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# How to specify viscoelastic material property in Nx?!

Creator

Dear nx nastran users

I have 2 questions..

1.

I would like to know how to model the viscoelastic that changes the Young's modulus and loss factor

depending on the frequency.

In the NX documentation, in the Advanced Dynamic Analysis User's Guide there is an example carried out in the Nastran environment.

However, it is difficult to know how to perform it only by looking at that part.

2. Is sol103(Normal mode analysis) also applicable for viscoelastic?

10 REPLIES 10
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# Re: How to specify viscoelastic material property in Nx?!

Gears Phenom

2. SOL103 calculate linear normal modes, It can not handle with nonlinear materials.

# Re: How to specify viscoelastic material property in Nx?!

Siemens Phenom

Viscoelastic properties are specified on the Viscoelasticity tab on the isotropic material dialog. You need to select a Model, then enter the values for that model (see below).

Note that this is just defining material table data. Whether it is exported to a solver input deck or used by the solver during the analysis depends on the solver, analysis type and settings, etc.

# Re: How to specify viscoelastic material property in Nx?!

Creator

Dear Jimb

Thank you for your reply. However,  I am going to new post abot " How to use isotropic materiall property"
because I am unfamiliar with the application method.

# Re: How to specify viscoelastic material property in Nx?!

Creator

Dear Karachun

Is it nonlinear that the modulus varies with frequency?

_

# Re: How to specify viscoelastic material property in Nx?!

Gears Phenom

In Frequency response (SOL108 or SOL 111) you can vary E vs. Freq, but not E vs. strain (Stress-Strain curve). SOL103 ignore Frequency dependent properties, Stress-Strain curve, Damping and calculate only linear modes with linear assumptions like infinitesimal strain theory.

Describe here your physical problem, maybe we can reduce it to simple linear solution. At this point, it is look like you are asking xy problem

# Re: How to specify viscoelastic material property in Nx?!

Creator

Dear Karachun

Thank you for mentioning xy issue. It was a chance to look back at me.

What I would like to do ultimately is to calculate the Sound Transmission Loss(STL) of the EPDM rubber.

STL is an index of sound insulation performance and is defined as the ratio of the incident sound energy to the transmitted sound energy.

STL=10*log10(I_i/I_t) , I_i=I_incident sound energy, I_t=Transmitted sound energy

I have found that the STL of rubber may be very different( Frequency dependent young's Modulus VS Independent

See Fig.1 Ref.Investigation_of_Sound_Transmission_Loss_of_an_automotive_door_Sealing_system_by_using_FEA)

STL calculation process is as follows.

1.acoustic excitation --> 2.calculate Rubber response --> 3.Calculate Transmitted intensity(Vibro-acoustic Solver)

NX provides Acoustic excitation(named as "Distributed Acoustic Plane Waves") but I dont't have vibro-acoustic Solution. but anyway i have other vibro-acoustic programs - Virtual Lab and VAONE

Virtual Lab and VAONE required mode analysis results or Forced response by Acoustic excitation

so In my opinions, I have to solve normal mode by considering frequency dependent young's modulus.

Please let me know if I have any wrong idea.

# Re: How to specify viscoelastic material property in Nx?!

Gears Phenom

Unfortunately I am not familiar with acoustic analysis. Check NX Nastran Acoustics User`s Guide, maybe you can find some answers here.

# Re: How to specify viscoelastic material property in Nx?!

Genius

Dear @JimB and @Karachun I'm also interested in this topic, but this is my first time that I work with elastomers and frequency response (SOL108). Does someone can suggest a tutorial to learn on NX Nastran 12 about the usage of elastomer model (with module function of frequency) in frequency domain analysis (e.g. FRF of a steel structure with elastomers pad)?

# Re: How to specify viscoelastic material property in Nx?!

Creator
Dear albertoM

I am glad to meet you who is experiencing a similar problem.

I am using sol108 to solve the acoustic problem.(Viscoelastic materials)

As you can see in the NX Nastran Advanced Dynamic Analysis User's Guide, you must enter TR and TI to model the viscoelastic material frequency dependent characteristics.

I figured out using the INCLUDE statement to write TR and TI in the INPUT DAT, but I found something strange.

I wonder if your problem is solved.