Need help with experiments

[survesh]

Hello,
I need help for the experiments I am doing on the polymer tube of thickness about 0.5 mm. OD~2mm.
I am doing stress relaxation test for those polymer tube.
I am not aware about the ASTM standard that would be applicable to this situation. I am confused about chosing the gauge length and strain rate. Can anyone tell me about such standard to test the thin polymer tubes in tension? If you know some other reliable reference then also give me.

[sq]

Have you checked ASTM D 2991?

[Jorgen]

Survesh,

I think ASTM D2991 has been withdrawn. If you haven't already, you should perform a search on astm.org for relevant standards.

I have found that it if often necessary to develop your own test methodology when characterizing polymer components. What exactly are you looking for (stress relaxation only)? What polymer? What temperatures? What strain levels? What range of times? And even more importantly, what do you plan to do with the stress relaxation results?

The main problem with tubes is using appropriate gripping. How do you plan to grip the specimens?

- Jorgen

[sq]

Oops.

[survesh]

Well, i fixed either end of the tube between 2 plates and bolted them. also the plates consist of soft rubber plates. Can you tell me other standard of refernece about selecting gauge length and strain rate ...may be from some hand book.

[Dave_Holmes]

Hi survesh, a useful paper I have found dealing with strain rates of thermoplastics is by O. Schang, N. Billon, J.M. Muracciole, and F. Fernagut, Polym. Eng. Sci., 36, 541 (1996).

Using constant cross-head speed and constant strain rate tests Schang was looking at extrapolating models formulated at quasi-static rates to account for impact type results. He did this by trying to account for strain induced power dissipation in the model. In doing so he found that the critical strain rate after which power dissipation must be taken into consideration was 5 x 10-3 s-1 (semicrystalline polyamide 12).

I see this paper as quite useful because it shows that there is a point where work heating starts to affect the material properties. While I'm not sure of the exact aim of your testing, if it is for use with constitutive model formulation etc this would seem to be a useful guide for the chosen strain rate of your testing depending on the type of model you hope to be incoporating.

Hope it helps