Evolution of Plastic Strain During a Flow Forming Process
  The distribution of equivalent plastic strain through the thickness of several AISI 1020 steel plates formed under different conditions over a smooth cylindrical mandrel using a single-roller forward flow forming operation was studied by measuring the local micro-indentation hardness of the deformed material. The equivalent plastic strain was higher at the inner and outer surfaces and lowest at the center of the workpiece. Empirical expressions are presented which describe the contribution of the roller and mandrel to the total local equivalent plastic strain within the flow formed part. The dependence of these expressions upon the thickness reduction during flow forming is discussed. 
M. J. Roy, R. J. Klassen, J. T. Wood
physics.class-ph cond-mat.mtrl-sci