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Software Use => Analyzing & Optimizing Stiffened Panels => Topic started by: orchidworld on October 16, 2012, 03:47:41 AM

Title: Smearing panel virtual moment calculation
Post by: orchidworld on October 16, 2012, 03:47:41 AM

Dear All,

according to the" Methods and Equations Thermoelastic Stiffness Formulation", i try to test with parameters in this paper.

Virtual moment: i think it should be equal:   Nx*(midplane of the top facesheet-X   neutral axis).
Nx?Compression or tension load
for example:
Nx=-1000N/m (Compression load)
Top facesheet thickness=0.05inch, so the the midplane of the top facesheet=-0.025inch;
X neutral axis(data is from Computed Properties tab.)= -0.5847238inch;


Virtual moment=Nx*delta h=-1000*(-0.025-(-0.5847238))= -559.7lb-in/in;

but, in fact, the result from FBD tab. is -576.271lb-in/in

why are they different? whether is it wrong about my understand and calculation??

thanks a lot

Title: Re: Smearing panel virtual moment calculation
Post by: James on October 17, 2012, 11:01:32 AM

The virtual moment is calculated from the ABD stiffness formulation. When you have coupling terms, it is not as simple as multiplying the applied Nx load by the offset of XNA to the reference plane.

From the ABD formulation, we have..
Mx = B11(e_x) + B21(e_y) + B62(gama_xy) + D11(kappa_x) + D12 (kappa_y) + D16 (kappa_xy)

where:
e = strain
gama = shear strain
kappa = curvature

If you are constraining the curvature for the panel, the virtual moment is calculated so..
kappa_x = kappa_y = kappa_xy = 0

Then the equation is simplified to...
Mx = B11(e_x) + B21(e_y) + B62(gama_xy)

Let me know if this is helpful
-James