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SANDWICH BUCKLING

SANDWICH BUCKLING. AIAA Paper-97-1142 AIAA 38th SDM Meeting, 1997. A good review of sandwich walls. Some earlier work on sandwich. Some sandwich failure modes. More sandwich failure modes. Effect of initial face sheet wrinkling.

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SANDWICH BUCKLING

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  1. SANDWICH BUCKLING AIAA Paper-97-1142 AIAA 38th SDM Meeting, 1997

  2. A good review of sandwich walls

  3. Some earlier work on sandwich

  4. Some sandwich failure modes

  5. More sandwich failure modes

  6. Effect of initial face sheet wrinkling L=critical buckling (wrinkling) halfwave length. Typical initial wrinkling amplitude, w0, is given by w0/L=0.001 (Plantema). Amplification of initial face sheet wrinkling during axial compression contributes to core crushing, face sheet pull-off, core shear failure, stress in sheet. Initial face sheet waviness Amplification of face sheet waviness under loading

  7. “Local” buckling of stiffened panel PANDA2 single module model, showing segments and discretiza- tion for a T-stiffened panel. Typical “local” buckling mode. See next slide for web-skin interaction

  8. Very local deformations of face sheet from amplification of a possible “local” buckling imperfection shape during loading

  9. Face sheet wrinkling formulas from Vinson and from Hoff

  10. Face sheet wrinkling from Bushnell Eigen-value

  11. Amplification of initial face sheet waviness during loading produces stress at core-facesheet interface

  12. Wrinkling halfwavelength and core cell size constraint. Eq.(13)

  13. What effects cause core crushing?

  14. Typical core crushing allowable from a Hexcel document PSI

  15. “L” and “W” directions in honeycomb sandwich core The core shear stiffnesses and allowables differ in the “L” and “W” directions.

  16. Margins generated in PANDA2 from sandwich behavior The next slide shows these two sets of margins Face sheet 1 Face sheet 2 The 2nd slide shows this set. Core

  17. Detail showing face sheet margins

  18. Detail showing core margins

  19. Typical margins generated by PANDA2 for a sandwich panel

  20. Unstiffened sandwich plate, showing decision variables, overall dimensions, and loading This case is called “VINSON” in honor of Professor Jack Vinson, the famous “sandwich” man!

  21. Optimization by PANDA2 of the unstiffened panel under various conditions Eq(13) is the cell size constraint; w0 is the initial face sheet waviness amplitude; L is the wrinkling wavelength; wimp is the amplitude of the initial general buckling modal imperfection.

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