Lecture 2 Flashcards
what are the differences between the properties of matrix and reinforcement?
matrix - soft & ductile.
Reinforcement - high strength and stiffness to enhance mechanical properties.
what is SAP and how does dispersion strengthened SAP’s its strength compare to other high strength metallic alloys over a temperature increase?
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.
what is internal oxidation?
Compact is heated in air and oxygen diffuses in to react
what are the 4 types of reinforcement
continuous fibres,
short fibres
whiskers
particles
what is the distinguishing feature of the reinforcement
aspect ratio
what is compocasting
mixing particles with semi-solid metal
what are simple characteristics of carbides particles?
How can they be improved? and why?
- carbides - hard and brittle
- toughness can be improved by including them in ductile metal matrix.
- Matrix isolates carbide particles and prevents crack propagation.
As the percentage of the binder is increased, how do the properties change?
Transverse rupture strength (TRS) improves whereas hardness and wear resistance decreases.
what attributes are good for tooling?
hard & wear resistant,
maintains red hardness
withstand thermal/chemical shock
able to be shaped to cut
application of cemented carbides?
inserts for cutting tools
what attributes are required for electrical contacts? What happens if not?
wear resistance,
electrical conductivity
If not, the contacts erode.
how do DISPERSED silicon carbide particles affect aluminium alloy castings?
what are applications?
strenghten and harden,
automotive
whats the production method of cast metal particulate MMC
compocasting
what is the minimum size requirements for a fibre
uniform diameter < 250um
Aspect ratio > 100
What is more flexible, matrix or fibre?
fibre more flexible.
what has more strength the thin fibre or a bulk material of the same composition
thin fibre
what is flexibility the inverse function of?
what does this mean?
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.
what is the flexural rigidity?
product of bending moment and radius
how are flexural rigidity and flexibility related?
inverse or each other
what is the equation for the flexibility?
since flexural rigidity is M*r, which is the inverse of flexbility,
flexibility = 1/Mr
therefore 1/Mr=1/EI
what are the attributes of boron? and what can they be used to improve
brittle material, used to stiffen aluminium for aircraft structures.
to allow bonding between boron and aluminium, what is done?
boron coated with SiC
what can be done with carbon fibre in terms of thermal expansion?
there is a negative CTE along fibre direction,
zero negative CTE can be made by combining with certain materials
what is a typical form of production for carbon fibre?
dipping/immersion
