Chapter 7 - Dislocations Flashcards
what is the difference between a edge and a screw dislocation?
Edge: dislocation line moves in the direction of the applied shear stress
Screw: dislocation line is perpendicular to the stress direction
Which type of material is dislocation motion the hardest?
ionic ceramics
covalent ceramics
metals
do dislocations tend to happen in polymers?
no, therefore slip is brittle failure is more likely then slip
why do ceramics fail brittley rather than by dislocation slip?
In ceramics, it is most likely to fail because of flaws rather than sufficient stress to cause dislocation movement.
dislocations in Carefully solidified metal crystals:
10^3 mm-2
dislocations in Heavily deformed metals:
10^9 to 10^10 mm-2
dislocations in Ceramic materials:
10^2 to 10^4 mm-2
dislocations in Silicon single crystals:
0.1 to 1 mm-2
what is strain energy?
Pot. energy that is gained during elongation.
what is a slip plane ?
A crystallographic plane on which slip occurs most easily.
What is slip direction ?
A crystallographic direction along which slip occurs most easily.
what does the formula 𝜏R = F’/A’?
𝜏R = tensile component of shear stress
F’ = force acting along the slip direction.
A’ = area of the slip plane
What is this formula: F’ = F * cos(λ)?
F’: Force along the slip direction
F: Applied tensile force
λ (lambda): Angle between the force direction and slip direction
What is this formula: A’ = A / cos(φ)?
A’: Area of the slip plane
A: Cross-sectional area perpendicular to the tensile force
φ (phi): Angle between the normal to the slip plane and the tensile force direction
What is this formula: 𝜏R = (F / A) * cos(λ) * cos(φ)?
𝜏R: Resolved shear stress
F: Applied tensile force
A: Cross-sectional area perpendicular to the tensile force
λ (lambda): Angle between the force direction and slip direction
φ (phi): Angle between the normal to the slip plane and the tensile force direction
What is this formula: 𝜏R = σ * cos(λ) * cos(φ)?
𝜏R: Resolved shear stress
σ (sigma): Applied tensile stress (F / A)
λ (lambda): Angle between the force direction and slip direction
φ (phi): Angle between the normal to the slip plane and the tensile force direction
When is resolved shear stress at its maximum
when phi and lambda is at 45 degrees
what is slip?
a small fraction of the metallic bonds across the interface needs to be a broker at a time.
does increasing dislocation mobility increase or decrease the strength
decreases
does reducing grain size increase or decrease dislocation motion?
it decreases
what is this formula: σyield = σ0 +ky d^-1/2
σyield: This represents the yield stress of the material. It is the stress at which the material begins to deform plastically.
σ0: This is the intrinsic yield strength of the material, which is the yield strength in the absence of any grain boundaries.
ky: constant given
d: This represents the average diameter of grain
What is this formula: d^n - d0^n = K * t?
d: Average grain size after heat treatment
d0: Initial average grain diameter before heat treatment
n: Exponent, typically around 2
K: Material constant (depends on temperature, T, but independent of time, t)
t: Heat treating time
what is solid solution strengthening, and what does it do to dislocation motion?
it introduces impurity atoms that distort the lattice, and act as barrier to dislocation motion
what is strain hardening?
plastically defomring metals at room temp, makes them harder and stronger. while introducing dislocations.
