M6.3 Composites Flashcards
What is a composite
Two or more materials combined to make it stronger than they would be on their own
What is the role of the matrix and what does it do?
. Bonds to fibre
. Transfers stress
. Adds strength to fibre
What are the parts of a 2 part matrix mix?
Resin, hardener
What are the 2 main elements that make up a composite (plus sometimes 3rd)
Matrix (bonding)
Reinforcing material (fabric)
Core (sandwich construction)
What are the 2 categories of a matrix?
. Thermoplastics
. Thermoset
What’s a thermoplastic?
Non permanent change and can be reversed
What are a few advantages of composites
Longer service life than metals
Higher corrosion resistance
High strength to weight ratio
Fibre to fibre transfer of stress
What is a Thermoset?
Permanent change and cannot be reversed
What’s a thermoset?
Permanent change and cannot be reversed
What are some disadvantages of composites
Inspections difficult to conduct
High cost production and repair
Lack of knowledge
Often toxic and hazardous
Describe epoxy resin?
. Most common
. Thermoset
. Bond almost any materials together
What is fibreglass
Small strands of silica glass and the spun into woven cloths
What are the two types of fibreglass
E glass
S glass
What are some advantages of fibreglass
Low density
Hugh strength
Good wet out💦💦💦💦💦
Does not absorb water
Not ductile
What is pre-preg? 😩🧐😉
. Controlled amount of resin added to a material to prevent errors
What are the properties of Aramid (Kevlar)
Yellow colour
Lightweight
Can repair with fibreglass
What is Kevlar used for
Belts for radial tyres
Bullet proof vests
What are the disadvantages of Kevlar
Very difficult to cut
Special cutters needed
Poor compressive properties
UV sensitive (turns brown)
What is CFRP
Carbon fibre (black graphite)
Where do you store pre-preg materials and how do you monitor it?
In a freezer and calculate time out of freezer with freezer log
What are some advantages of Carbon Fibre
Very strong and stiff
High resistance to temperatures
Stronger than Kevlar but more brittle
Disadvantages of pre-preg 😳🥵🤪😱🫠🥱🫶🏿
. Short life span
. Very expensive
What composite is corrosive with aluminium
Carbon fibre
What is carbon fibre used for on an aircraft
Primary structures
Ribs
Floor beams
What are some disadvantages of carbon fibre
Wears out tooling
Very conductive
Why is boron not commonly used
Expensive
Hazardous
What is laminate made of?
2 or more layers of reinforcing material bonded together with matrix
When would you use ceramic composites
For high temperature applications
What is a sandwich (not the food kind Sean 💀)?
. Core bonded between 2 thin fibreglass sheets
. High strength:weight
How much stronger is sandwich than laminate?
10x
What is the warp
Runs along the length of the fabric as it comes off a roll (0^)
What is the weft
Runs perpendicular to the warp (90^)
What is the Bias
Runs 45^ to warp
What is the selvedge edge
Prevents material from fraying or unravelling. Tightly woven edges run parallel to warp threads
What are examples of things a sealant seals?
Fuel tanks, skin joints, structures
What are the 2 core materials?
Honeycomb, Foam
What are the 4 styles of fabric
Unidirectional
Bidirectional fibre
Mats
Quasi-isotropic
What is unidirectional fabric style
Fibres run in single direction of the warp
What is bidirectional fibre style
Fibres run in 2 or more different directions
What are the advantages of plastic?
. Lightweight
. Cheap
. Corrosion resistant
. Durable
. Impact resistance
. Chemical resistance
What is mats style of fabric
Chopped fibres, offers little strength
What are the advantages of PTFE?
. Electrical insulator
. Low flammability
. Tear resistant
What is quasi-isotropic fabric style
Lay ups stacked in 90^, 45^, 90^ sequence
Or 0^, -60^, 60^
Provides strength and stiffness in all directions
What are the 3 types of fabric weave
Plane
Twill
Satin
What is plain weave
Simplest form
Very stable
Difficult to cover complex shapes, won’t drape
Lowest mechanical properties
What is twill weave
Good wet out and cover properties
Flatter and offers superior mechanical properties
How do you identify a thermoplastic?
. Heated dies
How do you identify thermosetting plastics?
White paint or ink
What is satin weave
Modified twill with fewer intersections
Flat, covers well, good wet out
Often used for repairs
However,
Difficult to handle
How do you identify transparent plastics?
Mark on metal bit or sand blasting
Where do you store film adhesive to slow resins cure rate
A freezer
What is a one part sealants?
Ready for application as packaged
What do two part sealant require in packaging?
Require separate packaging to prevent curing prior to application
What happens to film adhesive at room temp?
The resin starts to cure
What happens to foam adhesive under heating
Expands into crevices
What are foam adhesives used for?
Bond new honeycomb core segments to existing cores
What do in service defects include?
Impact strength
Environmental degradation
Cracks from load overload
Fatigue
What are the three categories of damage to composites
Negligible
Repairable
Non repairable
What are cosmetic defects
Defects on the outer surface, does not involve damage to structural reinforcing fibres
What does BVID mean
Barley visible impact damage - due to being difficult to see and deftest
What is delamination
Separation of the fabric layers of on a laminate
Due to impact, moisture or lightening strikes
What do erosion prone areas require?
Coatings and protection
When would a dye penetrant be used?
When called upon by manufacturer
What does a visual inspection consist of looking for?
Scorching
Stains
Dents
Penetration
Chips
What is disbonding
separation of the composite material from another material to which it has been bonded to
separation between the skin and core of a composite sandwich structure is called core disbond
Caused by poor adhesion impact damage
How can cracks be detected
Visually or by NDT
Thorough inspection
How can you inspection if there has been water ingress ion
Weight gain
Contamination of bond
Expansion/contraction (Therese thaw)
How does hole damage arise
Impact, over torquing, lightning strike pin holes
Can x rays detect delamination
No
What must be done in preparation to before bonding
Solvent Degreasing and de oiling
How is a surface checked to see if it has been properly prepared before bonding is applied
A water break test it carried out (if beads then it’s been done incorrectly)
What are the parts of a truss type wing?
Main and rear spar
Compression strut
Drag wires (drag and anti drag)
What are the parts of a truss type wing?
Main and rear spar
Compression strut
Drag wires (drag and anti drag)
How does the box spar help the wing?
Takes all of the torsional and bending load
What are the types of wood that could be used for an aircraft structure?
. Solid wood
. Laminate wood
. Plywood
. High density wood
What are the 3 preferred wood types for aircraft?
. Spruce
. Douglas Fir
. Noble Fir
What are the 5 types of composite repairs
Pre cured patches
Potted
Resin injection
Laminate repair (one surface)
Laminate repair (through part)
What’s the negatives of pre cured patches
Doesn’t provide the same aerodynamic properties
What’s potted repairs
Where a small hole is filled with foam filler instead of having a core
What do you asses in a wood inspection? (Pre plane built)
. Way it’s cut
. It’s grains
. Wood growth ring
. Grains slope
What’s the negatives of potted repairs
They can be dangerous as they make it heavier
What is solvent degreasing
Removes contaminates from surface, if not removed could effect bonding
What causes wood to decomposed?
Moisture, temperature, sunlight
What kind of hangars should wooden aircraft be stored in?
Well ventilated hangars, out of sunlight,
What could be used to preserve wooden structure?
Chemical preservatives
What is a water break test
To verify surface cleanliness
What does interior finishing do?
Protect against moisture using coatings
How’s resin injection carried and why is it carried out
Carried out when delamination occurs and it’s done by injecting the area with resin and clamped
What is exterior finishing in wooden aircraft?
Weathering protection, smooth surface as needs to be aerodynamic
What needs to happen before you make repairs to wooden structure?
. Degrease
. Remove sawdust
. Controlled temperature
. Seal bolt holes
What MSDS stand for
Material safety data sheet
What is a knot is wood?
. Where old branch grew
. Weakens wood
What is a pitch pocket in wood?
. Small opening in wood , fill with resin
What’s contained on the MSDS
PPE
ventilation
Fibre protection
Solvents safety
Material storage
How is compression wood formed?
. Leans one side during growth
. Rings out of sync
. Makes wood weaker
. Falls on slope or another log
Can’t use on aircraft’s
What is compression failure?
When a tree falls on uneven ground
Describe stained wooden structure?
. Has stains caused by decay
. Reduces toughness/strength
. Cannot be used
What’s happens if crazing isn’t detected
Can lead to cracking and failure
What is dry rot and what’s it caused by?
. Caused by fungi
. Has minimum moisture
Where should wooden structures be kept?
A well ventilated hangar
What part of the wooden wing takes all of the structural loading
The spar
How is the majority of wood damaged?
Moisture, temperatures, sunlight (UV)
What is the main characteristic of resorcinol glue?
Most water resistant
What separates the leading and trailing edge of the wing
Compression struts
Where would you use a pre cured patch repair
a temporary repair can be performed to cover holes or deep scratches by using a pre-cured patch installed with blind fasteners
Yet, does not produce same structural strength as original
How is wood testing done?
Test of joining technique
What prevents the leading edge of a wooden wing from collapsing
The drag wire
What things would you look for on the wood when you inspect it for damage?
Decay, splitting or cracks, bond failure, finish failure, stress damage
What prevents the trailing edge from collapsing forward
Anti drag wire
H
What does the box spar do
Takes all bending and torsional load
What wood is most commonly used for aircraft structure
Silka spruce
How many screws and nails per spar
No more than 2
Why should drain holes be kept clear
Because it can cause rotting of wood id not due to moisture being held in wind
How is a wood test sample performed?
. Wood glued together put in vice
. Hit apart with device of some sort
. The fractured face must have at least 75% wood to show a good joint glued
What size hole is a fabric patch repair used for
Up to 1 inch
What’s the limit of age rings that can be in 1 inch
6
What size hole for surface patched repair
Between 1 inch and 50inchs😏
What is a potted repair
Used for smaller holes up to 2.5cm and scratches. Filler is used instead of a new core.
Restricted to honeycomb core sandwich structure
What is a plug patch repair held in by?
Held in by a round or oval shaped ring called the doubler
What area of the part is plug patch repair done on
Only skin repair, only for damage not involving the supporting structure
What is the negative of nitrate dope
Extremely flammable
What defects in wood can’t be used in aircraft structures
Spiked knots and compressed wood
What is a resin injection used for
Minor internal delamination can be repaired by injecting a resin mix into delaminated area.
Have to check structural repair manual for limitations.
What types of
What is added to butyrate dopes to stop UV damage
Aluminium
What does stained wood indicate
Indicates that rotting has occurred
What are laminate repairs
Repairs damage on one side of the surface that does not penetrate the part.
Cut out the damage and replace with new material
Before joint two pieces of wood what process must it go have gone through before hand
Must have been left in the same temp for previous 24 hrs so that it can gain the same moisture levels
Can you do a laminate repair for damage that has gone through the part
Yes, can be repaired using a step cutting from both sides and meeting in the middle and the replaced.
Check AMM for limitations
What does MSDS mean
Material safety data sheets
What stitch is used to repair straight cut or tear
Ladder/baseball stitch (Herringbone stitch)
When testing bonding techniques between two pieces of wood what percentage of fibres must be on the piece of wood
75%
How is a good fit of a fabric achieved
Hot ironing
How’s solid wood repaired
By splicing
What is included within the MSDS requirements
PPE
Ventilation- proper ventilation, respirators provided
Fire protection- spark proof tools, eliminate fire hazards
Solvents Saftey
Material storage
What are the two most common solvent used
MEK (carcinogen) and acetone
Where should fabrics be stored?
At 20 degrees (68f) in dry clean condition away from direct sunlight
What’s the restriction related to splicing solid wood
No more than 2 per spar
What things would you look for in a fabric inspection?
Loose tape
Chafing under fairings
Brittleness
Tears
What are the 5 types of plastic failure
Environmental failure
Chemical failure
Mechanical failure
What’s used for wing rib repairs
Small sprite strips
What are 3 commonly inspected panels
Wood frames
Zip panels
Spring panels
What’s the restrictions for in which fabric patch repairs can be done.
Can’t be done on leading edge
How is fabric attached to the wood
Using dope
2 types of fabric testing devices
Seyboth punch tester- goes all the way through
Maule punch tester- doesn’t puncture , better as it doesn’t make hole
What’s the negative of using dope
It’s very flammable
When would darning be used?
Hole is no more than 50mm wide at any point (2inchs😏)
What is crazing
Internal cracking, can’t be removed or fixed as it’s separation of the material.
If left then could become extensive deep crack.
Prevention is paramount
What’s added to make dope less resistant to uv
Alluminium
When would an insertion be used for repair?
Damage over 100m (4inch😉)
When would an insertion be used for repair?
Damage over 100m (4inch😉)
How are fabric wings inspected
Using inspection panels
How can you get rid of scratches
Buffing or sanding
It is easier to prevent than remove
Refer to AMM for limitations
What are the three panels installed in wings
Spring, wooden frames and zip panels
What are the two tools used to measure tension of fabric
Seyboth and maule
What does cracking cause and how can you prevent it from getting worse
Renders the plastic beyond repair.
Can be stopped drilled to prevent further damage.
Will require replacement at some point.
Refer to AMM
Which one of the two devices that test tension are better
Maule is better and the seyboth punctures a hole in the fabric
