Composite And Non Metallic Flashcards
Composite
The combination of two or more materials to form a much stronger structure A matrix (Usually liquid) A reinforcing material
Advantages and Disadvantages of Carbon Fibre
High strength to weight ratio
Corrosion resistance
Resistant to wear
Expensive
Not easy to repair
Requires trained staff
Reinforcing materials
Gives strength to the reinforcing component when combined with the matrix
Nomex
Manufactured only as a fibre
Flame and temperature resistant
Fibreglass
Molten silica glass, spun together and woven into a cloth Low cost weighs the most Least strength E-Glass = Electrical resistance S-Glass = High tensile strength
Aramid
Yellow in colour
Good tensile strength
Heat resistant up to 1260 C
High toughness
Kevlar
Man made organic fibre
High tensile strength
Difficult to cut
Absorbs 8% moisture
Carbon fibre (CFRP)
High strength
Stiff
Low density
Electrical conductivity
Warp
Threads run along the length of the fabric
Weft/Fill
Runs perpendicular to warp fibres
Selvedge
Tightly woven edge runs parallel to warp edge
Bias
Runs 45 degrees to warp threads
Matrix Materials
Good stress distribution Heat resistant Chemical resistant Good durability Resins used as a matrix are two part systems
Thermoplastics
Use heat to form the part into a specified shape and this shape is not permanent
Thermoset
Once heated they form a permanent shape
Cannot be deformed
Most commonly used
Pre impregnated materials
A combination of a matrix and fibre reinforcement
Must be stored in a freezer at a temperature below 0 F
Many materials in aerospace are impregnated with Alan epoxy resin, cured at 250 F or 350 F
Honeycomb construction
This type of core material has the shape of natural honeycomb and has an excellent strength-to-weight ratio. Honeycomb materials can be constructed of aluminium, Kevlar, carbon, fibreglass, Nomex or steel. Nomex is a paper that has been impregnated with aramid and is very often used on so-called advanced composites.
Electrical Bonding
There are a lot of different methods used by manufacturers to dissipate the electrical charge on composite components:
• Flame spray
• Bonding jumpers
• Aluminium wires woven into the top layer
• Thin aluminium foils bonded to the top layer
Safety
All is listen in the MSDS
Wear correct PPE
No contact lenses
Polymerisation
Carried out in the presence of a catalyst
Creating a chemical reaction
Creates a monomer
No waste product
Polycondersation
Chemical reaction between two similar and dissimilar units
Polyaddition
Reduction of two different molecules
No by products
Hydrogen atoms migrate
Adhesives
An adhesive is a substance used to bond two or more surfaces together. Most adhesives form a bond by filling in the minute pits and fissures normally present even in very smooth surfaces. Adhesive bonds are economical; they distribute the stress at the bonding point, eliminate the need for fasteners and are moisture and corrosion-resistant.
Effectiveness of adhesives depend on
Resistance to slippage and shrinkage
Malleability
Cohesive strength
Surface tension
Synthetic adhesive
Used either alone or as modifiers of natural adhesives, perform better and have a greater range of application than the natural products. Most of them form polymers, which are huge molecules incorporating large numbers of simple molecules to form strong chains and nets that link surfaces in a firm bond.
Thermosetting adhesive
Bonding metallic parts of the aircraft
Thermoplastic adhesives
Bonding woods, glass, rubber and paper
Elastomeric adhesives
Join dissimilar metals without the hazard of producing galvanic corrosion.
Contact adhesive
Pressure will press two solids together if there is no air between the two plane parallel surfaces.
Solvent adhesive
Solvent adhesives contain plastics or resins dissolved in a solvent. The solvent has to evaporate to cure the adhesive.
Dispersion adhesive
Dispersion adhesives contain resins dissolved in a water solution, such as wood glue or wood paste.
Resin adhesive
Resin adhesives cure by chemical reaction. They contain two or more components.
Film adhesive
They are used for bonding metal to metal, sandwich core to skin.
Foaming adhesive film
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.
Plastic foams adhesive
Plastic foams are produced with either ”closed” or ”open” (interconnected) pores and as either preformed rigid sheets or as fluids for injection into cavities.
Thixotropic Agents
Micro balloons
Diameters = 10 - 300 microns
Forms a paste
Acts like a filler
Most common resins
Polyester
Epoxy
Vinyl Ester
Phenolic
Adhesion
Epoxies have high adhesion to metals, glass and ceramics. They can be formulated to give mixes of low viscosity with improved wetting, spreading and penetrating action.
Cohesion
When the resin is properly cured, the cohesive strength within the glue line is so great (and adhesion of the epoxy to other materials so good) that failure under stress often occurs in one of the adherents rather than in the epoxy or at the interface
100% Solids
Unlike phenolics and some other resinous adhesives, epoxies cure without releasing water or other condensation by-products. This makes it possible to bond epoxies at contact pressure only, or with no pressure at all.
Low shrinkage
Epoxies cure with only a fraction of the shrinkage of vinyl-type adhesives such as polyesters and acrylics; consequently, less strain is build into the glue line and the bond is stronger.
Epoxies resistance to moisture solvents
Epoxies are insensitive to moisture. Their resistance to solvents is also outstanding and accounts for their rapid advance in the coatings field. They are effective barriers to heat and electric current.
Positive effects of surface wetting
Should always be kept clean
Viscosity reduction
Time
Pressure
Negative effects of wetting
Finger prints
Incorrect glue
Low temperature
Bonding pre-treatment
De grease
De grease, abrade and wipe
De grease and chemically pre-treat
Composite damage investigation
Area
Extent
Type
Levels of damage
Allowable
Repairable
Non-repairable
Skin not perforated
Erosion/abrasion/scratches
Gouges/nicks/dents
Deboning/delimitation
Skin perforated
Lighting strike
Holes/FOD impact
Delimitation
Reinforcing materials spreading from each other in the matrix
Deboning
Two materials stop adhering to each other
BVID
The outer skin may be undamaged, however underneath the damage may be fatal
Corrosion
Galvanic corrosion may occur when an aluminium alloy part is in direct contact with a carbon fibre surface in the presence of a corrosive environment.
Erosion
Erosion could affect all the leading edge surfaces, especially when the initial surface protection system has been damaged. Erosion, when undetected or unrepaired, may generate composite deterioration. The component may be completely perforated and fluid ingress likely to occur. Restore the protection of the area and install additional protection if necessary.
Water abrasion
Any detected moisture has to be removed to avoid further damage.
During any repair procedure, ensure that repair parts are completely dry,
in order to avoid any material delamination during heat application. Water ingress in sandwich structures is due to porosity of the skin. It reduces performance and increases the weight of the affected structure. Water absorption is a phenomenon of resin properties. The absorption stops once the resin is saturated.
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.
Dents/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. On sandwich structure, the honeycomb is generally damaged and requires a repair.
NDT
Non destructive testing
Tap testing
Detects deboning or trapped water
Visual inspection
Quick assessment
Surface must be clean
Holography inspection
Locates small surface defects
Compare a normal to damage specimen
Lots of work to set up
Ultra sound inspection
Locates internal defects
Quick
X Ray inspection
Long process
