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Expanded polystyrene and a core of rigid fibre

 
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Bryan
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MessagePosté le: Mar 11 Mai - 18:17 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

I've been doing a few experiments today, though not with resin/bentonite, so this might be split off to a new thread if you think it appropriate.

I have found a composite, made from a thin plastic covering, expanded polystyrene and a core of rigid fibre, no idea what it is. My brother, who is an architect, says it looks like a room divider panel. I used just the outerskin for this experiment, as I wanted something with a little damping, and be light weight. I measured the main resonance frequency and damping factor using my usual methods. I then added 'newplast', a kind of alternative to plasticine, of measured weight. The results are as follows:

weight         resonance frequency   damping factor
grammes                 Hz

 11.7                       288                        0.133             original sample
 85.7                       248                        0.152             added damping
 251.7                     189                        0.190                 "           "
 481.7                     113                        0.229                 "           "

damping factor of newplast alone   =   0.398

plotting these data out shows a 2nd order polynomial relationship between weight and resonance freqency (r2 = 0.998) and a similar relationship between weight and damping factor ((r2 = 1.000).

I think this shows that adding damping material does not provide the returns on the amount added. Open to discussion:

       
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MessagePosté le: Mar 11 Mai - 18:17 (2010)    Sujet du message: Publicité

PublicitéSupprimer les publicités ?
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Rap
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MessagePosté le: Mar 11 Mai - 20:07 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

I think that depends on how you measure it Bryan, if you have the accelerometer on the same plane as the source of the signal (i.e on the same plane as is hit to produce the signal/vibration) your measuring a surface wave much like a P wave in earthquakes and adding material underneath will not change the dampening of it in a linear fashion, but if the accelerometer is on the opposite plane (other side of material from signal) you are measuring the true dampening or S wave and then I think linear-coefficients of dampening applies but depending on material some frequency anomalies are to be expected as the dampening coefficient of materials is frequency dependant. Can you take a photo of your set up?


p.s. What are the practical application of these new materials you were measuring?
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MessagePosté le: Mar 11 Mai - 22:13 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

Rap a écrit:


True, after all it was aerodynamically proven that the bumble bee could not possibly fly (calculated by it's weight to wing size) but the Bee just didn't know this so flew nonetheless Laughing


Those bees cheat. They're all Masked Mosquitoes.

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Piero Shocked
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MessagePosté le: Jeu 13 Mai - 00:13 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

Rap a écrit:
I think that depends on how you measure it Bryan, if you have the accelerometer on the same plane as the source of the signal (i.e on the same plane as is hit to produce the signal/vibration) your measuring a surface wave much like a P wave in earthquakes and adding material underneath will not change the dampening of it in a linear fashion, but if the accelerometer is on the opposite plane (other side of material from signal) you are measuring the true dampening or S wave and then I think linear-coefficients of dampening applies but depending on material some frequency anomalies are to be expected as the dampening coefficient of materials is frequency dependant. Can you take a photo of your set up?


p.s. What are the practical application of these new materials you were measuring?
I am only using the z axis, that is equivalent to p waves. Looking at the x or y axis (I can only record two of the three) only complicates the situation. I have made some more measurements, today, with a piece of acrylic, and incrementally added mass of newplast. The accelerometer is mounted on the same face as is struck, the damping newplast added to the other side. The new set of data look even better. I'll do more work before I draw conclusions, and post on here. Preliminary results suggest adding mass is proportional to damping, though not linearly. The correlation on a set of 10 data points has a correlation coefficient of 0.996, not bad at all.

I hope that after all the experimemts I want to run, I will be able to say what will happen if a damping material is added to a non-damping material. I need to do this to finish my G99 project, which has acrylic and walnut slats in a bries soleil type of arrangement, in a lossy nut/washer/threaded rod arrangement.

I'm sure the information is applicable to any such situations of adding damping. However, I don't know what affect the differing acoustic impedances will have.
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MessagePosté le: Jeu 13 Mai - 14:58 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

"Newplast" I sometimes use in my line of work, as do these guy's:



How do you bond it to the other material? Won't it have highly disparant properties (modulus/dampening) depending on room/TT temperature? It's seems to go quite soft with a little extra heat from ones hands. 
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MessagePosté le: Jeu 13 Mai - 16:51 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

yes, same stuff, Rap.

And I think it is temperature dependant, just working on that aspect at the moment, ooooh, spooky! Of course, all viscoelastic materials have this temperature dependance, so I'm not that worried. Might mean keeping the tt warm, but I think that is a good thing, a constant 23°C should do it! I had already decided to keep my cartridge warm when not tracking, by enclosing it in a small aluminium box, kept at 23°C with a Peltier device (with feedback control).
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MessagePosté le: Jeu 13 Mai - 17:15 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

Bryan a écrit:
yes, same stuff, Rap.
And I think it is temperature dependant, just working on that aspect at the moment, ooooh, spooky! Of course, all viscoelastic materials have this temperature dependance, so I'm not that worried. Might mean keeping the tt warm, but I think that is a good thing, a constant 23°C should do it! I had already decided to keep my cartridge warm when not tracking, by enclosing it in a small aluminium box, kept at 23°C with a Peltier device (with feedback control).


Don't forget to keep the "receptors" and "audio proccessing unit" warm as well Wink




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MessagePosté le: Jeu 13 Mai - 18:34 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

hearing devices kept at constant temperature, only the directors are prone to coldness. Laughing
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MessagePosté le: Sam 15 Mai - 07:07 (2010)    Sujet du message: Expanded polystyrene and a core of rigid fibre Répondre en citant

Gentlemen,

I have tried to make a little bit of order in the huge original "damping factors" thread dividing it in various threads.

bow

hats off
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MessagePosté le: Aujourd’hui à 03:25 (2016)    Sujet du message: Expanded polystyrene and a core of rigid fibre

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