Civil Engineering Reference
In-Depth Information
Chapter 3
The Effect of Electric Current on Metals
This chapter describes the fundamentals behind electroplasticity in metals.
Specifically, it focuses on electrical current flow, previous electroplastic theories,
and an overall explanation of the electroplastic effect on metals. This overall theory
will be supported with experimental results, and electroplastic conclusions will be
drawn at the end of the chapter.
3.1 Electrical Current Flow
When an electric field is applied to a material, there is a force exerted on the free
electrons (i.e., valance electrons) such that they experience acceleration in the
direction opposite to the electrical field as a result of their negative charge. Ideally,
the electrons would continuously accelerate such that the current would always
increase over time. However, internal friction forces (i.e., electron collisions with
ion cores) within the material limit electron acceleration, which settles at some
constant current value. These collisions in the lattice make up the electrical (vol-
ume-specific) resistivity of the material. The electrical resistivity of a material is
characterized by the atomic structure, spacing, and bonding. However, the electri-
cal resistivity is increased by the number of dislocations, point defects, and inter-
facial defects (e.g., grain boundaries, cracks, voids) within the lattice. The total
electrical resistivity can be described by Matthiessen's Rule:
ρ
E_TOTAL
= ρ
O
+ ρ
I
+ ρ
D
(3.1)
where
ρ
E_TOTAL
is the total electrical resistivity,
ρ
O
is the ideally pure and perfect
crystal resistivity which includes the influence of thermal vibration contribution,
ρ
I
is the contribution due to impurities in the lattice, and
ρ
D
is the contribution from
plastic deformation [
1
]. Also, it is assumed that the scattering mechanisms act
independently within the material.
