MSE 250 FINAL QUESTIONS AND ANSWERS
The region in a system of uniform (homogeneous) chemical comp (& structure), is
physically distinct (bounded), and mechanically separable (if multi-phasic) is a: -
Answer -A: phase
A relatively low-temperature reaction in which a liquid phase transforms isothermally
and reversibly upon cooling into two intimately mixed solid phases is the: - Answer -A:
eutectic
A solid solution that exists over a composition range extending to either composition
extreme of a binary phase diagram is a: - Answer -A: isomorphous solid solution
The locus of points on a phase diagram representing the limit of solid solubility as a
function of temperature is called: - Answer -A: solvus line
Explain briefly the difference between hypoeutectoid and hypereutectoid steels: -
Answer -A: A "hypoeutectoid" steel has a carbon concentration less than the eutectoid,
whereas "hypereutectoid" steel has a carbon content greater than the eutectoid.
For an 85 wt% Pb-15 wt% Mg alloy, make schematic sketches of the microstructure that
would be observed for conditions of very slow cooling at the following temperatures:
600C (1110F), 500C (930F), 270C (520F), and 200C (390F). Label all phases and
indicate their approximate compositions (4 points). - Answer -A: The illustration below
is the Mg-Pb phase diagram (Figure 9.20). A vertical line at a composition of 85 wt%
Pb15 wt% Mg has been drawn, and, in addition, horizontal arrows at the four
temperatures called for in the problem statement (i.e., 600C, 500C, 270C, and 200C).
From a plot of the stress
-strain curve, one may extract several
mechanical properties; briefly describe (in a line) how would you extract the following
properties? - Answer -A:
-Elastic modulus-it is the slope in the linear elastic region
-Yield strength-the stress corresponding to the intersection of 0.002 strain offset line
(parallel to the linear region) with the stress-strain curve
-Tensile strength-it is corresponding to maximum stress on the complete stress-strain
plot
-Ductility(lengthwise)-percent elongation due to plastic strain at fracture
-Fracture strength-stress corresponding the final point in the stress-strain curve
The energy stored in the elastic region is called: - Answer -A: Resilience
__________is estimated from the area under the full engineering stress-engineering
strain curve - Answer -A: Toughness
, A single crystal of aluminum is oriented for a tensile test
such that its slip plane normal makes an angle of 28.1 degrees
with the tensile axis. Three possible slip directions make angles
of 62.4 degrees, 72.0, and 81.1 degrees with the same tensile axis.
(a) Which of these three slip directions is most favored?
(b)If plastic deformation begins at a tensile stress of 1.95MPa,
determine the critical resolved shear stress (in MPa) for aluminum.
Given: Resolved shear stress is given by. tau=sigmaCOS(lambda)COS(phi) - Answer -
(a) Slip will occur along that direction for which (cos(phi)cos(lambda)) is a maximum, or,
in this
case, for the largest cos(lambda) for the possible
values are given below:cos(62.4)=0.46,cos(72)=0.31,cos(81.1)=0.15.
(b) Critical resolved shear stress calculated with:
tau=(1.95MPa)[cos(28.1)cos(62.4)]=0.80MPa
Define a slip system: - Answer -A: A slip system is a crystallographic plane, and,
within that plane, a direction along which dislocation motion (or slip) occurs.
Do all metals have the same slip system? Why or why not? - Answer -A: All metals do
not have the same slip system. The reason for this is that for most metals, the slip
system will consist of the most densely packed crystallographic plane, and within that
plane the most closely packed direction. This plane and direction will vary from crystal
structure to crystal structure.
What is the driving force for recrystallization? - Answer -A: The driving force for
recrystallization is the difference
or reduction in internal(or strain)energy
between the strained and unstrained material.
What is the driving force for grain growth? - Answer -A: The driving force for grain
growth is the reduction in grain boundary energy as the total grain boundary area
decreases.
A linear copolymer in which identical repeat units are clustered in blocks along the
molecular chain is called: - Answer -A: Block copolymer
A polymeric material that may experience large and reversible elastic deformations: -
Answer -A: Elastomer
Make comparisons of thermoplastic and thermosetting polymers (a) based on
mechanical characteristics upon heating, and (b) according to possible molecular
structures. - Answer -(a) Thermoplastic polymers soften when heated, whereas
The region in a system of uniform (homogeneous) chemical comp (& structure), is
physically distinct (bounded), and mechanically separable (if multi-phasic) is a: -
Answer -A: phase
A relatively low-temperature reaction in which a liquid phase transforms isothermally
and reversibly upon cooling into two intimately mixed solid phases is the: - Answer -A:
eutectic
A solid solution that exists over a composition range extending to either composition
extreme of a binary phase diagram is a: - Answer -A: isomorphous solid solution
The locus of points on a phase diagram representing the limit of solid solubility as a
function of temperature is called: - Answer -A: solvus line
Explain briefly the difference between hypoeutectoid and hypereutectoid steels: -
Answer -A: A "hypoeutectoid" steel has a carbon concentration less than the eutectoid,
whereas "hypereutectoid" steel has a carbon content greater than the eutectoid.
For an 85 wt% Pb-15 wt% Mg alloy, make schematic sketches of the microstructure that
would be observed for conditions of very slow cooling at the following temperatures:
600C (1110F), 500C (930F), 270C (520F), and 200C (390F). Label all phases and
indicate their approximate compositions (4 points). - Answer -A: The illustration below
is the Mg-Pb phase diagram (Figure 9.20). A vertical line at a composition of 85 wt%
Pb15 wt% Mg has been drawn, and, in addition, horizontal arrows at the four
temperatures called for in the problem statement (i.e., 600C, 500C, 270C, and 200C).
From a plot of the stress
-strain curve, one may extract several
mechanical properties; briefly describe (in a line) how would you extract the following
properties? - Answer -A:
-Elastic modulus-it is the slope in the linear elastic region
-Yield strength-the stress corresponding to the intersection of 0.002 strain offset line
(parallel to the linear region) with the stress-strain curve
-Tensile strength-it is corresponding to maximum stress on the complete stress-strain
plot
-Ductility(lengthwise)-percent elongation due to plastic strain at fracture
-Fracture strength-stress corresponding the final point in the stress-strain curve
The energy stored in the elastic region is called: - Answer -A: Resilience
__________is estimated from the area under the full engineering stress-engineering
strain curve - Answer -A: Toughness
, A single crystal of aluminum is oriented for a tensile test
such that its slip plane normal makes an angle of 28.1 degrees
with the tensile axis. Three possible slip directions make angles
of 62.4 degrees, 72.0, and 81.1 degrees with the same tensile axis.
(a) Which of these three slip directions is most favored?
(b)If plastic deformation begins at a tensile stress of 1.95MPa,
determine the critical resolved shear stress (in MPa) for aluminum.
Given: Resolved shear stress is given by. tau=sigmaCOS(lambda)COS(phi) - Answer -
(a) Slip will occur along that direction for which (cos(phi)cos(lambda)) is a maximum, or,
in this
case, for the largest cos(lambda) for the possible
values are given below:cos(62.4)=0.46,cos(72)=0.31,cos(81.1)=0.15.
(b) Critical resolved shear stress calculated with:
tau=(1.95MPa)[cos(28.1)cos(62.4)]=0.80MPa
Define a slip system: - Answer -A: A slip system is a crystallographic plane, and,
within that plane, a direction along which dislocation motion (or slip) occurs.
Do all metals have the same slip system? Why or why not? - Answer -A: All metals do
not have the same slip system. The reason for this is that for most metals, the slip
system will consist of the most densely packed crystallographic plane, and within that
plane the most closely packed direction. This plane and direction will vary from crystal
structure to crystal structure.
What is the driving force for recrystallization? - Answer -A: The driving force for
recrystallization is the difference
or reduction in internal(or strain)energy
between the strained and unstrained material.
What is the driving force for grain growth? - Answer -A: The driving force for grain
growth is the reduction in grain boundary energy as the total grain boundary area
decreases.
A linear copolymer in which identical repeat units are clustered in blocks along the
molecular chain is called: - Answer -A: Block copolymer
A polymeric material that may experience large and reversible elastic deformations: -
Answer -A: Elastomer
Make comparisons of thermoplastic and thermosetting polymers (a) based on
mechanical characteristics upon heating, and (b) according to possible molecular
structures. - Answer -(a) Thermoplastic polymers soften when heated, whereas
