Fibre Reinforced Metals (FRM)

FIBRE REINFORCED METALS (FRM)

Metal Matrix Composites (MMC) provide high temperature resistance, non-flammability and greater resistance to degradation by organic fluids when composed to polymer matrix composites.

Fibre reinforced MMCs contain continuous / discontinuous fibres or whiskers in a ductile metal matrix.

The ductile matrix materials are aluminium, magnesium, copper, titanium and super alloys. The continuous fibres are graphite, boron, alumina or silicon carbide. The whiskers of silicon carbide and silicon nitride are also used as reinforcement.

These composites offer high strength and stiffness, high coefficient of thermal expansion and enhanced resistance to fatigue, abrasion and wear. They also give high heat resistance and improved electrical and thermal conductivity.

Applications

• Aluminium reinforced with alumina fibres has been used in automotive connecting rods and pistons.

• Aluminium reinforced with boron fibres has been used extensively in aerospace applications, including struts for the space shuttle.

• Aluminium reinforced with SiC whiskers are used in girl aircraft wing panels.

• Copper based alloys reinforced with SiC fibres are used yem for producing high strength propellers for ships.

• Titanium reinforced with SiC fibres are considered for turbine blades and discs.

• Super alloys reinforced with tungsten maintain their strength at high temperatures. They are used in jet engines and turbine blades.

Advantages and limitations of composites

Advantages

1. Composite materials exhibit superior mechanical properties such as high strength, toughness, elastic modulus, fairly good fatigue and impact properties.

2. As FRP's are lightweight materials, the specific strength and modulus is much higher than conventional materials.

3.  In aeroplanes power to weight ratio is about 16 with composites compared to 5 with conventional materials. This helps in weight reduction and more pay load carrying capacity.

4.  Fabrication of composites to any desired shape and size can be achieved with ease.

5. They exhibit good corrosion resistance.

6. Assembly of components made of composites is much easy and quick.

7. The utilisation of materials can be done effectively to get the desired properties.

8. Not much sensitive to thermal shocks and temperature changes.

Limitations

• Polymeric composites cannot be used for high temperature application.

• Cost of composites is somewhat higher than many conventional materials.

Application of composites

Composite materials find a wide variety of applications in many fields. Some of the important applications are discussed below.

1. Commercial aircraft

Used for air conditioning duct, radar dome, landing gear door, seats, floorings, window reveals, ceiling panels, propeller blades, nose, wing body, elevators, aileron, air brake, portable water tank, etc.

2. Military aircraft

Used for speed brake, rudder trunnion, forward fuselage, elevators, ailerons, landing gear doors, horizontal stabilizers, etc.

3. Missiles

Used for remote piloted vehicles, filament wound rocket motors, wings, motor cases, etc.

4. Space hardwares

Used for antennas, structs, support trusses, trusses for telescopes, storage tanks for gases and fluids at cryogenic temperatures, etc.

5. Automobile and trucks

Used for drive shafts, bumpers, door and window frames, starter motor commutators body panels, radiator and other hoses, timing and V belts, drive chains, etc.