Optimization of 3D lattice cores in composite sandwich structures

Abstract

Hybrid lattice cores for sandwich structures containing both solid struts and polymer foam are a recent option available to designers. These cores benefit from a synergistic effect in which the foam supports the slender struts against buckling in addition to carrying a portion of the applied loads directly. This work will optimize these hybrid cores to minimize unit cell density given compressive and shear strength constraints for a variety of unit cell configurations. An analytical model is developed for prediction of failure using the assumption that the foam is an elastic foundation that supports the struts; however, the unit cells are found to be optimal when no polymer foam is used. With the problem thereby simplified, analytical optimization solutions are derived and studied extensively, revealing qualitative insights about efficient lattice core designs. Optimal strut inclination angle, failure mode, and configuration are plotted against loading, which show that, for the large majority of strength constraints, the lowest unit cell density is achieved with tetrahedral cores whose struts fail in compressive yielding.