Displacement and stereo tracking

[Krishnendu-Ocean]

Hi,

I have been exploring DICe to study the deformations/strain along the flexible membrane. As a start I have tried to capture the images of the membrane tested on a uniaxial testing machine. I used the draw rectangle tool to outline the area of interest. As the material stretches' the displacement along the Y axis goes out of the rectangle box and the displacement is distorted. Attaching few screenshots for reference. How can I measure the displacement along the membrane in such cases?

Also, there is a clause in the running analysis that the stereo tracking is not fully operational. If I had to use DICe software to study the membrane deformation underwater is there anyway? any help is much appreciated.

Thank you very much,

Best, Krishna

[dicengine]

Hi Krishna,

I don't know how rapidly your membrane is deforming, but have you tried running DICe on this problem with a frame interval of 1? or 10? It could be that at 100 frames the membrane is deforming too much to correlate well.

Also, I can't see what your speckle pattern looks like from the images. It looks like you have your calibration pattern on the sample, but depending on how large your subset size is, if it's too small the white spots in the calibration pattern may be hard to track since there no contrast.

[Krishnendu-Ocean]

Hi,

Thank you very much for your response.

The membrane deformation is very gradual over time, the 100 frames was selected as there will be many images to analyze if frame interval is taken as 1 or 10 frame interval. Even if we select smaller frame interval after some point the membrane will extend beyond the rectangle box. Please do you have any suggestion to avoid this?

I haven't used the speckle pattern, instead I used a 10 mm x 10 mm rectilinear grid with 4 mm diameter circular markers. I used the calibration pattern to get the images to measure the deformation. Is that a wrong approach? The white spots weren't small, I applied white dots on the black membrane to bring contrast. The plan is to try and use DICe for underwater measurements, that is why a point based approach was selected. I am not quite sure how this will work. Any suggestion on using DICe to measure the deformation of a 500 mm long and 200 mm wide membrane exposed to waves under water?

Best, Krishna

[dicengine]

Depending on the limitations of your applications, you typically want to have lots of contrast variation in the pattern applied to your sample. For example in a normal speckle pattern the random blobs are on the order of 3 to 5 pixels in diameter. The dots from your calibration pattern are probably much larger than that which will lead to a large loss of accuracy depending on how big you set the subset size.

You might be interested to take a look at the Good Practices Guide for DIC: https://idics.org/guide/#:~:text=The%20Good%20Practices%20Guide%20(GPG,are%20outlined%20in%20the%20GPG).