6.3 Aircraft Materials Composite Flashcards
Some modern aircraft have what percentage of composite structure?
50%
What does the term composite mean?
Two or more materials combined to make one much stronger material.
What is the simplest composite composed of?
Matrix- bonding
Reinforcing material
What third material can sometimes be added?
A core material such as honeycomb
What is the tensile strength of composite compared to steel or ally?
4-6x
What is the primary load carrying element of composites?
The fibre
What are some of the most common fibres used?
Fibreglass
Aramid
Carbon fibre
Boron
Ceramic
Is fibreglass a conductor?
Yes
What are the two most common types of fibreglass?
E glass
S glass
What is E glass fibreglass?
Used for electrical applications due to its huge resistance to flow and is the most common fibreglass.
What is S glass fibreglass?
High strength
What does Aramid stand for?
Aromatic Polyamide Polymer
What is aramid more widely known as?
Kevlar
What are the two most common aramids used?
Kevlar 49 and Kevlar 29
Where is aramid used to be a benefit?
Areas where impact resistance is req.
What is the density of aramid?
1.35g/cm
What is the heat resistance of aramid?
260 degrees c
What is the negative of aramids?
They can absorb liquids
What happens when aramid is exposed to UV?
It turns brown.
What is the differences between aramid and carbon fibre?
CF has stronger compressive strength but is more brittle than aramid.
To what metal is carbon fibre galvanic?
Aluminium, a sheet of fibreglass must be used to isolate them.
How are boron fibres made?
Applying a small amount of vaporised boron onto thin tungsten or carbon wire.
What is the most common use for boron?
Used to repair cracked aluminium parts and panels.
Where are ceramic fibres used?
High temps up to 1200 degrees c
What is the warp?
Lengthwise threads
Is the fabric normally stronger in the warp or weft?
Warp
What is the weft?
Width
What is the selvedge edge?
Tightly woven edge that runs down the warp to prevent unravelling
What happens to the selvedge edge before the fabric is used?
It is removed
What is the bias?
The diagonal, facilitates manipulation of the fabric
What four different styles of lay up are used?
Unidirectional
Bidirectional
Quasi-isotropic
Mats
What are unidirectional fibres?
The major fibres run in the warp direction with only occasional traverse threads to hold it together.
What are some examples of unidirectional lay up?
Glass fibres
Carbon fibres
Aramid fibres
What are bidirectional fibres?
Where the threads run in two directions. Warp normally outnumbers the weft threads.
What is a quasi-isotropic lay up?
When the layers are at 45 degrees to the previous layer, such as carbon fibre.
What are some of the most common weaves?
Plain
Twill
Satin
What does twill weave provide?
Superior wet out
Why are polyester resins not suitable for any loads?
Too brittle
What is the modern resin matrix?
Epoxy
Resin matrix systems are a type of plastic, what two types are there?
Thermoplastic
Thermosetting
What is an example of thermoplastic parts?
Windshields and side windows
What is key about anything made in a thermosetting process?
It is irreversible.
Are epoxy resins thermosetting or thermolastics?
Thermosetting
When unmixed what is the shelf life of epoxy resin?
One year at 22 degrees c
What do prepreg fabrics help eliminate?
Error during mixing and application process
Although prepreg has lots of pros what are some of the cons?
Must be stored frozen
Full rolls must be purchased
More expensive
What are the two ways to construct fibre reinforced composite?
Laminate
Sandwich
What is an interply hybrid?
When two different fabrics are used in a laminate to combine their characteristics.
What is a sandwich construction?
When the core is bonded with two thin fibreglass sheets.
What is the benefit of sandwich construction?
It is approx 10 times stronger than laminate and only 6 times heavier
What are the two most common core materials?
Honeycomb and foam
What is honeycomb normally made from?
Aramid paper
Most honeycombs are hexagonal but what two other forms are available?
Flexi core and over expanded core
What are some foam cores made of?
Polystyrene
Polyvinyl Chloride
Polyurethane
What range of uses do plastics have?
Structural components to decorative trim to windows.
What is polyetherketone (PEEK)?
Semi-crystalline organic polymer
What are some of the characteristics of PEEK?
Superior mechanical and thermal properties
Creep resistance
Low flammability
What is the operating temp of PEEK?
Up to 232 degrees c
What is thermosetting polyimide used for?
Stand offs, and a variety of moulded parts
Where is PAI (polyamide-imide) used?
Aircraft thrust reverser assemblies due to its high mechanical strength which it keeps up to 260 degrees c
What two forms can transparent plastic be formed in?
Monolithic
Laminated
What is a monolithic plastic sheet?
Made in a single layer
What are clear laminated plastic sheets bonded with?
Layer of clear resin material.
How are thermoplastics marked?
Heated dyes
What is heated dye marking not suitable for?
Tubular sections
Celluloid and vinyl acetates
How are thermosetting plastics marked?
Vibro-etching (preferable)
White paint and marking ink
How are transparent plastics marked?
Ideally not at all.
What two forms are sealant available in?
One part
Two part to be mixed
What are some of the applications of sealant?
Fuel tanks
Skin joins
Aerodynamic smoothing
What is film adhesive?
It pre-blends the resin and catalyst on a film of plastic.
What are adhesive films used for?
Bond patches to a repair area.
What is another form of adhesive primarily used to bond foam to honeycomb?
Foaming adhesive, can also be used to permanently install fasteners.
Where is detection of defects in composite started?
Manufacturing process
How is a resin starved areas identified?
Fibres showing on the surface.
What can delaminations form?
Matrix cracks
What does the severity of delam depend on?
Dimensions
Number of delams at location
Location
Loads
Honeycomb structures have face sheets which are subject to three categories of defect, what are they?
Low resistance to impact
Liquid ingression
Erosion
Damage that goes unchecked to a honeycomb structure can lead to what?
Liquid ingress into the core
When a core has water ingress what is required before carrying out a repair?
Drying cycle to completely remove any moisture.
When a core has skydrol ingress what is required before carrying out a repair?
Complete removal of contaminated core as it cannot be dried.
What are some of the typical types of visual damage?
Scorch
Stain
Dent
Penetration
Abrade
Chip
How are internal defects inspected?
NDT
What is the most common test for detecting delam?
tap/coin testing
What four ultrasonic techniques are used?
Through transmission
Pulse echo
Ultrasonic bond
Phased Array
What is x-ray best at detecting?
Flaws parallel to the beams centreline.
As most composites are transparent to x-rays what is used?
Low energy rays
What is thermography most affective for?
Thin laminates or defects near the surface
Ife dye penetrant sits on composite too long what happens?
The fibres can absorb the dye.
How does a moisture meter work?
The meter measures the RF power loss caused by the presence of water.
What are the three damage classifications to composite?
Negligible
Repairable
Non-repairable
What is BVID?
Barely visible impact damage
What are the five basic types of composite repairs?
Pre-cured patches
Potted
Resin Injection
Laminate repair (one surface or through part)
What are bolted and bonded repairs?
Temporary
What are resin injection and potted repairs for?
Repair small holes or voids.
What steps are required to prepare a surface for repair?
Solvent degreasing
Water break test
What is the water break test?
A test to see what the surface tension of the water is.
How long must the water remain on the surface in a water break test?
30 seconds
What are the 8 basic steps when assessing damage for repair?
Find
Assess
Define SRM
Prepare
Lay up
Clean
Inspect
Document
How does a potted repair, repair a hole?
Filler is used instead of new core material.
What is the maximum size for a potted repair?
2.5cm
What are the two most common honeycomb repairs?
Puncture
Honeycomb core
If honeycomb damage is more than one inch, a potting repair can’t be used, what can be done instead?
A honeycomb plug cut and bonded in place.
What are the two common solvents used to clean composite?
MEK
Acetone
What types of plastic wear are there?
Crack, degradation, distortion and aesthetic alteration.
What are the four types of plastic failure?
Environmental
Thermal
Chemical
Mechanical
What are the rules for cleaning an externally exposed surface?
Flush the surface with water and use a hand to remove all the dirt. Sponge with hot water and soap, dry.
What are the rules for cleaning an internal plastic surface?
Dust the surface, use a damp cloth and dry. Use approved plastic cleaner/polish.
What is crazing?
Small surface fissures, can lead to major cracking.
How can scratches be removed?
Buffing
Sanding
What can be done to cracks in plastic?
They can be stop drilled , but the component must still be replaced at next check.
