Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments.

A critical review on 3D printed continuous fiber-reinforced composites: History, mechanism, materials and properties

Additive manufacturing of continuous fibre reinforced thermoplastic composites using fused deposition modelling: Effect of process parameters on mechanical properties

3D printed meta-sandwich structures: Failure mechanism, energy absorption and multi-hit capability

Continuous fiber reinforced thermoplastic composite (CFRTPC) auxetic honeycomb structures were fabricated using the 3D printing technology with a specific printing path planning. For comparison, auxetic honeycombs were also fabricated with pure polylactic acid (PLA). In-plane compression tests were conducted, with corresponding damage types explored using Scanning Electron Microscopy (SEM) images. A printing path-based finite element (FE) method was developed to mimic both small and large deformations of CFRTPC auxetic honeycombs, while analytical model was proposed to predict their effective stiffness and Poisson ratio. Good agreement was achieved among analytical predictions, FE simulation results and experimental measurements. A systematic parametric study was subsequently carried out to quantify the dependence of in-plane mechanical properties on geometrical parameters. Compared with pure PLA structures, the presence of continuous fibers efficiently prohibited crack propagation in the matrix for each ligament of CFRTPC auxetic honeycombs. Adding continuous fibers increased the mass only by 6%, but led to dramatic increase in compressive stiffness and energy absorption by 86.3% and 100% respectively and smaller Poisson ratios. The proposed 3D printing technology has great potential in integrated fabrication of continuous fiber reinforced composite lightweight structures having complex shapes, attractive mechanical properties, and multifunctional attributes.

3d printed continuous fiber reinforced composite auxetic honeycomb structures

Many modern aircraft components are made from carbon fiber reinforced polymer sandwich structures with two outer skins possessing high tensile and compressive strengths separated by a lightweight core that provides shear stiffness. However, the conventional manufacturing method involves a complicated and costly bonding process. This study used a continuous carbon fiber 3D printer to manufacture sandwich structures with honeycomb, rhombus, rectangle, and circle core shapes as a single piece. The functional properties of the sandwich structures were quantified by shape evaluations and three-point bending tests. Three-point bending tests showed maximum load and flexural modulus increased as effective density increased for all core shapes, but the rhombus core shape was the strongest. Because the mechanical properties depended on the core shape, continuous carbon fiber 3D printers can be used to flexibly design core shapes that satisfy the desired strength and stiffness.

3D printing of composite sandwich structures using continuous carbon fiber and fiber tension

3D printing of optimized composites with variable fiber volume fraction and stiffness using continuous fiber

The present study investigated the effects of set radius of curvature and fiber bundle size on the precision of the radius of curvature during continuous carbon fiber three-dimensional (3D) printing. First, individual circles with various radii using various sizes of fiber bundles were printed with a 3D printer. It was demonstrated that with a larger fiber bundle size or a smaller set radius, the printed radius would be lower than the set value. Based on the printing experiments, twist and path length difference models were constructed to predict the actual printed radius. Comparison between the models and experimental values verified that the twist model provides the upper bound on the printed radius and the path length difference model provides the lower bound.

Effects of Set Curvature and Fiber Bundle Size on the Printed Radius of Curvature by a Continuous Carbon Fiber Composite 3D Printer

In the coming years, it is expected that the application of composite in the aerospace and automobile industry will be increased through the development of 3D printing technology using carbon fiberreinforced resin. Sandwich structures currently used in aerospace components are formed of a skin material and a core material adhered to each other to form an integral structure. In these structures, it is necessary to thoroughly investigate the functional characteristics of the core material and shape it in the best way to take full advantage of its unique characteristics. Therefore, in this research, we investigate the possibility of designing and fabricating a free-form core shape, and investigate the feasibility of molding these integrated sandwich structures using a 3D printer capable of laying continuous carbon fibers. In the proposed experimental method, the diameter of the filament is smaller than that used in a general FDM-type 3D printer; to accommodate thin filaments in the molding process, we modified a 3D printer accordingly. As continuous carbon fiber 3D printers have a simple arrangement without a cutting mechanism, all shapes molded must be formed under single-stroke writing conditions. Therefore, in forming the core material in this research, the unit cell must satisfy the periodic boundary condition, making one-stroke molding possible. Notably, the tension in the continuous carbon fiber enables the formation of wide bridge spaces without the support material. Experimental results show that it is both possible to design core shapes such as a honeycomb structure freely and to mold integrated sandwich structures using the proposed method.

Kentaro Sugiyama

Papers

3D printing of composite sandwich structures using continuous carbon fiber and fiber tension

3D printing of optimized composites with variable fiber volume fraction and stiffness using continuous fiber

Effects of Set Curvature and Fiber Bundle Size on the Printed Radius of Curvature by a Continuous Carbon Fiber Composite 3D Printer

3D printing of integrated composite honeycomb sandwich structures with continuous carbon fiber