Filament for bridge-like structure

Hey guys,

I'm pretty new to 3D printing and am wondering if anyone can advise on the best filament to use for a bridge-like structure. It's a structure about an inch thick, 4 inches wide, and 6 feet long (it will be printed in sections and then fused together). It will have a lattice structure that is designed to allow flex, but I'd like to print it with a filament that meets 3 main criteria:

1. Like a bridge, it needs to be somewhat ductile. Supported at each end, it needs to be able to flex several inches up and down without compromising structural integrity or wearing out too quickly.
2. Given the printing in sections, it obviously needs to be easy to fuse these sections together post-print.
3. I'm trying to go for light weight as well. I imagine most filaments are pretty close in density, but given the size of the finished product and the desire for low weight, I'd like to be able to go with a light filament, but this is more a 'nice to have' than a 'need to have'.

I'd be very grateful for any advice the forum has to offer here! Thanks all!

A one inch thick bridge structure is unlikely to have much strength. Consider even a one inch by four inch piece of lumber that is six feet long. If the ends are supported, the center will bow and flex easily.

You've not presented the amount of weight this panel is required to support, and that's an important aspect to such a project.

If I had to make a test, I'd use PETG, which is reasonably light weight and quite strong compared to ABS and PLA. If you aren't going to use exotic filaments, PETG is a good choice on a well-tuned printer.

For the "fused" sections, you'll want some means of mechanically joining the segments. Looking from above the panel, a dovetail shape would make a good compromise connection.

Because it is necessary to print in a horizontal plane, consider that traditional bridge truss design results in layer breaks in the worst location for structural reasons. If you aren't required to have a closed surface (or even if you are) use openings in the vertical axis to reduce mass. I'm thinking of something along the lines of graph paper when viewed from above. One can also accomplish this by using a high layer count for top and bottom and a sparse infill percentage, even as low as five percent.

If your slicer supports variable layer settings, use a higher infill level for the portions near the surfaces and gradually reduce them as you near the center. This should give a good distribution of stress over weight on the span.

Alternatively, quickly build your own White Knight printer and print it all in one piece!