Composites Flashcards
What are composites
A composite is a material structure that consists of at least two macroscopically identifiable
materials that work together to achieve a better result.
Advantages of Composites
*Weight saving
*A high degree of freedom in form,
material and process
*Easy to colour
*Translucent
*A high degree of integration of
functions possible
*Strength, stiffness, thermal and
electrical resistance can be designed
*Low total maintenance costs
*Water- and chemically resistant
*Use of durable materials possible
*Automated manufacturing possible
Disadvantages of Composites
*High material costs
*Sophisticated computational
methods sometimes required
*Colour and gloss preservation
not always predictable
*Relatively limited knowledge on
structural behaviour of details
and connection methods
*Finishing not yet well developed
*Stiffness and failure behaviour
can be undesirable; sensitive to
temperature, fire and lightning
strike
*High costs of raw materials
*Sensitive to UV light
*Recycling is not yet well
developed
*Sometimes capital intensive
production methods (e.g.
automated methods)
Role of Fibres in composites
The fibres generally determine the strength and stiffness of the composite material
Most commonly used fibres
glass fibres and carbon fibres (carbon/graphite)
Most common type of glass
E-glass.
Types of glass
S-glass (increased strength and stiffness)
C-glass (chemically resistant)
D-glass (low dielectric constant and thus highly suitable for application in radomes, for example)
Raw materials used to manufacture carbon fibres
*PAN (polyacrylonitrile- manufactured product with well-defined properties and preferred for consistent quality)
*Pitch (natural product and is cheaper)
*Rayon/viscose (stronger than cotton, it’s lasting and breathable and versatile)
Properties of glass fibre
*High tensile strength.
*Dimensional stability.
*High heat resistance.
*Good thermal conductivity.
*Great fire resistance.
*Good chemical resistance.
*Outstanding electrical properties.
*Dielectric permeability.
*Compatibility with organic matrices.
*Great durability.
*Non-rotting.
*Highly economical.
Properties of carbon fibre
*Physical strength, specific toughness, lightweight.
*Good vibration damping, strength, and toughness.
*High dimensional stability, low coefficient of thermal expansion, and low abrasion.
*Electrical conductivity.
*Biological inertness and x-ray permeability.
*Fatigue resistance, self-lubrication, high damping.
*Electromagnetic properties.
*Chemical inertness, high corrosion resistance
Roles of polymers in composites
*The polymer acts as an ‘adhesive’ and
binds the fibres together. By encapsulating a fibre with polymer, the fibre can absorb
higher compressive loads
*The polymer transfers loads from one fibre to the other through shear stresses. External loads
are thus better distributed over the fibres in a composite than in a dry fibre bundle. When
one filament breaks, the load is distributed over the other filaments.
*The polymer largely determines the sensitivity of the composite to external influences such as moisture, chemicals, and ultraviolet light.
*It often determines the colour
and surface quality, opacity, and fire safety
What are thermoplastics
Thermoplastics are polymers that melt upon heating, becoming formable and regain
their solid shape upon cooling. Most commonly used unreinforced polymers are
thermoplastics. In molecular terms, thermoplastics consist of long entangled chains. Upon
heating, some freedom of movement is gained through the molecular movements.
What are thermosets
Thermosetting resins (in short: thermosets) do not melt on heating but ultimately
disintegrate. From a molecular point of view, most thermosets consist of relatively short
chains ensuring the non-cured polymers have very low viscosity
The difference between thermoplastics and thermosets
Thermoplastics melt when heated while thermosets disintegrate when heated.
The most commonly used thermosetting plastics
polyesters, vinylesters and
epoxies
