Sharp Corners Research Articles

Investigation of Railway Ballast Breakage Through Large-Scale Triaxial Tests and a New Particle Breakage Approach in Discrete Element Modeling

Crushed aggregates with irregular shapes and sharp corners are preferred ballast materials to ensure proper track bearing capacity because of good contact between the particles. Meanwhile, crushed aggregates are prone to deterioration and breakage under repeated train loads. The effect of particle degradation on the mechanical behavior of ballast has been investigated before, but previous research rarely separates ballast breakage during sample compaction from breakage during shearing. This study investigates ballast particle breakage at different stages through large-scale triaxial tests and discrete element modeling. The results show that corner breakage is the primary particle breakage mode and mostly happens during compaction instead of during the shearing process. The results also indicate ballast corner breakage during sample compaction would increase the peak strength of the ballast but would not change Young’s modulus. A rubber pad is strongly recommended to reduce ballast breakage during the triaxial test sample compaction.

Coronary type of blood supply to the calf's heart

The high variability of branching of the heart vessels in animals is a proven and irrefutable fact in veterinary morphology. In individuals of the same species and breed, quite high discrepancies can sometimes occur in the topography of the coronary arteries of the heart. When studying the coronary bed of the heart of animals, we recorded a case of the presence of a right-handed type of blood supply in a two-month-old Blackand- White calf in the absence of a left coronary artery. In this regard, we set ourselves the goal of studying the features of the vascularization of the right half of the heart in a two-month-old Black-and-White calf with a right-sided type of blood supply.To achieve this goal, the heart of the corpse of a two-month-old Black-and-White calf, obtained from a private farm in the Leningrad Region, was studied. The study was conducted at the Department of Animal Anatomy, St. Petersburg State University of Veterinary Medicine. To study the vascularization of the heart of the studied animal, classical and modern anatomical techniques were carried out, such as fine anatomical preparation, photography, and the manufacture of corrosion preparations using latex.According to the results of the study, it was found that in the absence of the left coronary artery in the studied two-month-old calf of the Black-and-White breed, the right coronary artery completely and completely compensates for its absence. The presence of the right interventricular artery was established, which has such branches as the artery of the right septomarginal trabecula and atrioventricular branches that supply blood to the tricuspid valve area and the right septomarginal trabeculae of the heart. It was determined that the vessels that vascularize the structures of the right atrium and right ventricle in their topography in the studied individual are inferior in the number of S-shaped bends and sharp corners in comparison with the arteries of the left half of the heart, which can reduce the risk of developing coronary pathologies in the right half of the heart. It was established that the subsinus artery differs from the generally accepted classical topography and plunges into the thickness of the myocardium of the right ventricle and interventricular septum, and practically does not pass as part of the subsinus sulcus.

Crystalline AuNP-Decorated Strontium Niobate Thin Films: Strain-Controlled AuNP Morphologies and Optical Properties for Plasmonic Applications.

Gold nanoparticle (AuNP) decoration is a commonly used method to enhance the optical responses in many applications such as photocatalysis, biosensing, solar cells, etc. The morphology and structure of AuNPs are essential factors determining the functionality of the sample. However, tailoring the growth mechanism of AuNPs on an identical surface is not straightforward. In this study, AuNPs were deposited on the surface of a perovskite thin film, strontium niobate (SNO), using pulsed laser deposition (PLD). AuNPs exhibited a dramatic variation in their growth mechanisms, depending on whether they were deposited on SNO thin films grown on magnesium oxide (SNO/MgO) or strontium titanate (SNO/STO) substrates. On SNO/MgO, the Au aggregates form large NPs with an average size of up to 3500 nm2. These AuNPs are triangular with sharp edges and corners. The out-of-plane direction of growth is favored, and the surface coverage ratio by AuNPs is low. When deposited on SNO/STO, the average size of AuNPs is much smaller, i.e., ∼250 nm2. This reduction in the average size is accompanied by an increase in the number density of NPs. AuNPs on SNO/STO have a round shape and high coverage ratio. Such an impact from the substrate selection on the AuNP structure is significant when the sandwiched SNO film is below 80 nm thickness and is weakened for 200 nm of SNO films. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize all samples. Strain analysis was used to explain the growth mechanism of AuNPs. The average height of AuNPs was measured by using atomic force microscopy (AFM). Ellipsometry in the visible-near-infrared (vis-NIR) region was used to characterize the optical response of all samples. AuNP-decorated SNO/MgO and SNO/STO thin films exhibit different optical properties, with only gold-decorated SNO/MgO samples showing a size-dependent epsilon-near-zero behavior of nanoparticles. These results provide an additional route to control the structure of AuNPs. They can be used for various plasmonic applications like the design and development of strain-engineered gold-nanoparticle-decorated devices for surface-enhanced Raman spectroscopy (SERS) and photocatalysis.

3D mesoscale investigation on the compressive fracture of concrete with different aggregate shapes and interface transition zones

The purpose of this work is to investigate the effect of aggregate shape parameters and interface transition zone (ITZ) thickness on the mechanical properties and failure behavior of concrete under uniaxial compression. A 3D mesoscopic model including mortar, shape-alterable aggregate and thickness-controllable ITZ was established in ABAQUS software by programming. Based on the concrete damaged plasticity (CDP) method and the cohesive element approach, the simulation analysis was carried out from the aspects of macroscopic mechanical response, macroscopic failure morphology, mesoscale fracture propagation, and energy dissipation. Results indicate that polyhedral aggregate and spherical aggregate have no significant effect on the macroscopic mechanical properties of concrete. Aggregates with sharp edges and corners may cause concrete to be destroyed into more fragments. The ITZ with 0 thickness and medium thickness can predict the compressive strength of concrete, ITZ model with solid thickness is more suitable for meso-crack research. Thinner solid ITZ fits poorly with the experimental value, and the change of ITZ has little influence on polyhedral aggregates. It is proposed to establish a polyhedral aggregate and medium thickness ITZ model for mesoscale concrete numerical simulation.

Evaluation of erosion–corrosion process of Ti(C, N)-based cermets in acidic SiO2 slurry

This study investigates the erosion-corrosion process of Ti(C, N)-based cermets and compares it with WC-based cemented carbides in acidic SiO2 slurry. During the process, corrosion pits caused by corrosion expose the hard phase's sharp corners. The exposed corners crack, break and form debris due to the impact of SiO2's erosion. The slurry washes away the debris, and further corrodes the pits. Eventually, the binder surrounding the hard phase is destroyed, and the hard phase peels off due to the lack of bonding. In the initial stage, chemical corrosion is the main mode of destruction, followed by mechanical erosion. As the erosion time increases, the volume loss rate of cermets and cemented carbides also increases. The volume loss rate of medium-grained cemented carbide is the highest, followed by submicron-grained cemented carbide, and the smallest for the cermet. The erosion effect of SiO2 particles was more significant than the corrosion effects on volume loss in acidic SiO2 slurry.

New aspects of the CISAMR algorithm for meshing domain geometries with sharp edges and corners

Several new algorithmic aspects of the conforming to interface structured adaptive mesh refinement (CISMAR) mesh generation technique are presented for creating high-fidelity finite element models of 3D problems with non-smooth (C0–continuous) geometries. The Stereolithography (STL) file characterizing the domain geometry is first pre-processed to identify its sharp edges and corners, followed by overlaying that on a structured background mesh composed of tetrahedral elements to identify elements cuts by material interfaces/boundaries. Three non-iterative algorithms, namely hierarchical r-adaptivity, element deletion, and Kirigami-inspired sub-tetrahedralization are then introduced to generate a high-quality conforming mesh by relocating background mesh nodes, eliminating degenerate elements, and subdividing non-conforming tetrahedra to match material interfaces and domain boundaries. These algorithms either upgrade or fully replace different phases of the original CISAMR technique, which was limited to modeling problems with smooth interfaces. The example problems provided in this manuscript demonstrate the upgraded CISAMR algorithm to handle domain geometries with complex, non-smooth interfaces.

Design and experiment of high load-bearing acrylic connection node for the world's largest acrylic spherical vessel

Acrylic is a kind of polymer material and is gradually applied to load-bearing components. The working stress and ultimate bearing capacity of the acrylic structure are the main design indexes. Aiming at the world’s largest acrylic spherical vessel, the structural design, finite element analysis and full-size prototype tensile test of a new acrylic connection node were carried out in this paper. This acrylic node will bear 90 kN tension force for 20 years. According to the viscoelastic characteristics of the material and the working environment, the stress of acrylic should be controlled below 3.5 MPa for long term used. At the time, the ultimate bearing capacity should be greater than 6 times the working load. According to the stress-strain curve of acrylic, its tensile strength is about 75 MPa. There is no obvious plastic deformation after fracture, showing the material characteristics of brittle fracture. According to the failure analysis of previous acrylic node structures and the characteristics of acrylic, the new acrylic node structure is proposed in this paper. Its performance is improved by reducing the cutting amount of acrylic nodes, optimizing the structure of embedded part and avoiding sharp corners. A 1/4 symmetrical acrylic node model is established FEA software, and the nonlinear problems such as material nonlinearity and friction contact are solved by finite element method. The FEA results show that the maximum principal stress of the node is about 2.92 MPa. The relative error between the FEA results and the experimental results is 7.24%, indicating that the FEA results are credible. The ultimate tensile load of the node can reach 1000 kN, which is about 11 times the working load. The failure of the node occurs at a sharp corner of the groove, instead of the maximum stress point. Therefore, stress concentration caused by sharp corners should be avoided in the design of acrylic structure.

Numerical modelling of planned corner deposition in 3D concrete printing

Analysis of different path planning strategies and the effects of changing printhead direction in the geometrical conformity and the process precision around 90 corner in order to enable a simple and cost-effective way of facilitating the determination of an optimal printing mode for fast and accurate print corners in 3D concrete printing.The material flow is characterized by a viscoplastic Bingham fluid. The printhead moves according to a prescribed speed to print the trajectory. The model solves the Navier-Stokes equations and uses the volume of fluid (VOF) technique. The acceleration steps and jerk (j) carry out the direction change. A smoothing factor is provided to smooth the toolpath. Several simulations were performed by varying the smoothing factor and jerk.Overfilling at the sharp corner was found when the printhead velocity was kept constant while extruding mortar at a fixed extrusion velocity; however, proportional extrusion velocity with the printhead motion has improved the quality of the corner. Otherwise, a slight improvement in the corner shape related to applying a jerk was found.The Computational Fluid Dynamics (CFD) model could take an important amount of computing time to solve the problem; however, it serves as an efficient tool for accelerating different costly and time-consuming path planning processes for 3D concrete printing. Smaller angles and tilted printhead positions should be numerically and experimentally investigated in future research.The developed CFD model is suited for executing parametric studies in parallel to determine the appropriate printing motion strategy for each trajectory with corners.Computational Fluid Dynamics investigation of the path planning strategy for printing trajectory with a right-angle corner in 3D concrete printing.

Topologically Enabled On‐Chip THz Taper‐Free Waveguides

AbstractWaveguide tapers are seemingly indispensable elements in silicon photonics that usually operate adiabatically to maximize the coupling efficiency between waveguides with different cross‐sections, which, however, necessitate large footprints. To date, great efforts have been made to minimize the tapers’ footprints while maintaining their efficiency. Contrary to conventional wisdom, here, a concept of taper‐free waveguides is proposed in which waveguides with different cross‐sections couple with each other efficiently without using tapers, which are enabled by the recently discovered photonic topological phases. This concept is experimentally demonstrated on an all‐silicon on‐chip terahertz (THz) wave platform. It is further shown that the topologically enabled taper‐free waveguides are robust against sharp corners and large‐area potential barriers. This work provides a promising taper‐free solution for future compact optical/THz photonic integrated circuits.

Natural convection in platonic solids

Natural convection in enclosures is a phenomenon significantly affected by the geometry of the physical domain, however, comparing different formats is challenging because features such as the characteristic length varies with the geometry. This study proposes examining natural convection in 3D convex regular polyhedra, also known as Platonic solids, using the number of faces as a parameter. Differentially heated enclosures were analyzed to investigate the effect of shape on fluid flow and energy distribution. By comparing the different solids, it was found that the dodecahedron and the icosahedron exhibit very similar behaviors and tend to be the more efficient shapes for improving convection heat transfer. In contrast, the tetrahedron is much less efficient due to its structure, which does not favor the presence of a single convective cell. In general, increasing the number of faces, which leads to a more spherical shape and eliminates sharp corners, tends to enhance fluid recirculation and increase the average Nusselt number. For example, the icosahedron showed a 12% increase in the Nusselt number compared to the commonly studied hexahedron for Ra = 106. On the other hand, the tetrahedron demonstrated a 50% decrease in the Nusselt number relative to the cube, making it the least efficient shape among those evaluated.

Minimum-Lap-Time Planning of Multibody Vehicle Models via the Articulated-Body Algorithm

Minimum lap-time planning (MLTP) is a well-established problem in the race car industry to provide guidelines for drivers and optimize the vehicle’s setup. In this paper, we tackle the 3D nature of the problem in its full extension, making no simplifying assumptions on the mechanics of the system. We propose a multibody vehicle model, described by rigorous dynamical equations. To effectively handle the resulting complexity, we devised an efficient direct dynamics computational method based on Featherstone’s articulated-body algorithm (ABA). To solve the MLTP, we employed a direct-collocation technique, discretizing the problem so that all information of the 3D track is pre-processed and directly embedded into the discrete problem. This discretization approach turns out to be perfectly compatible with our vehicle model, leading to a solution in accessible computational time frames. The high level of detail of the model makes the proposed approach most useful for in-depth vehicle dynamics analyses on complex tracks. To substantiate the analysis, we provide a comparison with the results obtained by a double-track model on the Nürburgring Nordschleife circuit. Consistently with the average trend defined by the double track, the proposed model features a more dynamically rich behavior, realistically capturing the higher-order effects elicited by the sharp corners and the highly variable slope of the track.

Highly-efficient electrochemical rounding process of sharp corner improved by a tube electrode insulation method

Highly-efficient electrochemical rounding process of sharp corner improved by a tube electrode insulation method

Tunable topological phase transition in the telecommunication wavelength

Recent progress in the Valley Hall insulator has demonstrated a nontrivial topology property due to the distinct valley index in 2D semiconductor systems. In this work, we propose a highly tunable topological phase transition based on valley photonic crystals. The topological phase transition is realized by the inversion symmetry broken due to the refractive index change of structures consisting of optical phase change material (OPCM) with thermal excitation of different sites in a honeycomb lattice structure. Besides, simulations of light propagation at sharp corners and pseudo-spin photon coupling are conducted to quantitatively examine the topological protection. Compared with other electro-optical materials based on reconfigurable topological photonics, a wider bandwidth and greater tunability of both central bandgap frequency and topological phase transition can happen in the proposed scheme. Our platform has great potential in practical applications in lasing, light sensing, and high-contrast tunable optical filters.

Observation of Unidirectional Bulk Modes and Robust Edge Modes in Triangular Photonic Crystals

AbstractThe valley contrasting physics in photonic systems gives rise to many interesting phenomena such as photonic valley Hall effect and robust valley transport. However, most reported valley photonic crystals are demonstrated in the honeycomb lattice. Here, unidirectional bulk modes and robust edge modes are numerically and experimentally shown in triangular photonic crystals. By switching the phase vortex of an input chiral source, dynamic unidirectional propagation of bulk modes at different valleys is observed. Unidirectional edge modes are also demonstrated on the domain wall between two distinct triangular photonic crystals. In addition, robust edge modes around sharp corners are experimentally confirmed. This work paves the way for the realization of dynamic unidirectional photonic transport and robust valley transport in photonic crystals.

Numerical modeling and failure evolution of microstructure-based in-situ TiB2 and TiC+TiB2 reinforced Cu matrix composites

The optimal design of microstructure is the key to further improve the properties of particle reinforced metal matrix composites. In this study, in-situ TiB2 and TiC + TiB2 reinforced Cu matrix composites are used as examples to develop the microstructure-based representative volume element models to describe their damage evolution and strengthening mechanisms. The most critical features including size distribution and morphology of the particles as well as the fracture of metal matrix, brittle damage of ceramic particles and traction-separation debonding of the interface were integrated into the modeling. Simulation results show that the model could well predict the performance of the composite and reveal its damage mechanism. When the particle size is normally distributed, the composite exhibits higher strength due to the size effect of different particles, which is more consistent with the experimental result. Both matrix and ceramic particles in mixed-phase particle reinforced metal matrix composites can be subjected to higher stresses, which results in higher strength of (TiC + TiB2)/Cu composites. Additionally, the spherical TiC particles facilitate the relaxation of stress concentration within the composite, resulting in a synergistic enhancement of strength and ductility. Under compression, localized interface damage first appears around the sharp corners of the hexagonal particles and induces crack initiation toward the matrix. These microcracks are interconnected and propagate along the direction of high stress, eventually leading to the failure of the composite. This work provides the basis and new ideas to reveal the failure mechanism of composites and further optimize their configuration design.

Machine learning approach to the temperature gradient in the case of discontinuous temperature boundary conditions in a triangular cavity

In this study, a prediction for the temperature gradient close to the sharp corners on a right triangle having singularity is proposed utilizing statistical techniques. This singularity is a result of different Dirichlet types of boundary conditions at the corners. In most of the numerical methods, refinement on corners is done, and computational difficulty in gradient calculation is softened. However, the increased refinement results in a blow-up in the temperature gradient close to the problematic corner. A natural convection flow problem is concerned in a right isosceles triangle in two cases of singularity at the left top corner. In Case 1, the left vertical hot wall and the right inclined cold wall, and in Case 2 the left vertical cold wall and the right inclined hot wall are considered. In the present approach, input data is built from the numerical solution of the problem by cutting the region at a chosen cutting point where almost blow-up starts at the temperature gradient along the hot wall. Then, model functions are derived by using machine learning techniques either multivariate adaptive regression splines (Mars) in R project or Trilayer Neural Network (TNN) in Regression Learner Toolbox in Matlab. The obtained model function for the temperature gradient is used to predict the temperature gradient of points above the cutting point. Therefore, the temperature gradient along the hot wall is calculated by combining the temperature gradients of numerical-below and predicted-above. Average Nusselt number as an integral of the temperature gradient along the concerned hot wall is compared with a reference study, and good agreement is observed. That is, modeling of the temperature gradient on singular points is a way of approach for computing accurate results of the temperature gradient.

Fermi arc surface state and topological switch in the gyromagnetic metamaterials

A landmark feature of the Weyl system is that it possesses the Fermi arc surface states. In this work, we demonstrate that the Fermi arc surface states connect the vacuum state and the Weyl points of gyromagnetic metamaterials (GMs). The nonzero Chern numbers and Berry phases show the nontrivial topological property of the GMs in momentum space. Full-wave simulations demonstrate that the chiral surface waves on the boundary between the GMs and vacuum state can achieve robustness against sharp corners of step-type configurations. Remarkably, the topological switch can be realized by adopting the Fermi arc surface states between two different GMs. We theoretically prove that the physical mechanism of realizing topological switch is caused by different gap Chern numbers of the material system. Moreover, the direction of the topological switch can be operated by manipulating the gyromagnetic parameters of the GMs in the ‘button’ region. Our work may provide more flexibility for the flexible and robust topological devices.

Interfacial delamination of porous thermal barrier coatings based on SEM image processing in finite element model

Numerical analysis of interfacial delamination and the effect of microstructural pores and rough interfaces on the field variables in thermal barrier coatings (TBCs) based on a real scanning electron microscope (SEM) image is performed. The interfacial delamination is modelled by the utilization of cohesive zone method (CZM) in finite element (FE) analysis. The empirical TBC sample considered in this study is constructed via air plasma spray (APS) method and comprises ZrO27-8wt.%Y2O3 ceramic top coat (TC), thermally grown oxide (TGO) made of Al2O3 and NiCrAlY metallic bond coat (BC). A compatible geometry is provided by applying image processing technique to SEM image of the sample's cross-section. SEM image-based geometry imported into FE software to scrutinize the interplay effects of porosity and rough interfaces on temperature fields, thermal stresses and interfacial debonding of TC/TGO and TGO/BC interfaces of the TBC structure. FE analysis reveal that porosity distribution has a prominent role on the stress concentration zones at the sharp corners of pores especially adjacent to undulations of the TC/TGO interface, which is responsible for possible internal cracks and interfacial fracture, respectively. The main findings demonstrate that the porosity near the TC/TGO interface has detrimental effect as leads to aggravation in the TC/TGO interface damage, which causes an increment in TC/TGO interfacial crack length. While, the porosity within the BC has the ability to reduce the stress and damage level along the TGO/BC interface. In addition, considering creep for all layers leads to lower stress levels up to 24.82 % and consequently alleviates the TC/TGO interface damage.

Improvement of normal estimation for point clouds via simplifying surface fitting

During the last decade, stimulated by the roaring success of neural networks in the realm of point clouds, learning-based normal estimation has been a dominating direction and it has attained outstanding performance. The introduction of modern neural networks significantly enhances the robustness of algorithms to noise levels and sampling scales. A method that combines least-squares surface fitting with weight-learning neural networks is particularly prominent. Despite persistent efforts, there is room for improvement. We observed that a simplified surface-fitting process can significantly improve the accuracy of this type of hybrid approach. In this study, two simple yet effective strategies are proposed to boost the accuracy of normal estimation. Specifically, a dynamic Top-K selection strategy is presented to focus on the critical points of a given patch. The selected point hammer fits a local surface using a simple tangent plane, which improves the normal estimation accuracy when encountering patches with sharp corners or complex patterns. Moreover, to further improve the quality of the estimation, a point-update strategy was delicately designed to smooth the sharp boundaries of the patches before the local surface fitting process. Thus, our method can reduce the fitting distortion while simplifying the surface-fitting process. Extensive experiments and ablation studies demonstrated the superiority of our proposed method over contemporary state-of-the-art approaches.

Wear reliability and failure mechanism of inkjet-printed conductors on paperboard substrate

In this research, we conducted a wear test on inkjet-printed silver conductors using different loads and counter materials (two paperboards, brushed steel sheet, and sandpaper) with similar surface roughness values. The conductor’s reliability was characterized by resistance measurement, the failures and tested counter materials were analyzed using an optical microscope, profilometer, scanning electron microscope, and energy dispersive spectrometer. It was found that the counter material has a dominant impact on a conductor’s reliability and failure mechanism compared with load. The conductors were exceptionally reliable but subject to adhesive wear when tested by paperboards. They were also highly reliable when tested by brushed steel sheet although the silver became severely detached, and the conductivity was lost suddenly when a major scratch was caused by two-body and three-body abrasive wear mechanisms. Sandpaper rubbing caused the most severe silver detachment and quick loss of conductivity, as a large amount of small-size (5–15 µm) silicon carbide particles with sharp edges and corners caused a dense cutting effect via two-body abrasive wear (by cutting) mechanism. Additionally, the failures in almost all samples occurred in the areas in contact with the counter edges, suggesting that failure was accelerated by the edge effect. This study proves that inkjet-printed electronics on the investigated paperboard is exceptionally durable when rubbed by paperboards and steel sheets, and thus provides a reliable solution to intelligent packaging. To promote intelligent packaging, more paperboards, as well as approaches for reducing the edge effect can be investigated.