This research proposes a multicavity and a graded structure design method for triply periodic minimal surface (TPMS) structures with broadband and perfect sound absorption. TPMS structures were manufactured by laser powder bed fusion. The sound absorption coefficient curves and acoustic band structure of TPMS are analyzed using a two-microphone impedance tube. As the thickness of TPMS structures increases, the noise reduction coefficient of TPMS structures increases linearly, and the first resonance frequency shifts to the lower frequency. The acoustic band structures indicate that the acoustic bandgap of TPMS structures shifts to a lower frequency with increasing thickness. Diamond has the highest noise reduction coefficient among these four types of TPMS. The TPMS with a multicavity design has multiple resonance peaks. Notably, the five resonance peaks of the multicavity-I-Wrapped Package (IWP) are all above 0.94, achieving near-perfect sound absorption over a wide frequency range. The semi-absorption bandwidth of the multicavity-TPMS structure has been widened, except for multicavity-diamond structures. Both uniform and multicavity TPMS present a subwavelength absorption peak. The graded design method can broaden the semi-absorption bandwidth of TPMS, and the combination of graded and multicavity designs can further enhance broadband and achieve perfect sound absorption.

In response to the growing demand for advanced materials with inherent infection resistance, this research investigates the properties of 316L stainless steel with copper, produced through laser-directed energy deposition additive manufacturing. The study focuses on three compositions: pure 316L, 316L with 3 wt.% Cu, and 316L with 5 wt.% Cu. Compressive strength measurements and Vickers hardness tests were conducted to assess mechanical properties, while microstructural characterization and X-ray diffraction analysis provided insights into the material’s physical properties. This research extends beyond physical and mechanical properties by exploring the on-contact antibacterial efficacy against Staphylococcus aureus and Pseudomonas aeruginosa up to 72 h. The addition of Cu reduced the ability of bacterial colonization of both strains on the metal surface. The findings of this investigation have the potential to benefit the biomedical devices, contributing to both structural and biofunctional properties of materials.

This study investigates the influence of varying deposition angles on the tensile strength and low cycle fatigue (LCF) performance of National Aeronautics and Space Administration (NASA) HR-1 alloy using laser powder-directed energy deposition. This study investigates the influence of varying deposition angles on the tensile strength and LCF performance of NASA HR-1 alloy using laser powder-directed energy deposition. Two sets of build parameters, 1,070 W and 2,620 W, were employed alongside three different build angles to assess their influence on mechanical properties following a uniform heat treatment regimen. This heat treatment encompassed stress relief, homogenization, solution annealing, and double aging. Samples deposited at 1,070 W showed a slightly lower porosity percentage compared to those produced at 2,620 W. All samples displayed similar grain sizes and a homogenized microstructure, indicating the effectiveness of the heat treatment in achieving a uniform microstructure across samples deposited at different build angles and laser power settings. The varying deposition angles did not significantly affect the microstructure or mechanical properties of the alloy. Fractography analysis revealed that all samples fractured through transgranular micro-void coalescence, with fracture initiation predominately occurring at the edges of both tensile and fatigue samples.

The electromagnetic field is a non-contact physical field that can influence the internal flow of the melt pool and regulate the microstructure properties of alloy through electromagnetic force during laser melting deposition (LMD). This study proposes a 3D numerical model of LMD Ti-6Al-4V coupled with an electromagnetic field and investigates the effect of the electromagnetic field on the fluid dynamics of the melt pool during LMD. The results indicated that a steady electromagnetic field can suppress the internal flow of the melt pool. In an electromagnetic field of 39.40 mT, the length of β-columnar grains significantly decreases from 490 to 354 μm, resulting in fragmentation and equiaxed tendencies, thereby enhancing the hardness of the deposition layer. This study provides a new method for in situ manipulation of the microstructure and mechanical properties of titanium alloys during LMD.

Additive manufacturing (AM), commonly referred to as 3D printing, has revolutionized the modern manufacturing world by providing comprehensive benefits in terms of mass customization, automation, design optimization, quick prototyping, and reduced lead times among other factors. Given the increased popularity, rapid development, and implementation of AM technologies in numerous engineering applications, new methods to enhance the AM process for improved efficiency and to attain sustainability goals are being considered. One approach to achieve sustainability in AM is by considering greener input materials such as natural fiber-reinforced composite filaments (NFRCFs) with lower embodied energy. This review focuses on the latest advancements made in the research and development of advanced NFRCFs for the AM process. In the first section, the rationale of using natural fibers in modern NFRCFs is outlined, followed by a description of the key stages of their fabrication process involving the pre-processing of fibers and the addition of plasticizer to enhance their performance. In the second part of this review, a detailed overview of the typical fibers and matrices used in the development of NFRCFs is provided, and some of the typical challenges encountered when utilizing natural fibers, such as their lack of homogeneity, are highlighted. The fiber-matrix interaction and corresponding properties are further discussed, and means to achieve homogeneous NFRC filament are outlined. Finally, the degradability characteristics and recycling methods for NFRCF are discussed, and further means to optimize their performance for increased usage in AM and related applications are presented. To address and overcome the foregoing limitations posed by present-day NFRCF, further research for breakthrough solutions is still required. Further research and development in this area is a prerequisite to attain sustainability in AM, which will also promote the usage and integration of sustainable AM parts into a wider range of engineering applications in our modern society.

This study investigates the application of topology optimization (TO) in combination with laser powder bed fusion (LPBF) to design a lightweight, high-performance bicycle pedal crank using AlSi10Mg alloy. The optimization process was carried out using Fusion 360 and nTopology, resulting in a 20% mass reduction while ensuring compliance with the ISO 14781 standards for pedal cranks. The component was characterized in terms of microstructure, surface roughness, dimensional accuracy, powder distribution, and Vickers hardness. The microstructure exhibited the characteristic melt pool patterns associated with LPBF, indicative of the manufacturing process. Surface roughness measurements showed a mean value of 23.4 μm, with dimensional analysis revealing a mean deviation of 7% from nominal dimensions. The powder distribution analysis indicated a narrow particle size distribution, contributing to consistent print quality. The component’s hardness was measured at 134 HV0.3, highlighting its promising mechanical properties. This work demonstrates the potential of TO and LPBF to produce structurally optimized, lightweight components with enhanced performance, providing valuable insights into the application of Design for Additive Manufacturing for metallic materials.

Oxide dispersion-strengthened (ODS) ferritic/martensitic steels have emerged as a promising structural material for nuclear power applications due to their high heat resistance. However, the fabrication of complex ODS steel components remains a significant challenge. This study presents the influence of the main selective laser melting process parameters and heat treatment on the densification, microstructure, and tensile properties at room and elevated temperatures of high chromium ferritic/martensitic ODS steel strengthened with 0.25 wt.% yttrium oxide (Y2O3). The optimization of process parameters and platform pre-heating enabled the production of parts with a density above 98%. The application of pre-heating allowed for higher scanning speeds to be used to achieve similar relative density and avoid cracking. Partial recrystallization after heat treatment was noted, affecting grain morphology by increasing equiaxedness and decreasing size. X-ray analysis was employed to determine the phase composition. However, the results were ambivalent and required confirmation by other methods. The addition of 0.25 wt.% Y2O3 resulted in an ultimate tensile strength value of 978 MPa for the as-built material at room temperature. At elevated temperatures, the properties are comparable to those of the base steel, indicating the necessity for further research.