Damage Characteristics of Composite Honeycomb Sandwich Panels in Bending under Quasi-static Loading

Abstract

Damage characteristics of composite-skinned honeycomb sandwich panels in bending are investigated with both hemispherical (HS) and flat-ended (FE) indenters. The thickness of the cross-ply skins varies from 8 to 16 plies, whereas the density of the 12.7-mm thick aluminum honeycomb core varies from 50 to 70 kg/m3. Clamped panels with a 100-mm testing area are loaded quasi-statically either in bending or on a rigid base. The effects of varying these parameters on damage mechanisms are examined through response curves as well as cross sections of selected specimens. Special emphasis is placed on their potential change induced by the variation of skin thickness and core density with a specific indenter. Damage mechanisms are identified as core crush, top-skin delamination, and fracture or shear-out. The threshold and ultimate loads as well as the initial slope increase significantly either on increase of skin thickness or change of the nose shape of indenter from a hemisphere to a flat-end. The increase in the post-initial-damage slope is small and can be attributed to membrane stretching of the damaged top skin. Increasing the core density affects substantially not only the threshold load, but also the initial slope associated with the FE indenter. Changing the nose shape of the indenter has an overriding effect on the nature of damage mechanisms. In particular, top-skin delaminations occur after core crush. The panel deflection contributes to 20-53% sandwich deformation. The bottom skin in all the tests remains intact.