Problems with Composite Layup

[mbgm8ndb]

Hi All,
I have been modelling a simple (0.050x0.025x0.005m) Aluminium plate, fixed round the edge. I predict the natural frequencies and mode shapes with frequency analysis and the forced response with steady state dynamics. This has been done with both 3D solid elements and 2D shell elements. All seems to work ok. I have attached the .inp file for the shell plate.

Next I add a viscoelastic polymer layer and another aluminium layer to add damping to the plate. When using 3D solid elements this is done by either:
- Extruding on the plate surface where the damper is located and partitioning the separate layers.
- Creating the separate layers and tying them together.

Natural frequencies, modes and the strain energy in the polymer layer are predicted using frequency analysis, and forced response is predicted using steady state dynamics.

I am trying to do the same with shell elements by creating a composite layup material, and applying this where I want the dampers. I create 3 layers:
1 – Aluminium constraining layer – material ALU – Thickness 0.001m
2 – Polymer damping layer – material POLYMER – Thickness 0.00013m
3 – Aluminium Plate – material ALU – Thickness 0.005m
I have also set the offset to bottom.

When I run this, the natural frequencies I see in the composite regions fall from 489Hz to 0.2Hz. I am assuming due to a very large drop in stiffness.

Does any one have any ideas where I am going wrong? I have attached the input files for normal plate and composite plate for any one who is interested.

Thanks in advance for your help.

Regards,

Nigel

Undamped Plate - <

http://files.engineering.com/getfil...47-442cac05a4f2&file=Shell-Plate-No-Damp.inp>

With Composite Layer - <

http://files.engineering.com/getfil...-a1b6f42265e1&file=Shell-Plate-with-comp.inp>

 

[mbgm8ndb]

Does any one have any good tutorials on using the composite layup tool?

Thanks for your help,

Nigel