Dislocations Flashcards
How is the orientation of a dislocation specified?
By the direction of the tangent vector
What is a Burgers vector?
The vector needed to close a circuit (around a dislocation), from its final point to the starting point
How does a Burger vector change for two dislocations?
The circuit measure the total Burgers vector inside the contour
Describe an edge location.
Introducing a cut signifies a dislocation line, the faces of the cut displace relative to each other by the Burgers vector
Describe screw dislocations.
A ‘cutting-displace-gluing’ mechanism, where the displacement faces are parallel to the edge of the cut
Describe a mixed dislocation.
Tangent vector varies along the dislocation line, the Burgers vector will be expressed in terms of the perpendicular and parallel components
Describe how we know that the Burgers vector of dislocations is conserved.
-Consider a dislocation segment with Burgers vector b1
-If the dislocation splits into two other segments with Burgers vectors b2 and b3
-Since the Burgers circuit measure the Burgers vector of dislocations contained within it, b1 = b2 + b3
What parameters determine the energy of a dislocation?
Shear modulus and magnitude of the Burgers vector
What are partial dislocations?
Dislocation which has Burgers vector whose magnitude is a fraction of the lattice spacing, the atoms between the partials form a stacking fault
Why do partial dislocations form?
When there is a reduction in enegry
How do we determine if a dissociation will occur?
If the energy change associated with the reaction at the first dislocation is greater than that associated with the split dislocations
How do we determine if two dislocations will combine to form a new segment?
If the energy associated with with the reaction at the first dislocation is lower than that associated with the split dislocations
What does the Orowan-Bailey relation describe?
Shear strain increment
