Abstract: Two different types of strain rate control mode were described. The first is the control of the strain rate itself, Le, that is based on the feedback obtained from an extensometer. The second is the control of the estimated strain rate over the parallel length, Lc, which is achieved by controlling the crosshead separation rate at a velocity equal to the desired strain rate multiplied by the parallel length. At the same time, the difference between the estimated strain rate over the parallel length, Lc, and traditional crosshead separation (method C) was offered.