DOM and Frame Performance
The steel terminology changes from country to country, when you say you use standard steel tubing, are you using seamed tube or dom (drawn over mandrel,seamless).
I live in Australia and without checking the legislation am sure the frame would have to be dom, to be accepted by department of transport. How would this effect the frame performance. Also dose the removal of the down tube (center) have any effect on the torsion or twisting strength thus altering the handling of the bike (ie walla) when used with a big twin with separate transmission. Regards, Brenton Dunne.
Here's Your Answer:
The analysis was ran with DOM tubing - Drawn over mandrel - seamless steel tubing. I checked the Australia website and was not able to find any documentation on frame construction for motorcycles. There was a lot of documentation with regards to emissions, sound, lighting and other items but I did not find anything that specified the type of tube. Just to be safe, I recommend going with seamless, DOM steel tubing.
I ran FEA using seamless tubing and the frame held 1000 kg. The tubes did not deform to failure with this load. The failure was at the rear axle plate.
The frame easily held a load of 1000 kg with only 0.05" of deformation. The loads were well below yield strength of the steel on the tube. (See images below)
Then I removed the center down tube that connects the backbone to the horizontal pieces on the two down rails. I ran analysis with the same
load case of 1000kg. The deformation on the frame with this load is 0.09". The tubes did not yield under this stress and change of geometry. You can remove this tube or even turn it so that the tube is arched upward for added strength if you like. Please see dom tubing and bobber frame images below showing exaggerated deformation and stress
.The frame as designed is very rigid
and over designed for the loads
that it will see. There should not be any issue with torsion or twisting since those load cases will be much less than the 1000 kg load case that was tested. If you have any additional concerns,
please feel free to let us know and we'd be happy to take another look
at it for you.
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