Non-Contacting Video Extensometers
Non-contacting extensometry offers many benefits over traditional contacting devices including:
- More accurate results because they don’t influence the test specimen
- More repeatable results because there’s no inertia and no chance of knife-edge slip
- Consistent results regardless of operator due to automatic gauge length measurement
- Lower maintenance costs due to a lack of moving parts
- Increased uptime because it’s immune to energy release at failure
- Wider application range because it can be used with environmental chambers over a wide temperature range
Principle Of Operation
Strain is measured by using a high-resolution digital camera to track two contrasting marks on the specimen. The marks can be in the form of dots or lines, and the use of optional Digital Image Correlation software supports speckle or even natural patterns on the specimen surface.
Real-time image processing algorithms locate the centers of the two gauge marks (or up to four marks if a transverse strain option is installed). Specimen strain is then calculated from the mark separation at the start of the test (gauge length) and the current mark separation. Tracking the center of the mark eliminates possible errors caused by stretching of the marks at high elongations.
Gauge length is automatically measured before the beginning of each test and used for strain calculation, eliminating errors introduced by multiple operators marking specimens slightly differently.
The video extensometers are fully supported and integrated into Bluehill® 3 software which allows for easy set-up, calibration, and defining the area of interest. Recognition of the marks and the measurement of strain takes place automatically once the test is started.
If your test system cannot run Bluehill 3 software then the camera can output strain as a 0-10V signal. This allows it to be used on any mechanical tester that can accept voltage signals.
- Measure strain properties of almost any material, including plastics, metals, composites, textiles, films, elastomers, paper, components, and bio-materials without contact
- Metals tests including ASTM E8, ISO 6892, ASTM E517, and JIS Z2254
- Plastics tests including ASTM D638, ISO 527-2, ASTM D882, and ISO 527-3
- Composites tests including ASTM D3039 and ISO 527-4
- Elastomer tests including ASTM D412 and ISO 37
- Dynamic strain control tests up to 20 Hz
- Compatible with Instron environmental chambers for non-ambient temperature tests
- Type of loading: tensile, flexure, compression