NX Nastran frequency dependent shear modulus

[modeldamper]

Dear forum members

Can someone explain how to write a frequency dependent shear modulus and damping, and the corresponding TABLED1 entries?

Thanks

 

[BlasMolero]

Hello!,
The CBUSH element of NX NASTRAN allows you to define Stiffness, Damping, and Structural Damping for each individual DOF using the PBUSH card. Stress/Strain Recovery coefficients in the translational and rotational DOF can also be defined.

Also, the CBUSH element allows you -when peerforming a Frequency Response analysis- to define Stiffness vs. Frequency, Force/Velocity vs. Frequency, and Struc­tural Damping vs. Frequency in each DOF.

And finally, for a Nonlinear analysis, Force vs. Displacement can be defined for each DOF.

As you see, the CBUSH element of NX NASTRAN is a jewell!. Using FEMAP (or other FEA pre/postprocessor) will write the corresponding TABLE1 entries.

Best regards,
Blas.



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[modeldamper]

Thanks Blas.

But, I need it for HEXA elements. How do I write the MAT1 and the corresponding Tabled1 entries?

Thanks for your help.

 

[BlasMolero]

Hello!,
Well, the problem is not "how to do it" that is simply, but what values to enter!!. I run FEMAP & NX Nastran, then if I would know the variation of Shear Modules "G" vs. frequency simply I will write a function and will make the above "G" material property a fuction dependent, linking the function with the property. Then FEMAP will write the MAT1 & TABLE1 entries accordly.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[modeldamper]

Thanks Blas for your reply. Further, I have 3 Visco elastic materials and all of them are frequency dependent. I had 3 SDAMPING cards in NX Nastran to illustrate the tables for 3 visco elastic materials. The analysis ran without any errors. But, only one SDAMPING card was considered(the last one) and the other two cards were ignored. Basically only one frequency dependent material was considered and the other two were ignored.

Have you encountered a similar case?

 

[BlasMolero]

Hello!,

Take a look to the NX NASTRAN Manual of "Advanced Dynamic Analysis User's Guide > Dynamic Solution Techniques > Viscoelastic Material Properties", there you can read the following:

"The mechanical behavior of many glasses, rubbers, and high polymers under stress is described in terms of a combination of elastic 
and viscous phenomena that may be approximated by linear viscoelastic theory. The dynamic behavior of such material is characterized by a 
strong dependence on frequency; and, under sinusoidal excitation, these materials exhibit a steady-state response in which the stress lags
the associated strain. The general three-dimensional state of stress can then be described in terms of a complex frequency-dependent shear 
modulus and a real constant value for Poisson’s ratio.   This method was developed for the analysis of rubber-like materials such as solid 
rocket propellants. In that case, the dominant strain energy terms were the shear strains."

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/