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Need a little help on a guess at a matrerial stiffness


AeroBuffallo
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(@AeroBuffallo)
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I am trying to assess, for what more or less can be thought of as, the force trajectory to slide a cylinder across a pipe intersection. The cyliner is a 1 plastic cylinder cover by 1/4 thick urethane with a interference fit (as best as it can be measured) of 0.002 ( a rough strain of 0.8%). I was given an E=37 psi for the urethane, durometer shore A=32.5 (+/-0.5) (no idea at what strain it was measured - so I am assuming it is the initial tangent stiffness which might not be a good call. Other material data from the same source has 3 stiffness starting at 100% strain so I wonder). Friction coeff is ~0.5.

I am about 3 orders of magnitude low on the force prediction. From Wikipedia ([url] http://en.wikipedia.org/wiki/Hyperelastic_material [/url]) it shows some generic plot of a couple of models near the bottom that show a substantial difference between the compression side of the stress strain curve and the tension side.

Is that typical of very low stiffness materails of say rubbery urethanes? If so does anybody has a feel for what say the compression side tangent stiffness would be if you knew the tension side?

I can always just guess at this stuff till I get something that correlates to the force data but it would be really nice if I had some sort of rationale to explain why the stiffness I was supplied is likely not a reasonable estimate for the modelling approach. Any help, thoughts, insights or points to a reference would be very much appreciated.

Thanks,

Billmce

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Jorgen
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That difference between tension and compression is typical for polymer foams, and materials with porosity. But it is not necessarily common for solid polyurethane.

-Jorgen

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