LAUSR

Abstract Fused Filament Fabrication (FFF) is an extrusion-based technology in which a heated print-head extrudes a thermoplastic material layer by layer onto a platform. Due to the partial healing at the interface between extruded filaments in the FFF process, stress singularity points are created. These stress singularity points significantly reduce the reliability of FFF parts and result in premature interlaminar fracture. This work is a comprehensive study of fracture toughness evaluation of FFF parts. Another aim of this study is to provide recommendations on how to tune process parameters such as “gap setting” for improvements of fracture mechanics properties of FFF parts. Although the stress singularity points resemble V-notches, we have shown that for FFF manufactured parts with a negative gap setting up to 2%, the hairline crack solution could be used as the singularity order of the singular points remain close to (1/2). In other words, the classical linear fracture mechanics solution can be applied for such notch geometries and the stress intensity factor could be used as a measure for fracture toughness. In addition, for filaments with different cross-section geometries or higher negative gap settings, depending on the opening angle of the notch at the interface, singularity order of the singular points may increase. Hence, the Eigenfunction Expansion Method should be used to determine the singularity order of the singular points. Overall, it is determined that with increase of the notch angle, singularity order increases, and better fracture properties are achieved at the interface. Furthermore, the fracture mechanics properties of FFF parts can be significantly improved by increasing the diameter of filaments and the negative gap setting. Alternatively, new extrusion geometries could be utilized to optimize the interface length of the filaments.