@ Biaxial tensile tests are usually carried out on a special test-machine in which a square rubber specimen is stretched on two sides in order to measure or obtain mechanical magnitudes of the rubber compound.
The improvement consists therein that the biaxial tensile condition is obtained by a symmetric extension of a circular rubber specimen (1). This arrangement greatly simplifies the kinematics of the rubber extension, with the advantage that only one pulling force via a wire (9) is applied. In this way an accurate and reliable biaxial tensile test can be arranged with a relatively simple device mounted on a standard test-machine which can be connected to a recorder for visualizing the pulling forces and rubber elongations.