Three commercial filaments for Fused Deposition Modeling (FDM) were selected to study the influence of polymer formulation on the printing quality and mechanical properties of FDM specimens. The three filaments were all based on polylactic acid (PLA) as the matrix, and they are sold as PLA filaments. The printing quality was tested by printing one complex shape with overhang features. The marked shear thinning behavior for two filaments was observed by rheology. The filaments were also studied by scanning electron microscopy and thermogravimetric analysis (TGA) to unveil their composition. The filaments with the best printing quality showed the presence of mineral fillers, which explained the melt behavior observed by rheology. The tensile testing confirmed that the filled PLA was the best-performing filament both in terms of printing quality and thermomechanical performance, with a p-value = 0.106 for the tensile modulus, and a p-value = 0.615 for the ultimate tensile strength.

https://www.mdpi.com/1996-1944/11/7/1191/pdf

Polylactide (PLA) Filaments a Biobased Solution for Additive Manufacturing: Correlating Rheology and Thermomechanical Properties with Printing Quality

Cork–PLA composite filaments for fused deposition modelling

Additive manufacturing (AM) is rapidly evolving as the most comprehensive tool to manufacture products ranging from prototypes to various end-user applications. Fused filament fabrication (FFF) is the most widely used AM technique due to its ability to manufacture complex and relatively high strength parts from many low-cost materials. Generally, the high strength of the printed parts in FFF is attributed to the research in materials and respective process factors (process variables, physical setup, and ambient temperature). However, these factors have not been rigorously reviewed for analyzing their effects on the strength and ductility of different classes of materials. This review systematically elaborates the relationship between materials and the corresponding process factors. The main focus is on the strength and ductility. A hierarchical approach is used to analyze the materials, process parameters, and void control before identifying existing research gaps and future research directions.

https://www.mdpi.com/1996-1944/12/10/1664/pdf

Effect of Material and Process Specific Factors on the Strength of Printed Parts in Fused Filament Fabrication: A Review of Recent Developments.

The fracture properties (stress intensity factor and energy release rate) of additively manufactured (AM) polylactic acid (PLA) and its short carbon fiber (CF) reinforced composites have been studied. The effects of CF reinforcement, nozzle geometry and bead lay-up orientations in fracture properties, void contents, and interfacial bonding were investigated. The fused filament fabrication (FFF)-based AM specimens using both circular and square shaped nozzle were printed and compared with the conventional compression molded (CM) samples. Compact tension (CT) specimens with different CF concentrations (0 wt.%, 3 wt. %, 5 wt.%, 7 wt.% and 10 wt.%) were printed with two bead lay-up orientations ( 45 0 / - 45 0 and 0 0 / 90 0 ) using PLA and CF/PLA composite filaments. The results show significant improvement in fracture toughness and fracture energy for CF/PLA composites in comparison to neat PLA. The fracture toughness was increased by 42% for 0 0 / 90 0 and 38% for 45 0 / - 45 0 bead orientations, respectively with 5% CF loading. The increase in fracture energy was observed to be about 77% for 0 0 / 90 0 and 88% for 45 0 / - 45 0 bead orientations, respectively for the same fiber reinforcement (5 wt. %). Such improvement in fracture properties is expected to be higher for all 90 0 bead orientations. The samples printed by square-shaped nozzle showed enhanced fracture toughness with less inter-bead voids and larger bonded areas in comparison to the circular-shaped nozzle. Although the fracture toughness showed very negligible differences between 0 0 / 90 0 and 45 0 / - 45 0 specimens, distinguishable variation may be seen in the case of 0 0 and 90 0 bead orientations. The crack propagation path and fracture mechanisms were studied using optical microscopy (OM) and scanning electron microscopy (SEM) examinations. Fractography revealed different modes of failure with a very high fiber orientation along the printing direction and a relatively higher void contents for 7 and 10 wt. % fiber reinforcement.

Fracture toughness of additively manufactured carbon fiber reinforced composites

The employment of 3D printing for the fabrication of advanced multi-functional composites is attracting increased interest of the research community due to the opportunities offered by this technology (i.e. the wide range of materials that can be printed, short time, low costs). Numerous attempts are being presented every year regarding the incorporation of specific functionalities such as conductive, magnetic, embedded circuitry, thermal, sensing and self-healing to composites by employing different 3D printing processes and materials. This review provides an overview of the main functionalities that have been incorporated, homogeneously or locally, to polymer based composite materials via 3D printing. A strong emphasis is laid on the two main pillars enabling functionalisation: additives and printing methods. Finally, promise offered by the maturation of technology and recommendation on research efforts that are imminently needed to fulfil the untapped potential of functional 3D printing is given.

3D printing to enable multifunctionality in polymer-based composites: A review

Fused deposition modeling (FDM) has been gaining industrial interest due to its potential to simplify and lower the cost of complex manufacturing. To better understand the mechanical response of these materials—due to potential integration of FDM parts into structural components—compact tension samples of acrylonitrile butadiene styrene (ABS) were printed in three orthogonal orientations to analyze how the fracture toughness varied with mesostructure. Furthermore, in each of these orientations the raster pattern was either an alternating +45/−45° or a 0/90° pattern. When the alignment of extruded filament layers changed from parallel to perpendicular with respect to the crack plane, a 54% increase in fracture toughness was observed. However, the raster pattern only had a significant effect in one of the print orientations; the fracture toughness decreased by 11% when a 0/90° pattern was used in place of a +45/−45° pattern in layers oriented perpendicularly to the crack plane. The orientation of individual tracks of deposited material with respect to the crack tip appeared to have the most pronounced role in altering the fracture toughness of FDM ABS. This research provides useful information and insight to future designers determining how processing affects the crack stability of these new materials used for space hardware

The impact of print orientation and raster pattern on fracture toughness in additively manufactured ABS

3D printed fused deposition modeling (FDM) material parts have distinct anisotropic mechanical properties based upon their as-built print orientation. The strength of material printed perpendicular to the deposition layers can be as low as 50% of values for injection molded parts due to less than optimum interlayer fusion, limiting their use for critical applications. The focus of this work is to present a novel way of utilizing design freedoms available in FDM to improve strength in weak orientations. Vertically processed FDM ABS parts were manufactured with cavities printed perpendicular to the interlayer direction and were subsequently plasma surface treated, filled with an epoxy resin, and mechanically tested. Plasma treatment was shown to beneficially modify the surface chemistry, which resulted in a 50% improvement in shear strength over untreated specimens. Samples that underwent plasma treatment and epoxy infiltration demonstrated a 130% increase in flexural strength over that of as-printed FDM material. The failure strain was also shown to increase by two-fold. The addition of milled carbon fiber (MCF) filler within the epoxy infiltrate was also evaluated and was shown to increase the flexural modulus by as much as 76% at 10 wt% loading levels, though negligible increases in strength were observed.

https://link.springer.com/content/pdf/10.1007%2Fs40964-017-0032-0.pdf

Joseph V. Severino

Papers

The impact of print orientation and raster pattern on fracture toughness in additively manufactured ABS

Strengthening of plasma treated 3D printed ABS through epoxy infiltration