Composite And Non Metallic Flashcards
What is a composite material
Two or more materials joined together to make a strong structure
What are the advantages of composites materials
- High strength-to-weight ratio
- Reduction of parts and fasteners
- Reduction of wear
- Corrosion resistance
What are the disadvantages of composite
Generally expensive
Not easy to repair
What is nomex
very high thermal stability and temperature and flame resistance
Manufactured as a fibre
Gives major strength when combined with a matrix
What is nomex used for
Flame proof clothing
Primary flight controls
What is the relationship between nomex and Kevlar
Contrast chemical isomer
What is fibre glass
Made of Sillica glass spun into cloth
Weights more and has less strength than other fibers
Low cost
What are the 2 types of fibre glass
- E-glass highly resistant to electricity
* S-glass very high tensile strength
What are the characteristics of fibre glass
◦ Low density (2.1 g/cm3)
◦ High Strength
◦ Hight fracture toughness
◦ Circular cross-section and smooth surface
◦ Good ‘wet out’
◦ The fibre does not absorb water/humidity
◦ The fibre is not ductile (ceramic properties)
◦ For sanding, aluminium-oxide or silicon-carbide sand paper can be used. Silicon-carbide will last longer than aluminium-oxid
What are the characteristics of aramid fibre
◦ Low Density (1.45 g.cm3) ◦ High tensile strength ◦ Heat resistance up to 260°C ◦ Non-flammable and non-fusible ◦ Good chemical resistance ◦ Very good resistance against abrasion ◦ High toughness
What is aramid fibre
Yellow colour
Repaired with fibre glass
What is aramid used for
Rotor blades
Bullet proff vests
Use for leading edges
What is kevar
Man made
Organic fibre
What is Kevlar used for
Aircraft panels
Belts for radial Tyree
Bullet proff vests
What are the advantages of Kevlar
High tensile strength
Flexible
What are the disadvantages of kevlar
Absorbs up to 8% moisture
Poor compressive properties
Can’t be used to UV light
Difficult to cut
What are the advantages of carbon fibre
High strength High stiffness Low density Light weight High temperature resistance
What are the disadvantages of carbon fibre
Electively conductive
Can only the cut with air tools
Expensive
What is the relationship between Kevlar and graphite
Graphite is stronger in compressive strength than Kevlar, however, it is more brittle than Kevlar.
What happens with graphite is bonded with aluminium
Will become corrosive
Very course
What is the warp
Runs along length of fabric
What is the weft/fill
Runs perpendicular to the warp fibres.
What is the bias
The bias runs at 45° to the warp threads
What is the selvage edge
Runs parallel to the warp
What is a mat fabric
consist of chopped fibres that offer little strength compared with unidirectional or bi-directional threads.
What is a unidirectional fibre
Unidirectional fibres are ones in which the major fibres run in the direction of the warp
What is a bi-directional fibre
Bi-directional fabric calls for the fibres to run in two or more different directions
What properties do a matrix materials
good stress-distribution, heat-resistant, chemical-resistant and durability properties.
What is a thermo plastic
Can only with stand heat up to 750
Not permanent
Acrylic
What is a therm set
Thermosets use heat to form and set the shape permanently. The plastic, once formed, cannot be reformed even if it is heated.
Bakelite
What is pregreg
Pre impregnated fabrics
With a resin
Stored in a freezer to prevent curing
What is sandwich construction
When a core is bonded between 2 thin faces sheets
What is honey comb
Good strength to weight ratio
Nomax paper
What are the 2 honey comb fabrication methods
- Corrugationprocess:Materialwhichcanbeconvertedusingthisprocess include metals, plastics, plastic reinforced glass and paper.
- Expansionprocess:Inthisprocess,allbondsaremadesimultaneously(the corrugation process is essentially a one-layer-at-a-time operation).
What are methods use to dissipate the electraal change from composite
- Flame spray
- Bonding jumpers
- Aluminium wires woven into the top layer
- Thin aluminium foils bonded to the top layers hat
What is the MSDS
Materials safety data sheet
What will there be on MSDS
- Health precautions
- Flammability of the material
- Ventilation requirements
- Information for health professionals in the event of an accident
What is polymerisation
Carried out in the presence of a catalyst
Monomers becoming polymers
Chemical reaction
No waste product
What is polycondensation
chemical reaction between two similar or dissimilar basic units which have at least two functional groups.
Waste product of water
Bakelite and polyester
What is poly addition
two different types of molecules when reactive groups are brought together. No by-products are produced
Polyurethanes
Epoxies
What is an adhesive
Bonds 2 or more surface together
What do we use adhesives
economical; they distribute the stress at the bonding point, eliminate the need for fasteners and are moisture and corrosion-resistant.
What is the effective ness of a adhesive dependent on
- Resistance to slippage and shrinkage
- Malleability
- Cohesive strength
- Surface tension, which determines how far the adhesive penetrates the tiny depressions in the bonding surfaces.
What is a thermosetting adhesive
Used for bonding metallic parts of aircraft and space vehicles
What is a Thermoplastic resins,
which can be softened by heating, are used for bonding wood, glass, rubber, metal and paper products
What is a aerosil
white powder, which is a product of combustion. Aerosil is used as a thixotropic agent
What is a elastrometric adhesive
Used for joining dis similar metals with out galvanic crosion
What is a contact adhesive
Atmospheric pressure will press two solids together if there is no air between the two plane parallel surfaces
What is a solvent adhesive
Solvent adhesives contain plastics or resins dissolved in a solvent. The solvent has to evaporate to cure the adhesive
What is a dispersion adhesive
Dispersion adhesives contain resins dissolved in a water solution, such as wood glue or wood paste.
What is a resin adhesive
Resin adhesives cure by chemical reaction. They contain two or more components.
What is a film adhesive
Similar to pre preg
Metal to Metal
Kepted in freezer m
What is a foaming adhesive
A foaming adhesive film is an adhesive in sheet form which expands during the curing cycle to fill gaps and adhere strongly to all parts of the structure with which it comes into contact
Kept in freezer
What is a plastic foam
Plastic foams are produced with either ”closed” or ”open” (interconnected) pores and as either preformed rigid sheets or as fluids for injection into cavities.
What is a thixotripic agents
Thinking agent
What are the 2 types of thixotropic agents
Aerosil
Micro bollon
What is a micro balloon
Phenolic balls
Gently folded in
Trowled in time surface
Mixing resins
Wax free container
3 to 5 minutes
Resin based stored in freezer
What is a thermosetting resin
Epoxy resins are used for external components due to their good mechanical properties.
Phenolic resins are used for cabin furnishing due to their fire resistance and low toxicity.
Mixed with specific hardened and cured
What is a thermo plastic resin
When heated, thermoplastic resin becomes a plastic. After cooling, the resin sets and hardens in a given form. Hardening is reversible. Thermoplastic resins are very seldom used on composite structures.
What is a good polymer resin
- It must have the correct mechanical properties.
- It must coat every single fibre and bond well to them.
- It must be fairly easy to use.
What is a polymer resin
Polymers are combined with the fibres by melting or by using a liquid polymer (resin) that can be hardened (cured).
Polyester Resin
typically used with glass fibre to form a strong durable material.
Epoxy resin
thermosetting resin that provides excellent adhesive strength and can be used for glueing metals together.
Vinyl Ester resins
are tough resins that have a high resistance to corrosion even in the presence of fuel. This makes them extremely useful for repairing fuel tank liners.
Phenolic resin
used extensively inside aircraft due to good resistance to smoke generation in fires.
What should you never mix together
Catalyst and a accelerator
What are epoxy resins
Expensive
Viscous liquids
Mechanical properties
What happens if too much hardener is added
- Unreacted resin in the final cured resin
* Unreacted hardener in the final cured resin
What are the disadvantages of epoxies
Toxicity
Low pot and shelf life
High cost
Epoxy resin characteristics
High adhesion Cohesive strength 100% solid Low shrinkage Resistance to moisture and solvents
What is a good surface wetting
- Removal of surface contamination
- Viscosity reduction through application of heat
- Viscosity reduction by solvent or diluent addition
- Time
- Pressure
What is mechanical booking
Must penatrate into cavities before curing other wise trapped air will reduce the strength of the joint
What is surface wetting
Water drop test
What are the pre treatments for bonding
- Degrease only
- Degrease, abrade and remove loose particles
- Degrease and chemically pre-treat
What is the first thing done when damage is done
A complete investigation into damages area
SRM
52-57
Damage detection
Scheduled inspection
Unscheduled inspection
Damage evaluation
Of the type
Extent
And importance
What are the acceptance levels
- Allowable
- Repairable
- Not repairable
What are the 2 damage classification
Skin perforated damage
Skin not perforated damage
What is Skin perforated damage
- Lightning strike
- Holes
- Impact by foreign object, requiring investigation for delamination moisture contamination
What is skin not performates damage
- Abrasion
- Scratches
- Gouges
- Nicks
- Debonding
- Delamination
- Dents
What is delamination
Reinforcing layers to separate from each other in the matrix m
What is Barely Visible Impact Damage (BVID)
Lower velocity impact
Outer skin appears in damaged
What is debonding
when two materials stop adhering to each other
What testing methods used for BVID
Tap testing
Ultrasonic
X-rays
What is abrasion
damage to a surface caused by scuffing, rubbing or scraping of the component.
Lightening strike
Damage on carbon fibre structures will usually be less significant (spots, small holes, or charring).
What is erosion
When moisture penetrates into composite
Leading edge surface
Water absorption
Any moisture detected must be removed
Effects the resin
Reduces performance
Increases weight
Chemical degradation
Chemical degradation principally affects the resin and is generally due to accidental contact with aggressive chemical liquids or products. If chemical degradation is detected, the whole contaminated area must be repaired.
Dent / depression
A dent or depression is a deformity in the thickness of an area. It may be caused by impact. This type of defect requires further NDT (Non Destructive Testing) to detect delamination or debonding
What is NDI
Non destructive testing
Tap testing
Widely used as it is quick Detects debonding Tapping surface lightly Flat sound unacceptable Subjected to operator
Visual or optical inspection
Dosent detect interval flaws
For fibre glass a light is shined through colour change when delamated
Holography
rapid assessment of flaws in surfaces of composite structures.
Optical holography is extremely sensitive in measuring small surface defects.
The part to be inspected is stressed by the application of heat, a static load or vibration to bring out the effect of the flaw on the surface displacement
Ultrasound
Locates internal defects
Inexpensive
Radiography
X-ray inspection technique is widely used for quick and low-cost inspection of composite structures. X-ray equipment can be adapted to handle small parts up to relatively large parts.
A radiograph is like a shadow picture; the darker regions on the film represent the more penetrable parts of the test specimen and the lighter regions are more opaque to the radiation.
Repair types
- Temporary repairs
- Permanent cosmetic repairs
- Permanent structural repairs
Preparation before repair
Surface protection removal
Clean and degrease area
Drying of area
Removal of surface protection
Mechanical methods only
What is scarfing
Removing a damaged composite material 1 later at a time
Removing a layer reveals 1/2 inch of the layer below
What is a wet lay-up
Wet lay-up consists of applying several layers of fabric material impregnated with resin onto the repair surface, in order to restore the damaged skin.
Pot life
(the amount of time you have to work with the resins
Shelf life
The shelf life is the time which the product is still good in an unopened container and varies from product to product.
Resin rich
If too much resin is used, the part is called resin rich. This is undesirable, as it affects the strength of the composite by making the part brittle and adds extra weight (negating the reason for using composites in the first place).
Resin starved
If too little resin is used in the lay-up, it is described as being resin starved. This is undesirable as there is insufficient resin to successfully transfer stresses to the fibres
Why is vacuum bagging used
- To use atmospheric pressure to consolidate the layers in the laminated repair
- To remove trapped air and gases produced during curing
- To hold heater blankets, thermocouples and other materials in place during the curing cycle
- To produce the desired surface finish on the repair
What are the vacuum bagging principal
- Theairandgasesinsideavacuumbagmusthaveaneasypathtothe vacuum pump over the entire repair surface.
- Theamountofresinlostfromtherepairpliesmustbekepttoaminimum. Additionally, it is necessary to ensure that none of the bagging materials adhere to the repair and that the heater blanket is protected from resin contamination.
Perforated parting film
This is a thin, non-stick film placed directly on the surface of the repair to prevent the bagging materials sticking to the repair surface. The film is perforated with small holes to allow air and gases to escape from the repair piles
Peel ply
This is a thin, woven, nylon or polyester fabric which has a non-stick coating. It can be used instead of, or underneath, a perforated parting film.
Its main effect is on the surface finish of the repair.
What are disadvantages of peel ply
- It absorbs some resin, and may lead to a resin-starved repair.
- It may contaminate the repair surface with its non-stick coating.
Bleeder cloth
The function of this layer is to provide an easy path for air to escape and to absorb any resin which comes through the holes in the perforated parting film.
Non perforated parting film
This is placed on top of the bleeder fabric to prevent resin soaking through onto the other bagging materials and the heater blanket.
Breather fabric
This is a thick, porous, non-woven material and is used over the entire repair surface to allow the air and gases to escape easily
Caul plate
- To help even-out the temperature over the entire repair
- To help even-out the pressure over the whole repair
- To improve the flatness of the surface of the repair
Heater blanket
The heater blanket is a silicone rubber pad which contains an electrical heating element. It is used to control the temperature of the repair during the warm-up, cure and cool-down stages of the repair. It is flexible and will bend to gentle curves. Heater blankets can be used for cures up to 350°F (175
Insulation
Insulation in the form of breather fabric or glass cloth is normally placed on top of the heater blanket to reduce heat loss and to minimise the effects of draughts on the repair.
Bagging film
This is a nylon film which is sealed over the repair materials so that a vacuum can be applied. It is available in a variety of temperature / elongation resistant types. The higher temperature-resistant films normally stretch less.
Bag seating tape
This material is a high temperature mastic type of tape and is used to seal the vacuum bag to the surface of the item under repair. It is available in a number of temperature ranges.
Thermo couples
positioned under heating mats in order to accurately monitor the repair temperature.
J type
Flash breaker tape
It will not be affected by high temperatures. It is the only type of tape which should be used on the surface of the heater blanket.
