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Testing of Wires and Cables

All metals can be formed into wire, which is a very common metal product. Wires are used in all areas of the manufacturing industry: in construction engineering, in electrical technology and energy technology, in aircraft and automobile manufacture, and in medical technology. Wire braided into cables is used in load-bearing applications in cable railways, elevators, cranes, bridge-building, anchorings, and fastenings. This wide range of applications means that mechanical demands are extremely varied and that testing material properties is often highly relevant to safety.

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Tensile tests on submarine cables

ZwickRoell’s materials testing machine for submarine cables features a horizontal configuration. The aim of the test is not to load the cable up to failure, but to measure how the conductivity of the fiber optics inside the cable changes under different axial loadings. The 41-meter-long machine bed rests on flexible hinged supports with adjustable counter-bearing, enabling tests on submarine cables up to 40 meters in length. If required, the testing machine can be extended with a deflection sheave to allow cables up to 80 meters long to be tested. A movable carriage on the test stand additionally permits deflection tests to be performed, simulating bending of the cable at various points.

Tensile tests

Tensile tests on wire represent a challenge for specimen grip design. Wires can be very thin and at the same time of very high strength. They cannot be machined for testing, and therefore cut-off lengths are used and require suitable gripping arrangements. Simply clamping wires between jaws can cause failure at an unwanted location. ZwickRoell can supply specimen grips featuring various gripping technologies for safe, reliable testing. For strain measurement the videoXtens optical extensometer can be used with thin wires; with thicker wires optical or contact-type extensometers can be employed.

For tensile tests on cables, in addition to a fork head for connecting the customer's cable attachments, hydraulic grips in a separate second test area are used to grip the specimen. This makes it possible to test normal round specimens—an additional tensile testing machine is not needed for round materials.

The testXpert testing software helps users set up and perform tests, and evaluate test results. 

Hardness testing

Hardness testing of wires is not only performed on the surface, but also in the wire core. For hardness testing of the core, grindings of the wire cross-section are made and the hardness values are determined primarily to Vickers (DIN EN ISO 6507-1). Wires are rolled and wires with smaller diameters are pulled. The material undergoes cold hardening and a change in the grain geometry. Elongated metallographic constituents develop in cold-drawn wire, which can be efficiently tested to Knoop (DIN EN ISO 4545-1). The hardness testing methods used here are performed using ZwickRoell's hardness testers for low-load Vickers hardness testing and micro Vickers hardness testing.

Rotating bar bending fatigue tests

In many applications, wires are subjected to various cyclic stresses. Fatigue strength can be determined quickly and easily in rotating bar bending fatigue tests in which the rapidly rotating (up to 6000 rpm) specimen is additionally loaded with a force perpendicular to the axis of rotation. This flexure plus rotation provides a tensile-compression loading of the specimen surface. Specimen preparation is especially important here, an undamaged surface being essential.

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