Curved Surface Structures Research Articles

Compressive Mechanical Properties and Energy Absorption of Cubic Spherical Hollow Cellular Material Based on the Rod and Curved Surface Structure

Cellular materials, such as lattices and honeycombs, were widely used for structural protection owing to their excellent mechanical properties. By combining the excellent characteristics of lattice and honeycomb curved surface structures, this study designed a cell called Cubic Spherical Hollow (CSH), which had the advantages of orthogonal isotropy and better spatial connectivity. Inspired by the micro-structural arrangement of bamboo fiber and conch shell, we designed the new CSH cellular materials through the interlayer offset strategy. Then, the effects of interlayer offset on the mechanical properties and compression deformation behavior were explored experimentally and simulatively. Compared with other cellular materials, CSH cellular materials exhibited excellent mechanical properties with higher specific strength and specific modulus. The arrangement offsets of the CSH cells between different layers led to a change in the deformation mechanism from a rod’s compressive mode to a combination of a rod’s compressive mode and curved surface’s bending mode. The initial peak stress and plateau stress decreased with the increased arrangement offsets of the CSH since the extruded protrusions of the structure filled the holes and reduced the lateral expansion behavior of the material in the pressurized environment. This phenomenon also reduced the transverse expansion and prevented the sudden change in stress in the constrained space, indicating that the structural deformation was stable and had excellent cushioning and energy absorption properties. In this study, the cellular material design strategy opens a new avenue for energy absorption.

Numerical analysis of electrohydrodynamic printing under electric field focusing mode

As an emerging micro/nanoscale 3D printing technology, Electrohydrodynamic (EHD) printing has undergone rapid development in recent years. However, in most EHD printing processes, voltage is directly applied to both the nozzle and the substrate, resulting in the electric field being influenced by the printing height. This poses challenges for printing three-dimensional curved surface structures. This study presents a comprehensive investigation into the EHD jetting process, utilizing a novel voltage loading method that separates electrodes from both the nozzle and the substrate. Through experimental setups and numerical simulations, this research was conducted to examine the effects of printing height, voltage, and electrode diameter on jetting behavior. The results show that compared to the traditional electrode form, the new voltage loading method will increase the electric field intensity of the liquid surface before ejection by 37.1% and is more conducive to the formation of Taylor cones. It can ensure that the printing fluctuation is less than 2.4% when the printing height varies between 1.5–2.5 times the nozzle diameter, which is more favorable for printing multi-layer structures. The threshold voltage for ejection is provided in this model. When the electrode is reduced, the efficiency of electric field utilization will be further improved, but the acceleration of the jet velocity will cause an increase in droplet size. The findings highlight the method’s capability to maintain consistent droplet sizes and electric field intensities across varying conditions, thereby enhancing printing stability and efficiency. The study’s innovations provide valuable insights for advancing micro/nano 3D printing technologies, emphasizing the potential for improved EHD printing processes in practical engineering applications.

Numerical modeling of triply period minimal surface structures with catalyst coating for hydrogen production of methanol steam reforming

The catalyst support structure has a significant influence on the performance of the methanol steam reforming (MSR) microreactor for in-situ hydrogen production. Triply period minimal surface (TPMS) structures are emerging as an attractive option as porous MSR catalyst supports owing to their excellent specific surface area, smooth surface and highly interconnected pores. This paper develops a numerical model of the sheet TPMS unit structures with catalyst coating to investigate the flow and reaction characteristics for hydrogen production of MSR reaction. The P, G, and D curved surface structural models were constructed with different porosities. The numerical results indicated that the P curved surface structure with the porosity of 90% had the lowest pressure drop of 0.15 Pa and the highest permeability of 6.31 × 10−9 m2, while the G curved surface structure always demonstrated excellent flow performance within the porosity range of 50–90%. The D curved surface structure exhibited the best reaction performance with hydrogen production exceeding P and G curved surface structures by about 23% and 78% respectively. Furthermore, the performance differences between the two flow phases of the sheet TPMS structures were investigated for the bicontinuous characteristic. The flow phases of the G curved surface structure demonstrated the best consistency in flow and reaction performances. Finally, the optimal design of the sheet, network, and multi-unit heterogeneous TPMS structural catalyst supports was discussed.

Computational fluid dynamics simulation analysis of the effect of curved rice leaves on the deposition behaviour of droplets

BackgroundAlthough previous studies on the droplet deposition behaviour of rice leaves have modelled the leaves as flat surface structures, their curved surface structures actually have a significant effect on droplet deposition.ResultsIn this paper, the statistical distribution of the coordinate parameters of rice leaves at the elongation stage was determined, computational fluid dynamics (CFD) simulation models of droplet impact on rice leaves with different curvature radii were built, and the effect of leaf curvature radius on the deposition behaviour and spreading diameter of droplets on rice leaves was studied using validated simulation models. The results showed that the average relative errors of the CFD simulation models were in the range of 2.23–9.63%. When the droplets struck the rice leaves at a speed of 4 m/s, the 50 μm droplets did not bounce within the curvature radii of 25–120 cm, the maximum spreading diameters of 200 and 500 μm droplets that just adhered to the leaves were 287 and 772 μm, respectively. The maximum spreading diameters of 50, 200, and 500 μm droplets that just split were 168, 636, and 1411 μm, respectively. As the curvature radii of the leaves increased, the maximum spreading diameter of the droplets gradually decreased, and droplet bouncing was more likely to occur. However, a special case in which no significant change in the maximum spreading diameter arose when 50 μm droplets hit a leaf with a curvature radius exceeding 50 cm.ConclusionSplitting generally occurred for large droplets with a small curvature radius and small tilt angle; bouncing generally occurred for large droplets with a large curvature radius and large tilt angle. When the droplet was small, the deposition behaviour was mostly adhesion. The change in spreading diameter after stabilisation was similar to the change in maximum spreading diameter, where the spreading diameter after stabilisation greatly increased after droplet splitting. This paper serves as a reference for the study of pesticide droplet deposition and its application in rice-plant protection.

As-built FE thermal analysis for complex curved structures in automated fiber placement

This research aims to predict and manage material temperatures on complex curved surface structures during automated fiber placement (AFP). A thermal analysis model is developed by incorporating the information of path points as well as the heating time into the radiative heat transfer model. In it, the heating time is determined by the layup speed which is formulated using the S-shaped speed forward planning method. Finally, the thermal analysis algorithm is integrated into a three-dimensional (3D) finite element (FE) model to predict and regulate material temperatures on complex curved structures. In this paper, the thermal analysis method is exemplarily applied to a C-beam. The predicted material temperature under the condition of the constant power is validated by the AFP experiments. A good agreement between the temperature-predicted value and the experimental results is observed. Moreover, the power design method based on laying temperature analysis is proposed to manage the material temperatures within the optimal laying specification.

In-situ preparation and performance of cold resistant K2O·5SiO2 based anti-fire glass

We describe a method for the synthesis of cold resistant K2O·5SiO2 based anti-fire material using a new high content and low viscosity SiO2 core–shell emulsion (HSLVCS SiO2 emulsion). The anti-fire glass which wasn’t frozen at −71 ± 1 °C was prepared by the in-situ reaction. The onion-shaped core–shell structure was clearly shown in scanning electron microscopy (SEM) micrographs, the viscosity of HSLVCS SiO2 emulsion (50 wt%) was 431.4 ± 12.1 mPa·s(48 rpm). Its in-situ reaction process for preparation of the K2O·5SiO2 followed a first-order reaction, the reaction rate constant kn = 1.774 × 108 exp (−Ea/RT) with the apparent activation energy Ea = 79.80 kJ/mol. The low-temperature-withstanding capability was tested at extreme-cold environment (−71 ± 1 °C), and the reasons for this were found by the thermogravimetric analysis (TG). The weather resistance capacity was more than 1000 h through ultraviolet (UV) test and the sponge-like microporous insulation layer can increase the fire insulation time by the fire-resistant test. This work provided a new routine toward the synthesis of the high quality anti-fire glass with various shapes, including curved surface structures.

High-Performance Single-Side Fabricated (111)-Silicon Dual-Cantilever Accelerometer with Squeeze-Film Air Damping Modulation

This study proposes a novel design and micromachining process for a dual-cantilever accelerometer. Comb and curved-surface structures are integrated into the sensing structure to modulate the squeeze-film damping, thus effectively optimizing the response frequency bandwidth. Owing to the high stress concentration on the dual-cantilever integrated with a fully sensitive piezoresistive Wheatstone bridge, a high sensitivity to acceleration is achieved. In addition, the dual-cantilever accelerometer is fabricated using a specifically developed low-cost and high-yield (111)-silicon single-side bulk-micromachining process. The test results show that the proposed dual-cantilever accelerometer exhibits a sensitivity of 0.086–0.088 mV/g/3.3 V and a nonlinearity of ±(0.09%–0.23%) FS (full-scale). Based on dynamic characterization, an adequate frequency bandwidth of 2.64 kHz is verified. Furthermore, a resonant frequency of 4.388 kHz is measured, and a low quality factor (Q) of 7.62 is obtained, which agrees well with the design for air-damping modulation. The achieved high performance renders the proposed dual-cantilever accelerometer promising in applications such as automotive and consumer electronics.

Heteroepitaxy of flexible piezoelectric Pb(Zr0.53Ti0.47)O3 sensor on inorganic mica substrate for lamb wave-based structural health monitoring

Active Lamb wave detection is an effective and simple monitoring method for structural health monitoring (SHM). Piezoelectric lead zirconate titanate (PZT) ceramics are most commonly used as transducers to excite and receive Lamb wave. However, due to their hardness, thickness and brittleness, PZT ceramics are severely limited in detecting damage on curved surface structures. Herein, we report that flexible PZT film sensor is an excellent candidate for receiving Lamb wave used in Lamb wave-based SHM of aircraft. An improved piezoelectric coefficient d33 (~130 pm V−1) is obtained in epitaxial PZT films grown on flexible inorganic mica substrates via van der Waals heteroepitaxy. Superior stable ferroelectricity and piezoelectricity retain in flexible PZT film after bending 104 cycles under a radius of 8 mm. As proven by experiment and simulation, flexible PZT film is demonstrated as an ultrasonic sensor with high sensitivity to be bonded on the curved aluminum plate for Lamb wave-based damage monitoring. Our work demonstrates that flexible PZT films have enormous potential for real-time light-weight and high-sensitivity receiver sensors for the SHM of aging aircraft.

Curvature-Modulated Si Spherical Cap-Like Structure Fabricated by Multistep Ring Edge Etching.

To create approximately spherical structures with curved sidewalls, this paper presents a method for building a series of decreasing slopes along the sidewall of a circular truncated cone. The multistep ring-edge etching technology of first reducing the concentric mask and then cutting the top off to create a mesa shape can be used to form the slopes. This wet-etching method avoids the constraints of crystallographic properties with surfactant-added Tetramethylammonium hydroxide (TMAH), enabling the manufacture of successive given inclination angles, the precise modulation of the spherical curvature by reduction design of concentric masks, and the setting of etching time. The newly approximated spherical Si microstructure patterns can be used for microlenses, quartz crystal resonators, micropulleys, and other applications. The present research is an approach to fabricate advanced microelectromechanical systems (MEMS) curved-surface structures, extending the range of 3D structures fabricated by silicon wet etching.

Experimental and numerical study on stability behavior of reticulated shell composed of plate members

Steel plates have great potential in being used as main structural members in single-layer reticulated shells (SLRS). The main advantages of steel plates include high-precision and flexible outline shape fabrication as well as convenient transportation and storage, which make them suitable for curved surface structures. To improve the buckling resistance of plate members, two strengthening methods, i.e., double-limb method and sub-unit method, are introduced. In this study, the stability behavior of a 3.27 m × 3.27 m spherical SLRSs strengthened by using the proposed methods is comprehensively investigated via an experimental test and a finite element (FE) simulation. Specifically, the equivalent FE models for double-limb plate members and semi-rigid joints are proposed. The comparison results indicate that the presented FE model is effective for predicting the development of member stress and the structural ultimate load. Then parametric analysis is conducted, which reveals the effects of the sub-units, the bending stiffness of the joints and the geometric imperfection on the structural stability. The results obtained in this study may provide guidance for the design and analysis of this type of structure.

Influence of complex geometries on the properties of laser-hardened surfaces

Laser surface hardening provides for many advantages in terms of flexible production due to very localized and controlled energy input into the material. Laser processing offers the possibility to treat surfaces in order to locally strengthen the areas that are prone to fatigue cracking. It is well known that laser energy absorption depends on many parameters, e.g., the surface structure and the surface orientation. The incident angle of the laser beam plays a key role in this regard. When complex geometries like crankshaft fillets are treated, the surface cannot be considered a series of flat surfaces. Obviously, this leads to locally varying degrees of energy absorption. In the present work, curved surface structures were chosen in order to analyze the impact of the geometrical characteristics on surface and subsurface material properties after laser treatment. Microstructure evolution generally was found to be similar for flat and curved geometries. However, even if higher absorption in the groove due to the illumination at larger incident angles was expected, the outer parts of the curved geometry were not fully hardened. Thus, the increased effective length of the complex geometry-treated and the larger heat-affected volume are expected to have a more dominant influence on the final appearance of the subsurface microstructure. Eventually, for austenitization of the complete illuminated surface volume, the energy density needs to be increased.

Surface based variable thickness slicing modeling for laser metal deposition

Laser metal deposition (LMD) has been a promising additive manufacturing technology widely used in mold rapid manufacturing. In order to improve the capacity of LMD for complex curved surface structures, a surface based variable thickness slicing (S-VTS) model is proposed to adaptively generate the LMD process based on the geometric characteristics of structures. Two deposition strategies in scanning and overlapping directions are designed to enable variable thickness of each cladding layer by dynamically adjusting the scanning speed and overlapping rate. To improve the surface quality and forming efficiency, the discrete particle swarm optimization (DPSO) algorithm is adopt to optimize the process parameters of S-VTS model, including the number of cladding layer, scanning pass, and segment per pass. Several experiments are conducted to form the cuboid samples with wavy and freeform surface and verify the feasibility of the S-VTS model. The results demonstrate that under the open-loop control condition, the geometric accuracy, surface quality, and efficiency of the proposed method is improved in comparison with uniform thickness slicing (UTS) deposition. Moreover, heterogeneous microstructure is always generated by the S-VTS method in terms of grain size and growth direction.

TO-FDTD Method for Arbitrary Skewed Periodic Structures at Oblique Incidence

For accurately modeling general periodic structures with arbitrary skewed grids at oblique incidence, a novel finite-difference time-domain (FDTD) method based on the transformation optics theory (TO-FDTD) is proposed in this article. First, by choosing the appropriate transformation of coordinate and applying the transformation optics theory, the original space of the skewed grid is mapped to the virtual space of the Cartesian grid, and the electromagnetic parameter tensors in the virtual space are known accordingly. Then, based on the covariance of Maxwell’s equations, both the basic difference equations and the boundary conditions of FDTD for the virtual space are derived. After that, the phase delay of the periodic boundary condition caused by the oblique incidence is eliminated by adopting the technique of field transformation, and the final explicit-iterative equations of the TO-FDTD method are obtained as well. At last, some examples are analyzed to verify the numerical properties of the proposed method. The idea of modeling based on the transformation optics theory is not only suitable for skewed periodic structures but also applicable for some ultrathin or (and) curved-surface structures after further expansion.

Mechanically rational forms of curved surface structures shaped from the uniform strain elements

The paper proposes a method for finding mechanically rational and practical forms of curved surface by using the uniform strain elements. Numerical methods for form finding already published give exact solutions but the application is restricted to the problems with the conditions possible to form a minimal surface. This is because the methods use the mechanical model without material stiffness but with only the geometric stiffness of isotropic tension. When the uniform strain elements composing a structural form have even isotropic strain in all over the form, the form is an isotropic tension form. Since the uniform strain element has the material stiffness, the method can stably yield a form with the strains varying as narrowly as possible in the curved surface under the condition impossible to shape a minimal surface.

Structural deterioration of curved thin-walled structure and recovery by rib installation: Verification with structural optimization algorithm

Structural improvements for curved-surface thin-walled structures were examined. In such structures, installations of ribs—support structures for out-of-plane deformations—are often effective. These out-of-plane deformations are attributed to internal loadings induced from plane stresses. Shapes of solid curved I-sectional beams models were optimized using a structural optimization algorithm—the traction method. Ribbed structures were created semi-automatically by the structural optimization when adequate rib-triggers—striped shape constraints or humps in the initial shapes—were applied to the models. This result validates the effectiveness of rib installations on curved surface structures. It is notable that the rib formation created substantial topology changes.

Comparison of Kinect and Terrestrial LiDAR Capturing Natural Karst Cave 3-D Objects

Modeling natural phenomena from 3-D information enhances our understanding of the environment. Dense 3-D point clouds are increasingly used as highly detailed input datasets. In addition to the capturing techniques of point clouds with LiDAR, low-cost sensors have been released in the last few years providing access to new research fields and facilitating 3-D data acquisition for a broader range of applications. This letter presents an analysis of different speleothem features using 3-D point clouds acquired with the gaming device Microsoft Kinect. We compare the Kinect sensor with terrestrial LiDAR reference measurements using the KinFu pipeline for capturing complete 3-D objects $( . The results demonstrate the suitability of the Kinect to capture flowstone walls and to derive morphometric parameters of cave features. Although the chosen capturing strategy (KinFu) reveals a high correlation $({\rm R}^{2} = 0.92)$ of stalagmite morphometry along the vertical object axis, a systematic overestimation (22% for radii and 44% for volume) is found. The comparison of flowstone wall datasets predominantly shows low differences (mean of 1 mm with 7 mm standard deviation) of the order of the Kinect depth precision. For both objects the major differences occur at strongly varying and curved surface structures (e.g., with fine concave parts).

How to Eliminate Machining Marks on the Surface of Impeller Blades by CimatronE CAM

The impeller blades are hard to machine for its complex and curved surface structures. It is almost impossible to manufacture the blades by manual programming on Numerical Control Tool. Now, the program almost is completed by the three-dimensional CAD/ CAM software, such as UG, Pro/Engineer, CimatronE which have a lot of machining strategies suitable for a wide variety of parts. However, the result is not perfect if you choose improper strategies. Even more, machining marks will be left on the parts’ surface. This paper takes the impeller for an example and gives the solutions for eliminating machining marks left on the impeller blades’ surface through a comparative analysis on the 3-axis finish machining strategies in CimatronE.

Precision Grinding and Resistance Reduction of Micro-grooves Curved Surface of Ceramic Flying Body

In order to reduce flight resistance and increase radar scattering, a hybrid method of precision grinding and micro grinding is proposed to fabricate micro-grooves curved surface structures on surface of ceramic flying body. The precision-trued diamond wheel edge is employed to grind ceramic surface into smooth curved surface along CNC curve interpolation paths; the micro-trued diamond wheel with V-tip of 60° is employed to grind micro-grooves structures on ground curved surface along the axial direction of flying body; the wind-driven experiments are performed to investigate the effect of different curved surface structures on air resistance. The experimental results show that micro-grooves structures with the depth of 578-581 μm, angle of 61.56° and tip radius of 48 μm may be fabricated on curved surface of ceramic with the height of 32 mm, diameter of 30 mm and surface roughness of 0.262 μm. The depth error of micro-grooves is only 3 μm. The average form error of curved surface is only 142 μm and it can be controlled below 0.5% by the proposed precision grinding method. Moreover, different grain sizes of diamond wheel and various grinding processes have great influence on surface roughness for curved surface of ceramic. The wind-driven experimental results indicate that micro-grooves structure may reduce axial resistance by 36% and 42% compared to smooth and rough curved surface, respectively. The micro-grooves structure may also reduce lateral resistance by 39% against smooth curved surface. It is confirmed that the regular and controllable micro-groove structures machined on smooth curved surface of ceramic flying body may reduce flying resistance.

Lithography with UV-LED array for curved surface structure

The technology to fabricate high-aspect ratio and micro curved surface structures is needed for optical device fabrication such as micro lens, light guiding device, and so on. In this study, micro curved surface structures were fabricated by using novel lithography technique with UV-LED array and rotary stage (Hanai et al. in Proceedings of the 22nd sensor symposium, pp 516–519, 2005). Smooth surface structures can be fabricated in this technique, because UV-LED which has wide directivity characteristics makes the difference of the UV dose. In addition, the structures can be formed with high uniformity in large area by only one exposure process, because rotation reduces the unevenness of exposure. This technique can control the shapes of structures by changing exposure time and applying gray scale mask method (Waits et al. in Sensors Actuat A 119:245–253, 2005). We fabricated structures of hemisphere, semi-cylinder, and semi-cone by using this technique. High-aspect ratio structures were obtained and they had smooth curved surface. Then, they were used for micro lens fabrication. By using molding technique, micro lenses of the UV curable resin were fabricated on the silicon wafer.

Theoretical prediction of electronic structures of fully pi-conjugated zinc oligoporphyrins with curved surface structures.

A theoretical prediction of the electronic structures of fully pi-conjugated zinc oligoporphyrins with curved surface, ring, tube, and ball-shaped structures was conducted as the objective for the future development of triply meso-meso-, beta-beta-, and beta-beta-linked planar zinc oligoporphyrins. The excitation energies and oscillator strengths for the optimal ring and ball structures were calculated using the time-dependent density functional theory (DFT). Although there is an extremely small energy difference of < 0.1 eV between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the ring structure relative to the same-sized triply linked planar one, the Q and B bands of the former are smaller redshifted excitation energies and intensified oscillator strengths than those of the latter due to the structurally shortened effective pi-conjugated lengths for the electron transition. It is expected that the ball structure becomes an excellent electron acceptor and shows the highly redshifted Q' band in the near-IR region relative to the monomer. The minimum value of the HOMO-LUMO energy gaps of the infinite-length ring structures was estimated using periodic boundary conditions within the DFT, resulting in the metallic characters of both the tube structures with and without the spiral triply linked porphyrin array. The relation between the diameters and strain energies of the tube and ball structures was also examined. The present fused zinc porphyrins may become more colorful materials with new optelectronic properties including artificial photosynthesis than the carbon nanotubes and fullerenes when the axial coordinations of the central metal of porphyrins are functionally used.