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MPM052 - Composite and nano-composite material > Lecture 3 - Reinforcement and matrices > Flashcards

Lecture 3 - Reinforcement and matrices Flashcards

1
Q

What 2 kinds of reinforcement can you have?

A

fibrous and particulate

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2
Q

Why do we use reinforcement?

A

To complement matrix properties

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3
Q

Which geometrical shape is the best?

A

Platelets

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4
Q

Order what reinforcement that is best to increase stiffness,
voids, long fibers (transverse direction), long fibers (longitudinal direction), hard particles, elastomeric particles

A
  1. Long fibers (Longitudinal direction)
  2. Hard particles
  3. Long fibers (Transverse direction)
  4. Elastomeric particles
  5. Voids
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5
Q

What relationship does fiber diameter and strength have?

A

Smaller diameter –> Higher strength

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6
Q

Why are materials typically more stronger in fiber form?

A

polymers: highly aligned and extended polymer chains

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7
Q

what do you call a single fiber?

A

Filament

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8
Q

What do you call several hundreds of thousands fibers?

A

Strands, rovings, yarns, tows

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9
Q

What do you call 10^5 fibers?

A

Heavy tows

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10
Q

What is Sizing?

A

Coating

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11
Q

Why do we use sizing?

A

• promotes chemical bonding between fibre and matrix, often by means of organosilanes or organo-
titanates, which are referred to as coupling agents (CA) or adhesion promoters (AP)
• protects the fibre from abrasion and hostile environments
• acts as a binder holding filaments together to form tows and the like
• soft or hard sizing may be desirable for a given manufacturing technique (‘soft’ or ‘hard’ in the present context refers to the tendency during processing to allow for de-bundling or not, respectively).

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12
Q

What 2 formations of fiber packing is there and what What is the maximum packing for both??

A

Hexagonal packing formation (90.7%) and Square packing formation (78.5%)

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13
Q

What range is usually fiber of volume fraction?

A

0.3-0.75

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14
Q

What is the most common issue with fiber packing?

A

getting it closed packed and even spread

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15
Q

How is fibers made?

A

By extrusion. Pellets are heated up and extruded through a small nozzle. The fiber is being “Pulled” with a faster speed to get aligned molecule chains and stronger material.

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16
Q

What happens long before the bending curvature is sufficient to cause tensile failure in a fiber?

A

The compression region of the fiber

undergoes yielding by the development of deformation (or kink) bands

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17
Q

When bending a fiber, what kind of stresses do you get?

A

Both compressive and tensile stresses

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18
Q

Does fibers follow normal distribution?

A

No, it is skewed, There is more bad fibers then excellent fibers.

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19
Q

What does a high Weibull value mean?

A

Smaller distribution

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20
Q

What does the Weibull parameter mean?

A

Degree of fiber flaw sensitivity

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21
Q

What is special with the solidification when injection moulding?

A

The surface will solidify first because of the cold mould. This will give compressive stresses at the surface and tensile stresses in the core

22
Q

When looking at discs to se the fiber orientation, which 3 patterns are available?

A

Random orientation, Radial orientation and Tangential orientation.

23
Q

What can you produce carbon fibers from?

A

Pitch (by-product of petroleum refining or coal coking) and poly(acrylonitrile) PAN (preferred preparation for
high stiffness grades)

24
Q

What kind of bindings does carbon fibers have?

A

Covalent bondings between atoms and van der Waals bondings between graphene layers.

25
Q

What are the 3 types of Carbon fibers available?

A
  • high strength (HS) - most commonly used ones
  • high modulus (HM) - most expensive ones
  • intermediate modulus (IM).
26
Q

Give som typical parameters for Carbon fiber

A
  • diameter typically of 8 μm
  • Young ́s modulus in fibre direction from about 230 to about 850 GPa, and strengths in the range 1.5 to 4.5 GPa
  • density of 1.77 to 2.16 g/cm3
  • transverse Young ́s modulus of about 6-35 GPa
  • strain to break from 0.6 to close to 2%
  • hydrophobic and inert (but oxidation resistance at high temperatures is low)
  • heating in oxygen, nitric acid, sodium hypochlorite is useful to roughen the surface and produce functional groups -CO2H- -C-OH- -C=O; this increasing adhesion to polymers. Silicon carbide etc can be deposited on surface; […]
  • electrically (HM types have higher conductivity) and thermally (particularly ex- meso-pitch) conductive
  • negative thermal expansion in axial direction down to -1.6 x 10-6 1/K, and slightly positive in transverse direction
  • service temperatures can be limited by oxidation onsetting in air between 300 and 400 ̊C, otherwise the fibre can withstand temperatures around 2000 ̊C
  • large variability in strength (stochastic) (Weibull parameter is low).
27
Q

How do you produce glass fibers?

A

You extrude molten glass

28
Q

What kind of glass fibers are available?

A
  • E-glass (electro-glass - early electrical applications) high strength and rather low stiffness at low cost
  • S-glass is a high-performance expensive grade (e.g. military applications), R-glass in europe, T-glass in Japan
  • C-glass - enhanced chemical resistance
29
Q

Give som typical parameters for glass fiber

A

• diameter typically of 8 to 15 μm
• Young ́s modulus of 69 to 85 GPa, depending on the type
• strength 3.45 to 4.60 GP, depending on the type
• density of 2.48-2.69 g/cm3, depending on the type
• types: E-glass (common), C-glass (resistance to chemical corrosion) and S-glass (higher stiffness and max. service temperature) (types are ranked with increasing silica content; various amounts of Al2O3, Fe2O3, CaO, MgO, Na2O+K2O, Ba2O3, BaO are also present)
• hydrophilic (moisture, alkali and acids decrease its strength); thus must be protected from environmental influences
• susceptible to abrasion and static fatigue
• service temperatures: tensile strength begins to decrease between 220 and 260 ̊C, falling to 50% by
480 to 560 ̊C
• coefficient of thermal expansion 5 x 10-6 1/K
• large variability in strength (Weibull parameter is low).

30
Q

How do you prepare Aramid fibers?

A

extruding an acidic solution of a proprietary precursor (possibly a polycondensation product of terephthaloyol chloride and p-phenylenediamine) from a spinneret

31
Q

What is the microstructure like in aramid fibers?

A

highly crystalline organic fibre, and aramid is a generic term for aromatic (lots of it!) polyamide

32
Q

What is the trade name for Aramid?

A

Kevlar

33
Q

Give som typical parameters for Aramid fiber

A

• density of 1.44 to 1.47 g/cm3
• depending on the type of fibre, the Young ́s modulus varies from 65 to 135 GPa
• tensile strength is 2.4-3.0 GPa and strain to break is 2.5 to 4.4%
• compressive strength is low (about 1/8 of tensile strength, the fibre fibrillates) (for
this reason among others it could be unsuitable for use in marine FRPs which can carry high compressive or bending loads, unless hybridized with glass or carbon)
• negative coefficient of thermal expansion of -2 x 10-6 1/K
• longterm service temperatures up to 160 to 180 ̊C, and up to 300 ̊C for a limited time
• fibre is highly damping (epoxy composites with Kevlar have 5x higher damping capacity compared to glass fibre/epoxy)
• sensitive to UV, even fluoroscent lamps
• plasma and light treatment improves adhesion to polymers.

34
Q

What does UHMWPE stand for?

A

Ultra-high molecular weight polyethylene

35
Q

How do you prepare UHMWPE?

A

gel spinning (to make it extrudable) from a dilute solution of PE in e.g. paraffin oil

36
Q

How do you achieve very high stiffness in polymeric materials like UHMWPE?

A

molecules need to be oriented and extended

37
Q

Give som typical parameters for UHMWPE fiber

A

• density of 0.97 g/cm3
• Young ́s modulus of 89-120 GPa
• tensile strength of 2.7-4.0 GPa, and strain to break 2.9-4.1%
• compressive strength only 2-3% of tensile strength
• excellent chemical and abrasion resistance
• strain rate sensitive and, unfortunately, prone to creep
• maximum service temperature is approximately 90 ̊C; pronounced loss of properties above 130 ̊C
• poor adhesion to polymer matrices (cold plasma treatment, corona discharge and
chemical etching improves the adhesion)

38
Q

Name some natural plant fibers

A

flax, hemp, jute, cotton, sisal, coniferous and deciduous wood

39
Q

What does the chemical composition always include in natural plant fibers?

A

cellulose (38-99%), hemi-cellulose (3-39%), lignin (3-34%) and also often ash, pectin and silica.

40
Q

Give som typical properties for natural plant fibers

A

• suitability for recycling/biodegradability, renewable material
• potential for improvement
• low density
• benefits derived from one- step, abrasion-free and lower-
pressure processing
• wood composites as compared to solid wood are that they are more homogeneous (e.g. without knots), the anisotropy can be controlled, and products can be designed in almost any shape
• attractive to combine natural fibres with polymer resins, particularly bioresins, for example poly(lactic acid)(PLA) or poly(trimethylene terephthalate)(PTTA)
• Plant fibres are hydrophilic - problem in wetting out the fibre is encountered, and rather ineffective interfaces are found
• still high per-weight cost, lower mechanical properties, moisture absorption and low temperature resistance

41
Q

What is a CSM?

A

A commonly used form of reinforcement, particularly for low-cost applications, it is a chopped strand mat (CSM), Bundles of discontinuous fibres are assembled together with random in-plane orientations.

42
Q

What does CSM stand for?

A

Chopped strand mat

43
Q

What kind of fiber array is used for advanced composites?

A

Textile technologies of weaving, braiding and knitting are used

44
Q

What do we use fillers for?

A

To lower the cost, to impact electrical conductivity, increase the functionality, reduce flammability.

45
Q

What are the idealized shape classes?

A

Sphere, cube, block, flake and fibre

46
Q

What can flakes be called with another name?

A

platelets

47
Q

What are hollow glass microspheres called?

A

microballons

48
Q

what is the advantage with glass beads?

A

for thermoplastics the viscosity increases less than for short fibres. Also compressive, shrinkage and abrasion resistance properties are increased. More recently,
hollow microspheres of increased crushing resistance have been developed, this facilitating the processing of composites. They do not reinforce but reduce weight and
dielectric constant.

49
Q

What is the challenge with recycling composites?

A
  • composites are multiphase systems
  • the dispersed phase (usually fibers) is very finely dispersed

This makes it hard to recycle

50
Q

What are the 4 stages of recycling and what do they mean?

A

• Primary recycling
regaining from waste, a material having
properties equivalent to the original material
• Secondary recycling
conversion of waste into a material having
properties inferior to those of the original material, for example blending of composite waste
• Tertiary recycling
conversion of waste into chemicals and fuels
• Quarternary recycling conversion of waste into energy.

51
Q

How do we recycle thermosets and thermoplastics today?

A

thermosets:milled –> powder –>new composite
Thermoplastics: melting –> reshaping

MPM052 - Composite and nano-composite material (12 decks)

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