composites

Basics of Composite Materials

What is a Composite?A Composite Material signifies that two or more materials are

combined on a macroscopic scale to form a useful third material.

Wood is a common example of a natural composite, combining cellulose fibre and lignin.

Earliest known man made composites are Mud bricks. The combination of mud with straw gives the brick a good tear and squeeze resistance.

Alloy Vs CompositesAlloys also have the same definition as the composite

material.

Now how does a composite differ from an alloy?. When alloys are formed the individual components lose their individuality and they behave as a whole homogeneous structure.

While Composites individual components retain their nature and look as a heterogeneous structure.

Types of Composite Materials Fibrous Composite Materials

Laminated Composite Materials (e.g. Laminated Glass)

Particulate Composite Materials. (e.g. Concrete)

Components The Basic Components which make up a composite are

Reinforcements ( Fibres)

Matrix

Types of FibresGlass

Carbon

Aramid (Kevlar)

Boron

Ceramic

Metallic

Types of Matrices

Polymers

Metals

Ceramics

Function of the Fiber

Carry the load70 to 90% of load carried by fibers

Provide structural properties to the compositeStiffnessStrengthThermal stability

Provide electrical insulation

Function of the Matrix

Binds the fibers together

Provides rigidity and shape to the structure

Isolates fibers to slow crack propagation

Surface quality

Corrosion and wear protection for fibers

FibresGlass Fibres:

Glass is produced from silica sand, limestone, boric acid, and other elements.E-glass: Alumina-calcium-borosilicate glassS- glass: Magnesium alumino silicate glass

AdvantagesApplicable to wide range of geometries and sizes, Seamless

construction.Good strength and durability,Lower tooling costs, Increased design flexibility.Minimal maintenance &Corrosion resistant.Disadvantages:Mechanical properties are not as good as metals or other reinforcing

fibres.

Carbon Fibres: Types of graphite fibres include:Polyacrylonitrile (PAN)-Based fibresPitch-Based fibresRayon-Based fibresAdvantages:Excellent strength & stiffness,Excellent specific strength and stiffness, andCorrosion resistant.DisadvantagesSignificantly more expensive than glass fibres.Brittle behaviour.

Aramid Fibres: (Kevlar TM)Para aramid fiber characterized by high tensile strength and modulusAdvantages: Very high strength & stiffness,Very high specific strength & stiffness,Excellent impact resistanceHigh toughness.Corrosion resistant.Disadvantages:Significantly more expensive than glass fibres, andProperties may be affected by environmental factors

(e.g. ultra violet radiation).

Matrices Polymers The polymer matrices are the most commonly used and they offer good bonding characteristics when compared with other matrix types.

In commercial usage these polymers matrices are called Resins. There are different types resins available. Some of the most used resins are Polyester Epoxy Phenolic

Polyester Resin Polyester is a thermoset polymer that is formed from a condensation polymerization. Polyester has been widely used in commercial applications with fiberglass.Advantages: Low cost A wide assortment of di acids and diols can be used to

give physical and chemical properties.Disadvantages:Poor temperature capabilities, Poor weather resistancePoor mechanical properties (stiffness and strength) as

compared to advanced composites

Epoxy ResinEpoxy is a thermoset polymer that forms a strong rigidly cross-linked network of polymer chains. Epoxy has been widely used in commercial applications with fiberglass, graphite, and aromatic fibres.AdvantagesExcellent adhesionExcellent mechanical properties (strength and stiffness),Excellent chemical resistance, Excellent weather

resistance.Low shrinkage, Good fatigue strength.Good corrosion protection and Versatility in processing.

Disadvantages

Poor high temperature capabilities

Uncured resin is toxic

Poor handling properties (uncured)

Relatively expensive.

Phenolic resinPhenolic is a thermoset polymer with good high temperature properties. It is now being used as a composite resin with graphite, and aromatic fibresAdvantages:Good mechanical properties (strength and stiffness),Good thermal properties with an ablative nature, andGood processabilityDisadvantages:Absorbs moisture easily,Brittle behaviour, andRelatively expensive (more than epoxies).

Laminated Fibre Reinforced Composites The laminated fibre reinforced composites combine the

laminated and fibrous composites to produce high strength and stiffness properties.

These composites consists of stack of layers or sheets called “lamina”.

The lamina are the building blocks which has fibres aligned in a matrix.

The stacks of lamina are called a laminate which make up the composite.

Sandwich CompositesSandwich panel is also a kind of layered composite. It

consists of ‘faces’ and ‘core’With increase in thickness of core, its stiffness

increases as seen in the most common sandwich panel ‘honeycomb’.

Faces:-They are formed by two strong outer sheets.Core:-Core is layer of less dense material.Honeycomb:-Structure which contain thin foils forming

interlocked hexagonal cells with their axes oriented at right angles in the direction of face sheet.

Manufacturing Techniques

Some of the manufacturing methods of composites are

Hand Lay up Method

Vacuum bag Moulding Process

Filament Winding Process

Sheet Moulding Compound

Hand Lay Up Process

• Advantages: low cost tools versatile: wide range of products

• Disadvantages: time consuming easy to form air bubbles and disorientation of fibers inconsistency

Vacuum Bag Moulding Process

Advantages: simple design any fiber/matrix combinationok with cheap mold materialbetter quality for the cost

Disadvantages: cannot be heated up too muchbreeder clothe has to be replaced frequentlylow pressure (760 mm Hg the most)slowest speedinconsistency

Filament Winding ProcessProcess by which continuous reinforcing fibers are

accurately positioned in a predetermined pattern to form a shape (usually cylindrical).

Use machine to wrap composite around mandrelMandrel is then removed, leaving hollow composite

partAngles generally set at -45,0,+45

Advantages: using existing textile processes. quick, easy to handle package.parts can have huge size.

Disadvantages: spinning speed is limited due to resin penetration

and splashing, traveler speed and yarn breakage.curing by heat is not easy to apply.shape of the products limited (only cylindrical

possible).

Sheet Moulding Compound

Sheet moulding compound (SMC) refers to both a material and a process for producing glass fibre reinforced polyester resin items.

The material is typically composed of a filled, thermosetting resin and a chopped or continuous strand reinforcement of glass fibre

The glass fibre is added to a resin mixture that is carried onto a plastic carrier film.

After partial cure, the carrier films are removed. The sheet moulding material is cut into lengths and placed onto matched metal dies under heat and pressure

AdvantagesHigh productivity thus inexpensiveconsistencyExcellent part reproducibility. Minimum material scrap. Excellent design flexibility.

Disadvantageslow volume fraction.Only board can be made.

Cure

To irreversibly change the properties of a thermosetting

resin by chemical reaction, i.e., condensation, ring,

closure, or addition. Cure may be accomplished by

addition of curing (cross-linking) agents, with or without

heat.

Oven Cure

Once the layup is accomplished and the part is debulked, we can put it into a furnace to cure the resin. Typically the parts are instrumented with a thermocouple to track the temperature of the part in the oven. The temperature of the oven is increased until the thermocouple registers the correct curing temperature and then the part is “soaked” at temperature until it is cured.

Autoclave

Autoclave is a pressure vessel with pipework to allow a vacuum to be maintained in the bagged work piece.

Temperature control is normally by gas- or electric-heating

AdvantagesLight Weight - Composites are light in weight. Their

lightness is important in automobiles and aircraft, for example, where less weight means better fuel efficiency

High Strength - Composites can be designed to be far stronger than aluminium or steel. Metals are equally strong in all directions. But composites can be engineered and designed to be strong in a specific direction.

Strength Related to Weight - Strength-to-weight ratio is a material’s strength in relation to how much it weighs. Composite materials can be designed to be both strong and light.

High-Impact Strength - Composites can be made to absorb impacts—the sudden force of a bullet, for instance, or the blast from an explosion.

Design Flexibility - Composites can be moulded into complicated shapes more easily than most other materials. This gives designers the freedom to create almost any shape or form.

Part Consolidation - A single piece made of composite materials can replace an entire assembly of metal parts.

Nonconductive - Composites are nonconductive, meaning they do not conduct electricity.

Low Thermal Conductivity - Composites are good insulators—they do not easily conduct heat or cold.

Radar Transparent - Radar signals pass right through composites, a property that makes composites ideal materials for use anywhere radar equipment is operating, whether on the ground or in the air

Corrosion Resistance - Composites resist damage from the weather and from harsh chemicals that can eat away at other materials

Disadvantages

High cost of raw materials and fabrication.Composites are more brittle than wrought metals and

thus are more easily damaged.Transverse properties may be weak.Matrix is weak, therefore, low toughness.Reuse and disposal may be difficult. Inspection Methods are costly.

Applications in Aerospace- Civil

Airframes, Wing Spars, Fuel Tanks, Helicopter Rotor Blades, Engine Nacelles, Nose Cone & Landing Gear Doors

Tunnel supports, Airport facilities such as runways Roads and bridge structures , Marine and offshore

structures Concrete slabs Architectural features and structures such as exterior

walls, handrails, etc.

In Sports

Canoes and Kayaks

Vaulting Pole

Golf & Polo rods

Archery equipment

Hand gliders

Wind surfer boards

Chemical & Nuclear Reactors

Double-wall FRP vessels with an early warning system for leakage detection

Underground storage tanks

pumps and blowers, columns.

As Cladding material and Control Rods

Marine & Electrical Propellers vanes, Fans and Blowers

Gear cases

Valves and Strainers Structures for overhead transmission lines for railway

Power line insulators

Lightning poles

Automotive

Fibre Glass/Epoxy Springs for Heavy Trucks and Trailers

Rocker Arm Covers, Suspension Arms, Wheels and Engine Shrouds

Filament-Wound Fuel Tanks

Electrical Vehicle Body Components and Assembly Units

Valve Guides

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