Search Results (131)

Laser powder bed fusion (L-PBF) is a unique technology that enables manufacturing geometrically complex metal alloys, including Ti-6Al-4V parts. The microstructure of Ti-6Al-4V is determined by its localized thermal history, which is affected by not only the L-PBF process but also the geometry of the part. Understanding the microstructure at specific locations in complex geometries is of great importance in predicting the mechanical performance of Ti-6Al-4V parts. This work investigates the effects of geometric features on the local microstructure. Three geometries, namely, holes, overhangs, and penholders, were designed and used for this study. Three different laser powers, namely 150 W, 250 W, and 350 W, were set to print those geometries. The use of a lower laser power results in improved print quality. While the martensite phase dominates the bulk of the L-PBF Ti-6Al-4V parts, a fine α+β lamellar structure can form at down-skin regions of printed horizontal holes and overhangs. Moreover, the direction of the columnar prime β grain can shift due to directional heat dissipation. The local microstructural evolution after heat treatment is investigated as well. Full article

Laser beam powder bed fusion of metals (PBF-LB/M, or simply L-PBF) has emerged as one of the most competitive additive manufacturing technologies for producing complex metallic components with high precision, design freedom, and minimal material waste. Among the various categories of additive manufacturing processes, L-PBF stands out, paving the way for the execution of part designs with geometries previously considered unfeasible. Despite offering several advantages, parts with overhang features require the use of support structures to provide dimensional stability of the part. Support structures achieve this by resisting residual stresses generated during processing and assisting heat dissipation. Although the scientific community acknowledges the role of support structures in the success of L-PBF manufacturing, they have remained relatively underexplored in the literature. In this context, the present work investigated the impact of laser power and scanning speed on the dimensioning, integrity and tensile strength of single-walled block type support structures manufactured in AISI 316L stainless steel. The method proposed in this work is divided in two stages: processing parameter exploration, and mechanical characterization. The results indicated that support structures become more robust and resistant as laser power increases, and the opposite effect is observed with an increment in scanning speed. In addition, defects were detected at the interfaces between the bulk and support regions, which were crucial for the failure of the tensile test specimens. For a layer thickness corresponding to 0.060 mm, it was verified that the combination of laser power and scanning speed of 150 W and 500 mm/s resulted in the highest tensile resistance while respecting the dimensional deviation requirement. Full article

The recent discovery of TIGR-Tas (Tandem Interspaced Guide RNA-Targeting Systems) marks a major advance in the field of genome editing, introducing a new class of compact, programmable DNA-targeting systems that function independently of traditional CRISPR-Cas pathways. TIGR-Tas effectors use a novel dual-spacer guide RNA (tigRNA) to recognize both strands of target DNA without requiring a protospacer adjacent motif (PAM). These Tas proteins introduce double-stranded DNA cuts with characteristic 8-nucleotide 3′ overhangs and are significantly smaller than Cas9, offering delivery advantages for in vivo editing. Structural analyses reveal homology to box C/D snoRNP proteins, suggesting a previously unrecognized evolutionary lineage of RNA-guided nucleases. This review positions TIGR-Tas at the forefront of a new wave of RNA-programmable genome-editing technologies. In parallel, I provide comparative insight into the diverse and increasingly modular CRISPR-Cas systems, including Cas9, Cas12, Cas13, and emerging effectors like Cas3, Cas10, CasΦ, and Cas14. While the CRISPR-Cas universe has revolutionized molecular biology, TIGR-Tas systems open a complementary and potentially more versatile path for programmable genome manipulation. I discuss mechanistic distinctions, evolutionary implications, and potential applications in human cells, synthetic biology, and therapeutic genome engineering. Full article

Background/Objectives: To review the dimensions of the round window region (round window niche, bony structures surrounding the niche, and the membrane itself). Methods: Medline, EMBASE, Cochrane Library, and Google Scholar databases were searched by two independent reviewers. Anatomical and radiological studies on the round window region were screened. Studies reporting at least one dimension for the round window (RW) niche and/or the RW membrane were included. Results: Sixteen studies met the inclusion criteria (13 anatomical and 3 radiological studies) for a total number of 808 temporal bones with at least one dimension reported. The structures measured varied across the different studies with 12 reporting RW membrane dimensions (area and/or at least one distance), 8 detailing RW niche dimensions (height, width or depth) and 6 which measured at least one element of the RW bony overhangs (posterior or anterior pillar, RW tegmen). Surface area of the RW membrane varied between 0.32 mm² and 2.89 mm², with a minimum dimension (minimum diameter or height or width) comprising between 0.51 mm and 2.1 mm. When the bony overhangs surrounding the membrane were not considered, the minimum diameter was between 1.65 mm and 1.97 mm. Conclusions: The dimensions of the RW region are intrinsically variable, but the heterogeneity of the measurements reported also contributes to these variations. Posterior pillar, RW tegmen, anterior pillar, and their relative development probably account for a large part of this variability. The future RW membrane devices should be ≤1 mm in their maximum dimension, whether or not individually tailored, to fit most of the RW membranes. Full article

This paper outlines a structural qualification process to assess the use of newly developed high-modulus (HM) glass fiber-reinforced polymer (GFRP) bars with headed ends in the joint between concrete bridge barriers and decks. The main goals of the study are to evaluate the structural performance of GFRP-reinforced TL-5 barrier–deck systems under transverse loading and to determine the pullout capacity of GFRP anchorage systems for both new construction and retrofit applications. The research is divided into two phases. In the first phase, six full-scale Test-Level 5 (TL-5) barrier wall–deck specimens, divided into three systems, were constructed and tested up to failure. The first system used headed-end GFRP bars to connect the barrier wall to a non-deformable thick deck slab. The second system was similar to the first but had a deck slab overhang for improved anchorage. The third system utilized postinstalled GFRP bars in a non-deformable thick deck slab, bonded with a commercial epoxy adhesive as a solution for deteriorated barrier replacement. The second phase involves an experimental program to evaluate the pullout strength of the GFRP bar anchorage in normal-strength concrete. The experimental results from the tested specimens were then compared to the factored applied moments in existing literature based on traffic loads in the Canadian Highway Bridge Design Code. Experimental results confirmed that GFRP-reinforced TL-5 barrier–deck systems exceeded factored design moments, with capacity-to-demand ratios above 1.38 (above 1.17 with the inclusion of an environmental reduction factor of 0.85). A 195 mm embedment length proved sufficient for both pre- and postinstalled bars. Headed-end GFRP bars improved pullout strength compared to straight-end bars, especially when bonded. Failure modes occurred at high loads, demonstrating structural integrity. Postinstalled bars bonded with epoxy performed comparably to preinstalled bars. A design equation for the barrier resistance due to a diagonal concrete crack at the barrier–deck corner was developed and validated using experimental findings. This equation offers a conservative and safe design approach for evaluating barrier–deck anchorage. Full article

Electron beam melting (EBM) technology has gained prominence owing to its ability to enhance production efficiency and meet green manufacturing standards. However, overhang structures are a significant issue for additive manufacturing due to their need for supporting structures during printing. This increases manufacturing time, requiring more material, extra effort, and a more complex engineering procedure. Therefore, this research aims to develop an intelligent optimization method based on AI-ANFIS/Al-ANN and improved NSGA-III, integrating the AM design, 3D printing, and post-processing phases to enhance the performance of block support structures and the quality of the EBM parts produced. To achieve this, statistical analysis was performed to detail the simultaneous influence of block support type, block support structure design, and EBM parameters on fabricating performance, warping deformation, support removal time, and support volume. After that, intelligent models based on ANFIS/ANN and the advanced NSGA-III method were developed for monitoring and optimizing the performance of specified block support structures. The results reveal that the block support type, block support structure design, and EBM parameters simultaneously significantly affect block support structures’ performance. This study illustrated that the AI models based on ANFIS might provide more accurate and reliable estimation models for monitoring and predicting support volume, support removal time, and warping deformation, exhibiting reduced errors of 0.992%, 1.2%, 1.28%, and 1.06%, respectively, in comparison to empirical measurements, ANN models, and regression models. Finally, the developed intelligent method obtains the optimal block support type, block support design, and EBM parameters to enhance the quality of produced parts, reduce material wastage, and reduce the post-processing time of fabricated EBM Ti6Al4V. Henceforth, smart systems may be employed to create innovative solutions that integrate the AM design, 3D printing, and post-processing stages. This will allow for the monitoring and improvement of AM process performance, as well as the fulfillment of Industry 4.0 requirements. Full article

This study examines the combination of overhang constraints and Reliability-Based Topology Optimization (RBTO) in additive manufacturing (AM). AM offers intricate component production but faces challenges due to support structures. Incorporating overhang constraints in topology optimization enables self-supporting structures. RBTO addresses uncertainties in design variables to enhance reliability. This research investigates build direction parameter solutions using deterministic and RBTO algorithms. Topological properties, compliance, sensitivity, and density filters are assessed, alongside optimization techniques like Method of Moving Asymptotes (MMA) criterion and Optimality Criteria (OC). In numerical experiments on the MBB beam, the AM-RBTO algorithm reduced 3D printing time by approximately 18.3% and improved structural performance by lowering the objective function value by 1.85% compared to conventional RBTO. Results contribute to merging overhang constraints and RBTO in AM topology optimization, improving design by considering uncertainties. The study enhances computational efficiency and stability in optimizing build direction parameters, offering valuable insights for future AM applications. Full article

Corals in the Galápagos present diverse reef configurations from biogenic coral reefs to coral communities growing on rocks and sand. These corals have experienced decades of disturbances including recurring El Niño and mass bleaching events. However, traditional methods in ecology have limited capacity in describing coral demographic trends across large spatial scales. Photogrammetry—a form of 3D imaging, has emerged over the past decade as a popular method for benthic surveys. However, the majority of protocols in the field utilize the 2D products of photogrammetry, ignoring overhangs and leaving significant information unexploited. We surveyed seven reef sites across the archipelago using underwater photogrammetry and developed new methods for 3D annotation and fractal dimension calculation. Our findings reveal variation in coral cover, diversity, and structural complexity across the archipelago. Our results align with previous studies in the region and add important information on reef structural complexity which was not measured here before. We release a unique dataset: Galápagos_3D, including seven 3D models and over 17,000 annotated images. This study establishes an important baseline for long-term monitoring, research, and conservation in the Galápagos, potentially informing evidence-based policies and advancing our understanding of coral resilience and recovery. Full article

This study investigates the electromagnetic analysis and optimal design of outer rotor type brushless DC (BLDC) motors for fan filter applications. The primary objective is to develop a method that integrates three-dimensional (3D) structural effects with efficient two-dimensional (2D) equivalent analysis. This study proposes a 2D equivalent analysis method that addresses the unique features of outer rotor type BLDC motors, particularly the permanent magnet (PM) overhang structure. This approach transforms the operating point on the B–H curve to facilitate accurate modeling in a 2D framework, overcoming traditional analysis limitations. An analytical method using spatial harmonics is introduced to derive essential electromagnetic quantities, namely flux linkage and back electromotive force (EMF). The method compensates for slot effects using the Carter coefficient, ensuring precise evaluation of circuit parameters and electromagnetic losses. To optimize motor performance, a multi-objective optimization technique is implemented using the Non-dominated Sorting Genetic Algorithm-II (NSGA-II), aiming to maximize both efficiency and power density. The research validates the proposed analytical approach against the finite element analysis method (FEM) results to confirm its accuracy. Full article

Additive manufacturing processes such as the material extrusion of metals (MEX/M) enable the production of complex and functional parts that are not feasible to create through traditional manufacturing methods. However, achieving high-quality MEX/M parts requires significant experimental and financial investments for suitable parameter development. In response, this study explores the application of machine learning (ML) to predict the surface roughness and density in MEX/M components. The various models are trained with experimental data using input parameters such as layer thickness, print velocity, infill, overhang angle, and sinter profile enabling precise predictions of surface roughness and density. The various ML models demonstrate an accuracy of up to 97% after training. In conclusion, this research showcases the potential of ML in enhancing the efficiency in control over component quality during the design phase, addressing challenges in metallic additive manufacturing, and facilitating exact control and optimization of the MEX/M process, especially for complex geometrical structures. Full article

During coal resource mining, hard roof mining is prone to causing rock-burst disasters because traditional blasting–cutting roof technology has the disadvantages of low efficiency and high cost. This article studies the theoretical basis and engineering application of fracturing technology with a static expansion agent (SCA). The influences of borehole diameter and spacing on the fracturing effect of a rock mass are studied through theoretical analysis and simulation. Rock mass models of a cantilever beam for a single rock layer and multiple layers were established, and the mechanical properties of the roof strata under three working conditions were analyzed. The research results show that the maximum annular stress value occurs along the drill hole wall between the adjacent drill holes, and the annular stress at the center line between two drill holes is the smallest. As the spacing between the holes increases, the annular stress at the center line decreases; however, the annular stress at the center of the drill line becomes larger with the increase in hole diameter. The degree of stress concentration increases sharply with the decrease in distance f from the borehole center to the free surface. Relative to the cantilever beam model of a single rock layer, the combined rock layers can effectively control the displacement and deformation of the cantilever roof. Based on the above research results, a drilling method with a 75 mm diameter and a 10° inclination angle is used, demonstrating that the suspended roof area can be reduced to below 20 m² using the fracturing technology with a static expansion agent, allowing the roof strata to fall simultaneously during mining. Full article

The instability in rare-earth material supply and rising costs have driven research into rare-earth-free electric motors. Among various alternatives, wound rotor synchronous motors (WRSMs) stand out due to their adjustable excitation, enabling high torque at low speeds, and efficient field weakening at high speeds. Unlike permanent magnet synchronous motors (PMSMs), WRSMs offer greater operational flexibility and eliminate the risk of demagnetization. However, accurately modeling WRSMs remains challenging, especially when considering axial fringing flux and leakage components, which significantly affect motor performance. To address this challenge, this paper proposes a 3D nonlinear magnetic equivalent circuit (MEC) model that explicitly incorporates axial flux components and leakage paths in WRSMs with overhang rotor structures. Unlike conventional 2D MEC models, which fail to capture axial flux interactions, the proposed approach improves prediction accuracy while significantly reducing computational costs compared to full 3D finite element analysis (FEA). The model was validated through comparisons with 3D FEA simulations and experimental back-EMF measurements, demonstrating its accuracy and computational efficiency. The results confirm that the 3D nonlinear MEC model effectively captures axial flux paths and leakage components, making it a valuable tool for WRSM design and analysis. Future research will focus on further refining the model, incorporating hysteresis loss modeling, and developing hybrid MEC–FEA simulation techniques to enhance its applicability. Full article

As the correlation between design rules and process limitations is of the upmost importance for the full exploitation of any manufacturing technology, we report a design guide for hybrid-additive manufacturing of Inconel 718. Basic limitations need to be evaluated for this particular hybrid approach that combines laser powder bed fusion (PBF-LB/M) and in situ high-speed milling. Fundamental geometric limitations are examined with regard to the minimum feasible wall thickness, cylinders, overhanging structures, and chamfers. Furthermore, geometrical restrictions due to the integrated three-axis milling process with respect to inclinations, inner angles, notches, and boreholes are investigated. From these findings, we derive design guidelines for a reliable build process using this hybrid manufacturing. Additionally, a design guideline for the hybrid-additive manufacturing approach is presented, depicting a step-to-step guide for the adjustment of constructions. To demonstrate this, a powder nozzle for a direct energy deposition (DED-LB/M) process is redesigned following the previously defined guidelines. This redesign encompasses analysis of the existing component and identification of problematic areas such as flat angles, leading to a new construction that is suitable for a hybrid-additive manufacturing approach. Full article

In the laser powder bed fusion (LPBF) process, the surface quality of intermediate layers impacts interlayer bonding and part forming quality. Due to the complex dynamic process inherent in LPBF, current monitoring methods struggle to achieve high-quality in situ online monitoring, which limits the in-depth understanding of the evolution mechanisms of the surface morphology of LPBF intermediate layers. This paper employs an optimized coaxial optical imaging method to monitor key LPBF processes and analyzes the intermediate layer surface morphology evolution mechanism considering heat, force, and mass transfer. Results indicate that LPBF intermediate layer surfaces are influenced by energy density, melt pool behavior, and previous layer morphology, forming complex topological structures. At a low energy density, insufficient powder melting causes balling, extended by subsequent melt pools to form a reticulated structure and local large-scale protrusions. Heat accumulation at a high energy density promotes melt pool expansion, reduces melt track overlap, and effectively eliminates defects from previous layers via remelting, with spatter becoming the main defect. Additionally, the melt pool wettability on the part contours captures external powder, forming unique, overhanging contour protrusions. This paper enhances understanding of LPBF intermediate layer surface morphology formation mechanisms and provides a theoretical basis for optimizing surface quality. Full article

When printing overhanging parts with traditional additive manufacturing (AM) equipment, it is necessary to add support structures under the overhanging structure. The process of printing support structures not only wastes materials, but also increases the manufacturing time. Therefore, in order to reduce or eliminate the need for support structures when printing parts with overhanging structures, such as propellers, a five-axis support-free printing method for overhanging parts is proposed for one of the most commonly used processes involving AM technology: fused deposition modeling (FDM). By offsetting the surface of the basic part, the offset surface is intersected with the model to be printed to obtain the spatial surface-layered curve. The contour offset method for the spatial curve is used to obtain the printing path, and continuous path planning is performed on it. While the presented method is targeted specifically at this ideal overhanging part, physical experiments on five-axis FDM equipment are performed. Compared with the traditional three-axis AM method, the time taken to print parts using this support-free five-axis AM method is shortened by 13.76–26.93%, and the printing material required is reduced by 17.24–29.29%. The experimental results show that this method realizes support-free printing of overhanging parts with the five-axis AM equipment, which not only saves materials and time consumed during part of the printing, but also improves the surface quality of the parts. Full article