Why do some metals damp so well? 5

[BrianE22]

Cast iron damps real well. Aluminum rings and rings. What causes damping in metal materials?

 

[Stick.]

Assuming you're referring to gray iron and other types where the graphite microstructure is sharp and flaky, I believe it's due to the sharp graphite flakes causing high stress concentrations (at the microstructure level) that then help to dissipate energy. Ductile/Nodular iron has a spherical graphite microstructure, so it lacks the stress concentrations and doesn't damp as well. This document: Damping Properties of Selected Steels and Cast Irons seems like it might be worth a read based on the abstract.

As for Aluminum, I don't have a clue.

 

[TugboatEng]

In terms of modulus of elasticity, the aluminum deforms more for a given stress and stores more energy as a result allowing it to continue to ring for an extended period.

 

[mfgenggear]

Observation only. Soft dead blows absorb the energy. Si it does not deflects as a harden ball peen hammer.
Some cast iron will be hard and brittle and will crack

 

[EdStainless]

The actual mechanics are related to the energy absorption when vibrating (hysteresis loss).
This is also a function of the frequency.
I was in a museum once and they had tubular bells all of the same dimensions made from about 12 different metals.
Huge range of sounds (Al sounds like crap, leaded brass sounds the 'richest').

 

[BrianE22]

The actual mechanics are related to the energy absorption when vibrating (hysteresis loss).
This is also a function of the frequency.
I was in a museum once and they had tubular bells all of the same dimensions made from about 12 different metals.
Huge range of sounds (Al sounds like crap, leaded brass sounds the 'richest').

So EdS - the hysteresis you are referring to is the stress/strain loop and the area enclosed by the loop?

 

[mfgenggear]

Some times to get the job done do physical test from the theories. And record the results

 

[dik]

The volume within the loading-unloading hysteresis curve is a measure of the energy lost in the loading-unloading.

When I was a kid, I used to have an inelastic rubber ball. It was made of a rubber that had a huge volume within the stress-strain curve (I didn't know that at the time). You could 'wind up' and throw it on the sidewalk and it would only bounce an inch or two. The opposite of 'superballs' available at the time. The type of rubber was used for vibration isolators.

 

[EdStainless]

No, it would be a loop at some microstrain level

 

[GregLocock]

One way of thinking about it -'quiet' cast iron in particular has large lumps of carbon interspersed in the grain structure of the metal. When the metal is strained the stiffness of the carbon is different to that of the metal, and so the stress pattern becomes non uniform which takes energy to set up. It's actually a form of impedance mismatch.

 

[mfgenggear]

soft brass is very good. isused often. well as hard rubber.

 

[Dhurjati Sen]

In gray cast iron, the graphite flakes could be treated as voids. Energy, in the form of waves, cannot pass through them. So gray cast irons have excellent damping properties. The same is even higher in spheroidal cast irons because the highly distributed spheroids act as super damping agents. However, in white cast iron, the carbon is present mainly in the form of iron carbide and therefore, it has poor damping property.

 

[dik]

No, it would be a loop at some microstrain level

The volume within the hysteresis curve is a measure of the energy expended in the loading and unloading of the material. l