Cylindrical sheet forming analysis of hexagonal cell honeycomb core using 3D finite element analysis
This document presents the creation of a detailed 3D numerical model of a fiberglass/phenolic hexagonal honeycomb core for studying in-plane and flexural responses. The core cell geometry was modeled in detail to be representative of the actual characteristics of the honeycomb studied, including the cell wall curvature, double walls, and full adhesive fillet. A building block approach (BBA) starting with the cell ribbons was followed to create the final multi-cell honeycomb core model using LS-DYNA's finite element package. In addition, mesh sensitivity studies were conducted to minimize the computational costs of the final multi-cell model without compromising the accuracy of the solution. Uniaxial in-plane numerical analyses were conducted over a representative volume (RV) and a 10×10 cell model to compare to the available experimental data. The simulation results capture the non-linear orthotropic behavior of the structure and failure modes seen experimentally. Ribbon fracture and debonding of the adhesive were the main causes of failure. Flexural numerical simulations of the forming process were conducted by bending a 30×40 cell core model over a female-male cylindrical tool. Three radii (50, 75, and 100 inches) and two orientations of the core with respect to the tooling were investigated to determine the forming limits, which were defined based on the failure of the structure. The core fails catastrophically when formed over the 50 in. radius tool. Substantial failure exists when using the 75 in. radius tool. The 100 in. radius bending simulations do not present any damage during the process. Failure occurs due to high shear strains caused by a state of biaxial tension/compression when transitioning from anti-clastic bending to cylindrical forming, which coincides with the exponential increase of the load needed to bend the core panel. Free edge effects are only substantial along the direction perpendicular to the panel’s orientation direction along the symmetry plane.