Damping properties of materials 9

[WIM32]

I've been looking for documentation on damping properties of materials, non-dependend on the dimensions and construction. Until now it seems that damping ratio is not a material property or constant (like Youngsmodulus). Is there anybody who can shed some light on this subject???
There are many sites and publications that state that concrete has better damping properties than steel. This is oc course true, but a value is not given (at least not un-depending on the structure)...
Any info is welcome!
rgrds
Wim

 

[GregLocock]

There's two test for engine durability. The quick and dirty is one hundred hours at full power. That is the make or break for a new design generally, once you can pass that the rest is just details. The other is a rather longer procedure at multiple loads and speeds, which probably adds up to 500 hours (3 weeks).

There are no two ways about it, forged steel cranks are the way to go, everything else is a compromise - but production cars are a compromise all the way from one bumper to the other.



Cheers

Greg Locock

 

[EnglishMuffin]

That sort of jibes with what I once heard when I was at college from from a lecturer (= professor US) who had worked at Ricardo's, which was something to the effect that, as a rule of thumb, if an engine could get through one of their 10 hour tests, then it would probably be OK. 10 hours seemed a bit short to me, but it was a long time ago and maybe I misheard. It sounds as though the crankshaft material thing may have to remain one of those unanswered paradoxes.

 

[unclesyd]

If we have some Auto buffs out there I remember in Sports Car Magazine or Hot Rod Magazine as to who had what in cranks. I think it was the Japanese that led the way in DI cranks. I know that Ford did use some CI at one time as we melted tons of the in the early fifties. They had been in the weather for years and based on the chemistry they would have had around been Grade 45.

There ought to be some new information around concerning the acoustic properties on metals as all the new ultrasonic techniques come about.

 

[Franko]

unclesyd (Materials) Dec 4, 2003 Wtote:
"I have an old grey-iron properties handbook that gives the relative vibration damping qualities of Gray Iron, Ductile (Nodular)Iron, and steel as pictorial graph. ........
...........The damping capacity is little affected by either temperature, vibrational frequency, or stress history."

I would not trust this statement. Damping capacity of steels changes with alternating stress amplitude, and also usually decreases as steady-state stress is increased. Frequency related to machinery is usually not an issue, but high temperature such as for steam turbine materials (12 % chrome - type AISI 403 etc.) also has an effect.

For some good information, see Tom Irvine's 3/19 post.

 

[unclesyd]

Franko,
After I looked over the statement, its stated in 2 hadbooks that I have, they could have ment CI only as its not too clear in the preceding sections as to the limitations of the statement. One booklet does mention graphite flakes. the more the better damping. I had a friend check and the references are given are not available. As I stated it has graphs that show the % damping as the stress increases, very low for steel much higher for CI's.

These booklets were derived from the "Grey Iron Castings Handbook" from the Gray and Ductile Iron Founders Society.
I don't have a publishing date but it was a long time ago as the 607 page book only cost $10.00.

 

[rmax]

Re: vanstoja's reply:
I can't find the article "Damping capacity of structural Materials" in Shock and Vibration Digest(?),pp 3-11 by Birchak,J.R.

Can anyone help me locate this article?
thanks rmax

 

[vanstoja]

To rmax
I have a hard copy of the 11 page Birchak literature review paper on "Damping Capacity of Structural Materials" but no means to transmit it electronically. If you want to post an e-mail or USA mailing address I can furnish you (only) a copy. The "circa 1976" date was based on the latest date of the 34 references and it could have been published later than 1976. None of the pages identify the publication, but it looks like a Shock and Vibration Digest article based on other self-dated & identified S&VG articles I have. The author's affiliation is Babcock and Wilcox, Lynchburg Research Center, Lynchburg, Virginia 24505. He acknowledges assistance from Dr. G.W.Smith and others at General Motors Research Laboratories.

 

[rmax]

Thanks vanstoja.
Could you send to /////rmaxbaok@aol.com\\\\\?

 

[SignalToNoise]

A good source for the damping properties of materials can be found in Cremer and Heckl's book Structurborne Sound, Springer-Verlag, 1988, Tables III-2 and III-4, Mechanical properties of Metals and Building Materials, respectively. As with any design, acoustics is one of many important parameters to be taken into consideration(including static and dynamic loading, stress concentration, fatigue, weight, costs, etc). You may also consider using viscoelastic damping materials to reduce structural vibrations on the steel. This has worked well for me.

 

[aarul]

WIM32,

I have done some work on meassuring damping properties of materials and the two techniques that gives you a reasonable estimate of damping is the constrain beam method and the DMTA (Dynamic Mechanical Thermal Analyser). I have used the latter quite extensively to measure damping properties of adhesive materials.

If you are trying to get damping values of similar type materials, perhaps worth testing it as it is pretty hard to find values of handbooks as described by other members so far.