Extensometer

These can be applied to the specimen automatically by a motorized system and produce much more repeatable results than the traditional clip-on devices.

In addition these devices can remain on the specimen until failure and measure very high extensions (up to 1000 mm) without losing any accuracy.

When using a laser extensometer it is not necessary to attach marks to the specimen, bringing substantial time savings for material testing laboratories.

Resolutions less than one micrometer (typically 0.1 μm) and elongations up to 900 mm can be achieved, which renders these devices suitable for the most complex testing.

When measuring the modulus of elasticity on 50 mm gauge length plastics to ISO 527 an accuracy of 1 μm is required.

Some video extensometers cannot achieve this, whilst for production testing it is better to use automated motorized digital extensometry to avoid operators manually attaching marks to the specimen, and spending time setting and adjusting the system.

Note that some video extensometers have difficulty in achieving acceptable results when used to measure strain within temperature chambers.

For applications demanding high accuracy, non-contact strain measurement, video extensometers are a proven solution.

In certain test applications they are superior to other technologies, such as laser speckle because of the ability to measure strain over a large range.