Composite Reinforcement Notes

Reinforcement Shape Categories

• Principal inclusion shapes:
  • Particle: Short dimension.
  • Fiber: Long dimension/continuous.
• Particulate inclusion variations:
  • Platelet
  • Whisker
  • Flake
  • Spherical
• Examples of reinforcement:
  • Glass fiber
  • Boron fiber
  • Carbon fiber
  • $SiC$ and $Al<em>2O</em>3$
  • Natural fiber

Reinforcement or Filler Shapes/Forms

• Chopped fibers (random)
• Oriented short fibers
• Fiber/particulate hybrids
• Short fiber hybrids
• Unidirectional continuous fibers
• Filament wound cylindrical
• Type A fibers
• Long/Interpenetrating
• Woven fabrics
• Type B fibers
• Continuous/hybrid
• Orthogonal 3-D
• Multi-axial 3-D weave
• 3-D braid
• Figure 1.2 (a): Possible combinations of several forms of fibers composite type.

Glass Fibers

• Amorphous (non-crystalline) and isotropic (equal properties in all directions).
• Long, three-dimensional network of silicon, oxygen, and other atoms arranged randomly.

Characteristics

• Inorganic, synthetic, multifilament material.
• Most common reinforcing fibers for polymeric (plastic) matrix composites.
• Strong, low in cost, nonflammable, nonconductive (electrically), and corrosion-resistant.

Weaknesses

• Low tensile modulus.
• High specific gravity (among commercial fibers).
• Sensitivity to abrasion with handling (frequently decreases tensile strength).
• Low fatigue resistance.
• High hardness (causes excessive wear on molding dies and cutting tools).

Classification

• Three main categories:
  • E-glass: Used for electrical conductivity material.
  • S-glass: High-strength glass (S-glass, S-2 glass, and S-2 hollow glass fiber).
  • C-glass: Corrosion resistance to acids in chemical applications.

Fiber Glass Roving

• Fiberglass is made from glass (same as windows and kitchen glasses).
• Manufacturing method:
  • Glass is melted and forced through superfine holes.
  • Filaments are extremely thin and can be woven into sheets or made into puffy substances for soundproofing and insulation.

Manufacturing

• Two main types of glass fiber manufacture process:
  • Direct melt process
  • Marble re-melt process
• Both start with raw materials in solid form.
• Materials are mixed together and melted in a furnace.

Direct Melt Process

• Textile-grade glass fibers are made from silica ($SiO_2$) sand, which melts at $1720°C/3128°F$.
• $SiO<em>2$ is the basic element in quartz (crystalline, rigid, highly ordered atomic structure) and is 99% or more $SiO</em>2$.
• If $SiO_2$ is heated above $1200°C/2192°F$ then cooled ambiently, it crystallizes and becomes quartz.
• Glass is produced by altering the temperature and cooldown rates.
• If pure $SiO_2$ is heated to $1720°C/3128°F$ then cooled quickly, crystallization can be prevented, yielding amorphous or randomly ordered atomic structure (glass).

Step 1: Batching

• Other ingredients added to reduce working temperature and impart specific properties useful in applications.
• Composition includes $SiO<em>2$, $Al</em>2O_3$, $CaO$ (lime), and $MgO$ (alkali-resistant alternative to soda lime glass).
• Materials are carefully weighed in exact quantities and thoroughly mixed (batched).

Step 2: Melting

• Mixture sent to a high-temperature ($≈1400ºC/2552ºF$) natural gas-fired furnace for melting.
• Three sections:
  • First section: Receives the batch, where melting occurs, uniformity is increased, and bubbles are removed.
  • Second: Molten glass flows into the refiner, where its temperature is reduced to $1370ºC/2500ºF$.
  • Final section: Forehearth, beneath which is a series of four to seven bushings used to extrude molten glass into fibers.
• Large furnaces have several channels, each with its own forehearth.

Step 3: Fiberization (Fiber Formation)

• Combination of extrusion and attenuation.
• Extrusion: Molten glass passes out of the forehearth through a bushing plate (erosion-resistant platinum/rhodium alloy) with fine orifices (200 to 8,000).
• Bushing plates are heated electronically, and temperature is precisely controlled to maintain constant glass viscosity.
• Water jets cool the filaments as they exit the bushing at roughly $1204ºC/2200ºF$.
• Attenuation: Mechanically drawing the extruded streams of molten glass into fibrous elements called filaments, with a diameter ranging from 4 to 34 micrometers (one-tenth the diameter of a human hair).

Marble Re-Melt Process

• Molten marble material is shredded and rolled into marbles, which are cooled and packed.
• Marbles are taken to the fiber manufacturing facility, where they are inserted into a can and re-melted.
• Molten glass is extruded to the bushing plate to be formed into fiber.
• The bushing acts more like a furnace as it melts more of the material.

Aramid Fibers

• Commercial names: Nomex, Technora, Kevlar.
• Tensile strength seven to eight times that of steel wire.
• Excellent stability against temperature change.
• Light weight, high tensile strength, and resistance to impact damage.
• Applications: automotive industry for tire cords, timing belts, and brake friction materials; concrete reinforcing materials; high-performance ropes; marine and aerospace applications.

Grades (Kevlar)

• Kevlar 29
• Kevlar 49

Characteristics

• Highly crystalline aramid (aromatic polyamide) fibers.
• Lowest specific gravity.
• Highest tensile strength-to-weight ratio among current reinforcing fibers.

Disadvantages

• Low compressive strengths.
• Difficulty in cutting and machining.

Processing

• Synthesized in solution from the monomers 1,4-phenylene-diamine (para-phenylenediamine) and terephthaloyl chloride in a condensation reaction yielding hydrochloric acid as a byproduct.
• Extruding an acidic solution of a proprietary precursor from a spinneret.
• During filament-drawing process, molecules oriented in the direction of the filament axis.
• Weak hydrogen bonds hold them together in the transverse direction.
• Fiber is stretched and cold drawn to align the structure.
• Resulting filament is highly anisotropic, better physical and mechanical properties in the longitudinal direction than in the radial direction.

Reaction Process of Kevlar

• Chemical reaction diagram of 1,4-phenylene-diamine + terephthaloyl chloride resulting in polyparaphenylene terephthalamide (Kevlar).

$\text{NH2} - \text{C6H4} - \text{NH2} + \text{ClCO} - \text{C6H4} - \text{COCl} \rightarrow [-\text{NH} - \text{C6H4} - \text{NHCO} - \text{C6H4} - \text{CO}-]_n + 2n \text{HCl}$

Carbon Fiber

• i) Rayon
  • Conversion of cellulose fiber to graphite by controlled heat.
  • Decomposition process causes loss of weight; fiber lost weight shrinkage takes place during pyrolysis in range of 200-400°C as organic precursor decomposes to carbon.
  • Followed by carbonization (gradually ordering the structure).
  • Graphitization at higher temperature yielding 15-30% with low strength and stiffness.
  • Increase up to 50% by hot stretching in the temperature range of 2700-3000°C.
  • Increase the modulus and strength by developing orientation and porosity.
• ii) Polyacrilonitrile (PAN)
  • First stage involved stretching and oxidation.
  • Fiber are initially stretched 500-1300°C to improve molecular alignment.
  • Then heated in air while still under tension 200-280 °C.
  • Result in intramolecular rearrangement to give ladderlike polymer.
  • Followed by oxidation and called oxyPAN.
  • OxyPAN heated in nitrogen or argon at 900-1200°C produced low modulus, high strength carbon fiber but have pair degree porosity and low density.
  • Heating argon up to 2800°C cause graphitization and produced high modulus and increase the density.
• iii) Pitch
  • Derive from petroleum or coal tar-pitch that contains complex mixture of high molecular weight.
  • Tar pitch is heated above than 350 °C to polymerize to the 1000 of molecular weight.
  • The polymer is extruded through the holes in a hot-walled metal cylinder rotates known as melt spinning, orientates the hot mesophase pitch.
  • After oxidation to induce crosslinking, the fiber are carbonized up to 2000 °C.
  • The carbon yield is high at about 80%.
  • The degree of graphitization is control by heat treatment up to 2900°C.

Boron

• Chemical vapour deposition (CVD) process from boron trichloride on heated substrate.
• Involve high temperature with high melting point of tungsten subtract.
• Boron trichloride mixed hydrogen gas and decomposed according to:

$2BCl<em>3 (gas) + H</em>2 (gas) \rightarrow 2B (solid) + 6HCl (gas)$

• Boron exist in two crystalline form:
  • i) Rhombohedral
  • ii) Tetragonal
• After formation, fiber may be subjected to annealing to reduce residual stress.
• Chemical treatment is done to remove surface flows and increase strength.

SiC

• Establish silicon fiber is $SiC$

• Two methods of SiC production:

  • i) Deposition on substrate

    • Fiber produced from chemical deposition process.

    • Typical reaction of carbon containing silane to form SiC:

      $CH<em>3SiCl</em>3 (gas) \rightarrow SiC (solid) + 3HCl (gas)$

    • The subtract core is usually tungsten or carbon/Silicon.

    • The deposits consist of fine crystal of β-SiC.

    • Reaction occur at the Sic- core interface after prolong used at temperature above 1000°C.

    • The fiber produced is monofilament are thick and depending on the size of core.

  • ii) Precursor decomposition

    • Thermally decomposed of polydimethylsilane to produced SiC (Nicalon) fiber involved high pressure stage in autoclave followed by lower temperature vacuum distillation treatment.
    • Result low molecular weight of poly(carbomethylsilane) at about 1500.
    • The polymer is melt spun and oxidized in air at 200 °C to induce crosslinking.
    • The temperature is taken up slowly until 1300 °C to form β-SiC.
    • SiC is not pure with remaining of oxygen.
    • Growth of the SiC crystal present with the prolong heating at elevated temperature.

Natural Fibers

• Natural fiber (NF) are in increased demand from automotive and aerospace industries.
• Natural fibers can compete with synthetic glass fibers in terms of mechanical thermal and acoustic properties.
• Moreover, natural fibers are biodegradable and recyclable which make them eco-friendly and suitable for both circular economy and sustainable development.
• Jute, sisal and flax fibers are between the most successfully used natural fibers as reinforcements in composite structures.

Natural fibers processing Method

• Banana fiber
  • Sheaths are cut into strips and fed into a machine to extract the fiber and remove the pulp.
  • The fiber is then dried in the sun, bundled, and sent for processing.
  • The filaments themselves are 5 to 10 feet long
• Bamboo Fiber
  • There are two ways to process bamboo into a textile: mechanically or chemically.
  • The mechanical process includes crushing the woody part of the plant and then applying natural enzymes to break the bamboo cell walls, creating a mushy mass.
  • The natural fibers can then be mechanically combed out and spun into yarn.

Pineapple Leaf Waste Processing

• Pineapple leaf waste (substrate) is cut, oven-dried at 60 °C, and pulverized to 0.2 mm size to make pineapple leaf powder.
• Lignin, cellulose, and hemicellulose are the components.
• Laccase (enzyme) is mixed and maintained at appropriate temperature for enzyme-substrate reaction.
• Results in distorted structure, pretreated substrate, and residual enzyme.
• Characterized using XRD, SEM, and FTIR.

Oil Palm Empty Fruit Bunch Fiber Processing

• Empty fruit bunch (EFB) undergoes delignification to produce EFB powder.
• LTTMs (Low Transition Temperature Mixtures) are used for lignin precipitation.
• Solid-liquid separation occurs.
• Recovered cellulose fibers are obtained.
• Lignin Heirelle and EFB paper are produced.

Fiber Forms

Roving (Tows)

• Group of essentially parallel strands of fibers gathered into ribbon and wound onto cylindrical tube.
• Contain 12 to 120 individual strands.
• Multi-ends roving process begins by placing oven-dried forming packages into a creel.
• Ends are gathered together under tension.
• Collected on a precision roving winder with constant transverse-to-winding ratio.
• Used in spray-up fabrication process:
  • Roving is chopped with air-powered gun, which propels chopped-fiber strand into a mould.
  • Used for bathtubs, shower stalls, and marine applications.

Yarns

• Obtained by combining single strands by twisting and plying.
• Produced by simply twisting two or more single strands together and subsequently plying.
• Essentially involves re-twisting the twist strands in the opposite direction from original twist.
• Fine fiber strands of yarn from forming operation are air dried on the forming tubes to provide sufficient integrity for twisting operation.
• Twisting provides additional integrity before subjected to weaving process.
• Typical twist consists of up to two turns per 5 cm.
• The twisting and plying operations vary the strength, diameter and flexibility.

Z- and S-Twist Yarn

• Diagram illustrating Z-twist and S-twist yarns, and two-ply configurations.

Chopped Strands

• Continuous roving or chop strand can be chopped into short lengths.
• Available in different sizes for compatibility with most plastics.
• The amount and size influence integrity of strands before and after chopping.
• Used in spray-up process:
  • Chopped strands are sprayed simultaneously with liquid resin.
  • Build plastic parts on mould.
• Used for injection molding and extrusion before moulding.
• Used for many applications.
• Can be used in thermoset resin.

Mats

• Blanket of chopped strands or continuous strands laid down as a continuous thin flat sheet.
• Strands are distributed in a random pattern.
• Held together by adhesive resinous binders or mechanical bound.
• Chopped strands mat form by randomly depositing chopped fiber onto belt or chain and binding them with a chemical binder.
• Continuous strands mat is formed similarly without chopping.
• Uses less binder because of increase in mechanical entanglement.
• Reinforcing ability of chopped and continuous is the same, but having different handling and moulding characteristic.
• Continuous strand mat can be moulded to more complicated shape without tearing.
• Needled mat have some fiber vertically oriented.
• Softer and more easily draped than non-needle-mat.
• Distinguished by the binder used to hold them together, have high or low solubility.
• Solubility designates the rate of binder dissolution in a liquid resin matrix.
• Mat with high solubility of binder used in hand lay-up process or whatever rapid wetting is important.
• Low solubility of binder used in press moulding or whatever the flow of the liquid resin may wash away.
• Example: Mat form of kenaf fiber and glass fiber.

Woven Roving/Yarn

• Woven are produced by weaving fiber roving/yarn into fabric form.
• Manufacture by interlacing warp (lengthwise) and fill (crosswise) on conventional weaving looms.
• Variety styles of weaves to control thickness, weight and strength.
• Principal factors that define woven fabric style is fabric count, warp and fill yarn/roving and weave pattern.
• Weave configuration are depends on the requirement of the laminate.
• Plain or twill weaves provide strength in both direction.
• Woven roving is heavier and thicker than woven yarns fabric.
• Provide in plain weave although special weaves have been developed.
• Usually moulded by hand lay-up.
• Typically applications include boat hull and cargo containers.
• The fabric counts identify the number wrap and fills yarns per inch square.
• Warp run parallel to the machine direction and fill perpendicular.
• Fabric count plus the properties of wrap and fill yarns determine the fabric strength.
• The weave of the fabric refers how wrap and fill yarns are interlaced.
• Weave determine the appearance and some of the handling and a function characteristic of fabrics.
• The popular weave pattern is plain, twill, basket, crowfoot satin, long-shaft satin, leno

Weave Types

• Plain weave:
  • One warp end repetitively woven on one fill yarn and under the next.
  • The most stable construction, providing porosity and minimum slippage.
  • Strength is uniform in both direction.
• Twill weave:
  • One or more warp ends passing over under two, three or more fill packs under regular pattern.
  • Weave draped better than regular pattern.
• Basket weave:
  • Two warp end repetitively woven on two fill and under the next
• Leno weave:
  • Two or more parallel warp end interlocked
  • Tend to minimize flimsiness
• Five-harness satin weave:
  • A configuration having one warp end passing over four and under one fill yarn
• Crowfoot and long-shaft satin weave:
  • One warp end is woven over several successive fill yarns, then under one fill yarns
• Eight-harness satin fabric:
  • One warp end pass over seven fill yarn then under one fill yarn

Braids

• Ability to combine continuous fibers in an oriented pattern over a mandrel of nearly any shape or size.
• The braiding process creates an interlaced structure of continuous fibers, providing stability to the preform and desirable strength to weight properties in the final part.
• Fabrication of tubular and three-dimensional shapes is inherently efficient via braiding.
• Mechanised textile process which a mandrel is fed through the center of the braiding machine at a uniform rate
• Fibers moving from moving carriers on the machine braids at the controlled angle
• The machine carries working in pairs to accomplish over-under braiding sequence
• Complete coverage of the mandrel can be achieved during one pass using an interwoven layer consisting of roving lying at plus and minus the braiding

Braiding Process

• Diagram illustrating braiding with bias yarns and braiding angle β.

Mechanics

• Friction variation due to sliding of yarn during process

Knits

• Interlooping chain process of roving or yarn
• Knitting does not crimp the roving or yarn as weaving does
• Higher mechanical properties observed
• Easy to handle and can be cut without falling apart
• Basic types of knits:
  • warp unidirectional
  • weft unidirectional
  • bidirectional
  • triaxial
  • quadraxial direction axially-oriented continuous fiber in desire direction
• Used to reinforced flat section or sheet of the composites
• Complex 3-dimensional preforms have been created by using prepreg yarn

Preform

• Preform are the cut shape fibre forms of reinforcement in two dimensional materials
• Material that has undergone preliminary shaping but is not yet in its final form, e.g., mats, woven yarns, prepregs.
• In forming process, two dimensional materials are converted into three dimensional material.
• Material may be laid up in any orientation using many plies as necessary to achieved desired thickness.
• Ply drop-off can be handle ease and foam cores and metal insert can be incorporated
• Once the pattern are cut, they are assembled into the shape of the part can be produced
• Then, held together by 3 methods:
  • i) sewing- hand or machine
  • ii) stitching or quilting
  • iii) molten materials- uncatalyze solid epoxy resin is spray between ply