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face sheet failure
face sheets fail by yielding or fracture
face sheet material exceeds allowable stress/strain
core shear failure
core fails in shear, usually with cracks at 45 deg. to midplane
core carries almost all transverse load - mainly subjected to shear
honeycomb - cell wall buckling (not always visible when load is removed)
core crushing
face sheets move toward each other - bending/thickness loads
core has insufficient compressive strength
core tensile failure
core has insufficient tensile strength
face sheet to core debonding
bond has insufficient shear/peel/tensile strength
local indentation
point loads - fittings, corners, joints
loaded face sheet bends independently to opposite sheet - if stress exceeds core’s compressive strength, core will fail
can be avoided by spreading load over large area
face sheet wrinkling
buckling face sheet, accompanied by core crushing, core tearing, face sheet to core debonding
prevalent with thin face sheets and low density core
face sheet dimpling (aka intracell buckling)
local instability - buckling of face sheet into or out of confines of cell
thin face sheets and large cell size
general buckling
resembles classical buckling, face sheets and core remain intact
shear crimping
instability that occurs when wavelength of each buckle is same order as cell size
local core shear failure, lateral dislocation of face sheets
can occur when core shear modulus is low
Transition to solid laminate
face sheet changes direction: core subject to flatwise tension/compression
tension: adhesive bond must be strong enough
compression: crushing strength must be enough
normal shear force at maximum at fastener centerline
ramp region: core must have adequate shear strength