Damping Coefficient for 416 Stainless Steel 5

[aggie74]

I have a customer looking for the above. I have not been able to find any literature listing. Your help would be appreciated. Thanks

 

[btrueblood]

Should be about the same as for "any steel". You can see some specific data for various steels and other alloys in Shock and Vibration Handbook, Cyril M. Harris, McGraw-Hill. Generally, the damping is pretty low, I think I remember analysts using .05% of critical, for typical steels. Cast iron and magnesium alloys have much higher internal damping.

 

[btrueblood]

Oh, should have specified "Chapter 36" of the cited reference, it's a pretty thick book...good luck.

 

[btrueblood]

Also, see thread 384-49887

 

[GregLocock]

SS will have a bit more damping than a typical steel.

Cheers

Greg Locock

 

[hacksaw]

Depends on the temperature, time scale, amount of strain, heat treatment, etc.

The damping is inversely related to the modulus so that high modulus materials generally show the least damping. As a rule the 400 series has better damping characteristics than the 300 series.

The Japanese literature seems to have the best data for commercially available alloys.

 

[MikeyP]

A little OT, but does anyone know how the loss factor for a material such as steel is measured by the manufacturers? I would guess for most conceiveable situations that the damping due to the internal loss factor of steel is tiny compared to other sources of damping (eg acoustic radiation, transfer of energy to supporting structures, friction etc). Do they levitate it in a vacuum chamber or something? Do they ever quote a confidence interval for the data?

M

--
Dr Michael F Platten

 

[hacksaw]

Mike,

The specifics depend on what you are after. There are several damping mechanisms involved and generally frequency and strain dependent.

Internal rather than structural damping is always referenced in the materials literature.

 

[GregLocock]

I do it by looking at the frequency response of a bit of bar, free free, hammer test. Admittedly that will include some air damping, but it does in the car as well.

Cheers

Greg Locock

 

[MikeyP]

Ah, I'm beginning to get it now. If you have a bar of the material (suspended free-free) and excite it longitudinally, then the longitudinal modes will produce very little acoustic radiation. A modal analysis will yield the modal damping for each longitudinal mode and from that you can estimate the loss factor at the resonant frequencies. If you repeat the test with different lengths of bar then you will eventually get loss factor estimates over a range of frequencies.

You just have to hope that no-one wants to know the loss factor at 10 Hz or you would have to test a bar that was 250 metres long (for steel)! Although you could probably use bending modes instead of longitudinal modes at those frequencies as the radiation would be poor.

Call me cynical, but I can't believe that steel alloy manufacturers really go to such lengths, especially if all they do is quote a single figure at the end of the day.

OK, now I'm waffling. Past my bed time.

M

--
Dr Michael F Platten

 

[vanstoja]

Schetky,L.M. & Perkins,J., "The Quiet Alloys", Machine Design, Apr.6,1978 ranks various metals by Specific Damping Capacity(SDC)which is based on decay rate of strain energy obtained from decay of free oscillation after an initial torsional, bending or axial deflection of a sample bar. The range of SDCs is from 49(Magnesium,wrought) to <0.2(Brasses, bronzes, titanium, nickel-based superalloys). Austenitic, ferritic, and martensitic stainless steels have SDCs of 1, 3 and 8, respectively. The 400 series martensitics have better damping due to magneto-mechanical effects according to Lazan,B.J. & Goodman,L.E., "Effect of Material and Slip Damping on Resonance Behavior", 1956, ASME, Shock and Vibration Instrumentation, pp.55-74. See thread384-49887 for a previous discussion of materials damping.