Extensometers for material testing machines - Zwick

Catalogue Extensometers for material testing machines

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Zw/ck # Roell

5.4 optiXtens - Non-contact extensometer without measurement marks

Range of application

The optiXtens is used to run deformation tests on a range of materials. Measurements on metals, plastics and composites are carried out optically without mechanical contacting and without application of measurement marks.

Especially suitable is the optiXtens for measurements on notch sensitive specimen as well as specimen with low test loads. Its high accuracy and its constant high resolution enable measurements on deformations in the range below the elasticity limit up to strain at break.

Function description

optiXtens consists of two optical measurement heads with evaluation units and a linear carriage system. Each measurement head illuminates the specimen surface via a lens system in lines with coherent laser light.

The reflected light generates a characteristic interference pattern the speckle pattern that is characteristic of the specimen surface.

This speckle pattern with typical bright and dark speckles is reproduced by a sensor via the optics.

Reference speckles are selected from this pattern with distance as the initial gauge length L₀ These speckles are followed during specimen deformation

Fig. 28: optiXtens - The new direction in extension measurement

in real time. The extension between both

measurement points is determined in this manner.

The measurement heads track the reference speckles when they move towards the end of the optic's field of view. Hereby the speckles always get reproduced in the sensor at the same place. The movement travel in the macro measurement range is identical to the extension of the specimen.

Fig. 29: optiXtens (Upper measurement head) setup and principle

of tracking the reference speckle