Rubber experimental testing for combined load - Finite Element Modeling
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https://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11723
Mon, 19 Oct 2015 01:48:05 +0000Finite Element ModelingOSU_Yanyihttps://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11723
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Wed, 14 Oct 2015 08:14:31 +0000in reference to your points:1. any deformation on elastic materials can be decomposed in volumetric (volume changing) and distorsional (shape changing, shear) deformation. By saying that rubber is incompressible, it is certainly not meant that it is rigid in compression: certainly steel is stiffer in compression than rubber. What is meant by that is that the volumetric stiffness is so much bigger than the distorsional one, that practically the first can often be neglected. In this sense, rubber is a liquid. Of course one can use the term shear strain when referring to how the angles between material lines change: in this sense a tensile deformation seems shear-less. But this definition depends on your reference system: that is why for example the pure shear test piece, essentially a very wide tensile tests, get its name from. The topic is addressed in much more rigour in many excellent books.2. I understand better now. It is difficult to help. You are certainly right in that sensitivities analysis might help. The problem with those very high compression is, as I said, that a lot of assumptions might get too inaccurate: for example, hydrostatic and shearing stress might not decouple like commonly assumed. Or maybe, the very small viscoelastic relaxation in compression becomes not negligible. The stiffer a rubber is, the bigger impact little errors might have. I understand the test you performed: I would still perform the compressive test in fully confined, constrained set-up, not so sure if it covered by any Standard but would clearly tell you, by comparison with the test you performed, how well compression is captured. You can test and model both the set-ups, lubricated and laterally constrained, and compare. The bonded compression test (I think, mentioned in the same ISO standard you quote) might be also very useful: it will not give you a material property, but you might FE model it and see how your comparison works: in the bonded compression test the barrelling induces plenty of shear strains and might be mimiciking what happens in practice. As an additional validation, maybe a more complex test such as measuring the deflection and force exterted on the upper metallic plate on your gasket might or might not be feasible. This is what I can say without touchin the gasket...I think very few could say that gasket-modelling is easy, so best of luck]]>Finite Element Modelingbw_compositehttps://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11722
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Tue, 13 Oct 2015 07:06:53 +0000Finite Element ModelingOSU_Yanyihttps://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11721
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Fri, 09 Oct 2015 08:23:14 +0000Finite Element Modelingbw_compositehttps://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11720
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Wed, 07 Oct 2015 07:33:56 +0000I have a similar problem. I am modeling gasket compression between two thin metal plates (gasketed plate heat exchanger). Until now I have used uni-axial tensile test and uni-axial compression test.In a recent project we had some problems with gasket sealing and we could not reach the required pressures due to leakages. We then used a different and a bit stiffer material and the problem got solved. So my aim is to find out why the first material and the numerical model did not achieve the expected (and calculated) results. Among many variables I chose to take a look into material models and the experimental data need to fit the hyperelastic model.From the literature I have read (a lot of advice is given by Axel Products Inc., check: http://axelproducts.com/) it is often suggested that for complex strain states being analyzed it is desirable to have experimental data from multiple states of strain. Therefore you need additional experimental data to model the behaviour correctly.I had a discussion with my former professor about the tests needed for my numerical model. He suggested that additional shear and biaxial tension test would not increase my model accuracy nor give me any advantage. However it would be better if a compression experiment would be made in such a way that it resembles the actual geometry in state of strain. I could then measure the stress - strain relation similar as it appears in real case. By real case I mean a gasket between two thin metal plates, compressed together.For now I would somewhat disagree for the case that a shear test is not needed. When you perform a uni-axial compression test you get frictional force at the contact of the pressing plates and the test piece. Therefore shear stresses are generated. This frictional force has an effect to the stress-strain response of the material. The same could be assumed for a gasket pressed between two heat plates in a heat exchanger assembly - shear stresses are also generate since the physical problem is practically the same. From this point of view I think shear stress experimental data is necessary since shear stresses will appear. I have not yet studied the numerical models and tested how additional data affects the numerical results so I am just hypothesizing at this moment.Thats my two cents. If anyone with more experience can elaborate further on this topic it would be useful.Best regards,M.]]>Finite Element ModelingOSU_Yanyihttps://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-11719Rubber experimental testing for combined load
https://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-29401
Wed, 23 Sep 2015 03:16:30 +0000Im trying to predict with FEA the stiffness of a rubber spring.The spring will get a axial pretension of x mm and while is compressed a lateral displacement of y mm.My question is, for modelling do I need other experimental testing beside the uniaxial experimental test?Usually this test was enough.Thank you!Best regards!]]>Finite Element Modelingjax1588https://polymerfem.com/community/finite-element-modeling-aa/rubber-experimental-testing-for-combined-load/#post-29401