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Weird deformation behaviour

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willsen

Mechanical
Sep 2, 2016
5
Hi,

I have been developing a constitutive model (implemented in VUMAT) which describes the deformation behaviour of fibrous glass tows that constitute a plain weave textile. This constitutive model is just a new extension of small elasticity in the hyperelastic framework. I am interested in understanding the compaction behaviour of such textile architecture. The attached picture (top) shows the uncompacted textile assembly. The textile is to be compacted between two analytically rigid plates (not shown in the picture). Explicit general contact is used to model the tow-tow interaction and plate-tow interaction. Following the compaction, I keep getting a weird compaction behaviour as can be referred to the same attached picture (bottom). Notice that for each interacting tow, only one is deforming severely and the other barely compacted. This is weird because for this initial run I specified the "transverse modulus" of each tow to be uniform throughout. I have checked every single possible reason: 1. Using fully integrated elements instead of reduced integration (to make sure that this is not an hour-glass effect). 2. Increase the total compaction time (to ensure that this is not a dynamic effect). But when I use a simple linear elastic material model from the ABAQUS library, the deformation behaviour is as expected. Before I am concluding that there is something wrong with my VUMAT, I am hoping that maybe anyone can point out any obvious mistake with the way I set up the simulation?

Thank you very much in advance.


Regards,


Willsen
 
 https://files.engineering.com/getfile.aspx?folder=25895c8b-9072-4862-8537-efd7f94d2fe3&file=Capture.JPG
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I suggest using more elements per thickness, two may not be enough. Can you show the deformed shape obtained for the case where linear elastic materials was used ? If it looks as expected contrary to the case with VUMAT then unfortunately the subroutine may be a reason.
 
Hi Mr FEA way!

Thank you very much for your reply. I did that investigation already but having more elements through the thickness did not change anything.
Anyway, attached is a picture where the top shows the nicely deformed shape when using the ABAQUS in-built linear elastic material. The bottom shows the simulation using the VUMAT with 4 elements through the thickness.
 
 https://files.engineering.com/getfile.aspx?folder=706c0f43-fd2b-468f-9be4-9b4ae0e39b16&file=Capture2.JPG
If material model is the only difference in these two analyses, I think that ythere’s a problem with material stiffness in one direction in your VUMAT. Did you assign material orientations during the analysis setup ?
 
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