Failure of bolt pattern

[fbwr75215]

I am designing a machine to take a push cart and dump it in a tote. I have a holder that is to bent out of sheet metal and I need to know what thickness I need for that. I currently have it at 3 gage but that is not easily bent into shape. Here are some pictures of my design

I see the sheet metal as being the mode of failure since
I 20 3/8-16 bolts holding it between two plates. From some of my recent research about this problem is that if the pretension of the bolts is high enough I would have to over come the force of friction to shear the sheet metal. If I am correct at my assumptions how do I figure out the material thickness that I can have. I am only lift about 300lbs. This is a high estimate but that will factor in with my factor of safety.

Thanks for the help.

 

[CoryPad]

Is the 300 lbf applied in the vertical direction of your first image? In the same image, is the brown piece the one you want to size? Is it supposed to have threaded holes?


Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[fbwr75215]

The 300lbs will be place down (towards the bottom of your screen in the second picture). The first picture is a top view and the second is a front view. These both are assembly views. The only part that has threads in it is the white piece in the second picture. I am trying to size the green piece.

 

[CoryPad]

If the green piece has oversized holes, and the applied forces are resisted by frictional forces from the fastener preload, then the thickness of the sheet should be determined according to non-fastening loads: out-of-plane deflection, net-section failure through the bolt holes, etc.


Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[fbwr75215]

Ok then how would I figure out the load that the friction between the three surfaces. I would need to know the Mu for the surfaces and is there a resource that tells you the Mu for different surface to surface contacts. I am currently designing the green piece to be 3 gage sheet metal to be bent into shape. That is a large gage to have that done. I would like to see if I could go with like around a 10 gage and still have it work.

 

[fbwr75215]

Ok I broke out one of my old textbooks and found a section on calculating loads for joints. I came up with 10 gage sheet metal made of A36 was bound by the tensile load. It can hold 69,310 lbs/in^2. This is still the same design as above. Does this sound resonable. My worry about tare out of the sheet metal ended up not being a problem because I have so many bolts in there to help keep this thing in a friction load. So this should be able to hold my design requirement of 500lbs.

 

[CoryPad]

Yes, you need to know the friction coefficient. The best published data is in VDI 2230 (available at

http://www.beuth.de).

However, this document covers all aspects of bolted joint design, so it is large and expensive. From my experience, 90% of joints will have mu between 0.1 and 0.2. As far as tear-out, you will need to balance this calculation with the friction joint calculation. It seems like you have a good understanding of your needs.




Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.