Introduction and Theory
Torsion Test and its significance:
A Torsion test is a mechanical testing method that evaluates the properties of materials or devices under
stress caused by angular displacement.[1]
Figure 1: Torsion testing machine
Torsion testing evaluates a material's mechanical properties by applying twisting forces
to a specimen, measuring its response in terms of shear stress, shear strain, and modulus
of rigidity. This method assists in selecting materials and designing components that can
withstand torsional loads, crucial for applications like shafts and mechanical parts.[1]
Strain gage:
Strain gauges are devices used to measure the deformation or strain in a material. They
operate by detecting changes in electrical resistance as the material undergoes
mechanical stress. This allows engineers to accurately assess strain levels in structures and
mechanical components, aiding in tasks such as structural monitoring and load testing. It
comes in many different shapes, sizes, and patterns depending on the parameter being
measured. A strain gage designed for torque measurement is shown below.[2]
Figure 2: An example of a torque-pattern strain gage[2]
In the Torsion System of the strain gauge trainer, where stress and strain occur at a 45degree angle to the rod's length, four strain gauges are positioned at the same angle to
accurately measure this strain. [3]
In a torsion test, several essential properties and characteristics of a material under torsional forces
are measured:
1- Torsional Strength: The maximum twisting force a material can endure before failure, crucial
for applications with significant torsional forces.
2- Shear Modulus (G): Also known as modulus of rigidity, it quantifies a material's deformation
under shear stress, reflecting its stiffness.
3- Torsional Stiffness: Resistance to twisting, determined by the torque needed to produce a unit
angle of twist, indicating the material's rigidity under torsional loads.
4- Yield Strength under Torsion: The torsional stress level at which a material starts to deform
plastically, is important for understanding its behavior beyond the elastic limit.
5- Brittleness: How a material fractures under torsional stress, revealing its propensity for sudden
failure.
6- Ductility and Toughness: Ability to deform without losing strength, essential for materials
requiring energy absorption without failure.
7- Fatigue Properties: Behavior under repeated or fluctuating torsional loads, critical for
components subjected to cyclic loading.
8- Torque vs. Angle Curve: Relationship between applied torque and resulting angle of twist,
providing insights into material behavior across torque ranges.
9- Strain Hardening and Elastic Limits: Revealing how the material hardens with deformation
and its elastic limits, aiding in designing components for specific torsional stresses.[4]
Reference:
1- [1]https://step-lab.com/torsiontest/#:~:text=During%20a%20torsion%20test%2C%20a,shear%20stress%2C%20and%2
0shear%20strain.
2- [2]https://binsfeld.com/what-is-a-strain-gage-and-how-does-itwork/#:~:text=Strain%20gages%20designed%20for%20torque,an%20output%20FROM
%20the%20gage.
3- [3] Torsion test, student manual
4- https://biopdi.com/torsion-testing/