Corner Angle Research Articles

Optimal trajectory smoothing for direct energy deposition additive manufacturing processes

In free form additive manufacturing processes (e.g., metal blown powder, glass filament, ceramic paste extrusion), part quality depends on both the rate at which the part is built and where material is deposited. This creates a natural conflict between these two criteria at locations where the curvature of the programmed path is small, such as corners, because at these locations it is not possible to precisely follow the path without changing acceleration and, hence, varying the part build rate due to the variation in path velocity. In some additive manufacturing processes it is not possible to easily vary the material feed rate to maintain a constant part build rate when path velocity varies; thus, uneven material deposition occurs. In this work an optimal trajectory smoothing methodology is created that formulates the path following problem as an optimal dynamic system boundary value problem. The methodology naturally allows a trade-off between path following error and velocity error and is experimentally applied in a blown powder direct metal deposition additive manufacturing process. The results show that path and velocity errors increase as the corner angle decreases and the velocity entering the corner increases; however, they can be decreased by increasing the corner's leg length. Further, as the weight on velocity error increases, the velocity error, excess deposited material, and total print time decrease asymptotically while path error increases asymptotically.

Three-dimensional bubble jetting inside a corner formed by rigid curved plates: Boundary integral analysis

Three-dimensional dynamics of a transient bubble inside a corner formed by two rigid curved parabolic plates (walls) is studied numerically using boundary integral method (BIM) based on the potential flow theory. The bubble dynamics, including the expansion and collapse phases until the jet impact, are investigated for different corner angles associated with different focal lengths k of the parabolas. However, for all the simulations, the dimensionless initial vertical standoff distance of the bubble’s center from the corner edge (h∗) is fixed at 4. The bubble remains almost spherical during expansion, except for parts of its surface that flattens near the walls. When the bubble is initiated at the bisector plane of the two intersecting walls, it oscillates symmetrically with respect to the bisector plane and becomes oblate during the late stages of the collapse phase. A high-speed liquid jet forms towards the end of bubble collapse, pointing to the corner. If the corner angle decreases, the bubble becomes more oblate along the bisector plane making the ensuing liquid jet wider and slower. In addition, a bubble initiated closer to one of the two walls is mainly influenced by the closer wall, oscillates non-symmetrically with respect to the bisector plane and the liquid jet formed in this case is inclined towards the closer wall due to the greater Bjerknes force of that wall.

Odd-viscosity-induced passivation of Moffatt vortices

Odd viscosity is associated with a number of striking physical phenomena: a disk rotating in a viscous liquid experiences a normal compressive or tensile stress depending on its sense of rotation; chiral active matter interfacial deformations level off in a manner akin to surface tension; and unstable thermocapillary films become stabilized. In this article we show that odd viscosity decreases the size and intensity of Moffatt vortices in a corner formed by a solid substrate and a free interface. The effect is present because odd viscosity creates a normal-stress-induced shear stress at the liquid–gas interface. The new shear stress is out of phase and oppositely directed with respect to the interfacial liquid velocity. It squeezes the vortices and damps their rotation. As a consequence, Moffatt vortices can now be observed with greater facility in an experiment. Odd viscosity also increases the range of corner angles over which Moffatt vortices can be observed, and, in general, it shows a tendency to moderate singular behaviour.

Elasto-Inertial Particle Focusing in Microchannel with T-Shaped Cross-Section

Recently, particle manipulation in non-Newtonian fluids has attracted increasing attention because of a good particle focusing toward the mid-plane of a channel. In this research, we proposed a simple and robust fabrication method to make a microchannel with various T-shaped cross-sections for particle focusing and separation in a viscoelastic solution. SU-8-based soft lithography was used to form three different types of microchannels with T-shaped cross-sections, which enabled self-alignment and plasma bonding between two PDMS molds. The effects of the flow rate and geometric shape of the cross-sections on particle focusing were evaluated in straight microchannels with T-shaped cross-sections. Moreover, by taking images from the top and side part of the channels, it was possible to confirm the position of the particles three-dimensionally. The effects of the corner angle of the channel and the aspect ratio of the height to width of the T shape on the elasto-inertial focusing phenomenon were evaluated and compared with each other using numerical simulation. Simulation results for the particle focusing agreed well with the experimental results both in qualitatively and quantitatively. Furthermore, the numerical study showed a potential implication for particle separation depending on its size when the aspect ratio of the T-shaped microchannel and the flow rate were appropriately leveraged.

Optimization of Machining Parameters for Corner Accuracy Improvement for WEDM Processing

Corner accuracy occurring in wire electrical discharge machining (WEDM) is influenced by machining parameters such as wire vibration, wire lag, and excessive discharge, etc. This study proposed an optimization method which can improve the corner accuracy of the WEDM process. The parameters of pulse-on time (ON), pulse-off time (OFF), open circuit voltage (OV), servo voltage (SV), wire tension (WT), and flushing pressure (WA) were selected to investigate the influences of the major parameters on the machining accuracy in this study. Three different corner angles of 30°, 60°, and 90° were chosen for the verification experiments. The response surface methodology (RSM) was used to analyze and investigate the effect of each parameter on the corner error. After integrating the response surface value and algorithm, an optimization system with a friendly human–machine interface, which has a procedure guiding function, was developed with use of C# language. The system can predict the corner error and also recommend optimal machining parameters for smaller corner error and faster machining speed based on the original machining parameters. Finally, cutting experiments were conducted to verify the proposed system, and the results showed that the proposed method can effectively improve the corner accuracy by 39%, 20%, and 33%.

Numerical simulation and experimental validation of deposited corners of any angle in direct ink writing

Direct ink writing (DIW) belongs to material extrusion–based additive manufacturing (MEAM), and the molding quality of deposited corners has an impact on the geometrical quality of three-dimensional (3D) parts fabricated by DIW. To fully understand the DIW process and improve the geometrical quality of parts, numerical simulations have been widely used to model the DIW process. However, the previous research works for numerical simulation of deposited corners could only achieve the corner simulation under the condition of small angle and failed to realize corner simulation of any angle. Herein, an improved numerical simulation of deposited corners of any angle is proposed based on the use of volume of fluid (VOF) method and then the simulation is validated experimentally. In the numerical simulation, deposited corner is realized by constructing two calculation areas where two nozzle velocities with the corner angle are applied on the substrates of two calculation areas. The effectiveness of the proposed numerical model is validated through corner deposition experiments using a commercially available microcrystalline wax (MW)-based ink in a DIW 3D printer as the simulated corner angles fit experimental angles well and the maximum value of maximum distance deviation between simulated and experimental outlines (MDDSEO) is 1.06 ± 0.06 mm. It was observed that the MDDSEO of corners is larger than MDDSEO of straight filaments and decreases as corner angle increases. The current work demonstrates an effective approach for the prediction of the deposited corners of any angle in DIW based on numerical simulations.

Does elastic stress modify the equilibrium corner angle?

We consider the influence of elasticity and anisotropic surface energy on the energy-minimizing shape of a two-dimensional void under biaxial loading. In particular, we consider void shapes with corners for which the strain energy density is singular at the corner. The elasticity problem is formulated as a boundary integral equation using complex potentials. By incorporating the asymptotic behavior of the singular elastic fields at corners of the void, we develop a numerical spectral method for determining the stress for a class of arbitrary void shapes and corner angles. We minimize the total energy of surface energy and elastic potential energy using calculus of variations to obtain an Euler-Lagrange equation on the boundary that is coupled to the elastic field. The shape of the void boundary is determined using a numerical spectral method that simultaneously determines the equilibrium void shape and singular elastic fields. Our results show that the precise corner angles that minimize the total energy are not affected by the presence of the singular elastic fields. However, the stress singularity on the void surface at the corner must be balanced by a singularity in the curvature at the corner that effectively changes the macroscopic geometry of the shape and effectively changes the apparent corner angle. These results reconcile the apparent contradiction regarding the effect of elasticity on equilibrium corner angles in the results of Srolovitz and Davis (2001) and Siegel, Miksis and Voorhees (2004), and identify an important nontrivial singular behavior associated with corners on free-boundary elasticity problems.

Coordinated effect of microstructure and defect on fatigue accumulation in dual-phase Ti-6Al-4V: Quantitative characterization

Fatigue accumulation in dual-phase Ti-6Al-4V is strongly associated with the combined effects of microstructure and defects in itself, which is experimentally challenging to be characterized and quantified. Based on crystal plasticity finite element method (CPFEM), the present work aims to address the coordinated effect of microstructure and defect on fatigue behavior in Ti-6Al-4V, highlighting the influence of morphology and orientation of defects, in conjunction with the designated idealized microstructure. In light of these considerations, a modelling strategy is proposed to focus on defect morphology and orientation in polycrystalline RVE models. Firstly, the geometric roundness parameter is adopted to characterize the diverse defect morphology and is quantitatively correlated with the characteristic of fatigue accumulation in Ti-6Al-4V. Secondly, a liner relationship with respect to corner angle and plastic deformation is formulated to characterize the influence of defect orientation, reflecting the microstructural heterogeneity in dual-phase Ti-6Al-4V. The proposed modelling strategy overcomes the experimental limitation on characterizing the complex effect of microstructure and defect, holding the potential of revealing fatigue mechanism around defects in metal alloys.

Fabrication and quality analysis of angle composite part by vacuum-bag-only process with interleaved woven fiber/prepreg layup

This study used the vacuum-bag-only (VBO) process to fabricate angle composite parts with interleaved layup of prepreg and dry fibers. The quality of angle parts is investigated by statistical methods, which are divided into two parts: geometric characteristics and internal characteristics. The results indicated that the part fabricated by the convex mold presented higher dimension stability and uniformity as compared to that by the concave mold. According to the results, increasing the laminate thickness and decreasing the angle mold could effectively reduce the corner thickness deviation and angle deviation percentages. In addition, the lead caul plate could effectively improve the thickness change in the corner area in both the concave and convex molds, and both the lead and Si-rubber caul plates could significantly reduce the angle deviation. For the internal characteristics, to quantify the void content of the laminate, we propose a scoring mechanism to analyze angle part. The part fabricated by the convex mold has a higher score than that by the concave mold. In order to fully understand the thickness variation of the part at the corner region, a semi-empirical model was proposed to calculate the corner thickness deviation in different mold geometry and stacking thickness. In this study, the prediction errors of the semi-empirical model for the parts by the concave and convex molds are 17.6% and 16.1%, respectively. The results of this research can also be extended to other VBO processes with more complicated geometries and provide advice and guideline on mold design and process conditions.

Influence of shear stress state on dynamic fracture of a glass ceramic Macor

The effect of shear stress on the dynamic failure of ceramic materials is not sufficiently investigated in the published literature. With the use of a bespoke split Hopkinson pressure bar, this paper presents an effort to investigate the dynamic shear compressive response of Macor, a model ceramic material with zero porosity and light weight characteristics. A cone specimen and cylindrical specimens with varying inclined angles are used to introduce the shear stress to the Macor ceramic. The dynamic failure initiation and crack propagation are monitored by the high speed photography and Digital Image Correlation techniques. It is found that the equivalent stress of Macor at the initiation of failure decreases nonlinearly with the increase of shear stress. The high speed images show that the crack originates from the minimum cross-section of the cone specimen and the obtuse angle corner of the inclined cylindrical specimens. The cracks propagate parallel to the inclined plane instead of the axial loading direction. The fractographic analysis shows the compacted zone in the shear fracture surfaces of the cone specimen and the inclined cylindrical specimens. This indicates a significant role of shear loading in the dynamic failure process of Macor.

Examining the relationship between gas channel dimensions of a polymer electrolyte membrane fuel cell with two-phase flow dynamics in a flooding situation using the volume of fluid method

Liquid structures such as droplets and slugs exist inside gas channels of polymer electrolyte fuel cells in low-temperature applications. The efficiency of these electrochemical devices depends on the effective removal of the produced water. The gas channels’ specifications like section geometry, corner angles, and surface wettability properties substantially control the liquid removal process. Here, five channels with various section geometries are modeled and the liquid-slug discharge process is investigated using a transient volume of fluid method. The numerical model consists of a segment of the cathode-side gas channel with the working conditions of an operational fuel cell. The dynamic two-phase flow simulations show that channels with smaller width and height eventuate in proper flow distribution at the gas feed. A channel with the sectional dimensions of 0.5 mm × 0.5 mm results in. 35.18% faster GDL (Gas-Diffusion Layer) clearance, 29.32% faster liquid expulsion compared to other channels having 2–3 times higher dimensions. Therefore, this channel is recommended as the best design for improved fuel cell performance.

Research on the Simulation Model of Continuous Fiber-Reinforced Composites Printing Track.

The rapid development of additive manufacturing technology (AM) is revolutionizing the traditional continuous fiber-reinforced polymer (CFRP) manufacturing process. The combination of FDM technology and CFRP technology gave birth to continuous fiber reinforced thermoplastic composites (CFRTPC) 3D printing technology. Parts with complex structure and excellent performance can be fabricated by this technology. However, the current research on CFRTPC printing mainly focuses on printing equipment, materials, and the improvement of mechanical properties. In this paper, the CFRTPC 3D printing track errors are investigated during the printing process, and it is found that the polytetrafluoroetylene (PTFE) tube in the nozzle of the printer head is often blocked. Through detailed analysis, a line-following mathematical model reflecting the deviations of the CFRTPC printing track is established. According to the characteristics of the fiber and its track during actual laying, a modified line-following model, without the minimum curvature point, is further proposed. Based on this model, the actual printing track for the theoretical path is simulated, the process tests are carried out on the printing track at different corner angles, and the relevant rules between the parameters of the model and different corner angles are obtained. The mathematical model is verified by experiments, and the clogging problem of the printer head caused by the fiber track error is solved, which provides theoretical support for the rational design of the fiber track in CFRTPC printing.

Caterpillar-Inspired Insect-Scale Climbing Robot Using Dry Adhesives

Surface-to-surface transitions, vertical and inverted locomotion, and high payload capacity are important requirements for a climbing robot. Despite many previous approaches, the miniaturization of climbing robots that satisfy these requirements is still a big challenge. In this letter, we present an insect-scale wheeled climbing robot that employs a low-cost dry adhesive technology. The design, inspired by caterpillars, consists of 2 main links that are connected by a pivot joint. The prototype robot measures a length of 40 mm and a width of 10 mm, and it weighs 1.7 g. On a horizontal surface, the robot moves with a speed of 12.3 mm/s and can drag a load weight of 10 g (six times its weight) at a speed of 4 mm/s. The high torque-to-weight ratio achieved by two micro-geared ultrasonic motors permits vertical and inverted locomotion while carrying a high payload capacity (120% of the robot’s weight). The locomotion strategy for surface-to-surface transitions, i.e., movements at right angle corners, is substantiated by the functionality of the pivot joint. To satisfy the design requirements, many dry adhesive tapes are evaluated, and the climbing robot with an appropriate adhesion force is demonstrated.

Effect of Anisotropy on the Quality of Laser Cutting Corner of CFRP Plate

Abstract Carbon fiber reinforced polymer (CFRP) composites are widely used in the aerospace field because of their outstanding performance. Laser is an effective method for CFRP composite processing. However, there are corner errors and obvious thermal damage in laser corner cutting, which affect the cutting quality. This article mainly describes the corner error and thermal damage behavior, and the effect of anisotropy of nanosecond UV laser when cutting different corners of CFRP plates. Select six corner angles to perform a full factorial experiment with a right-angled triangle hole cutting under the horizontal and vertical baselines and different laser repetition rates. The results show that there are obvious corner errors and heat affected zone (HAZ) and matrix recession (MR) in laser corner cutting. The corner error always shows that the cut-in error is smaller than the cut-out error (28.06% on average), and the cut-in error and HAZ decrease with the increase of the corner angle, but the difference between the cut-in and the cut-out error increases with the increase of the corner angle. In vertical baseline cutting, the corner error can be reduced to a certain extent, but the HAZ (average 38.42%) is seriously increased, and the thermal damage of linear cutting under a large pulse repetition rate is increased. The large laser repetition rate increases the thermal damage due to the increase of the overlap rate of adjacent pulses but has less effect on the corner error, especially the cut-in error.

Mechanisms of performance degradation in a double-suction centrifugal pump under inflow distortions

Inlet pipes of the centrifugal pump are generally bent to fit in the limited installation space, which can cause inflow distortions for two sides of the double-suction impeller. This study aimed to understand the effect of primary geometric parameters of inlet pipes, including corner angle, straight pipe length downstream of elbow, and turning radius, on pump performance and pressure fluctuations. The pump head, efficiency, and pressure fluctuations were measured for six kinds of inlet pipes in the experiment. Unsteady numerical simulations were performed to understand the flow mechanisms. Results indicate that the bending of inlet pipes is a significant reason for the loss of pump head and efficiency. The penalty on pump performance is augmented by the increase in corner angle, decrease in turning radius, and installation of a short straight pipe downstream of the elbow. Pump efficiency could be maximally reduced by 6.58% with a large corner angle and a small turning radius. The bending of inlet pipes induces pressure imbalance for the two sides of the impeller and increases low-frequency disturbance in the suction chamber, which are responsible for the performance loss. Numerical results reveal that the low-frequency disturbance is caused by the vortex formed in the suction chamber, and the accompanying secondary vortex aggravates the pressure fluctuation synchronously. Parametric studies conclude that the corner angle should be minimized to reduce the penalty on pump performance and pressure fluctuations, and a long straight pipe downstream of the elbow can be installed to decrease vibration for the pump with bent inlet pipes.

P‐108: Study of Trace Mura in ADS LCD

When the picture of L255 is pressed or slid, the cell gap is changed and the arrangement of liquid crystal molecules(LC) is disordered, resulting in the decrease of the brightness of the corresponding position, which cannot be recovered within the specified time (≤5s), it is called trace Mura. In this paper, the principle of trace Mura is introduced in detail, and a new simulation model is proposed. Using TechWiz software, the risk of trace Mura can be accurately simulated and quantified, and the simulation results are consistent with the actual phenomena. It is confirmed that the square angle of LC at the end of the electrode is changed suddenly (i.e. the opposite direction of the normal deflection direction of LC), and the mutation angle is −20°, which prone to trace Mura. In addition, four groups of influence factors (total 12 splits) are proposed for physical and simulation verification, and the optimized design scheme of pixel electrode is obtained. The following conclusions are obtained: the inner corner is cancelled, the length of the outer corner is ≥ 3um, and the angle of the outer corner on the right side (which has been referred to in Figure 4, and other pixel directions can be adjusted accordingly) is ≥ 45°, and the turning direction of the left side is in the same direction as the slit or at an acute angle with the slit direction; This scheme can reduce the dark area of the opening area and maximize the transmittance without risk of trace Mura.

Vehicle Sideslip Angle Estimation Based on Interacting Multiple Model Kalman Filter Using Low-Cost Sensor Fusion

This study proposes a new method for vehicle sideslip angle estimation utilizing the competitively priced sensor fusion using in-vehicle sensors and low-cost standalone global positioning system (GPS). To estimate unmeasurable vehicle states, vehicle sideslip angle and tire cornering stiffness, an interacting multiple model (IMM) Kalman filter is proposed that combines two extended Kalman filters (EKFs), each including kinematic and dynamic equations of vehicle lateral velocity. To properly combine the outputs of these model-based EKFs, a weighted probability of each model based on the stochastic process is designed, which reflects the characteristics of each of the kinematic and dynamic equations in real-time. Also, the observability of the proposed estimation algorithm is checked by observability functions of nonlinear systems. The estimation performance in various driving scenarios is verified using an experimental vehicle, and its superiority is confirmed through a comparative study. The proposed algorithm makes the following main contributions for estimating the vehicle sideslip angle: 1) the high optimality of estimation results and 2) the accurate estimation of tire cornering stiffness.

Evaluation of parameters related with upper lip aesthetics and dynamic smile following Le Fort I osteotomy

ObjectiveThe present study aimed to investigate how upper lip aesthetic and dynamic smile parameters are changed following a Le Fort I osteotomy. MethodsTwenty-seven patients who underwent Le Fort I osteotomy with or without mandibular osteotomy were included in this retrospective study. Upper lip aesthetic parameters which were Cupid's bow angle, lip angle, lip length, lip width, philtrum width and lip corners were evaluated on pre and postoperative rest photos using Image J software. Lip corner movement direction, buccal corridor area with respect to canine and last visible tooth were also measured on posed smile photos with respect to dynamic smile evaluations. Measured variables were submitted to statistical analysis and significance level was determined as 0.05. ResultsThere was a significant reduction in buccal corridor area according to last visible teeth for right and left side at postoperative period. However, buccal corridor area with respect to canine for the right and left side was not significant. The angle between the lip corner movement direction and Y-axis of the face for the right and left sides was not significant between pre and postoperative period. The changes in this angle were not also correlated with the changes in buccal corridor area and maxillomandibular movements. Not only the Cupid's bow angle, lip angle but also lip length, lip width, philtrum width and lip corner have not been changed significantly. ConclusionBuccal corridor area investigated in dynamic smile shows significant improvement after orthognathic surgery especially in the means of maxillary impaction. Lip corner movement during smile was not associated with the changes in buccal corridor area. Landmarks around perioral area in static state were affected clinically with no statistical significance following the surgery.

Altering the Reflection Phase for Nano‐Polaritons: A Case Study of Hyperbolic Surface Polaritons in Hexagonal Boron Nitride

AbstractPolaritons—confined light–matter waves—in van der Waals (vdW) materials are a research frontier in light–matter interactions with demonstrated advances in nanophotonics. Reflection, as a fundamental phenomenon involving waves, is particularly important for vdW polaritons, predominantly because it enables the investigation of polariton standing waves using the scanning probe technique. While previous works demonstrate a rigid phase ≈π/4 for the polariton reflection, herein is reported the altering of the polariton reflection phase by varying the geometry of polaritonic microstructures for the case study of hyperbolic surface polaritons (HSPs) in hexagonal boron nitride (hBN). Specifically, it is demonstrated that the polariton reflection phase can be systematically altered by varying the corner angle of the hBN microstructures, and that it experiences a π jump around a specific angle. This behavior, which is a consequence of the mathematical nature of the reflection coefficient, is therefore expected in other physical phenomena.

Experimental study of impinging flame structures and thermal characteristics in ceiling flow generated by fuel jet diffusion combustion with air entrainment constraint in a corner

This paper presents an experimental investigation and analysis of impinging flame structures as well as thermal characteristics in ceiling flow generated by fuel jet diffusion combustion with air entrainment constraint in a corner of various angles, which had not been quantified in the literature. The impinging flame length, as well as the temperature and heat flux profile along the ceiling centerline were measured for various corner angles (from 30° to 150°), heat release rates (HRRs) and source-ceiling heights, with a total of 183 experimental conditions considered comprehensively. Experimental results show that the impinging flame behaviors have a complex variation nature with the change of corner angles. The impinging flame under the ceiling presented a particular V-shape structure. The measured impinging flame length decreases monotonously with the increasing corner angles. Then, a new global formula was proposed to predict the impinging flame length by considering the effect of corner angles and source-ceiling height on air entrainment and fuel combustion, including both before- and after- impingement stages. The temperature rise and total heat flux at a given position also decreased with the increasing of corner angles. Previous correlations based on a characteristic plume radius are not in agreement with the data for different corner angles. Then, the normalized formulas for the temperature and total heat flux decay profiles along the centerline were proposed using the total flame length as the characteristic length scale and the experimental data were better represented. The present work provides, for the first time, a general model for describing the impingement flame behavior and thermal characteristics in the ceiling flow produced by a jet diffusion combustion with air entrainment constraint in a corner of various angles.