NON-CONTACTING VIDEO EXTENSOMETERS Measurement of strain during material testing is traditionally carried out using some form of contacting strain measurement device. While providing accurate measurement in many applications, contacting extensometers can have an adverse effect on test results. Non-contacting extensometry offers many benefits over traditional contacting devices including:
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• No influence on the test specimen • No problems with knife-edge slip • No errors due to inertia of moving parts • No moving parts eliminate errors due to wear • No possibility of damage due to energy release at failure • Can be used with environmental chambers over a wider temperature range
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Extensometers
Instron® introduced the first commercial video extensometer in 1991, then the industry’s first all-digital video extensometer in 2004. This second generation of Instron’s video extensometers utilizes patented measurement technology in the fastest, most accurate non-contacting strain measurement devices commercially available.
Principle of Operation A high-resolution digital camera and advanced real-time image processing are used to make precise strain measurements on material test samples. High performance is matched by an ergonomic design that allows easy setup, and provides very good operator access to the test area. Strain is measured by tracking contrasting gauge marks placed on the specimen. The gauge marks can be in the form of dots or lines and can be applied to the specimen by a variety of methods. The center of the gauge marks is tracked constantly during the test. 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 inaccurate specimen marking. Two versions of the extensometer are available - standard video extensometer SVE 2 and advanced video extensometer AVE 2. The SVE 2 is ideally suited for everyday applications such as rubber, soft plastics, elastomers and other materials with high strain to failure. The AVE 2 offers greater accuracy for tests on rigid materials such as metals and composites, it conforms to the most rigorous testing standards, such as ISO 527 and ASTM D638, and is also available with a transverse measurement option for r-value determination on sheet metals. AverEdge32 is for improved repeatability of r-value testing. It utilizes markless edge-detection to provide a real-time average value from 32 transverse gauge widths and is the recommended method per ISO 10113. The AVE 2 offers greater accuracy and versatility for testing under multiple environmental conditions, and can be used for advanced strain measurement with digital image correlation (DIC) for full-field strain and displacement mapping synchronized with all test data.
Application Range • Non-contacting strain measurement on a wide range of materials and specimen types including plastics, metals, textiles, paper, thin sheet, foil, wire • Type of Loading: Tensile, compression, flexure • Specimen shapes: Round and flat specimens with or without shoulder tab ends
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Discover More with Non-Contacting Dynamic Strain Measurement In addition to its excellent performance for static testing, the Instron AVE 2 is now available with an option for cyclic testing and high speed monotonic test measurement. Capable of tracking displacement at up to 500 mm/s enabling cyclic test frequencies up to 20 Hz, it offers the speed and flexibility scientists and engineers have been waiting for to study the dynamic behavior of materials without contacting the specimen.
