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This paper studies the mechanical properties of polylactic acid (PLA) and aluminum fiber-reinforced PLA composite (Al/PLA) specimens fabricated by fused deposition modeling (FDM) process. The effect of raster angle (0°, 90°, 45°, 0°/90°, and ± 45°) on dynamic mechanical thermal property and tensile property of FDM-printed PLA and Al/PLA has been studied. The results show reduced tensile strength and Young's modulus in Al/PLA composite specimen in comparison with pure PLA specimen. However, the elongation-at-break increases, which is due to Al fiber with the higher elasticity and lower tensile strength than PLA. The addition of Al fibers improves the dynamic mechanical thermal property of pure PLA because of the good interaction of the PLA matrix with the surrounding Al fibers. Raster angle plays an important role in FDM process. All specimens printed with 0°raster angle show highest tensile strength and dynamic mechanical properties, while specimens printed with 90°raster angle have the lowest values. Fractured surfaces indicate that the failure of the specimen with 0°raster angle is due to breaking of individual layers, while for 90°raster angle, specimen fails under separation of the adjacent raster layers. KEYWORDS fused deposition modeling, dynamic mechanical analysis, tensile properties, raster angle 1 | INTRODUCTION Additive manufacturing (AM) technology constructs components layer by layer through a digital model. It has gained considerable attention because of a lot of advantages compared with traditional manufacturing methods. 1,2 Applications of AM technology are emerging in several fields, such as agriculture, biomedical, aerospace, automobile industry, machinery industry, and food production. 3-7 As one of the most popular AM technologies, fused deposition modeling (FDM) is widely used for polymer printing. 8-10 FDM typically fabricates parts using environment-friendly thermoplastic materials like polylactic acid (PLA), polyglycolic acid (PGA), acrylonitrile butadiene styrene (ABS),and nylon, which are melted in the form of filaments and stacked layer by layer to fabricate parts. [11][12][13] A composite material is a material made by many materials having different properties. The formed composite materials have excellent overall properties compared with a single material. 9 Many researchers have begun to develop polymer matrix reinforced composites to broaden the range of materials available for FDM processing. Some selected materials are employed to reinforce polymer, like carbon, glass, Al 2 O 3 , SiC, metal, graphene, and others. [14][15][16][17] observed an increase in ultimate strength of 39% (from 26.9 to 37.4 MPa) and an 86% reduction in strain at failure when ABS was reinforced with 10 wt% vapor-grown carbon fiber. Ning et al 19 found that the tensile strength of 5 wt% carbon fiber (CF)-reinforced ABS composite specimen prepared by FDM was increased 22.5%, although the ductility of CF/ABS composites was lower than that of pure ABS. Zhong et al 16 added short glass fibers of different volume

In this paper, fused deposition modeling is used to process pure polylactic acid (PLA) and copper fiber reinforced PLA composite (Cu/PLA) specimen. Comparative experiments are performed on printed specimens of different raster angles (0°, 90°, 45°, 0°/90° and ± 45°, respectively). Tensile testing, dynamic mechanical analysis (DMA), and fracture surface analysis are employed to characterize all the specimens. The DMA exhibits remarkable improvement on storage modulus and loss tangent of Cu/PLA composite specimen. Due to the lower tensile strength and higher elasticity of Cu fiber compared with PLA, the tensile strength of Cu/PLA composite specimen decreases with the addition of Cu fiber, while the elongation-at-break increases. Both PLA and Cu/PLA specimens printed at a raster angle of 0° show highest tensile strength and dynamic mechanical properties, while the 90° raster angle with the lowest value. Fracture morphologies indicate that the failure of a specimen of 0° raster angle is intra-layer fracture, while inter-layer fracture occur in the specimen of 90° raster angle.

Abstract:As the applications for additive manufacturing have continued to grow, so too has the range of available materials, with more functional or better performing materials constantly under development. This work characterizes a copper-filled polyamide 6 (PA6) thermoplastic composite designed to enhance the thermal conductivity of fused filament fabrication (FFF) parts, especially for heat transfer applications. The composite was mixed and extruded into filament using twin screw extrusion. Because the fiber orientation within the material governs the thermal conductivity of the material, the orientation was measured in the filament, through the nozzle, and in printed parts using micro-computed tomography. The thermal conductivity of the material was measured and achieved 4.95, 2.38, and 0.75 W/(m·K) at 70 • C in the inflow, crossflow, and thickness directions, respectively. The implications of this anisotropy are discussed using the example of an airto-water crossflow heat exchanger. The lower conductivity in the crossflow direction reduces thermal performance due to the orientation in thin-walled parts.

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This article investigates the effects of nozzle diameter, resin viscosity, and filler size and volume content on the melt flow properties and clogging of composites in the material extrusion additive manufacturing process. The flow behavior was systematically characterized by a custom nozzle flow test (NOFT) device, thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Results indicated that the viscosity of the material, the particle size, and the diameter of the nozzle were important factors for clogging. TGA results showed deviations from the designed filler volume fraction, which could be due to the buildup of filler material in the nozzle and subsequent partial clogging. SEM observations showed that particle agglomeration tended to be more prevalent in strands with high filler volume content. The agglomeration could be seen near the edge of the strand. A model for the clogging formation in NOFT was summarized into four stages: particle deposition on the wall of the nozzle, creation of dendrites, particle agglomeration, and particle clogging, which explained the clogging mechanism in the NOFT.