Overview

I have always been intrigued by the results that generative and topology optimization can produce – it is aesthetically pleasing. I have recently regained access to FFF 3D printers and wanted to design 3D printed shelving brackets using Fusion 360’s shape optimization study.

To fully generate a shape optimized part, I let the mathematical algorithm decide what the first initial shape should be based on the constraints and loading. I did this to not influence the shape optimization too much and to get the organic aesthetic as much as possible.  With the initial design of the shelf done, I passed it through a second shape optimization study to remove more material and get the overall aesthetic. 

I then removed material based on the result of the second shape optimization and performed an FEA analysis for 60 lbs of distributed loading on the top face. The FOS result was 9. A structural buckling mode study was also performed to see how well the part will perform under buckling conditions. Based on the FEA results, the design can handle the buckling modes and will most likely fail due to printing quality. 

Lessons Learned

FEA results should not be treated as how a part will exactly fail, but they can be an indicator of how the part will perform in real life if set up properly. FDM 3D printed parts are anisotropic and the material properties in Fusion 360 are only for isotropic materials, so the results will need to be taken with a grain of salt and validated with a proper testing setup.

Applying a load by hand that is roughly 10-15 lbs, the 40 % and 60 % infill prints handled it well for being made out of extruded molten plastic. The part seems to suffer from fatigue failure as I’ve applied the load multiple times and layer separation is starting to creep, especially in the 40 % infill print. This seems to stem from the fact that the corner has a huge stress concentration because it is a square corner. This can be reduced by filleting the corner to lessen the stress concentration or changing the print speed and layer height parameters in the slicing software.