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How to perform stress analysis on a part with screws and shear pins?

Question asked by Kyle Muschalek on Mar 20, 2012
Latest reply on Dec 1, 2015 by Li Quan

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I am currently trying to analyze a part that will have 4 screws and 2 shear pins connecting it to another part of an assembly. The assembly I am trying to analyze is shown in the pictures.

The problem that I am having is that I do not know for sure which items or surfaces to fix. I want to not only analyze the main part, but I also want to analyze the 4 screws and shear pins with it.

The analysis that I am showing in the pictures below was completed by fixing the surface tips of the 4 screws and 2 shear pins protruding through the part. This causes the screws and shear pins to act as if they were beams which is not correct, hence the high concentrations of stress on the screws and shear pins.

How do I correctly anlalyze this part INCLUDING the screws and pins?

Thanks in advance,

Kyle

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Anthony Botting Mar 20, 2012 4:35 PM

Hi Kyle; It appears you've done it using actual solid models of the fasteners and contact sets. Alternatively you could use "Bolt Connectors". They are virtual fasteners and will report the shear, axial loads and bending moments on the fasteners in a table. They are located in the Simulation Tree under folder item "Connections/Bolt" - for specifying bolts between components, and folder item "Fixtures/Foundation Bolts" to fasten the bolts to a ground plane. Hope that helps. -Tony

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Kyle Muschalek @ Anthony Botting on Mar 22, 2012 11:10 PM

Thanks for the response Anthony. I would acutally like to use the solid models of the screws and pins when running the anlaysis so that stress is analyzed on them as well. I tried the method you described and it works great but I need to see the stress on the actual screws and pins themeselves as well. Is there a way I can do this with the part as an assembly?

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Jody Byram @ Kyle Muschalek on Nov 30, 2015 5:12 PM

If you are trying to find the stress in the bolts, be sure to include the preload, or clamp force - the stress in the screw from being torqued during assembly will be the majority of the stress it sees. A properly torqued bolt will be stressed to over 50% of its yield strength, even more for critical applications with high strength bolts. Also note that tensile stress in the bolt will not change very much as the assembly is loaded, unless there is gapping between the bracket and the mounting surface.

Since your assembly is pinned and bolted, I'd guess that the shear loads are taken up entirely by the pins (assuming close fit or match drilled holes), and only tensile force is on the bolts (assuming a clearance hole in the bracket).

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Li Quan Dec 1, 2015 5:17 PM

I would suggest to bring in another part (Say Part "B") into your model and create proper connection between the part you want to analyze (say part "A") and Part "B" (Non-penetration contact with friction between Part "A" and "B", Bonded contacts between bolt thread to part "B", non-penetration contacts between bolt heads to Part "A", shrink-fit (or just non-penetration contact if there is a gap between the pin to the hole) between shear pins to Part "A" / "B"). Then apply fixture somewhere on Part "B".

How the force distribute to the 2 pin and the bolted joint will depend on the stiffness of the model.

If the solid bolts have to be included in the model, then you can use shrink - fit between the bolt head the Part "A" to generate the correct clamping force, but you might need to try 2 ~ 3 times to get the right preload on the bolts

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Anthony Botting Mar 20, 2012 4:35 PM
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Hi Kyle; It appears you've done it using actual solid models of the fasteners and contact sets. Alternatively you could use "Bolt Connectors". They are virtual fasteners and will report the shear, axial loads and bending moments on the fasteners in a table. They are located in the Simulation Tree under folder item "Connections/Bolt" - for specifying bolts between components, and folder item "Fixtures/Foundation Bolts" to fasten the bolts to a ground plane. Hope that helps. -Tony
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- Kyle Muschalek @ Anthony Botting on Mar 22, 2012 11:10 PM
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  Thanks for the response Anthony. I would acutally like to use the solid models of the screws and pins when running the anlaysis so that stress is analyzed on them as well. I tried the method you described and it works great but I need to see the stress on the actual screws and pins themeselves as well. Is there a way I can do this with the part as an assembly?
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  - Jody Byram @ Kyle Muschalek on Nov 30, 2015 5:12 PM
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    If you are trying to find the stress in the bolts, be sure to include the preload, or clamp force - the stress in the screw from being torqued during assembly will be the majority of the stress it sees. A properly torqued bolt will be stressed to over 50% of its yield strength, even more for critical applications with high strength bolts. Also note that tensile stress in the bolt will not change very much as the assembly is loaded, unless there is gapping between the bracket and the mounting surface.
    Since your assembly is pinned and bolted, I'd guess that the shear loads are taken up entirely by the pins (assuming close fit or match drilled holes), and only tensile force is on the bolts (assuming a clearance hole in the bracket).
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Li Quan Dec 1, 2015 5:17 PM
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I would suggest to bring in another part (Say Part "B") into your model and create proper connection between the part you want to analyze (say part "A") and Part "B" (Non-penetration contact with friction between Part "A" and "B", Bonded contacts between bolt thread to part "B", non-penetration contacts between bolt heads to Part "A", shrink-fit (or just non-penetration contact if there is a gap between the pin to the hole) between shear pins to Part "A" / "B"). Then apply fixture somewhere on Part "B".

How the force distribute to the 2 pin and the bolted joint will depend on the stiffness of the model.

If the solid bolts have to be included in the model, then you can use shrink - fit between the bolt head the Part "A" to generate the correct clamping force, but you might need to try 2 ~ 3 times to get the right preload on the bolts
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How to perform stress analysis on a part with screws and shear pins?

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