|
|
The
flow stress is the stress that must be applied to cause a material to deform
at a constant strain rate in its plastic range. Because most materials
work harden under these conditions the flow stress is a function of the
degree of plastic strain, eP.
Work hardening is dependent upon the dislocation density in the material,
and this increases as a function of the plastic strain. The diagram (a)
shows a case for which the dislocation density,
r, increases linearly with
the plastic strain. As the dislocation density increases, the mean spacing,
< r >, between dislocations decreases such that <
r > = 1/ r0.5.
The flow stress increases as (1 / < r >) due to the elastic interactions
between the dislocations and so sflow
= A eP0.5,
where A is a constant. Diagram (b) shows the form of the flow stress as
a function of plastic strain for these assumed conditions. |
|
|
|
|
|
|
|
