Sem 2 - Composites Flashcards

1
Q

Describe Pearlitic steel structure

A

microstructure of alternating cementite (Fe3C) and ferrite layers (α).
α is soft and ductile
Fe3C is hard and brittle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Generally describe Large particle strengthened composites

A

particulate phase is harder and stiffer than the matrix
particle tend to restrain movement of the matrix
its large because the particle interactions are not at atomic or molecular scale

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe carbon black reinforced rubbers

A

Added to vulcanised rubber to enhance toughness and abrasion resistance.
The particles must be evenly distributed and form a strong adhesive bond with the matrix.
Tyres have about 15-30vol% of carbon black.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Advantages and disadvantages of cement

A

it is a pulverized material that develops binding force due to a reaction with water
It can be poured and set at room temperature even under water
Disadvantages:
relatively weak and brittle
tensile strength is only one tenth of the compression strength
large structure experience considerable thermal expansion and contraction with temperature
water can get into external pores and cause cracking in cold weather

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why is steel used in reinforcing concrete

A

they have similar thermal coefficients
it does not corrode in cement environments
relatively strong adhesive bonds forms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe dispersion strengthened materials

A

The matrix-particle interactions lead to strengthening to occur on the atomic level
The matrix bears a major portion of the load and particles hinder the motion of dislocations
Plastic deformation is restricted so yield and tensile strengths are improved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Factors which have a significant affect on strength in a composite material

A
  • arrangement and orientation of fibres relative to each other
  • fibre concentration
  • distribution
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

2 stages of the stress strain graph of reinforced composite materials

A

Stage one
fibres and matrix deform elastically and this is linear
Stage two
the matrix yields and deforms plastically, fibres continue to stretch elastically
Tensile strength of the fibre is greater than the matrix
Onset of composite failure begins as fibres start to fracture corresponds of strain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does composite failure differ from regular materials

A

It is not catastrophic as not all the fibres don’t fracture at the same time. The matrix stays intact, so the fractured fibres are still embedded in the matrix and are capable of sustaining a diminished load

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is transverse strength influenced by

A

Properties of the matrix and fibres
fibre-matrix bond strength
presence of voids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why are randomly orientated fibre composites used?

A

in applications with multidirectional stresses
reinforcement given is around 20% of an aligned composite but its the same in all directions
fabrication costa are lower and production rates are more rapid than continuous fibre reinforced composites

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Describe the fibre phase of whiskers

A

V thin crystal strands with extremely large length to diameter ratio
virtually flaw free as it had a perfect crystalline structure
strongest known materials
They are rarely used as they are very expensive (graphite, silicon carbide and aluminium oxide)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe the fibre phase of fibres

A

can be polycrystalline or amorphous
have small diameters and are usually polymers or ceramics
examples glass carbon boron aluminium oxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the fibre phase of wires

A

large diameter
used in the wire wound high pressure hoses
examples : steel molybdenum tungsten wire used in radial steel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe the matrix phase in fibre reinforced composites

A

the phase binds together the fibres and acts as a medium to transmit applied stress and distribute to fibres
Matrix is ductile
Elastic modulus of the fibres&raquo_space; matrix
Protects fibre from mechanical abrasion and chemical reactions
separates fibres to stop crack propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why are the bonding forces important between the matrix and fibre

A

the bonding must be high to reduce fibre pull out
to an extent the ultimate strength of a composite depends on the magnitude of this bond
adequate bonding ensures maximum stress transmittance between the weak matrix to the strong fibres

17
Q

Describe a polymer matrix

A

a polymer resin as the matrix and fibres as the reinforcement medium
it has a diverse composite applications
they have useful temperature properties, so they can be easily fabricated with relatively low cost

18
Q

Limitations of Glass fibre reinforced polymer

A

high strength but not very stiff

Limited to applications at temperature <200C because polymers start to flow and deteriorate.

19
Q

Why is carbon used in advanced composites

A

carbon fibres have the highest specific modulus and strength of all reinforcing fibres
Retain high tensile modulus and strength at high temps
At room Temp carbon fibres aren’t affected by moisture or solvent acids and bases
relatively inexpensive and cost effective manufacturing