Daniel Kioshi Cavalcanti

Additive manufacturing enables the production of multi‐material components and graded structures that are impractical or impossible to achieve using traditional assembly‐based manufacturing. This capability offers significant benefits for applications requiring tailored properties, including components intended for marine environments, such as parts of underwater acoustic recorders used by the Brazilian Navy. In this study, the durability of 3D‐printed multi‐material structures exposed to seawater was evaluated. Sandwich specimens comprising ABS outer layers and a PLA core were fabricated using Fused Filament Fabrication (FFF). Three configurations were produced with one, three, and five ABS layers. Aging was conducted in natural seawater for 60 days, followed by tensile and flexural testing of both unaged (control) and aged samples. Water absorption behavior was also assessed. PLA exhibited the highest uptake, while ABS showed the lowest. Hybrid specimens absorbed less distilled water than pure PLA, indicating a potential barrier effect of the ABS layers. For unaged samples, tensile and flexural properties increased with the number of ABS layers. After aging, mechanical responses among configurations converged, suggesting a performance plateau due to seawater exposure. These findings support the potential of FFF multi‐material structures for marine applications while highlighting the need for improved moisture‐resistant design strategies.

The scope of 3D printing is limited by its maximum printing area, necessitating joints for assembling larger structural elements. Natural fibers have been employed to reinforce printed materials, enhance their mechanical properties, and reduce polymer usage. However, the effects of these fibers on bonded joints, particularly in the context of continuous natural yarns, remain underexplored in the literature. This study investigates the mechanical behavior of 3D‐printed single‐lap joints (SLJ) with biocomposite adherends, using Fused Filament Fabrication (FFF). Continuous Jute Fiber Reinforced Polymer (JFRP) and Polylactic Acid (PLA) were used to fabricate the adherends. Mechanical characterization, including surface roughness analysis and single‐lap shear tests, was performed on PLA‐PLA, JFRP‐JFRP, JFRP‐steel, and JFRP‐wood joints. Results show that the addition of continuous jute fibers in mono‐material joints increased the failure load by 66.53% compared to neat PLA‐PLA joints, due to a 47.20% increase in surface roughness. Jute Fiber Reinforced Polymer‐wood joints demonstrated the best performance, achieving a failure load of 2543.76N, 56.85% higher than JFRP‐JFRP joints, indicating their potential for mixed‐material, sustainable structures. Analytical models were applied to assess the load distribution along the adhesive. Highlights: Continuous natural yarn improves composite behavior, reducing brittle failure. Natural fibers enhance failure load and mode toughness of bonded joints. Jute yarn in joints raises SLJ failure load by 66.53%, enhancing contact area. Analyses of 3D‐printed parts with natural fibers bonded to wood and steel. Bi‐material joints show better results due to higher rigidity.

In this paper, the effect of a novel fibre reinforcement architecture in the adhesively bonded joint efficiency of natural fibre reinforced composites (NFRC) was investigated. Two different reinforcement techniques were used: intralaminar reinforcement (2D) and orthogonal-through-the-thickness reinforcement (3D). The aim of the novel architecture is to enhance the transverse properties of the adherend (transverse strength and fracture toughness) in order to delay or avoid delamination failures. A jute bidirectional fabric was used as a base primary reinforcement phase and curauá, sisal, ramie, hemp and glass fibres were used as secondary reinforcement phases for the 2D and 3D fibre reinforcement architectures. Single lap joints (SLJs) bonded with an epoxy adhesive used in the automotive industry were fabricated with these adherends and the efficiency of the joints was investigated by comparing them to glass (GFRP) and carbon (CFRP) pure synthetic fibre reinforced composite joints. It was found that the novel architecture was successful in reaching the failure load of the synthetic composite joints for SISAL 3D, CURAUÁ 2D and CURAUÁ 3D SLJs. Therefore, NFRC bonded joints can be a viable replacement for synthetic fibre composite joints at no load-bearing loss.

Additive manufacturing (AM) also called 3D printing, is an emerging process in the manufacturing sector with increasing new applications in aerospace, prototyping, medical devices and product development, among others. The resistance of the AM part is determined by the chosen material and the printing parameters. As novel materials and AM methods are continuously being developed, there is a need for the development and mechanical characterization of suitable materials for 3D printing. In this study, the influence of the material and the 3D-printing parameters on the mechanical properties of additive manufactured thermoplastic parts was investigated. Three different filaments that are commercially available: Polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and Tritan were used. Tensile and flexural tests were carried out, in accordance to ASTM standards, to investigate and compare the mechanical properties of the AM parts as a function of material used. The results showed that the type of filaments had the greatest influence on the mechanical properties of the AM parts. The maximum strength and stiffness were obtained for the PLA specimens. Tritan displayed the highest deformation, while the PLA manifested the lowest deformation capacity. The mechanical properties of the printed parts also depend on the printing parameters. The parameters used in this work are a good compromise between the printing time and the mechanical properties.

The main objective of this study was to investigate the efficiency of the sonication process and of multi-walled carbon nanotubes (MWCNTs) content on the mechanical and thermal properties of an epoxy matrix. Three different sonication powers (25, 50 and 75 W) were used to disperse the MWCNTs (0.2%, 0.4% and 0.6% wt.) in the epoxy matrix. Tensile tests were performed to determine the mechanical properties of the nanocomposites, while the thermal properties were determined by the thermogravimetric analysis (TGA) and the Differential Exploratory Calorimetry (DSC). Finally, a SEM analysis was used to investigate the morphology of the tensile fractured surface and the dispersion of the nanotubes in the polymeric matrix, since the quality of dispersion influences the mechanical and thermal properties of nanocomposites. It was found that the addition of carbon nanotubes to the epoxy matrix and the parameters of the sonication process affect the mechanical and thermal properties of nanocomposites. An increase of approx. 14% in tensile strength and 15% of Young’s modulus, when compared to the pure epoxy matrix was found for 75 W sonication power output and 0.6% MWCNTs weight percentage. The thermal analysis indicated that the presence of MWCNTs increased the T_onset of the nanocomposites when compared to pure epoxy resin. Finally, increasing the sonication power output leads to higher T_g of the nanocomposites studied here.

In this work, the effect of environment and fatigue loading on the mechanical behaviour of a structural adhesive modified with thermally expandable particles (TEPs) was investigated. Tensile tests were performed to get the tensile properties of the TEPs-modified adhesive as a function of moisture. It was found that the presence of moisture affects the mechanical properties of TEPs-modified adhesive. Large increases in ductility and reductions in tensile strength and Young´s modulus were measured for the water-saturated specimens, but after drying the tensile properties are recovered. Further, fatigue tests were performed on single lap TEPs-modified adhesive joints (0, 10 and 20 wt% TEPs) and a decrease in fatigue life was found for TEPs-modified adhesive joints compared to unmodified joints. Finally, a scanning electron microscope (SEM) analysis was performed in order to examine the fracture surfaces of the tensile specimens tested. SEM analysis showed that the absorbed moisture changes the fracture mechanisms and the morphology of the specimens.

The objective of this work was to analyze the influence of the alkalization and alkalization + silanization (mixed) treatments on the interfacial adhesion and mechanical properties of intralaminar hybrid composites (jute + sisal, jute + curauá, jute + ramie, and jute + glass fiber). Single‐fiber tensile tests, fragmentation, and short beam tests were performed. Finally, a SEM analysis was used to study the influence of surface chemical treatments on the morphology of the natural fibers used. SEM images showed that the chemical treatments altered the morphology of the natural fibers. The chemical treatments improved the tensile strength of the fibers studied. It was found that the alkaline treatment is the best suited for jute, ramie, and curauá fibers, while the sisal fiber presented the best results after the mixed treatment. The superficial chemical treatments also affect the interfacial/interlaminar adhesion of the hybrid composites studied here. The best superficial treatments for each type of hybrid composite were: alkaline treatment for jute + ramie and jute + sisal, while for jute + curauá the best results were obtained for the untreated specimens.

The main objective of this work is to study the effect of chemical treatment on the thermal properties of hybrid natural fiber‐reinforced composites (NFRCs). Different chemical treatments [i.e., alkalized and mixed (alkalized+ silanized)] were used to improve the adhesion between the natural fibers (jute, ramie, sisal, and curauá) and the polymer matrix. A differential scanning calorimetry, thermogravimetry, and a dynamic mechanical analysis were performed to study the thermal properties of hybrid NFRC. It was found that the chemical treatments increased the thermal stability of the composites. Scanning electron microscopy images showed that the chemical treatments altered the morphology of the natural fibers. A rougher surface was observed in case of alkali treated fiber, whereas a thin coating layer was formed on the fiber surface during the mixed treatment. However, for some fibers (i.e., sisal and rami), the chemical treatment has a positive impact on the composite properties, whereas for the jute and curauá composites, the best behavior was found for untreated fibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47154.