The importance of understanding deformation and fatigue of materials (metals, composites, elastomers etc.) under multiaxial loads, resulting from service conditions, has gained significant recognition by the scientific community towards the development of materials for various engineering structures (piping in nuclear power plant, aircraft, civil, mechanical, vehicles, windmills etc.). Torsional testing reproduces pure shear. Characterization of axial-torsion response serves the development of material constitutive relationships and appropriate failure criteria.
Several challenges confront the development of axial torsion testers: These include (a) cross-talk between the axial and torsional channels that affects the quality of both control as well as measurement – axial response affects stiffness in torsion and vice versa, an axial load can distort torsional moment readout and vice versa; (b) specimen alignment to ensure coincidence of axial, torsional and specimen axes; (c) extensometry to handle both axial and torsional displacement on the specimen and (d) specimen fixturing without backlash along either axis.
BISS has developed and supplied axial-torsion test systems (ATTS) worldwide, with rating ranging from 10N to 600kN axial load and 10Nm to 2kNm torsional load with test frequency range up to 50 Hz.