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When is a Digital Image Correlation System the right tool?

Digital Image Correlation System

Digital Image Correlation systems are the next wave of advanced deformation and strain measurement tools.  Most test labs or stress labs have a few primary measurement tools. Strain gauges for measuring strain. LVDTs for measuring displacement. Accelerometers for measuring acceleration. These are all very accurate tools for collecting a very specific type of data, and often this data is only provided in one direction. Let’s consider the process for collecting strain and deformation data at a few points vs. thousands of points with Digital Image Correlation (DIC) systems.

What is the typical procedure for using these tools to collect strain data and displacement data at a few different points? First the placement of each sensor must be carefully considered; each sensor must be calibrated and adhered to the surface of the part, referenced or zeroed, and connected to its specific data acquisition system. This process can take days for some complex measurements. Often each institution or company has an expert for EACH of these sensors.

Your test program could take months! Just to collect data on a few points of the object during a test.

What if there was a method that could save you huge amounts of time and improve the quality of data that is being collected? Let’s compare the traditional vs. the Digital Image Correlation system setup for collecting data at thousands of points.

Digital Image Correlation system:

ARAMIS - Digital Image Correlation system

ARAMIS – Digital Image Correlation system

Traditional Set Up:

Traditional Setup

In spite of the expertise of the technician applying these sensors, inevitably some of these sensors might fail during the test. This could be due to heating, or sample geometry, excessive forces, or even issues with the adhesive that applies them to the surface. When you have 5 strain gauges and one fails, you’ve just decreased your amount of strain data by 20%!

What are the implications of spending all this time setting up for a measurement only to lose data at a critical sensor?

Of course you don’t just want to run one test. In order to get statistically significant information you would like to run a few tests. This procedure that was just described will now be repeated for every test that you run. The quality of the data that you collect will hinge on the amount of sensors, the placement and the accuracy.

Hopefully the sensors were also placed in a meaningful area. Otherwise you will be left scratching your head and squinting at all of these graphs and tables you’ve just created, wondering what it all means.

If this sounds familiar to you, then a digital image correlation system could be perfect for your test lab.

DIC systems are optical measurement systems that measure strain and displacement in 3D at thousands of points on the surface of the part. Every point on the surface of the part within the optical systems field of view becomes a 3D measurement point.

Instead of calibrating and applying each sensor one by one, the DIC system is calibrated and then directed at the test article. This process takes 15 minutes, and then you are ready to collect data at thousands of points.

During the test the DIC system samples data at a user defined interval and saves it for post-processing later. Once a test is finished you can bring another test article into the frame and test that one with no additional calibration needed by the DIC system.

Now tests that lasted days last hours or minutes, and your months long test series can now be completed in a week.

To make the interpretation even easier, the data is presented in 3D contour plots similar to finite element analysis (FEA).  With this 3D contour plot any point can be analyzed; section cuts can be made, and this data can be fed directly back in to you FEA model for validation.

Now let’s compare the data from the traditional methods to the data collected using DIC.

Traditional Method:

ARAMIS - Digital Image Correlation system vs strain gauge results

ARAMIS – Digital Image Correlation system vs strain gauge results

DIC Method:

ARAMIS - Digital Image Correlation system full field results

ARAMIS – Digital Image Correlation system full field results

 

To learn more about our Optical Strain measurement and Digital Image Correlation systems fill out our contact form.

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Trilion Quality Systems

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Phone: 215-710-3000
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Website: http://www.trilion.com
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