Importing STL file with 4 objects turning into 1

Hi! I have a simple object comprised of four blocks as shown in the CAD below. I'm modeling it as 4 separate objects with different material properties. My problem is that when I import it in matlab using the code below, it turns it into a single object, as shown

Is there a way for the stl file to accurately be imported?

Is there a quick way to edit this object in matlab to mirror the CAD file?

structuralmodel = createpde('structural','modal-solid');
importGeometry(structuralmodel, 'plateproblem2.stl');

figure
pdegplot(structuralmodel,'EdgeLabels','on');
view(100,100)

[darova]

I think you should import each body separately

[Ammiel Barros]

Tried, but as expected, assemblies of models aren't currently supported. Thanks anyway

[Bastiaan]

Ammiel Barros, how is it now? multiple bodies cant be assembled into the Matlab PDE Modeler?

Best regards

Bastiaan Pierik

Answer 1

[Cris LaPierre]

Perhaps the tip on the importGeometry page is applicable here:

The STL format approximates the boundary of a CAD geometry by a collection of triangles, and the importGeometry function reconstructs the faces and edges from this data. Reconstruction from STL data is not precise and can result in a loss of edges and, therefore, the merging of adjacent faces. Typically, lost edges are the edges between two adjacent faces meeting at a small angle, or smooth edges bounding blend surfaces. Usually, the loss of such edges does not affect the analysis workflow.

Can you share your stl? You'll have to either change the extension or zip it first, then attach it using the paperclip icon.

[Ammiel Barros]

Hi Cris! Thanks for the response. I see what you mean.

"Usually, the loss of such edges does not affect the analysis workflow." - Do you think this is the reason why there's no AddEdge function?

Attached is the stl file. This is generated using export from AutoCAD.

Thanks.

[Cris LaPierre]

Your issue appears to be with how you have exported your stl. It is a solid body, so you likely lost any internal faces when exported. When I view the slt in an stl viewer, it does not detect any internal faces.

In other words, MATLAB has not removed the faces. AutoCAD did.

[Ammiel Barros]

I see. Let me see how I can export it properly, and then import it in MATLAB. I'll get back to you afterwards.

Thank you!

[Ammiel Barros]

Hi Cris, I edited the stl file before importing it. Solved my problem. Appreciate the help.

[Cris LaPierre]

That's looking more like it.

[Julian Mecklenburgh]

I have a similar problem I get this error message from matlab

Error using pde.DiscreteGeometry

Failed to create geometry. The stl file is invalid, more than two facets share an edge.

I have created the stl file from FreeCAD of three separate parts that fit together. Stl file of one part works just with more than one part. Can I import a number of parts and join them? Any help much appreciated.

Julian

[Cris LaPierre]

You will need to combine your stl files in FreeCAD. A quick google search shows there are results for this. I obvioulsy can't comment on if this is a valid solution for you or not, but here's one result that looked promising: https://grabcad.com/tutorials/how-to-combine-stl-files-freecad-combine-stl-files-stl-format-stl-3d-printing