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no convergence and rule of thumbs for dic settings #34
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Hi! Thanks for your interest in this DIC toolkit.
Best regards |
Thank you so much for your valuable comments. I send you the data link (https://www.dropbox.com/sh/um2vd311fsxpugb/AAAc64FY4t7WgevdcZldhIywa?dl=0) where you can see the input images and the movies from where I took those images. When I use only the first part (up to a visible crack, but not too much open) I can achieve convergence, but when I add the second part it is very hard to achieve convergence. The reason is that there is a too big displacement and anyway a poor possibility of correlating the images successfully due to excessive damage. I think the updating of the frames consent big strains, but the missing parts make virtually impossible to correlate the images unless maybe changing the region of interest (the meshed portion) during analysis removing the parts where excessive spalling and damaging occurs? What do you think? |
The choice of element type is very dependent on what you want to measure. In your case, I would suggest sticking to Q4. Also, the B-spline elements are limited to rectangular meshes. Regarding the images, what are you aiming to measure? If you want to resolve the deformation field around the crack, I don't think the speckle is fine enough? |
I will try to stick with Q4 elements. Now I will create the mesh for all the L-shaped region of interest and try to change the element size to test how it performs. A colleague of mine noticed that ncorr with subsets method seemed to achieve some results, although in a step we compared before the opening of the big crack, the results where somehow different between mudic and ncorr, and ncorr results appeared more correct from first rought calculations. We will for shure dig a bit more on that. We wanted to measure first in elastic regime the principal strains distribution in order to see if the typical distribution with an inclined strut is visible. Then after the crack formation we wanted to se if different mechanisms arise. I was afraid too that the speckle is fine enough. This was just a first attempt. From what I found in literature it appears that the size of the "dots" should be on the order of 3-5 pixels (Here I think we are more in the 10-15 pixels for an average size). Do you agree? |
The displacement fields determined by ncorr and mudic should be identical. Note however about the definition of the coordinate systems when dealing with displacements.
The dots are pretty large and the speckle pattern is not very dense, so you will be limited to relatively large elements. So for resolving fine details around the crack tip, it's for sure too coarse.
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Sendt: torsdag 10. februar 2022 11:29:16
Til: PolymerGuy/muDIC
Kopi: Sindre Nordmark Olufsen; Comment
Emne: Re: [PolymerGuy/muDIC] no convergence and rule of thumbs for dic settings (Issue #34)
I will try to stick with Q4 elements. Now I will create the mesh for all the L-shaped region of interest and try to change the element size to test how it performs. A colleague of mine noticed that ncorr with subsets method seemed to achieve some results, although in a step we compared before the opening of the big crack, the results where somehow different between mudic and ncorr, and ncorr results appeared more correct from first rought calculations. We will for shure dig a bit more on that.
We wanted to measure first in elastic regime the principal strains distribution in order to see if the typical distribution with an inclined strut is visible. Then after the crack formation we wanted to se if different mechanisms arise. I was afraid too that the speckle is fine enough. This was just a first attempt. From what I found in literature it appears that the size of the "dots" should be on the order of 3-5 pixels (Here I think we are more in the 10-15 pixels for an average size). Do you agree?
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thanks for your comments. I will try again. diego |
Hi, first of all thanks for this awesome library. I found this library after reading your paper of 2020.
I have a couple of questions that I hope can be answered:
Bests
Diego
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