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Belleville Washers

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Thanks for the response.  Ed's reference to the "Bolt Tension" thread is the one I was looking for, and the concept relies on considering whether the washers are back-to-back, or nested (parallel).
 
 
"It sounds like stacking (nesting) two *might* give you something like twice the resistance if everything worked exactly right, like stacking two beams without connecting them to one another, but there also seems to be a lot that could go wrong.  If they bind and try to act compositely, you could end up with too much load.  Good point.  Let's "oil" them.  If they don't overlap exactly, you could start to bend them one after the other, each would fail one after the other at the same load, kind of like the CMU block analogy.  I might try this if I was putting up something in my garage, and I don't really need the intended load, but I wouldn't stake anything important on it.  Might be a good time to find the right tool for the job, instead.  ...
 
Regis
The washer doesn't "fail" because it is designed to remain elastic throughout the deformation and pulls up onto a flat surface.
 
"Seems to me that two washers in direct contact with one another would have equal loads in them.  Force/reaction equilibrium?  The washers will behave as springs.  The deflection doubles but the load remains the same."

Gerry
According to the Belleville site given by Regis, they are often used in multiples.  But, I think you are right.  The washers are springs, but only if in series.  I.e., because the load in a spring is proportional to the displacement, in series, 2 springs need additive displacement to achieve the load.  I.e., in series they would only produce the load of a single spring, at twice the deflection of a single spring?  Hence originally used in gun mounts.  It now seems to me that to get double the load I would have to use them in parallel, i.e. along side each other, or nested?  Two springs in parallel?  They would have to be "oiled" to avoid "composite action"?

"From an April 1998 SEAINT posting (Under "Bolt Tension"):

If you turned the concave surfaces towards each other (or away from each other) you load the washers in series and the total force to flatten two is the same as one (the reaction from the top washer is the load on the bottom washer).  The trick is to nest the washers so they are loaded in parallel (the load required to flatten the top washer can be thought of as reacting through the perimeter of the lower washer into the foundation, with additional load required to flatten the lower washer)."

Ed Marshall, PE
Atlanta

I recall some old cars using these washer-type springs back-to-back instead of "real" springs.

 
 " ... The version that we will discuss here at length is the standard disk Belleville product, high carbon steel in the range of HRC 50. As the washer properties chart previously illustrated, this product is designed to flatten at approximately 2/3 of the recommended joint clamping load.  Therefore, it contributes to the spring rate of the joint only after 33% of the load has been lost. The chart previously shown illustrates some of the good points and conditions of the conical washer. While the original  Belleville washers were used in stacked packages, both for increased travel with minimum load in series and increased load with minimum deflection in parallel, most usage today is with headed fasteners and almost always as part of a bolt or nut assembly. Some non-vehicle usage is found in structural applications and military gun mounts. ...  "

Thor A Tandy P.Eng
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)sprint.ca