Effect Of Geometrical Structure Research Articles

Study on methods measuring mechanical properties of arterial wall by macroscopic indentation

Accurately evaluating the local biomechanics of arterial wall is crucial for diagnosing and treating arterial diseases. Indentation measurement can be used to evaluate the local mechanical properties of the artery. However, the effects of the indenter's geometric structure and the analysis theory on measurement results remain uncertain. In this paper, four kinds of indenters were used to measure the pulmonary aorta, the proximal thoracic aorta and the distal thoracic aorta in pigs, and the arterial elastic modulus was calculated by Sneddon and Sirghi theory to explore the influence of the indenter geometry and analysis theory on the measured elastic modulus. The results showed that the arterial elastic modulus measured by cylindrical indenter was lower than that measured by spherical indenter. In addition, compared with the calculated results of Sirghi theory, the Sneddon theory, which does not take adhesion forces in account, resulted in slightly larger elastic modulus values. In conclusion, this study provides parametric support for effective measurement of arterial local mechanical properties by millimeter indentation technique.

Segregation of P and S to frequently occurring grain boundaries of Cu: Single atoms and cooperative effects

Materials design and performance prediction relies on detailed knowledge of the distribution of solutes that can affect the materials properties. Here we report a study on the distribution and mechanisms of interaction of S and P atoms at four relevant grain boundaries (GBs) of fcc Cu: Σ3, Σ5, Σ9 and Σ11. Segregation site preference was investigated for single atoms and compared to the case where impurities segregate as pairs. Both the driving force for segregation—local minima—and the interactions between impurities at the GBs—global minima—have been investigated. An analysis of geometric and electronic structure effects in segregation was performed.Single S-atoms bind more strongly to GB sites than single P-atoms. For all GBs the driving force for segregation decays fast with distance from the planes and reaches the bulk values already at ≈ 4 Å. In the near vicinity of the GBs, with increased concentration, the interactions between S-atoms are mostly attractive, while for the same sites the interactions between P-atoms are mostly repulsive. S-atoms are capable of displacing P-atoms and the accumulation of P is not favorable at the GB planes, while the accumulation of S is favorable. We also performed geometric and electronic structure analyses using symmetry quantifying indicators and developed a descriptor of electronic structure effects called “impurity projected density of states (DOS)” for analyzing the bonding between the impurities and the Cu matrix. Overall, segregation is favored by an increase in the asymmetry of the segregation sites. S binds more asymmetrically to those sites preferring an off-center position while P-atoms bind more symmetrically adopting a central position. At GBs with the same excess volume, S-atoms bind stronger than P-atoms and fitting functions that describe these trends were obtained. The balance between bonding states, antibonding states, and the covalent contributions to the bonding between the impurities and the copper matrix are at the origin of the observed preferences.

Effect of geometric structure and fiber orientation on crashworthiness of honeycomb‐inspired composite thin‐walled tubes

AbstractThis study investigates the crashworthiness of biomimetic composite thin‐walled tubes under quasi‐static axial crushing, focusing on the effects of geometric structure and fiber orientation. The thin‐walled tubes, inspired by honeycomb structures, were manufactured using carbon fiber composites through multi‐cavity preform mold method. Quasi‐static crushing tests and CT scanning observation were conducted to characterize the mechanical response, crashworthiness mechanisms and energy absorption capacity of the thin‐walled tubes. Results demonstrated excellent energy absorption capacities across all configurations, with the C‐0/45 configuration achieving the highest specific energy absorption at 115.03 kJ/kg. The optimal crushing energy absorption process for thin‐walled tubes involves achieving high peak loads and maintaining high load levels. Sustaining high loads requires progressive and stable damage without the formation of extensive intermediate cracks between different plies (indicative of strong interlaminar shear strength). The structural integrity of the uncrushed sections must remain intact without significant damage during the crushing process. Fiber orientation parallel to the loading direction enhances peak load levels and interlaminar shear strength between plies, but may compromise circumferential stiffness and structural stability. The influence of geometric configuration is primarily manifested in the progressive and stable crushing phase, where the tube requires sufficient space to accumulate its own debris without causing damage to the uncrushed thin‐walled structure.Highlights Structures and fiber orientation boost crashworthiness in biomimetic composite tubes. Biomimetic structures were produced using a multi‐cavity preform mold method. CT scans were conducted to characterize the energy absorption mechanisms. Composite tubes demonstrated excellent energy absorption capacity of 115 kJ/kg.

Effects of geometric structures on the sub-Kelvin porous media heat exchanger

A dilution refrigerator is an essential apparatus for achieving sub-Kelvin temperatures. Porous-media heat exchangers used inside dilution refrigerators at temperatures below 100 mK are crucial components that determine their optimal performance. In this study, a numerical model of a porous-media heat exchanger is developed. The local thermal non-equilibrium heat transfer model captures the Kapitza heat transfer between solid and fluid components, whereas the coupled Brinkman-Forchheimer and Navier-Stokes equations describe fluid flows in porous media. Results indicate that a liquid gap can enhance the thermal conduction between the flow channel and porous media, thus improving the heat-exchange efficiency of the porous media. For a constant-volume and -thickness porous media, the most suitable length-to-width ratio is 5. The concentrated phase exhibits a lower outlet temperature, whereas the dilute phase exhibits an appropriate pressure drop. For a constant-volume and -length porous media, the optimal width-to-thickness ratio is 10, which provides the best thermal and hydrodynamic performances. For a full-width liquid gap, increasing its thickness enhances both the thermal and hydrodynamic performances but also increases the usage of 3He. Under a constant volume of liquid gap, a partial-width liquid gap can improve the heat-exchange efficiency, thus achieving better thermal and hydrodynamic performances than the conventional full-width one.

On-machine measurement method of hole parallelism error based on multi-sensor fusion

The hole parallelism error (HPE) is one of the key quality parameters for mechanical parts. However, HPE can usually be out-of-tolerance due to the coupling effect of residual stress, cutting stress, and geometric structure during its machining process. Thus, on-machine measurement and timely adjustment are important guarantees for HPE. This paper proposes an on-machine measurement method of HPE based on multi-sensor fusion that is low-cost, efficient, and suitable for mass production of parts. First, the axis of the cylindrical surface is directly extracted using five points according to the spatial line position relation. Then, the mathematical model of the HPE of two holes’ axes was established through the theory of spatial analytic geometry. The HPE is characterized using two parameters: parallelism magnitude and parallelism direction. Finally, the feasibility of the measurement method in principle and practical application is verified by simulation and experiment. The simulation tests show that the maximum value of the relative error of parallelism magnitude and parallelism direction is −1.38‱. The actual experiments show that the relative error of the measurement results compared with the coordinate measuring machine is 6.23%. None of the standard deviations exceeds the order of magnitude of 0.01 mm. The difference in measurement uncertainty is 0.0003 mm.

The single effect of microstructure, residual strain and geometric structure on the stress corrosion cracking behavior of scratched alloy 690TT

Scratched area on alloy 690TT were treated by relief annealing (RA) and solution annealing plus thermal treatment (SATT), respectively, and then detailed characterization and immersion tests in simulated pressurized water reactor environment were carried out. RA reduces residual strain but not changes microstructure stratification, which causes stress corrosion cracking (SCC). SATT eliminates both strain and microstructure stratification, preventing SCC. Meanwhile, the independent effects of geometric structure, strain and microstructure on SCC behavior were investigated. Specifically, geometric structure is necessary but not sufficient for crack initiation. While the residual strain mainly enhances propagation, and the microstructure promotes both initiation and propagation.

Influence of Geometric Structure, Convection, and Eddy on Sound Propagation in Acoustic Metamaterials with Turbulent Flow

The problem of reducing noise in the transportation is an important research field to prevent accidents and to provide a civilized environment for people. A material that has recently attracted attention in research to reduce noise is acoustic metamaterial, and most of the research projects so far have been limited to the case of static media without flow. We have studied the sound transmission properties of acoustic metamaterial with turbulent flow to develop acoustic metamaterial that be used in transportation. In this paper, the effect of geometrical structure, the convective effect, and the eddy effect on sound propagation in acoustic metamaterial with turbulent flow are investigated, and the relationships between them are analyzed. The convective effect and the eddy effect both reduce the resonant strength of sound transmission loss resulting from the unique geometry of the acoustic crystal, but shift the resonant frequencies in opposite directions. In addition, when the convective effect and the eddy effect of the airflow, as well as the intrinsic interaction effect generated from the unique geometrical structure of the acoustic metamaterial cannot be ignored, they exhibit competition phenomena with each other, resulting in a widening of the resonance peak. As a result, these three effects cause the shift of the resonance frequency of the sound transmission loss and the widening of the resonance peak. The results of this study show that even in the case of turbulent flow, acoustic metamaterial can be used for transportation by properly controlling the geometric size and shape of the acoustic metamaterial.

Effect of three-dimensional geometric structure and surface wettability on two-phase flow behavior in a proton exchange membrane fuel cell gas flow channel: modeling and simulation

Improving water management capability is crucial for enhancing the performance and extending the lifespan of a proton exchange membrane fuel cell (PEMFC). To achieve this goal, this study investigates the coupling effects of geometric features induced by actual gas flow channel (GFC) manufacturing processes and the surface wettability on the dynamic droplet change by simulating 32 cases using the volume of fluid (VOF) method. In addition, the simulated dynamic characteristics of the droplets, such as the centroid position and droplet height, have been verified by comparing them with experimental observations. The reliable results of the simulation show that varied draft angles contribute to different local vortices in the flow channels, arousing two drainage mechanisms—spontaneous and overflow drainage. Besides, the compared results of velocity contours suggest that the curvature effect along the water movement direction could strengthen the speed-up effect around a water droplet, thereby facilitating its detachment. By contrast, a cross-section with filleted corners could cause velocity loss and poor drainage efficiency. A geometric structure with a draft angle of 30° and a bend radius of 1 mm of wavy GFC is beneficial to shorten the water removal time and minimize gas diffusion layer (GDL) water coverage. The hydrophobic treatment of the GDL and channel wall meets both criteria of rapidly reducing liquid water coverage on both the GDL surface and the entire channel. This study's findings are expected to guide the target of both geometric manufacturing and surface treatment processes.

Molecular Dynamics Simulations Correlating Mechanical Property Changes of Alumina with Atomic Voids under Triaxial Tension Loading

The functionalization of nanoporous ceramics for applications in healthcare and defence necessitates the study of the effects of geometric structures on their fundamental mechanical properties. However, there is a lack of research on their stiffness and fracture strength along diverse directions under multi-axial loading conditions, particularly with the existence of typical voids in the models. In this study, accurate atomic models and corresponding properties were meticulously selected and validated for further investigation. Comparisons were made between typical material geometric and elastic properties with measured results to ensure the reliability of the selected models. The mechanical behavior of nanoporous alumina under multiaxial stretching was explored through molecular dynamics simulations. The results indicated that the stiffness of nanoporous alumina ceramics under uniaxial tension was greater, while the fracture strength was lower compared to that under multiaxial loading. The fracture of nanoporous ceramics under multi-axial stretching, was mainly dominated by void and crack extension, atomic bond fracture, and cracking with different orientations. Furthermore, the effects of increasing strain rates on the void volume fraction were found to be similar across different initial radii. It was also found that the increasing tension loading rates had greater effects on decreasing the fracture strain. These findings provide additional insight into the fracture mechanisms of nanoporous ceramics under complex loading states, which can also contribute to the development of higher-scale models in the future.

In Situ Exfoliated Polymer/Boron Nitride Thermal Conductors via Hybrid Geometry Induced Local Ball Milling

Preparing thermal conductive polymeric composites under a premise of low filler content is currently a research hotspot. In this work, boron nitride (BN) with different geometries was used to enhance the thermal conductivity (TC) of a polymer, for the purpose of fabricating advanced polymeric thermal conductors. The effect of filler content and hybrid geometric structure on the properties of composites was investigated. When the proportion of hexagonal BN (h-BN) and spherical BN (s-BN) in the composite was 7:3, the TC of the sample was the highest, which reached 0.88 W/(m·K) and 3.49 W/(m·K) for 20 and 50 wt % overall loadings of BN, respectively. Moreover, the results of X-ray diffraction and numerical simulation analysis also confirmed that the effect on exfoliation would be significantly enhanced by loading hybrid geometric fillers, resulting in producing more BN sheets consisting of thermal paths. The obtained results provided a new explanation for the interaction of hybrid geometric fillers in complex flow fields and a new solution for the fabrication of advanced thermal management materials.

Stress-wave propagation in multilayered and density-graded viscoelastic medium

Uncovering the dynamic behaviors of viscoelastic medium with complicated internal geometric structures, i.e., graded density and multilayers, is of great significance in the fields of impact energy absorption and structure protection. Herein, a theoretical solution for the stress wave propagating in density-graded viscoelastic medium is first obtained by combining the Laplace transform method and the Eulerian governing equation. Effects of graded density (e.g., materials with density increasing or decreasing) and multi-layers on wave dispersions in viscoelastic medium are then discussed. The propagation of shear stress in striped density-graded medium is deduced and analyzed while subjected to oblique impacting. The wave propagation rate of shear stress across the interfaces of multi-layered medium is discussed. Dynamic mechanical parameters of density-graded TiB2-TiB-Ti ceramics are experimentally studied by the split Hopkinson pressure bar (SHPB) technique. The dynamic laser irradiating technique combined with the advanced velocity interferometer method is employed to detect the mechanical parameters of shell with layered-structure (composed of nacre and chalk). The effects of internal geometric structures and contents on dynamic behaviors of viscoelastic medium are revealed, and the theoretical results are preliminarily validated by experimental results. This work provides a useful method to calculate and analyze the dynamic viscoelastic properties of complicated mediums, which could be also used as a guideline for designing anti-impacting composites with density-graded and layered structures.

Design of periodic arched structures integrating the structural nonlinearity and band gap effect for vibration isolation

In this study, a Roman-bridge-inspired metamaterial for vibration isolation is proposed that simultaneously realizes a geometrical nonlinear structure and band gap effect, through the arrangement of periodic materials in a semicircular arched structure. Finite element analysis and band diagram analysis are performed to verify the effect of the periodic arch-structured metamaterial by calculating the transmissibility and band gap frequency range of cuboid, arched and periodic arched models. Based on the calculation results, the relationship between the geometrical parameters of the periodic arch structure and band gap frequency are analyzed, and an empirical correlation is formulated for the generation of a training database for a machine learning optimization model. The geometrical parameters of the metamaterial were optimized using the machine learning model based on an autoencoder architecture with supervised learning. An optimized metamaterial with a band gap area at three target frequencies is generated by the trained neural network, and the effectiveness of the optimized structure is validated by both numerical analysis and a frequency response test.

Optimizing metal geometrical structure of transition metal phosphides/P doped g-C3N4 enabling boosted water splitting

Metal geometrical structure engineering of composite catalysts is powerful to boost their photocatalytic performance of hydrogen evolution. Herein, by rationally designing, transition metal phosphides (TMPs) have been loaded onto the P doped g-C3N4 (PCN) to construct catalysts TMPs/PCN. For the first time, the effect of geometrical structure of TMPs on the photocatalytic activity is optimized and a geometrical-site-dependent photocatalytic hydrogen evolution is experimentally determined. Tri-metallic FeCoNiP/PCN, having 59.6% occupancy of tetrahedral cobalt sites, gives hydrogen production rate of 205 μmol/g/h, better than that of mono-metallic (FeP, CoP, NiP), bi-metallic (FeCoP, CoNiP, FeNiP) TMPs/PCN, and even much superior to that of Pt/b-g-C3N4 and Pt/PCN. Trimetallic TMPs/PCN catalysts also show excellent OER performance. In addition to the efficient electron transfer between FeCoNiP and PCN, which can effectively improve the separation of photogenerated carriers, the high occupancy of tetrahedral cobalt sites of FeCoNiP as a co-catalyst promotes the formation of active intermediates, being the key to significantly improve the catalytic performance of ternary FeCoNiP/PCN. The findings in this work, especially about a link of the photocatalytic performance of TMPs/PCN composites and occupancy of tetrahedral cobalt site in co-catalysts TMPs, can open new occasion for creating novel composite catalysts and extending to other applications.

Reversible lithium deposition/dissolution reaction with low polarization through a cross-linked polymer: Geometrical structure effects of the polymer protective layer on lithium metal anodes

A lithium metal anode was coated with a cross-linked PEO-based polymer composed of poly(ethylene glycol) diacrylate (PEGDA) as a cross-linker and poly(ethylene glycol) methyl ether acrylate (PEGMA) as a base polymer to suppress electrolyte decomposition and lithium dendrite formation, thereby improving its electrochemical performance. The ca. 10 μm thick polymer membranes with flat and pore-free surface were successfully fabricated on the lithium metal electrode. Physicochemical characteristics of the synthesized polymer membrane such as elastic modulus, electrolyte uptake and mesh size indicate that polymer structure is changed from a linear structure to a bridged network one and increased in its crosslinking density by mixing PEGDA. The PEGDA increased the connectivity of the nanosized cross-linked domains, which led to improvement of the lithium ion transport number in membrane, and polarization and reversibility of deposition/dissolution reaction of lithium. Additionally, no dendrite formation was observed during lithium deposition/dissolution reaction through the bridged network structured polymer membrane. The structure of the PEO-based coating polymer is one of the important factors in the stabilization of the deposition/dissolution reactions of lithium metal anodes, and a bridged-network structure with preferential ion transport capability is more effective to improve these reactions than a straight-chain structure.

Theoretical Study on the Aggregation and Adsorption Behaviors of Anticancer Drug Molecules on Graphene/Graphene Oxide Surface.

Graphene and its derivatives are frequently used in cancer therapy, and there has been widespread interest in improving the therapeutic efficiency of targeted drugs. In this paper, the geometrical structure and electronic effects of anastrozole(Anas), camptothecin(CPT), gefitinib (Gefi), and resveratrol (Res) on graphene and graphene oxide(GO) were investigated by density functional theory (DFT) calculations and molecular dynamics (MD) simulation. Meanwhile, we explored and compared the adsorption process between graphene/GO and four drug molecules, as well as the adsorption sites between carriers and payloads. In addition, we calculated the interaction forces between four drug molecules and graphene. We believe that this work will contribute to deepening the understanding of the loading behaviors of anticancer drugs onto nanomaterials and their interaction.

Experimental investigation of factors influencing acoustic liner drag using direct measurement

Nacelle acoustic liners inevitably generate greater aerodynamic drag than smooth walls. It is necessary to study the factors influencing acoustic liner drag to reduce engine fuel consumption and emissions. In this study, experimental measurements were conducted in a grazing flow tube with bulk Mach numbers ranging from 0.1 to 0.6. A drag balance was designed to measure the liner drag directly. This balance can eliminate the interference of the vertical force and moment by arranging the sensors appropriately. A wedge-shaped sidewall was proposed that can eliminate the side effects of the differential pressure force effectively. The test samples involved Helmholtz resonator liners, including conventional acoustic liners and multislot acoustic liners, and a smooth wall set as a reference for comparison. The effects of geometric structures on the acoustic liner drag were studied, including perforation size, plate thickness, porosity, perforation, slot patterns, and fabric mesh. Experimental results show that Mach number (M) 0.4 is the critical point. At M < 0.4, the acoustic liner drag is proportional to the perforation diameter. At M > 0.4, the opposite trend is observed. Moreover, the acoustic liner drag is directly proportional to the porosity and perforated plate thickness at M = 0.1 to 0.6. Experimental results also indicate that some structural characteristics can effectively reduce the acoustic liner drag, including placing a fabric mesh under the perforated panel, adopting a staggered hole layout, and slotting perpendicular to the flow direction. The summarized influencing factors are helpful for avoiding high flow drag structures in the design of acoustic liners and subsequently, reducing the aircraft fuel consumption.

Functional groups anchoring-induced Ni/MoOx-Ov interface on rice husk char for hydrodeoxygenation of bio-guaiacol to BTX at ambient-pressure

Bio-char is a promising carrier for the catalysts applied in hydrodeoxygenation (HDO) of bio-oil. The impact of bio-char surface microenvironment on the active phase needs to be further explored. In this work, O-containing functional groups were employed in adjusting the surface microenvironment of biomass-derived char with Ni–Mo loading. And the effect of geometric structure and electronic modification of Ni/MoOx-Ov interface on the atmospheric HDO activity of guaiacol over Ni-MoOx/bio-char catalyst was studied. Multiple characterizations revealed that the O-containing functional groups on bio-char carriers not only promoted the dispersion of active metals, but also decreased the particle size, thus resulting in the boosting of Ni/MoOx-Ov interface. Moreover, the intrinsic active sites were sumi-quantitatively analyzed via H2-TPD, and a positive correlation was established between BTX yield and quantity of Ni/MoOx-Ov interface. Furthermore, the effects of hydrothermal parameters for preparing bio-char, HDO conditions (temperature, WHSV and stability) and the metal loadings on the catalytic performance of Ni-MoOx/bio-char catalysts were studied in detail. This work provides a theoretical support to develop cost-effective catalysts with the utilization of biomass waste material.

An investigation into the effects of geometric scaling and pore structure on drug dose and release of 3D printed solid dosage forms

A range of 3D printing methods have been investigated intensively in the literature for manufacturing personalised solid dosage forms, with infill density commonly used to control release rates. However, there is limited mechanistic understanding of the impacts of infill adjustments on in vitro performance when printing tablets of constant dose. In this study, the effects and interplay of infill pattern and tablet geometry scaling on dose and drug release performance were investigated. Paracetamol (PAC) was used as a model drug. An immediate release erodible system (Eudragit E PO) and an erodible swellable system (Soluplus) were prepared via wet granulation into granules and printed using Arburg Plastic Freeforming (APF). Both binary formulations, despite not FDM printable, were successfully APF printed and exhibited good reproducibility compared to pharmacopoeia specification. The physical form of the drug and its integrity following granulation and printing was assessed using DSC, PXRD and ATR-FTIR. Two infill patterns (SM1 and SM2) were employed to print tablets with equal porosity, but different pore size, structure and surface area to volume ratio (SA/V). Geometry scaling (tablet height and diameter) of Eudragit-PAC tablets was not found to significantly influence the release rate of the tablets with 30 to 70% infill density. When increased to 90% infill density, geometric scaling was found to have a significant effect on release rate with the constant diameter tablet releasing faster than the constant height tablet. Soluplus-PAC tablets printed using different infill patterns demonstrated similar release profiles, due to swelling. Geometric parameters were found to significantly influence release profiles for tablets printed at certain infill densities giving new insight into how software parameters can be used to tune drug release.

Experimental research on surface characteristics and subsurface damage behavior of monocrystal sapphire induced by helical micro abrasive tools

Sapphire crystals have been widely used in the fields of national defense and optical devices due to good chemical stability and high temperature resistance. In this study, the surface quality, edge fracture characteristic and subsurface damage behavior of sapphire induced by helical micro abrasive tools were experimentally investigated. Effects of geometrical structure of helix micro abrasive tool and process parameters on surface topography, section profile height and surface roughness of sapphire were analyzed. To reveal formation mechanism of subsurface damage of sapphire induced by micro-grinding process, the high temperature chemical corrosion was used to etch sapphire workpiece, and the transformation law of surface morphology and crack layer information with corrosion time were obtained. Besides, effects of geometrical structure of helix micro abrasive tool and process parameters on edge collapse feature and surface fracture length for sapphire crystals were discussed. Furthermore, the ratio of etching surface defect area was put forward to qualitatively the degree of subsurface damage and experimental results indicated that the ratio of etching surface defect area of sapphire was increased with the increase of feed speed and grinding depth. This research can supply a theoretical basis for understanding surface feature and subsurface damage behaviors of monocrystal sapphire involved in micro-grinding process and provide important guidance for high surface quality and low subsurface damage grinding of hard brittle materials.

Effect of Topology and Geometric Structure on Collective Motion in the Vicsek Model

In this work, we explore how the emergence of collective motion in a system of particles is influenced by the structure of their domain. Using the Vicsek model to generate flocking, we simulate two-dimensional systems that are confined based on varying obstacle arrangements. The presence of obstacles alters the topological structure of the domain where collective motion occurs, which, in turn, alters the scaling behavior. We evaluate these trends by considering the scaling exponent and critical noise threshold for the Vicsek model, as well as the associated diffusion properties of the system. We show that obstacles tend to inhibit collective motion by forcing particles to traverse the system based on curved trajectories that reflect the domain topology. Our results highlight key challenges related to the development of a more comprehensive understanding of geometric structure's influence on collective behavior.