I 3d printed the struts for my rear wheel fender.
I used ABS m30i on a stratasys fortus250mc we have at work. These worked fine until i moved the fender to the outside of the existing mudguard, which caused the bike to hit the fender and thus break one strut when i went over a bump with my wife sitting behind me. (I moved it to the outside to allow for some more travel after i got 1 size bigger rear tire). I did print some tests using PLA, but these were never something intended to last (more of a form/fit test).
For the second version i printed the same parts using a Markforged printer having nylon and chopped carbon fiber combined with carbon fiber, which makes it much tougher than abs plastic. Now for security measure i also cut the fender flip on the rear side, as it was positioned better before i got the larger sized tire. The nylon-carbon fiber does allow for more abuse, but the main improvement was avoiding to allow the bike hitting down onto the fender. (By the looks the material is just the same colour as Doug S', which matches the bike well without painting).
So for anyone considering 3D-printing parts, i would advice you to research a bit what kind of stresses the part will have to endure. In my case, the failure i had was not catastrophic, and it would be unlikely that it would be. I have attempted making a guard for my belt by 3D-printing, but i decided to not use it, because of fear of how it may induce a failure.
When it comes to your windshield brackets Doug, how to you consider the brittleness of your polycarbonate blend?
I have only seen polycarbonate samples and charts for 3D-printer materials, so my concern by using polycarbonate would be brittleness.
On my design, printing nylon (with our without chopped carbon fiber) without added carbon fibers would have been soft, possibly too soft (but i did not check). By adding the carbon fiber i got the much needed stiffness of the struts, while maintaining a part that can withstand heavy abuse, since the nylon is unlikely to tear due to its flexibility. In my experience however adding fibers (chopped or continuous) does not help if the issue is layers coming apart, so orientation plays a huge role when printing parts..
PS: The images shown here is from the first version before i painted them.