Real-Time Full-Field Strain Measurements
Up to 10,000 data points at 10Hz.
What are the benefits of full-field real-time measurements?
As the world-leader in digital image correlation, Correlated Solutions has developed the most efficient digital image processing algorithms that are commercially available, resulting in the fastest 3D processing speeds available. Our highly efficient algorithms are particularly important when high density image acquisition sequences need to be analyzed very quickly.
The VIC-3D Real-Time Processing Module by Correlated Solutions, Inc. allows full-field test data to be displayed live while a test is running. The Vic-3D Real-Time Module can provide users with information needed to make critical adjustments during the test, ensuring the loading is applied as expected. The module proves to be especially valuable when monitoring specimens that are either very expensive and/or have been produced in a limited quantity. Image acquisition via Vic-Snap is performed concurrently with seamless external analog data synchronization for post-processing images to create denser data sets.
With this module users can freely choose the data density for processing rates of 2-10 Hz (up to 100,000 data points/second). Live data is displayed in an unlimited number of user specified 3D plots, 2D contour image overlays, and cross-sectional graphs. Even if you choose not to use the Real-Time module, your work can be carried out much more efficiently using our systems. Consider a test sequence of 150 images, each of which contains 200,000 data points to be measured. With Vic-3D, this entire sequence can be processed in just over 5 minutes on a standard i7 single CPU computer. Other conventional digital image correlation system would likely require approximately 1 hour to process the same data on the same computer.
This module is also compatible with VIC-Gauge 3D, which allows the user to save images and record data from virtual strain gauges or extensometers, which are exported as a scaled voltage via the included DAQ system in real time up to 250Hz. Simply set the voltage scaling (e.g. E1 1% = 1V), and now the system can operate as a controlling sensor for the test.
To our knowledge, there is no other DIC system on the market that can accomplish real-time measurements at these speeds.
Crushing “Cans” Is Rocket Science
For most of us, the crushing of aluminum cans is a familiar scene. But, what if you had to precisely model the crush load of a can? And, what if the “can” was a complex structure with a diameter of 27.5 feet? This was the challenge facing NASA engineers.
Cylindrical rocket shells are subject to loads similar to soda cans. Their strength under lifting loads is referred to as a “Shell Buckling Knockdown Factor” or SBKF. The original SBKF models were developed back in the 1960’s. The available technology of the era limited the accuracy of these models. As a result, rocket designs had to be over-engineered for safety, and were unnecessarily heavy.
Today, technologies such as Finite Element Modeling permit more detailed models. But, these models must be validated through the testing of real specimens. Actual specimen displacements under load are a critical part of the validation process, and when it comes to this data, more is definitely better.
NASA started a program to update their SBKF models. An important milestone was reached on March 23, 2011, when NASA successfully tested a full-scale specimen to failure. This test was broadcast live on the internet, and is archived at www.ustream.tv (NASAtelevision: World’s Largest Can Crusher).
To get the quantity and quality of displacement data they would need, NASA relied on 3D Digital Image Correlation (DIC) systems supplied by Correlated Solutions, Inc. Random black-and-white patterns were applied to the surface of the specimen (see photo right and note the size of the mobile lift below the specimen). Digital cameras continuously monitored the entire surface of the specimen, and VIC-3D software allowed NASA engineers to monitor detailed full-field three-dimensional displacement and strain data in real-time! A total of seven systems were used to cover the entire 360 degree area.
The specimen was pressurized to 1psi and gradually loaded to more than 800,000 pounds. Although the outer wall was smooth, the effects of internal ribs and welds can be plainly seen in the out-of-plane displacement data w or Δz (see image left). As one NASA test engineer in the video feed put it: “this is the type of real time data we get to observe during the test so we know exactly what’s going on.”
The real-time VIC 3D data was used to monitor and control the testing process. High-Speed cameras captured images at 3,000 frames per second at the moment of failure. And, all of the synchronized video images were saved. As a result, NASA engineers have access to detailed, full-field, 3D deformation measurements of the specimen, throughout the entire test cycle.
Digital Image Correlation has played a key role in the successful NASA SBKF test program. As the video footage shows, the VIC-3D system provides information that would be unimaginable with any other technology. Used in conjunction with FEA modeling, it will allow NASA to decrease weight and increase the payload of future rockets.
Photos courtesy of NASA public outreach site: www.nasa.gov/topics/technology/features/buckling2.html
Application Example Video
NASA’s explanation of digital image correlation @ 3:55NASA Completes First Round of Composite Shell Buckling Tests with a Bang
VIC-3D Real-Time Features