Lecture 2 - How To Choose A Material ? Flashcards
What are 3 factors to consider when choosing a material
Stiffness, strength, density etc
What are the 6 classes of materials
Metals, ceramics, glasses, polymers, Composites and natural materials
What are 3 electrical properties of Cu
Highly conductive metals
Adding impurity atoms increases resistivity
Deforming Cu increases resistivity
What are 3 mechanical properties of metals
Stiff with range
High density of range
Mouldable ( can be shaped and worked)
What are ceramics
Crystalline, mainly metal oxide
What type of conductivity and chemical attack does ceramics have
Low thermal conductivity
Good resistance to chemical attack
What type of structure does ceramics have
A highly defined crystallographic structure
What are 5 typical properties of ceramics
Generally stiff and hard, but brittle
Medium density
Low liquid uptake
Good thermal stability
Can suffer from low crack growth
What type of material is glass
Disordered or amorphous ( no long range atomic order)
6 properties of glasses
Amorphous
Medium stiffness
Very brittle
Very notch sensitive
Generally transparent
Used in optical fibre for data transmission
What is a polymer
A large molecule composed of many subunits called monomers
What are polymers mostly made from
Carbon
Hydrogen
Oxygen
Synthetic polymers includes plastics and are natural biopolymers such as DNA
6 properties of polymers
Flexible
Long extension to failure
Tough
Low density
Many soften and melt at relatively low temperatures (thermoplastics)
Some don’t melt at any temperature ( thermosets)
In metals what are the charge carriers
Electrons
What are the charge carriers in semiconductors
Either electrons or missing electrons (a hole)
What happens in semiconductors when electrons and holes meet
They emit light
What are semiconductors
Materials that have conductivity between conductors and insulators.
Not as conductive as metals
Engineered with tiny amounts of impurities of different alloys
Conductions only when excited
Specific electrical properties
What is a superconductor
A material that has no electrical resistance and doesn’t allow magnetic fields to penetrate when cooled below a certain temperature
Can support current at 0 resistance and produce high magnetic fields
What is the use of composites
Optimise the properties of the phases
3 typical properties of composites
Depends on -
Component materials
Method of production of the composites
Amounts and shapes
4 examples of natural materials
Wood
Cork
Leather
Bone
When applying a force what does this produce
Deformation
When results when you apply defromation
Results in a force
What happens when you apply force/stress
Causes an object to deform
What is normalised deformation called
Strain
What does tensile stress produce
Produces longer and thinner specimen
What does compression produce
Shorter a nd fatter specimens
What is strain nearly proportional to when in small amounts
Strain is nearly proportional to stress
What is bulk modulus
Resistance to uniform compression