Experiments were carried out to generate data on the upset forming of circu
lar solid cylinders of hot-rolled magnesium alloy ZM-21. During the experim
ental investigation, the magnesium alloy cylinders were observed to show a
change Born a circular contact area on the top and bottom surfaces to an el
liptical surface area. Calculations were made on the assumptions that the c
urvature of the barrel surface followed the geometry of both circular and e
lliptical arcs. It was observed that the measured radius of curvature of th
e barrel exhibited a straight-line relationship with a new geometrical shap
e factor, irrespective of the orientations, i.e., irrespective of whether t
he specimens were machined in the rolling, transverse or thickness directio
n of the hot-rolled plate. Further, empirical relationships were found to e
xist between the measured radius of curvature of the barrel and other varia
bles such as the hydrostatic stress and the stress-ratio parameter. (C) 200
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