Density-Graded 3D Voronoi Cellular Structures for Improved Impact Performance

Density-graded cellular polymers have unique mechanical properties, leading to exceptional impact protection. Furthermore, they can be designed for custom requirements. The current study is part of an effort to develop efficient impact-resistant structures. The impact response of density-graded 3D Voronoi cellular structures is studied and compared to its uniform density counterpart. The specimens are fabricated via photopolymer jetting technology, an additive manufacturing technique that enables high accuracy of intricate features and complex shapes that are distinctive of Voronoi cellular structures. The density gradation is achieved by changing the cell size along the impact direction. The foam specimens are impinged by a freely falling rigid mass with the help of a drop tower that allows determining the response at intermediate strain-rate regime. A series of images are captured using a high-speed camera to capture the deformation mechanisms of the specimen, and a piezo-based load cell is used to measure the dynamic force. The performance is analyzed by studying the energy absorption and transmitted force as a function of density gradation. It is found that density-graded Voronoi cellular structures can be designed to mitigate a wide range of impact conditions.