High-Elongation Strain Measurement – Pushing a Strain Gage and Adhesive to Their Limits
We recently received an inquiry from a customer who needed to measure strain up to 5% (50,000 με), yet they were only able to achieve 0.9% (9,000 με). During a visit at the customer’s site, a Micro-Measurements Technical Sales Manager and Applications Engineer helped the customer solve the problem; here is what was done.
The scaling of the data system was verified.A Micro-Measurements VE-40 Strain Gage Simulator was set to a resistance equivalent to the output of a strain gage at 50,000 με.This proved that the data system and software being used was scaled properly for the high strain measurement.
The CEA-06-250UW-350 strain gage is capable of measuring up to 50,000 με, but achieving that performance requires the use of a strain gage adhesive that is also capable of 50,000 με.In this case, the customer was using M-Bond 200 Adhesive with a strain range up to 3% (30,000 με).A recommendation was made to use M-Bond AE-10 Adhesive, which has a room-temperature strain range of 6% (60,000 με) to 10% (100,000 με).
- A recommendation was made to:
- Utilize a separate terminal for the heavy instrumentation lead wires, and to use a fine wire (134-AWP) between the terminals and the strain gage. Also, the fine wire was routed in a curve to decouple the wire from strain.
- Keep solder connections on the strain gage and terminal as small as possible.
The image below shows the installation with all of the recommendations applied.
As a result of using the correct adhesive and correct wiring techniques, the customer was able to achieve the required measurements to 5% repeatably.
In the future, the customer stated a need to measure strain to 10% (100,000 με). For this requirement, the following Micro-Measurements gages and adhesives were recommended:
EP-08-250BG-120 , capable of 20% (200,000 με) elongation
M-Bond A-12 Adhesive, capable of 20% (200,000 με) elongation
A complete guide to installing strain gages for high-elongation strain measurements is available in the form of Micro-Measurements Tech Tip TT-605 High-Elongation Strain Measurements.