6.3 Flashcards
(54 cards)
What is the definition of a composite.
Two or more materials that are combined to form a much stronger structure than either material by itself.
Disadvantages of composites.
Inspection methods are difficult to conduct
Lack of long-term design database
High cost in production and repair
Very expensive processing equipment
General lack of repair knowledge and expertise
Products + materials are often toxic and hazardous
Lack of standardised methodology for construction and repairs.
Advantages of composites
Corrosion resistant
High strength to weight ratio
Longer life span
Fibre-to-fibre transfer of stress allowed by chemical bonding
Bonded constructions eliminates need for bolts and fasteners
Tensile strength 4-6 times more then steel or aluminium
Fibreglass
Most widely used in the industry
E-glass (electrically resistant)
S-glass (strong)
Does not conduct electricity
Aramid fibre (kevlar)
Two most common types in aviation:
- kevlar 49
- kevlar 29
Resistant to impact damage.
Sensitive to UV light turns it from yellow to brown.
Complex construction and maintenance.
Carbon fibre / black graphite
Used on primary aircraft structures (e.g. Ribs and floorboards)
Stronger compressive strength than kevlar, but more brittle.
Wears out tools
Corrosive when bonded with aluminium.
Boron fibres
Very hard wearing
More used on military aircraft
Repair of cracked aluminium
Apply boron vapour to tungsten
Corrosion resistant
Ceramic fibres
Used when high temperature applications are needed
Fabric orientation
Warp - runs along the length of the fabric
Weft - runs perpendicular to the warp
Selvedge edge
Tightly woven edge that runs parallel to the warp
Quasi-isotropic lay up
Orientation of fibres are balanced resulting in constant stress and stiffness
Mats
Chopped fibres, compressed together.
Not as strong.
Not common in aviation
Plain weave
Over under … etc
Lowest mechanical properties
Difficult to cover complex shapes
Twill weave
Superior wetout
The preferred weave
Superior mechanical properties (strongest)
Flatter
Satin weave
Often used for repairs.
Resin matrix
Transfers stress to the reinforcing fibres.
Consists of resin and hardener.
Two types
- thermosetting
- thermoplastics
Epoxy resins
Aviation use thermosetting
The MSDS sheets must always be referred to
Pre-impregnated fabrics
Fabrics already saturated with correct amount of resin.
Expensive
Stored in a freezer
Short shelf life / out of freezer time.
Laminated composites
Two or more layers of re-informing material bonded together and embedded in a resin matrix.
Sandwich composites
Core bonded between two fibreglass sheets.
Used in flying control surfaces.
Stronger then laminate
Core materials (sandwich)
Honeycomb
- aramid paper
- high strength to weight ratio
Foam
- found in smaller aircraft
- styrofoam
PEEK
Poly-ether-ether-ketone
- valve seats, pump gears
Thermosetting polyamide
A good insulator
Excellent mechanical properties, high chemical resistance
PCTFE (Teflon)
Fire + chemical resistant
Low moisture absorption
