6.3.1 Flashcards
What is nomex (reinforcing material) used in?
Flame resistant clothing and radiation resistance
What is fibreglass made from?
Small strands of molten silica glass that are spun together to create a cloth
What is the benefit of E-glass?
Highly resistant to electricity
What is the benefit of S-glass?
Very high tensile strength
What colour is Kevlar and aramid fibres?
Yellow
How would aramid fibres be repaired?
With fibreglass
What is the main disadvantage of Kevlar?
It is sensitive to the environment (moisture and sunlight)
What is used to stop the corrosion between carbon fibre and aluminium?
A layer of fibreglass to isolate them
What direction force is Kevlar stronger in?
Tension
What direction of force is graphite/ carbon fibre stronger in?
Compressive
What is the warp in fabric orientation?
The length of the fabric as it comes off the roll
What is the weft/fill of fabric orientation?
It runs perpendicular to the warp fibres
What is the salvage edge in fabric orientation?
It runs parallel to the warp to prevent the edges unraveling
What is the bias in fabric orientation?
It runs 45° to warp
What direction can fabric be stretched in?
In the bias but not along the warp or weft/fill
What is meant by unidirectional fibres in relation to fabric orientation?
major fibres which run in direction of the warp
What is meant by bi-directional fibre in relation to fabric orientation?
When fibres run in multiple different directions
What are mats in relation to fabric orientation?
They consist of chopped fibres
What are fabric weaves?
The different varieties of fibre cross hatching
What are the two parts to a resin?
A resin and a hardener (catalyst)
What are the two categories of resins?
Thermoplastics and thermosets
What is special about a thermoplastic resin?
It can constantly change its shape when heated is added
What temperature must thermoplastic resin not exceed unless you’re changing its shape?
750°F
Name an example of a thermoplastic?
Plexiglass/acrylic
What is special about thermoset resin?
Once heated and set it cannot be changed
What are most composite structures bonded with?
Thermoset resins
Name an example of a thermoset resin?
Bakelite
What type of resin are epoxy resins?
Thermoset resin
Where are epoxy resins mostly used?
When bonding metal to composite
What is prepeg an abbreviation of?
Pre-impregnated fabrics
What is prepreg?
Fabrics that already have resin impregnated in them
Why does prepreg need to be stored in a freezer?
To prevent the resin curing at room temperature
What is a sandwich construction?
When a core material is bonded between two thin face sheets
What are the two types of honeycomb fabrication?
Corrugation process and the expansion process
What is the main advantage of honeycomb materials?
Very high strength to weight ratio
What is honeycomb ribbon direction?
The direction in which the length of strips make up the core
What happens if you pull honeycomb perpendicular to the ribbon direction?
It will separate
What happens if you pull honeycomb parallel to the ribbon direction?
It is impossible to separate
What are the four ways to disperse electrical charge on composite components?
- flame spray
- bonding leads
- aluminium wires woven in
- thin aluminium foil bonded in
What must be used when working on composite materials?
Material safety data sheets (MSDS)
What is an adhesive?
It’s a substance used to bond two or more surfaces together
How does surface tension affect adhesion?
It determines how far the adhesive penetrates the tiny depressions in the surface
What happens to thermosetting adhesives when a catalyst or heat is added?
It will set into a hard solid adhesive
What happens when heat is reapplied to a thermoplastic resin?
It will go back to a soft resin to be applied again
What is special about solvent adhesives?
The solvent has to evaporate to cure the adhesive
What is a dispersion adhesive?
An adhesive that dissolves in a water solution
What is a resin adhesive?
An adhesive that can only cure by a chemical reaction
What is film adhesives?
A material that has adhesive on both side already
What temperature must film adhesives be stored at?
-18C
What is foaming adhesive film?
An adhesive sheet that expands during curing to fill gaps
What is a thixotropic agent?
It is an agent used to thicken a liquid
How should resins be mixed?
In a wax free container by adding the accelerator to the resin base
How long should the mixing process of resins take?
3 to 5 minutes
If a resin base has been stored in a freezer what should you do?
Allow to reach ambient temperature before weighing and mixing
What happens if you add too much catalyst to resin?
Decreases in strength of mix and could combust
Why cant you store pre mixed resin?
Because the catalyst massively reduces the shelf life
Why and Where are epoxy resins used?
External components due to good metal adhesion
Why and Where are phenolic resins used?
Cabin furnishing due to their low toxicity in a fire
Why and where are polyester resins used?
Used with glass fibre to for a strong durable material
Why and where are vinyl Ester resins used?
Repairing fuel tanks due to high corrosion resistance
Why must you never add catalyst and accelerator together?
It will create a large exothermic reaction resulting in fire and explosions
Why is it important to get the correct ratio of resin and hardener?
if the ratio is wrong then unreacted resin/hardener will be left in the cured resin
If you cant find the correct mixing ratio who should you contact?
The manufacturer
How do you speed up a cure for room temperature resins?
Increase the atmospheric temperature
Why is it important to remember epoxy rein cure by linking molecules together?
Because the exact amount of molecules must be present to get the best cured resin
What does phr mean in relation to resin ratios?
Parts per hundred resin
What is mechanical hooking?
When adhesive must penetrate into cavities before curing, otherwise trapped air will reduce the strength of adhesion
What is the phenomenon of surface wetting?
The contact angle that is formed between droplet of liquid and a solid
What is used to investigate the damage to a composite material?
The structural repair manual
How do you tell if damage is acceptable?
Using the structural repair manual
What are the two main categories of damage to a composite material?
Skin perforated or skin not perforated
What is delamintaion of a composite material?
When the reinforcing material layers separate from the matrix
What is BVID?
Barely visible impact damage
What is deboning in composites?
When the skin stops adhering to the core material
What is used to determine the amount of barely visible impact damage?
Close visual inspections and NDT
What is the definition of a scratch?
Contact with a sharp object and only surface fibres are affected
What is a gouge?
Wider and deeper than a scratch, several plies are affected
How would you repair a gouge?
Remove damaged plies then performing a hand lay up
What is classified as abrasion damage?
Small damage to the surface protection by scuffing or scraping
How and why is abrasion repaired?
Restoring the protective surface to prevent fluid ingress
What happens to a non conductive material if it is hit by lightning?
It will be blown out and the core will be vaporised
What happens to a conductive material if it is hit by lightning?
Small damage to the material will be found
Where is erosion most likely to take place?
Leading edge surfaces
During a repair why is it important to ensure it is completely dry?
Heating of the liquid could cause delamination
What must be done if a dent is found?
NDT
When tap testing honeycomb what must you do?
Tap test both sides of the honeycomb
What are the three types of repairs?
- Temporary repair
- permanent cosmetic repair
- permanent structural repair
Where are repair instructions found?
Structural repair manual
How is surface protection removed ready for repair?
Mechanical methods only
Why cant chemical strippers be used to remove surface protection?
It may cause deterioration of the resin
What is the name of the technique used to remove composite materials?
Scarfing
If damage reaches the core material of a composite what must you do?
The damaged core should be routed out carefully and replaced with a similar material
If you’re repairing honeycomb with more honeycomb what must you ensure?
That the honeycomb is joined in the same ribbon direction
What should you not do when cleaning a repair surface?
Apply cleaning agent directly on the repair surface
What is meant by pot life?
How long the resin is usable once mixed
What is meant by shelf life?
How long a resin can sit in storage in an unopened container
What is meant by resin rich?
Too much resin is used
What happens to the composite if it is resin rich?
Makes it brittle and heavy
What is meant by resin starved?
There is too little resin
What is the result if a composite is resin starved?
It wont be able to correctly transfer stresses to the fibres
When mixing resin into a fabric what must you take care with?
To not distort the weave of fabric
What are the two types of wet lay up?
Pre-peg and wet application
What material is used for vacuum bagging?
Nylon