The effect of material mixing on interfacial stiffness and strength of multi-material additive manufacturing

Multi-material additive manufacturing, as an additive manufacturing technique with the ability to simultaneously print multiple materials, is widely used in generating composites with multi-colors, complex multi-material structures, and materials with gradient properties. It also becomes a powerful tool in the study of structure-property relationship in composites, mechanical metamaterials, biological and bioinspired materials. However, the material mixing at the printed interfaces leads to unpredictable material properties which will significantly affect the overall performance of the 3D printed materials or parts. In this study, we systematically investigate the tensile properties, including stiffness and strength, of 3D printed multi-material interfaces. The specimens with double and multiple interfaces are designed, fabricated, and tested. The effect of the material jetting process on the topology of the interface and the effect of printing orientation and material thickness on the mechanical properties are evaluated experimentally. A material mixing model based on hyperbolic tangent function is proposed to quantitatively describe the material property distribution at the interface. The findings reported here provide a deep understanding of the mechanical properties of 3D printed multi-material interfaces, and therefore provide guidelines for the design and fabrication of 3D printed multi-material architectures and materials with desired properties.