Tensile tests are the central testing method for determining the mechanical properties of wires. They provide decisive characteristic values such as tensile strength, Yield strength, and elongation at fracture, and form the basis for quality assessments in many standards and applications. In practice, however, wire testing is associated with challenges that can compromise the validity of the results.

With a well-configured testing system from Hegewald & Peschke, consisting of the inspekt testing machine with LabMaster testing software, the appropriate grip, and modern optical strain measurement, these challenges can be reliably mastered.

Challenge 1: Clamping

Wires have small cross-sections and high strengths, which makes clamping difficult. High forces act on a small area of the clamping device, so that unsuitable grips crush the wires and cause notch effects in the clamping area. This leads to clamping breaks or slippage of the specimens, which render the measurements unusable. Specialized pneumatic or mechanical rope grips are controlled gently by a force reduction curve. Wedge type grips with extended clamping jaws also reduce the local notch effect, as they apply the clamping force more gently to the specimen. Hydraulic grips also enable slip-free clamping, even with high loads.

Challenge 2: Clamping alignment

Another problem area is clamping alignment. Eccentric clamping leads to bending components and distorted characteristic values. Centric, symmetrical clamping and finely adjustable, synchronized clamping systems ensure even force distribution.

Challenge 3: Strain measurement

Measuring strain on wires is challenging due to the small contact surfaces. Classic tactile extensometers reach their limits with very thin or twisted specimens. Non-contact extensometers for strain measurement ensure standard-compliant, reproducible results even with demanding specimens. Optical extensometers, such as the ONE1 video extensometer, offer clear advantages because they measure without contact and can therefore also locate and evaluate off-center sample breaks within the strain measurement range. The single or multi-camera systems reliably and standard-compliantly record all relevant characteristic values such as modulus of elasticity, proof strength, tensile strength, and elongation at fracture.

Challenge 4: Standard-compliant execution

Test software and measurement data acquisition must precisely reflect the standard specifications. The LabMaster test software offers all the necessary functions for the tensile test of metallic wires, which is often performed in accordance with DIN EN ISO 6892-1. For certain conductor wires, DIN EN 60851-3 also provides specific specifications for elongation at fracture and tensile strength.

Conclusion

For reliable wire testing, machines, grips, and strain measurement must be perfectly coordinated. With modular universal testing machines featuring intuitive testing software, proven grips, and video extensometers, Hegewald+Peschke offers testing solutions that are specifically designed to meet the typical challenges of wire testing. This ensures the quality of wires can be permanently and reliably guaranteed.

The author is Tom Göpfert, Hegewald+Peschke Meß- und Prüftechnik GmbH.

Hegewald+Peschke Meß- und Prüftechnik GmbH

Am Gründchen 1, 01683 Nossen/Germany

Tel.: +49 35242 445-0

marketing@hegewald-peschke.de

www.hegewald-peschke.com