L8 Polymers composites and ceramics Flashcards
Three main reasons to use plastics?
- Good mechanical properties in relation to density
- Easy to form
- Cheap materials
When polymer chains crossbond there are three different ways they can do this. What are they and what materials are bonds found in?
- Weak hydrogen bonds = Thermoplastics
- Some strong covalent bonds = Rubber
- Dens strong covalent bonds = Thermosetting
Three types of polymeric materials?
- Thermoplastics
- Thermosettings
- Rubber
What happens when polymer is heated up
It has no distinct melting temperature and becomes gradually softer with higher temperature
Four types of shaping thermoplastics?
Injection molding
Blow-forming
Vacuum forming
Extrusion
How do you shape thermosettings?
Casting and hardening
How do you shape rubber?
Forming and vulcanization (Vulcanization of a hardening form of rubber)
Thermoplastics can be recycled (True/False)
True
Thermosettings can be recycled (True/False)
False
Rubber can be recycled (True/False)
False
What are the properties of carbon fiber?
It is strong in the directions of the layers but weak between the layers.
What are the properties of graphene? (3st)
- High conductivity
- Extremely good mechanical properties.
- High price and CO2 footprint
What are the properties as glassfiber?
(Basically ordinary glass) (4st)
* Cheap and low CO2 footprint
* Isolator
* Brittle
* High compressive strength
Mechanical properties and bindings of kevlar?
C-C bindings in the fiber direction
It is a strong material
Properties and bindings of spectra/dynema?
C-C bindings in the fibre direction
It is a strong material
What is the properties of a fiber? (2)
A fiber can have very good properties that are better than homgeneous materials.
It has a direction of its chemical bonds. (it is strong in that direction)
What is requiered to use a fiber as an engineering material?
The fibre strings or planes must be held together, which will cause it to be a composite.
What are the two main fibers used?
Ceramic and polymeric
What is a laminate?
A composite built up from fiberplanes (lamellas) with different directions. This causes it to be strong in all directions.
What is a matrix in a composite?
The material that binds
together, usually a plastic (even
metal or ceramic)
What are reinforcements in a composite?
Strong material added to make the composite stronger
What are distance materials?
It is a material added to increase bending stiffness such as polymer foam.
Four upsides up composites?
- Can use fiber properties
- Often low density
- Can provide good crime toughness
- Can control properties
Three downsides of composites?
Manufacturing becomes more difficult and expensive
More difficulty in predicting properties
Difficult to recycle
