Publication Date


Document Type


First Advisor

Chen, Niechen

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Industrial and Systems Engineering


Multi-material Fused Deposition Modelling (FDM) enables the cost-effective realization of designs in complex geometries built with multiple materials. However, achieving an adequate level of bonding strength between different materials remains a significant challenge. Besides the traditional way of addressing this challenge by strengthening material bonding at the molecular scale by optimizing the printing parameters, introducing a new design methodology that creates stronger multi-material interface geometry could also offer effective solutions. This work studied the mechanical properties of multi-material printed objects, with a particular focus on the interface zone formed between different materials at their geometrical boundaries. A new mathematical simulation model is introduced to analyse the strengths of the geometrical interface, hence eliminating the need of multiple iterations of design trials and physical printing experiment. This mathematical model is created considering the anisotropic property of FDM prints due to its nature of a bead-by-bead build process. In this research, material bonds along both horizontal and vertical directions are considered and four types of specimens were designed, printed, and tested to obtain the necessary data for model development and validation: (A) single-material uni-body specimens; (B) single-material specimens with linear boundary interface; (C) bi-material specimens with a planar boundary interface; and (D) bi-material specimens with new boundary interlock geometry design interface. The comparison of the mechanical performance between Type-A, - B, and -C specimens demonstrated the impact of the geometrical boundary interface between the same material and different materials on the part strength; and The comparison between Type-C and -D demonstrated that the mechanical strength (tensile strength) of multi-material prints can be greatly improved with the new boundary interlock geometry design. From the experiments, bond strength data for bead-bead in-layer and inter-layer is obtained to support the development of the mathematical simulation model. This model is proven to be effective in predicting the strengths of FDM part by comparing with the Taguchi experiment results. According to the mathematical simulation model, a set design guidelines is established to improve the tensile strength of the print part. Following these design guidelines, a case study was conducted to create and validate improved designs that boost the part strength. This work proves the significance of boundary interlock geometry design in multi-material printing and provides a new methodology and guidelines to create boundary interlock geometry designs that strengthen the multi-material interface for additive manufacturing parts.


66 pages




Northern Illinois University

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