Steel strands and concrete-reinforcing steel are commonly used in the construction industry to reinforce and pre-stress concrete. For tensile tests on these components, the testing lab chose the Z600E materials testing machine from ZwickRoell. In addition to the testing machine’s flexibility and reliability, ZwickRoell’s solution for steel-strand testing, which reduces the number of jaw breaks to a minimum, also played a roll in the purchasing decision.
Tensile tests on steel strands can prove to be problematic due to the nature of the tested elements: the mechanical stress is discharged near the clamping area due to the helical geometry of the component and the inhomogeneous clamping surface. This results in a higher risk for jaw breaks, which invalidate the test.
In addition, the determination of elongation requires non-contact strain measurement due to the type of specimen break—which would cause damage to a mechanical extensometer. Therefore, the non-contact lightXtens extensometer, which can be used for initial gauge lengths up to 900 mm, is ideal for testing of steel strands.
Special jaws with an extended clamping surface are used to securely grip the specimen. With the use of double-actuator hydraulic grips the gripping pressure can be individually adjusted to avoid jaw breaks.
Flexibility and application versatility are important requirements for testing laboratories. This testing system is equipped with a second, contact-type extensometer: the makroXtens meets the requirements for closed-loop strain rate control according to ISO 6892-1 Method A1 and can remain on the specimen up to break. This allows for automated determination of strain at break.