Damping properties of materials
Damping properties of materials
(OP)
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
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
RE: Damping properties of materials
The material damping will generally be a very small part of a total damping of the structure because welds, bolted or riveted connections and other interfaces will have much higher contribution to the overall damping.
I have collected some material on the matter over the years. There is an article in Jouirnal of Applied Mechanics (from 1946!!) called "Internal friction in Engineering Materials" which describes the concepts quite good, and give some examples of material damping of engineering materials.
Good luck!
Bernt
RE: Damping properties of materials
I will send you the data if you send an Email request to me.
Tom Irvine
Email: tomirvine@aol.com
www.vibrationdata.com
RE: Damping properties of materials
I also have a list of emperically attained damping ratio's of several structures, both steel and concrete. The problem is that these ratio's are depending on the construction, and they are not valid for a different structure. For example: a damping ratio of steel, obtained via measurements of a one-sided clamped beam, may not be valid for a structure containing welds and bolted items.
I'm looking for actual material constants, valid for any structure. This constant should then be substituted in a formula, where also form and other material constants are present.
RE: Damping properties of materials
You are asking for the impossible. I have measured the real damping characteristics of steel structures (car bodies) for 20 years (no wonder I'm eccentric). The variation in modal damping seems inexplicable to me, and my friends (loosely speaking) in the FEA world have yet to come up with a good way of deriving damping ratios, even for structures where the material is well know, and the construction techniques are reasonably consistent.
The best way of acquiring knowledge/cynicism on this subject is to grab a two channel analyser and an impact hammer and an accelerometer. Then hit things. Some companies used to hit every component they made. It seemed silly at the time, but the database they built led to a rapid understanding of which modal characteristics were important.
Cheers
Greg Locock
RE: Damping properties of materials
I'd rather not bite Tom's hand off, 'cause then typing becomes mre difficult and we'd not get these fast replies ;)
thanks for your advise though
RE: Damping properties of materials
A simple example, for me, is the difference in damping between the first torsional mode of a car body-in-white, and the first bending mode. The frequencies are typically at say 27 and 24 Hz, respectively. The material and joints in the car that are involved are roughly the same for both modes. The damping ratio could be 25% different for these two modes.
Cheers
Greg Locock
RE: Damping properties of materials
I agree with Greg and the guy without the hand (Hi!), the devil is in the damping.
It is just one of those parameters that everyone knows is bogus, but which everyone uses to explain the measurements. It is more than viscous, almost never entirely structural, and usually non-linear, so about all you can do is allow for a certain amount of ignorance. A good starting point is to take advantage of a helping hands to sort out the dead-ends...
RE: Damping properties of materials
Thank you.
Mike
RE: Damping properties of materials
RE: Damping properties of materials
In my opinion damping ratio isn´t a material property or constant. Meanwhile there is a relationship between damping ratio of a structure and Young Modulus of the material.
So when you say:
"Because if I make a beam of steel and the same beam, but now of concrete, there is a clear difference in damping, so damping IS material related",
in fact damping of the structure changes because the Young Modulus of the materials are differents.
Regards
Margaria
RE: Damping properties of materials
Strokersix did not mention damping ratio. He/She talked about internal damping.
Strokersix,
There will be differences in the inherent levels of damping of the two materials. However the total damping of a crank mechanism will be determined to a much greater extent by the effect of bearings, interference tolerances etc. The damping effects of these will be several orders of magnitude greater than the inherent material damping.
As for the real reason they changed the material? I favour EMs theory, but then I'm a cynic too.
M
--
Dr Michael F Platten
RE: Damping properties of materials
Thank you to all who responded and look forward to any more thoughts!
RE: Damping properties of materials
It also has another chart that shows "The Percent Decrease in Amplitude per Cycle at varying stress levels.
Steel is almost a flat line from a 1% decrease @5,000 psi to a 2% @ 30,000 psi stress.
Class 50 CI goes from a 3% decrease @ 1,000 psi to a 9% decrease @ 21,000 psi stress.
Class 25 CI goes from a 16% decrease @ <1,000 psi to a 20% decrease @ 2500 psi stress.
A couple of other general statements given.
The damping capacity is little affected by either temperature, vibrational frequency, or stress history.
Direct quote.
"The acoustic properties are closely related to the damping capacity since the entire duration of sound emanating from a vibrating metal only continues for the actual vibration period of the metal part.
The acoustic resistivity increases with the increasing elastic modulus and specific gravity and is expressed:
mu = sqrt (E x rho)
mu = acoustic resistivity in 10^4 cm^-2 sec^-1
E = modulus of elasticity in kg/mm^2
rho = specific gravity in g/cm^3
The acoustic resistivity is listed as 255 and the velocity sound as 12,000 ft/sec in plain grey iron (Critical Tables).
Both the acoustic resistivity and velocity of sound decrease with increasing temperature."
RE: Damping properties of materials
RE: Damping properties of materials
Lazan,B.J.& Goodman,L.E.(1956), "Effect of Material and Slip Damping on Resonance Behavior" ASME Booklet Shock and Vibration Instrumentation, pp.55-74
Birchak,J.R. (circa 1976), "Damping Capacity of Structural Materials" Shock and Vibration Digest(?), pp.3-11
Schetky,L.M. & Perkins,J. (1978)"The Quiet Alloys", Machine Design, 4/6/78, pp.202-206
Lazan (who contributed to a book on the subject)provides tabled and plotted data for gray iron, magnesium, aluminum, 1020 steel, 403SS, and some superalloys using a damping parameter called specific damping energy in in-lb
per cu-in per cycle.
Birchak's literature review of 34 papers plots specific damping capacity vs stress for 2 plastics and 17 metals or metal alloys including cast iron, steels, brasses, magnesium alloys, stellite and a titanium alloy. He identifies Lazan's book input as:
Lazan,B.J. "Structural Damping" (J.F.Ruzika,ed.), ASME, 1959
Schetsky's article provides Specific Damping Capacity(SDC) values for 20 metals or alloys with SDC's ranging from 49%(Magnesium) to less than 0.2%(aluminum/nickel/titanium alloys and brasses). High-damping alloys are assigned SDCs of 20% or higher. SDC is defined as the percent of strain energy that is dissipated per cycle from decay of free oscillation after initial deflection of torsional, bending or axial deflection of a sample bar, assuming strain energy is proportional to amplitude.
An internet search of "material damping of vibration" indicated that most of the current work on development of high damping materials is related to composites rather than metals or metal alloys.
RE: Damping properties of materials
I know this is not a direct comparison, but it is indicative that the damping of CI could more than compensate for its lousy fatigue life.
TVs are relatively poorly damped in an engine, so the basic material is one of the few ways of introducing damping into the system unless you add explicit components like a TV damper.
This is in contrast to many resonances on an engine which are damped by gaskets or joints, rather than the innate material of the component.
Cheers
Greg Locock
RE: Damping properties of materials
RE: Damping properties of materials
Oh, if you want examples where intrinsic damping is important then there are many applications in the noise and vibration world - diff housings (CI not aluminium) - intake manifolds (plastic not aluminium) - engine covers (plastic not aluminium again).
If you want examples where the innate damping is useful against structural failure of the same component, yes I agree, that is rare.
My /guess/ is that the internal discontinuities required to generate damping also compromise the molecular structure of the material, so what you gain in damping you lose in yield strength. Also, these localised discontinuities are a good way of pumping energy into the lattice, which will speed the growth of dislocations.
Well that's a damn fine theory, completely unprovable!
Cheers
Greg Locock
RE: Damping properties of materials
RE: Damping properties of materials
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
RE: Damping properties of materials
RE: Damping properties of materials
There ought to be some new information around concerning the acoustic properties on metals as all the new ultrasonic techniques come about.
RE: Damping properties of materials
"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.
RE: Damping properties of materials
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.
RE: Damping properties of materials
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
RE: Damping properties of materials
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.
RE: Damping properties of materials
Could you send to /////rmaxbaok@aol.com\\\\\?
RE: Damping properties of materials
RE: Damping properties of materials
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.