L8 polymers composites and ceramics Flashcards
Three main reasons to use plastics? (3)
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 fibre?
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 for glassfibre? 4
(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 fibre 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 for 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
