Chapter 7 Flashcards
Strength and hardness are a measure of ____.
A material’s resistance to deformation.
Ref: Pg 181
On a microscopic scale, plastic deformation corresponds to ___.
A net movement of large numbers of atoms in response to applied stress.
Ref: Pg 181
True or False
During plastic deformation, atomic bonds are fractured then reformed.
True
Ref: Pg 181
In crystalline solids, plastic deformation most often involves the motion of ____.
Dislocations (linear crystalline defects).
Ref: Pg 181
What are the two fundamental dislocation types?
Edge and screw
Ref: Pg 182
Describe an edge dislocation.
A half-plane of atoms is inserted into a lattice (a piece of paper inserted between bread slices but only halfway).
Book Def: A localized lattice distortion exists along the end of an extra half-plane of atoms which also defines the dislocation line. See fig 4.4 in the book.
Ref: Pg 182
Describe a screw dislocation.
A dislocation that is the result of shear distortions; its dislocation line passes through the center of a spiral, atomic plate ramp (See fig 4.5 in the book).
Ref: Pg 182
What are mixed dislocations?
A combination of screw and edge dislocations.
Ref: Pg 182
True or False
Plastic deformation corresponds to the motion of large numbers of dislocations.
True
Ref: Pg 182
True or False
Before and after the movement of a dislocation through some particular region of the crystal, the atomic arrangement is ordered and perfect; it is only during the passage of the extra half-plane that the lattice structure is disrupted.
True
Ref: Pg 182
Define “slip.”
The process by which plastic deformation is produced by dislocation motion.
Ref: Pg 182
Define “slip plane.”
The crystallographic plane along which the dislocation line traverses.
Ref: Pg 182
True or False
With respect to the motion of a screw dislocation in response to applied shear stress, the direction of movement is perpendicular to the stress direction.
True
Ref: Pg 183
Define “dislocation density,” and give its units.
The total dislocation length per unit volume
or
The number of dislocations that intersect a unit area of a random section.
Units: mm of dislocation per cubic millimeter
Ref: Pg 183
A heavily deformed material will have a ____ dislocation density.
High
Ref: Pg 183
True or False
When metals are plastically deformed, some fraction of the deformation energy is retained internally; the remainder is dissipated as heat.
True
Ref: Pg 184
What are littice strains?
Strains that occur simply because there is a deformation present regardless of applied shear stress.
Ref: pg 184
Two dislocations of the same slip plane that have the same sign are ____.
Repulsive.
Ref: Pg 184
Two dislocations of the same slip planes but are opposite in sign will ____.
Attract one another.
Extra Notes: See figure 7.5 in the book
Ref: Pg 184
True or False
Dislocations can move with the same degree of ease on all crystallographic planes of atoms and in all crystallographic directions.
False. There are variations between how difficult it is to move in certain directions or against different planes of atoms. Typically there is a preferred plane that defines which directions along which dislocation motion occurs.
Ref: Pg 185
Define the slip plane.
The preferred plane that defines which directions along which dislocation motion occurs.
Extra Notes: The direction of motion is called the slip direction.
Ref: Pg 185
What is the slip system?
The combination of the slip plane and the slip direction.
Ref: Pg 185
For a particular crystal structure, the slip plane is the plane that has ___.
The densest atomic packing (greatest planar density–see section 3.11)
Ref: Pg 185
For a particular crystal structure, the slip direction corresponds to ___.
The direction in this plane that is most closely packed with atoms (highest linear density, see section 3.11)
Ref: Pg 185
