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Sound-absorbing panels are widely used in the acoustic design of aircraft parts, buildings and vehicles as well as in sound insulation and absorption in areas with heavy traffic. This paper studied the acoustic properties of sound-absorbing panels manufactured with three nozzle diameters (0.4 mm, 0.6 mm and 0.8 mm) by 3D printing from three types of polylactic acid filaments (Grey Tough PLA; Black PLA Pro; Natural PLA) and with six internal configurations with labyrinthine zigzag channels (Z1 and Z2). The absorption coefficient of the sample with the Z2 pattern, a 5.33 mm height, a 0.6 mm nozzle diameter and with Black PLA Pro showed the maximum value (α = 0.93) for the nozzle diameter of 0.6 mm. Next in position were the three samples with the Z1 pattern (4 mm height) made from all three materials used and printed with a nozzle diameter of 0.4 mm with a sound absorption coefficient value (α = 0.91) at 500 Hz. The highest value of the sound transmission loss (56 dB) was found for the sample printed with a nozzle size of 0.8 mm with the Z2 pattern (8 mm height) and with Black PLA Pro. The extruded material, the nozzle diameter and the internal configuration had a significant impact on the acoustic performance of the 3D-printed samples. [ABSTRACT FROM AUTHOR]

The 3D printing process allows complex structures to be obtained with low environmental impact using biodegradable materials. This work aims to develop and acoustically characterize 3D-printed panels using three types of materials, each manufactured at five infill densities (20%, 40%, 60%, 80% and 100%) with three internal configurations based on circular, triangular, and corrugated profiles. The highest absorption coefficient values (α = 0.93) were obtained from the acoustic tests for the polylactic acid material with ground birch wood particles in the triangular configuration with an infill density of 40%. The triangular profile showed the best acoustic performance for the three types of materials analysed and, from the point of view of the mechanical tests, it was highlighted that the same triangular configuration presented the highest resistance both to compression (40 MPa) and to three-point bending (50 MPa). The 40% and 60% infill density gave the highest absorption coefficient values regardless of the material analyzed. The mechanical tests for compression and three-point bending showed higher strength values for samples manufactured from simple polylactic acid filament compared to samples manufactured from ground wood particles. The standard defects of 3D printing and the failure modes of the interior configurations of the 3D-printed samples could be observed from the microscopic analysis of the panels. Based on the acoustic results and the determined mechanical properties, one application area for these types of 3D-printed panels could be the automotive and aerospace industries. [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication (FFF) is one of the frequently used material extrusion (MEX) additive manufacturing processes due to its ability to manufacture functional components with complex geometry, but their properties depend on the process parameters. This paper focuses on studying the effects of process parameters, namely infill density (25%, 50%, 75%, and 100%), on the mechanical and thermal response of the samples made of poly(lactic acid) (PLA) reinforced with short glass fibers (GF) produced using FFF process. To perform a comprehensive analysis, tensile, flexural, compression, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) tests were used. The paper also aims to manufacture by FFF process of composite structures of the fuselage section type, as structural elements of an unmanned aerial vehicle (UAV), and their testing to compression loads. The results showed that the tensile, flexural and compression strength of the additive manufactured (AMed) samples increased with the increase of infill density and therefore, the samples with 100% infill density provides the highest mechanical characteristics. The AMed samples with 50% and 75% infill density exhibited a higher toughness than samples with 100% infill. DSC analyses revealed that the glass transition (Tg), and melting (Tm) temperature increases slightly as the infill density increases. Thermogravimetric analyses (TGA) show that PLA-GF filament loses its thermal stability at a temperature of about 311 °C and the increase in fill density leads to a slight increase in thermal stability and the complete degradation temperature of the AMed material. The compression tests of the fuselage sections manufactured by FFF made of PLA-GF composite showed that their stiffening with stringers oriented at an angle of ±45° ensures a higher compression strength than the stiffening with longitudinal stringers. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is used in many fields and is a method used to replace wood components or wood-jointed furniture components in the furniture industry. Replacing wood joints by 3D printed connectors would be an advantage, considering the fact that during the process of assembling furniture, the execution technology of the joints is difficult, time-consuming, and labor-intensive. Advanced technology of AM applied in furniture manufacturing helps the designers to create new concepts of product design, with no limits of shape, number of joints, color, or size. The diversity of 3D printers and AM technologies provides the selection of materials in relation with the applicability of the 3D printed object. In this respect, the objective of the present research is to design a 3D printed connector to be used for jointing three chair components, namely the leg and two stretchers made from larch (Larix decidua Mill.) wood, and to use reinforced polylactic acid (PLA) fiberglass (20 wt. %) filament for 3D printing this connector using AM with fused filament fabrication (FFF) technology. The design of the connector, the possibility of using this type of material, and the deposition method of filament were investigated in this research. For this purpose, several evaluation methods were applied: microscopic investigation with 50×, 100×, and 200× magnifications, both of the filament and of the 3D printed connector; mechanical testing of corner joint formed with the help of connector between chair leg and the two stretchers; and a microscopic investigation of the connectors' defects that occurred after applying the compression and tensile loads on the diagonal direction of the L-type joint. The microscopic investigation of the composite filament revealed the agglomerations of glass fibers into the core matrix and areas where the distribution of the reinforcements was poor. The heterogeneous structure of the filament and the defects highlighted in the 3D printed connectors by the microscopic investigation contributed to the mechanical behavior of L-type connecting joints. The bending moments resulting from compression and tensile tests of the 3D printed connectors were compared to the results recorded after testing, under the same conditions, the normal mortise–tenon joint used to assemble the abovementioned chair components. The larch wood strength influenced the mechanical results and the conclusions of the microscopic investigations, as well as the analysis of the broken connectors after testing recommended the change of connector design and filament deposition direction. [ABSTRACT FROM AUTHOR]

Being a relatively new process, additive manufacturing needs many studies to be able to produce parts with the required properties. The aim of the paper is to establish whether, based on the physical and mechanical properties determined by tensile testing and by applying finite element analysis (FEA), viable results can be obtained regarding the behavior of the 3D printed structures at the different, static loading. The application of FEA for the tensile testing of 3D specimens led to the results close to those obtained by the tests. The values of the results obtained by simulation are higher by up to 7.2% compared with those recorded by tests. The simulation was applied both for the printed specimens from a single material and from two materials (multi‐material). Regardless of the materials used in printing and the simulation method, the results of applying FEA are close to those recorded by testing. [ABSTRACT FROM AUTHOR]

The additive manufacturing process is one of the technical domains that has had a sustained development in recent decades. The designers' attention to equipment and materials for 3D printing has been focused on this type of process. The paper presents a comparison between the results of the bending tests and those of the simulation of the same type of stress applied on 3D-printed PLA and PLA–glass structures. The comparison of the results shows that they are close, and the simulation process can be applied with confidence for the streamline of filament consumption, with direct consequences on the volume and weight of additive manufactured structures. The paper determines whether the theories and concepts valid in the strength of materials can be applied to the additive manufacturing pieces. Thus, the study shows that the geometry of the cross-section, by its shape (circular or elliptical) and type (solid or ring shaped), influences the strength properties of 3D-printed structures. The use of simulation will allow a significant shortening of the design time of the new structures. Moreover, the simulation process was applied with good results on 3D-printed structures in which two types of filaments were used for a single piece (structure). [ABSTRACT FROM AUTHOR]

Material Extrusion-Based Additive Manufacturing Process (ME-AMP) via Fused Filament Fabrication (FFF) offers a higher geometric flexibility than conventional technologies to fabricate thermoplastic lightweight sandwich structures. This study used polylactic acid/polyhydroxyalkanoate (PLA/PHA) biodegradable material and a 3D printer to manufacture lightweight sandwich structures with honeycomb, diamond-celled and corrugated core shapes as a single part. In this paper, compression, three-point bending and tensile tests were performed to evaluate the performance of lightweight sandwich structures with different core topologies. In addition, the main failure modes of the sandwich structures subjected to mechanical tests were evaluated. The main failure modes that were observed from mechanical tests of the sandwich structure were the following: face yielding, face wrinkling, core/skin debonding. Elasto-plastic finite element analysis allowed predicting the global behavior of the structure and stressing distribution in the elements of lightweight sandwich structures. The comparison between the results of bending experiments and finite element analyses indicated acceptable similarity in terms of failure behavior and force reactions. Finally, the three honeycomb, diamond-celled and corrugated core typologies were used in the leading edge of the wing and were impact tested and the results created favorable premises for using such structures on aircraft models and helicopter blade structures. [ABSTRACT FROM AUTHOR]