One of the most promising and innovative approaches in designing mechanical metamaterials for various applications is the use of bioinspired geometries. Nature offers a wide array of geometric forms and structures that have evolved to serve specific functions, including protection. Examples of such structures include the microstructure of pomelo peels and the geometry of starfruits (carambola), both of which are designed to protect the fruit from impact when falling from a height. Based on these natural structures, it is possible to develop metamaterials that exhibit low weight, high strength, and enhanced energy absorption properties. Furthermore, additive manufacturing technologies enable the fabrication of such metamaterials with unit cell geometries of arbitrary complexity. In this study, the microstructures of pomelo peels and the forewing of the Japanese rhinoceros beetle were used as source geometries for the design of metamaterials. Metamaterial specimens, consisting of 5 × 5 × 5-unit cells with an initial model porosity of 80%, were fabricated from Ti6Al4V alloy using the selective laser melting method. Quasi-static and dynamic compression tests were conducted to determine the mechanical properties and specific energy absorption of the metamaterials. The compressive yield strength of the metamaterial samples based on the Japanese rhinoceros beetle forewing microstructure was 134 MPa, compared to 115.87 MPa for those based on the pomelo peel microstructure. Under quasi-static compression, the energy absorption level of the metamaterial samples based on the rhinoceros beetle wing microstructure was 13.83 J, with a specific energy absorption of 4.61 J/g. The results demonstrate the overall promise of employing a bioinspired approach for designing energy-absorbing metamaterials. These findings will serve as a basis for further in-depth research and development of energy-absorbing systems and components based on the geometries presented in this work.

Accurate management of powder bed temperature is essential in binder jetting (BJ) to achieve dimensional accuracy and adequate mechanical properties. Three different models using the finite element method operating at different scales were developed in this study to compare their accuracy in predicting the thermal history of the powder bed during the BJ process. The simulated temperatures were compared with in situ experimental thermal measurements of the powder bed during printing. The first model relied on 2D Gaussian heat sources to model the movement of infrared lamps, achieving an absolute average error of just 1.5°C with the experimental data, but taking 28 h to simulate only 20 layers using eight CPUs. The second model employed a layer heating (LH) approach to reduce computation time while maintaining accuracy similar to that of the previous model. The second model was able to simulate 200 layers in 33 h with an average error of 1.7°C in comparison with the thermal measurements. The third model combines the LH and lumping approach to further reduce the model computational time, enabling simulation of the full process (2000 layers) in 33 h with an average error of 2.3°C compared to the experimental case. This parametric study suggests that thermal management of the powder bed during BJ can be improved using a combination of infrared lamps above the powder bed and a heated build box. This avoids bleeding, interlayer stitching issues, and other detrimental phenomena regardless of the nesting configuration.

The 2219 aluminum alloy is widely utilized in critical structural components owing to its superior overall performance, while additive friction stir deposition (AFSD) exhibits potential for large-scale manufacturing. However, research on the corrosion behavior of AFSD-fabricated materials remains limited, and the influence of process parameters on corrosion mechanisms requires further exploration. This study compares the microstructure and corrosion resistance of different deposition layers in 2219 aluminum alloy fabricated by AFSD at rotational speeds of 400 rpm and 700 rpm. Higher rotational speed (700 rpm) generated greater thermal input and plastic deformation, promoting dynamic recrystallization and leading to larger grain sizes (bottom layer: 3.40 μm [400 rpm] vs. 3.83 μm [700 rpm]; top layer: 2.50 μm [400 rpm] vs. 3.01 μm [700 rpm]) and increased high-angle grain boundaries (bottom layer: 71.5% [400 rpm] vs. 75.2% [700 rpm], top layer: 57.3% [400 rpm] vs. 63.0% [700 rpm]). The bottom layer, experiencing more thermal cycles, showed further grain growth and resulted in larger grain sizes. At 700 rpm, greater precipitation of the Al2Cu phase increased the number of micro-galvanic couples between precipitates and the aluminum matrix, accelerating corrosion. Conversely, greater thermal input in the bottom layer promoted Cu dissolution and reduced precipitate formation, improving corrosion resistance compared to the top layer. Consequently, the bottom layer processed at 400 rpm exhibited the optimal corrosion resistance, with the highest Rct value of 4.17 × 103 Ω·cm2. As the rotational speed decreased, the corrosion resistance was enhanced.

Additively manufactured composite tools are increasingly used in sheet forming, yet the influence of fiber orientation on tool durability remains poorly understood. In this context, the present study investigates the limited understanding of how different continuous-fiber deposition strategies affect the mechanical stability and durability of additively manufactured polymer punches for deep drawing. Polymer tools reinforced with continuous carbon fibers were fabricated using continuous fiber fabrication (CFF) with two reinforcement layouts—concentric and isotropic—and tested until fracture to assess the achievable drawing depth, punch deformation, and cup integrity. Failure onset was monitored and the dimensional stability of the produced cups was evaluated as indicators of tool performance. The results demonstrated that fiber reinforcement increased the maximum drawable depth from 15 mm (unreinforced onyx punch) to 18 mm for concentric and 19 mm for isotropic punches. Finite element simulations reproduced the deformation trends observed experimentally, confirming that concentric reinforcement leads to higher axial compression and radial expansion. The findings highlight the potential of CFF for producing lightweight, low-cost forming tools, underscoring that optimizing fiber orientation is critical for improving tool durability and process repeatability.

Metamaterials with a negative Poisson’s ratio (NPR) exhibit unique auxetic deformation mechanism that enables superior energy absorption and mechanical resilience. Topology optimization (TO) can effectively generate microstructures with NPR characteristics, but conventional optimized designs often suffer from sharp corners and stress concentrations, which compromise durability and limit multicycle energy absorption. To address this issue, we introduced a boundary-fitting derivable geodesics-coupled TO (B-DGTO) framework to construct explicit curvature constraints into the optimization process, ensuring smooth boundaries and more uniform stress distribution with optimal NPR properties. In numerical example and experiment, we provided different types of 2D/3D NPR microstructures under curvature control to demonstrate the versatility of the proposed approach. These results confirm that the curvature constraint significantly improves the stress distribution of NPR microstructures and enhances their robustness and reliability under repeated loading. This study highlights curvature-constrained TO as a general and practical strategy for developing durable NPR metamaterials with superior energy dissipation performance.

The selective laser melting (SLM) technology of Ti-6Al-4V (TC4) demonstrates significant advantages in fabricating clasps for removable partial dentures, whereas subsequent heat treatment plays a crucial role in performance optimization. This study systematically investigated the effects of heat treatment temperature and time on the fitness accuracy, retentive force, and permanent deformation of SLM TC4 clasps. TC4 clasp specimens were manufactured using SLM technology and subjected to heat treatment under different temperatures (700, 750, 800, and 850℃) and times (0.5, 1.0, and 1.5 h). The fitness accuracy, retentive force, and permanent deformation after 10,000 insertion/removal cycles were measured for each group and statistically analyzed. The results revealed that the 700℃/0.5 h group showed significantly reduced fitness accuracy. After cyclic testing, the retentive force of all groups decreased by 4.06%–12.18%, with heat treatment temperature significantly affecting both initial and final retentive forces. The time of heat treatment demonstrated no substantial influence. The permanent deformation of the clasps (31.15–38.05 μm) remained unaffected by variations in either heat treatment temperature or time. Based on overall performance, the 700℃/0.5 h heat treatment condition is not recommended. Instead, selecting shorter time protocols such as 0.5 h within the 750℃–850℃ range can help enhance production efficiency while maintaining performance standards.

Multi-material vat photopolymerization (MMVPP) is an emerging additive manufacturing technology with great potential in biomedical engineering, soft robotics, electronics, and customized manufacturing, particularly where functional gradients and spatially varying material properties are essential. The capability to precisely control composition at the voxel level enables the fabrication of bioinspired structures and multifunctional components with tailored mechanical and functional performance. This study presents the conceptual design and development of a compact and commercially viable MMVPP system that addresses key challenges in current state-of-the-art technologies. A two-vat prototype printer was fabricated to demonstrate the feasibility of precise multi-material printing. Critical challenges, including resin compatibility, interfacial adhesion, and mechanical property optimization, were systematically investigated. Novel strategies such as variable layer height exposure control, overlapped layer printing, and optimized curing parameters were introduced to improve interfacial bonding and overall structural integrity. The proposed methods were validated through mechanical testing, confirming enhanced interface strength and material cohesion. The study also details system-level innovations, including efficient vat-switching mechanisms and process synchronization for rapid material transition. These advances establish foundational methodologies for reliable multi-material photopolymerization and expand the design space of photopolymer-based additive manufacturing. The results demonstrate MMVPP’s transformative potential to enable next-generation manufacturing of functionally graded and multi-material components with superior performance and design freedom.