Presence Of Sharp Edges Research Articles

Optimization of Welded Joints under Fatigue Loadings

In this paper, the notch effect in weldments has been investigated, and the optimal configuration of different types of welded joints has been analysed using the implicit gradient approach. By considering this implicit gradient method, it is possible to calculate the effective stress related to fatigue damage, with the effective stress being a continuous scalar function of the real stress tensor components, even in the presence of sharp edges. Hence, the search for the optimal configuration that maximises fatigue life can be tackled as the condition of minimum effective stress obtained by changing the weld shape and geometrical parameters. Both load-carrying cruciform joints and spot welds made of steel have been considered. The structural details have been studied by modelling actual shapes without any geometric simplification. Moreover, the same numerical procedure has been considered independently of the size, shape or load condition without imposing restrictive rules on the FE mesh.

Semi-analytic solutions to edge singularities of three-dimensional axisymmetric bodies

Axisymmetric geometries, such as cylindrical elements, are widely used in offshore structures. However, the presence of sharp edges in these geometries introduces challenges in numerical simulations due to singularities. To address this issue, one possible solution is to represent the singularities using analytic eigenfunctions. This approach can provide insights into the essence of the problem and has successfully applied to two-dimensional (2D) corner problems. However, finding appropriate eigenfunctions for the three-dimensional (3D) edges remains an open challenge. This paper proposes a semi-analytic scheme for 3D axisymmetric problems utilizing a scaled boundary finite element method (SBFEM). A dimensional reduction is introduced to the 3D Laplace equation, and a 3D edge is handled on the generatrix plane while governed by a complicated equation. The algorithm for resolving the SBFEM fundamental space is improved, and the singularities are approximated using a fractional-order basis. The effectiveness of the proposed method is demonstrated through its application to solve the radiation problem of a heaving cylinder. The method accurately captures the singular velocity field at the edge tip, ensuring that the boundary condition on the body surface is strictly satisfied in the neighborhood of the singularity. Accuracy of the mean drift force is ensured by performing direct pressure integrations over the body surface using a near-field formulation, which becomes as accurate as the middle-field formulation.

Investigation of high-energy ultrasonication of RE 2BaCuO5 (RE = Y, Gd) on the growth and superconducting properties of REBa2Cu3O7−δ top-seeded melt textured bulks

Recently, an improvement in the flux pinning performance of REBa2Cu3O7−δ (REBCO) bulk was achieved employing high energy ultrasonic irradiation (up to 300 W and 60 min) prior to the infiltration-growth process. Here, we demonstrate that a higher ultrasonic power and shorter duration treatment (450 W for 30 min) of the RE 2BaCuO5 (RE211, RE= Y, Gd) powder produces individual, nanometer-sized and surface damaged RE211 particles (RE211Ultra). We study the growth of YBCO and GdBCO systems via the top-seeded melt-growth method, with the addition of 30 mol% of RE211Ultra, which were pre-treated by high-energy ultrasonication and compared with the conventional method. Isothermal growth experiments clarified that the addition of RE211Ultra particles enables faster and more effective crystal growth via an improved peritectic reaction due to their size in the nanometer range and presence of sharp edges, which are crucial for growing large, single grain bulks of REBCO. Microstructural investigations by scanning electron microscopy indicated the presence of two differently sized RE211 inclusions within the bulk GdBCO and YBCO superconductors. All samples showed an onset of superconductivity at ∼92 K or above. Utilizing the effective growth temperature window and the addition of RE211Ultra, single grain bulks of GdBCO and YBCO were fabricated by the slow-cooling method. The field dependent critical current density (J c) of the bulk samples using RE211Ultra were found to exhibit superior performance over the standard GdBCO/YBCO samples due to significant changes of sample growth and of their microstructures. Here, we discuss various factors affecting the addition of RE211Ultra on the development of the microstructure, growth of bulk, single grain materials and further, the superconducting properties of different REBCO superconductors.

‘CADSketchNet’ - An Annotated Sketch dataset for 3D CAD Model Retrieval with Deep Neural Networks

Ongoing advancements in the fields of 3D modelling and digital archiving have led to an outburst in the amount of data stored digitally. Consequently, several retrieval systems have been developed depending on the type of data stored in these databases. However, unlike text data or images, performing a search for 3D models is non-trivial. Among 3D models, retrieving 3D Engineering/CAD models or mechanical components is even more challenging due to the presence of holes, volumetric features, presence of sharp edges etc., which make CAD a domain unto itself. The research work presented in this paper aims at developing a dataset suitable for building a retrieval system for 3D CAD models based on deep learning. 3D CAD models from the available CAD databases are collected, and a dataset of computer-generated sketch data, termed ‘CADSketchNet’, has been prepared. Additionally, hand-drawn sketches of the components are also added to CADSketchNet. Using the sketch images from this dataset, the paper also aims at evaluating the performance of various retrieval system or a search engine for 3D CAD models that accepts a sketch image as the input query. Many experimental models are constructed and tested on CADSketchNet. These experiments, along with the model architecture, choice of similarity metrics are reported along with the search results.

Reconfigurable Floquet elastodynamic topological insulator based on synthetic angular momentum bias.

Originating with the discovery of the quantum Hall effect (QHE) in condensed matter physics, topological order has been receiving increased attention also for classical wave phenomena. Topological protection enables efficient and robust signal transport; mechanical topological insulators (TIs), in particular, are easy to fabricate and exhibit interfacial wave transport with minimal dissipation, even in the presence of sharp edges, defects, or disorder. Here, we report the experimental demonstration of a phononic crystal Floquet TI (FTI). Hexagonal arrays of circular piezoelectric disks bonded to a PLA substrate, shunted through negative electrical capacitance, and manipulated by external integrated circuits, provide the required spatiotemporal modulation scheme to break time-reversal symmetry and impart a synthetic angular momentum bias that can induce strong topological protection on the lattice edges. Our proposed reconfigurable FTI may find applications for robust acoustic emitters and mechanical logic circuits, with distinct advantages over electronic equivalents in harsh operating conditions.

Comparison of the finite strain macroscopic behavior and local damage of a soft matrix highly reinforced by spherical or polyhedral particles

Motivated by the different uniaxial responses of two actual materials filled with either sifted glass beads or sifted glass grits, the influence of the fillers shape on the finite strain behavior of highly filled composites (>50%) is examined through micromechanical finite element simulations accounting for matrix/filler debonding with a cohesive-zone model. Three-dimensional matrix cells filled with 64 monosized spherical particles are compared to cells filled with the same number of monosized polyhedra. For this purpose, an original generation process was developed to obtain periodic cells with random dispersions of non-regular polyhedra. Finite element simulations of uniaxial tensile tests on the periodic cells allow studying the influence of the fillers shape on the macroscopic behavior and on the local damage at the matrix/filler interfaces. Actually, the presence of sharp edges and apexes for polyhedral particles seems to have a second order impact compared to the cohesive-zone parameters. The damage fields demonstrate the same trends for both particles shapes. The different behaviors observed on actual composites are rather due to different adhesion properties between fillers and matrix than to the shape of particles.

1753 An “Eggstra-Ordinary” Cause of Esophageal Food Impaction: Esophageal Eggshell Food Impaction

INTRODUCTION: Food bolus impactions are commonly encountered GI emergencies, often from impacted meat. We report two patients with esophageal eggshell impaction who presented predominantly with chest pain and odynophagia. CASE DESCRIPTION/METHODS: Case 1: An 88-year-old female with a history of gastroesophageal reflux disease, prior hiatal hernia repair, and intermittent dysphagia to solid food presented to the emergency department with intermittent severe, sharp chest and epigastric pain that occurred with swallowing 30 minutes after eating a hard-boiled egg. The patient could not handle secretions due to dysphagia and had several episodes of non-bloody emesis. Chest x-ray was unremarkable. Gastroenterology was consulted, and she underwent EGD. A rectangular piece of eggshell was found in the middle third of the esophagus. The eggshell was grasped with standard forceps and pushed into the stomach without difficulty. No esophageal lesions or erosions were noted in the esophagus. Case 2: A 26-year-old female with a history of chronic intermittent reflux symptoms presented to the emergency department with sharp midsternal chest pain upon swallowing that started after she drank egg whites. She was found to have an elevated D-dimer, and a CT Angiogram Chest was obtained in the emergency department which revealed a calcified foreign body within the mid-esophagus at the level of the carina. The patient denied any history of dysphagia. Her physical exam was unremarkable. Gastroenterology was consulted, and EGD was performed, showing a piece of eggshell, which was extracted using rat tooth foreign body forceps. The patient had a healthy mucosal appearance of the esophagus. DISCUSSION: Eggshell food impaction is rarely documented in the literature. In both cases, we describe, chest pain/odynophagia as a predominant symptom, although one patient did describe concomitant dysphagia. The eggshell foreign body was visible on a CT scan, perhaps due to the calcified nature of the shell. Thus, this calcified eggshell could potentially be mistaken for an impacted bone fragment in the esophagus on imaging studies. However, the eggshell was not seen on a routine chest x-ray in the other case. Endoscopic management was achieved by grasping the eggshell with standard forceps and pushing the eggshell into the stomach by extraction of the eggshell using foreign body forceps. Neither patients exhibited erosions caused by the impacted eggshell, despite the presence of sharp edges.

Dynamics of Laser Ablation in Superfluid $$^4\hbox {He}$$

Pulsed laser ablation of metal targets immersed in superfluid $$^4\hbox {He}$$ is visualized by time-resolved shadowgraph photography and the products are analyzed by post-experiment atomic force microscopy (AFM) measurements. The expansion dynamics of the gaseous ablation half-bubble on the target surface appears underdamped and follows the predicted behavior for the thermally induced bubble growth mechanism. An inherent instability of the ablation bubble appears near its maximum radius and no tightly focused cavity collapse or rebound events are observed. During the ablation bubble retreat phase, the presence of sharp edges in the target introduces flow patterns that lead to the creation of large classical vortex rings. Furthermore, on the nanometer scale, AFM data reveal that the metal nanoparticles created by laser ablation are trapped in spherical vortex tangles and quantized vortex rings present in the non-equilibrium liquid.

Deep Learning for Robust Normal Estimation in Unstructured Point Clouds

AbstractNormal estimation in point clouds is a crucial first step for numerous algorithms, from surface reconstruction and scene understanding to rendering. A recurrent issue when estimating normals is to make appropriate decisions close to sharp features, not to smooth edges, or when the sampling density is not uniform, to prevent bias. Rather than resorting to manually‐designed geometric priors, we propose to learn how to make these decisions, using ground‐truth data made from synthetic scenes. For this, we project a discretized Hough space representing normal directions onto a structure amenable to deep learning. The resulting normal estimation method outperforms most of the time the state of the art regarding robustness to outliers, to noise and to point density variation, in the presence of sharp edges, while remaining fast, scaling up to millions of points.

Modeling Junctions in Sharp Edge Conducting Structures With Higher Order Method of Moments

Scattering targets are often made by complex structures constituted by thin metallic plates as wings, fins, winglets. When thin plates are connected together, they define surface junctions with the possible presence of sharp edges. In this paper we describe a complete procedure to handle junctions in presence of sharp edges in surface integral equation methods by defining the required basis functions and unknowns. This approach is based on the use of divergence-conforming higher order interpolatory vector basis functions, singular vector basis functions and on Kirchhoff's current law. The paper presents several numerical test cases that show the instability of solutions using classical methods and the full convergence of the proposed numerical scheme.

Implementation Methods of Wall Functions in Cell-vertex Numerical Solvers

Two different implementation techniques of wall functions for cell-vertex based numerical methods are described and evaluated. The underlying wall model is based on the classical theory of the turbulent boundary layer. The present work focuses on the integration of this wall-model in a cell-vertex solver for large eddy simulations and its implications when applied to complex geometries, in particular domains with sudden expansions (more generally in presence of sharp edges). At corner nodes, the conjugation of law of the wall models using slip velocities on walls and of the cell-vertex approach leads to difficulties. Therefore, an alternative implementation of wall functions is introduced, which uses a no-slip condition at the wall. Both implementation methods are compared in a turbulent periodic channel flow, representing a typical validation case. The case of an injector for aero-engines is presented as an example for an industrial-scale application with a complex geometry.

Modified electron-beam-induced deposition of metal nanostructure arrays using a parallel electron beam

A modified electron-beam-induced deposition method using a parallel beam of electrons is developed. The method relies on the buildup of surface potential on an insulating surface exposed to an electron beam. Presence of sharp edges on the insulating surface implies presence of large electric fields that lead to site-specific nucleation of metal vapor on those regions. Feature sizes as small as 20nm can be deposited without the need to use fine probes, and thus the limitation of probe size imposed on the resolution is overcome. The use of pure metal vapor also renders the process inherently clean.

Synthesis and Optical Properties of Gold Nanodecahedra with Size Control

The synthesis of nanoparticles with a tight control on their size and shape is a requirement for the achievement of many nanotechnology goals, since these are the main parameters determining the material properties at the nanoscale. Among the many different materials currently under investigation, semiconductor and metal nanoparticles are extremely attractive because of the possibility of controlling their electronic and optical properties through tailoring size and shape during synthesis. For instance, the presence of sharp edges or tips has been shown to increase electric-field enhancement, [1] which is important for applications involving metal nanoparticles as sensors. Additionally, nanoparticle morphology will ultimately determine the way in which nanoparticles can be assembled. While spheres, rods, cubes, and flat prisms are the most thoroughly studied shapes, there have been several reports on the synthesis and detailed characterization of other geometries, and it is believed that metal nanoparticles tend to grow with the structure of one of the Platonic solids, that is, with all faces made of the same regular polygon and the same number of polygons meeting at each corner. [2–4] Non-Platonic structures that have been reported for metal nanocrystals include nanorods, either with the geometry of single-crystal or pentatwinned prisms, [5–9] as well as flat platelets, usually with triangular or hexagonal shape, [10–13] in which faces are made of more than one polygon. Recently, other elaborate geometries have also been reported, such as nanocages [14] or nanostars. [15] In this paper we report the synthesis with tight size control and high monodispersity of nanometer-sized, uniform gold nanoparticles with decahedral morphology, in which all ten faces are equilateral triangles, but not the same number of triangles meet at every corner (four or five are possible), and for this reason they do not qualify as Platonic nanocrystals, but can rather be classified as Johnson structures. These decahedral particles have a lower symmetry (D5h) than Platonic solids, but still display a striking beauty and attractive optical properties that are strongly influenced by particle size. Although the geometry (and thus the aspect ratio) is precisely the same for particles with different sizes, clear changes in the optical responses have been observed and modeled through a boundary element method (BEM) for bicones. The synthesis is based on our previous work where N,N-dimethylformamide (DMF) was used as both solvent and reducing agent [16] to generate silver nanoparticles of various shapes, including spheres, [17] nanoprisms [18] and nanowires. [19] The

Electronic intertube transfer in double-wall carbon nanotubes

Effects of intertube interactions on transport are studied numerically in incommensurate double-wall carbon nanotubes. The intertube transfer at each lattice site oscillates around zero in a complex plane as a function of position in a quasiperiodic manner and therefore cancels each other when being summed up. The cancellation is not perfect in the presence of sharp edges, giving rise to an intertube conductance much smaller than ${e}^{2}∕\ensuremath{\pi}\ensuremath{\hbar}$ and determined by the structure at edges. The conductance exhibits a wild and almost irregular oscillation as a function of the length with average and fluctuations independent of the length due to the change of the edge structure.

Failure of suture material at suture anchor eyelets

Purpose: In the repair of soft tissue to bone using suture anchors, failure of the suture material can occur at the anchor eyelet. This study examines the load strength at which suture material fails with different metallic suture anchor eyelets. Type of study: Biomechanical study. Methods: Suture material (Ethibond No. 2, Ethicon, Norderstedt, Germany) was pulled out from 22 metallic suture anchor models at 60 mm/min, and tensile load at failure and failure mode were recorded. Tests were performed either by simultaneous pulling on 2 suture limbs in 3 different directions (straight, at 45°, and at 45° rotated by 90° to the suture anchor axis) or by pulling on 1 suture limb while measuring the resulting force on the second limb. All tests were performed until suture failure. Pulling was performed in single tests on an Instron materials testing machine (High Wycombe, UK), with the anchors held by a vise. Results: In all cases, the suture failed at the anchor eyelet. Failure load at straight loading ranged from 116 ± 5 N to 226 ± 5 N and from 69 ± 5 N to 193 ± 7 N when loaded at an angle of 45°. The best results were found with the Statak 5.2-mm (Zimmer, Warsaw, IN): 177 N; Corkscrew 6.5-mm anchor (Arthrex, Naples, FL): 174 N; and PeBA 4.0-mm anchor (OBL Orthopaedic Biosystems, Scottsdale, AZ): 169 N. With each eyelet, sutures failed preferentially in 1 direction, depending on the presence of sharp edges. Conclusions: Suture material can be cut at suture anchor eyelets. Failure load depends on sharp edges on the eyelet and occurs at forces up to 73% below the breaking strength of the suture material on a smooth hook. Anchors with suture-protecting channels are particularly sensitive to the orientation in which the sutures are loaded.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 9 (November- December), 2002: pp 1013–1019

A comparison of scalar singular finite elements applied to the analysis of homogeneous waveguides with sharp edges

When we solve the wave equation by the finite element method, the order of convergence and the accuracy of the solution are reduced by the presence of sharp edges. The employment of singular elements improves the solution and allows us to reduce the cost of computation. In this paper, three types of scalar singular finite elements with the capacity to handle singularities in the derivative, and which have previously been applied to mechanical problems, are examined, together with standard elements, in the context of homogeneous waveguide analysis. We solve two examples of homogeneous waveguides showing the different behaviour of the singular elements and obtaining information on the order of convergence and the approximation of the gradient of the unknown function. © 1997 John Wiley & Sons, Ltd.

Strategies for Evaluating Boundary Fractal Dimensions by computer aided image analysis

AbstractFor many profiles the values of the boundary fractals deduced by different exploration techniques are identical but the presence of deep fissures of convoluted structure can perturb the information gathered by the exploration technique. Data for different boundaries generated by different exploration techniques are used to illustrate the physical significance of the deduced fractal dimensions as evaluated using the different techniques. Heuristic programs for teaching an automated instrument to distinguish between different regions of ruggedness around a profile and to prevent “fractal rabbits” from appearing in the data are outlined. It is shown how the logic for removing fractal rabbits from the experimental data will also generate data on the presence of sharp edges on the profile. The possible occurrence of pseudo‐texture fractal dimensions from projection occlusion is discussed.

Oscillating and non-oscillating contributions in the Porod law

Experimental Ih 4 plots often show damped oscillating terms. The first non-oscillating term describing the interface curvature effects is given by the Kirste-Porod formula for regular surfaces. It provides a positive h -2 contribution to Ih 4 . In the presence of sharp edges and vertices on otherwise planar interfaces an additional negative h -2 term occurs. A cylinder cutted following a planar section parallel to its axis provides the simplest situation where oscillating, positive and negative h -2 terms have to be simultaneously token into account. The three additional asymptotic contributions to Ih 4 are evaluated. The exact correlation function is calculated. The difference between its fourier transform and the asymptotic intensity yields an estimate of the neglected contribution using the asymptotic expansion. The modification of the oscillating Ih 4 pattern resulting from the positive and negative h -2 contributions is examined

Temporal contrast sensitivity and speckled fields: effect of field size

On comparing the temporal contrast sensitivity functions TCSF obtained with and without speckle, a significant decrease in sensitivity can be observed in the presence of speckle. In the low temporal frequency zones this loss of sensitivity was due to a loss of sharpness in the test edges as a result of speckle. This possibility was tested by comparing the TCSF with and without speckle, for several observation field sizes (1, 2, 5 and 20 degrees ). If the presence of sharp edges improves sensitivity, speckle could be expected to have less effect when large fields are involved, since these fields have edges which lie beyond the region where the eye is capable of good spatial resolution. The results confirm this assumption: differences in sensitivity decrease considerably in the cases studied, both with and without speckle, when field size increases.

Measurement of the Mean Pressure Distribution About a Double-wedge Strut in Turbulent Shear Flow

SummarySurface pressure distributions have been measured on a cylinder with a double-wedge cross section in a two-dimensional channel flow. The flow is sheared in the direction of the cylinder axis, using a grid of parallel wires with variable spacing, in order to simulate the type of geometry and velocity variation which occur for annulus support struts in turbomachines. The strut had a 38° included angle at the leading and trailing edges and an aspect ratio of 1.33 based on the maximum thickness. This was fixed between the parallel walls of a rectangular wind tunnel with end leakage eliminated. Surface pressure distributions were measured over a Reynolds number range of 0.5 × 105 to 1.5 × 105 for three different shear flow conditions. Despite the presence of sharp edges at the mid-chord position, delayed boundary-layer separation beyond the plane of maximum thickness has been found for sufficiently high spanwise shear in the upstream flow. Surprisingly, therefore, some similarity with previous results for struts of circular cross section appears to exist. The influence of the shear flow conditions on the pressure drag force has been determined by numerical integration of the data. Only a slight dependence on the upstream flow conditions is found, although the effect of secondary velocity components may still be observed if the spanwise variations in the local drag force are examined.