Extensometers from Universal Test Machine Co.

Extensometers for Universal Testing Machines | Clip-On, Video, 2D, 3D & Non-Contact Strain Measurement

Universal Test Machine Co. offers a wide selection of extensometers for tensile, compression, and flexural materials testing. These strain-measurement systems are designed for precision, reliability, and compatibility with virtually any brand of universal testing machine (UTM) or tensile testing system, including Instron, MTS, Shimadzu, Tinius Olsen, Galdabini, and other leading manufacturers.

Extensometers are essential for accurately measuring strain during mechanical testing. While the displacement of the testing machine crosshead can provide a rough estimate of deformation, it also includes mechanical compliance from the load frame, grips, and fixtures. Extensometers eliminate this error by directly measuring deformation across the specimen gauge length, ensuring that strain data represents the behavior of the material itself rather than movement within the test system.

If you require an extensometer for materials testing—whether a non-contact extensometer, clip-on extensometer, or video extensometer—Universal Test Machine Co. provides solutions suitable for a wide range of applications and budgets.

 

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What is an Extensometer?

An extensometer is a strain-measurement device used with a universal testing machine to measure deformation in a specimen during mechanical testing. The instrument measures the change in length between two reference points located within the specimen gauge section.

Strain is defined as the change in length divided by the original gauge length. By directly measuring this deformation, extensometers allow accurate calculation of key mechanical properties such as elastic modulus, yield strain, and elongation at break.

Extensometers can also be configured to measure lateral strain in addition to axial strain. When both axial and transverse strains are measured simultaneously, Poisson’s ratio can be calculated. This value describes the relationship between axial elongation and lateral contraction during tensile loading and is commonly used in metallurgical and structural material analysis.

 

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Industry-Leading Strain Measurement Systems

The extensometers offered by Universal Test Machine Co. are designed to integrate easily with most universal testing machines equipped with a strain gauge input channel. Each system outputs a calibrated analog signal—typically 0–10 V—corresponding to the measured strain over the selected gauge length. This standardized output allows straightforward integration with a wide variety of machine controllers and data acquisition systems.

These extensometers provide precise and repeatable strain measurements required for compliance with many ASTM and ISO testing standards. Accurate strain measurement is particularly important when determining mechanical properties such as Young’s modulus, yield strain, and elongation at break.

Key characteristics of these extensometer systems include compatibility with most major testing machine brands, simplified integration with existing testing controllers, and reliable strain measurement performance suitable for both research laboratories and industrial quality control environments.

 

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Types of Extensometers Available

Universal Test Machine Co. carries a complete range of extensometer technologies designed to support a wide variety of materials testing applications.

Vector 3D Non-Contact Extensometer

The Vector 3D Non-Contact Extensometer utilizes advanced Digital Image Correlation (DIC) techniques to measure strain without contacting the specimen. High-resolution cameras track the movement of a stochastic speckle pattern applied to the surface of the specimen. Image-correlation algorithms then calculate displacement and strain across the test region.

The system incorporates GPU-accelerated processing, enabling rapid analysis of image data and high measurement accuracy. Because the instrument does not physically attach to the specimen, it is particularly useful for delicate materials, thin films, composites, and specimens experiencing large elongations.

Clip-On Extensometers

Clip-on extensometers are among the most widely used strain-measurement devices in tensile testing, particularly for metallic materials and other low-elongation specimens. The instrument attaches directly to the specimen using hardened knife edges positioned at two reference points along the gauge section.

Two key parameters define a clip-on extensometer: the gauge length and the maximum strain capacity. The gauge length is the distance between the two reference points where deformation is measured. Standardized tensile specimens commonly use gauge lengths of 25 mm (1 in) or 50 mm (2 in). The strain capacity defines the maximum elongation that the instrument can measure before reaching its mechanical travel limit.

Because clip-on extensometers are directly attached to the specimen, they are often removed before specimen fracture occurs to prevent potential damage to the instrument.

Long-Travel and Balanced Extensometers

Materials such as elastomers, thermoplastic polymers, and textiles may experience elongations well beyond the range of conventional clip-on extensometers. For these applications, long-travel extensometers are used.

Balanced extensometers are supported by the testing machine rather than by the specimen itself. Once the specimen is installed in the grips, the extensometer pivots into position and attaches to the gauge section. The instrument remains attached throughout the test, allowing measurement of very large strains and continued monitoring even during specimen failure.

Universal Test Machine Co. offers long-travel extensometers capable of measuring elongations exceeding 1000%, which are commonly observed in thermoplastic elastomers and other highly ductile materials.

2D Video Extensometers

Video extensometers measure strain optically using high-resolution cameras and image-tracking software. The system tracks reference markers or natural surface features on the specimen to calculate displacement between measurement points during testing.

Because the system operates without physical contact, it eliminates the risk of instrument damage during specimen fracture and simplifies specimen preparation. Video extensometers are particularly useful for testing materials with large elongations or for specimens that cannot easily accommodate a mechanical extensometer.

 

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Extensometer Integration and Compatibility

Some extensometer manufacturers design their instruments exclusively for use with proprietary testing systems. In contrast, extensometers from Universal Test Machine Co. are designed for broad compatibility with a wide range of universal testing machines.

Universal Test Machine Co. can assist with cabling, signal conversion, and connector interfaces to ensure reliable integration with existing testing equipment. This allows laboratories to upgrade their strain-measurement capability without replacing their current testing frame.

Many customers use these extensometers to replace aging OEM extensometers, upgrade to modern non-contact strain measurement technologies, or expand the functionality of legacy testing machines.

 

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Laser Extensometer Alternatives

Universal Test Machine Co. does not supply laser extensometers. Laser-based strain measurement systems have gradually been replaced by more advanced optical technologies such as Digital Image Correlation and camera-based video extensometry.

These modern approaches offer greater measurement flexibility, improved spatial resolution, and easier specimen setup. As a result, many laboratories now prefer DIC or video-based systems for non-contact strain measurement applications.

 

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Why Choose Universal Test Machine Co. for Your Extensometer Needs?

Universal Test Machine Co. provides extensive experience in materials testing instrumentation and offers a comprehensive range of extensometer technologies designed to support a wide variety of testing requirements.

The available systems cover applications ranging from precise modulus determination in metals to extremely large elongation measurements in elastomers and polymers. Technical guidance is available to assist laboratories in selecting, installing, and integrating extensometers with existing testing equipment, ensuring reliable and accurate strain measurement.

 

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Balanced Extensometers

Balanced extensometers are commonly used for testing materials such as elastomers, plastics, and textiles that may experience elongations greater than 50% or even 100%. These instruments are mounted to the testing machine so that their weight is supported by the frame rather than by the specimen.

When the specimen is secured in the grips, the extensometer moves into position and attaches to the gauge section. Because the device is supported by the testing machine, it can remain attached throughout the entire test and continue measuring strain during large deformations and specimen fracture.

Universal Test Machine Co. offers the Micron extensometer for applications requiring extremely large strain measurement. When used with compatible testing software, this extensometer can measure elongations exceeding 1000%, which are often observed during testing of thermoplastic elastomers.

 

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Other Types of Strain Measurement

Extensometers are primarily associated with tensile testing, but similar measurement devices are used for other types of mechanical testing. Compression tests often use instruments known as compressometers to measure deformation in specimens such as concrete cylinders or structural materials.

Flexural or bend tests frequently employ deflectometers that measure the deflection of a specimen subjected to bending loads. These devices provide more accurate measurements than relying solely on crosshead displacement because they measure deformation directly at the specimen rather than within the testing machine structure.

 

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Measuring Elongation in an Environmental Chamber

When materials testing is performed inside an environmental chamber, special consideration must be given to extensometer design. Elevated or reduced temperatures can affect both the specimen and the measurement device.

High-temperature extensometers are available for use in environmental chambers and furnaces where temperatures may exceed 1000 °C. These instruments typically incorporate ceramic components and heat-resistant materials capable of maintaining dimensional stability under extreme thermal conditions.

Universal Test Machine Co. offers extensometers designed for operation in high-temperature testing environments, enabling accurate strain measurement during elevated-temperature materials testing.

Extensometers in ASTM and ISO Materials Testing Standards

Extensometers are required or strongly recommended in many ASTM and ISO mechanical testing standards because accurate strain measurement is essential for determining fundamental material properties such as elastic modulus, yield strain, and elongation at break.

Standards such as ASTM E8 for metallic tensile testing and ASTM D638 for plastics explicitly specify that strain should be measured over the specimen gauge length using an extensometer rather than relying on crosshead displacement. This requirement ensures that strain measurements reflect the actual deformation of the specimen rather than mechanical compliance within the testing machine.

For composite materials, standards such as ASTM D3039 and ASTM D6641 frequently require axial and transverse strain measurement using extensometers or optical strain measurement systems in order to calculate properties such as modulus and Poisson’s ratio.

ASTM Standards That Require or Commonly Use Extensometers

Metals

ASTM E8 / E8M
Standard Test Methods for Tension Testing of Metallic Materials

ASTM E111
Young's Modulus Testing of Metals

ASTM A370
Mechanical Testing of Steel Products

 

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Plastics & Polymers

ASTM D638
Tensile Properties of Plastics

ASTM D3039
Tensile Properties of Polymer Matrix Composite Materials

ASTM D882
Tensile Properties of Thin Plastic Films

 

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Elastomers & Rubber

ASTM D412
Tensile Testing of Vulcanized Rubber

ASTM D624
Tear Strength of Elastomers

 

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Composites

ASTM D3039
Composite Tensile Testing

ASTM D6641
Composite Compression Testing (often uses strain measurement)

ASTM D3410
Compression Testing of Polymer Matrix Composites

 

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ISO Standards

ISO 6892
Tensile Testing of Metallic Materials

ISO 527
Tensile Testing of Plastics

ISO 37
Tensile Testing of Rubber