Hey there,
I am using Karamba for a project to analyze the structural behaviour (Buckling) of additive manufactured structural members. Because I modeled the geometry parametrically I wanted to do this in Karamba.
For a conventional rolled steel section I get similar results for the critical load compared to the analytical solution. But for the additive manufactured geometry I get weird results, the critical load is higher, despite all the geomtrical imperfections, especially when the mesh resolution is increased.
The number of faces and elements provided to Assembly component is very different. The smooth mesh you show in last post (around 200k triangles) seems degraded at some point. Thus, the shell elements finally considered in Karamba have poor geometries (probable ill condition). This may over-stiffen the Finite Element Model.
Hey
Thank you very much for your answer!
I think you’re right. I tried to fix the problem with the “Limit Distance” input for the “Assemble Model” component.
But then I get this error (even If i change the Absolute Tolerance to 0,001 in the Rhino Unit Settings).
Solution exception:Could not find node at (0.0203016560287321/-0.00556539624568338/2.2) where point-load number 1 is attached.
Hi! Your work is very interesting, at least for the 3D printing community.
Did you try a even smaller threshold? 0.0001, 0.000001, for example.
In addition, I would progressively increase the number of triangles in your mesh (200k perhaps it is too fine :-). For coarse meshes, your sketch should work as it is. This way you can perform a convergence test which is highly recommended in your analysis.
But maybe one of the @karamba3d team could also take a look at it (maybe @matttam )?
Furthermore, is there any possibilty (or approximation) in Karamba to simulate heat induced residual stresses that occur during the 3D printing/welding process).?
Hi @haschke.niklas,
could you reduce the model in size? Otherwise it is very hard to see where the problem could lie.
Dd you try the divide and conquer approach? For this reduce the features of the definition until the problem stops to occur. If you do this systematically It should be possible to precisely locate the issue.
One can simulate constant and linear temperature distribution along cross sections in Karamba3D 1.3.3. (see here)
Hey @cp1,
at first, thank you for your answer and sorry for not responding, I was quite busy with my exams.
I reduced the mesh resolution to 7 mm and now I get a realistic buckling load.
Maybe Karamba can’t handle the mesh if the resolution is too fine?
Another thing I am really interested in is the stability problem of the structure using imperfections.
(Since the loadcase “Imperfection” works only for beams and trusses)
Is there a possibilty to consider buckling with the Analyze Nonlin Component?
I mean when I apply a geometric displacement in the former geometry followed by a nonlinear calculation, can I get a feedback when stability is no longer achieved (the yield strength in one element is passed)?
And if so, how could I implement that in my definition?
Thanks a lot,
if the mesh is too coarse (i.e. the elements too large) the mechanical response of the structural system comes out too stiff. This might have been the problem.
You can use the ‘Buckling Modes’-component to calculate linear buckling based on a geometric non-linear analysis. Imperfections do not impact the buckling load factor. In case of beams imperfections result in additional bending moments caused by the eccentricity of the NII forces (see the manual for details).
Currently (Kramba3D 1.3.3) non-linear material behavior does not enter the calculation of buckling load factors.
–Clemens
