Help with design to minimze stress

[tlaaa]

Hi. I'm supposed to design an extension for a wheel wrench and then "build it" and see if it can hold 75 kg.

 

Since I'm an electric engineer student this is not what I'm very good at.

 

The project can be seen in this picture. I'm supposed to design and build the light blue part of it.

 

 

These are the only restrictions. So I can for example choose my own diameter of the cylinder( but max 30 mm) and put holes and fillets where I want.

 

But it has to hold 75 kg.

 

My drawings in Inventor

 

 

 

 

I put a force

 

9.8 m/s^2 * 75 kg = 735 N

 

and a moment

 

250 mm* 9.8 m/s^2 * 75 kg = 183750 N mm^2

 

But when i do the stress analysis i get way to much stress.

I think the max stress can only be about 275 MPa

 

 

 

These pictures are all without fillets.

 

I have tried to make fillet on either end or both ends and creating a hole thorugh but the stress doesn't go anywhere near the max value.

 

Can anyone help me?

[Bishop]

It looks like your limiting factors here are the 17mm hex and the materials used. Short of changing those ... I'd have to really play with this to see if I could come up with anything.

 

 

Couple things that might help you out a little though, some tricks for reading your FEA results.

 

1. Switch from using smooth shading to contour shading, and set the color bar to 10 or 12 segments. This will give you a clearer view of where the stresses actually are.

 

2. Set the max on the color bar to be whatever your desired max stress is, then you'll be able to see everything that's above that level called out very clearly.

[JD Mather]

What is the material? Yield Strength?

What is the minimum Factor of Safety (Inventor gives you this graphic).

What is the maximum Displacement (Inventor gives you this graphic).

Double click just below the VonMises Stress in the Browser.

 

I suspect your Moment load isn't set up correctly - can you attach the ipt file here?