Extensometers

What is an extensometer?

An extensometer is a high-precision instrument used in tensile testing for measuring strain (how the length of a sample changes when its pulled or pushed in compressive of flexural tests) in materials.

By directly measuring the actual deformation happening in the specimen’s gauge section, extensometers provide quality control inspectors and technical engineers with far more accurate and repeatable measurements than a universal testing machine’s crossheads position.

This is because it’s measuring the true deformation of the material rather than the position of the crosshead. Due to mechanical contributions these two values can vary significantly. Where accuracy is important an extensometer should always be used.

What does an extensometer measure?

As mentioned above, the primary purpose of an extensometer is to measure strain (or displacement) directly on the test specimen. The strain is calculated by dividing the change in the test specimen’s length by its original gauge length.

Other critical properties can also be captured using an extensometer, including:

• Poisson’s ratio.
• R-value.
• Strain at break.
• Tensile Modulus.
• Total elongation.
• Ultimate tensile strength.
• Yield point.
• Young’s modulus.

Understanding these material properties is crucial for engineering design, quality control purposes and safety evaluations, as it tells you how a material responds when it’s pushed to its limits.

What is an extensometer used for?

An accurate strain measurement is a requirement of most ASTM & ISO standards. An extensometer is the most common method of measuring this extension of a test specimen under load, across a diverse range of materials and industries. Examples of materials include composites, films, metals, paper, textiles, and wood. Like these materials, the applications of extensometers are also extremely widespread.

• Aerospace – Looking at how aircraft components respond to aerodynamic forces and turbulence.
• Automotive – Understanding how parts and assemblies will react to different conditions and forces
• Construction – Assessing how structural elements like beams and retaining walls deform under load.

Because of the varied nature of these applications, the technical requirements for these instruments are many and varied, meaning there’s rarely a single extensometer that satisfies so many different factors — test type, gauge length, desired accuracy, etc.

What are the different types of extensometer?

Clip-on Extensometers

Clip-on extensometers are clamped directly onto the specimen during a tensile or compression test, using integrated spring-loaded arms or clips.

We offer a large range of clip-on extensometers from both Epsilon and MF, including:

• Averaging, Bi-Axial and Axial/Torsional Extensometers
• Axial Extensometers
• Bolt Proof, Lap Shear and Speciality Extensometers
• Deflectometers (Deflection Gauges)
• Fracture Mechanics Clip on Gauges
• High Temperature Extensometers
• High Temperatures Transverse and Diametral Extensometers
• Rock, Concrete and Asphalt Extensometers
• Transverse and Diametral Extensometers.

Optical Extensometers

Optical extensometers (a type of non-contact extensometer) use high-resolution cameras to measure strain without touching the specimen. They work by tracking how the distance between two attached markers on the test sample changes under load.

We offer sophisticated, cutting-edge optical video extensometers, such as the Epsilon One, the X-Sight range of video-based extensometer, and the UVX3D Advanced Imetrum Video Extensometer that’s suitable for both static and dynamic testing applications.

Long Travel Extensometers

Our semi-automatic long-travel extensometer is a precision device that measures the strain on elastomers and plastics over a large extension range. These devices are used in conjunction with a Universal Testing Machine.

We also supply laser, averaging, bi-axial, and axial/torsional extensometers, as well as special solutions for high and low-temperature testing.

How does an extensometer work?

As there are so many different kinds of extensometers that utilise diverse designs and technologies, there is no standard working operation for measuring the deformation, displacement, or elongation of materials when subjected to stress.

However, the fundamental principle is the same — measuring the change in distance between two points. What is important is choosing the right extensometer to overcome your measuring challenges. This requires you to consider multiple factors:

• The application area.
• The material(s) being tested.
• Environmental conditions.
• Expected degree of deformation.
• Desired accuracy requirements.

Pick the right extensometer with AML Instruments

With over 40 years experience supplying and calibrating extensometers, we use our unique insight to offer extensometer technology and measurements you can trust. We’re also able to develop customised devices to meet your exacting needs.

With a wide variety of extensometers to fit a wide selection of applications and materials, contact us today for expert advice on the correct precision device for your exact testing requirements.