Sharp Corners Research Articles

Design guidelines for suppressing distortion and buckling in metallic thin-wall structures built by powder-bed fusion additive manufacturing

Controlling distortion in laser powder-bed fusion additive manufacturing is of critical importance especially for thin-wall structures, which typically experience significant deformation and buckling during the build process. We examine this issue from the perspective of design by systematically performing numerical simulations of the additive process of tubular components as a function of part design, including fillet radius, wall thickness, tube width and height. It is found that round corners, as opposed to sharp corners, suppress distortion even at small wall thickness (400 µm), while part width has a greater impact on distortion than part height. The buckling behavior of such structures is numerically investigated and analysis results show that for designs most prone to distortion, a critical height exists below which the component is distortion-free. The modeling was experimentally validated by manufacturing thin-wall components of IN718 alloy using the EOS M290 printer. The findings provide practical guidelines to manufacture metallic thin-wall tubular components with minimal to no distortion using powder-bed fusion additive manufacturing.

Surfactant‐Free and Microporous AlOOH/Al2O3 Nanosheets on TiO2‐Based Nanofibers: A Sustained‐Release Dominated Topotactic Transformation

AbstractUp to now, the synthesis of non‐ligand‐capped 2D transition‐metal nanostructures remained big synthetic challenges. Herein, ultrathin and microporous AlOOH/Al2O3 nanosheets were topologically grown on the surface of TiO2‐based nanofibers by a water‐only hydrothermal strategy starting from electrospun Al2O3/TiO2 nanofibers. The TiO2 nanofibers lowered the surface energy for the sustained‐released aluminum species and thereby allowed them in situ hydrated to laminar AlOOH. The metastable AlOOH tended to dehydrate to Al2O3 simultaneously, leaving a well‐maintained 2D structure with sharp corners and steps, as well as enriched micropores. The nanosheets‐on‐nanofibers exhibited 2856–3370 mg/g of adsorption capacity toward RhB and an efficient removal efficiency over 70% at high throughput (30 mL/h). The promoted light‐harvesting by the perpendicularly attached nanosheets further endowed a significant photodegradation for RhB within 1 h. The presented green and facile approach toward the fabrication of 2D metal oxide nanostructures paves the way to a new variety of oxide nanomaterials.

Coexistence of topological type-II Weyl and triply degenerate points in a chiral photonic metamaterial

In this work, we report the coexistence of type-II Weyl points and triply degenerate points while taking the nonlocal effect into account in a chiral photonic metamaterial system. The chiral effect introduces a break in the spatial inversion symmetry, which is necessary for the generation of nodal points. These nodal points are symmetrically distributed on the ${k}_{z}$ axis and possess the time-reversal symmetry-protection mechanism. Remarkably, the projections of all nodal points are connected by a Fermi arc surface state, and it agrees well with the single monopole charges of these nodal points, which demonstrates the topological characteristics of the band degenerate points. We theoretically show that the localized Fermi arc can be formed at the interface between the metamaterial and vacuum, which may improve the compactness of photonic devices. Especially, the nonreciprocal surface waves can propagate forward around the sharp corner without experiencing backscattering, which can be used for the robust transmission of information.

Slotted Waveguide Stress Concentration Factor

Sharp turns or corners within a structure lead to local failures well before the rest of the structure due to the creation of stress concentrations. For a load-bearing waveguide, these occur at the corners of the slots. After modeling a test waveguide, a bivariate curve fit was created to model these stress concentrations, based on four configurations for a single slot length, then refined into a trivariate form based on an expanded eight cases across two slot lengths. Once properly formatted, the integration of the bivariate function into an optimization allowed stress concentration to be estimated at the slot corners within a coarse low-fidelity model, rather than the high-fidelity model otherwise required, following the expected behavior and acting as a verification case. Implementation of the full trivariate form into a design optimization enabled use of the concentration factor to estimate the critical stress. The study showed that the inset copper waveguide could not be loaded from the outset, and that an offset of the copper waveguide could avoid overloading it.

Ballast loading plate design and mechanical behavior of under ballast mats

Geometry of loading plate which simulates the ballast contacting interaction is the critical factor for mechanical properties and durability test of the geotextile for railway track. In this study, a ballast indentation test with 3D laser scanning method was performed to study the actual contact characteristics of the bottom of the ballast. Based on this, the existing problems of geometric-ballast-plate (GBP) of the EN standard were presented. Therefore, a new ballast loading plate, Actual Ballast Plate (ABP), was designed and verified. The mechanical behavior of under ballast mats (UBMs) with different stiffnesses were studied by applying different ballast loading plates (the ABP, GBP, and flat plate). Results demonstrated that for the GBP, the geometric characteristics of sharp corners at the bottom of the ballast were largely overlooked, resulting in smaller contact stress in the fatigue test. The ABP resulted in a better simulation of the contact characteristics and load transfer relationship of the ballast. The stiffness test with the flat plate (FP) and GBP resulted in a higher static modulus for the hard UBM because of the overestimation of the contact area between the UBM and the ballast. It is recommended that the EN standards adopt the ABP to replace the GBP for the fatigue tests of the UBMs.

Highly selective colorimetric sensing for iodide in water based on a novel surface passivation of Ag nanoprisms

Because silver (Ag) nanoprisms with sharp edges are inherently unstable, it is very important to develop a facile method that can dramatically improve the chemical stability of Ag nanoprisms while maintaining their inherent properties, including their plasmonic properties. In the present work, we developed a novel surface passivation method based on a single-step water-based process and showed that it significantly improved the chemical stability of Ag nanoprisms. Specifically, tetramethylethylenediamine (TMEDA) was used as an organic capping ligand, and the TMEDA-treated Ag nanoprisms retained their triangular shape even when exposed to various strong etchants including bromide, chloride, and hydrogen peroxide. Only in the presence of iodide did the sharp corners of the nanoprisms become spontaneously etched, and this etching resulted in a dramatic change in their localized surface plasmon resonance (LSPR) properties. The extent of the change of the LSPR properties depended on the concentration of iodide; hence, aqueous solutions of the TMEDA-treated Ag nanoprisms with different concentrations of iodide showed different colors. Based on this relationship, a colorimetric sensing probe that can detect iodide in aqueous solutions was developed. The sensing probe exhibited very high selectivity for iodide and the ability to determine the concentration of iodide over a wide range of concentrations. In addition, the probe was found to provide significant advantages over previously developed systems for iodide analysis, including portability, ease of use, point-of-care analysis, and naked-eye detection.

The Dissolution of Olivine Added to Soil at 4°C: Implications for Enhanced Weathering in Cold Regions

Crushed olivine was added to a soil core to mimic enhanced weathering, and water was continually dripped through for ~6 months. Our experiments were conducted at 4°C, and are compared to previously run identical experiments at 19°C. Olivine dissolution rates in both experiments start out similar, likely due to fines and sharp crystal corners. However, after >100 days of reaction, the dissolution rate at 4°C was two orders of magnitude lower than at 19°C. The accumulation of heavy metals, such as Ni and Cd, was low in both experiments, but soil retention of these elements was proportionally higher at higher temperatures, likely due to enhanced sorption and formation of clays. Overall, this study suggests that olivine dissolution rates in experiments that mimic natural settings are orders of magnitude slower than in normal laboratory experiments, and that enhanced weathering may be a considerably less efficient method of carbon dioxide removal at low climatic temperatures. Both of these conclusions have implications for the application of enhanced weathering as a CO2 removal method.

Diurnal Preference Contributes to Maximal UVB Sensitivity by the Hour of the Day in Human Skin In Vivo

Diurnal Preference Contributes to Maximal UVB Sensitivity by the Hour of the Day in Human Skin In Vivo

Experimental study of the effect of temperature and velocity in channel forming of polyvinyl chloride composite reinforced by 3D-fiberglass with an aluminum middle layer

In this paper, the stamp forming process of a U-shaped cross-section channel with sharp corners of composite laminates including aluminum sheet and polyvinyl chloride (PVC) reinforced with 3D-fiberglass was investigated. The laminates were produced by manual layup and arrangement of fibers with different angles of [0°/90°] and [± 45°] degrees using hot press. The process of forming composite samples was carried out at temperatures of 25, 80, 120, 160°C and different velocities of punch. The effect of parameters including layup configuration, temperature, and forming speed on the spring-back of the formed laminates and the required forming force were evaluated. The results showed that as the forming temperature increased, the forming force decreased sharply. The lowest forming force was obtained for the laminate with [± 45°, Al, ± 45°] layout at 160°C temperature which was equal to 0.7KN. Also, with the increase in temperature, the spring-back angle has been reduced, the lowest of which is obtained with the laminate with [0°/90°] 3 layout equal to 8 degrees. Finally, it was concluded that increasing the speed of the forming process results in a decrease in the spring-back angle and this effect is more pronounced at higher temperatures.Graphical abstract

Performance Comparison of Different Building Shapes Using a Wind Tunnel and a Computational Model

A building-integrated wind turbine (BIWT) is an alternative way to assess renewable energy. BIWTs produces their own energy without relying on fossil fuels. However, only a few researchers have studied BIWTs. Greater wind velocity (V) results in greater potential energy (P). The aerodynamic design has an important role to play in increasing wind velocity and reducing turbulence intensity. CFD simulations taken from previous research have revealed that round-shaped buildings increase velocity up to 30%. This study focuses on the wind response of square and top-rounded-shaped building models, and their optimization based on variations in wind velocity. Wind tunnel studies were conducted to study wind flow around the building, followed by a computer simulation to verify the results. In a wind tunnel, three BIWT models (1:150 in scale) located in Seoul, South Korea (terrain B), were evaluated. The results of the study show that the streamline should be followed when installing wind turbines on rectangular rooves with flat surfaces. This method allows wind speed to be elevated significantly, when compared to a turbine at a higher height. In addition, round corners can produce wind velocity that is up to 34% greater than sharp corners beside a building. In summary, this paper presents a five-step analysis framework that can be used by researchers who wish to analyze BIWTs through wind tunnel experiments and CFD.

Characteristics of micro energetic semiconductor bridge initiator by depositing Al/MoO3 reactive multilayered films on micro bridge with different bridge size

Four types of Al/MoO3 micro energetic semiconductor bridge (MESCB) initiators were prepared by integrating 3 µm Al/MoO3 reactive multilayer films (RMFs) on micro semiconductor bridge (MSCB) with different bridge areas. The bridge areas were varied from 11661 µm2 to 489 µm2, and the ratio of length to width, the thickness, V-type angle were fixed at 0.54, 2.5 µm, 90°, respectively. The heating process of MSCB before electrical explosive was analyzed with multi physical simulation (MPS). The electrical explosive characteristics of these MESCB as well as MSCB were investigated under the stimulation of 47 µF tantalum capacitor discharge. The MPS results reveal that the V-shaped sharp corner of MSCB has highest temperature and the completed melting time of MSCB is decreased with lowing of bridge area. The critical burst time and critical burst energy of MSCB and MESCB also decrease with the decreasing of bridge area. When bridge area is 11661 µm2, the critical burst time of MSCB and MESCB drops with applied voltage, while critical burst energy is independent on applied voltage. Besides, the critical burst time and energy of MESCB are the higher than that of MSCB with bridge area of 11661 µm2. When the bridge area is reduced to 2915 µm2, the critical burst time and critical burst energy for MESCB are no significant difference with the corresponding MSCB. In addition, the critical burst time MSCB and MESCB have no relationship with outer stimulation energy as the bridge area further decrease at 489 µm2. The flame duration time of MESCB barely decreases when lowing the bridge area, which suggests that the energy consumption of MESCB can be reduced by decreasing the bridge area without weakening its firing performance.

Effect of heat treatment on microstructure and properties of modified hypereutectic high chromium cast iron

Abstract The effect of heat treatment on the microstructure, hardness and wear resistance of modified hypereutectic high chromium cast iron (HCCI) was investigated. The results show that the quenching treatment partially dissolves the edges of the primary carbides, and the sharp corners become rounded and blunt. As the quenching temperature increases, the carbide re-dissolves into the matrix, and the hardness and wear resistance first increase and then decrease. The hardness and wear resistance are the best when quenched at 1000 °C. After tempering, the martensite is transformed into tempered martensite, and the precipitation of secondary carbides increases. As the tempering temperature increases, the secondary carbides gradually become coarser. When the tempering temperature is 500 °C, the hypereutectic HCCI shows the highest hardness and the best wear resistance. When tempered at 400 °C, hypereutectic HCCI shows the best erosion and wear resistance.

On the milling strategy in machining curved surfaces based on minimum stress concentration by a 3-axis machining center

Three-axis computer numerical control machining centers are commonly used in machining due to their simple operations. When machining curved surfaces, the 3-axis CNC machining centers use interpolation line segment to fit the curved surfaces. The quality of the machined surface is affected by the length of the interpolation line segment. Sharp corners are formed at the junction of straight segments. The appearance of sharp corners will lead to increased stress concentration. To study the relationship between machined surface quality and interpolation straight line, this paper establishes the mathematical model of surface topography in ball-end milling multi-curved surfaces by a 3-axis milling center with considering the acceleration and deceleration controls. Based on the surface topography model, the stress concentration factor is analyzed in machining curved surfaces with different lengths of interpolation lines. The results show that the stress concentration factor decreases with the increase of the central angle when the length of interpolation lines and the radius of curvature are kept in constant, while decreases with the increase of the radius of curvature when the length of the interpolation lines and the central angle are held on. Moreover, the stress concentration factor increases as the length of the interpolation lines increases when the radius of curvature and the central angle are kept in constant. A method for selecting proper length of interpolation lines based on the stress concentration is proposed. In addition, the quality of the machined surfaces can be improved through the optimization of the tool path.

Time-optimal feedrate scheduling with actuator constraints for 5-axis machining

Cycle time minimization is one of the major goals to achieve in manufacturing. Maximizing feedrate is the direct solution; however, physical motions need to be under the specified motion limits to avoid high-frequency vibration, causing machining error. In this paper, a time-optimal feedrate scheduling approach with corner smoothing for 5-axis G1 toolpaths is presented for 5-axis machining. One key feature of the proposed method is to describe the orientation toolpath in the spherical coordinate system (SCS), instead of the commonly used unit sphere. With this, the position and orientation of the 5-axis toolpath are integrated to become a hyper-curve in a 5-dimensional (5-D) space. The feedrate scheduling and corner smoothing are designed for this 5-D hyper-curve. Thus, no synchronization of position and orientation feedrate scheduling is needed, making the feedrate scheduling easier. A quintic B-spline corner smoothing method is utilized to smoothen sharp corners in the toolpath. Then, the S-shape feedrate profile of each block is optimized under the actuator motion constraints, with the objective of minimizing the cycle time. Particle swarm optimization (PSO) is used to provide the optimized solution. Experiments are conducted to validate the proposed approach, and the results are compared with two other existing approaches. It is found that the proposed method can achieve shorter cycle time and less contour errors, showing the effectiveness of the proposed approach.

Systematic Approach for Static Steering Effort Reduction through Linkages Optimization in Small Commercial Vehicles (SCV)

The steering system design of a vehicle is of utmost importance as it not only acts as an interface between the driver and the entire vehicle but also is one of the key vehicle sub system which accounts for vehicle overall performance including vehicle handling and stability. With the recent infrastructure development and changes been witnessed in doing commercial vehicle business to hub and spoke and to door to door logistics delivery are expecting improved vehicle performance particularly in small and light commercial vehicles segments (SCV and LCV) where the business demands are more for the movement of vehicle in narrow city lanes and sharp corners. Also, now driver comfort is considered one of the key factors before purchasing any commercial vehicle. Thus, having power steering in SCV’s and LCV’s has not only become a mandate but also the vehicle steering system performance should be such that the driver is easily able to maneuver the vehicle in narrow city lanes and corners. Through this paper a methodology has been derived wherein factors contributing for achieving static lock to lock maneuverability in a power steering vehicle are analyzed without overdesigning the hydraulic power assistance of the vehicle. The approach mainly focuses on LH/RH symmetric hydraulic pressure build up in the system by critically designing the steering system linkages hard points such as drop arm length, drop arm SAP angle, steer arm length, track rod arm’s length. Also, this study ensures that the derived hard points not only enhances hydraulic assistance in the steering system but also ensures vehicle to have least turning circle diameter (TCD) and enhanced tire life by having least Ackermann error.

The Effect of Single-Sided Ribs on Heat Transfer and Pressure Drop Within a Trailing Edge Internal Channel of a Gas Turbine Blade

Abstract Convective cooling in a gas turbine blade internal trailing edge channel is often insufficient at the sharp trailing edge. This study examines convective heat transfer and pressure drop within a simplified nonrotating trailing edge channel. The internal passage has been modeled as a right triangular channel with a 9 deg angle sharp corner. A copper plate was heated from underneath via a uniform heat flux heater and examined via infrared thermography for two cases: smooth wall and single-sided ribbed wall. Nonuniformity in the heat flux due to conduction is corrected by a Reynolds-averaged Navier–Stokes (RANS) conjugate heat transfer calculation, which was validated by the mean velocity, friction factor, and temperature fields from experiments and large eddy simulation (LES). Nusselt number distributions illustrate that surface heat transfer is increased considerably with ribs and coupled with the vortices in the flow. Heat transfer at the sharp corner is increased by more than twofold due to ribs placed at the center of the channel due to secondary flow. The present single-sided ribbed channel utilizes secondary flow toward the corner and is presumed to have better thermal performance than a dual-sided ribbed channel. Thus, it is important to set the appropriate rib length within the channel.

Cornering the universal shape of fluctuations

Understanding the fluctuations of observables is one of the main goals in science, be it theoretical or experimental, quantum or classical. We investigate such fluctuations in a subregion of the full system, focusing on geometries with sharp corners. We report that the angle dependence is super-universal: up to a numerical prefactor, this function does not depend on anything, provided the system under study is uniform, isotropic, and correlations do not decay too slowly. The prefactor contains important physical information: we show in particular that it gives access to the long-wavelength limit of the structure factor. We exemplify our findings with fractional quantum Hall states, topological insulators, scale invariant quantum critical theories, and metals. We suggest experimental tests, and anticipate that our findings can be generalized to other spatial dimensions or geometries. In addition, we highlight the similarities of the fluctuation shape dependence with findings relating to quantum entanglement measures.

Topological One-Way Edge States in an Air-Hole Honeycomb Gyromagnetic Photonic Crystal

Topological one-way edge states have attracted increasing attention because of their intriguing fundamental physics and potential applications, particularly in the realm of photonics. In this paper, we present a theoretical and numerical demonstration of topological one-way edge states in an air-hole honeycomb gyromagnetic photonic crystal biased by an external magnetic field. Localized horizontally to the edge and confined in vertical direction by two parallel metallic plates, these unique states possess robust one-way propagation characteristics. They are strongly robust against various types of defects, imperfections and sharp corners on the path, and even can unidirectionally transport along the irregular edges of arbitrary geometries. We further utilize the one-way property of edge states to overcome entirely the issue of back-reflections and show the design of topological leaky wave antennas. Our results open a new door towards the observation of nontrivial edge states in air-hole topological photonic crystal systems, and offer useful prototype of robust topological photonic devices, such as geometry-independent topological energy flux loops and topological leaky wave antennas.

An ultrafast temperature response analysis of a MEMS-based igniter using the finite-element method

This study reports the simulation and experiments of a MEMS-based igniter for a semiconductor bridge (SCB), which is fabricated using complementary metal oxide semiconductor technology. The finite-element method was first employed to simulate the ultrafast temperature response of the ignition process of SCB under conditions of an electro-exploding ignition, electro-thermal ignition, and no-ignition and to conduct a capacitor discharge stimulation. The recorded voltage from an oscilloscope was used as the initial condition, and conductivity values based on experimental data were taken as a key parameter for the polysilicon material to ensure the accuracy of the heat source loaded into the model. Under the electro-exploding ignition, the SCB was initially ignited at the sharp corners at the valley of the first voltage peak instead of the secondary peak. The maximum temperature of the SCB was no more than the melting point of the polysilicon material (except for the sharp corners) and only at 1369 ​K under the electro-thermal ignition and no-ignition conditions, respectively. The optical testing and ablation results of the bridge area demonstrate that the numerically simulated temperature is quite accurate. This method can be easily extended to other MEMS-based igniters for temperature prediction applications.

Effect of Mn addition on the micromechanical response and failure of Al-12.6Si alloy using actual microstructure based RVE model

Eutectic Al-12.6Si alloy has been developed with and without Mn addition through the gravity casting method. Microstructure, mechanical properties, behavior of deformation, micromechanical response and failure propagation subjected to tension have been investigated. The representative volume elements (RVEs) technique and the deformation plasticity model (Ramberg-Osgood) have been employed to understand the effects of microstructure morphology on the micromechanical response and failure initiation under tension. It has been found that the Mn addition effectively modifies the Al-12.6Si alloy’s microstructure morphology, as an effect mechanical properties improved. Additionally, the alloy has a combination of brittle and ductile fracture modes under tension. The finite element analysis reveals that the stress and strain distribution (micromechanical response) and deformation behaviour of simulated Al-12.6Si Alloy RVEs change with changing Mn concentration in the alloy. Both the primary and eutectic Si phase and Al6Mn phase shared maximum load during tensile deformation. The primary mode of failure would be initiated by breaking of eutectic silicon flakes and unmodified primary Si particles and Al6Mn intermetallic. Both the Si particle's sharp corners and Al and Si phase interface are found as the preferable crack initiation site. Additionally, void initiation takes place at the narrow Al phase region in the microstructure. Eutectic Al-12.6Si with 1 wt% Mn is found to give more uniform stress and deformation distribution, therefore the simulated results have a great concurrence with the experimented results.