Material Science Flashcards
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Crystalline Material
Atoms are arranged in structured lattices with long-range order.
Amorphous Material
Atoms are arranged in random structures with short-range order.
Polymeric Materials
Atoms are arranged in chain-like molecules.
Ductile
Material property describing its ability to be drawn out into wire.
Brittle
Material property describing its high stiffness, but low toughness. Brittle materials have a very small plastic region.
Strong
Material property describing high maximum stress that can be endured before fracture.
Tough
Material property describing its ability to absorb a lot of energy before fracture.
Necking
The cross-sectional area at the weakest surface point due to imperfections decreases as the material deforms plastically.
Hysteresis
The different behaviour of polymeric materials in a stress-strain relationship during loading and unloading.
Dislocations
Gaps in the ordered atomic lattice structure of crystalline materials which allows adjacent atomic planes to break their bonds, slip and reform at the terminating edge of the dislocated plane under stress. This causes the dislocation to move through the material, decreasing its strength.
Grains / Grain Boundaries
Crystallites, small areas of atomic planes with similar orientation, within polycrystalline or crystalline materials (no material is a perfect crystal).
The interfaces between them are difficult for dislocations to cross due to differences in atomic planes, meaning introducing more boundaries increases the strength of the material
Crack Propagation
Due to surface imperfections, surface bonds will break, but most stress is concentrated on inner bonds which break, causing crack propagation downwards.
Brittle Materials under Compression
Putting brittle materials under compression decreases the rate of crack propagation as more energy is required to separate each side of the crack. E.g. steel under strain in concrete.
Cross-Links
Placing extra molecules between polymer chains increases stiffness.
Proportional Limit
Point where Hooke’s Law stops being obeyed, stress is not longer proportional to strain.
Elastic Limit
Maximum stress a material can endure before plastic deformation.
Yield Point
Point where a material begins to permanently plastically deform.
Experiment details
Procedure:
Use longer wire for lower uncertainty in length
Measure diameter at several points on the wire
Ensure there are no kinks in the wire
Add load in incremental steps and acquire varying extensions
More loads
Repeat measurements
Constant temperature
Analysis:
Plot a graph of stress-strain to find gradient (Young’s Modulus)
Negligible uncertainty
Very low percentage uncertainty may be negligible in calculations
as it is small relative to more impactful uncertainties.
3rd Law
Every force has an equal and opposite reaction force.
Not 3rd law if forces not same type
Not 3rd law if forces acting on the same body
2nd Law
Momentum is the rate of change of force or F = ma
momentum = change in force / change in time
1st Law
An object will remain in inertia (stationary or constant velocity) unless an external force acts on it.
Compare star properties
Surface temperature
Colour (based on peak intensity wavelength)
Brightness (light intensity)
Black Body
Object that absorbs all EM radiation that falls on it.
Drop time depends on…
Drop height
Vertical acceleration component / gravitational force
Vertical velocity component
Conditions for equillibrium
Net force = 0
Sum of clockwise moments = sum of anticlockwise moments
Experiment
[diagram]
1. Set up equipment as shown.
2. Measure unstretched length of wire by holding it taut, but not extended.
3. Measure diameter of the wire using a micrometer, making sure to not compress the wire.
3. Set up ruler with 0 mark at the end of the hung wire and keep it still.
4. Add incrementing loads to the wire, recording the respective extension of the wire for each by reading from the 0 mark on the meter ruler to the new end.
5. Plot a graph of force-extension/stress-strain and find gradient / Young’s Modulus.
Momentum conservation
Momentum in a closed system remains constant, providing there are no external forces acting.
Center of Mass
Point where weight of an object seems to act.
