6.3 Flashcards
what is a composite material
2 or more materials combined to form a stronger compound
what are composite materials made of generally
a matrix which is the bonding substance and a reinforcing material
what are some advantages of composite materials
high strength to weight ratio, longer service life, higher corrosion resistance
what are some disadvantages of composite materials
inspection methods are difficult to do, there is little to no knowledge and experience, lack of standardised methods
what are the most common types of fibreglass
E-glass and S-glass
what is the commercial name for aramid
kevlar
what is aramid sensitive to
ultra violet light
what are the characteristics of aramid reinforcing fibres
low density, extremely flexible, high tensile strength, high toughness
what are the characteristics of carbon fibre reinforcing fibres
very strong and rigid but corrodes rapidly when bonded to aluminium
why is boron fibres not used in commercial aviation
too expensive and very hazardous
where are ceramic fibres used and why
high temperature areas because they are heat resistant
what direction is warp
the length of fabric as it comes off the roll
what direction is weft
perpendicular to warp
what direction is the bias
diagonally across warp and weft
what is the selvage edge
the edge that keeps the fabric from unwinding
what are mats
chopped fibres compressed together
what are the three main types of weave
plain, twill and satin
what is the resin matrix
the bonding material that surrounds the fibres
what are the two types of plastic
thermoset and thermoplastics
what is the difference between thermoplastic and thermoset
thermoplastic can be reversed when heated
what are epoxy resins used for and what type of plastic are they
thermoset and used for bonding non porous and dissimilar materials
what are pre impregnated fabrics
fabrics that already have the correct amount of resin saturated into it already
what are the advantages of pre impregnated fabrics
doesn’t produce resin rich or resin lean as mixture has been mixed correctly and very accurately
what are the disadvantages of pre impregnated fabrics
very short life span and must be kept in the freezer
what is a laminated composite
2 or more layers of reinforcing material bonded embedded together and embedded in a resin matrix
what is a sandwich composite
a core bonded between 2 thin face sheets
what is the most common form for the core material
honeycomb
what are the 2 forms transparent is manufactured in
monolithic and laminated
what are the advantages of plastics
light, cheap, corrosion resistant
what are the 2 forms of sealant
one part and two part
which form of sealant needs an accelerator
two part
what are some common defects of composites from manufacturing
anomalies caused by improper curing process, micro cracking, delaminations from poor processing
what are some defects in composites from service
impact damage, fatigue, cracks from local overload
what are the three main problems for honeycomb structures
low resistance to local impact, liquid ingression, erosion
what does liquid ingression in honeycomb lead to
change in mass, freezing of water which splits the layers, degradation of core materials
what is a NDT
a non destructive test
what NDT doesn’t need any equipment and is the primary inspection
visual inspection
what are the three different types of audible testing
coin, hammer and instrumented tap testing
what are the 4 most common ultrasonic inspection techniques
transmission, pulse echo, ultrasonic, phased array
what does a radiography inspection reveal
the inside of the composite material
what does a thermograph test for and what is the reaction
defects in composites which do not conduct heat as well as areas not affected
what are the 3 categories of damage
negligible, repairable and non repairable
what are cosmetic defects
defects that are on the outer surface and don’t affect the structure
what are the five basic categories of composite repairs
pre cured patches, potted, resin injection, laminate repair on one surface, laminate repair through part
what are bolted and bonded surface patches classed as and why
temporary repairs because they don’t restore the full strength characteristics and affect aerodynamics
what is fundamental for the success of a composite repair
surface preparation
what are the 4 major types of plastic failure
environmental, thermal, chemical, mechanical
what is crazing
an optical defect that indicates separation or parting of plastic
what needs to be done for scratches on plastic
only sand it if its necessary or try and buff it out
what can be done to plastics when they crack
use 1/8 inch drill bit to drill at extremities to stop propagation
what is the standard for wood
Sitka spruce
what are the characteristics of wood
way its cut, how the grain is shaped, annual growth rings and slope of grain
what is the normal cut for wood
quarter sawn
what other wood can be used as a direct replacement for Sitka spruce
Douglas fir
what type of wood cannot be a direct replacement for Sitka spruce and why
yellow poplar because it is not as strong
what can be used to show the grain slope on woods
free flowing ink
where are pitch pockets allowed in wood
in the centre of the beam
what does a knot do
significantly compromises the rings in the wood
what causes compression wood and can it be used in aircraft
tree leaning whilst growing and it cannot be used
what causes compression failures in wood and can it be used in aircraft
tree fell on log or uneven ground and it cannot be used
what problems can occur in wood due to poor drying
splits, checks and shakes
why can casein glue not be used anymore
it breaks apart the modern adhesives
what is the bonding process for wood
prep the surface, utilise good glue prepared correctly and perform a good bonding technique
what must happen on a test piece when its broken apart
more than 75% of the fibres of the wood are still connected to the glued surface
what is the moisture content in kiln dried woods
70%
what are the 3 common access methods for inspecting fabric structures
wood frames, zip panels and spring panels
what is the only thing that degrades polyester fabric
ultra violet light
what are the 2 types of fabric testers
maule punch test and seyboth punch test
what type of fabric tester works on the traffic light system
seyboth punch test
what does the rate of deterioration of fabric depend on
climate, humidity and storage conditions
what type of stitch is used for straight cuts
herringbone stitch
what is darning
adding warp and weft into a void to fill a hole
what is the preffered method of repair for fabrics
scarf patch
what does a nitrate dope do to a fabric
tightens and stiffens the fabric stretched over frames
what can be added to a dope to protect against ultraviolet light
aluminium
what is the unidirectional style of fabric
major fibres run in the warp direction
what is the bidirectional style of fabric
fibres run in 2 or more directions
what is the quasi-isotropic lay up style of fabric
stacking of fibres at a 45° or 60° intervals
what is the damage assessment and repair process for composites
1 Find the damage - clean the damaged area and remove surface coatings.
2 Assess the extent of the damage - use visual and NDI techniques and mark out the damaged area.
3 Define the repair procedure by referring to Structural Repair Manual (SRM).
4 Prepare the new repair plies or patch.
5 Lay-up plies or install patch repair.
6 Clean up the repair area and restore the external finish.
7 Inspect repair for structural integrity (use NDI, if required).
8 Document and reference the repair carried out.
what is a potted repair and what are its limitations
filling a small hole with a filler mixture can only be used on damage up to 1 inch
what type of repair can repair minor internal delamination and how
resin injection by injecting a resin mixture into the delaminated area
what needs to be done to repair damage to laminate from one side
remove the damage and prepare bonding patches that get bigger each time, layer them over each other until they reach the top then make sure there is a overlap of 1 inch
what needs to be done to repair damage to laminate that is through the part
start a step cut from both sides until they meet then insert patches and make sure that one side has 1 inch overlap at the end
what is the worst type of wood knot
spike knot
what are the most common wood spars
box beam, I beam spar, C section spar, plain rectangular spar, routed box spar
when repairing a spar what thickness must the reinforcing plates be
one quarter as thick as the spar
