MECE 305: Comprehensive Review for Exam 2
A dislocation loop has how many Burger's vectors? - correct answer ✔✔single Burger's vector
Everything else remaining the same in a given slip system, if the magnitude of the Burger's vector
increases then the shear stress required to move a dislocation - correct answer ✔✔increases
Everything else remaining the same in a given slip system, if the interplanar spacing increases then the
shear stress required to move a dislocation - correct answer ✔✔decreases
The Burger's vector of a pure edge dislocation is - correct answer ✔✔always perpendicular to the
dislocation line
The Burger's vector of a pure screw dislocation is - correct answer ✔✔always parallel to the dislocation
line
The Burger's vector of a strictly mixed (never edge or screw) dislocation is - correct answer ✔✔neither
parallel nor perpendicular to the dislocation line
A pure edge dislocation - correct answer ✔✔may be in the shape of a straight or curved line or a loop
A pure screw dislocation - correct answer ✔✔must always be in the shape of a straight line
When an effective shear stress of sufficient magnitude is applied to a dislocation, a line segment of the
dislocation moves (slips) in - correct answer ✔✔the direction perpendicular to the tangent of the line
segment
A dislocation loop - correct answer ✔✔can be purely edge in character
Face Centered Cubic (FCC) metals are relatively soft and ductile because - correct answer ✔✔A)
their slip systems comprise of close packed planes
, B)
they have relatively large number of slip systems
C)
their slip systems comprise of close packed directions
Hexagonal Closed Packed (HCP) metals are typically more brittle than FCC or BCC metals because -
correct answer ✔✔HCP has much fewer slip systems
A dislocation line segment - correct answer ✔✔always moves in a direction perpendicular to itself
The direction of the effective shear stress to move a pure edge dislocation is - correct answer ✔✔always
perpendicular to the dislocation line
The direction of the effective shear stress to move a pure screw dislocation is - correct answer
✔✔always parallel to the dislocation line
After a piece of copper wire from a hardware store is heated it becomes softer. This is because - correct
answer ✔✔it has fewer dislocations
In heavily deformed metals, the density of dislocations is - correct answer ✔✔10^11 to 10^12 cm-2
If a rod of metal is pulled through a tapered hole smaller than the diameter of the rod, the strength of
the metal in the rod increases. This is because - correct answer ✔✔it has more dislocations
Polycrystalline aluminum has ten times or more yield strength than single crystal aluminum. This is
because the obstacles to dislocation motion in polycrystalline aluminum are - correct answer ✔✔grain
boundaries
Strain hardening is a useful strengthening mechanism but it has the following disadvantage - correct
answer ✔✔it decreases the ductility of the material
A twin boundary in a crystalline solid is an example of - correct answer ✔✔a planar defect
A dislocation loop has how many Burger's vectors? - correct answer ✔✔single Burger's vector
Everything else remaining the same in a given slip system, if the magnitude of the Burger's vector
increases then the shear stress required to move a dislocation - correct answer ✔✔increases
Everything else remaining the same in a given slip system, if the interplanar spacing increases then the
shear stress required to move a dislocation - correct answer ✔✔decreases
The Burger's vector of a pure edge dislocation is - correct answer ✔✔always perpendicular to the
dislocation line
The Burger's vector of a pure screw dislocation is - correct answer ✔✔always parallel to the dislocation
line
The Burger's vector of a strictly mixed (never edge or screw) dislocation is - correct answer ✔✔neither
parallel nor perpendicular to the dislocation line
A pure edge dislocation - correct answer ✔✔may be in the shape of a straight or curved line or a loop
A pure screw dislocation - correct answer ✔✔must always be in the shape of a straight line
When an effective shear stress of sufficient magnitude is applied to a dislocation, a line segment of the
dislocation moves (slips) in - correct answer ✔✔the direction perpendicular to the tangent of the line
segment
A dislocation loop - correct answer ✔✔can be purely edge in character
Face Centered Cubic (FCC) metals are relatively soft and ductile because - correct answer ✔✔A)
their slip systems comprise of close packed planes
, B)
they have relatively large number of slip systems
C)
their slip systems comprise of close packed directions
Hexagonal Closed Packed (HCP) metals are typically more brittle than FCC or BCC metals because -
correct answer ✔✔HCP has much fewer slip systems
A dislocation line segment - correct answer ✔✔always moves in a direction perpendicular to itself
The direction of the effective shear stress to move a pure edge dislocation is - correct answer ✔✔always
perpendicular to the dislocation line
The direction of the effective shear stress to move a pure screw dislocation is - correct answer
✔✔always parallel to the dislocation line
After a piece of copper wire from a hardware store is heated it becomes softer. This is because - correct
answer ✔✔it has fewer dislocations
In heavily deformed metals, the density of dislocations is - correct answer ✔✔10^11 to 10^12 cm-2
If a rod of metal is pulled through a tapered hole smaller than the diameter of the rod, the strength of
the metal in the rod increases. This is because - correct answer ✔✔it has more dislocations
Polycrystalline aluminum has ten times or more yield strength than single crystal aluminum. This is
because the obstacles to dislocation motion in polycrystalline aluminum are - correct answer ✔✔grain
boundaries
Strain hardening is a useful strengthening mechanism but it has the following disadvantage - correct
answer ✔✔it decreases the ductility of the material
A twin boundary in a crystalline solid is an example of - correct answer ✔✔a planar defect
