Composites Flashcards
What are the 3 most common types of glasses used in fibre form?
- E-Glass (electrical) - this has good strength / stiffness as well as good insulation and weathering properties.
- C-Glass (chemical) - this has very good all round chemical resistance. It is more expensive than E-Glass and has lower strength.
- S-Glass (strength) - again this is more expensive than E-Glass but has a higher strength and stiffness.
What is the structure of glass?
3D polyhedral network containing atoms around a silicon atom with strong covalent bonds.
What is the manufacturing process of glass fibre?
Raw material storage
Furnace 1370C - molten glass
Refiner 1340C
Forehearth 1260C - pressure head due to gravity, winding drum
Fibres are produced in bundles or strands which are treated with size as they are drawn. Several strands are put together to form ROVING.
Fibre diameter is largely controlled by?
- Head of glass (pressure)
- Viscosity (temperature / composition)
- Winding speed
What is the surface treatment process? What effects can size induce?
Often a coating of water based (SiH4 or PVA) is applied early in the processing.
- Coating and protecting the surface
- Helping to bind the fibres together
- Aiding Lubrication
- Acting as an anti-static agent
- Aiding fibre bonding to the matrix
What is the strength of glass fibre dependent on?
The 3D structure / network itself, dependent on the variety and relative proportions of the oxides present. the properties tend to be fairly ISOTROPIC due to random 3D structure.
Processing conditions and the environment. typically new (undamaged) fibres have a tensile strength of approximately 3.5Gpa (high) and show low variability.
Moisture, mineral acids and damage due to rubbing / abrasion can seriously degrade the properties, this adversely affects the tensile strength.
What are the characteristics of carbon fibre?
An extremely lightweight fibre is defined as a fibre containing at least 92wt% carbon. A strand can consist upto 50,000 fibres comprised of carbon atoms, each 5-10um thick.
High tensile strength
Lightweight
High strength to weight ratio and high elastic modulus
What are applications of carbon fibre?
Aerospace
Wind turbines
Helmets
Bicycle frames
Automotive (cars)
What are the 2 structures of carbon fibre?
Graphite structure - single crystal, the atoms are stacked in hexagonal arrays and are stacked ABAB planes. Layer B is misaligned with Layer A.
Held together WITHIN a plane by covalent bonds.
Held together BETWEEN planes by weak Van der Waals bonds.
Turbostratic structure - large number of very small crystals (crystallites). There is no regular stacking (no ABAB).During fabrication, sheet become entangled, randomly folder, tilted, crumpled
What structure is stronger for carbon fibre?
Turbostratic carbon is stronger than graphite
Graphite has greater elastic modulus
What are aramid fibres?
Aramid fibres (kevlar), based on the high strength and stiffness that is possible in fully aligned polymers. Chain alignment (crystallinity) and extension can occur during drawing, stretching and spinning.
What are applications of kevlar?
Kevlar 29 - brake lining, body armor
Kevlar 49 - ropes, cables
What are the different formats of fibre?
Continuous
Woven
Chopped
Hybrid
What do matrix materials do?
Binds fibres, transmits loads to fibres.
Matrix should be more ductile, fibre should have higher E modulus.
Matrix protects fibres from surface damage (cracks)
Matrix prevents cracks propagating from one fibre to the next which could cause catastrophic failure.
What are thermosetting resins?
The most common are epoxy or polyester based. They are available in a wide variety of formulations that cover a range of physical and chemical properties.
Mechanical properties depend largely upon:
1. The molecular units making up the chain
- The length of chains and the density of the cross-links (covalent bonds)
They do not melt, they char, degrade or burn.
