SANDWICH BUCKLING

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SANDWICH BUCKLING

• AIAA Paper-97-1142
• AIAA 38th SDM Meeting, 1997

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(No Transcript)
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A good review of sandwich walls
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Some earlier work on sandwich
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Some sandwich failure modes
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More sandwich failure modes
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Effect of initial face sheet wrinkling
Lcritical buckling (wrinkling) halfwave length.
Typical initial wrinkling amplitude, w0, is given
by w0/L0.001 (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
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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
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Very local deformations of face sheet from
amplification of a possible local buckling
imperfection shape during loading
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Face sheet wrinkling formulas from Vinson and
from Hoff
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Face sheet wrinkling from Bushnell
Eigen-value
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Amplification of initial face sheet waviness
during loading produces stress at core-facesheet
interface
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Wrinkling halfwavelength and core cell size
constraint. Eq.(13)
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What effects cause core crushing?
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Typical core crushing allowable from a Hexcel
document
PSI
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L and W directions in honeycomb sandwich core
The core shear stiffnesses and allowables differ
in the L and W directions.
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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
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Detail showing face sheet margins
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Detail showing core margins
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Typical margins generated by PANDA2 for a
sandwich panel
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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!
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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.