Search Results (479)

A femtosecond laser serves as an excellent tool for efficiently fabricating large-area anti-reflective microhole arrays on infrared windows. The impact of the arrangement of the microholes during processing on final performance, however, remains unclear. Here, microhole arrays were fabricated on MgF₂ windows using a femtosecond laser. The optical performance was analyzed by the finite-difference time-domain method, focusing on the effects of in-plane arrangement deviation and double-sided alignment error. Simulation results indicate that the arrangement variations alter the average transmittance by less than 0.02%. Analysis via effective medium theory revealed that, within the target band, the microstructure array collectively functions as a thin film with a gradient refractive index. Its macroscopic properties show little sensitivity to minor misalignments at the microscopic scale. As a proof of concept, a large-area (20 mm × 20 mm) double-sided antireflection window was rapidly fabricated by employing a zigzag scanning strategy, which achieved an average transmittance exceeding 97.5% and exhibited a high degree of consistency between the simulated and experimental results. Upon final integration into the infrared thermal imaging system, this window not only enhanced the richness of detail in captured images but also improved target contrast. Full article

The operational ability of a unit or mechanism depends mainly on the quality of the mechanically produced working surfaces. Many materials can be assigned to a group of hard-to-cut materials that includes titanium- and aluminum-based alloys, a new class of heat-resistant alloys, SiCp/Al composites, hard alloys, and other alloys. The difficulties in their machining are related not only to the high temperatures achieved on the contact pads under mechanical load and the extreme cutting conditions but also to the properties of those materials, which affect the adhesion of the chip to the tool faces, hindering chip flow. One of the possible solutions to reduce those effects and improve the operational life of the tool, and as a consequence, the final quality of the working surface of the unit, is texturing the rake face of the tool with microgrooves or nanogrooves, microholes or nanoholes (pits, dimples), micronodes, cross-chevron textures, and other microtextures, the depth of which is in the range of 3.0–200.0 µm. This review is addressed at systematizing the data obtained on micro- and nanotexturing of PCD tools for cutting hard-to-cut materials by different techniques (fiber laser graving, femto- and nanosecond laser, electrical discharge machining, fused ion beam), additionally subjected to fluorination and dip- and drop-based coatings, and the effect created by the use of the textured PCD tool on the machined surface. Full article

Aerostatic bearings incorporating micro-hole restrictors with diameters on the order of tens of microns demonstrate superior static and dynamic stiffness characteristics, while significantly reducing air consumption, and are increasingly adopted in precision engineering applications. This paper investigates the modelling of aerostatic bearings with micro-hole restrictors. First, a refined discharge coefficient formula is developed, incorporating the orifice length-to-diameter ratio effect using the computational fluid dynamics (CFD) simulation results on a centrally fed circular aerostatic bearing. A numerical solution scheme is proposed using the developed discharge coefficients to enable more accurate and efficient prediction of the bearing performance and flow characteristics. Finally, the proposed numerical approach is implemented using the finite difference method (FDM) and demonstrated through a circular thrust air bearing case study. The results are validated against both CFD simulations and experimental measurements, showing excellent agreement and confirming the reliability of the FDM-based numerical model. Numerical and experimental investigations consistently demonstrate that micro-hole-restricted air bearings can achieve both high load capacity and high stiffness, having the potential for application in more complex air bearing designs and systems. Full article

High-quality hole machining of Ti-6Al-4V is critical for precision aerospace components but remains challenging due to the alloy’s poor machinability. In this study, the influence of cutting parameters on milling force, burr formation and the hole quality of Ti-6Al-4V was investigated. The mechanical properties and microstructure of the milled holes were analyzed. The research results show that milling depth is the primary factor governing variations in milling force and burr formation. The minimum milling force of 3.61 N is achieved at a milling depth of 60 μm, a feed per tooth of 2 μm/z and a cutting speed of 31 m/min. Compared to pre-optimization parameters, the milling force is decreased by 91.74%. Correspondingly, entrance burr width and hole-axis deviation were substantially reduced, indicating marked improvement in hole quality and geometrical accuracy. Microstructural observations show no deleterious phase transformations or excessive work-hardening under the optimized regime. The results deliver quantitative guidelines for parameter selection and tool application in micro-hole milling of Ti-6Al-4V and provide a foundation for further process modelling and optimization for aerospace manufacturing. Full article

Fused Deposition Modeling (FDM) is an extensively employed additive manufacturing method for producing precise and complicated polymer models, with its industrial applications expanding under various loading conditions. A review of existing research highlights the insufficient investigation of the influence of geometric discontinuities in additively manufactured polylactic acid (PLA) members under fatigue loads. This study aims to analyze the combined effects of build orientation and geometric discontinuities on the static and fatigue performance and damage evolution of 3D-printed PLA. To achieve improved fabrication quality and minimize process-induced defects, the quasi-static tensile tests were conducted on specimens printed in on-edge orientation with a concentric infill pattern and the flat direction with a rectilinear infill pattern. The test results have shown that on-edge-printed objects have reduced micro-voids and improved layer bonding, resulting in a 19% increase in tensile strength compared to the flat-printed specimens. Consequently, this configuration was adopted for three specimen types, e.g., smooth, semi-circular edge-notched, and central-holed, tested under axial fatigue with a 0.05 load ratio. Fatigue test findings indicate that the stress concentration is more pronounced around central holes than near edge notches, leading to shorter fatigue life. This phenomenon is consistent with its effects under static tensile loading. Furthermore, using Digital Image Correlation (DIC) technique, damage initiation, progression, and failure mechanisms were analyzed in detail. According to fractographic analysis, the micro-voids in the 3D-printed specimens serve as potential regions for the initiation of multiple fatigue cracks. Additionally, the inherent internal defects can interact with geometric discontinuities, thereby weakening the fatigue performance. Full article

Carbon fiber reinforced silicon carbide (C/SiC) composite material exhibits exceptional properties, including high strength, high stiffness, low density, outstanding high-temperature performance, and corrosion resistance. Consequently, they are widely used in aerospace, defense, and automotive engineering. However, their anisotropic, high hardness, and brittle characteristics make them a typical difficult-to-machine material. This paper focuses on achieving high-quality micro hole machining of C/SiC composite material via electrical discharge machining. It systematically investigates electrical discharge machining characteristics and innovatively develops a hollow internal flow helical electrode reaming process. Experimental results reveal four typical chip morphologies: spherical, columnar, blocky, and molten. The study uncovers a multi-mechanism cutting process: the EDM ablation of the composite involves material melting and explosive vaporization, the intact extraction and fracture of carbon fibers, and the brittle fracture and spalling of the SiC matrix. Discharge energy correlates closely with surface roughness: higher energy removes more SiC, resulting in greater roughness, while lower energy concentrates on m fibers, yielding higher vaporization rates. C fiber orientation significantly impacts removal rates: processing time is shortest at θ = 90°, longest at θ = 0°, and increases as θ decreases. Typical defects such as delamination were observed between alternating 0° and 90° fiber bundles or at hole entrances. Cracks were also detected at the SiC matrix–C fiber interface. The proposed hole-enlargement process enhances chip removal efficiency through its helical structure and internal flushing, reduces abnormal discharges, mitigates micro hole taper, and thereby improves forming quality. This study provides practical references for the EDM of C/SiC composite material. Full article

Laser micro-drilling was applied to Fe substrates to enhance the interfacial properties of carbon fiber-reinforced polymer/iron laminates. This architecture is referred to as a resin-interlocked Fe-CFRP hybrid composite. Inspired by human hair follicles’ exceptional adhesion and filling efficiency, novel biomimetic frustum-integrated cylindrical cavities were engineered for Fe surface modification. Experimental results demonstrate that laser-processed surfaces with varied hole geometries (conical, conical frustum, cylindrical, and frustum-integrated cylindrical cavities) exhibit significantly improved interfacial performance compared to untreated Fe controls. Specifically, RI-Fe/CFRP specimens containing frustum-integrated cylindrical cavities achieved the highest shear strength, with a 44.8% increase over non-drilled counterparts. Subsequent molecular dynamics simulations confirmed the critical role of the cavity geometry, demonstrating that the frustum-integrated cylindrical cavity elevates the Fe–Diglycidyl ether of bisphenol-A interfacial energy and van der Waals interactions by 45.44% and 50.66%, respectively, versus the flat surface. The interfacial energy enhancement mechanism via distinct hole configurations was systematically studied. Furthermore, comprehensive micro-hole topology analysis elucidated the reinforcement mechanism in resin-interlocked Fe-CFRP hybrid composites. Results demonstrate that frustum-integrated cylindrical cavities significantly enhance DGEBA-3,3′-diaminodiphenyl sulfone fluidity during interface simulation, promoting mechanical interlocking and optimized resin-filling efficiency. Laser micro-drilling effectively improves Fe-DGEBA interfacial performance. These findings provide critical insights for designing high-performance composites in aerospace and automotive applications. Full article

This research numerically investigates the cooling performance of Diamond-type triply periodic minimal surface (TPMS) networks as a gas turbine effusion cooling layer, augmented with various jet impingement configurations. The study analyzes the internal and external flow characteristics, pressure loss, and overall cooling effectiveness using conjugate heat transfer simulations. The Diamond design is compared to conventional film cooling and micro-hole models within a blowing ratio range of 0.5 to 2.0. The jet hole diameter and jet-to-plate distance are varied to identify an optimal double-wall cooling configuration. The results reveal that the Diamond hole mitigates the strong discharge of coolant, resulting in a more adherent cooling film, which provides excellent surface coverage. While jet impingement enhances internal heat transfer, its contribution to cooling effectiveness is minor compared to the benefit of film coverage. At an equivalent total pressure loss coefficient, the Diamond with impinging jets demonstrates 101% higher cooling effectiveness than the film hole. The thermal-mechanical analysis indicates that the Diamond model exhibits a more uniform distribution of thermal stress and displacement. The average stress is reduced by 44.7% compared to the film hole. This work confirms the TPMS-based effusion as an advanced cooling solution for next-generation gas turbines. Full article

Background/Objectives: To perform a physicochemical characterization of urine and sediment in intermittent catheterization (IC) users and evaluate the impact of IC with micro-hole zone catheters (MHZC) and conventional two-eyelet catheters (CEC). Methods: Analysis of anonymized urine samples collected from four IC user groups with lower urinary tract dysfunction (LUTD): Newly diagnosed individuals with spinal cord injury (SCI) from an inpatient SCI clinic (A), and community-based IC users with SCI (B), multiple sclerosis (MS) (C), or other conditions than SCI or MS (D). Urine analysis included physicochemical properties, bacterial load, and sediment size, both after collection and following passage through MHZC and CEC. Results: Urine samples from 53 participants were analyzed (groups A: 11, B: 11, C: 9, D: 22). The physicochemical properties of urine were similar to reference values despite the prevalence of bacteriuria ranging from 54.5% to 77.3%. The median [99th percentile] sediment size in the total group was 8.6 µm [50.7 µm] and 8.5 µm [54.1 µm] for group A, 9.2 µm [40.3 µm] for group B, 7.9 µm [48.3 µm] for group C, and 8.9 µm [50.3 µm] for group D. Following catheter passage, the median sediment size for the total group was 8.9 µm with the MHZC and 8.9 µm with the CEC. Conclusions: This two-part study initially presented a novel approach to characterizing urine samples, including sediment from IC users, and, thereafter, an in vitro experiment using the samples to test sediment passage through MHZC and CEC. The results indicated similar urine properties and sediment sizes across groups and did not suggest differences or issues relating to urine and sediment passage through these IC technologies for these groups. Full article

The hole expansion process of high-strength steel is influenced by multiple factors, including the deformation path, UTS/YS ratio, uniform elongation, sheet anisotropy, sheet thickness, strain rate, material micro-defects and the work hardening exponent. Based on forming limit curves or instability criteria, the prediction of the hole expansion ratio (HER) often requires extensive initial boundary conditions that complicate the result. In this study, V-Nb bainitic steel was subjected to hot continuous rolling and underwent water quenching with different coiling temperatures, then subsequently followed by thermal simulation and mechanical testing to fit the work hardening exponent (n) and to obtain the necking deformation instability curve. The radial displacement at the hole edge during simulation was predicted with the ratio of ultimate tensile strength to fracture strength. Furthermore, based on the tensile fracture failure criterion, the HER was predicted with the true fracture strain derived from uniaxial tensile tests. Comparison between the simulated results and actual hole expansion tests shows that the crack resistance in the post-uniform stage, strain hardening capacity and deformation compatibility between the microstructure and matrix are critical factors. And the proposed model achieves a prediction accuracy of over 85% for the V-Nb bainitic high-strength steel. Full article

Background: Idiopathic macular holes (MHs) are typically treated with pars plana vitrectomy and internal limiting membrane (ILM) peeling. The inverted ILM flap (ILMF) technique has emerged for MHs, but long-term outcome data remain inadequately established. This study evaluates the long-term functional and anatomical outcomes of the ILMF in idiopathic MHs. Methods: We evaluated 71 consecutive eyes of patients with idiopathic MHs who underwent vitrectomy with the inverted ILMF. Follow-up duration was more than 12 months. Visual acuity was measured, and macular anatomy was monitored with optic coherence tomography (OCT). Long-term visual and anatomical outcomes were defined a priori and analyzed accordingly. Results: Final vision values showed significant improvement compared to preoperative ones, from 1.02 [Snellen Equivalent (SE), 19/200] ± 0.40 logarithm of the minimum angle of resolution (logMAR) to 0.47 (SE, 68/200) ± 0.39 logMAR (p < 0.001). The primary MH closure rates were 94.37% (67/71), while the secondary closure rate reached 97.18% (69/71). Factors associated with better final vision included smaller hole size, favorable hole stage, better preoperative vision, intact postoperative foveal microstructure and contour. The recovery of the external limiting membrane (ELM), inner and outer segment junction (IS/OS), and good foveal contour had improved to 73.4%, 40.3%, and 49.3% at one year and 80%, 71.4%, and 53.3% at three years postoperatively, respectively. Conclusions: In idiopathic MHs, the ILMF approach provides meaningful, long-term visual and microstructural recovery, especially with a favorable functional outcome and intact postoperative microstructure sustaining up to three years. Full article

This study investigates the combined effects of oxygen content in the purging gas and pre-weld surface finish on the discoloration and corrosion resistance of AISI 316L pipe joints, with relevance to pipe welding where internal cleaning is constrained. The hybrid GTAW–FCAW process was used. Welds were produced at two oxygen levels (500 and 5000 ppm) and two finishes (40- vs. 60-grit). Discoloration and oxide morphology were examined by SEM/EDS, and corrosion behavior was evaluated without oxide removal using cyclic polarization and electrochemical impedance spectroscopy. The results reveal that higher oxygen levels in the purging gas produced more porous, less protective oxide layers, along with intensified oxidation around surface defects such as micro-holes. Surface roughness was also found to influence corrosion behavior: rougher surfaces exhibited higher resistance to pit initiation, whereas smoother surfaces were more susceptible to initiation but offered greater resistance to pit propagation. The corresponding governing mechanisms were identified and discussed in terms of how surface preparation affects crystallographic texture, heterogeneities and recrystallization. Taken together, the results link oxide morphology and near-surface microstructure to electrochemical response and offer practical guidance for pipe welding when internal cleaning is constrained, balancing purging control with surface preparation to preserve corrosion performance. The findings further highlight the critical roles of both purging-gas composition and surface preparation in the corrosion performance of stainless steel welded pipes. Full article

Femtosecond laser has been widely utilized in functional microstructural surfaces for applications such as anti-reflection, radiative cooling, and self-cleaning. However, achieving high-efficiency manufacturing of high-consistency functional microstructures (with feature sizes ~1 μm) over large areas remains a challenge. Here, we report a femtosecond laser temporal and spatial modulation technique for fabricating large-area anti-reflective microholes on magnesium fluoride (MgF₂) windows. The beam was transformed into a Bessel beam to extend the Rayleigh length, enabling the fabrication of microhole arrays with sub-micron precision and surface roughness variations within 10 nm over a 6 μm focal position shift range (5–11 μm). By modulating MHz burst pulses, the aspect ratio of the microholes was increased from 0.3 to 0.7 without compromising a processing speed of 10,000 holes per second. As a proof of concept, large-area anti-reflective microholes were fabricated on a 20 mm × 20 mm surface of the MgF₂ window, forming a nanoscale refractive index gradient layer and achieving a transmittance increase to over 98%. This method provides a feasible solution for the efficient and high-consistency manufacturing of functional microstructures over large areas. Full article

Located in southern China, the five-hundred-meter aperture spherical radio telescope (FAST) is the world’s most sensitive radio telescope, especially for pulsar observation. Since its commissioning in 2016 and full operation in 2020, it has detected over 1100 new pulsars—boosting the globally known various pulsars to over 4000. In this concise overview, we highlight how harnessing FAST’s unique advantages—exceptional precision and ultra-high sensitivity—is set to fuel future discoveries of specialized pulsar types and exotic astrophysical objects. Notable targets include double millisecond pulsar binaries (MSP-MSPs), pulsar/millisecond pulsar–black hole systems (PSR-BHs or MSP-BHs), sub-millisecond pulsars, ultra-long-period pulsars, white dwarf pulsars, and short-orbit double neutron star systems (DNSs)—with orbital periods under one hour. As anticipated, in the 2040s, the combined capabilities of the FAST, the Square Kilometre Array (SKA), and other cutting-edge astronomical instruments will enable over 10,000 pulsar samples, which will usher in a golden era for pulsar research: such breakthroughs will not only significantly broaden and deepen our understanding of the “pulsar paradise” but also drive substantial progress in the field of multi-messenger astronomy. Beyond pulsar-focused research, FAST is poised to play a pivotal role in testing general relativity, detecting nanohertz gravitational waves, studying fast radio bursts (FRBs), and investigating the micro-structure of pulsar emissions. These investigations will not only strengthen our understanding of fundamental physics but also unlock deeper insights into the universe’s profound mysteries. Full article

Fine-grained Nb metal sheets were successively laser macro- and micro-polished for a potential use of the so-prepared materials in superconducting radiofrequency cavities in particle accelerators. The laser-treated Nb surfaces were investigated by a combination of white light interferometry, optical profilometry, electron microscopy with X-ray spectroscopy, and X-ray diffraction to study the influence of the conditions during the laser treatments on the resulting surface topography, the crystallographic structure, and the chemical composition of the material samples. For optimum polishing conditions, smooth, wavy surfaces with a minimum surface roughness could be achieved. However, local defects such as carbon contamination, as well as holes and cracks in the surface, were found. For the different prepared surfaces, the maximum acceleration field gradients, i.e., the onset fields for field emission (E_On), were determined, indicating that for smooth surface regions without defects, E_On may reach values of up to almost 1 GV/m, while for the pristine, rough surface and local defects such as particles and cracks, E_On is limited to values around 100 MV/m or less. The present study suggests that laser polishing should be considered as an alternative to conventional polishing strategies of niobium accelerator cavities. Full article