Relaxation Test for PC Wire

e are facing some confusion regarding system of relaxation testing.

We have gone through ASTM as well as Australian standard where there is provision to put Extensio meter and whenever there is any fault in the length alongwith load indicator it has to be upped and got to the original length. Thus, while making up this length, load also goes up. However, I am not very sure if this practice is ok.Because somewhere we have learnt that once load is applied, it’s not to be touched.

Can somebody guide me and share his knowledge of relaxation testing as practiced at various place.

On relaxation test there are three variables:
1.- Force applied
2.- Deformation
3.- Time

The test can be made on either constant force or constant deformation and at defined number of hours

If the test is made at constant force , the deformation mesure on a graph agaist time.
If it is made at constant deformation, the graph will show force applied agains time.

The purpose of the test is to predict the behavior of usually of a PC element subjected to a load after time exposed.

Eduardo Anaya
Senior Consultant
INDEPA S.C.
Mexico City
Tel(011-52)555-407-7451
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I have following to add to the same :

Mr.Anayae responded by saying that there are three variables. ASTM A 416 for P.C. Wire specifies to measure fall in force applied (tension load) against time. I believe, deformation has to remain constant. However, typically we find through reading on Extensio Meter that when a particular force is applied and sample is left for a long time, it will have some variation in the length (it registers minor shrink).

If we have opted for constant deformation route, as suggested in ASTM A 416, then length needs to be increased by applying more force and stretching sample little more to eliminate effect of shrink.

This, in fact reduces the total fall in force recorded by the system.

I would like to know ;

1) Is it normal to witness shrink phenomena recorded by Extensio Meter, after applying specific load, over a period of time.

2) If the sample has shrunk, the deformation does not remain constant. So should we try to reach earlier length by stretching it more during the period of test say 100 hours or 1000 hours.

I am trying to post this query myself, marking copy to you also. If I fail, then may be you can post in your name.

Best Regards
Mahesh Poddar / email: This email address is being protected from spambots. You need JavaScript enabled to view it.