Building a motorcycle, need classical mechanics help

[Feroyn]

TL;DR Summary

I am building a motorcycle subframe, and I want to calculate the strength/durability of the structure. I need help doing that!

Hi!

I am an engineering graduate that took my bachelor's degree in Mechanical Engineering much too long ago, but I have forgotten a lot of the classical mechanics/mechanics of materials theory that I had learned many years ago. I am building a motorcycle right now, and I want to calculate the strength and durability of my build, to make sure I can use these aesthetics.

Here is the subframe that I want to calculate from. Assume the entire piece will be fully welded on the mainframe (welded at 4 spots).
Tubing is 25 mm in diameter, with a wall thickness of 1.6mm. Steel is EN 10305-3 E220 non-alloy low carbon steel.

Here's a quick side-profile sketch of my silly forces/moments. I'm assuming the force is at one spot to make it simpler (my weight).

Does anyone have any idea of how to approach this problem in both a classical mechanics (assuming the tubing won't deform/flex), and in a materials strength aspect (since it does flex and might be prone to bending IRL).

Sorry for the stupid question if this is rudimentary. Thank you for any help!

 

[berkeman]

Welcome to PF.

This thread will likely get closed due to safety concerns, but can you say what distinguishes a subframe from the frame? I'm only familiar with the term frame in motorcycle construction.

Also, what FEA software do you have access to? That's obviously how the regular design folks do this type of task...

 

[Feroyn]

Thank you Berkeman!

Oh, safety concerns because it might cause me harm if I calculate it wrong? I take on full responsibility for anything that I build and maintain. :) I just want to learn how to approach an issue like this.

The subframe is basically the back frame that sticks out and is welded on 4 spots. Here's a better image of the top view for the subframe:

 

[Feroyn]

Oh and currently I don't have access to any FEM analysis program. Those are quite expensive aren't they? :)

 

[berkeman]

I take on full responsibility for anything that I build and maintain.

The subframe is basically the back frame that sticks out and is welded on 4 spots.

Hmm, so the part that your passenger sits on. Got it.

Oh and currently I don't have access to any FEM analysis program. Those are quite expensive aren't they? :)

The software is a lot less expensive than a negligent homicide lawsuit settlement usually runs. Thread is closed.