### PowerPoint

```Chapter 3
dislocation
The yield strength of a perfect crystal
=

maxsin( )

 = G = G
=

max

max =


Whiskers
defect-free crystal
 = G/30
for aluminum
y = 9 x 108 N/m ideal strength
7.8 x 105 N/m real strength
The edge dislocation
Slip by an edge dislocation motion
line defect ; an extra half plane
Peierls force
Shear stress is applied.
Dislocation
move
Peierls – Nabarro:
The friction for the
movement of
dislocation:

f = G exp[
]
−
G : shear modulus
 : Poisson’s ratio
Real strength
−
]

f = G exp[
w : dislocation width
Climb of edge dislocation
Glide : conservation motion
Climb : non-conservative motion
Topographic considerations
Burgers circuit
Motion of edge dislocation containing jogs
The parts of jogs can’t move due to its components do not lie on the slip plane.
The dislocations in
the 70% cold rolled
Fe-19%Cr alloy
Edge dislocation
Screw dislocation
Mixed dislocation
Positive dislocation and negative dislocation
phenomenon of recovery
Dislocation density 
m/m3, 1/m2
Annealed metals :  = 109 – 1011 m/m3
Heavily cold worked materials :  = 1014 -1016 m/m3
The relationship between dislocation movement and strain
and
BCC降伏点降下現象(yield drop)的説明
discontinuous yielding
v：dislocation average speed
ρ：dislocation density
Johnston and Gilman : from etching pits movement :
ｍ値: 因材料而異之定数

bcc： 運動差排密度 ρ 大、差排的運動速度 v小（dislocation
movement rate controlled process）
fcc, hcp： ρ 小、v大（dislocation multiplication rate controlled
process）

cross slip)之差排源的活化、螺旋差排之Peierls forceが大、移動

```