The Lankford coefficient (also called Lankford value, R-value, or plastic strain ratio)[1] is a measure of the plastic anisotropy of a rolled sheet metal.
This scalar quantity is used extensively as an indicator of the formability of recrystallized low-carbon steel sheets.
are the coordinate directions in the plane of rolling and
is the thickness direction, then the R-value is given by where
is the in-plane plastic strain, transverse to the loading direction, and
is the plastic strain through-the-thickness.
[3] More recent studies have shown that the R-value of a material can depend strongly on the strain even at small strains [citation needed] .
value is usually measured at 20% elongation in a tensile test.
values are usually determined for three different directions of loading in-plane (
to the rolling direction) and the normal R-value is taken to be the average The planar anisotropy coefficient or planar R-value is a measure of the variation of
This quantity is defined as Generally, the Lankford value of cold rolled steel sheet acting for deep-drawability shows heavy orientation, and such deep-drawability is characterized by
However, in the actual press-working, the deep-drawability of steel sheets cannot be determined only by the value of
In an ordinary cold rolled steel,
[2] In such cases, any press-forming process design on the basis of