Rounded Corners Research Articles

Shape recovery and energy absorption properties of 3D printed continuous ramie fiber reinforced thin‐walled biocomposite structures

AbstractContinuous fiber reinforced composites are widely used in thin‐walled structures due to their high specific strength and stiffness. In this work, continuous natural fiber was introduced into thin‐walled biocomposite structures via 3D printing technique to enhance energy absorbing properties and promote ecological compatibility. The effects of varying configurations of printing speed, layer thickness, and path optimization on the deposition quality of continuous ramie fiber and polylactic acid matrix were explored. The results showed that reduced printing speed (100 mm/min) and optimal layer thickness (0.25 mm) effectively minimized structural forming defects. In addition, further enhancements in the printing quality could be achieved by smoothing the path with rounded corners. Based on optimal printing strategies, different configurations of thin‐walled biocomposite structures were fabricated. Lateral monotonic and cyclic load tests were performed to investigate their energy absorption and shape recovery capacities. When the loading displacement was 10 mm (strain was 20%), the circular structure presented good shape recovery capability, with measured recovery ratio remaining above 89%. The hexagonal structure showed a similar variation in shape recovery ratio as the quadrangular structure, both remaining above 75%. Moreover, the specific energy absorption of all the structures converged after two cycles, indicating their remarkable and stable repeatable load‐bearing capacity.Highlights Continuous ramie fiber reinforced thin‐walled structures were prepared. The deformation patterns of structures under lateral compression were analyzed. Energy absorption and shape recovery radio were studied under cycle loading. Printed structures exhibited great and stable repeatable load‐bearing capacity.

Formability of 2195-T4 Al–Li alloy sheet by electromagnetic forming

This study explored the efficacy of electromagnetic forming in addressing the limited formability of aluminum–Lithium (AlLi) alloy at room temperature, focusing on the AA2195-T4 sheet. Comparative analyses were conducted to assess the formability. The results indicated that the limit strains obtained through electromagnetic forming were at least 50%, 10%, and 50% higher compared with those obtained through rigid punch forming under the uniaxial tension, plane strain, and biaxial tension. Upon utilizing forming limit diagrams, the failure processes during electromagnetic flanging were predicted. Notably, electromagnetic flanging enabled the creation of hole-flanging structures with a 60% increase in the flanging limit strain around the circumference, surpassing the capabilities of rigid punch flanging. Moreover, the maximum time window for electromagnetic flanging was extended to 168 h. Analysis of the flanging strain path indicated that cracks were prone to occur near round corners during electromagnetic flanging, contrasting with rigid punch flanging where cracks tended to form near the edges of straight walls. This study offered valuable insights for aerospace component formation utilizing Al–Li alloys at room temperature.

Effect of Elevated Acetabular Cup on Contact and Failure Analysis in Hip Implants for Different Microseparations and Cup Inclinations Under Routine Gait Activities Using In Silico Approach.

The acetabular cup design plays a critical role in reducing contact stress between femur head acetabular cup. Many studies used ellipsoidal and spheroidal geometry in acetabular cup design to effectively reduce contact stress. The present study focuses on elevated acetabular cup rim with round corner design to reduce contact stress with round corner geometry. The cobalt chromium femur head and cup are considered for finite element (FE) model of hip resurfacing. The gait loads of routine activities of humans like normal walking, stair ascending and descending and sitting down and getting up gait activities are applied to the developed 3D FE model. Five microseparations of 0.5, 1, 1.5, 2 and 2.5mm are considered in the present study. The acetabular cup inclination angle considered for this study are 35°, 45°, 55°, 65° and 75°. The contact stress and von Mises stress plot for each gait activities under these microseparations are analyzed for betterment of longevity of implants. Overall elevated cup rim design helped in reducing contact stress to a greater extent than conventional cup with different geometries. Also, the predicted von Mises stress for all the parameters considered in the current study are well within the yield strength of CoCr material. Therefore, elevated cup rim could be used as a better alternative to spline and, ellipsoidal and circular geometries of cup.

Study on the aerodynamic characteristics and flow mechanism of square cylinders with rounded corners

In order to elucidate the variation patterns of the aerodynamic characteristics of square cylinders with rounded corners with respect to corner radius ratio and angles of incidence, and to reveal their underlying mechanisms, a wind tunnel test was performed to examine the surface wind pressure of square cylinders with a corner radius ratio R/D (where R represents the corner radius and D signifies the characteristic dimension of the object) of 0, 0.1, 0.2, 0.3, and 0.4. The experiment was conducted at a Reynolds number of 120,000 while varying the angles of incidence between 0° and 45°. In this study, aerodynamic forces, Strouhal numbers, and wind pressure were analyzed. Additionally, the flow field was visualized using a large eddy simulation (LES). The results indicate that the critical angle of incidence αcr of square cylinders with rounded corners decreases as the corner radius ratio increases. αcr represents the angle at which the mean drag and fluctuating lift are minimum and the mean lift and Strouhal number are maximum. Significant negative pressure is observed near the windward rounded corner of the square cylinders with rounded corners in the vicinity of αcr, with the highest value occurring at an R/D of 0.2. Fluctuating wind pressures could attain larger values in the vicinity of the leeward rounded corners where α = 12.5°∼20° and α = 45°. Increasing R/D to a certain value significantly alters the flow structure compared to a square cylinder with R/D= 0. This is due to the shear layer flowing close to the wall, as it does not separate at the windward rounded corner.

Simulation and experimental study of nanofiber yarns prepared by disc electrospinning

Conjugated electrospinning is an exciting way to prepare nanoyarns. However, all currently reported preparations of nanofiber yarns by conjugated electrospinning use needles, which can cause discontinuous yarn production due to plugging needles during the preparation process. Herein, a novel disc treated with rounded corners as the spinneret of conjugated electrospinning was developed to spin continuously twisted nanofiber yarn to overcome the existing problems. First, finite element analysis was used to optimize the parameters of the disc. The disc exhibited the optimal field strength distribution on the spinning surface when the disc rounding angle was 0.7, and the coefficient of variation value of the field strength was only 12.6%. After that, we optimized the effect of spinning parameters on yarn yield by central composite design. In addition, the impact of spinning parameters on fiber morphology was also investigated. Under the optimized parameters, it is possible to spin continuously at a 360 m/h speed for at least 1 h without breaking. This innovative approach provides a novel idea for continuously producing nanofiber yarns.

Simulation of Vortex-Induced Vibration for a Cylinder with Different Rounded Corners under Re = 150

A comprehensive 2D numerical model was conscientiously developed to investigate the vortex-induced vibration phenomena in a cylindrical structure with rounded corners. The Navier-Stokes equation was adeptly solved under the specific condition of a Reynolds number (Re) of 150. The investigation reveals intricate details of the phenomena. The study aimed to systematically analyze the interaction between drag and lift force coefficients, cylinder vibration amplitude, and the patterns of vortex shedding modes under various conditions. This study systematically altered the radius of the cylinder’s rounded corners to evaluate their effects on both structural and hydrodynamic responses. This variation was crucial in comprehending how slight alterations in the cylinder’s geometry impact significant changes in the flow dynamics and correlated vibration behavior. The model’s numerical results revealed the significant impact of the curved edge ratio on both the hydrodynamic forces acting on the cylinder and its vibration response. The variation in edge curvature resulted in changes in drag and lift coefficients, leading to a significant impact on the amplitude of vibration. This elucidates the crucial role of geometric design in controlling and optimizing the structural behavior of cylindrical structures under fluid flow conditions.

Seismic performance of joints of prefabricated corrugated steel utility tunnels Part(I)–Experimental analysis

This paper presents the seismic performance of a corrugated steel plate utility tunnel, based on an engineering prototype. The research combines quasi-static testing and numerical simulation to investigate the behavior of the structure under cyclic loads in different directions. Specifically, six loading scenarios were considered: the quasi-static test was conducted for transverse tension and compression, transverse bending and shear, vertical shear test (Conditions (1–3)), while numerical simulations were performed for longitudinal tension and compression, transverse shear, and vertical bending shear test (Condition (4–6)) in Part(II). The results reveal comprehensive hysteresis curves for the plate under diverse loading directions, with an extended yield platform section that underscores its significant plastic deformation capacity. However, the “pinch” phenomenon of the hysteresis curve is obvious. The existence of rounded corners not only makes the hysteresis curve of the plate asymmetrical but also makes a great difference to the bearing capacity of the structure in the direction of positive and negative loading. The component exhibits superior bearing capacity and stiffness along the longitudinal direction compared to other orientations. Additionally, the structure demonstrates remarkable energy dissipation capabilities because of the inherent “accordion effect” of the corrugated steel plate. Moreover, the maximum energy dissipation coefficient in three directions is more than 1.0, illustrating its excellent energy dissipation capacity. The results provided valuable insight into the seismic performance of joints and contributed to the safe design of prefabricated corrugated steel utility tunnels.

METHODS FOR THE PRESERVATION AND RESTORATION OF DUNHUANG WALL PAINTINGS: FOREIGN EXPERIENCE

This article examines the genesis of planning solutions and ceiling designs of Dunhuang cave shrines. Based on the methods of defining features, graphic-and-analytical and system-and-structural analysis, the spread of types of plans and ceilings from dynasty to dynasty has been traced. Using auxiliary methods of historical, mathematical, and comparative analysis, a general picture of the development of the planning structure and constructive schemes of Dunhuang shrines from the Northern Lian period to the Yuan period has been created. By counting the types of plans and ceilings in each period, a group of the most common types of plans was determined: with a combination of larger and smaller rectangles (where the smaller is the altar part of a square or rectangular shape), a plan in the form of a square with a protruding trapezoidal altar, an altar in outline close to a rectangle or trapezoids with rounded corners, a horizontally elongated plan rectangle, based on squares with protrusions. The most common type of ceiling is fu-dou-ding with modifications.

Investigation into the effect of rounded building corner on wind loads of flat-roof-mounted solar arrays

Wind tunnel tests were performed to investigate the wind loading on flat-roof-mounted solar arrays. Effects of panel parameters (panel location and tilt angle β) and building parameters (parapet height hp and rounded building corner) were examined. Moreover, the aerodynamic mechanism was investigated by computational fluid dynamics (CFD) simulations. The largest most critical mean loads fluctuated greatly with panel locations for the sharp roof, whereas no large differences were found for the roof with rounded building corner. The largest most critical mean and negative peak loads for the roof with rounded building corner were significantly smaller than those for the sharp roof because the weak vortices occurred at panels on the roof with rounded building corner. The most significant influence of hp on wind loads occurred at roof corners. Peak loads were underestimated in JIS C 8955-2017, where turbulence intensity generated by roofs and solar arrays was not considered. The panel zoning was studied using the k-means approach. Solar panels on roofs with sharp and rounded building corners without parapets were divided into three zones. Regression analysis of the wind loads with β and hp in various panel zones on roofs with sharp and rounded building corners was conducted.

Numerical investigation of flow field characteristics around semi-submerged rectangular cylinders with rounded corners

The investigation of flow field characteristics of the semi-submerged rectangular cylinder (SRC) with rounded corners is of crucial industrial importance, but it faces two main challenges: a deficiency in diverse research SRCs with rounded corners and a lack of thorough experimental and analytical investigations in this domain. To mitigate these deficiencies, the present study increases rectangular cylinder diversity by adopting SRCs with different rounded corners. In this regard, the flow field characteristics of the SRC are examined under varying Reynolds numbers and aspect ratios to expand the research framework. The RNG k-ɛ model within the OpenFOAM was verified for the rounded corners by comparing it with experiments for the submerged rectangular cylinder. Meanwhile, mesh convergence analyses are performed to validate the reliability of the simulated results for the SRC with rounded corners. The results are compared with those obtained from the SRC with sharp corners. It is found that the rounded corner effectively reduces the disturbance from the bottom vortex and decreases the mean drag force. However, its effect on lift force is relatively small. Regarding the variations in flow field characteristics, the Reynolds stress results show that the upstream rounded corner reduces the velocity fluctuations and induces shear layer separation. Meanwhile, it is found that as the rounded corner radius increases, the interference caused by the bottom vortex reduces, thereby decreasing the amplitude of the pressure field on the bottom. Moreover, increasing the upstream rounded corner radius reduces the extreme values of turbulence kinetic energy on the SRC bottom. The results show that the evolution of the bottom vortex can be evaluated by analyzing the trend of the shape factor in the boundary layer characteristics.

Experimental and numerical evaluation of geometrical imperfection effects on the load bearing capacity of small-scaled voussoir arches

The study of the behaviour of masonry arches represents a complex problem, which involves different aspects that can significantly affect the load bearing capacity of such structures. In this regard, geometrical imperfections, such as the irregular shape of the arch blocks, the initial position of the first and last voussoirs (boundary conditions), the alignment between the adjoining blocks and the rounded corners of each block, play an important role. An experimental campaign was conducted on a toy arch made by eleven irregular blocks, with the aim of evaluating the effect of such irregularities. A numerical model was developed basing on lower bound (LB) and upper bound (UB) limit analysis approaches (referred to as the static and the kinematic theorem, respectively). A linear programming (LP) solving algorithm was implemented in the software MATLAB and used to solve the minimization/maximization problems. The probability distribution of each considered nonlinearity was estimated, the results of the numerical analysis were correlated with the experimental outcomes and a Montecarlo simulation was carried out to validate the hypothesised probability distributions.

Vibration characteristics of a downstream cylinder with rounded corners in an equilateral triangular arrangement at Reynolds number of 180

In this study, we numerically investigate the vibration response of a cylinder arranged in an equilateral triangle with two stationary upstream cylinders at a low Reynolds number of Re = 180. We concentrate on three different rounded corner arrangements: four rounded corners (FRCs), upwind rounded corners (URCs), and leeward rounded corners (LRCs). In addition, we examine three dimensionless rounded corner radii: 0.1, 0.3, and 0.5. The results indicate that as the dimensionless radius increases, the influence of the corner position on the dimensionless amplitude and frequency becomes more pronounced. Furthermore, the dimensionless amplitude and dimensionless frequency curves exhibit significant variations under the different corner arrangements. Within the reduced velocity range (Vr) of 2–5, rounded corners are observed to reduce both the lift and drag coefficients. An increase in the dimensionless radius for a given corner configuration acts to decrease both the lift and drag coefficients. Frequency-domain analysis of the lift coefficient and dimensionless displacement indicates that the observed frequency peaks caused by mutual interference are produced by irregular vortex shedding due to the mutual extrusion and merging of shear layers. At Vr = 4, the FRC, URC, and LRC configurations with a corner radius of 0.5 all exhibit the 2S vortex shedding mode. As Vr increases, the vortex shedding mode for LRCs with a corner radius of 0.5 progressively becomes irregular. At Vr = 16, the vortex shedding mode for LRCs with a corner radius of 0.5 is the regular 2P + 2S mode.

Short study on mechanism of morphology change of γ′ precipitates in IN718 Plus

γ′ Ni3Al phase (L12 structure) strengthened superalloy has become an important strengthening phase in Ni based superalloys because of its excellent high-temperature service performance, and has been widely used. The process of γ′ phase precipitation has also received a lot of attention and research. However, most studies focused on its growth rate. There were few studies on the morphology transformation of γ′ phase, and the morphology transformation process is complex. The mechanism of γ′ phase transformation process was systematically analyzed in this paper. Firstly, through molecular dynamics calculation, the most stable morphology of the γ′ phase in the nickel matrix was obtained under ideal conditions. The stability of spherical precipitates is higher than that of cubic precipitates. When the temperature is greater than 800 K, the stability is more obvious.Then through the micro EDS analysis of the γ′ phase in the morphology transformation process, it was shown that the soft impingement phenomenon exists in the nickel base alloy with high γ′ phase volume fraction. Further, by the derivation of the formula of solid-state phase transformation, it was found that the growth rate of precipitate is directly proportional to the concentration gradient of Al in the matrix at the interface, while increases with the rising of the Al concentration in the matrix at the interface. Finally, the way and mechanism of soft impingement affecting the morphology transformation were analyzed. The precipitates formed by soft impingement are nearly cubic precipitates with rounded edges and corners.

Genesis of the Planning Structure And Ceilings of Dunhuang Sanctuaries

The article is devoted to the study of the genesis of the plans and ceilings of the Dunhuang cave sanctuaries. Based on the methods of graphic-and-analytical, defining features and system-structural analysis, the spread of types of plans and ceilings from dynasty to dynasty has been traced. With the help of a group of auxiliary methods of historical analysis, mathematical analysis and comparative analysis, a general picture of the development of the floating structure and constructive schemes of the Dunhuang sanctuaries from the Northern Liang period to the Yuan period was created. By counting the types of plans and ceilings in each period, a group of the most common types of plans was determined: with a combination of larger and smaller rectangles (where the smaller is the altar part of a square or rectangular shape), a plan in the form of a square with a protruding trapezoidal altar, an altar in outline close to a rectangle or trapezoids with rounded corners, a horizontally elongated plan rectangle, based on squares with protrusions. The most common type of ceilings is fu-dow-din with modifications.

Post-trench restoration for vertical GaN power devices

The impact of the post-trench restoration on the electrical characteristics of vertical GaN power devices is systematically investigated in this work. Following the achievement of microtrench-free GaN trench structure with modified dry etching conditions, the post-trench tetramethylammonium hydroxide (TMAH)-based wet etching and UV/Ozone-based oxidation process are employed to further refine the trench profile. It is shown that the c-plane trench bottom is restored to the level of unetched surface, as evidenced by the improved Schottky interface. Additionally, the post-trench treatment exhibits the anisotropic characteristics with the preferred rounded corner profile on m-plane sidewall compared to a-plane sidewall. The simulations and experimental results demonstrate that the trench MOS barrier Schottky (TMBS) rectifier based on m-plane sidewall could suppress the electric field crowding at the trench corner and, hence, reduce the reverse leakage current by 1–2 orders of magnitude. Furthermore, the MOSCAP test structures were fabricated on the trenches. The extracted interface trap density (Dit) confirms the effective restoration of trench bottom. However, the sidewall surface exhibits the relatively large Dit, which emphasizes the necessity of optimizing the sidewall, particularly for devices incorporating sidewall channel. The demonstrated post-trench restoration technique improves the surface quality and trench structure for the significantly enhanced electrical performances, which is essential for the development of vertical GaN power devices.

Investigation on cavitation enhancement on flash boiling atomization using two-dimensional slit nozzles

Flash boiling and cavitation are two important topics in internal phase changing flow and spray atomization studies. They have been proven to be effective in improving spray breakup process, and hypotheses are proposed that these two phenomena could have coupled effects to achieve even better atomization. But few quantitative studies have made direct comparisons on whether the introduction of cavitation into flash boiling will result in finer droplets. This investigation aims to address this issue with optically transparent, two-dimensional slit nozzles with varied geometries. The round corner is introduced to suppress the generation of cavitation at the inlet, and thermal boundary conditions are adjusted to trigger flash boiling. Results from high-speed backlit imaging and phase doppler interferometry unveil that the introduction of cavitation can enhance the flash boiling process throughout the increment of superheat degree, yet the enhancement efficiency is different as thermal conditions change, and is strongly correlated with internal bubble spatial distributions. A model is proposed to explain the governing factor of cavitation enhancement on flash boiling atomization.

3D elasticity solutions for stress field around square hole in functionally graded plate

Since the square holes are widely used in many structures and machines, the purpose of this work is to obtain analytical solutions for the three-dimensional (3D) elastic stress field of transversely isotropic functionally graded (FG) infinite plates containing a single square hole with small round corners subjected to far-field loads or on the edges of the holes. Based on the generalized England-Spencer plate theory, material parameters can vary continuously and arbitrarily along the thickness direction of the plate, the solutions are obtained by using the conformal mapping technology combined with the Cauchy integral method. Concentration factors of internal forces Kij around the square hole are explicitly expressed. The obtained explicit expressions of solutions can be validated against the classical two-dimensional (2D) solutions when the material degenerates into an isotropic and homogeneous material. The detailed numerical examples are given to further investigate the influence of several parameters such as the material gradient factor and load conditions on the stress field around the hole. The present 3D analytical solutions can not only provide an in-depth understanding of the 3D stress field of FG plates with holes, but also be utilized as a benchmark to verify the numerical solutions of the same problems.

Rounded-corners-induced re-entrant non-occlusion in a horizontal tube

Keeping a tube from being plugged by a fluid is an important process in applications. An interesting re-entrant phenomenon for the capillary state with the occluding state sandwiching the non-occluding state from both the high- and low-Bond-number regions can appear by inserting a rod into a horizontal tube at an eccentric position (Tan et al., J. Fluid Mech, vol. 946, 2022, A7). Containers with rounded corners are very common. We theoretically investigate a situation for a horizontal open tube with rounded corner(s). The results show that a re-entrant non-occlusion at a contact angle can also appear without the insertion of any object. The competition between the rounded corner wetting/non-wetting effect and gravity effect can lead to a re-entrant non-occlusion. The re-entrant non-occlusion is affected by the shape and orientation of the rounded corner(s). For a tube with only one rounded corner, the re-entrant non-occlusion exists when the rounded corner has a not-so-large corner radius and is not in a landscape orientation. For a tube with two (or more) rounded corners, the corner(s) with the strongest corner effect will determine the existence or non-existence of the re-entrant non-occlusion. This paper provides an effective scheme for designing a high-performance capillary with corners that are not easily occluded by a fluid and removing fluid blockage from a capillary in optofluidic/microfluidic applications.

Rounded corner thicken strut re-entrant auxetic honeycomb: Analytical and numerical modeling

An analytical model is formulated for 2-D periodic negative honeycomb thicken strut re-entrant lattice structures and a modified rounded corner negative honeycomb structure that shows negative Poisson’s ratios (NPR). Analytical modeling is done using Castigliano’s second theorem, where each beam is modeled using Timoshenko beam theory, considering bending, stretching, and transverse shearing. Elastic modulus and Poisson’s ratio have been formulated for both structures in the form of non-dimensional geometrical characteristics, such as length ratios, angles of re-entrant arms, shear correction factor, and the material’s Young’s modulus and Poisson’s ratios. Numerical simulations conducted in ABAQUS-CAE explicit solver validate the analytical model. The effect of the non-dimensional parameters on the qualities of the developed structure is demonstrated. It is observed that the structures with a low curvature ratio have a high fluctuation of Poisson’s ratio and Elastic constant when plotted against the other parameters. The slenderness ratio has little impact on Poisson’s ratio but significantly influences elastic modulus. It is shown that various needs can be satisfied by customizing the Poisson’s ratios and elastic constant of both forms of lattice construction over an extensive range by carefully choosing the geometrical parameters and material.

Physically Realistic Inlet-Velocity Profiles in Duct Flows

A uniform inlet velocity profile is widely used in the numerical simulations of fluid flow and heat transfer in ducts for both incompressible and compressible flows. In incompressible flows, the calculated fluid pressure at the inlet edge is extremely high and affects the calculation of the average pressure. In compressible flows, the fluctuation of pressure in the flow direction results in the fluctuation in the velocity. This has motivated this study to numerically investigate a physically realistic velocity profile at the inlet of a pipe rather than using a uniform velocity profile. The numerical simulations were based on the control volume-based power law scheme and the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The continuity and momentum equations for a flow in a pipe with the rounded inlet corner were solved to obtain a physically realistic inlet velocity profile. The obtained inlet velocity profile was expressed by a simple expression in the range of Reynolds number from 100 to 2000. Using this velocity profile, both the incompressible and compressible flows in a pipe were numerically investigated. The results resolved the previously observed inconsistencies in the pressure that were previously observed in the numerical simulations with uniform inlet velocity profiles.