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A while back, I had worked on building a Yostwerks Sea Cruiser. Now I'm thinking of trying to create a 3D printable (or 3D millable) version of the plans.

The original design uses cross-sections cut from a half-inch thick HDPE sheet. However, I am considering changing this out for one of the easier to print materials, but I cannot find any comparative information about stiffness HDPE versus other 3D printing materials.

Can I get a suggestion for a alternative to HDPE that is as stiff or stiffer as well as same density or lighter. The Kayak frame is expected to be compressing the cross-sections.

An example set of cross-sections is as below: Kayak Frame Cross sections

Please note that I have also considering changing the shape of the cross-sections to make stiffer yet lighter cross sections, but that will require some trade-off between portable sized cross-sections versus the stiffness of the cross-sections.

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According to the chart on this page HDPE has a flexural modulus of between 0.75 and 1.575 Gpa; meanwhile PETG has a flexural modulus of 2.20 Gpa, meaning PETG is the stiffer material.

HDPE, by definition, has a density greater than 0.941g/cc. PETG has a density of about 1.25g/cc.

So while PETG may be denser (depending on the HDPE used), it is more rigid, while not being too rigid.

PETG is quite printable using FDM. If you were printing at a higher temperature and high % infill, I could see it holding up well enough. I've printed heavy duty parts with it using a 0.8mm nozzle.

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Because of the inherent nature of FDM, material properties will most certainly be always lower than casted/extruded sheet material. Furthermore, your question implies to use the same geometry of the ribs, I doubt whether there will be a filament that is able to get close to your requirements regarding strength and stiffness (for the same geometry). Your best choice for filament would be a high strength filament type like PC, certain co-polyester and ABS. But, I'm more inclined to say that this whole question is more of a design issues rather than material selection issue. For that reason I struggled to vote to close as being off topic for this site. In aerospace engineering t-stiffeners are used to make panels, e.g. wing or hull sections, more stiff by riveting T-profile shaped aluminium stiffeners onto the panels, this is something you could consider (bolt on aluminium profiles), as well as incorporating these stiff ridges directly printed in your design, but that would change the shape of the ribs.

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  • $\begingroup$ Yes, I considered changing the shape of the cross-sectional parts, but as I was looking at it from a materials viewpoint, I neglected to add that in. I will add in that into the question. $\endgroup$ – Samveen Nov 2 '18 at 15:43

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