Sample Midterm/Final Questions

Question 1

At 548 degrees celsius, aluminum can dissolve up to 6% copper as a substitutional solid solution. If this alloy is quenched in water to room temperature:

a) It becomes a super-saturated solid solution of aluminum of aluminum which can be further heat treated by aging to optimize the alloy’s mechanical properties.
b) The copper atoms squeeze into the spaces between the aluminum atoms but precipitate out of solution upon quenching.
c) The crystal structure is basically that of FCC aluminum with some of the aluminum atoms replaced by CuAl2.
d) The structure consists of grains of pure aluminum which makeup 94% of the weight of the material. The remaining 6% of the weight occurs as grains of pure copper.
e) The crystal structure of the solid so

Answer 1

a) It becomes a super-saturated solid solution of aluminum of aluminum which can be further heat treated by aging to optimize the alloy’s mechanical properties.

from Parv pack, p.1

Question 2

Which of the following may occur during an annealing heat treatment of a previously cold-worked alloy?

a) Internal stresses may be relieved.
b) Ductility will increase.
c) Toughness may increase.
d) A new microstructure may be produced.
e) All of the above.

Answer 2

e) All of the above.

from Parv pack, p.1

Question 3

Your company tells you to increase the factor of safety (N) for a component that has a working load of 20 kN. The component must not deform permanently under load. Which of the following changes would increase the factor of safety?

a) increasing the tensile load on the component
b) selecting a material with smaller work hardening coefficient (n)
c) decreasing the cross sectional area of the component
d) changing to a material with a higher yield strength
e) the safety factor is a constant that cannot be changed

Answer 3

a) or d)

from Parv pack p.2 & 22

Question 4

A cylindrical specimen of a metal alloy of 48.5 mm long and 9.72 mm in diameter is stressed in tension. A true stress of 393 MPa causes the speciment to uniformly plastically elongate to a length of 57.2 mm. If it is known that the strain-hardening exponent for this alloy is 0.20, calculate the true stress (in MPa0 necessary to plastically elongate a specimen of this same material from a length of 48.5 mm to a length of 54.7 mm.

a) 253
b) 368
c) 433
d) 529
e) 563

using true stress equation

Answer 4

b) 368

from Parv pack p.2 & 22

Question 5

A copper matrix is reinforced with 20% tungsten particles. The modulus of elasticity for copper is 110 GPa and that for tungsten is 407 GPa. Estimate the minimum modulus of elasticity for the composite material.

a) 348 GPa
b) 264 GPa
c) 169 GPa
d) 129 GPa
e) 52 GPa

using composite material formula for E

Answer 5

d) 129 GPa

from Parv pack p.3

Question 6

For a particular metal of σ_o=0, the grain size increases from 35 X 10^-6 m to 70 X 10^-6 m, the yield strength changes in the following way:

a) it decreases by a factor of 1.41
b) it increases by a factor of 1.41
c) it does not change
d) it decreases by a factor of 4
e) it increases by a factor of 4

Answer 6

a)

from Parv pack p.3 & 17 and another page too

Question 7

Which of the following statements is correct? For a cold worked material:

a) The higher the amount of prior cold work, the lower the recrystallization temperature.
b) The higher the melting temperature of the material, the lower the recrystallization temperature.
c) The density of dislocations increases with increasing temperature.
d) The longer the time of heating, the higher the recrystallization temperature.
e) Pure materials recrystallize at higher temperatures than solid solutions.

Answer 7

a)

from Parv pack p.3&17&another

Question 8

The elastic moduli in the 0 degree and the 90 degree directions of a unidirectionally reinforced composite (e.g. unidirectional carbon fibres in an epoxy matrix) can be calculated using the iso stress and iso-strain models. These models assume that:

a) The fibres are free to slide in the matrix
b) When the fibres are loaded in the iso-train case, the fibres and matrix both elongate by the same amount
c) When the fibres are loaded in the iso-stress case, the fibres and matrix both carry the same load
d) Answers (b) and (c) are correct
e) Answers (a), (b), and (c) are correct

Answer 8

d) or e) or B)?

from Parv pack p.4 & 18 and another

Question 9

In order to form tempered martensite in medium and high carbon steels, the correct heat treatment involves:

a) heat into the martensitic region and slowly cool to room temperature
b) heat into the austensitic region, quench and temper at 200 degrees - 600 degrees
c) heat into the austensitic region, quench and temper at 800 degrees.
d) heat into the ferritic region, quench and temper between 200 degrees - 600 degrees
e) heat into the martensitic region, quench and temper between 200 degrees - 600 degrees

Answer 9

d) heat into the ferritic region, quench and temper between 200 degrees - 600 degrees (but fact check this answer!!!)

from Parv pack p.4 & 18 &other

Question 10

With reference to the Charpy impact test, which of the following statements is true?
a) FCC metals typically show a strong dependence of impact energy absorbed as a function of test temperature
b) High strength metals always show high toughness and are not affected by test temperature
c) The Ductile-Brittle transition refers to the impact speed when the metal can no longer deform plastically
d) The Ductile-Brittle transition temperature occurs at a fixed temperature for a given metal (like a melting point)
e) For a structural steel, a lower Ductile-Brittle transition temperature is desirable

Answer 10

d) The Ductile-Brittle transition temperature occurs at a fixed temperature for a given metal (like a melting point) (or e), check!)

from Parv pack p.4 & p.19

Question 11

Which of the following statements concerning dislocations is false?
a) In an edge dislocation, b, the Burger’s vector, is parallel to the slip direction
b) In a screw dislocation, b, the Burger’s vector, is parallel to the slip direction
c) In an edge dislocation, b, the Burger’s vector, is perpendicular to the dislocation line
d) In a screw dislocation, b, the Burger’s vector, is perpendicular to the dislocation line
e) Both edge and screw dislocations can cause slip.

Answer 11

b) or e) or D?

from Parv pack p.5 p. 19

Question 12

Which of the following strengthening methods for metals and alloys is best suited for high temperature applications?
a) grain size reduction
b) strain hardening
c) dispersion strengthening
d) precipitation hardening
e) None of the above as the metals will recrystallize

Answer 12

c) dispersion strengthening

or maybe d? check in notes

from Parv pack p.5

Question 13

Which of the following statements is false?
a) The driving force for recrystallization is the difference in internal energy between the strained and unstrained material.
b) Prior cold working is essential for recrystallization.
c) Recrystallization removes dislocations which restores the ductility of the metal, without changing the size of the grains.
d) Recrystallization is a function of temperature and also a function of time at that temperature.
e) Cold working results in a change of grain shape, an increase in hardness and strength and an increase in dislocation density.

Answer 13

c) is false, the grains get finer

from Parv pack p.5, p.20

Question 14

The heat treating of steels (quenching and tempering) can be used to change some of the mechanical properties of the steel. This process can be described as:
a) a softening of the material during quenching, followed by a hardening treatment during tempering.
b) a “freezing in” of the soft, annealed microstructure, followed by the formation of martensite during tempering.
c) the formation of hard martensite during quenching, followed by a controlled softening during tempering.
d) the formation of a martensitic phase on quenching which gets harder with tempering
e) a recrystallization process that removes all dislocations followed by controlled deformation during tempering to increase the yield strength

Answer 14

c) the formation of hard martensite during quenching, followed by a controlled softening during tempering.

from Parv pack p.6, p.20

Question 15

A metal obeys the Hollomon relationship and has K = 581 MPa and n = 0.3. Knowing that the true strain at the onset of necking has a value equal to n, what is the true stress for this metal at this point?
a) 405 MPa
b) 175 MPa
c) 300 MPa
d) 581 MPa
e) 1.9 GPa

using the true stress equation

Answer 15

a) 405 MPa

from Parv pack p.6, p.20

Question 16

True or False:

When subjected to torsion, a brittle specimen breaks along planes perpendicular to the direction in which tension is a maximum, i.e., along surfaces at 45 degrees to the shaft axis whereas a ductile material fails along planes parallel to planes of maximum shear stress.

Answer 16

True
(Brittle materials are weaker in tension than in shear)

from Parv pack p.7

Question 17

True or False:

After cold-working, the recrystallization temperature is normally higher for a pure metal than for its alloys.

Answer 17

False

from Parv pack p.7

Question 18

True or False:

BCC metals (48 slip systems) are generally more ductile and easier to plastically deform than FCC (12 slip systems) and HCP (3 slip systems) metals because the BCC metals have more slip systems.

Answer 18

True

from Parv pack p.7

Question 19

True or False:

“Over-ageing” in reference to age-hardened alloys (such as Al-4%Cu) refers to the process by which the alloy gets harder and stronger with aging (in a similar fashion to cheese).

Answer 19

True?

from Parv pack p.7

Question 20

True or False:

One of the best ways of strengthening a metal is to increase the grain size. This means the dislocations have further to travel and thus the yield stress is increased. It is also the only strengthening method which does not decrease ductility.

Answer 20

True or False

from Parv pack p.7&16&24

Question 21

True or False:

Martensite is a super-saturated, solid solution of carbon in body centered tetragonal iron. It is a meta-stable phase that does not appear on the Fe-Fe₃C equilibrium phase diagram.

Answer 21

True

from Parv pack p.7,16 & 23

Question 22

True or False:

In ductile metals, sharp cracks are blunted by localized plastic deformation whereas in brittle materials such as ceramics the cracks stay sharp hence causing higher stress concentration.

Answer 22

True

from Parv pack p.7

Question 23

For plain carbon steels with pearlitic microstructures, the hardness and the yield strength increase as the carbon content of the steel increases but the impact toughness and the DBTT (ductile to brittle transition temperature) decrease.

Answer 23

True

from Parv pack p.8

Question 24

FCC metals usually exhibit a more severe ductile-to-brittle transition at low temperatures than BCC materials.

Answer 24

True

from Parv pack p.8

Question 25

During the recovery of a cold-worked material, the electrical resistivity increases as the dislocations rearrange into networks which slow down the free electrons.

Answer 25

False or True ?? (check)

from Parv pack p.8, 16, 23

Question 26

Metals bend at room temperature due to the movement of dislocations. Crystalline ceramics do not bend plastically at room temperature, therefore they do not contain dislocations.

Answer 26

True

from Parv pack p.8, 23

Question 27

For most metals there is a linear relationship between the Brinell Hardness and the tensile strength.

Answer 27

True

from Parv pack p.8

Question 28

A metal plate with a 3mm long edge crack perpendicular to the applied tensile stress is subjected to a stress of 425 MPa. The alloy has a KIC value of 36 MPa m1/2 and the Y parameter is 1.0. The plate will fail by fast fracture at this stress.

Answer 28

True

from Parv pack p.8 and 23

Question 29

In precipiration hardening, a higher strength and hardness are obtained from coherent precipitates than from incoherent (mismatched lattices) precipitates.

Answer 29

True

from Parv pack p.8, 15, 23

Question 30

Precipitation hardening is a two stage process: the first step is a solution treament in which a single phase material is formed at relatively low temperature (T₁) then quenched and the second stage is the precipitation (or ageing) treatment which is carried out a high temperature (T₂) where T₂ > T₁

Answer 30

True or False (on page 15), check

from Parv pack p.8, 15, 24

Question 31

The Charpy impact test is used to measure:
a) the yield stress of a material
b) the fracture stress of a material
c) the ductility at fracture
d) the energy absorbed by the specimen at fracture
e) the fracture toughness (K_IC) of a material

Answer 31

d) the energy absorbed by the specimen at fracture

from 2011 midterm

Question 32

The data for a single crystal hypothetical metal is given below. If the applied tensile stress is 100 MPa, the resulting resolved shear stress is approximately:

• Yield tensile strength = 130 MPa
• Angle between Burgers vector and close packed direction = 0
• Angle between the slip plane normal and tensile axis = 30
• Angle between the normal to the close placked plane and close packed direction = 90
• Angle between the slip direction and the tensile axis = 85
• Angle between the dislocation line and close packed direction = 60

a) 0 MPa
b) 7.5 MPa
c) 43 MPa
d) 50 MPa
e) 86 MPa

Answer 32

b) 7.5 MPa

from 2011 midterm

Question 33

A rod is cold drawn from an initial diameter of 1.0 cm to 0.5 cm. The amount of cold work in the final rod is closest to:

a) 10%
b) 25%
c) 50%
d) 75%
e) 100%

Answer 33

d) 75%

from 2011 midterm

Answer 34

from 2011 midterm

Answer 35

from 2011 midterm

Answer 36

from 2011 midterm

Answer 37

from 2011 midterm

Answer 38

from 2011 midterm

Answer 39

from 2011 midterm

Answer 40

from 2011 midterm