ISO 7800: Torsion test on wire
The international standard ISO 7800 describes the torsion test on wires. Wire tests according to ISO 7800 are carried out to evaluate the quality and mechanical properties of wire materials. These tests are essential to ensure that the wire meets the specific requirements and standards for various applications, such as in the construction industry, the automotive industry or for electrical cables.
Running a test Characteristic values Specimen dimensions Related products Downloads Contact
Running a test
In the torsion test to ISO 7800, a wire test piece is twisted around its own axis in one direction. The wire is twisted at a constant speed, until the specimen breaks or until a specified number of twists is reached. To ensure that the wire remains straight during the test, a tensile force can be applied using a dead weight. This force must not exceed 2% of the tensile strength of the wire. If the diameter is greater than 10 mm, the additional tensile force is not required. To check the number of twists, a colored line should be applied to the surface of the specimen. The torque to be applied is continuously recorded during the test.
If the number of twists meets the requirements of the relevant standard, the test is deemed to have been passed, regardless of the breaking point. However, if the number of twists does not meet the standard requirements, the test is invalid and must be repeated.
The TorsionLine torsion testing machine from ZwickRoell is particularly suitable for torsion tests to ISO 7800. The horizontal test axis allows the wire specimen to be gripped easily and securely in the specimen grips specially developed for wires. The high rigidity of the torsion testing machine ensures very accurate torsion angle measurement over the entire torque range. The specimen grips hold the wire specimen reliably, even at the high torque required by ISO 7800. The specimen grips are designed up to 20 kN and the maximum torque is 500 Nm.
The variable gripping system allows for torsion tests on various wire diameters. Changing the jaws is quick and easy.
Specimen shapes & dimensions
The specimen consisting of a piece of wire must be as straight as possible. If it is straightened, this must be done using a suitable method. During straightening, the surface of the wire must not be damaged and the specimen must not be twisted. Wire with sharp bends along the neutral longitudinal axis of the cross-section at certain points must not be tested.
Unless otherwise specified, the free nominal length between the terminals of the round wire must correspond to the following values
| Diameter d [mm] | Free length between the specimen grips [mm] |
|---|---|
| 0.1 ≤ d < 1 | 200 d |
| 1 ≤ d < 5 | 100 d |
| 5 ≤ d ≤ 10 | 50 d |
| 10 < d ≤ 14 | 25 d (for steel wire only) |
