plane strain

Hello

I am working on a thesis project dealing with flow stress in cold rolling, a plane strain operation. To determine the flow stress, tensile tests were carried out. I am aware, that the engineering strain/stress hast to be transfered to the true strain/stress and then the true strain/stress from the tensile test has to be mulitplied with the Von Mises yield criterion to yield the correspondent compressive flow stress in the rolling situation.