BONDING & COMPOSITES

GROUP MEMBERSMATHAN RAJ A/L MANIMARENTHEVENDRAN A/L GUNASELAN

What is Composite?

Bonded structure

using chemical methods

Combinations of 2 or more elements

– differ in

composition

Combinations of 2 or more elements –

differ in identities & properties

Multiphase material with significant proportions of phases.• Continuous phase (Matrix) – to transfer stress to

other phases and protect phases from environment.• Dispersed/reinforcing phase – purpose is to enhance

matrix properties.• Classification : Particles, fibers, structural.

ADVANTAGE

High Strength to Weight Ratio

Customizable Stiffness &

Strength

Corrosion Resistance

High Fatigue Resistance

Complex shape built using less

mould

Ease of Maintenance

Absorb radar microwaves

(stealth capability).

Simplify and reduces

inspection time.

DISADVANTAGE

Manufacture & repair cure time

Mechanical properties affected by temperature and moisture

Difficulty, reliability issue & cost in inspection

Low bearing and interlaminar strength

High material cost

Poor energy absorption and impact damage

May require lightning strike protection

MATRIX

Classification:• Metal Matrix Composite (MMC)• Ceramic Matrix Composites (CMC)• Polymer Matrix Composite (PMC)

Polymer Matrix Composite (PMC) or Fiber-Reinforced Plastics• Fibers (discontinuous and dispersed phase) + plastic matrix

(continuous phase)• Properties:

• Strong and stiff• High specific strength (strength to weight ratio)• High specific stiffness (stiffness to weight ratio)(Brittle and abrasive, less toughness and chemically degradable when exposed to the atmosphere)

• Percentages of fibers (by volume)–10% to 60% (limited by the average distance between adjacent fibers)

• Highest practical fiber content is 65% ( higher percentage can lower physical properties)

*Hybrid when more than one fiber is used.

REINFORCING FIBERS

• GLASS• GRAPHITE• ARAMIDS (KEVLAR)• BORON• Others

• (Nylon, Silicon Carbide, Silicon Nitride, Aluminium Oxide, Sapphire, Steel, Tungsten etc.0

Fiber Size and Length

• Mean diameter < 0.01mm• Oriented in longitudinal direction (strong and stiff in tension)• Small cross section (low defects exist)• Classified

• Short fibers (aspect ratio 20 – 60) : Improve mechanical properties as a result of increasing the average fiber length.

• Long fibers (200 – 500) : transmit load through the matrix better, commonly used in critical applications, particularly at elevated temperature.

Matrix Materials

• Thermosets – Epoxy (most commonly used ~ 80% of PMC), polyester, phenolics, fluorocarbons, polyethersulfone, silicon and polyimides

• Thermoplastics –Polyetheretherketone

Functions

• to support the fibers in place, transfer stresses to them.• to protect the fibers against physical damage and the environment.• to reduce the propagation of cracks, by virtue the greater ductility

and toughness.

Properties of Reinforced Plastics

• mechanical and physical properties depends on :• Type• Shape• Orientation of the reinforcing material • Length of the fibers• Volume fraction (%) of the reinforcing material

• type and amount of reinforcement effect the physical prop. and resistance (fatigue, creep and wear)

• Highest stiffness and strength = fibers are aligned in the direction of the tension force

• strength of the bond between the fiber and the polymer matrix

Metal Matrix Composite (MMC)• An alloy (Aluminium, Al-Lithium, Magnesium, Copper,

Titanium and superalloys)• Three types of such composites

1. dispersion-strengthened - in which the matrix contains a uniform dispersion of very fine particles (10–100nm)

2. particle-reinforced – particles of sizes greater than 1μm are present

3. fibre-reinforced - fibres may be continuous through out the length of the component, or less than a micro metre in length, and present at almost any volume fraction, from 5 to75%.

• Reinforcement materials• Graphite, Boron, Alumina, SiliconCarbide, AluminiumOxide,

Molybdenum, Tungsten

Advantages1. Higher elastic modulus2. Resistance to elevated temperature3. Higher toughness and ductility

Disadvantage4. Higher density thus greater difficulty in processing

the parts

Ceramic Matrix Composite (CMC)Properties:1. Strong and stiff2. Resist high temperatures.3. Lack toughnessMatrix materials (retain strength up to 1700 oC): Silicon Carbide, Silicon Nitride, Aluminium Oxide and Mullite(Al,Si,O2)Carbon-CarbonMatrixComposites – strength up to 2500 oC (Carbon and Aluminium Oxide)

Fabrication of Composite Materials

• Particulate• Laminar

I. Hot or Cold Roll BondingII. Explosive BondingIII. Adhesive BondingIV. Sandwich Structures

• Fiber-reinforced

Processes Designed To Combine Fibers and Matrix

• Prepregs• Sheet Molding Compounds (SMC)• Bulk Molding Compounds

Fabrication of Final Shapes from Fiber-Reinforced Composites

Pultrusion

• Continuous process that is used to produce simple shapes of uniform cross section eg: round, rectangular, tubular, plate, sheet and structural products.

• Extremely high strengths products (reinforcement can be up to 75% of the final structure).

• Crosssection – up to 1.5m wide and 0.3m thick.

Reinforcing fibers

Bundles of continuous reinforcing fibers are

drawn through a bath of thermoset polymer resin

The impregnated material is then

gathered to produce a desired cross-sectional shape

The material is then pulled through one or

more heated dies, which further shape the product

and cure the resin

Upon emergence form the heated dies, the product is cooled by air or water, cut

to length and then fabricated into products

e.g fishing poles, ski poles

Filament Winding

Resin-coated/ resin impregnated, high

strength, continuous filaments, bundles or

tape made from fibers of glass, graphite, boron,

Kevlar or similar materials can be used to

produce cylinders, spheres, cones and

other container type shapes that have

exceptional strength to weight ratios

The filaments are wound over a form or mandrel, using

longitudinal, circumferential, or helical patterns or combination in order to take advantage of their

highly directional strength properties

By adjusting the density of the

filaments in various locations and selecting the

orientation of the wraps, products can be designed to have

strength required and lighter weight in less

critical regions

After winding, the part and mandrel are placed in an

oven for curing, after which the product is

stripped from the form

The matrix (epoxy type) binds the

structure together and transmits the

stresses to the fibers

Final curing

Involving elevated temperature and possibly applied pressure

Multiple reinforcement sheetsPassed through a resin bath, faced with non stick sheet and passed through squeeze rolls.

For tubingThe impregnated stock is wound around a mandrel of the desired internal diameter

Pre preg sheets or reinforcement sheetssaturated in resin then compressed under pressure on the order of 7MPa.

Lamination and Lamination Type ProcessesLaminated materials can be produced as sheets Tubes rods

Lamination Type Processes

Vacuum - bag moldingAir pressure holds the laminate against the mold while the resin cures.Curing generally at room temperature but moderate elevated temperature may be used

Pressure bag moldingA flexible membrane is positioned over the female mold cavity and pressurized to force the individual plies together and drive out entrapped air and excess resin

Compression moldingFor large production quantities and high qualityThe dies are heated and curing occurs during the compression operation

Other processes

Spray Mold

ing

• No desired properties required.• Mixing chopped fibers and catalyzed resin and spraying the combination on to a mold form.• Rollers or squeegees can be used to remove entrapped air and work the resin in to the

reinforcement.• Room temperature curing, sometimes elevated temperature is used to accelerate the cure.

Sheet

Stamping

• Thermoplastic sheets reinforced with non woven fiber–heated and press-formed.

Injection

Molding

• Chopped or continuous fibers are placed in a mold cavity that is then closed and injected with resin

Fabrication of Fiber – Reinforced Metal Matrix Composites

Continuous fiber metal matrix composites can be produced by variations of filament winding, extrusion and pultrusion.

Fiber reinforced sheets can be produced by electroplating, plasma spray deposition coating or vapor deposition of metal on to a fabric or mesh, then shaped and bonded.

Fabrication of Fiber – Reinforced Ceramic Matrix Composites

Common method includes chemical vapor deposition or chemical vapor infiltration of a coated fiber base.

Hot pressing technique.

Secondary Process and Finishing

Can be processed further with conventional equipment (sawed, drilled, routed, taped, threaded, turned, milled, sanded and sheared).

Precautions should be used to prevent the formation of splinters, cracks, frayed or delaminated edges. Sharp tools, high speed sand low feeds are generally required.

Quickly remove cutting debris–prevent cutters becoming clogged.

Abrasive materials (in nature)–dull most conventional cutting tools. Use diamond or polycrystalline diamond tooling to achieve realistic tool life. Use abrasive slurry–smooth surface.

Lasers and Water Jets as alternative cutting tools

Adhesive Bonding

A variety of joining methods can be used to provide the assemblyfunction.

Alternative joining methods include adhesive bonding, welding,brazing, soldering, and mechanical fastening.

Adhesives are available in several forms: liquid, paste, solution, emulsion, powder, tape and film.

• Adhesives thickness ~0.1mm.

• Adhesive application may be required due to the following properties.

a. strength (shear and peel)b. toughnessc. resistance to various fluids and chemical.d. resistance to environmental degradation (heat, moisture)e. ability to wet the surfaces to be bonded

Type of Adhesives

Natural adhesives

starch, dextrin, soya flour, animal products

Inorganic adhesives

Sodium silicate and magnesium oxy chloride

Synthetic organic adhesives

thermoplastics, thermosets

Design for Adhesive Bonding

Butt joint design Lap joint design

Strap joint design