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Author Topic: Stiffness not changed for Buckling Constraint  (Read 357 times)

JanPio

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Stiffness not changed for Buckling Constraint
« on: October 01, 2018, 07:51:06 AM »
Hi,
I try to implement buckling constraint of 1 into my analysis.
My settings:
  • Failure analyses: only stiffness requirements
  • ABD components: all D_ij (also tested with all A_ij and all D_ij, same problem)
  • one buckling load case from ANSYS
  • panels in the region where buckling occurs first are "one stack unstiffened" starting at 2mm thickness, Max bound is sufficiently high
  • all elements are in a common display set that is selected for the constraint
  • FEA loads extraction: peak element filtered (if this makes a difference for FEA constraints)
Working:
  • Mode shape displayed in FEM Viewer
  • correct Eigenvalue displayed in FEM Viewer
  • max translation of 1 displayed in FEM Viewer
  • iterations run without error
  • buckling contraints, lambda_actual, lambda_req and the factor are shown in the iteration report
  • the thickness is increased once from 2 to 3 mm
However, the factor does not seem to be correctly translated into required stiffnesses of the panel (see table below).
Not working:
  • the thickness is not further increased
  • all component factors for stiffness are =1 (see table below)
  • all margins of safety are (slightly) positive (probably because the required stiffness matches the actual stiffness in the table)
  • there is no Mode Detection Parameter higher than the order of E-31, which seems very low to me
      
lambda limitlambda actualFactor
10.002128684469.7737189

D11D11,req CurrentD11,req NextFactor
181121.4823181121.4823181121.48231

Do you know why the obviously high "Factor" does not lead to further panel thickening?
Thanks,
Jan
« Last Edit: October 01, 2018, 09:12:58 AM by JanPio »