For procedures, see your mechanical laboratory manual.

Title: Torsion Test to destruction


Aim

To carry out a torsion test to destruction in order to determine the following mechanical properties:
1. The modulus of rigidity.
2. The shear stress at the limit of proportionality.
3. The general characteristics of torque and angle of twist relationship.

Theory

The torsion test is a destructive testing method that studies the plastic behavior of materials. In practice, components that are twisted in their application (e.g. screws, shafts, axles, wires, and springs) are studied with this test method. Torsion testing involves the twisting of a sample along an axis and is a useful test for acquiring information like torsional shear stress, maximum torque, shear modulus, and breaking angle of a material or the interface between two materials.

Torsion tests twist a material or test component to a specified degree, with a specified force, or until the material fails in torsion. The twisting force of a torsion test is applied to the test sample by anchoring one end so that it cannot move or rotate and applying a moment to the other end so that the sample is rotated about its axis. The rotating moment may also be applied to both ends of the sample but the ends must be rotated in opposite directions. The forces and mechanics found in this test are similar to those found in a piece of string that has one end held in a hand and the other end twisted by the other.

A Torsiometer (Torsion meter) is an instrument for determining the torque on a shaft, and hence the horsepower of an engine, esp. of a marine engine of high power, by measuring the amount of twist of a given length of the shaft.

Application

Torsion testing is appropriate for materials that may experience a torsional load like a metallic bone screw, an intramedullary rod, rubber tubing that may become twisted, or measure the shear strength of a bond between an implant and native tissue like bone.

References

1. Torsion Testing, sciencedirect.com
2. Torsion Test, testresources.net