Week 3 (not done)

Question 1

What happens to solid materials as we heat them?

Answer 1

THERMAL EXPANSION

Question 2

Define thermal expansion

Answer 2

How much something expands for a given temp

Question 3

Thermal expansion is a different _____ of strain

Answer 3

Type

Question 4

Atoms per unit cell for FCC

Answer 4

4

Question 5

Atoms per unit cell of BCC

Answer 5

2

Question 6

Atoms per unit cell for HCP

Answer 6

6

Question 7

Atoms per into cell for SC

Answer 7

1

Question 8

Volume of a sphere

Answer 8

Question 9

Why are sharp flaws worse than round flaws

Answer 9

They create stress CONCENTRATION points that lead to faster crack propogation

Question 10

How do we QUANTIFY resistance to crack propagation

Answer 10

Question 11

Define DBTT

Answer 11

The temp where a material changes from being predominantly ductile to predominantly brittle

Question 12

How is DBTT found experimentally

Answer 12

Charpy testing

(Energy absorbed by sample during impact is measured, temp which energy sharply decreases is the DBBT)

Question 13

What are the 3 stages of creep

Answer 13

Primary

Secondary

Tertiary

Question 14

What would you do to find the cross sectional area at which fatigue would not occur

Answer 14

Question 15

When would you use Paris law

Answer 15

When you need to predict the rate of fatigue crack propagation under cyclic conditions

Question 16

3 stages of creep on a graph

(And what are the axis labels)

Answer 16

X: strain rate
Y: time

Question 17

Define creep

Answer 17

Long term cyclic loading causes plastic deformation

Question 18

2 ways to reduce the risk of creep failure

Answer 18

Lower operating temp (temp accelerates creep deformation)

Reduce stress

Question 19

Answer 19

“Sudden failure, rupture”

Growth of micro cracks accumulates

Question 20

And why

Answer 20

Temperature

(Thermal energy enhances atomic mobility to accelerate creep)

Question 21

Define Bragg’s law

Answer 21

Describes the conditions for constructive interference of x rays/neutrons when they interact with a Crystal lattice

(X ray diffraction in a material)

Question 22

Bragg’s law formula

Answer 22

Question 23

What does Bragg’s law measure?

Answer 23

The spacing between crystal lattice planes in a material

Question 24

What materials will Bragg’s law not work on (and why)

Answer 24

Amorphous materials

(irregular/curved surfaces don’t give good x ray diffraction)

Question 25

3 examples of amorphous materials

Answer 25

Glass

Rubber

Plastic

Question 26

How is the strength of ceramics tested

Answer 26

3 point bending

Compression and tension

Question 27

Question 28

Question 29

Why does tensile strength vary in seemingly identical metal samples

(Is this the same for ceramics?)

Answer 29

Differences in grain size, orientation, impurities, defects

(Microscopic variations change the materials response to stress)

YES

Question 30

Define yield strength

Answer 30

Max stress a material can withstand without undergoing permanent deformation

Question 31

Increasing temp: what happens to yield strength

Answer 31

Decrease, atoms slip more easily from thermal activation

Question 32

Increasing temp: what happens to ductility

Answer 32

Increases

Question 33

Increasing temp: what happens to creep rate

Answer 33

Increases

Question 34

Increasing temp: what happens to impact energy absorbed at fracture

Answer 34

Increases

Question 35

Increasing temp: what happens to Young’s modulus

(Why)

Answer 35

STAYS THE SAME

(Temp doesn’t alter material’s elastic properties which are determined by its atomic and molecular structure)

Question 36

Increasing temp: what happens to electrical conductivity

(And why)

Answer 36

Goes down

(Collisions from thermal energy impede the flow of electrons)

Question 37

Increase in temp: what happens to tensile toughness

Answer 37

Depends

(for materials that remain ductile at high temps it may increase, alloys)

Question 38

Define coefficient of thermal expansion

Answer 38

How much a material expands or contracts in response to changes in temp

Question 39

Where is bond energy on this energy-distance graph

Answer 39

Weird E

Question 40

Where is equilibrium bond distance on this energy-distance graph

Answer 40

ro

Question 41

Where are the attractive and repulsive energy curves on this graph

Answer 41

Be careful of order!!!

Question 42

How would you draw these on an energy distance graph

Answer 42

Red: inner curve
Blue: outer curve

Think opposite (small goes to big)

Question 43

Which curve has a HIGHER CTE

Answer 43

A (since lower energy)

Question 44

Which curve has the higher melting point

(And why)

Answer 44

B

(more energy, steeper hill going up)