Effects of cell aspect ratio and relative density on deformation response and failure of honeycomb core structure

Abstract

The extensive applications of honeycomb (HC) core in sandwich structures necessitates the influence of the cellular geometry and cell wall base material on the mechanical response to be quantified. In this respect, this paper establishes the mechanics of the deformation and the failure processes of the HC core under the out-of-plane compressive, tensile, and shear loading. The corresponding mechanical properties are determined and the mechanisms of failure of the HC core structure are identified. The influence of the relative density (ρ * /ρ s ) and the cell aspect ratio (H/c) of the hexagonal HC core on the compressive deformation response, the out-of-plane properties and the characteristic dissipation energy density (DED) of the structure is established. Results show that the compressive strength increases exponentially from 1.5 to 10.6 MPa over the relative density range of 0.028(ρ * /ρ s ) 0.125. The out-of-plane shear modulus, G 13 and G 23 are 33.9 and 58.2 MPa, while the shear strength, τ 13 and τ 23 are 1.07 and 2.03 MPa, respectively. The HC core with a low aspect ratio (H/c<2.64) failed due to the early debonding of the double-wall hexagonal cells, while at H/c 2.64, by elastic buckling of the cells. A phenomenological model is formulated to highlight the combined effects of both parameters on the compressive strength (σ c ) of the HC cores, covering the range of 0.028(ρ * /ρ s )0.056 and 2.5(H/c)5.62. Furthermore, the characteristic dissipation energy density (DED) under the out-of-plane compression varies linearly within the range of 2.5<(H/c)<5.62 for the HC core with ρ * /ρ s =0.056. The HC core with H/c=3.96, but with twice higher ρ * /ρ s exhibits about twice larger DED. These resulting properties and failure mechanisms of the anisotropic paper-based HC core are useful for the validation of the predictive computational models. Nomenclature ρ * density of the HC core σ c axial compressive strength of HC core ρ s density of the bulk material A c cross-sectional area of HC core sample c hexagonal cell size E 3 Young's Modulus under compression loading E T Young's Modulus under tensile loading G 13 shear modulus in transverse direction G 23 shear modulus in ribbon direction H core height OPEN ACCESS RECEIVED

Representative Cell Analysis for Damage-Based Failure Model of Polymer Hexagonal Honeycomb Structure under the Out-of-Plane Loadings

“…The response-load values are normalized by the number of cells in each sample. The measured response is taken from the tests performed in accordance with the ASTM C297 standard, with the results presented in the previous research work [ 45 ]. The measured stiffness, as reflected in the slope of the P-d curve, is 5.1% lower than the calculated values.…”

“…The load values are normalized by the number of cells in the respective sample. The experimental testing of these HC cores is done according to the procedure elaborated in the previous research work [ 45 ]. The compression tests are conducted in accordance with the ASTM C365 standard.…”

“…The FE-calculated and measured responses of the polymer hexagonal HC core panel under the out-of-plane shear loading in the ribbon and transverse direction are compared in Figure 14 . The measured response is taken from the out-of-plane shear test, performed in accordance with the ASTM C273 standard, as discussed in the previous research work [ 45 ]. The FE simulation of the out-of-plane shear behavior employs the 6-cell HC core model, as shown in Figure 2 .…”

“…The failed polymer hexagonal HC core specimen following the out-of-plane shear in the transverse direction [ 45 ] is shown in Figure 15 a. Excessive deformation with buckling of the hexagonal cells is observed along the plane oriented at 45° to the applied shear loading direction (Path 1).…”

“…The boundary conditions for the symmetry of cell walls have been appropriately considered. These representative cell models employ the properties of the fiber-reinforced polymer cell wall material for the FE simulation [ 45 ]. In addition, the models with multiple cells (6- and 24-cell) are also examined for the tension and compression load case.…”