Material
Torsiontest
Mohammed Elmoursi Mohammed
Autotronics
Torsion test
During a torsion test, a specimen is subjected to a twisting or torsional force, which
induces a torque. This test is particularly useful for materials that are subjected to
torque in their application, such as shafts, rods, and fasteners.
How to perform a torsion test:
1. Specimen Preparation: Material: Select the material to be tested (metal,
polymer, etc.).
2. Shape and Size: The specimen is usually a cylindrical rod or tube, with a
uniform cross-section. Standard dimensions are specified in various testing
standards such as ASTM E143.
3. Coding: Mark the length of measurement (distance between handles) on the
specimen.
4. Preparation: Specimen Mounting: Clamp the specimen between the handles
of the torsion testing machine. One end is held stationary, while the other
end is fixed to the rotating handle.
5. Calibration: Ensure that the machine is properly calibrated according to the
material and size of the specimen.
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6. Test Procedure: Apply Torque: Gradually apply torque to the specimen by
rotating the movable handle. The applied torque rate should be increased at a
constant rate.
7. Data Recording: As the torque is applied, record the torsion angle and the
corresponding torque. The data is usually captured by the machine software,
which plots the torque-torsion curve.
8. Failure Note: Continue to apply torque until the specimen breaks or yields.
Note the maximum torque applied and the corresponding torsion angle.
9. Post-test analysis: Fracture inspection: Examine the fracture surface to
understand the failure mode (brittle or ductile).
10.Data interpretation: Use the torque-torsion curve to calculate the shear
modulus, yield strength and ultimate shear strength of the material.
Specifications for using a torsion testing machine Machine
capacity:
1. The machine must have a torque capacity appropriate for the material and
sample size. Common capacities range from a few Newton meters (Nm) for
small samples to thousands of Newton meters for larger samples.
2. Rotation speed: The machine must be able to apply torque at a controlled
rotational speed, typically ranging from 0.1 to 5 degrees per second,
depending on the material being tested.
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3. Grips: The grips must hold the sample securely without slipping. Different
grips are used for different sample shapes and materials (e.g., flat grips for
flat samples, V-shaped grips for cylindrical samples).
4. Torsion angle measurement: The machine must have a high-precision angle
displacement measurement system, typically using encoders or digital angle
sensors, with an accuracy within ±0.1 degrees.
5. Data acquisition system: The machine must be equipped with software to
automatically record and analyze torque and torsion data. It should also
provide a real-time display of the curve and allow data to be exported for
further analysis.
6. Calibration and Maintenance: Regular calibration of the device is essential
to ensure accurate measurements. The device should also be maintained
according to the manufacturer's recommendations.
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