6.3.1- Reinforcing Materials Flashcards
Name the common reinforcing fibres in composite. (6 examples)
Nomex Fibreglass Aramid Kevlar Carbon Fibre Graphite.
What material is a DuPont development, is an infusible, wholly aromatic polymer made only as a fibre?
Nomex.
What properties does Nomex have? (3 examples)
1) High thermal stability
2) Temp Resistant
3) Flame Resistant.
What type of clothing is Nomex used in?
Flame proof suits.
Nomex in contrast to its chemical isomer (twin) Kevlar has what property?
Radiation Resistance.
How is Nomex honeycomb made?
Nomex paper sheets and phenolic resin.
What is fibreglass made of?
Strands of molten silica gel then spun together and woven into cloth.
What makes fibreglass so popular? (2 examples)
1) Low cost
2) Wide range of applications.
What are two negative characteristics of fibreglass compared to other fibre materials?
1) weighs more
2) less strength.
Name the two types of fibreglass used in aircraft.
E-glass- electrically resistant
S-glass- High tensile strength.
What is the density of fibreglass?
2.1 g/cm³.
Does fibreglass have high fracture toughness?
Yes.
Does fibreglass have good ‘wet out’?
Yes.
What makes Aramid recognisable?
The fibres are bright yellow.
What company is Aramid the registered trade name to?
DuPont.
What is Aramid an ideal material for?
Parts subject to high stress and vibration e.g. rotor blades. Also used in bullet proof vests.
What is Aramid the shortened name form of?
Aromatic Polyamide.
What is damage to Aramid repaired with?
Fibreglass.
The word aromatic does not refer to the smell in fact it means…
a benzene compound.
What is the density of Aramid?
1.45 g/cm³.
To what temperature is Aramid heat resistant?
260°c.
Kevlar is another development from what company?
DuPont.
What is the description of Kevlar?
Man-made organic fibre with high tensile strength and flexibility.
What are some disadvantages of Kevlar? (3 examples)
1) fibres absorb moisture
2) ‘easily’ compressed
3) difficult to cut- special scissors and drill bits.
Kevlar is ultra-violet sensitive, what happens to the colour?
Goes from gold to brown.
What is the density of carbon fibre?
1.8 g/cm³.
What is the thermal extension in longitudinal direction of carbon fibre?
Nearly 0.
Name any of carbon fibres characteristics. (5 examples)
1) High Strength
2) High E-module
3) Low fracture resistance
4) High temp resistance
5) Electrically conductive
Black graphite/ carbon fibre is…
Strong and stiff and is used for its rigid properties.
What material is graphite stronger than in compressive stress.
Kevlar
However graphite is more brittle
What problem does graphite have when bonded with aluminium and what is the solution?
It is corrosive, so a layer of fibreglass must be used to isolate the two materials.
Give the definition of Warp.
Threads running the length of fabric.
Give the definition of Weft/fill.
Threads running the width.
Give the definition of Selvage Edge (Selvedge).
Tightly woven edge opposite to the warp that prevents unravelling of the weave.
Give the definition of Bias.
Diagonal threads at 45° to the warp. It allows the material to take contours. Material can be stretched along the bias but not any other direction.
Give the definition of Unidirectional Fibre.
The fibres that run in the direction of the warp. To hold them together there will occasionally be transverse threads.
Give the definition of Bi-directional fibre.
Fibres run in two or more directions. Normally warp threads outnumber weft threads.
Give the definition of Mats.
A mat of chopped fibres, it does not have the strength of uni or bi-directional.
What makes Fabric Weaves better than unidirectional.
They are more resistant to fibre breakout, there are different types of weaves.
Name the 4 different matrix (bonding) materials.
Thermoplastics
Thermosets
Epoxy Resins
Prepreg.
Give the definition of a matrix material.
A bonding material that surrounds the fibre to give strength and take shape.
Newer matrix materials have what 4 characteristics?
1) Good stress distribution
2) Heat resistant
3) Chemical Resistant
4) Durable.
What are most new matric materials?
Epoxy resins.
Matrix’s are two part systems consisting of what?
Resin and a hardener (catalyst), which acts as a curing agent.
Resins are a type of plastic and are in two categories, what are they?
Thermoplastics
Thermoset.
Thermoplastics are heated to form a shape, is this shape permanent or not?
It is not permanent. So if you heat it again it’ll take a new shape.
What max temperature can thermoplastics be used up too?
750°F.
Give an example of a thermoplastic?
Acrylic.
Thermosets use heat to form and the shape is set….
Permanently. An example of this is bakelite.
What are epoxy resins used to bond?
Non-porous and dissimilar materials, like metal to composite.
What are Prepregs?
Fabrics that already have resin in.
How must prepreg be stored?
In a freezer to prevent the resin from curing.
What is the central assembly of a composite called?
Core material.
When the core is bonded between two thin-face sheets it provides what?
A rigid, lightweight component. It is known as sandwich construction.
Why are there different types of foams for core materials?
Different applications.
What is the biggest benefit to honeycomb?
Excellent strength to weight ratio.
What materials can be used to make honeycomb?
Aluminium, Kevlar, carbon, fibreglass, Nomex or steel.
What are the two methods of honeycomb fabrication?
Corrugation
Expansion.
Give a simple description of the corrugation process for making honeycomb.
Materials are converted placing one layer at a time and then pulled to reveal the structure.
Give a simple description of the expansion process for making honeycomb.
All bonds are made simultaneously rather than layer by layer.
How many sides are in a honeycomb shape and why?
6 sides, providing a high strength to weight.
In reference to honeycomb, what is the ribbon direction?
The direction in which it can be pulled apart.
What happens if you pull a honeycomb perpendicular to its ribbon line?
It separates.
What happens if you pull a honeycomb parallel to its ribbon line?
It doesn’t separate.
Name some other core materials. (3 examples)
Styrofoam, urethane and wood.
Name the 4 methods used to electrically bond composite components.
1) Flame spray
2) Bonding Jumpers
3) Aluminium wires woven into the top layer
4) Aluminium foil bonded to top layer.
What is the purpose of paint? (Structurally not literally).
To seal a surface after manufacture or repair.
Where would you find safety precautions for working with composites?
Material safety data sheet. (MSDS)
What information will you find in the MSDS?
Health precautions
Flammability
Ventilation requirements
Information for doctors
Explain a simple chain reaction process of making plastics.
Chains of monomers link to become a polymer. A catalyst is generally required.
When was polymerisation first understood?
1930.
During polymerisation one of the monomers double bonds are broken, what are these bonds called and what’s their purpose?
Valency bond, to form a link with the next monomer in the chain, thus making a polymer.
Are there any by-products of polymerisation?
No.
In polymerisation Ethylene becomes what?
Polyethylene. (PE)
In polymerisation styrene becomes what?
Polystyrene. (PS)
In polymerisation vinyl chloride becomes what?
Polyvinyl-chloride. (PVC)
Different monomers can be polymerised together too, what is this called?
Copolymerisation.
What are two examples of copolymerised products?
Styrene/ acrylonitrile (SAN)
Acrylonitrile/ butadiene/ styrene (ABS)
Besides polymerisation, what are two other methods of making plastics?
Polycondensation
Polyaddition.
Polycondensation does create by products, what are two examples of these?
Water
Hydrochloric acid.
What commercial plastics are used made using polycondensation?
Bakelite resins (thermosets)
Nylon (Polyamides)
Polyester.
How does polyaddition work (simple description only)?
There are no by products produced, but hydrogen gas atoms migrate making valence (spare) bonds.
What two important plastics are made using polyaddition?
Polyurethanes
Epoxies.
What are the benefits of adhesives? (4 examples)
1) Economical
2) Distribute stress
3) Eliminate fasteners
4) moisture and corrosion resistant.
What 4 factors effect the adhesive bond?
Resistance to slip or shrink
Malleability
Cohesive Strength
Surface tension.
What is the advantage of synthetic adhesives?
They can be used alone or to modify a natural adhesive, which gives them a wider range of applications.
Where are thermosetting adhesives used?
Metallic bonding of aircraft parts as they are heat resistant.
Where are thermoplastic resins used?
Bonding wood, glass, rubber, metal and paper.
Aerosil is a white powder, what is it used as?
A thixotropic agent, combined with resin, lacquer and even toothpaste.
Name 3 advantages of elastomeric adhesives.
1) Join dissimilar metals without galvanic corrosion
2) Provide same strength as welded joints
3) Provide noise reduction
There are a load more examples in the notes page 100.
What do contact adhesives use to bond?
Atmospheric pressure.
Solvent adhesives work by the solvent evaporating to cure, what is left behind to form the bond?
Plastics or resin.
Dispersion adhesives contain resins dissolved in water solutions, what is an example of these.
Wood glue/paste.
Film adhesives are similar to prepreg, what are they used to bond?
Metal to metal
Core to skin (composites)
What does a supported film adhesive contain?
Woven nylon carrier.
How must a film adhesive be stored?
Refrigerated at -18°c.
What is the definition of micro balloons?
Hollow phenolic balls with a range of diameters of 10-300 microns. They are mixed into resins.
How should resins be mixed?
In a wax free container adding accelerator to the resin base. It should take 3-5 minutes.
What must you do if a resin base has been stored in a freezer?
It must be allowed to reach ambient temperature as its heavier when cold.
What happens when you add a catalyst to resin?
It reduces the pot life.
