Nitrile Isolator Creep 2

[mamoore]

This is an application of using Nitrile blocks as foundation shock absorbers; the type of application one would see in a seismically active area.

My question concerns Nitrile and how its shock absorbing (static and dynamic spring constants) change with time.

Questions:

I understand there are different spring constant for static and dynamic loading, but I haven't been able to find out if these spring constants (k-values) remain the same over a period of many years (say 50 years). After being compressed for many years, how do the k-values change?

Should I expect these isolators to respond differently (increased stiffness)?

Is there a similar change in k-value if the isolators are not statically loaded?

Any literature, data, or manufacturer's references would be very helpful.

Thank You,
mm

 

[JIM317]

Chloroprene (neoprene) has always been a choice for bridge bearing pads and for architectural pads--you should contact DuPont and Laxness (Bayer) --they have a lot of background
Your nitrile info should be available from your supplier--I believe Laxness also produces nitrile--Zeon is another one.

 

[polym3]

Probably the only reference I have seen to a study over any period of time is in a book edited by Alan Gent: Engineering with Rubber.

He describes a test done by the British Dept of Transportation of bridge bearings after 20 years. These tests on both NR and CR showed virtually no change in any property, including stiffness.

Also, NR has a couple of advantages over CR; price and Tg. Aging is usually not an issue since degradation/oxidation over, even very long periods, is usually only one or 2 mm deep.