MAE 381 EXAM 3 (chapter 7)

LOCK IN DAWG

Real crystals contain_____.

defects

Plastic deformation corresponds to the______.

Motion of dislocations.

Slip is ____.

plastic deformation resulting from dislocation motion

Slip Plane

The plane along which slip occurs

For an edge dislocation, the dislocation motion is ________ to the motion of applied shear stress.

parallel

For a screw dislocation , the dislocation motion is ______ to the motion of applied shear stress.

perpendicular

The preferred plane is called the

slip plane - the plane with the highest planar density

Slip direction

the direction along which dislocation motion occurs - the direction within the slip plane that has the highest linear density

The combination of a slip plane and a slip direction is a ______.

slip system

FCC and HCP have _____

close packed planes and close packed directions.

BCC and SC have______.

Close packed direction but not close packed planes.

Burgers vector for FCC crystal structure

b = (1/2)<1 1 0>

Burgers vector for BCC crystal structure

b = (1/2)< 1 1 1>

Burgers vector for HCP crystal structure

b = (1/3)<1 1 2̅ 0>

Stress required to move a dislocation

Peierls-Nabarred Stress ( and doesn’t involve temp)

For a low PN-stress we want:

low b and high d

BCC primary slip system:

{110} <110>

HCP primary slip system:

{0001} <1 1 2̅ 0>

FCC and BCC are more _______

ductile due to large number of slip systems

HCP are more _____.

brittle due to limited slip systems available.

Resolved Shear Stress:

T_r = (σ)cos(Φ)cos(λ)
Φ: The angle between the applied tensile force direction and the normal (perpendicular) to the slip plane.

λ: The angle between the applied tensile force direction and the slip direction.

Critical Resolved Shear Stress

T_crss, the shear stress, resolved within a slip plane and direction, required to initiate slip. (involves temp).

A single crystal plastically deforms when:

T_^(r,max)>T_crss

Single crystals ______ creep, which is critical at a high temp.

decrease. (no grain boundaries there is less creep)

Grain boundaries make slip _______.

more difficult.

Polycrystalline metals are_______than a single crystal of same metal.

stronger