3D Printing Enabled Structural Composites – Fabrication, Testing, and Numerical Analysis

This work introduces a structural composite material enabled by 3D printing technologies. The composite consists of a 3D-printed frame filled with another material for property enhancement. Unlike traditional composites that are designed by volume ratio and 2D structure (i.e., laminate orientation), the 3D printed composite can be built in a complex 3D configuration, such as lattice and honeycomb. In addition, instead of being a reinforced composite, the 3D printed composite is more like a dual-function material provided by two distinct phases. In this study, two types of the composite are developed and analyzed. The type I composite consists of a 3D printed brittle frame filled with a hyperelastic material, aimed for enhanced structural toughness. The type II composite consists of a 3D printed ductile frame filled with a viscoelastic foam for an enhanced impact resistivity. The objectives of this research are developing manufacturing methods for these composites by using both additive and molding processes, conducting experiments to evaluate the mechanical properties, and establishing numerical models to describe the mechanical behaviors and damage modes. The results show that both of the volume ratio and structural configuration determine the mechanical properties of the composite. For type I composite, the 3D printed brittle frame dominates the stiffness and the strength, and the hyperelastic material provides the toughness. Both experimental and numerical studies show that type I composite does not rupture suddenly under quasi-static bending test. This is because of the gradual development of the microcracks in the brittle frame as a result of contraction force provided by the hyperelastic filler. An FEA method includes a brittle cracking and a hyperelastic model successfully captures the bending behavior of type I composite. Comparing to other conventional FEA models, this model enabled the analysis with coarse and uniform mesh in the structure to represent the crack evolution inside the material. Type II composite is tested under the low-velocity impact condition. The experimental results show that different foams affect the impact properties differently and do not necessarily show the improvement. The flexible foam can enhance the material ductility, absorb more energy, and slow down the crack propagation speed during the impact. An FEA method includes an elastoplastic and a viscoelastic model successfully represent the impact behaviors of the type II composite. The FEA results suggest that the foam reinforcement redistributes the stress and mitigates stress concentrations during impact. Consequently, the foam reinforcement enhances the material ductility without changing the structural stiffness and weight significantly