torsietest

A torsietest, or torsion test, is a mechanical test used to characterize the response of a material or component to twisting about its longitudinal axis. During the test, a specimen, typically cylindrical or prismatic in cross-section, is clamped at both ends. Torque is applied to one end while the other end is held fixed or rotated at a controlled rate, and the resulting torque and angle of twist are recorded.

From the data, properties such as the shear modulus (polar modulus), torsional strength, and ductility in shear can be determined. For homogeneous shafts, the relation T = G J φ / L holds in the elastic range, where T is torque, φ is angle of twist, L is length, G is shear modulus, and J is the polar moment of inertia of the cross-section. Other quantities include the maximum shear stress τ = T c / J, where c is the outer radius, and the angle of twist at failure, which gives ductility under torsion.

Equipment includes a torsion testing machine or a universal testing machine with a torsion head; fixtures must grip the ends without inducing premature failure. Tests can be conducted under constant twist rate or constant torque. Applications include characterizing metals, polymers, and composites for shafts and drive components, quality control, and research into material anisotropy.

Standards from ISO and ASTM families specify procedures for torsion testing and interpretation of results. Limitations include gripping effects, nonuniform cross-sections, and scale effects; results depend on geometry, temperature, and strain rate. See also torsion, shear modulus, and polar moment of inertia.