linear and nonlinear gaps

[rahuld899]

I ma Rahul working for aerospace company.

I would really appreciate if anyone cansend me some info regarding linear and non linear gaps in patran .
Here is my problem description:

I am Working on a problem where I have L-Shape angle.

The horizontal flange of the angle is attached to the aircraft skin(treat the skin as a plate).

On the vertical flange of the Angle, I am applying load at three locations in the transverse direction to the Vertical flange.

The Horizontal flange of the angle and the skin are attached at three fastener locations.

I think I have to use gap elements in this case, I am using gap elements all along the edge of horizontal flange (creating gap elements using two nodes, one node-on angle horizontal flange, another node on the skin.)

when I try to run nonlinear analysis (as I have used 1D gap elements in patran), I am really getting some huge stresses in the aircraft skin,
say for example load around 1000lb on tip of the vertical flange of angle (angle dimensions. 0.08 inches thk- 6inches lingth and 4 inches wide. same horizontal and vertical flange dimensions)

aircraft skn thk:0.07inches.

I am getting stresses in skn around 250ksi, where the gaps are connected, which is meaning less.

is it because of the GAP elements, or do i need to use much big thickness.

could you please help me in this case.


thanking you,

yours sincerely.,
Rahul

 

[40818]

Have you carried out a hand analysis of the structure?

 

[normm]

Rahul

I think your model should include the flexibility of the aircraft skin. Because of the shape of the aircraft skin, there will be deformation at the support and the high local stresses will spread out.

Can you attach your model diagram to see how you have modelled the support?

 

[aeroAFRIX]

Rahul,
Do you have a screen shot of your model or a hand sketch. Also, as a rule of thumb (good FEA post processing practice) does the deformation (i.e DISPLACEMENT) plot resemble what you were expecting?

"....or do i need to use much big thickness." I thought the idealized aircraft skin had a defined thickness, why do you want to increase the thickness?

Include a Screen shot and the DISPLACEMENT plot of your model set-up if you really want a precise response.

As already pointed out, have you carried out hand calculation to verify your FEA results