6.3 Composite And Non Metallic Flashcards
What is the term composite used to describe
Two or more materials that are formed to make a stronger structure than either material by itself
What 2 elements does a basic composite consist of
- Matrix (Adhesives or resin)
- A reinforcing material (Fabric)
What type of form would a matrix normally come in
A liquid form
What are the 4 main advantages of composites
- High strength to weight ratio
- Reduction in parts and fasteners
- Reduction of wear
- Corrosion resistance
What are the 2 main disadvantages of composites
- Expensive to repair
- Requires specialist equipment and people to carry out a repair
What are the advantages of nomex
High temperature resistance
What is nomex used for
Flame proof clothing
What are the 2 main types of fibreglass used
- S glass
- E glass
What properties do S glass and E glass have
S glass - Very High tensile strength
E glass - Highly resistant to electricity
What are the characteristics of aramid also known as aromatic polyamide
- Yellow in colour
- Light weight
- Excellent tensile strength
If aramid structures get damaged what can be used to repair them
Generally fibreglass
What is Kevlar mainly used for
Bullet proof vests and radial tyres
What are the main disadvantages of Kevlar
- The fibres absorb moisture
- not great in compression
What happens when Kevlar fibres are exposed to sunlight
They will turn from a gold/yellow to brown. Kevlar is very sensitive to sunlight
What are the biggest advantages of carbon fibre
- High strength
- Low density
- Low fracture resistance
- High temp resistance
What are the biggest disadvantages of carbon fibre
- Wears out steel cutting blades
- Requires skilled tooling and personnel to make
What is used between graphite and aluminium to help prevent corrosion
A layer of fibreglass
Resins are a type of plastic broken down in to which two categories
- Thermoplastic
- Thermoset
How do thermoplastics work
They can be reshaped with the addition of heat
How do thermosets work
Once they have been heated and set the shape is permanent. Composites such as carbon fibre are made with thermoset resins
When would epoxy resins be used
When bonding metal and composite or two dissimilar materials
What is the purpose of a honeycomb structure
Great strength to weight ratio
What can honeycomb constructions be made from
Aluminium, Kevlar, carbon, fibreglass, nomex and steel
What are the 4 main ways manufacturers use for dissipating electrical charge on composite components
- Flame spray
- Bonding jumpers
- Aluminium wires woven in to the top layer
- Thin Aluminium foils bonded on the top layer
What type of information would be found on the Material Safety Data Sheet (MSDS)
- Health precautions
- Flammability of the material
- Ventilation requirements
- Information for health professionals in event of emergency
How are plastics made
- Polymarisation
- Polycondensation
- Polyaddition
How does polymerisation work
A chemical reaction carried out in the presence of a catalyst which makes small molecules into a long chain
What important polymers are made by polycondensation
- Bakelite
- Nylon
- Polyester
What important polymers are made by Polyaddition
- Polyurethane
- Epoxies
What is the advantage of adhesives
Cheap, strong, efficient, corrosion resistant, eliminates the requirement of fasteners
What is aerosil
Used as a thrixatropic agent in resins to thicken them up
Must what happen to solvent adhesives for them to set
The solvent must evaporate
What are dispersion adhesives used for
Wood glue or paste
What are film adhesives
Come on a roll and are similar to pre preg
What are thixotropic agents
A thickening agent
What are the 2 most common thixotropic agents used
- Aerosil
- Micro balloons
When mixing resins how are the ingredients measured
By weight, mixing should take 3-5 mins
Where would phenolic resins be used
In cabins due to their fire resistance
What should not be mixed directly together to prevent a fire
Catalyst and accelerator. This will have an exothermic reaction
When investigating damage on a composite panel what documentation should be used
The SRM
What are the 3 categories of composite damage when it is initially assessed
- Allowable
- Repairable
- Not repairable
After the composite panel is initially assessed what would the 2 sub categories be in the SRM when assessing composite damage
- Skin not perforated
- Skin perforated
What is the difference between a scratch and a gouge
Gouges are deeper and wider than scratches and gouges affect structural strength and scratches don’t
What is the principle method for damage detection on a composite panel
GVI
What is abrasion
Scuffs, rubbing or scraping
Is carbon fibre electrically conductive
Yes
Are glass fibres and aramid fibres conductive
No
What are the advantages and disadvantages of holography
Advantage - Speed of inspection
Disadvantage - Long set up time
When are ultrasonics used in NDT
Quick and inexpensive assessment of composite parts
What is the purpose of radiography
Quick and inexpensive examination of composite structures
What are the 3 recommended types of repairs for composite structures
- Temporary repairs
- Permanent cosmetic repairs
- Permanent structural repairs
When prepping composite panels for repair how should the surface protection be removed
By mechanical means only, use of chemicals may damage the composite
When removing damage from composites how should it be done
By one layer at a time (scarfing)
What is wet lay up
Applying several layers of material impregnated with resin applied straight to the surface
What is shelf life
How long the product is good for in an unopened container
What material is used for vacuum bagging due to its high tensile strength
Nylon
What is the purpose of peel ply
Improves surface finish on a composite repair
What is the purpose of a caul plate when carrying out a composite repair
- Evenly distributes temperature
- Even out pressure over the whole repair
- To improve the flatness of the surface
What is a heater blanket
An electrical pad which regulates the temperature of a composite repair
