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Properties & Applications of Engineering Materials Lesson 2
Andrew Pattendenon 3 March 2016
Transcript of Properties & Applications of Engineering Materials Lesson 2
Expansion and contraction
The movement of electrons causes electricity
Mechanical & Physical Properties
Aims of Lesson
Be able to describe, explain and understand
The range of mechanical, physical, thermal, electrical and magnetic properties as applied to engineering materials
Properties of engineering materials
What materials were used?
What properties are required of them?
What lessons are learned from this?
How would you stop this happening now?
Materials require a wide range of properties depending upon their given role
What is the difference between mechanical and physical properties?
Mechanical properties are defined as those material properties that measure a materials reaction to an applied force - Tensile strength and fatigue strength
Physical properties are properties other than mechanical properties that depend on the physics of the material, including density, thermal and electrical conductivity, and thermal expansion
strength, ductility, hardness, impact resistance, and fracture toughness are a few mechanical properties
This is the materials ability to withstand deformation
Maximum load before failure is apparent
How do we test for strength?
The amount of deformation will depend on the material being ductile or brittle
Effects of grain size on strength
How does grain size in metals affect their yield strength?
change in grain size affects the yield strength due to the dislocations interacting with the grain boundary as they move. The boundaries act as obstacles, hindering the dislocation glide along the slip planes. As subsequent dislocations move along the same slip plane the dislocations pile-up at the grain boundaries.
Capacity of material to deform permanently in response to stress
Steel is ductile - Glass is brittle
Ductile materials have an elastic limit
Beyond this the deformation is permanent
This is a materials ability to resist change when a compressive force is applied
Why is this useful?
Resist wear from external factors
Reduce wear on components
The amount of stress required to propagate a pre existing flaw in the material
An important quality -
- all material has flaws
Wide range of physical properties.
These may be the reason for its application in a given role
the state or quality of shining by reflecting light; glitter, sparkle, sheen, or gloss: the luster of satin. a substance, as a coating or polish, used to impart sheen or gloss
Melting and Boiling point
Why is this an important proprty?
In an engineering context where may this be important?
Yeah but no but............
Density = Mass / Volume
Where would you require a high density material?
Specific and Latent heat
How do metals transfer heat?
Amount of plastic deformation
Insulation through low density
What is electricity?
Why do certain materials conduct electricity better than others?
Valence electrons in the outer shell
Made out of metalloids such as Silicon
Silicon on its own is an insulator
But add a small amount of impurities such as......?
Boron, Arsenic or Gallium
All have odd number in outer electron shell
This allows the free electron to move and conduct electricity
When certain materials are super cooled to around -197 or below they strongly oppose magnetic fields.
All materials possess this property but it is very weak
This can produce some interesting reults
Electrically uncharged materials that strongly attract
Such as Iron
Used in a wide range of applications such as.......
Will become magnetic in the presence of a strong magnetic field
Used in MRI Scanners
Diamond is the hardest material known
Issues when used in industry
It disolves in Iron making it inefficient when cutting steels
Materials above 40Gpa on the Vickers test
Other materials are Cubic Boron Nitride
Boron Carbon Nitride