Reinforcement Materials Flashcards by Yashna Bully

What are ideal requirements for a composite material?

Good stiffness (or desirable property).
Good bonding with matrix
Rough surface better
Small particles better
Coating (stearic acid, silanes)
Chemical and thermal stability.
Low cost
Low health and environmental concern.

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What type of particle fillers are there?

Calcium carbonate CaCO3
Silica SiCO2
Calcium hydroxide (talc)
Mica
Koalin
Wollastonite
Glass Spheres
Titanium dioxide
Metal powders

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What are the properties of Calcium carbonate CaCO3 (particle filler)?

Including chalk
General purpose / low cost filler.
Gives good stiffness.
Whiteness and UV protection.

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What are the properties of Silica SiO2 (particle filler)?

Good stiffness
Good bonding so good strength
Can give whiteness.

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What are the properties of Calcium hydroxide (talc) (particle filler)?

Plate like
gives reasonable stiffness.
it allows easier colouring than silica and calcium carbonate.

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What are the properties of Mica (particle filler)?

Plate-like in nature, and easily fractures along the plates can cause strength reductions and so is less common.

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What are the properties of Kaolin (particle filler)?

Tend to give better crack resistance than the other filters, but they do impart a darker colour to the material.

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What are the properties of Wollastonite (particle filler)?

Has a needle like morphology, and can almost be considered to be a fibre reinforcement.
As such, it does tend to give good strength properties.

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What are the properties of Glass spheres (particle filler)?

Can be used to give reflectivity and smooth surfaces, although the bonding to the polymer tend to be worse than for the rougher particle shapes.

Hollow spheres produced by including a gas forming agents dissolved in a glass particle which expands on heating.

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What are the properties of Titanium Dioxide (particle filler)?

Also quite commonly used as filler.
Although it is primarily present for its colouring behaviour.

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What are the properties of Metal Powders (particle filler)?

Used to increase density and electrical conductivity or give magnetic behaviour.

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What are graphene nanoparticles?

Serval atom layers to 10 nm.
Micro-structure graphite.
Thickness of up to 1 um.

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What are carbon nanotube?

Graphite like structure.
Joined up in cylinders.
Interesting electrical, chemical properties.
Very good structural properties.
can be MWNT or SWNT

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What is the difference between single walled nanotube (SWNT) and multiple walled nanotube (MWNT)?

MWNT’s can be either concentric or spirals.
SWNT’s have diameter ~ 1nm
MWNT’s up to 10nm

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How are carbon nanotube produced?

Commercial production based on CVD of carbon monoxide.
Either on metal catalyst particle (Ni, Fe, Co).
Or on seed tubes.
MWNT’s easier to produce and so are cheaper.

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What are the properties of carbon nanotube?

Stiffness: 1,000 GPa
Strength: 60 GPa
Density: 1,400 kg/m3
Toughness: unknown, but quite good.

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Why are carbon nanotube used?

Use in composites limited by cost.
Mass production may reduce this.
Need excellent dispersion and bonding.
Damascus steel has been found to contain CNT’s

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What are critical challenges for GNP dispersion in composite?

To ensure good dispersion.
To ensure limited curling.
To ensure good bonding.
To get improved orientation.
Functionalisation may help chemical method with graphene oxide.

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What is the structure of glass fibre?

Based on silica tetrahedra
- Si atoms bonded to 4 O atoms.
- Gives overall compositions of SiO2.
- Would be very hard to process.
- Structure modified with other atoms.
- Na, Mg, Ca, K, Al, B

How are glass fibre bonded?

The Si atoms are bonded to O atoms by covalent bonds, so quite stiff.
The direction of the bond random on average and so only some covalent bonds go along the fibre direction.
In addition, network modifiers open up the structure with more flexible ionic / secondary bonds.

How is glass fibre processed?

Simply melted and passed through circular dies.
Pulled into fibres (typically 10 um diameter).
Coated with a “size”
To protect the surface from damage.
To give better bonding to matrix.

Types of Glass Fibres

E-glass: Best processibility and good general purpose fibres.
C-glass: Better chemical resistance.
S-glass: Higher strength.
ECR and AR Glass: Good acid and alkali resistance.

What are the properties of glass fibre?

Stiffness: 70-85 GPa
Strength: Up to 2GPa (E-glass)
Up to 3GPa (s-glass).
Density: 2,500 kg/m3
Toughness: 0.75 MPa.m(1/2)
Strength limited by brittleness.

How are graphite like structure bonded?

In carbon fibres, they’re covalently bonded between C atoms.

However graphite sheets are oriented along the fibre axis, so covalent bonds are oriented along the fibre, giving a higher modulus.

The modulus can be further increased with more orientation to give HM fibres.

How can carbon fibre produce and what are there charcteristic?

Cannot process graphite. - To brittle - Melting point 3675 degree Start with fibre of carbon-based material. - PAN most common. - Pitch also used. Convert this to graphite like structure by heat treatment.

What are polyacrylonitrile?

Polyacrylonitrile (PAN) are when molecules are stretched and heated (in air to 280 deg) to produce oriented ladder-like molecules.

What cause graphitisation?

Heating up argon up to 2800 degs

Type of carbon fibre

HM fibres - More hear treatment leads to better alignment of graphite structure. - Greater stiffness - More defects and so lower strength. HS Fibre - Less heat treatment gives converse.

What are the properties of carbon fibres properties?

Stiffness: 230 (HS) - 380 (HM) GPa Strength: 4.5 GPa (HS) 2.7 GPa (HM) Density: 1,800 kg/m3 Toughness: 1- 1.5 MPa.m(1/2)

What are polyaramids (polymer fibres)?

- Kevlar (Du Pont) is most famous. - Rigid polymer chains. - Liquid crystalline polymers (order in liquid phase).

How are Polyaramids processed?

- Processed by extruding fibres from solution. - Then extend and heated. - Gives very highly crystalline fibres.

What are properties of polyaramids?

- Tough fibres. - Do not melt. - Limited to temperatures below 300 deg. - Low flammability for a polymer. - Do degrade in sunlight (UV).

What are the properties for Aramid (polymer) fibre?

Stiffness: 130 GPa Strength: 2.5 GPa Density: 1,450 kg/m3 Toughness: > 5 MPa. (1/2)

What are polyethylene (polymer fibres)?

- Stiffness of up to 300 deg. - For this, needs to be 100% crystalline and 100 % oriented. - Gel - spun - Tradenames: 'spectra', 'dyneema'

What are characteristic of polyethylene (polymer fibres)?

- High toughness, high strength, high stiffness and low density. - Limited to temperatures below 100 deg (melts at 130 deg). - Poor bonding to matrix materials. -Expensive.

What are the properties polyethylene (polymer) fibres?

Stiffness: 170 GPa Strength: 2.7 GPa Density: 970 kg/m3 Toughness: >5 MPa.m (1/2)

What do covalent bonding give?

- High stiffness - High strength - High temperature resistance - Low toughness

What are Silicon Carbide? (Ceramic Fibres)

- Chemical vapour deposition (CVD). - Uses a tungsten (or carbon) core. - Many small crystals of SiC grown on core. CH3SiCL3 (gas) > SiC (solid) + 3 HCI (gas)

What does CVD method produce?

Chemical Vapour Deposition (CVD) method produce large diameter (150 um) "monofilaments".

What is silicon carbide (ceramic fibre) used for?

- Can use a polymer fibre pre-cursor (as with C fibres). - Polycarbosilane (PSC) most common. - Converted to SiC (and some SiO2) - Comprises many small crystals. - "Nicalon" most widely used commerical version.

What are silicon carbide whiskers?

- The only type that are single crystals (and so get best strength and stiffness). - Produced from chemical reactions in gas phase. - Or extracted from rice husks. - Small ( <1um diameter, 50 um length).

What are the properties of silicon carbide (ceramic fibre)?

Stiffness: 250 GPa (Nicalon) 700 GPa (Whiskers) Strength: 2.2 GPa (Nicalon) 8 GPa (Whisker) Density: 2,600 kg/m3 (Nicalon) 3,200 (whisker)

How are Boron Fibres (ceramic) produced?

- Produced by chemical vapour deposition onto a tungsten core. - Produces large diameter monofilaments, similar to SiC. 2BCI(3) (gas) + H(2) (gas) > 2B (solid) + 6HCI (gas)

What are the properties of Boron Fibres (ceramic)?

Stiffness: 400 GPa Strength: 4 GPa Density: 3,000 kg/m

How thin does a fibre need to be to never crack?

K1C = 1.1*stress(c)*(sqrt(pi*a)) K1C: fracture toughness = 0.75 MPa/m(1/2) Stress(c): stress required to get crack to propagate. a: crack length (yield stress = 2GPa).

How much can you bend a fibre?

- Important for properties, but especially for processing. - Determined by strength, stiffness, diameter. Maximum surface tensile stress: Sigma(f) = d*E / 2R d - fibre diameter E - modulus R - radius of curvature When tensile stress equals failure, sigma(f), can find the smallest radius of curvature possible R = d.E /2*sigma(f) Smallest radius of curvature = tighter bend).