Week 9: Composites Flashcards
What is a composite made up of?
Matrix and a filler
Matrix
Holds the filler together like a glue
(chocolate in the kit-kat)
Filler
Part of the composite to increase elastic modulus, TS and hardness (biscuit in kit-kat)
PMC
Polymer matrix composite
CMC
Ceramic matrix composite
MMC
Metal matrix composite
What do the properties of composites depend on?
Volume fraction, particle shape, particle size, size distribution and orientation
Are the properties the same in longitudinal and transverse directions?
No, they’re different
Longitudinal deformation
Fibers aligned in the longitudinal direction, so stronger there compared to transverse
Ultimate TS
TS before failure
What does elongation at break measure?
The ductility of a material
What does increasing the fiber volume lead to?
+ Impact strength
+ Flexural strength
+ Storage modulus
PFRP
Natural composites
GFRP
Glass-fiber reinforced composites
CFRP
Carbon-fiber reinforced composites
SFRP
Silk-fiber reinforced composites
Why is the orientation of fibers important?
It can change the strength of a composite
Critical Fiber Length
Length that determines effective stiffness and strength of a composite
What are the 2 types of GFRP?
E: electrical - used because of its electrical resistance (ladder)
S: high strength - used in military and aerospace
What bonds do aramid fibers have?
Hydrogen bonds
What are the 4 main manufacturing processes?
- Pultrusion
- Filament winding
- Closed mould
4.Open mould
Pultrusion
Where continuous fibers are pulled through resin impregnation tank, then pulled to shape
Filament Winding
Where continuous fibers are fed though a resin bath and then wound and heated
What are the 3 closed mould processes?
- Injection
- Transfer
- Compression
Injection moulding
Pellets put through hopper and heated then injected into a mould
Transfer moulding
Moved through narrow channels into desired shape
Transfer moulding
Moved through narrow channels into desired shape
Compression moudling
Resign and filler squashed into desired mould
Where are closed mould processes used?
Mass production of identical parts and for smooth surfaces
What are some open mould processes
- Hand lay up
- Spray up
- Tape lay up
- Vacuum infusion
What are the 5 parameters for successful manufacturing?
- Choice of matrix (thermoset vs thermoplastic)
- Low moisture
- Thermal transition temperatures
- Resin flow / rheology (viscosity of polymer)
- Heat of reaction and exotherm
What are 3 structural composites?
- Laminar composites
- Sandwich panels
- Nano-composites
Laminar composites
Composites arranged in different directions
Why are sandwich panels used?
High strength and low ductility
What’s a material used to make nano-composites?
Graphene
