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Gyroid Lattice Repair issue

3 REPLIES 3
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Message 1 of 4
farouqcr9
703 Views, 3 Replies

Gyroid Lattice Repair issue

Hello everyone,
I'm a mechanical engineering student currently doing my final year project studying the effect of different Triply Periodic Minimal surface architectures on cell growth. One of the structures i have to generate and 3D print is the Gyroid lattice structure. I used MATLAB to generate the OBJ file and then imported the file to Netfabb and Meshmixer to give thickness to the OBJ file and repair it for 3D printing. However, i cant seem to get either Netfabb or Meshmixer to appropriately repair it. Here are the images gyroid lattice (5x5x2) after the failed repair. Repair fail.PNGgyroid fail.PNGi suspect that the issue comes from the 2 circled areas in the front where the orange portions self intersect, those are the areas that lead to the failed repair in contrast to the 3rd circled portions where there are no self intersections and the repair in that region is successful noi suspect that the issue comes from the 2 circled areas in the front where the orange portions self intersect, those are the areas that lead to the failed repair in contrast to the 3rd circled portions where there are no self intersections and the repair in that region is successful no

May i please get any assistance in regards to the matter? whether it maybe a way to repair the lattice correctly or by altering the code. Here is the code i used to generate the OBJ file 
a=5*pi;
s=pi/10;
[x,y,z]=meshgrid(-a:s:a,-a:s:a,-2*pi:s:2*pi);
cx = cos (2*x);
cy = sin(2*y);
cz = cos (2*z);
u = 10*(2*cos (x).* sin (y) + cos (y).* sin (z) + cos (z).* sin (x))-6;
[f,v]=isosurface(u,0);
vertface2obj(v,f,'Gyroid6.obj');

3 REPLIES 3
Message 2 of 4
MagWeb
in reply to: farouqcr9

Bit hard to explain the reason for your issue. Hope you can follow:

MM's Inspector closes each open boundary loop per se. On your structure there are boundary loops where a loop cuts surfaces with a "positive" surface normal direction (an open boundary being enclosed by a white surface - marked green). MM closes that hole as expected (where you see the different face group colors). Now there are also boundary loops enclosed by a "negative" surface normal direction (where you see the stripe pattern - marked red). To be "normal consistent" these are closed by flipped surfaces.

 

Ohne Titel.jpeg

To repair this issue you would need to build bridges between  corresponding "negative" holes ( SELECT>Edit>Bridge). Here I did some of such bridges. Note: Now there's a boundary loop enclosed by "positive" surfaces which can be filled just fine:

Ohne Titel 2.jpeg

Now to build all bridges will be a hassle.....

Instead I would generate a bigger structure (plus at least two rapports on each dimension) and crop it to the final size using EDIT/PlaneCut.

PlaneCut fills the cuts coherently.

This result was done cropping the upper example on each side:

Ohne Titel 3.jpeg 



Gunter Weber
Triangle Artisan

Message 3 of 4
farouqcr9
in reply to: MagWeb

First and foremost, thank you for taking the time to assist me.
The issue is that even after i select the portions I need to bridge and then select the bridge function the message "an unknown fatal error has occurred in the current tool"
As for the other solution, plane cut would lead to changing the structure architecture of the lattice, which is not ideal considering that the complexity of the architecture needs to be preserved, even if i generate a bigger structure, the structural integrity of the lattice will not be preserved.  

Message 4 of 4
MagWeb
in reply to: farouqcr9

Bridge needs exactly two selections of faces on boundaries of the same object like this:

Ohne Titel.jpeg 

If you missed some faces the Bridge will fail and you get the error message you mentioned:

Ohne Titel 2.jpeg

A common issue is that you forgot to start a new selection (hitting S) after you did a bridge. The bridge result stays selected. So if you select two further regions: There are actually three selections which isn't allowed.

----

Hmm I can't see a reason why the PlaneCut way should not work. Basically your structure is made of cells where each cell contains the very same shape, isn't it? Now if your target is, let's say a 5x5x5 grid and you do a 7x7x7 grid to cut off one cell-slice on each side you end up in a 5x5x5 result.

The only issue I can see is (not familiar with MATLAB) if MATLAB uses a normalised space where a 5x5x5 result's size is equal to a 7x7x7 result. But scaling the 7x7x7 result by factor 1.4 (=7/5) should set the scale right.

Or do you have problems to cut at a exactly defined position? Just dragging the PlaneCut widget by eye isn't the only way...



Gunter Weber
Triangle Artisan

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