I read an article in a textbook which says stiffer rubber increases vibration damping and softer rubber increases vibration isolation.

Can anyone explain this how?

What is the difference between vibration damping and vibration isolation..?

  • $\begingroup$ This combined with your other question about engine mounts makes it seem like this is homework... Lots of texts have the formulae to do with vibration and vibration damping... $\endgroup$
    – Solar Mike
    Aug 7 '19 at 15:19

Vibration isolators work because there is relative movement between different parts of the isolator. Softer rubber tends to create more relative movement.

Vibration damping in rubber depends on the amount of strain energy transmitted through the damper. For the same vibration amplitude, higher stiffness tends to result in increased strain energy.

Think about the extreme situation where there is no connection at all between the two components (but something magical prevents the structure falling apart). The vibration isolation is perfect, because nothing is transmitted from one component to the other, but the amount of vibration damping is zero because nothing is absorbing energy from the system.

Warning: general statements like the comment in your textbook can be misleading unless you think carefully about what is changing and what is kept constant. For example, changing the stiffness of part of the structure can change its vibration response (by change the resonant frequencies) independent of any effect on the system damping.

  • $\begingroup$ Sir thank you very much for very detailed information. I have one more doubt, I have read that rubbers are usually soft and make very good insulators but at high frequency low amplitude vibrations they become harder due to increase in dynamic stiffness which makes it poor insulator. How do engineers overcome these problems in say rubber bushings of engine mounts. $\endgroup$
    – SS4
    Aug 7 '19 at 14:33
  • $\begingroup$ For engine mounts see engineering.stackexchange.com/q/29532/10902 $\endgroup$
    – Solar Mike
    Aug 7 '19 at 15:18

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