Exam Questions Flashcards
(31 cards)
Which material (polymers, metals, ceramics) is ionic bonding mainly found in?
Polymers
What is the fracture appearance of the surface of a ductile material?
Dull with voids
What test is used to determine the ductile brittle transition temperature?*
Impact test
When stress or temperature increases, what else occurs?
- Steady state creep rate increases
- Instantaneous strain increases
- Rupture lifetime decreases
Which crystal structures have the same APF?
FCC & HCP
(74%)
What is Poisson’s ratio?
A contraction perpendicular to the extension caused by a tensile stress
How do you thermally toughen glass?
Creating compressive stresses in the surface layer (air jets)
Which materials are most difficult to recycle?
Composites
Isotropic Materials
Deformation is the same in all directions
What is a key feature of fibres in composites?
High E
What material typically has a high embodied energy?
Aluminium
What is a typical sacrificial material for cathodic protection of steel?
Zinc or Aluminium (boat blocks)
What happens when you increase temperature when tensile testing PE?
TS decreases, E decreases, YS decreases, %EL increases
(Fails later)
Which material is an oxidizing film typical for?
Aluminium
What are thermoplastics composed of?
Long chain-like molecules held together by weak van der Waals forces
Why does diamond have a higher yield strength than copper wire?
Covalent bonds in diamond cause dislocations to be immobile
Less dislocations means higher YS
An amorphous ceramic is heated just above the glass transition temperature. This
transition causes it to become a…
Supercooled liquid
How do you determine the ductile-brittle transition temperature?
Using a Charpy impact test
You find the average of the max and min impact energies
Tangent Modulus
Finding the gradient at a specific poitn
Secant Modulus
Finding the gradient through a specific point
Poisson’s ratio takes the ratio of what two strains?
Lateral / Longitudinal
What is viscoelasticity?
Where a material has properties of both an ideal elastic body and viscous liquid, leading to a time dependency when returning to undeformed state
How are relaxation and viscoelastic creep tests different?
Relaxation (Maxwell):
- Stress is measured against time
- Strain is held constant
- Dashpot and spring in series
Creep (Voight-Kelvin):
- Strain is measured against time
- Stress is held constant
- Dashpot and spring in parallel
What’s the difference in oxidation and reduction?
OIL RIG
Oxidation is a loss of electrons and occurs at the anode.
Reduction is a gain of electrons and occurs at the cathode
