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Owing to their great potential to enhance the structural, mechanical, and electrical properties of materials, numerous researchers have dedicated their efforts to manufacturing multi-walled carbon nanotubes (MWCNTs)-reinforced composites via additive manufacturing (AM) to leverage AM's ability to fabricate intricate structural components. However, there is currently limited research on MWCNTs in photosensitive resin (PR) systems processed via a type of vat photopolymerization AM technique - digital light processing (DLP). Additionally, the distribution pattern of MWCNTs in PR systems is still unknown. To address these research gaps, this investigation focuses on fabricating MWCNTs-reinforced PR (MWCNTs-PR) via DLP and studying the effects of MWCNTs content on microstructure characterizations and mechanical properties of MWCNTs-PR. These results show that PR with 0.05 wt% MWCNTs addition exhibits a 25 % increase in elastic modulus and a 2 % increase in bending strength compared to pure PR. To achieve a more uniform distribution of MWCNTs in the PR, a combination of an ultrasonic bath and mechanical stirring was adopted. To further investigate the mechanism behind MWCNTs-enhanced bending resistance, a multi-material layered 3D printing structure was developed. The experimental findings reveal that the 10001 structure yields the highest bending modulus, surpassing the control group by 14.9 %. To validate the bending resistance mechanism attributed to MWCNTs-PR, finite element analysis was conducted.

Due to its excellent corrosion and oxidation resistance, good formability, and affordability, 316L stainless steel (SS) is widely used in industries such as biomedical, marine, chemical, and water treatment. However, to further enhance its mechanical properties, scholars have turned to reinforcing 316L SS with ceramic additives. Among ceramic additives, tungsten carbide (WC) is favored due to its good wettability ability to bond closely with iron-based materials. Despite these benefits, defects of cracks, pores, and balling commonly exist in WC-reinforced metal matrix composites due to the agglomeration of WC particles. In response to these problems, author propose a novel method that combines acoustic field (AF) with powder bed fusion (PBF) to process WC-reinforced 316L SS materials. This approach takes advantages of AF's ability to homogenize materials, smooth out thermal gradient, reduce cracks, and refine grains in liquid materials, while also utilizing PBF's capabilities to fabricate complex-shaped customized parts with high density and good quality. Experimental results have shown that adding an AF to the PBF can reduce dislocation density, mitigate stress, alleviate cracks, refine grain size, and alter grain shape, ultimately enhancing the tensile properties of WC-reinforced 316L SS composites. By adopting this method, a balance of strength and ductility can be achieved, with ultimate tensile strength and percentage elongation falling into a narrow but high range of 750–930 MPa and 44–55%, respectively.

In a powder bed fusion (PBF) process where powder bed preheating is needed, the powder bed will be subjected to an aging issue, which limits the reuse of powders. In response to the powder aging issue and to recycle powders, extensive attention has been attracted to study powder aging mechanisms in PBF to explore potential solutions. In this investigation, we have studied the aging mechanisms and proposed an epoxy resin solution (EP) infiltration method to mitigate side effects of powder aging in PBF-sintered nylon12 (PA12) specimens. Particularly, a comprehensive study on effects of powder recycling, building directions, and EP infiltration on microstructure characterizations, part quality, as well as thermal and mechanical properties of PBF-sintered PA12 specimens has been presented, for the first time. The quantitative relationships between sintering window width and warpage degree have been developed. A finite element analysis method has been utilized to learn stress distribution and concentration in PBF-sintered PA12 specimens and to predict fracture features. An insight into the strengthening effects induced by the EP infiltration at an atomic level has been provided by conducting molecular dynamic simulations.

Despite the large demand, the current biomass composites still exhibit problems of low mechanical properties, strong hydrophilicity, and poor thermal resistance, which limit biomass composites' application fields. Facing these problems, starch-based fiber-reinforced composites with foam structures were fabricated by hot pressing and foaming process, for the first time. In these composites, the corn starch serves as matrix while the sisal fiber acts as skeleton. Aluminum hydroxide (ATH) has been added to alter microstructures. To identify microstructure and material composition changes induced by ATH, scanning electron microscopy, X-ray diffraction analysis, and Fourier transform infrared spectroscopy have been performed. Experimental results show that an appropriate ATH content can improve composite's ultimate tensile strength by as much as 37%. Molecular dynamic simulations were performed to understand ATH effects on tensile properties at an atomic level. In addition to tensile properties, the addition of ATH is also beneficial to improve the compressive properties, water resistance and thermal stability of starch-based fiber-reinforced composites, making the composite a potential candidate to replace traditional packaging materials. Therefore, this investigation will benefit the current packaging industry in that sustainable utilization of packaging materials can be realized.

Material extrusion (ME) is considered as an effective and economic method to process continuous carbon fiber (CCF)-reinforced polymer composites with complicated structures. In this investigation, water absorption tests and tensile tests were conducted on ME-printed CCF-reinforced polymer composites under hydrothermal conditions. The purpose is to meet the growing need of CCF-reinforced polymer composites for high-humidity and high-heat aerospace applications. In order to achieve optimal comprehensive performance, both the L16 (45) orthogonal array method and the fuzzy reasoning algorithm were employed to carry out multi-objective optimization of four selected input variables, including layup angle, nozzle temperature, fiber filling density, and layer thickness. Experimental results show that the comprehensive performance of composites obtained by inputting data into the fuzzy reasoning system was greater than that obtained from orthogonal test results. Specifically, the optimized input variables are 0° layup angle, 260 °C nozzle temperature, 80% fiber filling rate, and 0.6 mm layer thickness.