Pushing the Boundaries of Materials Testing: The Increasing Demand for Specialized Extensometers

Interview conducted by Mychealla RiceJul 14 2017

In this interview, Dr Wes Womack, from Epsilon Technology talks to AZoM about how they are seeing an increasing demand in specialized Extensometers.

This new trend is pushing performance boundaries while requiring minimal setup time and operator skill.

Please give a brief overview of the company and the work you do at Epsilon Technology?

Accurate strain measurement is of critical importance in engineering, yet it presents some unique challenges. Epsilon Technology was founded to meet these requirements by making best-in-class extensometers and extensometer calibrators for materials testing.

We see applications from nearly every sector of manufacturing and materials science.

Why is strain measurement important?

Strain measurement is an essential part of characterizing and qualifying most engineering materials. Design parameters, structural function, reliability, and determination of design allowables all rely on properties obtained using strain measurement.

Hot mount feature

What products and technologies are available for strain measurement?

There are three primary sensor types in widespread use for strain measurement: mechanical / contacting extensometers, non-contacting extensometers, and bonded strain gages. Test engineers will select the method based on accuracy, time to set up, operator skill requirements, and cost.

Contacting extensometers often provide the best combination, particularly when more than a few specimens have to be tested.

Materials testing applications across many industries are becoming more sophisticated. There is a new trend towards specialized extensometers for materials testing.  What does this mean for test engineers and strain measurement?

That’s true - test engineers and lab managers need better accuracy and repeatability than ever to maintain tight quality control and get the best statistically-valid properties (design allowables).

At the same time, productivity in every test lab is getting more attention; test set-up time and test operator training must be minimized.

In response, Epsilon Technology is introducing more application-specific extensometers to give test engineers the best scenario: accurate measurements, with minimal time to install and use.

Many recent models install on the specimen with a simple clip-on or slide-on motion. Additionally, Epsilon is expanding our range of high temperature models that automatically set their own gauge length and slide into place to “hot mount” on the specimen. The hot-mount feature saves a great deal of time when testing with furnaces.

Likewise, fatigue tests need to be performed in the shortest time possible, and upgrading to an extensometer that operates at a higher frequency can be a big advantage.

Our design process includes dynamic characterization of the extensometer itself over a broad range of frequencies.

Some extensometers have to be purpose-built: shear testing of sandwich cores, tension testing of rebar couplers, averaging extensometers for lap shear of adhesives, strain measurement inside triaxial compression cells, bi-axial strain control at 1600 °C, and many more.

Adhesive Lap Shear Strain Measurement. Image Credit: Epsilon Tech

Extensometer for high-temperature bi-axial strain control. Image Credit: Epsilon Tech

Labs are requiring extensometers for temperatures from liquid helium (-270 °C) to +1600 °C. Our product line has grown to 36 models, all of them configurable, and we are expanding the range constantly.

Are the extensometers compatible with other pieces of equipment?

Many customers ask “are the extensometers compatible with my testing machine?”. Epsilon Technology’s extensometers are compatible with nearly every brand of testing system. We always ask customers what connector they need before we build a unit.

The Aerospace and Automotive industries are intensely focused on fuel efficiency. Which high temperature extensometers are optimized for these applications? Why?

Getting good performance from materials at higher and higher temperatures is at the core of improving engine fuel efficiency. We are experiencing quite a rise in demand from materials producers and engine manufacturers for these types of extensometers.

We recently added six new models to the range of extensometers and COD gages rated for 700 °C, 1200 °C or 1600 °C. All of these extensometers offer upgraded accuracy and higher fatigue test frequencies compared to previous models.

For example, several new extensometers enable tension, fatigue, crack growth, and KIC/JIC testing at 700 °C with the extensometer inside the furnace. Test frequencies can be from 25 Hz to 100 Hz at those temperatures.

High temperature extensometer. Image Credit: Epsilon Tech

Previous generations were limited to 600 °C or 540 °C and much lower test frequencies.

Another new model is rated for 1600 °C fatigue testing up to 10 Hz; the new, higher test frequency rating has the potential to dramatically reduce the time required for some fatigue tests.

How can Epsilon Technology’s range of Extensometers help a materials lab operate more efficiently? Why is this important from a business perspective?

Nearly every lab cares about efficiency and productivity to control costs and get the test results in the shortest time possible. Extensometers that are designed for high repeatability and ‘clip it on, pull a pin’ simplicity can help achieve this goal.

In addition, newer extensometers that are engineered to maximize cyclic test frequency enable fatigue tests to run at higher frequencies, and therefore take less time to complete.

An example is the extensometer we recently introduced for sandwich core shear testing. Labs used to measure shear strain using home-built setups with clamping blocks and an LVDT.

Results with the home-built devices were not very good - inconsistencies in mounting from test to test caused data scatter, and extensometer setup for each test was time-consuming. Several labs asked Epsilon to help out, and we developed a ‘quick attach’ clip-on extensometer for this type of test.

The result is less data scatter and very consistent mounting with installation in under five seconds.

Sandwich Core Shear Extensometer. Image Credit: Epsilon Tech

How does Epsilon Technology’s range of products compare to other products on the market?

We manufacture all types of extensometers, including ‘all-purpose’ extensometers for standard tension and compression tests of metals, composites, and plastics.

All-purpose "quick attach" extensometer. Image Credit: Epsilon Tech

In addition, we manufacture many specialized extensometers, some that are for one specific test standard. We have extensometers for nearly every materials testing application, and every model is configurable.

What sets our extensometers apart is the combination of performance, durability, and ease of use for each specific test application.

We design them to be accurate, repeatable, and so simple to use that operator skill can be very minimal. Nearly every model can be left on through specimen failure with most materials.

What does the increasing demand for specialized extensometers mean for the future of materials testing and Epsilon Technology?

Epsilon is exploring technologies and design methods that will provide even better accuracy, repeatability, and range of application.

We anticipate that labs will need extensometers that are optimized for their applications, while seeking productivity, efficient lab operations, and more repeatable test results.

Where can our readers go to find out more?

For more information about extensometers and extensometer calibrators, visit www.epsilontech.com or give us a call. Readers who want to learn more can also sign up for our newsletter.

About Dr. Wes Womack

Dr. Wes Womack is Director of Engineering at Epsilon Technology. He joined Epsilon in 2011 and his background includes mechanical design, controls, and signal processing. He leads Epsilon’s engineering team as they develop specialized extensometers and improved strain measurement technologies, as well as ensuring compliance of Epsilon’s products with ISO and ASTM standards. Wes is active in ASTM standards committees for mechanical testing and transducer calibration.

Wes is also involved in the Jackson, WY community as a mentor for the high school robotics club. He has also given seminars on materials science to high school students with a career interest in engineering.

Wes holds a PhD in Mechanical Engineering and a PE certification.