermoplastics, Elastomers) Reinforcement Phase
dispersed phase, discontinuous phase (e.g.
Fibers, Particles, or Flakes) ?? ? Interface
between matrix and reinforcement Interfacial
properties - the interface may be regarded as a
third phase. Examples Straw in mud Wood
(cellulose fibers in hemicellulose and lignin)
Bones (soft protein collagen and hard apatite
minerals) Pearlite (ferrite and cementite)
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Micro mechanics/ Macro mechanics?
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Major Constituents

• Fiber
• Matrix
• Fillers
• Coupling agents
• Colorants

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FIBERS

• Principle Load carrying member
• Main constituent and they occupy largest volume
  fraction
• Diameter of a single fiber is about 10 microns
• They may be continuous or discontinuous in length.

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TYPES OF GLASS FIBER

• E-Glass E stands for electrical
• S-Glass S stands for high silica content
• High thermal expansion coefficient
• High fatigue strength
• C-Glass C stands for Corrosion
• Used in Chemical applications
• Storage tanks
• R-Glass R stands for Rigid
• Structural applications
• D-Glass D stands for Dielectric
• Low dielectric constants
• A-Glass A Stands for appearance
• To improve surface appearance
• For ornamental works
• E-CR Glass E-CR stands for Electrical and
  corrosion resistance
• AR Glass AR stands for Alkali resistance

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Critical fiber length for effective stiffening
strengthening
fiber strength in tension
fiber diameter
shear strength of fiber-matrix interface
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Efficiency fiber length
Shorter, thicker fiber
Longer, thinner fiber
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Poorer fiber efficiency
Better fiber efficiency
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Why are Fibers of a Thin Diameter?

• 1. Thinner fiber has higher ultimate strength
  because less chance
• for inherent flaws. Similar phenomenon in metals
  and alloys
• (Strength of a thin wire can be higher than its
  bulk material).
• 2. For the same volume of fibers, thinner fibers
  has larger
• surface area thus has stronger bond with matrix.
  (The total
• surface area of fibers is inversely proportional
  to the diameter
• of fibers)
• 3. Thinner fiber has larger flexibility ( 1/(EI))
  and therefore is
• able to be bent without breaking (Woven fabric
  performs can
• be made before impregnated with polymer matrix).

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Composite Strength Longitudinal Loading

• Continuous fibers - Estimate fiber-reinforced
  composite strength for long continuous fibers in
  a matrix
• Longitudinal deformation
• ?c ?mVm ?fVf but ?c ?m
  ?f
• volume fraction isostrain

Remembering E ?/? and note, this model
corresponds to the upper bound for particulate
composites
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Matrix / Resins

• - The resin or polymer is the glue that holds
  the composite together
• -The primary functions of the resin are to
  transfer stress between the reinforcing fibers.
• Examples Polyester, Epoxy, Vinyl Ester,
  Polyurethane

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Role of Matrices in Composites

• Transfer stresses between the fibers.
• Provide a barrier against an adverse
  environment.
• Protect the surface of the fibers from
  mechanical abrasion.
• Determine inter-laminar shear strength.
• Determine damage tolerance of composites.
• Determine in-plane shear strength.
• Determine the processibility of composites.
• Determine heat resistance of composites.

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Role of Matrix

• The primary roles of the matrix alloy then are to
  provide
• efficient transfer of load to the fibers and to
  blunt cracks in
• the event that fiber failure occurs and so the
  matrix alloy for
• continuously reinforced composites may be chosen
  more for
• toughness than for strength.
• On this basis, lower strength, more ductile, and
  tougher
• matrix alloys may be utilized in
  continuously reinforced composites.
• For discontinuously reinforced composites, the
  matrix may govern composite strength.
• -Then, the choice of matrix will be influenced
  by consideration of the required composite
  strength and higher strength matrix alloys may be
  required.

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Functions of Matrix

• Holds the fibres together.
• Protects the fibres from environment.
• Distributes the loads evenly between fibres so
  that all fibres are subjected to the same amount
  of strain.
• Enhances transverse properties of a laminate.
• Improves impact and fracture resistance of a
  component.
• Helps to avoid propagation of crack growth
  through the fibres by providing alternate failure
  path along the interface between the fibres and
  the matrix.
• Carry inter-laminar shear.

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Desired Properties of a Matrix

• Reduced moisture absorption.
• Low shrinkage.
• Low coefficient of thermal expansion.
• Good flow characteristics so that it penetrates
  the fibre bundles completely and eliminates voids
  during the compacting/curing process.
• Must be elastic to transfer load to fibres.

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Desired Properties of a Matrix

• Reasonable strength, modulus and elongation
  (elongationshould be greater than fibre).
• Strength at elevated temperature (depending on
  application).
• Low temperature capability (depending on
  application).
• Excellent chemical resistance (depending on
  application).
• Should be easily processable into the final
  composite shape.
• Dimensional stability (maintains its shape).

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FILLERS

• Control Composites Cost
• Improved Mechanical Properties
• Improved Chemical Properties
• Reduced Creep Shrinkage
• Low Tensile Strength
• Fire Retardant Chemical Resistant

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TYPES OF FILLER

• Calcium Carbonate
• Kaolin
• Alumina Trihydrate
• Mica Feldspar
• Wollastonite
• Silica, Talc, Glass

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ADDITIVES

• Improved Material Properties
• Aesthetics
• Enhanced Workability
• Improved Performance

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ADDITIVE TYPES

• Catalysts
• Promoters
• Inhibitors
• Coloring Dyes
• Releasing Agents
• Antistatic Agents
• Foaming Agents

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Composites Offer

• High Strength to weight ratio
• High Stiffness to weight ratio
• High Modulus to weight ratio
• Light Weight
• Directional strength
• Corrosion resistance
• Weather resistance
• Dimensional stability -low thermal conductivity
  
• -low coefficient of thermal expansion
• Radar transparency
• Non-magnetic
• High impact strength
• High dielectric strength (insulator)
• Low maintenance
• Long term durability
• Part consolidation
• Small to large part geometry possible
• Tailored surface finish  
• Design Flexibility

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Property comparison
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Composite strength depends on the following
factors

• Inherent fiber strength, Fiber length, Number of
  flaws
• Fiber shape
• The bonding of the fiber (equally stress
  distribution)
• Voids
• Moisture (coupling agents)

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Classification of Composite Materials

• Traditional composites composite materials that
  occur in nature or have been produced by
  civilizations for many years
• Examples wood (cellulose fibers in lignin
  matrix), concrete, asphalt
• Synthetic composites - modern material systems
  normally associated with the manufacturing
  industries, in which the components are first
  produced separately and then combined in a
  controlled way to achieve the desired structure,
  properties, and part geometry

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Classification of Synthetic Composites Based on
Matrix
MMCs CMCs PMCs Metal Matrix
Composites Ceramic Matrix Comps.
Polymer Matrix Comps
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Classification of Synthetic Composites Based
on reinforcements

• There are five basic types of composite
  materials Fiber, particle, flake, laminar or
  layered and filled composites.

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1. Fiber Composites
In fiber composites, the fibers reinforce along
the line of their length. Reinforcement may be
mainly 1-D, 2-D or 3-D. Figure shows the three
basic types of fiber orientation.

• 1-D gives maximum strength in one direction.
• 2-D gives strength in two directions.
• Isotropic gives strength equally in all
  directions.

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2. Particle Composites

• Particles usually reinforce a composite equally
  in all directions (called
  isotropic). Plastics, cermets and metals are
  examples of particles.
• Particles used to strengthen a matrix do not do
  so in the same way as fibers. For one thing,
  particles are not directional like fibers. Spread
  at random through out a matrix, particles tend to
  reinforce in all directions equally.

• Cermets
• (1) OxideBased cermets
• (e.g. Combination of Al2O3 with Cr)
• (2) CarbideBased Cermets
• (e.g. Tungstencarbide, titaniumcarbide)
• Metalplastic particle composites
• (e.g. Aluminum, iron steel, copper particles)
• Metalinmetal Particle Composites and Dispersion
  Hardened Alloys
• (e.g. Ceramicoxide particles)

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3. Flake Composites

• Flakes, because of their shape, usually reinforce
  in 2-D. Two common flake materials are glass and
  mica. (Also aluminum is used as metal flakes)

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Flake Composites

• A flake composite consists of thin, flat flakes
  held together by a binder or placed in a matrix.
  Almost all flake composite matrixes are plastic
  resins. The most important flake materials are
• Aluminum
• Mica
• Glass

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Flake Composites

• Basically, flakes will provide
• Uniform mechanical properties in the plane of the
  flakes
• Higher strength
• Higher flexural modulus
• Higher dielectric strength and heat resistance
• Better resistance to penetration by liquids and
  vapor
• Lower cost

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4. Laminar Composites

• Laminar Composites are composed of
  layers of materials
• held together by matrix.
• Laminar composites involve two or more layers of
  the same or different materials. The layers can
  be arranged in different directions to give
  strength where needed. Speedboat hulls are among
  the very many products of this kind.

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Laminar Composites

• We can divide laminar composites into three basic
  types
• Unreinforcedlayer composites
• (1) AllMetal
• (a) Plated and coated metals
  (electrogalvanized steel steel plated with
  zinc)
• (b) Clad metals (aluminumclad,
  copperclad)
• (c) Multilayer metal laminates
  (tungsten, beryllium)
• (2) MetalNonmetal (metal with plastic,
  rubber, etc.)
• (3) Nonmetal (glassplastic laminates, etc.)
• Reinforcedlayer composites (laminae and
  laminates)
• Combined composites (reinforcedplastic laminates
  well bonded with steel, aluminum, copper, rubber,
  gold, etc.)

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Laminar Composites

• Like all composites laminar composites aim at
  combining constituents to produce properties that
  neither constituent alone would have.
• In laminar composites (Un reinforced) outer metal
  is not called a matrix but a face. The inner
  metal, even if stronger, is not called a
  reinforcement. It is called a base.

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Laminar Composites

• A lamina (laminae) is any arrangement of
  unidirectional or woven fibers in a matrix.
  Usually this arrangement is flat, although it may
  be curved, as in a shell.
• A laminate is a stack of lamina arranged with
  their main reinforcement in different
  directions.

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Laminate Sequence
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5. Filled Composites

• There are two types of filled composites. In one,
  filler materials are added to a normal composite
  result in strengthening the composite and
  reducing weight. The second type of filled
  composite consists of a skeletal 3-D matrix
  holding a second material. The most widely used
  composites of this kind are sandwich structures
  and honeycombs.

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• Sandwich Structure Foam Core
• Consists of a relatively thick core of low
  density foam bonded on both faces to thin sheets
  of a different material

Figure 9.7 - Laminar composite structures (b)
sandwich structure using foam core
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• Sandwich Structure Honeycomb Core
• An alternative to foam core
• Either foam or honeycomb achieves high
  strength-to-weight and stiffness-to-weight ratios

Figure 9.7 - Laminar composite structures (c)
sandwich structure using honeycomb core
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6.Combined Composites

• It is possible to combine several different
  materials into a single composite. It is also
  possible to combine several different composites
  into a single product. A good example is a modern
  ski. (combination of wood as natural fiber, and
  layers as laminar composites)

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