Magnetic Particle Assembly During 3D Printing for Computationally Optimized Actuation and Reinforcement

Recent advances in environmentally-responsive materials have inspired novel solutions to a wide range of national security issues, introducing opportunities to design components that autonomously alter their function based on external stimuli. Improvements are needed, however, to material performance, manufacturing methods capable of realizing complex designs, and computational design tools that can make the most of a large design space. This work develops a hierarchical materials system to meet these needs: environmentally responsive materials are programmed during 3D printing via magnetically assembly of hierarchical nano- and micro-scale building blocks. For shape change applications, these are based on liquid crystals in elastomer matrices which contract or expand with heat, and for energy absorption these are based on magnetically functionalized ceramic particles (yielding anisotropy in stiffness of up to 7x). In contrast to previous systems where the actuation or geometry of a part is highly constrained (e.g. in a single direction for an entire part, or to thin films), this enables printing of complex components where each voxel has individually user-defined actuation or reinforcement direction, enabling advanced shape change and highly tunable energy absorption. The resulting design space includes both the geometrical freedom of 3D printing and the added degrees of freedom of molecular alignment of each voxel in 3D, so to navigate this space computational design optimization tools are developed. For a desired shape change or mechanical response (and other criteria e.g. light weighting, conductivity, optical properties), computational tools optimize both part shape and molecular alignment simultaneously. Harnessing this complexity yields large performance gains and advances the frontier of autonomous materials problem solving. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-870637-DRAFT