Transcript MODE JUMPING - Shell 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
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
“Local” buckling of stiffened panel
PANDA2 single module model,
showing segments and discretization for a T-stiffened panel.
Typical “local” buckling mode. See
next slide for web-skin interaction
Very local deformations of face sheet from
amplification of a possible “local” buckling
imperfection shape during loading
Face sheet wrinkling formulas
from Vinson and from Hoff
Face sheet wrinkling from Bushnell
Eigenvalue
Amplification of initial face sheet waviness during loading
produces stress at core-facesheet interface
Wrinkling halfwavelength and core cell
size constraint. Eq.(13)
What effects cause core crushing?
Typical core crushing allowable
from a Hexcel document
PSI
“L” and “W” directions in
honeycomb sandwich core
The core shear
stiffnesses and
allowables differ in
the “L” and “W”
directions.
Margins generated in PANDA2 from
sandwich behavior
Face sheet 1
Face sheet 2
Core
The next
slide
shows
these two
sets of
margins
The 2nd
slide
shows
this set.
Detail showing face sheet margins
Detail showing core margins
Typical margins generated by PANDA2 for a sandwich panel
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!
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.