Damage resistance of aluminum core honeycomb sandwich panels with carbon/epoxy face sheets

Abstract

The damage resistance of composite sandwich structures with eight and 16 ply quasi-isotropic, carbon/epoxy face sheets and aluminum honeycomb core is evaluated. The external damage is induced quasi-statically, using spherical steel indentors under displacement control, to be in the vicinity of the barely visible threshold. In addition to the face sheet thickness, other parameters that are varied include the core thickness, core density, face sheet layup, and indentor diameter. The effect of these parameters on the extent of damage is evaluated using the damage metrics of dent depth, dent diameter, and planar area of delamination. When dent depth or dent diameter is considered as the damage metric, specimens containing a higher density core are always found to be the most damage resistant. When planar area of delamination is considered as the damage metric, the eight ply configuration comprised of a lower density core and face sheets containing only small ply angle changes are found to be the most damage resistant. However, this configuration is found to be the least damage resistant when this damage metric is applied to the 16 ply specimens. Rather, the best delamination resistance is provided by a 16 ply configuration with a high density core and face sheets that have AE45 ply groups at the beginning and ending of their stacking sequence.

Compressive strength of aluminum honeycomb core sandwich panels with thick carbon–epoxy facesheets subjected to barely visible indentation damage

“…The C-scan also allowed ply-by-ply delaminations to be determined, and the damage metric of planar area of delamination was calculated based on these results. 20,24,25 Note that the C-scan was able to measure delaminations down to ply-11 only. 20 Edgewise compression testing of undamaged specimens…”

An analytical model for the response of carbon/epoxy-aluminum honeycomb core sandwich structures under quasi-static indentation loading

“…The model is validated using experimental results for sandwich structures consisting of quasi-isotropic 8- (thin) and 16- (thick) ply carbon/epoxy face sheets and aluminum honeycomb cores, as reported by Singh et al. [1,2].…”

“…Regime III is between delamination onset and the load that corresponds to barely visible external damage and IV is the unloading regime. The inelastic processes in the face sheet, primarily matrix cracking and delamination, occur in the “transition region” [1,2,4]. The low load elastic regime (I) is modeled using a combination of local Hertzian indentation of an elastic half-space and small deflection plate theory for a circular plate on an elastic foundation.…”

“…Sandwich composites are stiff, light-weight structures that offer high resistance to compressive stresses and bending moments. Accidental low-velocity impact (LVI) on these structures often result in damage that is only barely visible externally but internally exist as face sheet debonding, delaminations, matrix cracking and core crushing [1–4]. Damage as a result of LVI reduces the strength of the structures causing them to fail catastrophically at a fraction of their design loads [5,6].…”

In-plane and out-of-plane compressive mechanical properties of Nomex honeycombs and their prediction

“…They exhibit prospects for broad application in various crashworthy buffer structures [6][7][8]. The dynamic and static mechanical characteristics of honeycomb [9][10][11][12] and honeycomb-filled [13,14] structures were investigated by using theoretical calculations, simulations, and various experimental techniques. Many empirical expressions for the mean out-of-plane, and in-plane, plateau stresses acting upon such double-walled or single-walled hexagonal honeycomb cores were suggested [15][16][17][18].…”