This video shows how to install a strain gauge on a curved surface using M-Bond AE-10 two part epoxy. Watch an ITM test technician walk through each step of the M-Bond AE-10 strain gauge installation procedure.
A commercial airliner touches down and brakes safely so hundreds of passengers can exit at their destination. A solid rocket booster separates from a space flight as the main payload overcomes gravity to head into orbit. A military drone completes its mission over enemy territory.
In a very real way, the team of engineers at Integrated Test and Measurement (ITM) goes along for the ride during plenty of crucial moments in the aerospace realm. From doing data collection to measure the stress load of an airplane’s landing gear to installing strain gauges on rocket components to gather more than a thousand channels of data, ITM’s testing and measurement services are going to incredible heights.
Ryan Welker, ITM vice president of operations, says their aerospace partners most often turn to the Milford, Ohio, engineering service and software company for their expertise in testing and design validation, particularly if the project involves complex strain gauge work.
“A lot of times when you are dealing with aerospace requirements, it involves challenging materials. You aren’t just working with steel, and it’s quite a bit different installing strain gauges on titanium or carbon fiber. It makes the installation process a little more challenging, but we’ve been taking tough measurements in extreme environments around the globe for 20-plus years. Our experience in strain gauging is more of an art than a science.”
Welker points out that ITM won’t hesitate to put boots on the ground for their aerospace partners who have complex challenges. That was the case when a high-end aerospace company rang him up in desperate need of structural testing on a crucial component ahead of a launch. Though the job would require several people on-site for multiple months, Welker and team made it work. They installed strain gauges around the clock for three months so their client could complete crucial validation testing on a design. ITM delivered, and the client made their deadline.
Often during these intricate instrumentation processes, the ITM team employs the capabilities of their custom iTestSystem software to monitor stresses during complex assemblies. Aerospace companies may also rent ITM’s custom-built acquisition hardware to record data, even if it means that ITM needs to conduct onsite demonstration, support or help with analysis.
“We don’t just offer the ability to run a test,” says Welker. “We train your folks to use it.”
In the end, ITM offers innovative test solutions and a range of aerospace testing services designed to help the industry develop superior products and processes.
Key Services for Aerospace Clients
Strain Gauge Installation
Installing strain gauges in the field for structural and fatigue measurements requires expertise and experience. Our field service technicians and engineers have installed strain gauges on structures and machinery around the globe for decades. Whether you use our iTestSystem software to stream and analyze strain signals for static measurements and real-world fatigue data acquisition, or contract our software engineers to build a real-time strain monitoring system, we will make sure you acquire quality strain data for your aerospace project.
Structural and Mechanical Testing
Our team of engineers have decades of experience in performing structural testing in aerospace and many other markets. Testing services include Impact Testing and Modal Analysis, Structural Dynamics Operating Tests, Data Logging and Unattended Data Acquisition.
Our engineers can assist you with any part of the testing process. This includes test planning, onsite sensor installation and data acquisition and remote test monitoring.
High Channel Count Structural DAQ Systems
In our work, we often collect strain, vibration, voltage, and other signals simultaneously that require well over a thousand total sensor channels. Network synchronization technology embedded within the NI cDAQ chassis allows users to account for the sheer number of channels during these structural tests. The true secret to our success in these high-channel jobs has been our iTestSystem software which leverages the cDAQ’s synchronization technology while providing an intuitive data acquisition and sensor configuration and setup.
Rugged Data Acquisition Systems for Rent
If the right tool doesn’t exist, build it. For years that has been the approach ITM engineers have taken when it comes to gathering data and building tests for clients. And after decades of performing structural testing in aerospace, off-highway, automotive, industrial and many other environments, we’ve built up an impressive line of custom Rugged Data Acquisition (RAC) Systems which will perform under harsh testing conditions.
Obvious signs of fatigue — cracks at the corners of doors — had begun to surface on an in-service Railcar. A railcar structural testing case study.
A case study describing a strain gauge DAQ system used to validate several new designs of a heavy lift lattice boom crane to comply with SAE J987 standards.
At ITM, we understand that our customers do not settle for good enough. When it comes to measuring and capturing data for real-world applications and structural analysis, you cannot compromise, so neither can we. Instead of having to pick and choose the most critical locations to measure, we ensure that you can capture every piece of data you need, simultaneously. Whether that is a single strain bridge, or thousands of strain channels, we make your data logging project a success.
On past projects, we have worked with our customers in the manufacturing industry to test the structures of their aerospace, mining, construction and other transportation equipment. Some of these applications not only needed to collect strain, vibration, voltage, and other signals simultaneously but also required well over a thousand total sensor channels. Network synchronization technology embedded within the NI cDAQ chassis allow users to account for the sheer number of channels during these structural tests. The true secret to our success in these high-channel jobs has been our iTestSystem software which leverages the cDAQ’s synchronization technology while providing an intuitive data acquisition and sensor configuration and setup.
iTestSystem is far more than just a barebones data collection software. It can be a time saver to our engineers by helping to sort channels, keep various tasks organized, and even provide an easy and quick way to view results with the integrated TestView Plus Application (shown below).
The mining shovel pictured below, which is similar to other equipment that ITM has instrumented in the past, illustrates a distributed data acquisition system for collecting data. Using iTestSystem, we can implement a modified tree synchronization topology to collect data from over 20+ cDAQ chassis simultaneously. Data can be collected in one giant file containing all sensor channels or saved into separate files based on location. In past projects, we saved over 1000 channels from strain, acceleration, and voltage sensors into a new file every 10 minutes. We added the sensor location to the sensor description, including the Boom, Operator Cab, Main Frame and Base. This allowed us to easily sort data both during and after the collection.
Our goal at Integrated Test & Measurement is to provide efficient testing solutions and services to address your company’s needs. If you need to measure high channel counts, or have questions about our rugged DAQ systems, software, rental equipment or testing services, then please contact ITM by phone or e-mail.
Contact Information: For more information on this Article, please visit iTestSystem.com or contact: Ryan Welker – Integrated Test & Measurement (ITM), LLC – firstname.lastname@example.org or (844) 837-8797
When it comes to measuring structural stresses and load, every application is unique, and sometimes that means using a different solution. In some cases where strain gauges are applied, it can be advantageous or even necessary to use weldable strain gauges instead of chemical bonding the strain gauges to the specimen.
Since many epoxies used to chemically bond strain gauges require specific heat and pressure for curing, it can be difficult or even impossible to use this method on large or irregular structures. Weldable strain gauges offer an advantage in this situation as they eliminate the need to clamp and cure any epoxies for bonding. In addition, weldable gauges can be installed in a variety of environments and weather conditions which offers additional advantages over traditionally bonded strain gauges. Although weldable strain gauges are applied differently, they function in much the same way as their bondable counterparts.
To properly install a weldable strain gauge, you will need:
- Proper PPE
- Weldable Gauges
- Straight Edge
- Scribe, Pen or Marker
- Grinding Pads
- Spot Welder
Always remember to have the proper safety equipment on hand, such as eye protection and gloves, as well as any PPE required by your environment.
When installing a weldable strain gauge, you must first prep the area. Unlike bondable gauges, the area does not need to be polished to a fine degree. Simply degrease the gauge area, sand down any paint, coatings or excess debris and ensuring the area is purely metallic and free of chemicals is enough. A clean metal surface is important to the welding process.
After the part has been cleaned, you can position the gauge. Most weldable gauges come marked so you can align the grid properly. When the gauge is properly aligned, spot weld the gauge on either side of the gauge along the centerlines, to hold it firmly in position and prevent shifting as the gauge is welded further. Once secure, the gauge should be welded all around the carrier surface, as illustrated below.
- Clean the area to be bonded (Remove all paints, coatings, residue and debris until the surface is smooth).
- Mark center-lines for the gauge location with scribe and straight edge.
- Place the gauge on the part, lining up the center-lines.
- Spot weld the gauge on each line, to secure it in place.
- Weld the entire perimeter of the gauge in the pattern shown above.
The most common strain gauges used to quantify the state of stress on a test specimen’s surface, are uniaxial and rosette gauges. For accurate measurements of stress and strain, these uniaxial and rosette gauges are independently connected as a Wheatstone bridge in a 3-wire quarter-bridge or half-bridge arrangement.
Today, most high-end data acquisition equipment manufacturers provide signal conditioning options for collecting data from single strain gauges. Signal conditioning for strain gauges usually includes circuitry for bridge excitation voltage, quarter and half bridge completion arrangements, and shunt calibration.
Sometimes you may need to view or collect data from a single strain gauge using a device that only has analog voltage inputs and no strain signal conditioning. This was precisely the case when I was working with the HX711 load cell/strain amplifier. The HX711 requires a full bridge input so I instrumented my test specimens as such. If I needed to use a single strain gauge with the HX711, I would have had to use an external bridge completion circuit.
What are your options for measuring single strain gauges with a device that only has voltage inputs or full bridge inputs?
Option 1: Buy a commercial off the shelf bridge completion modules.
The list below gives the specifications for some available bridge completion modules. I plan on adding more completion modules to this list for future reference, so send me any additional completion options.
Strain Gauge Completion Modules
|Model #||NI 9926, NI 9945, NI 9944||MR1-10C-129, MR1-350-130, MR1-120-133||4WFBS1K, 4WFBS350, 4WFBS120|
|Description||3-Wire Quarter Bridge Completion||3-Wire Quarter Bridge Completion||3-Wire Quarter Bridge Completion|
|Resistance||1000 Ω, 350 Ω, 120 Ω||1000 Ω, 350 Ω, 120 Ω||1000 Ω, 350 Ω, 120 Ω|
|Strain Gauge Connector||Terminal Block||Solder Tab||Terminal Block|
|Device Connector||RJ50||Solder Tab||Pins and Lead Wire|
Option 2: Build your own circuit.
If you are building a product or are in the strain business long term, building your own circuit may be a cost effective alternative to the potentially more expensive off the shelf bridge completion option. I have built a few bridge completion circuits in the past. Here is a list of things to keep in mind when designing a circuit.
- Use high precision, low resistance temperature coefficient resistors
- The voltage source used for bridge excitation should be from a stable source like a reference since the output of a Wheatstone bridge is inversely proportional to the excitation voltage Vout/Vex.
- Use remote sensing to compensate for errors in excitation voltage from long lead wires
- Amplification will increase measurement resolution and improve signal-to-noise ratio
- Filter data to remove external, high-frequency noise
When troubleshooting structural failures or validating FEA models through testing, strain gauge rosettes are used to find the full state of strain at areas of concern around the structure. iTestSystem’s Rosette Analysis tool is used to calculate the principal strain, principal strain angle, shear strain, principal stress, and other values from strain gauge rosette data. This video shows how to use the Rosette analysis tool.
For questions about using the Rosette Analysis tool or other iTestSystem analysis tools contact Chase Petzinger.
Download your free version of iTestSystem today.
Image1: Shaft torque strain gauge installation example for field testing
Our engineers and technicians have epoxied, soldered and spot welded strain gauges for applications ranging from high temperature exhaust systems to miniature load cell measurements. Every application requires a unique understanding of the strain measurement requirements including installation environment.
If the strain gauge installation is to survive in the field you must plan for the conditions it will undergo. Three important variables that you should account for are temperature range, liquid exposure, and potential impact forces. These variables determine the type of strain gauge, epoxy, solder, wiring, coating, and impact/wear protection to use in the application. The table below shows which variables affect your installation choices.
Table1: Strain gauge installation variables
For more information about ITM’s strain gauging services contact Ryan Welker at email: email@example.com or phone: 1.844.837.8797 x702
Come see us at the VIATC 2019 Exhibit Hall in Booth 33!
Ryan Matthews and Mark Yeager (CAT III Vibration Analysts) will be there to answer questions about our iTestSystem engineering measurement platform, our on-site testing services, LabVIEW consulting, and strain gauging services.
When: July 24 & 25th
Where: The VIATC 2019 conference and exhibit hall will take place at the Lexington Center, connected by a joint lobby to the Hyatt Regency Lexington.
ITM | Integrated Test + Measurement
227 Water Street, Suite 300
Milford, OH 45150
Email: ITM Sales
ITM provides software development, structural and mechanical testing services, industrial monitoring, strain gauging, and data analysis solutions to clients on six continents. ITM is a recognized National Instruments Gold Alliance Partner.