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Composites > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

what are the differences between the properties of matrix and reinforcement?

A

matrix - soft & ductile.

Reinforcement - high strength and stiffness to enhance mechanical properties.

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2
Q

what is SAP and how does dispersion strengthened SAP’s its strength compare to other high strength metallic alloys over a temperature increase?

A

SAP-sintered aluminium powder

it is not as strong at low temps but strength degrades at a slower rate than alloys and at +300C it has better strength.

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3
Q

what is internal oxidation?

A

Compact is heated in air and oxygen diffuses in to react

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4
Q

what are the 4 types of reinforcement

A

continuous fibres,
short fibres
whiskers
particles

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5
Q

what is the distinguishing feature of the reinforcement

A

aspect ratio

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6
Q

what is compocasting

A

mixing particles with semi-solid metal

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7
Q

what are simple characteristics of carbides particles?

How can they be improved? and why?

A
  • carbides - hard and brittle
  • toughness can be improved by including them in ductile metal matrix.
  • Matrix isolates carbide particles and prevents crack propagation.
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8
Q

As the percentage of the binder is increased, how do the properties change?

A

Transverse rupture strength (TRS) improves whereas hardness and wear resistance decreases.

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9
Q

what attributes are good for tooling?

A

hard & wear resistant,
maintains red hardness
withstand thermal/chemical shock
able to be shaped to cut

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10
Q

application of cemented carbides?

A

inserts for cutting tools

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11
Q

what attributes are required for electrical contacts? What happens if not?

A

wear resistance,
electrical conductivity

If not, the contacts erode.

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12
Q

how do DISPERSED silicon carbide particles affect aluminium alloy castings?
what are applications?

A

strenghten and harden,

automotive

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13
Q

whats the production method of cast metal particulate MMC

A

compocasting

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14
Q

what is the minimum size requirements for a fibre

A

uniform diameter < 250um

Aspect ratio > 100

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15
Q

What is more flexible, matrix or fibre?

A

fibre more flexible.

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16
Q

what has more strength the thin fibre or a bulk material of the same composition

A

thin fibre

17
Q

what is flexibility the inverse function of?

what does this mean?

A

inverse function of the modulus of elasticity and the 2nd moment of area.
determined by shape, mod of elasticity is intrinsic and independent of size.

18
Q

what is the flexural rigidity?

A

product of bending moment and radius

19
Q

how are flexural rigidity and flexibility related?

A

inverse or each other

20
Q

what is the equation for the flexibility?

A

since flexural rigidity is M*r, which is the inverse of flexbility,
flexibility = 1/Mr

therefore 1/Mr=1/EI

21
Q

what are the attributes of boron? and what can they be used to improve

A

brittle material, used to stiffen aluminium for aircraft structures.

22
Q

to allow bonding between boron and aluminium, what is done?

A

boron coated with SiC

23
Q

what can be done with carbon fibre in terms of thermal expansion?

A

there is a negative CTE along fibre direction,

zero negative CTE can be made by combining with certain materials

24
Q

what is a typical form of production for carbon fibre?

A

dipping/immersion

25
Q

what are 4 challenges of carbon fibres

A

weak perpendicular to fibre direction
conduct electricity
volumetric defects occur (organic and inorganic inclusions, voids from rapid coagulation, issues in manufacturing)
tendency to generate aluminium carbide

26
Q

how can you ensure less defects in carbon fibre?

A

heat treatment, hot stretching

27
Q

how does aluminium carbide affect the carbon fibre?

A

detrimental to the thermal conductivity and material stability

28
Q

what is a filament and yarn?

A

filament - single thread like fibre

yarn - twisted collection of filaments

29
Q

what is a roving

A

untwisted bundle of filament, yarns or tows.

30
Q

how many filaments is a tow?

A

over 100,000

31
Q

What creates the electric conductivity in a carbon fibre?

A

the galvanic coupling between the matrix and the fibre

Composites (5 decks)

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