ME 429 Introduction to Composite Materials

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ME 429 Introduction to Composite Materials

• Dr. Ahmet Erklig
• 2005-2006 Fall Semester

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Composite materials Introduction

• Definition any combination of two or more
  different materials at the macroscopic level.
• OR
• Two inherently different materials that when
  combined together produce a material with
  properties that exceed the constituent materials.
  
• Reinforcement phase (e.g., Fibers)
• Binder phase (e.g., compliant matrix)
• Advantages
• High strength and stiffness
• Low weight ratio
• Material can be designed in addition to the
  structure

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Applications

• Straw in clay construction by Egyptians
• Aerospace industry
• Sporting goods
• Automotive
• Construction

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Types of Composites
MMCs CMCs PMCs Metal Matrix
Composites Ceramic Matrix Comps.
Polymer Matrix Comps
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Costs of composite manufacture

• Material costs -- higher for composites
• Constituent materials (e.g., fibers and resin)
• Processing costs -- embedding fibers in matrix
• not required for metals Carbon fibers order of
  magnitude higher than aluminum
• Design costs -- lower for composites
• Can reduce the number of parts in a complex
  assembly by designing the material in combination
  with the structure
• Increased performance must justify higher
  material costs

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Types of Composite Materials

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

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A. 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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Composite strength depends on 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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B. 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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C. Flake Composites - 1

• 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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C. Flake Composites -2

• 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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C. Flake Composites -3

• 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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D. Laminar Composites - 1

• 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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D. Laminar Composites - 2

• Like all composites laminar composites aim at
  combining constituents to produce properties that
  neither constituent alone would have.
• In laminar composites 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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D. Laminar Composites - 3

• 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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D. Laminar Composites - 4

• 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 at least two
  different directions.

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E. 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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F. 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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Forms of Reinforcement Phase

• Fibers
• cross-section can be circular, square or
  hexagonal
• Diameters --gt 0.0001 - 0.005
• Lengths --gt L/D ratio
• 100 -- for chopped fiber
• much longer for continuous fiber
• Particulate
• small particles that impede dislocation movement
  (in metal composites) and strengthens the matrix
• For sizes gt 1 mm, strength of particle is
  involves in load sharing with matrix
• Flakes
• flat platelet form

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Fiber Reinforcement

• The typical composite consists of a matrix
  holding reinforcing materials. The reinforcing
  materials, the most important is the fibers,
  supply the basic strength of the composite.
  However, reinforcing materials can contribute
  much more than strength. They can conduct heat or
  resist chemical corrosion. They can resist or
  conduct electricity. They may be chosen for their
  stiffness (modulus of elasticity) or for many
  other properties.

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Types of Fibers

• The fibers are divided into two main groups
• Glass fibers There are many different kinds of
  glass, ranging from ordinary bottle glass to high
  purity quartz glass. All of these glasses can be
  made into fibers. Each offers its own set of
  properties.
• Advanced fibers These materials offer high
  strength and high stiffness at low weight. Boron,
  silicon, carbide and graphite fibers are in this
  category. So are the aramids, a group of plastic
  fibers of the polyamide (nylon) family.

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Fibers - Glass

• Fiberglass properties vary somewhat according to
  the type of glass used. However, glass in general
  has several wellknown properties that contribute
  to its great usefulness as a reinforcing agent
• Tensile strength
• Chemical resistance
• Moisture resistance
• Thermal properties
• Electrical properties
• There are four main types of glass used in
  fiberglass
• Aglass
• Cglass
• Eglass
• Sglass

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Fibers - Glass

• Most widely used fiber
• Uses piping, tanks, boats, sporting goods
• Advantages
• Low cost
• Corrosion resistance
• Low cost relative to other composites
• Disadvantages
• Relatively low strength
• High elongation
• Moderate strength and weight
• Types
• E-Glass - electrical, cheaper
• S-Glass - high strength

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Fibers - Aramid (kevlar, Twaron)

• Uses
• high performance replacement for glass fiber
• Examples
• Armor, protective clothing, industrial, sporting
  goods
• Advantages
• higher strength and lighter than glass
• More ductile than carbon

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Fibers - Carbon

• 2nd most widely used fiber
• Examples
• aerospace, sporting goods
• Advantages
• high stiffness and strength
• Low density
• Intermediate cost
• Properties
• Standard modulus 207-240 Gpa
• Intermediate modulus 240-340 GPa
• High modulus 340-960 GPa
• Diameter 5-8 microns, smaller than human hair
• Fibers grouped into tows or yarns of 2-12k fibers

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Fibers -- Carbon (2)

• Types of carbon fiber
• vary in strength with processing
• Trade-off between strength and modulus
• Intermediate modulus
• PAN (Polyacrylonitrile)
• fiber precursor heated and stretched to align
  structure and remove non-carbon material
• High modulus
• made from petroleum pitch precursor at lower cost
• much lower strength

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Fibers - Others

• Boron
• High stiffness, very high cost
• Large diameter - 200 microns
• Good compressive strength
• Polyethylene - trade name Spectra fiber
• Textile industry
• High strength
• Extremely light weight
• Low range of temperature usage

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Fibers -- Others (2)

• Ceramic Fibers (and matrices)
• Very high temperature applications (e.g. engine
  components)
• Silicon carbide fiber - in whisker form.
• Ceramic matrix so temperature resistance is not
  compromised
• Infrequent use

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Fiber Material Properties
Steel density (Fe) 7.87 g/cc TS0.380 GPa
Modulus207 GPa Al density2.71 g/cc TS0.035
GPa Modulus69 GPa
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Fiber Strength
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Matrix Materials

• Functions of the matrix
• Transmit force between fibers
• arrest cracks from spreading between fibers
• do not carry most of the load
• hold fibers in proper orientation
• protect fibers from environment
• mechanical forces can cause cracks that allow
  environment to affect fibers
• Demands on matrix
• Interlaminar shear strength
• Toughness
• Moisture/environmental resistance
• Temperature properties
• Cost

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Matrices - Polymeric

• Thermosets
• cure by chemical reaction
• Irreversible
• Examples
• Polyester, vinylester
• Most common, lower cost, solvent resistance
• Epoxy resins
• Superior performance, relatively costly

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Matrices - Thermosets

• Polyester 
• Polyesters have good mechanical properties,
  electrical properties and chemical resistance.
  Polyesters are amenable to multiple fabrication
  techniques and are low cost.
•  
• Vinyl Esters
• Vinyl Esters are similar to polyester in
  performance. Vinyl esters have increased
  resistance to corrosive environments as well as a
  high degree of moisture resistance.

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Matrices - Thermosets

• Epoxy
• Epoxies have improved strength and stiffness
  properties over polyesters. Epoxies offer
  excellent corrosion resistance and resistance to
  solvents and alkalis. Cure cycles are usually
  longer than polyesters, however no by-products
  are produced.
• Flexibility and improved performance is also
  achieved by the utilization of additives and
  fillers.

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Matrices - Thermoplastics

• Formed by heating to elevated temperature at
  which softening occurs
• Reversible reaction
• Can be reformed and/or repaired - not common
• Limited in temperature range to 150C
• Examples
• Polypropylene
• with nylon or glass
• can be injected-- inexpensive
• Soften layers of combined fiber and resin and
  place in a mold -- higher costs

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Matrices - Others

• Metal Matrix Composites - higher temperature
• e.g., Aluminum with boron or carbon fibers
• Ceramic matrix materials - very high temperature
• Fiber is used to add toughness, not necessarily
  higher in strength and stiffness

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Important Note

• Composite properties are less than that of the
  fiber because of dilution by the matrix and the
  need to orient fibers in different directions.

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MANUFACTURING PROCESSES OF COMPOSITES

• Composite materials have succeeded remarkably in
  their relatively short history. But for continued
  growth, especially in structural uses, certain
  obstacles must be overcome. A major one is the
  tendency of designers to rely on traditional
  materials such as steel and aluminum unless
  composites can be produced at lower cost.
• Cost concerns have led to several changes in the
  composites industry. There is a general movement
  toward the use of less expensive fibers. For
  example, graphite and aramid fibers have largely
  supplanted the more costly boron in
  advancedfiber composites. As important as
  savings on materials may be, the real key to
  cutting composite costs lies in the area of
  processing.

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• The processing of fiber reinforced laminates can
  be divided into two main steps
• Layup
• Curing
• Curing is the drying and hardening (or
  polymerization) of the resin matrix of a finished
  composite. This may be done unaided or by
  applying heat and/or pressure.
• Layup basically is the process of arranging
  fiberreinforced layers (laminae) in a laminate
  and shaping the laminate to make the part
  desired. (The term layup is also used to refer
  to the laminate itself before curing.) Unless
  prepregs are used, layup includes the actual
  creation of laminae by applying resins to fiber
  reinforcements.

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• Laminate layup operations fall into three main
  groups
• Winding and laying operations
• Molding operations
• Continuous lamination
• Continuous lamination is relatively unimportant
  compared with quality parameters as not good as
  wrt other two processes. In this process, layers
  of fabric or mat are passed through a resin dip
  and brought together between cellophane covering
  sheets. Laminate thickness and resin content are
  controlled by squeegee rolls. The layup is
  passed through a heat zone to cure the resin.

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A. Winding Operation

• The most important operation in this category is
  filament winding. Fibers are passed through
  liquid resin, and then wound onto a mandrel.
  After layup is completed, the composite is cured
  on the mandrel. The mandrel is then removed by
  melting, dissolving, breakingout or some other
  method.

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B. Molding Operations

• Molding operations are used in making a large
  number of common composite products. There are
  two types of processes
• Openmold
• (1) Hand layup
• (2) Sprayup
• (3) Vacuumbag molding
• (4) Pressurebag molding
• (5) Thermal expansion molding
• (6) Autoclave molding
• (7) Centrifugal casting
• (8) Continuous pultrusion and pulforming.

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1. Hand Lay-up

• Hand layup, or contact molding, is the oldest
  and simplest way of making fiberglassresin
  composites. Applications are standard wind
  turbine blades, boats, etc.)

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2. Spray-up

• In Sprayup process, chopped fibers and resins
  are sprayed simultaneously into or onto the mold.
  Applications are lightly loaded structural
  panels, e.g. caravan bodies, truck fairings,
  bathtubes, small boats, etc.

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3. Vacuum-Bag Molding

• The vacuumbag process was developed for making a
  variety of components, including relatively large
  parts with complex shapes. Applications are large
  cruising boats, racecar components, etc.

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4. Pressure-Bag Molding

• Pressurebag process is virtually a mirror image
  of vacuumbag molding. Applications are sonar
  domes, antenna housings, aircraft fairings, etc.

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5. Thermal Expansion Molding

• In Thermal Expansion Molding process, prepreg
  layers are wrapped around rubber blocks, and then
  placed in a metal mold. As the entire assembly is
  heated, the rubber expands more than the metal,
  putting pressure on the laminate. Complex shapes
  can be made reducing the need for later joining
  and fastening operations.

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6. Autoclave Molding

• Autoclave molding is similar to both vacuumbag
  and pressurebag molding. Applications are
  lighter, faster and more agile fighter aircraft,
  motor sport vehicles.

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7. Centrifugal Casting
Centrifugal Casting is used to form round objects
such as pipes. 8. Continuous Pultrusion and
Pulforming

• Continuous pultrusion is the composite
  counterpart of metal extrusion. Complex parts can
  be made.

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• Pulforming is similar to pultrusion in many ways.
  However, pultrusion is capable only of making
  straight products that have the same volume all
  along their lengths. Pulformed products, on the
  other hand, can be either straight or curved,
  with changing shapes and volumes. A typical
  pulformed product is a curved reinforced plastic
  car spring. (shown in figure.)

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B. Closedmold

• (1) Matcheddie molding As the name suggests,
  a matcheddie mold consists of closely matched
  male and female dies (shown in figure).
  Applications are spacecraft parts, toys, etc.
• (2) Injection molding The injection process
  begins with a thermosetting (or sometimes
  thermoplastic) material outside the mold. The
  plastic may contain reinforcements or not. It is
  first softened by heating and/or mechanical
  working with an extrusiontype screw. It is then
  forced, under high pressure from a ram or screw,
  into the cool mold. Applications are auto parts,
  vanes, engine cowling defrosters and aircraft
  radomes.

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Material Forms and Manufacturing

• Objectives of material production
• assemble fibers
• impregnate resin
• shape product
• cure resin

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Sheet Molding Compound (SMC)

• Chopped glass fiber added to polyester resin
  mixture

• Question Is SMC isotropic or anisotropic?

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Manufacturing - Filament Winding

• Highly automated
• low manufacturing costs if high throughput
• e.g., Glass fiber pipe, sailboard masts

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Prepregs

• Prepreg and prepreg layup
• prepreg - partially cured mixture of fiber and
  resin
• Unidirectional prepreg tape with paper backing
• wound on spools
• Cut and stacked
• Curing conditions
• Typical temperature and pressure in autoclave is
  120-200C, 100 psi

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Manufacturing - Layups
compression molding
vacuum bagging
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Material Forms

• Textile forms
• Braiding or weaving
• Tubular braided form
• can be flattened and cut for non-tubular products

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Fabric Structures
Woven Series of Interlaced yarns at 90 to each
other   Knit Series of Interlooped
Yarns   Braided Series of Intertwined, Spiral
Yarns   Nonwoven Oriented fibers either
mechanically, chemically, or thermally bonded
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Woven Fabrics

• Basic woven fabrics consists of two systems of
  yarns interlaced at right angles to create a
  single layer with isotropic or biaxial
  properties.

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Physical Properties

• Construction (ends picks)
• Weight
• Thickness
• Weave Type

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Components of a Woven Fabric
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Basic Weave Types
Plain Weave
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Basic Weave Types
Satin 5HS
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Basic Weave Types
2 x 2 Twill
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Basic Weave Types
Non-Crimp
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Braiding
A braid consists of two sets of yarns, which are
helically intertwined.   The resulting structure
is oriented to the longitudinal axis of the
braid.   This structure is imparted with a high
level of conformability, relative low cost and
ease of manufacture.
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Braid Structure
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Types of Braids
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Triaxial Yarns
A system of longitudinal yarns can be introduced
which are held in place by the braiding
yarns These yarns will add dimensional
stability, improve tensile properties, stiffness
and compressive strength. Yarns can also be
added to the core of the braid to form a solid
braid.
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Fabric effects on material properties
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Resin transfer molding (RTM)

• Dry-fiber preform placed in a closed mold, resin
  injected into mold, then cured

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Material Forms

• Pultrusion
• Fiber and matrix are pulled through a die, like
  extrusion of metals -- assembles fibers,
  impregnates the resin, shapes the product, and
  cures the resin in one step.
• Example. Fishing rods

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Pultrusion
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Manufacturing

• Tube rolling - tubular products
• Examples
• fishing rods
• golf clubs
• oars
• Prepreg tape typically used wrapped in 2
  directions or spiral wrapped