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I'm concerned with application of rubber sealings. I need to find out what Force is needed to compress this piece of rubber (the rubber cannot move in the z direction, consider the width of rubber there dz=const). A relevant property I've found is the bulk modulus, but it is about a uniform compression. Thanks.

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  • $\begingroup$ Rubber is really a crosslinked liquid. In compression it behaves like one. It's basically incompressible. $\endgroup$
    – Gert
    Nov 29 '20 at 19:55
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This calculation is not trivial at all, you will need very accurate data, characteristically trickie to measure ecperimentally. Let us assume in first approximation that your rubber is incompressible (infinite bulk modulus). For small deformation, the elastic modulus will allow you to calculate the force you are after. For larger deformations, like what is expected in a seal, rubber will behave non-linearly, and you need to characterise a suitable material model. You will as a minimum need experimental data in compression, not something you will find on a typical datasheet. A practical, engineering, workaround exists, to get an order of magnitude estimate. In a real scenario, friction will prevent the deformation mode you highlight: compressing a seal will reduce the height of it, and friction will prevent lateral contraction. Then, the bulk modulus, that you should find on a datasheet, could be used. Calculate the volumes before and after compression, and use the bulk modulus to estimate the force required for the volune contraction

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  • $\begingroup$ Thanks! How good is this estimate going to be? Or what does "order of magnitude estimate" mean, if that has the answer in it about goodness of estimate? $\endgroup$ Nov 29 '20 at 20:12
  • $\begingroup$ It really depends on how constrained your seal is, and what pre-compression you are looking at. For a square cross section seal, in a tight groove, it is going to tell you if you need 1, 10 or 50 kilos, that is what i meant. And it gives you an upper bound, which is also practically convenient. An accurate calculation is really really trickie, stay assured seal manufacturers themselves are not performing it, it is just measured. $\endgroup$
    – Smerdjakov
    Nov 29 '20 at 20:39
  • $\begingroup$ The deformation you picture, could be handledby knowing the stiffness for large compressive strains (you could find references online). The case of full lateral constraint is the upper bound i mention. The real case, with some friction on the bottom and top and lateral barrelling, is in between. $\endgroup$
    – Smerdjakov
    Nov 29 '20 at 20:41
  • $\begingroup$ The paper journals.sagepub.com/doi/10.1243/PIME_PROC_1959_173_022_02, will give you some interesting insights $\endgroup$
    – Smerdjakov
    Nov 29 '20 at 20:44

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