Learning Forum

[cryptonary]

Hi everyone. 

I have the task of clamping two copper plates together, in order to create the largest contact pressure between them, ideally in the middle. The copper plates have conductive channels running through them, so I want to ensure that the deformation is not large enough so that the channels are deformed by a substantial amount.

I have designed a structure on both sides of the plates (modelled as structural steel) and I am simulating 4 bolts being tightened at the 4 holes in each corner of the plates, by applying a force on the faces of the 4 bosses, and fixing the displacement of the faces of the bosses on the other side. The total force is 140kN. I have set the connections between the clamping structures and the plates as frictional, with a coefficient of 0.2.

However, a problem that I am getting is that the structure seems to bow upwards, creating zero contact pressure between the copper plates! I have run into this problem with all kinds of designs that I try, and I am convinced it is because of the setup/constraints that I am using

Any help is appreciated, whether on how to solve this particular issue, or even if you have a better idea for the design of the clamps to squeeze the plates together.

See the attached screenshots of the arrangement.

Thanks!

[jj77]

Well I think that is normal. Take a beam put it on a foundation and bolt it down at the two edge, the centre will lift up. 

Have in mind that you are exaggerated the scale, and it only moves by a couple of hundreds of a mm, so tiny amount.

 

Same thing corners are being squeezed together and the centre stays where it is and moves up while the corners move down.

 

 

[cryptonary]

Thanks for the reply.

Yes, I have exaggerated the scale, but it still doesn't change the fact that the contact pressure is zero in the middle.

I have tried to solve the issue by taking off some material from the bottom of the 4 arms that extend from the circular middle section, so that when they are bolted together, the middle section makes contact with the plates and applies a pressure.

[jj77]

Well if you are squeezing the edges why would the centre start getting a lot of contact pressure there - the corners will since they are being pressed together. If you want that then one needs to add something to press it together in the centre (that could be one possible way).

When we bolt something locally you will get a high contact pressure there but not necessarily elsewhere.

 

See what happens in a flanged connection (figure 7 in  the doc. below), where the contact pressure is very local at and around the bolts, but not so much away from them. In the contact pressure you showed, similar things can be seen, so similar phenomena.

http://www.wseas.org/multimedia/journals/mechanics/2016/a305811-308.pdf

 

 

Also this is good.

 

[peteroznewman]

Hi cryptonary,

I suggest the bottom face of the tan colored structure be machined into a large radius sphere. When the structure is placed on the flat copper plate, it will touch only at the edge of the center hole and there will be a gap under each bolt hole. As the bolts are tightened, the gap will close and the tan structure will flatten, and it will provide a significant pressure to the center of the copper plate.  The amount of pressure can be adjusted by modifying the radius of the spherical profile cut into the bottom face, as well as the height of the ribs.

[cryptonary]

Thanks all for the help!