Analysis of the interface properties of multi-material fused filament fabricated (FFF) printed polymer composite structures

Interface characteristics in multi-material 3D-printed (MM3DP) structures are a critical factor in determining the strength of the structures and predicting failure. This study investigated the shear behavior of multi-material single-lap joints fabricated entirely in a single process using Fused Filament Fabrication without the use of adhesives or post-processing techniques such as welding. The joints, comprising various combinations of PLA, PETG, and carbon-fiber reinforced PETG (PETC) were fabricated. The lap joints were subjected to shear testing, with strain fields and failure locations analyzed using two-dimensional digital image correlation (2D DIC) from synchronized front and side camera views. Results show that certain multi-material joints, particularly PETG-PETC, achieved a shear strength of 2.701 MPa, comparable to the 2.923 MPa strength of the strongest homogenous joint (PLA-PLA), and exceeding that of other homogenous joints. The presence of short carbon-fibers in PETC enhances adhesion, likely due to mechanical interlocking taking place at the interface region. These findings demonstrate that multi-material FFF, when optimized for interface compatibility and process parameters, can yield composite structures with superior mechanical properties compared to single-material prints. The successful fabrication of lap joints in a single print process highlights the feasibility of producing robust, functional multi-material components for advanced engineering applications.