Honeycomb composites are now common materials in applications where a high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the effective properties of these honeycomb polymer composites is limited, so further research is needed to better characterize the behavior of these materials. In this research, the Abaqus finite element software is employed to perform parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A pinned rigid wall model was created as an upper bound on the deformable wall model’s performance, and an empty honeycomb model is employed to better understand the mechanisms of stiffness amplification. Parametric studies have been completed for infill material properties and the cell geometry, with the effective Young’s modulus studied in two in-plane material directions, as well as the two in-plane Poisson’s ratios. The effective moduli are computed using a strain energy approach under homogenization theory. The mechanisms by which the stiffness amplification occurs is studied, and comparisons to existing analytic models are made. It has been observed that both the volume change within the honeycomb cell under deformation, and the mismatch in Poisson’s ratios between the honeycomb and infill influence the effective properties. Either of these mechanisms may govern the behavior of the material, and this has been found to be largely dependent on the honeycomb geometry. Effective moduli of over three orders of magnitude greater than the infill alone have been observed, with stiffness amplification limited by deformation of the honeycomb walls. Additionally, the effect of large deformation strains, up to 10%, is explored, where the cell geometry changes significantly. Under these deformations, the change in effective properties is explained by this change in cell geometry. The rigid model is found to act as an upper bound on the material’s performance, where the amplification of the infill is independent of its material properties and wall deformations due to the infill are zero. Comparisons are made to existing analytic models, and limitations are noted of previous research. Most importantly, inability to accurately predict the effective properties over a large range of infill moduli, and the lack of consideration for out-of-plane effects, leads to discrepancies with the finite element results. This research provides an important step toward understanding the design space and benefits of honeycomb polymer composites.


Mechanisms of Stiffening in Polymer-Filled Honeycomb Composites

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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