Week 3 (not done) Flashcards
What happens to solid materials as we heat them?
THERMAL EXPANSION
Define thermal expansion
How much something expands for a given temp
Thermal expansion is a different _____ of strain
Type
Atoms per unit cell for FCC
4
Atoms per unit cell of BCC
2
Atoms per unit cell for HCP
6
Atoms per into cell for SC
1
Volume of a sphere
Why are sharp flaws worse than round flaws
They create stress CONCENTRATION points that lead to faster crack propogation
How do we QUANTIFY resistance to crack propagation
Define DBTT
The temp where a material changes from being predominantly ductile to predominantly brittle
How is DBTT found experimentally
Charpy testing
(Energy absorbed by sample during impact is measured, temp which energy sharply decreases is the DBBT)
What are the 3 stages of creep
Primary
Secondary
Tertiary
What would you do to find the cross sectional area at which fatigue would not occur
When would you use Paris law
When you need to predict the rate of fatigue crack propagation under cyclic conditions
3 stages of creep on a graph
(And what are the axis labels)
X: strain rate
Y: time
Define creep
Long term cyclic loading causes plastic deformation
2 ways to reduce the risk of creep failure
Lower operating temp (temp accelerates creep deformation)
Reduce stress
“Sudden failure, rupture”
Growth of micro cracks accumulates
And why
Temperature
(Thermal energy enhances atomic mobility to accelerate creep)
Define Bragg’s law
Describes the conditions for constructive interference of x rays/neutrons when they interact with a Crystal lattice
(X ray diffraction in a material)
Bragg’s law formula
What does Bragg’s law measure?
The spacing between crystal lattice planes in a material
What materials will Bragg’s law not work on (and why)
Amorphous materials
(irregular/curved surfaces don’t give good x ray diffraction)
3 examples of amorphous materials
Glass
Rubber
Plastic
How is the strength of ceramics tested
3 point bending
Compression and tension
Why does tensile strength vary in seemingly identical metal samples
(Is this the same for ceramics?)
Differences in grain size, orientation, impurities, defects
(Microscopic variations change the materials response to stress)
YES
Define yield strength
Max stress a material can withstand without undergoing permanent deformation
Increasing temp: what happens to yield strength
Decrease, atoms slip more easily from thermal activation
Increasing temp: what happens to ductility
Increases
Increasing temp: what happens to creep rate
Increases
Increasing temp: what happens to impact energy absorbed at fracture
Increases
Increasing temp: what happens to Young’s modulus
(Why)
STAYS THE SAME
(Temp doesn’t alter material’s elastic properties which are determined by its atomic and molecular structure)
Increasing temp: what happens to electrical conductivity
(And why)
Goes down
(Collisions from thermal energy impede the flow of electrons)
Increase in temp: what happens to tensile toughness
Depends
(for materials that remain ductile at high temps it may increase, alloys)
Define coefficient of thermal expansion
How much a material expands or contracts in response to changes in temp
Where is bond energy on this energy-distance graph
Weird E
Where is equilibrium bond distance on this energy-distance graph
ro
Where are the attractive and repulsive energy curves on this graph
Be careful of order!!!
How would you draw these on an energy distance graph
Red: inner curve
Blue: outer curve
Think opposite (small goes to big)
Which curve has a HIGHER CTE
A (since lower energy)
Which curve has the higher melting point
(And why)
B
(more energy, steeper hill going up)
