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We investigated the suppression of residual warpage using a negative thermal expansion (NTE) material filler, Zn1.6Mg0.4P2O7. To focus on the effect of thermal expansion on residual warpage, we used acrylonitrile-butadiene-styrene, which is an amorphous polymer with a small volume change around the liquid–solid phase transition, as the matrix. Composite pellets were prepared using a kneader, and filaments were produced for fused deposition modeling (FDM) using an extruder. We fabricated a bar-like test piece using a standard FDM machine and measured the warpage deformation using 3D scanning. The experimental results were supported by the finite element method. We also compared similarly sized SiO2 powders to discuss the advantages of NTE over conventional fillers. The warpage of a 100 mm x 5 mm x 2 mm bar-like test piece was reduced by approximately 75% by introducing Zn1.6Mg0.4P2O7 at 40 vol%. The effect of Zn1.6Mg0.4P2O7 at 30 vol% is similar to that of a conventional SiO2 filler at 40 vol%. Reducing the residual deformation through fillers would reduce energy consumption and simplify the device by avoiding build stage and chamber heating.

This study proposes a systematic inverse design framework for constructing multistable mechanical metamaterials with programmable gradients. Herein, we designed the tailored bistable cells with precisely controlled maximum instability forces through the topology optimization approach. Then, the designed bistable structures were programmed to construct the multistable mechanical metamaterials with different target gradient snapping sequences and deformation models. Consequently, the simulation and experimental results showed the feasibility of the design method, which successfully produced two- and three-dimensional mechanical metamaterial structures with different functions. Finally, we verified the expected deformation sequences and multistable behaviors of mechanical metamaterials by testing the designed specimens prepared via additive manufacturing. Overall, our findings show that the proposed design strategy offers a new paradigm for developing precisely tailored and programmable mechanical metamaterials.

Biodegradable materials have demonstrated promising potential for the treatment of bone fractures. Therefore, it is crucial to design biodegradable composites considering the degradation effect. Accordingly, to realize a composite material with controlled stiffness at the bone repair stage, this study introduces a novel topological optimization technique for the material layout design in microstructure, considering material degradation. In this approach, two sets of variables are adopted: a density field that defines the material layout, which is also the design variable, and a time field that determines the effect of material degradation on composite material properties. A continuous degradation update formula is proposed by integrating the Heaviside function and the Kreisselmeier–Steinhauser function to guarantee its derivability. The objective of this study was to maximize the material stiffness in some fixed time steps under a specified volume fraction. The sensitivity of the aforementioned objective relative to the design variable was deduced by considering the material degradation over time. The proposed design approach was demonstrated with several design examples, considering different degradable interface boundary conditions. Furthermore, the obtained results were compared with the results obtained without considering material degradation, thereby verifying the effectiveness of the proposed method.