dynamic simulation elastomer

[James92]

Good evening to all,

I am interested in evaluating the damping effect of an elastomeric mat where a component is attached above. I have a time history known and given an entrance I want to see how the mat behaves: amplifies or cuts in input stress. to do this it is more appropriate to use a non-linear model where I input an effort curve -deformation of the elastane or a hyperelastic model such as the mooney rivilin or ogedn model?

 

[Stan9411]

I'm not a super expert. but I happen to see similar works.

that I know the model of mooney rivilin however requires to define a whole series of coefficients, which you must extract from experimental measures. so I would say that at this point it is worth giving directly to your material a stress-deformation curve not linear.

But I repeat, perhaps I do not see the pros and cons of the two solutions, not being an expert.

a calculation with a multibody approach (shaping the whole mat as a parallel spring-smower system) did you try it? in this case however the modeling works well as long as you maintain your material in the linear visco-elastic zone. . that however to me seems a minimum requirement for the good functioning of a shock absorbing system ..

 

[James92]

@Stan9411 thanks to the prompt response. then let's say that my simple multibody approach was as follows: being more interested in the response to the shock of the system (it takes 200g with half breast form in 0.5ms) I calculated the srs of such time history and wanting to halve the accelerations due to the shock I within the srs with 100g are about 300hz that then I define as the way to vibrate desired of my component. modeling therefore the elastom as a spring and a dampener define the constant elastic k:

♪[ \frac{{E}{A}}{l}=k \]where and is the elastic module, to the surface of the elastom and its thickness. putting l in function of the frequency I can get an 'equation that provides me the value of the elastic module given the geometry of the elastom.

♪[ E=\frac{{m}w^{2}{l}}{A} \]inserting a m=0.25kg (damping component mass) , l=5mm (elastomer thickness), a=7cm x 9 cm (elastomer area ). I get about 17kpa. I don't think I find an elastomer on the market with such a low value of elastic module but I'll inform myself.

Can you come back as your approach?

 

[Stan9411]

Well but the srs is an analysis tool.. not synthesis! You cannot define a project variable from the srs ... because the srs te you are procured/measured/calculated starting from a system that is already defined. .

Am I wrong?

Again. I am not a mega-expert.. but I work in the company where these themes are also dealt, so I often see them striving.

Just to prove I'm not saying shit, how did you get the srs?

 

[James92]

the srs analyzes all the maximum answers to a shock of a single degree of freedom system therefore does not consider a precise system already defined. in the calculation you examine a natural frequency at a time, you see the answer to the time history in the input and you take the maximum and do it for all frequencies. Perhaps a third voice in understanding would not be bad

for the calculation I am based on the works of the good tom irvine , I use its code on matlab . in particular the algorithm of smallwood ramp invariant is used .

http://www.vibrationdata.com/newsletters/august2001_nl.pdf

modeling with solidworks the real system with the elastomer with elastic module 17kpa get a way to vibrate at 100 hz. I expected to match a little more with the 300 but I have to say that 1 mesh is poor and tomorrow I try to work on and 2) the system is a little more articulated because there is an elastomer both above and below and this could change things a little.
on the market however I found elastomers with module of 27.5kpa that they approach much to what maybe could do to my case.

If the srs is correct then it seems to me a good procedure also to evaluate how to vibrate from a simple frequency analysis, use this way to estimate the load on the unit. In the next few days, I'll talk to the bosses and if he likes, we'll do a practical test.

 

[Stan9411]

mmm ok .. the link still do not look at it, but I think I understood the passage I missed regarding the srs.. the frequencies that are in ascissa are not the frequencies of the exciting (because the exciting is a shock.. as an impact), but the own frequencies of the system I'm planning.

in practice to use it, not to build it, you enter the chart from the vertical axis and exits with a number from the horizontal axis.

Then your reasoning comes back.
consider that in principle to stay in the seismic zone (where you have the damping effect) you must ensure that the proper frequency of your system is well below the frequency of the exciting.. that then in your case the exciting does not have a real characteristic frequency ... but it should work the same way