Microstructure and performance Flashcards
What is the incompressibility condition?
Plastic deformation occurs without a change in volume, plasticity depends on shear independent of pressure
What is the effective stress?
A multiaxial measure of shear
What are principle stress/strain?
Normal to orthogonal planes on which there are no shears
What is an edge dislocation?
Burgers perpendicular to dislocation line
What is a screw dislocation?
Burgers parallel to dislocation line (screw goes in parallel to screwdriver)
Compare the stored energy of the types of dislocations
Stored energy for edge is higher than that of screw but both are proportional to the burgers vector squared
Where is slip likely to occur?
In the farthest separated (a large), most densely packed (b small) planes in close-packed directions
What are microcantilever beams used for?
To identify the activated slip systems and their critically resolved shear stress
What is a constraint and what is its effect?
Can be a gb or hydrostatic stress state
It leads to a rotation of the lattice in order to shear
What is the deformation vector composed of?
The undeformed vector and the displacement vector
What is the deformation matrix?
3x3 that maps the undeformed material to its deformed configuration
What are the components of the deformation tensor in 2D?
symmetric part - strain
asymmetric part - rotation
What are the Cauchy Green tensors?
Measures deformation
C - with respect to the undeformed configuration
B - with respect to the deformed configuration
What are the almanac strain tensor and the true strain tensor with respect to?
the deformed configuration
What is the green strain tensor with respect to?
the undeformed configuration
What is the polar decomposition theorem?
Any arbitrary deformation can always be multiplicatively decomposed into a rigid body rotation and stretch
What are the properties of the rotation tensor?
R - Orthogonal
What is the property of the stretch tensor?
Symmetric
What is the shear strain?
The relative displacement of two slip planes with unit distance separation
For single crystal what are the components of shear?
Symmetric - plastic strain
Asymmetric - rotation
What is the Peierls energy?
The energy to move dislocation
What determines the glide velocity?
Local thermal activation
What is the total dislocation density?
The sum of sessile and glissile dislocations (SSDs and GNDs)
What are SSDs?
Statistically stored dislocations are sessile and contribute to no net open burgers circuit, proportional to plastic strain accumulation
What are GNDs?
Geometrically necessary dislocations are glissile and give lattices curvature and net open burgers circuit
What is the length scale effect?
Smaller samples under strain gradient experience greater plastic strain hardening
Which circumstances does the length scale effect occur?
Presence of particles
Polycrystal deformation
Two-phase alloys
What is the strain rate sensitivity of alloys dependent on?
The activation volume
What is EBSD?
Electron back scatter diffraction
What are the main components of EBSD?
SEM column, control
Computer
Output
Camera
What is the convention of euler angles?
1 - rotation about z axis
0 - rotation about new x axis
2 - rotation about new z axis
