Reliant Technology LLC.
2334 E Boulder Street
Colorado Springs, CO 80909 USA
Yes, Reliant extensometers are designed for use through specimen failure. However, when testing hard / high strength materials, accelerated
knife edge wear should be expected. The knife edges should also be inspected regularly for wear / chipping and spare sets may be needed.
One way limit wear-and-tear to your extensometer is to follow the procedure in ISO 6892-1: “If the extensometer is removed or if the extension measurement is interrupted before fracture, but after maximum force (Fm), then it is permitted to use the crosshead displacement to determine additional elongation between removal of the extensometer and fracture.”
We recommend the following: select an extensometer with a lower measuring range (5 to 20 % strain), run your test until maximum force is achieved, pause the test, remove the extensometer, and resume the test using the actuator or crosshead travel to obtain the rest of the test data to specimen failure. This procedure allows approximate measurement of elongation to failure (the data at elongation to failure is not normally as critical). Using this procedure will reduce the amount of wear and chance of damage to your extensometer's knife edges.
The majority of Reliant's extensometers are strain gage based and compatible with most brands of materials testing controls. If your machine
includes a strain-channel for sensor input, we can supply your extensometer with the proper connector to directly plug-in to your controls. We stock
interface connectors for every common brand of test machine including Instron, MTS, ADMET, and United.
If you have an older control designed for LVDT extensometers or you are using a chart recorder / data acquisition board to acquire test data, we can provide a stand-alone signal conditioner to attain the required high level signal.
The majority of our extensometers are strain gage based and utilize a full Wheatstone bridge design. As such, they will require some sort of
signal conditioner (excitation supply / amplifier). Most modern test controls have the signal conditioning electronics built-in or have space for
an optional signal conditioning card.
For older machines / controls, Reliant can proved a stand alone signal conditioner / extensometer system to allow you to use a chart recorder / data acquisition card to acquire test data.
Selecting an extensometer with the proper measuring range is a trade-off of sorts. In general, the extensometer's measuring range should match the
amount of specimen elongation your are seeking data for. For testing modulus of elasticity or yield strength, an extensometer with a smaller measuring
range will give the best results. However, an extensometer with insufficient measuring range may prevent measurement of larger elongations.
For example: when testing ductile materials (most metals and plastics), tensile tests are often run to specimen failure to obtain the whole stress-strain curve. If your extensometer has a high measuring range (50 or 100 % strain), the accuracy of the measurements at low strain levels will be somewhat degraded (yield strength and modulus of elasticity often occur in the range of 0.1 to 2 % strain).
One way to obtain data for the full stress / strain curve with a low measuring range extensometer (5 to 20 % strain) is as follows: Run the test until a maximum strain is reached, pause the test, remove the extensometer, and resume the test using the actuator or crosshead travel to obtain the rest of the test data to specimen failure. This procedure allows approximate measurement of elongation to failure (the data at elongation to failure is not normally critical) with a low measuring range extensometer. Using this procedure will also reduce the amount of wear and chance of damage to your extensometer's knife edges. However, not all test controls allow you to pause a test; please check your system's capability.
For those using a high measuring range extensometer, it is possible to get more accurate low strain measurements by adjusting the electronics during calibration. Since the data at elongation to failure is not normally critical, the gain of the electronics can be adjusted to maximize the accuracy at the low measuring end. The trade-off is more error at the end of the measurement range where the accuracy of the data is less critical.
In general, Reliant's extensometers will meet the high accuracy requirements in today’s standards, such as ASTM E83. This assures reasonably accurate measurements at the low end of the range can still be made
The crosshead displacement does not just measure strain in a defined region of a test specimen. It also measures of the compliance in the whole
system (there is deflection in the load cell, specimen, grips, test frame, etc.).
An extensometer is needed to define the test region's initial length (gauge length). Strain is defined as the change in length divided by this initial length (gauge length). As such, an extensometer is required to measure the change in length over this defined area to accurately measure strain.
We can do electrical repairs on most any strain gage based extensometer. We have experience in repairing MTS, Instron, United Calibrations, Shimadzu,
Epsilon, etc. Please note: we do not repair LVDT based or mechanical extensometers at this time.
Please contact us for a free inspection and quote of your extensometer repair.
We have experience in interfacing to most all electronics. We can install the required interface connector on your extensometer or build a custom adapter cable for you.
Yes, we can replace strain gages / cables and apply the coatings / protection needed to convert the temperature range of your extensometer.
2334 E Boulder Street
Colorado Springs, CO 80909 USA
If you have any questions or would like a quote, please contact us HERE.
If your extensometer is in need of service or repair, please fill out an RMA form HERE.