6.3 - Composite/Non Metallic Flashcards
What are the two basic elements of a composite and what do they do?
Matrix:
- bonding substance
- transfers stress to the fibre
Reinforcing material(fabric)
What are the advantages and disadvantages of composites?
+high strength to weight ratio
+reduction in fasteners
+corrosion resistance
- expensive
- not easy to repair
What is the main purpose of the reinforcing material?
Gives the major strength to the composite material
What is Nomex used for?
Flame-proof clothing due to its high heat resistance
What are the two main Fibreglass types and what are their perks?
E-glass: electricity resistant
S-glass: high tensile strength
What are the main characteristics of fibreglass?
- low density
- high strength
- NOT water/humidity resistant
What are the main characteristics and uses of Aramid?
- yellow
- light weight
- high tensile strength
- non-flammable
- used in high vibration/stress areas
e. g. props
What are the main uses of Kevlar?
Bulletproof vests
Belts for radial tyres
Cables
Reinforced composites for aircraft
What are the main disadvantages of Kevlar?
-fibres absorb moisture
-not compression
resistant
-difficult to cut
-UV sensitive(turns brown)
What is main property of Carbon Fibre?
Electrical conductivity
What is the orientation of the Warp?
Threads run along the length
What is the orientation of the Weft?
Perpendicular to the Warp
What is the selvage edge?
Tightly woven edge, runs parallel to the Warp
What is the bias?
Runs 45deg to the Warp, allows for the creation of complex contours.
What are Unidirectional Fibres?
The major fibres run in the direction of the Warp
What are Bi-Directional Fibres?
The fabric runs in two or more directions
What is the newer type of matrix?
Epoxy resins
What are the two categories of Resins?
Thermoplastics
Thermosets
What is a thermoplastic?
Once heated, the final shape is not permanent
What is a thermoset?
Once heated the final shape is permanent
What is an Epoxy resin?
A type of thermoset plastic resin, used to bond dissimilar materials
What is Prepreg?
- Pre-impregnated fabrics
- already have the resin in them
- stored in a freezer
What is a ‘sandwich’ construction?
The core is bonded between two thin sheets, makes a light weight, rigid structure
What are the two honeycomb fabrication processes?
- corrugated
- expansion
What is Polymerisation?
Creating a long chain of Molecules from small Monomers, doesn’t create any by-products.
What is Polycondensation?
Removes by-products such as water/acids
What is Polyaddition?
Reaction of different molecules when reactive groups are brought together.
What is a Thixotropic agent?
A thickening agent
Name two examples of Thixotropic agents?
Micro-balloons
Aerosil
What considerations must taken when mixing resins?
Never mix in a wax container
Always weigh at an ambient temperature
Mix between 3 and 5 minutes
Do not mix too quickly, bubbles may form
What is BVID?
Barely Visible Impact Damage
What is Delamination?
The separation of composite surfaces, damage may not be visible on the surface.
Name examples of NDT’s
Tap testing Visual Bond tester Ultrasonic Radiography (X-ray)
What must be remembered when removing surface protection?
Always use mechanical methods, chemical methods can deteriorate the resin.
What is Wet Lay-Up?
The application of several layers of resin impregnated fabric over a damaged area.
