6.3 Composites Flashcards
what is a composite
2 or more materials that are combined to form a much stronger structure
what are the 2 elements of a composite
matrix (resin)
reinforcing material (fabric)
what are the most common used firbers used in aviation industry
fiberglass
aramid
carbon fibre
boron
ceramic
what are the 2 types of fibreglass (think of mercedes)
e glass
s glass
what is aramid
kevlar
disadvantage of carbon fibre
corrosive when bonded to aluminium
where is ceramic fibres used
high temperature applications (retains its strength up to 1200c)
what direction does warp run
length of the fabric
what direction does the weft/fill
perpendicular to the warp (weft to right)
what direction is selvedge edge
parallel to warp threads
what direction is bias
diagonal to warp
what are mats
chopped fibres, compressed together
what are the types of fabric weave
plain, twill, satin
what weave is often used for repairs
satin weave
what are the types of plastic
thermoset
thermoplastic
what are thermoplastic resins
use a heat to form the part into desired shape, shape not always permanent
reversible process
what are thermos set resisn
cured by heat, catalyst
once used and cured, cant be converted back to og state
what type of resin is epoxy (thermoset or thermoplastic)
thermoset
will the resin in pre-preg cure if not kept in cold storage
yes
what is the procedure for opening pre-preg bags
bags must be opened in controlled environment, not opened until the material has reached room temp. bags must be resealed and returned to freezer. time out of freezer must be recorded
what are the 2 main ways of constructing a fibre-reinforced composite
laminated composites
sandwich composites
what is a laminated composite
2 or more layers of reinforcing material bonded together and embedded in a resin matrix
what is a sandwich composite
when the core is bonded between two fibreglass sheets
what is the main advantage of sandwich composites over laminated
extremely high strength to weight ratio
how many times stronger is a sandwich composite over a laminated composite
at least 10x stronger
weight is 6x more
what are some typical applications of sandwich composites
flying control surfaces, wing-to-body fairings, helicopter rotor blades
what are the 2 most common types of core material used in sandwich composite
honeycomb and foam
what are the two forms of transparent plastics
monolithic
laminated
how are thermoplastics marked
heated die
how are thermoset plastics marked
vibro etching
white paint and marking ink
how is transparent plastic marked
apply to metal portion if its attached to metal
if any markings must be applied, mark the inside of the panel by means of mild sandblasting and stencil
labels must not be stuck directly to the material
what is difference between adhesives and resins
resins used for laminating are thinner
adhesives are used for bonding two parts together
where does detection of defects within composite materials start
at the manufacturing process
why is too much resin an issue
added weight
how can delaminations form
from matrix cracks or impact
what is applied to composited to protect from UV
top coating
special UV primers and paints
what is the most common technique to detect delamination
coin tapping
what sound indicates a well bonded structure using coin tap test
clear, sharp, ringing sound
whats the best method to detect internal delaminations
ultrasonic inspection
how does thermograph inspection works
surface is heated, mapping the temperature.
defect free areas conduct heat more efficiently than areas with defects
what material is thermal methods most effective on
thin laminates or for defects near the surface
can dye penetrants be used on composite
no (unless specified by manufacturor)
what is used to detect water in sandwich honeycomb strtuctures
moisture detector (often used in nose radomes)
what are the 3 classifications of damage
negligible
repairable
non repairable
where is cosmetic defects found
outer surface skin
what is the most common cause of impact damage
careless handling during ground ops
what is BVID
barely visible impact damage
what is delamination
separation of fabric layers of material in a laminate
what causes delamination
impacts
moisture
lightning strikes
what is disbonds
separation of composite material from another material to which it has been bonded to
what is core disbond
separation between skin and core of composite
what causes disbond
poor adhesion
service loading
impact damage
how can water cause disbond
freezing during flight
how can holes occur
impact damage
over torquing
fasterner pull through
holes drilled in wrong location
lightning strike
what are the 5 types of composite repairs
pre-cured
potted
resin injection
laminate repair (one surface)
laminate repair (through part)
what are temporary repairs
bolted and bonded surface patches due to strength characteristics and aerodynamic smoothness
what is a permanent composite repair
removing damaged skin and replacing it with new repair plies
why is surface preparation important
significantly affects long term environmental durability
what test is used to verify surface cleanliness
water break test
what is an issue with using mechanical blind fastener
casue damage to honeycomb core and lead to delamination
what are potted repairs used for
smaller holes and scratches
eg bird strike or mechanical damage
what is potted repair
filler
what is the downside to potted repair
dont provide same structural strength
adds weight
decrease flexibility
what is the max size for potted repair
damage up to 1 inch 2.5 cm
how can minor delamination be repaired
injecting a potting compound, resin mixture
what is laminate repair
removing and replacing damaged laminate piles
what are the two most common types of honeycomb sandwich structure repairs
puncture repair
what are the major types of plastic failure
environmental
thermal
chemical
mechanical
are cracks in plastic repairable?
no it is rendered beyond repair
how to prevent cracks from spreading
stop drilling
what design did early wooden aircraft have
truss type wing and fuselage with fabric covering
in a truss type wing, which members in the wing are the spars?
lengthwise members
how is the truss held together
high strength solid steel wires
what are antidrag wires
attach rear spar inboard and go to front spar outboard
what is box spar
box structure is built between the spars, to carry bending and torsional loads
what is the most common wood used
sitka spruce
how is aviation wood usually cut
quarter sawn to reduce shrinkage
what is the maximum grain count for soft wood
six rings per inch
how can you finish repaired ribs, spars, interior of plywood skin and other internal members
by applying one thinned coat of varnish or acceptable finish
followed by two full coats
how much strength does wood lose at 50c
25%
how can bolt holes lead to decay or splitting
variations in moisture content around bolt holes
entry point for moisture
how can you seal bolt holes
application of varnish or acceptable sealer
must dry or cure thoroughly
how is wood quality assessed
how straight the grain is
the number of knots
how many pitch pockets
splits
what type of knots is not allowed in aircraft
spike knot
what is a spike knot
cut parralel to branch
what is a pitch pocket
opening in wood
when is a pitch pocket acceptable
in the middle of the beam
what is compression wood
when tree grows to one side
what is compression failure
when tree falls and lands across a log or uneven ground
what is a split in wood
runs lengthwise
what is a check
a crack in the wood that runs across the rings of a board
what is a shake
crack or separation of the board, occurs when 2 annual rings separate
how is decay caused
fungi
how can decay be prevented
proper seasoning and storage
how to prevent dry rot
use kiln dried wood with a moisture content of 20% or less
use good surface finish like varnish or paint to protect the paint
how is casein glue made
milk
is casein glue used in aviation
no its bad and incompatible with modern glues, deteriorates with moisture
is resin glue used in aviation
no, it is susceptible to moisture
what is the most common type of glue in aviation
resorcinol glue
two part glue
synthetic
most water resistant
should you use sandpaper to smooth the surface of the wood you are glueing
no
what is the glue test sample
fractured wood must show atleast 75% of wood fibres
what device is best to cut fabric
pinking shears
what is dope
coating for fabrics, helps tighten, airtight, weatherproof.
what is a drawback for nitric dope
extremely flamable
is cotton a good fabric for aircraft
no
short service life
mildew, uv sensitive
not considered cost effective
what is polyester susceptible to
uv
can be prevented with coatings
where is glass fibre applied to
mainplane and tailplane in a spanwise direction
in what conditions should fabric be stored in
20c
dry
clean
out of direct sunlight
what are the 3 main common inspection panels
wood frames
zip panels
spring panels
are piercing fabric testing devices allowed
no
used at discretion of the engineer to form an opinion
what are the 2 types of fabric tester
maule
seyboth
are seyboth and maule fabric strength testers allowed on polyester
no
only allowed for cotton and linen
what stich is used for repairing cuts or tears
herringbone stitch
what is the selvage edge of a fabric
tightly woven edge that prevents fabric from unravelling
