Stent crimping

[yomi1]

Hello,

I am trying to crimp a stent with magnesium material.
I am getting error messages of missing element property definitions even after many attempts.
Could anyone please look at the file and provide some guidance.

And also I am not sure of the boundary conditions while running it says too many increments or too little increments.
Could you please suggest what's wrong with the model in order to complete the exact simulation process?

 

[Mustaine3]

You have assigned a shell section to a solid with tet elements. That's the reason for the error.

In general:
There is special functionality in Abaqus to model stent crimping. If you are commercial customer, then you can access the Support system and check the Answer QA00000018351.

https://www.3ds.com/support/knowledge-base/

 

[yomi1]

Thank you Mustaine3. I will try solid feature in the analysis.
I am student working on research with school provided software.

 

[yomi1]

I still get the following error message
1. Missing property definitions
2. Independent variables must be arranged in ascending order.
Could anyone please suggest the corrections to be done for this model?

 

[Dave442]

Your crimp surface is meshed with surface elements but you have assigned a continuum shell section.

You should mesh the crimp surface with reduced-integration surface elements (SFM3D4R) and assign a surface section. That's what's causing your first error. Also the slope of the plastic stress strain curve is negative between the last two points - you might want to check that. Also you've meshed your stent with linear tets (C3D4). I would avoid using these elements for modelling a stent.

Check the literature, there is a ton of published work on FEA of stents.

 

[yomi1]

Thank you Dave 442 for the feedback. I will work on the suggestions look for the literature.

 

[yomi1]

The section assignment manager do not provide the section assigned in section manager for one of the stent designs.
And element type-family in mesh do not provide 3D stress option. Why does this happen when a stent model is changed? How could this be fixed?

 

[Dave442]

Are you trying to do something that's not possible? Like mesh a surface with 3D elements? Or assign a solid section to a surface? Assigning element types and section properties is explained well in the documentation. Have a read the CAE Users guide, Analysis Users guide and the Example Problems guide.

 

[yomi1]

Hi Dave,
Yes, I am trying to assign solid to surface.
The stent that is attached in above posts could be assigned 3d stress.
But when the stent design is changed then this option is not available in Abaqus.
Thickness of stent is changed from 0.08mm to 0.14 mm, even then this option is not working.
The design itself is considered as shell part.

 

[IceBreakerSours]

I may very well be wrong but, after reading this conversation, I fear that the suggestions here may not be sufficient. Do you have some background in FEM?

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[yomi1]

I have worked on basic stress-strain analysis using workbench few years back. After that I lost touch. I am new to Abaqus trying to crimp and expand stent to check few results.
Since last few weeks trying to understand the concepts and following the tips provided in other posts in this forum.
And checked this site for element types.

http://imechanica.org/files/l2-elements.pdf

The cad model is designed in Solidworks. Changed the file from IGES (imports-shell faces) to SAT (imports-solid faces). SAT file provides 3D stress option in element type but HEX-C3D8R is not allowed to choose for the mesh. Only tets are allowed.
I don't understand why solid feature is differing from one stent design to other although have same thickness of 0.08mm.

 

[Dave442]

You cant use hex C3D8R because your geometry is too complicated. You need to partition your geometry into smaller, simple-shaped regions if you want to mesh using hex elements (which is recommended for this type of analysis). On your second issue - If you are only importing faces (surfaces), like you say, your geometry will not have a volume and you will not be able to assign a solid section or hex/tet elements. Just guessing here but that could be your issue.

This is basic stuff and shouldn't take weeks to work through. These steps (geometry,partition,mesh,section) are explained well in the documentation - CAE Users guide, Analysis Users guide and Example Problems guide. Sounds like a chore but you would save yourself a lot of time and trouble by working through them.

 

[yomi1]

Hi Dave,
Thank you for the information and explaining the element that could be used in the simulation process. As I was going through other posts C3D8 was recommended. So, I thought that was the only option to be used for stent analysis. That's the reason I was looking for solid faces. I was trying other methods for crimping from past few weeks like designing plates etc. I am following your suggestions provided in the previous post -

http://www.eng-tips.com/viewthread.cfm?qid=356649

Thank you for all your suggestions.