I want to perform an uni-axial compression test (along with simple tension and planar tension) on a rubber compound to characterize its hyper-elastic behaviour. However, there will be frictional effects causing non-homogeneous strain in the specimen. Can Teflon sheet with some lubricants minimize the friction value close to zero?
Note: I do not have access to Equi-Biaxial tension equipment.
i think this is worth a try and a common problem in compression testing.
Typically lubricaion is used for e.g. compression set tests. Possibly the combination with the teflon sheet helps additionally.
In parallel you could monitor the shape of your sample (a cylinder i assume) and check whether the outside contour remains straight or develops the typical barrel shape which indicates friction.
Hi Matthias,
Is there a possibility for slip between the specimen and the compression platen when only lubricants are used? Have you experienced any other issues?
in a well lubricated condition it becomes extremely important that your sample is parallel (or at least symmetric, not wedge shaped), otherwise it can slip between the plates during stress application.
I do not recommend using Teflon with grease. Our research shows that in this case the coefficient of friction is greater than during dry friction. This applies to friction couples: steels-PTFE.
Thanks Piotr for your valuable input. It would be great if you can share your research if it has been published.
PTFE is a rather soft material, so I would not use PTFE sheets between an elastomer with high, e.g. 85-90 Shore A, hardness when collecting data for FEA. A simple silicon lubricant is better, in my opinion. As Matthias pointed out it makes it is very slippery and I had specimens slipping out in a well adjusted system, i.e. friction was very low. When it comes to barrelling, I did not experience it at nominal compressive strains up to 20 % , beyond that a slight barrelling was there, possibly due to partial squeeze-out of the lubricant and increased friction.
Hope that helps.
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