TESTING THE PLASTIC BEHAVIOUR OF BARS AND THIN SHEET BY TORSION TESTS.

Abstract

The (cold and hot) torsion test on cylindrical bars and the recently developed (cold) plane torsion test on thin sheet are discussed with respect to their communities and differences. In torsion of bars the test results are conventionally used for calculating stress and strain at the specimen surface. However, since the material properties are distorted at the surface it is recommended to calculate stress and strain at a 'critical radius', where shear stress at a given torque is almost independent of the shape of flow curve by a new series expansion method. The plane torsion test is evaluated in similar way. Sources of error as well as the uncertainty of the yield criterion are discussed. (Edited author abstract