[mache]

Hey,

So I've got a schoolproject that i need to get going on, so some help would be nice. I'm supposed to design a hardtail frame for street riding.
I've got all the angles etc figured out, and I've chosen to use steel as it's the easiest to work with.
What I need however are some calculations to fill out the report..
What strikes me as the most important is the headtubes maximum stess capacity. So what's the best way to calculate what kind of loads will be put on it?
I've figured out that the headangle and forklength will create a 0,178m long "arm" trying to pry the headtube off the frame.
But how do I grasp what kind of forces 4130 steeltubing can withstand, (so I can figure out how thick the tubes need to be, etc.).

Other tips?

 

[brittmtb]

You should go ask you professor how to do it because it is not simple. For a start look up the yield strenth of 4130 and add a factor of safety. Also see if one of your friends has a stregth of materials book.

 

[Leethal]

Most tubing companies post their tubings tensile and yield strength as well..

 

[Evil4bc]

You can find allot of useful information on TrueTemper.com

The one main problem your going to run into testing a full 3d model fo a bicycle frame is that even if you do calculate the yeild strengh of the tubes and every machined part correctly , the computer is going to tell you the bike will fail at the welds , this is the weekest point in any structure .

Good luck , sounds like a fun project

 

[giantrider89]

Yeah, especially with the head tube, unless you ovalize it, the welds are going to be the first thing to break....but if you know how to weld, well, it shouldn't be a problem....hopefully you don't find out the quality of your welds first hand and the hard way :biggrin: lol

 

[Evil4bc]

Yeah, especially with the head tube, unless you ovalize it, the welds are going to be the first thing to break....but if you know how to weld, well, it shouldn't be a problem....hopefully you don't find out the quality of your welds first hand and the hard way :biggrin: lol

I was refering to what most FEA systems will tell you are the weakest points on a tested structure , IE: the welds

 

[AirAddict]

If you have decent welds, it shouldn't break right along the weld. It should break right above it. Welds are usually stronger than the tubing... unless you have extremely thick walled tubing. That would make it hard to weld though and you don't want a 12 lb hardtail frame.

All i can say is just overbuild it on the design. Add some gussets for extra support/stregnth. It gets into some extremely indepth stuff calculating forces put on the headtube of a bike at an angle... Gets into physics (newtons, joules, enerty, and work) and stregnth limits of materials. Unless you're really good in physics, it's going to be hard to fill out that report in full... maybe just BS is at little about how how the frame undergoes a lot of stress when landing, blah, blah...

I'm doing the same sort of thing... I'm designing and building a hardtail frame for a senior project. It's a pain in the ass... the most i'm getting out of it is realizing that buying a nice $400-$600 hardtail frame is well worth the money.