Twist Angle Research Articles

On the anisotropic fracture behaviour of AA2050-T84 thick plate

Anisotropy in the fracture behaviour of AA2050-T84 was investigated using 2D digital image correlation (DIC)-assisted 3-point bending fracture toughness test on specimens with crack propagation direction oriented along the normal direction (ND) and rolling direction (RD). The tensile properties along the RD indicated slightly higher yield strength (482 ± 8 MPa) than ND sample (469 ± 9 MPa), while the fracture toughness in terms of energy release rate was higher when the notch was oriented along the ND (35.3 ± 1 kJ/m2) compared to the RD (18.5 ± 0.9 kJ/m2). Fractography of the fractured surfaces and detailed electron backscatter diffraction (EBSD) analysis of the microstructure along crack paths unveiled higher crack tortuosity with extensive secondary cracking in the TD-ND specimen than in the TD-RD. DIC measurements clearly showed a larger deformation zone for the TD-ND specimen also as which corroborated the plastic zone size determined using linear elastic fracture mechanics (LEFM). Additionally, the crystallographic model of tilt and twist angle differences between the neighbouring grains was employed to explain the increase in crack path tortuosity and higher dissipation of plastic work contributing to superior fracture toughness for the TD-ND sample.

Investigation of the effect of rectangular winglet angles on turbulent flow and heat transfer of water/Cu nanofluid in a three-dimensional channel

This numerical simulation studies a homogenous and single-phase nanofluid's turbulent flow and heat transfer behavior in a three-dimensional rectangular microchannel. This study's main purpose is to investigate the use of rectangular winglet angles on flow path and its effect on turbulent flow regime and heat transfer parameters. In the current study, the Reynolds number, winglet attack angle (θ), and twisted angle range (α) (or Pitch angle) from 3000 to 12000, 30°≤ θ ≤ 60°, and 15°≤α ≤ 45°, respectively. Also, Cu nanoparticles with volume fractions of 0–4% are used in water as the base fluid. Results of this study show that heat transfer and flow physics of cooling fluid are affected by the variations of attack angle and winglet twist, and the creation of secondary flows leads to the mixture and deviation of flow. A decrease in the attack angle of the winglet causes the creation of strong vortexes and an increase in Nusselt number and heat transfer. In all investigated situations, with the angle of attack constant, increasing the twist angle can improve the Nusselt number between 11 and 18 percent. Also, increasing the angle of attack of the winglet from 30 to 60° can reduce the Nusselt number by 4–8 percent. The results indicate that changing the winglet angle increases the friction coefficient, and at higher Reynolds numbers, this parameter decreases. Also, by increasing Reynolds number, the ratio of friction coefficient to Nusselt number reduces, leading to the decrease of performance evaluation criterion (PEC).

Repairing of Reinforced Concrete T- section Beam with Web Opening Subjected to Torque by Using Ultra- High Performance concrete (UHPC)

Abstract Due to harsh weather factors, overloading, poor design, and material defects, reinforced concrete (RC) constructions’ early degradation has grown significantly over the last few decades. RC element repair is crucial to improving existing structures’ service life. Also, the transverse openings are frequently utilized in beams in modern structures to supply the service pipes. Because stresses are concentrated in a limited region above and below the opening, the presence of openings in concrete beams causes cracks to grow around the openings. Repairing, maintaining, and upgrading structural elements may be among the most important issues in civil engineering applications. This paper studies the effect of the presence of an opening and repairing of reinforced concrete T-section beam with web opening was subjected to torsion by using ultra-high performance concrete panels with a thickness of 20mm; The experimental work included casting seven beams: one beam without an opening and another beam with an opening, and five rest beams were repaired with UHPC panels in different locations. The results show the effect of an opening by decreasing the ultimate torque and increasing the ultimate angle of twist. The increase in ultimate torque for repairing beams compared to the control beam reached 153%, and a decrease in ultimate twist angle for repairing beams compared to the control beam reached 98%.

Пьезоэлектрический дисковый актюатор кручения с дискретно-спиральными электродами

A mathematical model of a disk (ring) torsion actuator with curvilinear interdigital electrodes – «villi» of a spiral form, which are characterized by a constant value of the orientation angle of an arbitrary section of the villus to the circumferential direction of the disk, has been developed. Bases of electrode-villi interacting with each other through local areas of piezoelectric layer are connected with periodic alternation to central or peripheral concentric circular base electrodes, to outputs of which control voltages are connected. As a result of numerical modeling of the «twisting bimorph» graphs of the dependence of the twist angle and the blocking torque on the ratio of the inner and outer radii and the values of the control voltage at the outputs of the base electrodes of the annular two-layer actuator with symmetrical (relative to the radial line) directions of the spiral orientations of the electrode-villi and, as a result, the spiral polarization lines of the piezoelectric layers working for tension/compression.

Enhancing 2D Photonics and Optoelectronics with Artificial Microstructures.

By modulating subwavelength structures and integrating functional materials, 2D artificial microstructures (2D AMs), including heterostructures, superlattices, metasurfaces and microcavities, offer a powerful platform for significant manipulation of light fields and functions. These structures hold great promise in high-performance and highly integrated optoelectronic devices. However, a comprehensive summary of 2D AMs remains elusive for photonics and optoelectronics. This review focuses on the latest breakthroughs in 2D AM devices, categorized into electronic devices, photonic devices, and optoelectronic devices. The control of electronic and optical properties through tuning twisted angles is discussed. Some typical strategies that enhance light-matter interactions are introduced, covering the integration of 2D materials with external photonic structures and intrinsic polaritonic resonances. Additionally, the influences of external stimuli, such as vertical electric fields, enhanced optical fields and plasmonic confinements, on optoelectronic properties is analysed. The integrations of these devices are also thoroughly addressed. Challenges and future perspectives are summarized to stimulate research and development of 2D AMs for future photonics and optoelectronics.

Factors Influencing the Postoperative Flexion Angle in Cruciate-Sacrificing Rotating Platform of Total Knee Arthroplasty.

Various factors affect the improvement of range of motion (ROM) after total knee arthroplasty (TKA). However, there are few reports specific to cruciate-sacrificing rotating platform (CSRP) TKA. In this study, factors affecting postoperative ROM improvement of CSRP TKA were investigated. The study included 79 patients with knee osteoarthritis who underwent unilateral CSRP TKA at our institution. The group with an improvement of 5° or more (Δflexion angle) than the preoperative was defined as the good Δflexion group (38 knees), and that with less than 5° was defined as the poor Δflexion group (41 knees). The assessments were performed one day before and one year after surgery. Factors including rest and walking pain, knee flexion and extension angle, isometric knee extension strength, the five subscales of Knee injury and Osteoarthritis Outcome Score (KOOS), α, β, γ and δ angles, femoro-tibial angle (FTA), and condylar twist angle were assessed. Unpaired t-test, Mann-Whitney U test, and Chi-square test were used to test differences between the good and poor Δflexion groups. Multiple logistic regression examined the association between each factor and the dependent variables (good Δflexion or poor Δflexion). Significant differences in the preoperative knee flexion, postoperative knee flexion, preoperative knee extension, and postoperative knee extension angles, postoperative KOOS pain and activity of daily living, β, ɤ angles were observed between the good and poor Δflexion groups. The model Chi-squared test revealed that the ɤ angle was significantly affected by the Δflexion angle. With the CSRP TKA, flexion insertion of the femoral component was associated with postoperative flexion ROM improvement.

Optical measurements of the twist constant and angle in nematic liquid crystal cells

We present a reliable optical method for measuring the twist elastic constant K2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {K}_2$$\\end{document} and for assessing the total twist angle in a standard nematic twist cell. The method relies on the use of a non-standard configuration of crossed polarisers and a twist cell, which allows us to measure accurately the twist-cell parameters by reducing the degeneracy between them. Grid patching and an efficient beam propagation method are utilised in the numerical models used for fitting the experimental data. The modelling shows that the polarisation dynamics in a twist cell is non-trivial and much more complex than in a planar cell. The twist elastic constant of three commonly used liquid crystals (5CB, 6CHBT and E7) was successfully extracted from cross-polarised intensity measurements.

Adaptive Neuro-Fuzzy Inference System-Based Predictive Modeling of Mechanical Properties in Additive Manufacturing

Predicting the mechanical properties of Additive Manufacturing (AM) parts is a complex task due to the intricate nature of the manufacturing processes. This study presents a novel application of the Adaptive Neuro-Fuzzy Inference System (ANFIS) to predict the mechanical properties of PLA specimens produced using Fused Filament Fabrication (FFF). The ANFIS model integrates the strengths of neural networks and fuzzy logic to establish a mapping between the inputs and the output mechanical properties, specifically maximum stress, strain, and Young’s modulus. Experimental data were collected from three-point bending tests conducted on FFF samples fabricated from PLA material with different manufacturing parameters, such as infill pattern, infill, layer thickness, printing speed, extruder and bed temperature, printing orientation (along each axis and twist angle), and raster angle. These data were used to train, check, and validate the ANFIS model. The results reveal that the proposed predictive model can effectively predict the mechanical properties of FFF-printed PLA samples, demonstrating its potential for broader applications across various AM technologies and materials, ultimately enhancing the efficiency and effectiveness of the AM fabrication process.

Designable exciton mixing through layer alignment in WS2-graphene heterostructures

Optical properties of heterostructures composed of layered 2D materials, such as transition metal dichalcogenides (TMDs) and graphene, are broadly explored. Of particular interest are light-induced energy transfer mechanisms in these materials and their structural roots. Here, we use state-of-the-art first-principles calculations to study the excitonic composition and the absorption properties of WS2–graphene heterostructures as a function of interlayer alignment and the local strain resulting from it. We find that Brillouin zone mismatch and the associated energy level alignment between the graphene Dirac cone and the TMD bands dictate an interplay between interlayer and intralayer excitons, mixing together in the many-body representation upon the strain-induced symmetry breaking in the interacting layers. Examining the representative cases of the 0° and 30° interlayer twist angles, we find that this exciton mixing strongly varies as a function of the relative alignment. We quantify the effect of these structural modifications on exciton charge separation between the layers and the associated graphene-induced homogeneous broadening of the absorption resonances. Our findings provide guidelines for controllable optical excitations upon interface design and shed light on the importance of many-body effects in the understanding of optical phenomena in complex heterostructures.

Exciton interacting with a moiré lattice: Polarons, strings, and optical probing of spin correlations

The ability to create and stack different atomically thin transition metal dichacogenide (TMD) layers on top of each other has opened up a rich playground for exploring new and interesting two-dimensional (2D) quantum phases. As a consequence of this remarkable development, there is presently a need for new sensors to probe these 2D layers, since conventional techniques for bulk materials such as x-ray and neutron scattering are inefficient. Here, we develop a general theory for how an exciton in a TMD monolayer couples to spin and charge correlations in an adjacent moiré lattice created by a TMD bilayer. Virtual tunneling of charge carriers, assumed for concreteness to be holes, between the moiré lattice and the monolayer combined with the presence of bound hole-exciton states, i.e., trions, give rise to an effective interaction between the moiré holes and the exciton. In addition to the Umklapp scattering, we show that this interaction is spin-dependent and therefore couples the exciton to the spin correlations of the moiré holes, which may be in- as well as out-of-plane. We then use our theory to examine two specific examples where the moiré holes form in-plane ferromagnetic or antiferromagnetic order. In both cases, the exciton creates spin waves in the moiré lattice, which we analyze by using a self-consistent Born approximation that includes such processes to infinite order. We show that the competition between magnetic order and exciton motion leads to the formation of a well-defined quasiparticle consisting of the exciton surrounded by a cloud of magnetic frustration in the moiré lattice sites below. For the antiferromagnet, we furthermore demonstrate the presence of the elusive geometric string excitations and discuss how they can be observed via their smoking gun energy dependence on the spin-spin coupling, which can be tuned by varying the twist angle of the moiré bilayer. All these phenomena have clear signatures in the exciton spectrum, and as such our results illustrate that excitons are promising quantum probes providing optical access to the spin correlations of new phases predicted to exist in TMD materials. Published by the American Physical Society 2024

Twisting Between Topological Phases in 1D Conjugated Polymers via a Multiradical Transition State

AbstractIn recent years, it has become possible via on‐surface bottom‐up synthesis to engineer the topological character of carbon nanostructures. Graphene nanoribbons and 1D conjugated polymers (1DCPs) have thus tailored so as to host either topologically trivial or non‐trivial phases. Molecular design is the primary means to set the topological class of these nanomaterials. However, external control over topology is also demonstrated via electric fields or top‐down hydrogenation. Inspired by the connection between topology and π‐conjugation, here it is demonstrated via first‐principles calculations that aryl ring twist angles also serve as topological knobs. Focusing on rationally designed 1DCPs composed of triarylmethyl (TAM) units, it is shown that rotation of certain aryl rings enables a transition from the trivial to the topologically non‐trivial phase. Accordingly, fixing a particular twist angle configuration (e.g., via chemical functionalization) is equivalent to robustly setting a targeted topological phase. It is also found that in considered 1DCPs, the quantum phase transition occurs without the electronic band gap closing, due to a multiradical antiferromagnetic phase emerging at the transition point. All in all, this study highlights the potential of aryl ring twisting for engineering topological properties in carbon nanomaterials and establishes TAM 1DCPs as exotic topological 1D systems.

Twist angle-driven photoreduction of carbon dioxide on bilayer black phosphorus – A first-principles study

Utilizing first principles calculations, the product selectivity in photocatalytic CO2 reduction was modulated by manipulating the twisted angle in bilayer black phosphorus. Four twisted angles, 0° (AA stacking), 15.40°, 19.00° and 24.66°, were constructed. Comprehensive investigations revealed enhanced carrier mobility and lifetime, especially at a 24.66° twist. Furthermore, an in-depth analysis of the CO2 reduction processes in these four systems was undertaken. Our simulations indicate that in the AA stacking, the photocatalytic CO2 reduction yields multiple products, including HCHO, CH3OH, and CH4, demonstrating limited product selectivity. However, when the surface is twisted at 15.40°, 19.00°, or 24.66°, the sole product is CH4. Remarkably, the 24.66° configuration exhibits the lowest energy barrier for the rate-determining step, measuring just 1.29 eV. These observations suggest that by carefully adjusting the twisted angle in bilayer black phosphorus, we can significantly improve both the activity and selectivity of CO2 photoreduction.

Twist Angle Error Statistical Analysis and Uncertain Influence on Aerodynamic Performance of Three-Dimensional Compressor Rotor

Twist angle errors along the blade radial direction are uncertain and affected by cutting force, tool wear, and other factors. In this paper, the measured twist angle errors of 13 sections of 72 rotor blades were innovatively analyzed to obtain the rational statistical distribution. It is surprisingly found that the under-deflection systematic deviation of twist angle errors shows a gradually increasing W-shaped distribution along the radial direction, while the scatter is nearly linear. Logically, the statistical model is established based on the linear correlation of the scatter by regression analysis to reduce variable dimension from 13 to 1. The influence of the radial non-uniform twist angle errors’ uncertainty on the aerodynamic performance of the three-dimensional compressor rotor is efficiently quantified combining the non-intrusive polynomial chaos method. The results show that the mean values of mass flow rate, total pressure ratio, and isentropic efficiency at the typical operating conditions are lower than the nominal values due to the systematic deviation, indicating that the under-deflection twist angle errors lead to the decrease in compressor thrust. The compressor’s stable operating range is more sensitive to the scatter of twist angle errors, which is up to an order of magnitude greater than that of the total pressure ratio and isentropic efficiency, indicating the compressor’s safe and stable operation risk increases. Additionally, the flow field at the tip region is significantly affected by twist angle errors, especially at the shock wave position of the near-stall condition.

Quasi-1D Moiré superlattices in self-twisted two-allotropic antimonene heterostructures.

Two-dimensional heterostructures, characterized by a twist angle between individual sublayers, offer unique and tunable properties distinct from standalone layers. These structures typically introduce a realm of exotic quantum phenomena due to the appearance of new, long range periodicities associated with Moiré superlattices. Using molecular beam epitaxy, we demonstrate the growth of bi-allotropic 2D-Sb heterostructures on a W(110) substrate composed of twisted α (α-Sb) and β (β-Sb) phases of antimonene. Due to the relatively weak interaction between sublayers, the twist angle is intrinsically determined for each heterostructure, revealing its inherent self-twisted nature. The different atomic lattice symmetries of both allotropes lead to the formation of distinctive quasi-1D Moiré superlattices, while the random nature of the twist angle allows for a wide modulation of the Moiré potential landscape. The observed Moiré patterns on β-Sb/α-Sb heterostructures were compared with a simple model, revealing satisfactory agreement with the experiments and strongly validating the formation of self-twisted β-Sb/α-Sb heterostructures. The samples were characterized in situ using low energy electron microscopy and diffraction techniques providing a real-time tracking of the growth process and insight into the atomic structure of the synthesized nanostructures.

Room Temperature, Twist Angle Independent, Momentum Direct Interlayer Excitons in van der Waals Heterostructures with Wide Spectral Tunability.

Interlayer excitons (IXs) in van der Waals heterostructures with static out of plane dipole moment and long lifetime show promise in the development of exciton based optoelectronic devices and the exploration of many body physics. However, these IXs are not always observed, as the emission is very sensitive to lattice mismatch and twist angle between the constituent materials. Moreover, their emission intensity is very weak compared to that of corresponding intralayer excitons at room temperature. Here we report the room-temperature realization of twist angle independent momentum direct IX in the heterostructures of bulk PbI2 and bilayer WS2. Momentum conserving transitions combined with the large band offsets between the constituent materials enable intense IX emission at room temperature. A long lifetime (∼100 ns), noticeable Stark shift, and tunability of IX emission from 1.70 to 1.45 eV by varying the number of WS2 layers make these heterostructures promising to develop room temperature exciton based optoelectronic devices.

The impact of twisted wind on pedestrian comfort around two non-identical-height buildings in tandem arrangement: a wind tunnel study

Due to the impact of urbanization, an increasing number of buildings are being constructed near hilly terrains because of the limited availability of land resources. The influence of twisted wind profile (TWP) on pedestrian-level wind comfort surrounding two tandem non-identical-height buildings, with a height ratio H1/H2 ranging from 3:1 to 1:0.33, was investigated by wind tunnel experiment with two twist angles (13 ° and 25 °), and compared with the conventional wind profile (CWP). The assessment of thermal comfort was based on Physiologically Equivalent Temperature (PET) using wind velocity measured from the wind tunnel and observation results. Both the mean and gust wind velocities were investigated and compared with wind assessment criteria. The results reveal a significant disparity in the mean and gust wind fields for various H1/H2 under both CWP and TWPs, with the influence of twist being more pronounced for step-up building configuration (H1<H2). The influence of TWPs on the low wind velocity region demonstrated contrasting patterns for buildings with step-up and step-down configurations. The pedestrian level wind environment varies significantly with H1/H2 under CWP and TWPs in the passage between the two tandem buildings, categorized as “Sitting long” for identical-height buildings and modified to “Strolling” and “Walking fast” for step-up building configuration. The twisted wind shifts the “Sitting short” area toward the direction of the approaching twisted wind flow and amplifies the “Strolling” area on the other side. The twisted wind can diminish the thermal comfort surrounding the two tandem structures during summer while enhancing the thermal environment in winter.

Twisted Stacking Metasurface for Complete Amplitude and Phase Control of Circularly Polarized Terahertz Waves

AbstractTerahertz (THz) metasurfaces have emerged as a powerful tool for manipulating THz wavefronts, typically achieved by adjusting various geometric parameters. In this study, an approach is introduced by incorporating interlayer coupling into twisted stacking metasurface design to completely control the amplitude and phase of circularly polarized THz waves. By leveraging the interlayer coupling effect and the Pancharatnam–Berry phase, the study achieves efficient control over transmission phase and amplitude by simply adjusting the relative twist angle between paired C‐shaped split‐ring resonators. To validate the concept, a holographic metasurface is fabricated and characterized, providing experimental evidence of its THz wavefront manipulation capabilities. This design strategy presents a versatile and tunable solution for THz wave control, promising applications in a wide range of functional devices.

Flatbands in a bilayer surface plasmon crystal at a large twist angle due to interlayer strong coupling.

The twisted bilayer system provides an excellent platform for the study of flatbands. In this work, we propose a bilayer hexagonal boron nitride (h-BN)-like surface plasmon crystal at a large twist angle of 38.213° due to the interlayer strong coupling, in which the adjacent pillars are in different radii. We numerically and theoretically calculate the band structure while tuning the pillar radius ratio (PRR) and the interlayer separation distance. As a result, both increasing the PRR and decreasing the separation distance contribute to the transition from weak coupling to strong coupling, leading to the flatbands with slow velocity and large density of state. Consequently, the in-layer geometry as well as the separation distance offers the degree of freedom to achieve flatbands in the bilayer surface plasmon crystal. Our work provides a fundamental understanding of the band structure of the twisted bilayer photonic system, which enriches the methods to obtain flatbands at a large twist angle.

Twisted MoSe2 Homobilayer Behaving as a Heterobilayer.

Heterostructures (HSs) formed by the transition-metal dichalcogenide materials have shown great promise in next-generation (opto)electronic applications. An artificially twisted HS allows us to manipulate the optical and electronic properties. In this work, we introduce the understanding of the energy transfer (ET) process governed by the dipolar interaction in a twisted molybdenum diselenide (MoSe2) homobilayer without any charge-blocking interlayer. We fabricated an unconventional homobilayer (i.e., HS) with a large twist angle (∼57°) by combining the chemical vapor deposition (CVD) and mechanical exfoliation (Exf.) techniques to fully exploit the lattice parameter mismatch and indirect/direct (CVD/Exf.) bandgap nature. These effectively weaken the interlayer charge transfer and allow the ET to control the carrier recombination channels. Our experimental and theoretical results explain a massive HS photoluminescence enhancement due to an efficient ET process. This work shows that the electronically decoupled MoSe2 homobilayer is coupled by the ET process, mimicking a "true" heterobilayer nature.

Collective Charge Excitations between Moiré Minibands in Twisted WSe_{2} Bilayers Probed with Resonant Inelastic Light Scattering.

We establish low-temperature resonant inelastic light scattering (RILS) spectroscopy as a tool to probe the formation of a series of moiré bands in twisted WSe_{2} bilayers by accessing collective inter-moiré-band excitations (IMBEs). We observe resonances in RILS spectra at energies in agreement with inter-moiré-band transitions obtained from an abinitio based continuum model. Transitions between the first and second moiré band for a twist angle of about 8° are reported and between the first and the third, and higher bands for a twist of about 3°. The signatures from IMBE for the latter highlight a strong departure from parabolic bands with flat minibands exhibiting very high density of states in accord with theory. These observations allow one to quantify the transition energies at the K point where the states relevant for correlation physics are hosted.