Civil Engineering Reference
In-Depth Information
Fig. 3.1
Edge dislocation represented as a cylindrical dislocation core surrounded by a defect-
free lattice
transient wave of vibrational energy from the exterior surface. However, once the
material is completely heated and soaked at the elevated temperature, the vibra-
tional energy will be uniform within the material's lattice. This is one beneficial
aspect to using EAF over conventional elevated temperature forming.
Aside from using bulk observations to quantify this phenomenon [
2
-
4
], this
chapter introduces physics-based models to determine the significance of the
present electroplastic theories. Specifically, the transient energy provided to the
dislocation core and that transferred to the surrounding lattice are compared and
quantified. A schematic is shown in Fig.
3.1
where an edge dislocation is repre-
sented by a cylindrical dislocation core. The core geometry is characterized by a
right circular cylinder with a diameter (
D
) and length (
L
). The diameter used in
this work provides an equivalent area to the actual dislocation core area which is
represented by an elliptical cross section.
3.2 Previous Electroplastic Theories
The two primary theories for electroplasticity are localized heating at lattice defects
[
5
-
7
] and the electron wind effect [
8
-
10
]. The most recent work on electroplastic
theory suggests that the two phenomena occur simultaneously when an electric cur-
rent is applied during deformation [
4
]. This work compares the energy magnitude of
these two as related to the movement of a dislocation core in a metal's lattice.
3.2.1 Localized Heating
The localized heating is a result of increased scattering at defects, which creates
areas of greater atomic vibrations or “hot spots” (i.e., the Joule heating effect
increased at defect sites), whereas the electron wind effect is based on actual
