Energy propagation through air vs. metals 4

[Nortomo]

Hello,

I am looking for some information and thought of posting it here.
I have looked at various sites on sound, sound propagation, and sound attenuation but don’t seem to be able to find the answer I need.
I need to determine whether the sound will be damped better/easier/quicker through air vs. metal.
Intuitively, since air is easier to push around, it seems that it would dissipate the energy quicker/better than metal.

The 2nd part of my question is;
having a large quantity of tiny strands of metal in a wire with many small air spaces around them
vs. the same amount of metal and air space but with larger strands and large air spaces around the strands.

(Working with an engineer, he determined that there is essentially the same amount of air in both spaces)

Is the energy damped quicker by the tiny strands and air spaces, or is the attenuation the same in both cases?

If this type of information is shown or can be calculated on a site, please point me to it.

Thanks for any tips, pointers, or advice.

 

[GregLocock]

The finer the fibre the more the attenuation. That's because there's more surface area to slow the airflow.

 

[Nortomo]

Thanks for that reply.

I appreciate your reply because I have not found any useful info anywhere else.

So, if I am interpreting your answer correctly, any increase in the metal-to-air contact interface results in a higher energy attenuation.

Do I also understand that if energy is input to an equal area of air and metal, more energy will be shunted into the air compared to the metal?

In the graphic below, it seems to me that although the smaller strands result in more surface, overall, it is closer than you would think.

I'm trying to justify using a higher strand count wire in a high-vibration environment. On some machines, the vibration work hardens the copper, resulting in the circuit becoming intermittent. So, I need to justify the higher-cost wire, which is easy if it means the product will have a longer service life.

Thanks.

 

[3DDave]

There is more friction between the fibers as they rub against each other with vibration.

It's why a hammer head will bounce but a sack of steel dust won't.

 

[goutam_freelance]

Below is a paper on the damping of composite materials. There may be some guidance here by assuming that there is no matrix.

https://www.sciencedirect.com/science/article/abs/pii/S1359836815002139

 

[3DDave]

Work hardening isn't because of damping or vibration, it's because of deflection of the wire. If you were to secure the wire so it could not move/bend/flex it would survive.

Fatter wire means that for a given deflection the surface sees more strain, which causes work hardening and fatigue. Fine wire will have less strain for the same deflection.

What is best is finer wire that has a high amount of twist - this is what is done to wire rope to prevent it from work hardening/fatigue failure. If in a cable it is necessary that all wires get a common twist.

The path of the wire can also change the resistance to failure. If the wire crosses a hinge it is better to have a full loop than just bending without a loop. If the vibration seems too high to use a loop, consider using a piece of spring wire or flat spring stock to secure the wire to and then secure that support to either side of a hinge.