Hello there,

Do you have an automatic control grips?. This is very useful kit. Variations of surface roughness in the gripping, different grit sizes of sanding paper may help, but may not full resolve your issue. But you can always try. Other option, work with other type (for example Type IV) for the sample.

Hope this will help

Mayb one of the options listed below can help.

I hope these help, because I have them all to varying degrees of success.

Thank you all, we tried almost all the suggested solutions, using different samples size changes, increasing the roughness of samples at the grips, sand paper etc,

As Geoffrey also suggested maybe the best alternative is going toward DMA. We gonna run it, thank you all for your useful mind sharing.  

There are different types of grips for different materials. Depending on the type of grip that you have a practical and simple way is to hold sandpaper on claw or in material.

Try putting thin layers of epoxy (or some other hardening adhesive) on the ends of the dogbone. I'm not sure what your polymer is, but you could potentially get much better adhesion between the epoxy and the polymer than with sandpaper. We've done this before in our lab with some success. 

u can use fixture with rubber lined grips typically used for tensile testing of thin film samples

Hi Reza,

First off, I would like to say that all the answers above are very useful! I work with grips and fixtures and am very much aware of the slippage and other issues that might occur based on each different test specimen and application and that often lead to frustration. There are many useful suggestions given above that you can try. Also, as stated above, making sure the grips that you have in-house are the most appropriate ones for your samples is essential. There are many grip options for various samples. I wanted to add the link below so anyone reading these posts, experimenting similar issues, can check out some different options. 

http://www.admet.com/products/test-fixtures-and-accessories/test-fixtures/

I would also like to add the below link, which is a new blog post covering the issues experienced with grips and the decision-making process to choose the right grips for your testing. I hope it will be found useful. 

http://www.admet.com/5-things-know-buying-tensile-testing-grips/

Hi

When you do the test once again. try this

use teflon cloth in the bone end and hold it. It will work out. sure.

good luck

arun

We are working on the mechanical response of elastomeric polymers. We also encountered the issue of slipping of dog bone samples at the grips. I would like to suggest a few things:

1) The use of sand paper will solve the problems to some extent but more number of samples are to be tested to get the repeatability.

2) If the samples are thick enough, then rub the sand paper on the gripping area to make it rough. Clamping with precision and rubbing with sand paper will solve the problem to some extent. With 4 to 5 samples repeatability can be achieved. Note that this depends on the nature of polymer and also the thickness of the specimen. ( Eg. Rubber, this will work).

3) Having an automated grip which will keep on actuating the gripping force as the specimen elongates during the test.

4) Having a spring coupled grip which keeps exerting the force on the grips throughout the test.

To conclude the methods 3) and 4) can produce reliable results.