Viscoelastic material properties

[adampar]

Hi everyone,

I am using Femap 11.1.2 and i wanted to use the SDAMPING card referencing TABLEDi in a direct frequency analysis (S108) in order to express the damping of a viscoelastic layer as a function of frequency. This procedure is explained in Nastran Advanced Dynamic Analysis Manual in section 5.6. The problem is , that there is no way to enter these frequency dependent properties in damping values in FEMAP, and even if i input manually the SDAMPING command card and the TABLEDi tables myself, the solver does not take them into account... Anyone can shed some light??

Thanks

 

[modeldamper]

Hi
This is how you should use it. You can give only one frequency dependent material. Can't use for multiple frequency dependent visco elastic material. Make sure that you don't enter GE values in other material cards

ACCELERATION(SORT1,PUNCH,REAL) = 1
SDAMPING = 9
.
.
.
$This is the visco elastic material. enter shear modulus as 0.001 and GE as 1000 so that the product is 1. Now it will call for the frequency dependent tables 9 and 10. Where Table 9 will be the real value of shear modulus and Table 10 will be the imaginary value of shear modulus. Whatever # that you give for SDAMPING, that number will correspond to real value table (9 in this case). The imaginary will be real value table # + 1 (i.e 10 in this case)
$2345678123456781234567812345678123456781234567812345678123456781234567812345678
MAT1 3 .001 .48 9.705-2 1.21-4 72. 1000.

TABLED1 9 +
+ 100.100.2168 200.109.2984 300.132.8878 400.152.2837+
+ ENDT
$23456781234567812345678123456781234567812345678123456781234567812345678
TABLED1 10 +
+ 100.114.5005 200.156.3961 300.189.4612 400.217.9865+
+ ENDT

Table 9 gives the real shear modulus (storage modulus) and Table 10 gives the loss modulus (product of storage modulus and loss factor)

I don't have any values for GE in other material cards.

MAT1 1 1.+7 .33 2.588-4 1.272-5 72.
$ Femap with NX Nastran Material 2 :
MAT1 2 999900. .48 1.771-2 2.58-5 72.

Hope this helps