Shape optimization for stiffness enhancement of multi-material 4D-printed structures

초록

4D printing has emerged as a promising technology in engineering, enabling printed structures to exhibit shape-morphing behaviors and novel functionalities. However, ensuring structural stability under external stimuli remains a critical challenge. In this study, we propose a shape optimization framework to enhance the stiffness of fully deployed 4D-printed multi-material structures. Acrylonitrile butadiene styrene (ABS) and polycarbonate/acrylonitrile butadiene styrene (PCABS) were employed to realize sequential morphing at their respective glass transition temperatures of 105 °C and 125 °C. Structural bending was controlled by adjusting longitudinal and lateral printing orientations, and the geometry was parameterized by width values. Tangent stiffness was maximized under a volume constraint using FEM-based transient thermal and structural analyses combined with gradient-based optimization. The proposed approach was applied to two case studies: a self-actuating table leg and a prosthetic leg. The optimized designs achieved up to a 25.71% increase in stiffness compared to the initial designs. Fabricated prototypes, thermally actuated and experimentally tested, showed less than 8% deviation from FEM predictions, thereby validating the proposed framework. These findings demonstrate that the method effectively improves the performance of 4D-printed multi-material morphing structures and highlights its potential for adaptive and load-bearing applications.

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