A torsion test can be conducted on most materials to determine the torsional properties of the material. These properties include but are not limited to:

• Modulus of elasticity in shear
• Yield shear strength
• Ultimate shear strength
• Modulus of rupture in shear
• Ductility

While they are not the same, they are analogous to properties that can be determined during a tensile test. In fact, the “torque versus angle” diagram looks very similar to a “stress versus strain” curve that might be generated by a tensile test.

Why Perform a Torsion Test?

Many products and components are subjected to torsional forces during their operation. Products such as biomedical catheter tubing, switches, fasteners, and automotive steering columns are just a few devices subject to such torsional stresses. By testing these products in torsion, manufacturers are able to simulate real life service conditions, check product quality, verify designs, and ensure proper manufacturing techniques.

Types of Torsion Tests

Torsion tests can b e performed by applying only a rotational motion or by applying both axial (tension or compression) and torsional forces. Types of torsion testing vary from product to product but can usually be classified as failure, proof, or product operation testing.

• Torsion Only: Applying only torsional loads to the test specimen.
• Axial-Torsion: Applying both axial (tension or compression) and torsional forces to the test specimen.
• Failure Testing: Twisting the product, component, or specimen until failure. Failure can be classified as either a physical break or a kink/defect in the specimen.
• Proof Testing: Applying a torsional load and holding this torque load for a fixed amount of time.
• Operational Testing: Testing complete assemblies or products such as bottle caps, switches, dial pens, or steering columns to verify that the product performs as expected under torsion loads.

Typical Configuration

An electromechanical or hydraulically-powered testing machine can be used for torsion testing. An electromechanical drive system transfers the rotational motion of a motor to the specimen while a hydraulic system employs closed loop servo control together with a hydraulic power supply to apply torsion loads.

Both electromechanical and hydraulic systems should be fitted with a control system that is capable of controlling the test and collecting data at high frequencies.

(source: http://www.instron.us/wa/applications/test_types/torsion/default.aspx)