Large Twist Angles Research Articles

On the role of texture in governing fatigue crack propagation behavior of 2524 aluminum alloy

The texture evolution of AA2524 cold-rolled sheet during annealing process and texture effect on fatigue crack propagation (FCP) behavior were investigated. Results showed the sample annealed at 400°C for 45min and solid solution-treated at 490°C for 20min had the strongest Goss and P textures, and possessed the lowest FCP rates. EBSD examination indicated Goss, P, Q, Cube, R and S grains induced great crack deflection to retard crack growth, when having large twist and tilt angle component boundary or pure twist boundary with neighboring grains. In the case of small angle boundary or relatively large angle tilt boundary with adjacent grains, Cube, Copper and R grains induced little crack deflection. Additionally, SEM results showed, in the presence of large twist angle component boundary or pure twist boundary, more severely plastic deformation presenting numerous slip bands occurred in Cube, R and S grains than that in Goss, P and Q grains during crack propagation. In contrast, no evident slip bands formed in Cube, Copper and R grains when having small angle boundaries or relatively large tilt angle boundary.

Magnetoresistance (MR) of twisted bilayer graphene on electron transparent substrate

We studied the magnetoresistance (MR) of twisted bilayer graphene (tBLG) on electron transparent substrate. Samples of tBLG were assembled on free-standing silicon nitride (SiNx) membranes (<100nm thick) by transferring chemical vapor deposition (CVD)-grown single layer graphene (SLG) twice; this allowed the measurement of the angle of rotation between the two layers, the twist angle, by electron diffraction using a transmission electron microscope (TEM). To compare with the previous reports on tBLG, we performed Raman spectroscopy on our samples. We measured the MR of tBLG for two different twist angles: 2° (small) and 18° (large). The MR showed superposition of two Shubnikov de Haas (SdH) oscillations for both angles. An analysis of the oscillation peaks by Landau fan diagrams showed difference as twist angle. While the large twist angle (18°) sample had two anomalous π Berry’s phases, the small twist angle (2°) sample had conventional 2π and anomalous π Berry’s phase depending on carrier density.

Two-State Intramolecular Charge Transfer (ICT) with 3,5-Dimethyl-4-(dimethylamino)benzonitrile (MMD) and Its Meta-Isomer mMMD. Ground State Amino Twist Not Essential for ICT.

From X-ray structure analysis, amino twist angles of 90.0° for 2,4-dimethyl-3-(dimethylamino)benzonitrile (mMMD), 82.7° for 4-(di-tert-butylamino)benzonitrile (DTABN), and 88.7° for 6-cyanobenzoquinuclidine (CBQ) are determined, all considerably larger than the 57.4° of 3,5-dimethyl-4-(dimethylamino)benzonitrile (MMD). This large twist leads to lengthening of the amino-phenyl bond, 143.5 pm (mMMD), 144.1 pm (DTABN), 144.6 pm (CBQ), and 141.4 pm (MMD), as compared with 136.5 pm for the planar 4-(dimethylamino)benzonitrile (DMABN). As a consequence, the electronic coupling between the amino and phenyl subgroups in mMMD, DTABN, CBQ, and MMD is much weaker than in DMABN, as seen from the strongly reduced molar absorption coefficients. The fluorescence spectrum of MMD in n-hexane at 25 °C consists of two emissions, from a locally excited (LE) and an intramolecular charge transfer (ICT) state, with a fluorescence quantum yield ratio Φ'(ICT)/Φ(LE) of 12.8. In MeCN, a single ICT emission is found. With mMMD in n-hexane, in contrast, only LE fluorescence is observed, whereas the spectrum in MeCN originates from the ICT state. These differences are also seen from the half-widths of the overall fluorescence bands, which in n-hexane are larger for MMD than for mMMD, decreasing with solvent polarity for MMD and increasing for mMMD, reflecting the disappearance of LE and the onset of ICT in the overall spectra, respectively. From solvatochromic measurements the dipole moments μe(ICT) of MMD (16 D) and mMMD (15 D) are obtained. Femtosecond excited state absorption (ESA) spectra at 22 °C, together with the dual (LE + ICT) fluorescence, reveal that MMD in n-hexane undergoes a reversible LE ⇄ ICT reaction, with LE as the precursor, with a forward rate constant ka = 5.6 × 10(12) s(-1) and a back-reaction kd ∼ 0.05 × 10(12) s(-1). With MMD in the strongly polar solvent MeCN, ICT is faster: ka = 10 × 10(12) s(-1). In the case of mMMD in n-hexane, the ESA spectra show that ICT does not take place, contrary to MeCN, in which ka = 2.5 × 10(12) s(-1). The ICT reactions with MMD and mMMD are much faster than that of the parent compound DMABN in MeCN, with ka = 0.24 × 10(12) s(-1). Because of the very short ICT reaction times of 180 fs (MMD, n-hexane), 100 fs (MMD, MeCN), and 400 fs (mMMD, MeCN), it is clear that the picosecond fluorescence decays of these systems appear to be single exponential, due to the insufficient time resolution of 3 ps. It is concluded that the faster LE → ICT reaction of MMD as compared with DMABN (ka = 0.24 × 10(12) s(-1) in MeCN) is caused by a smaller energy gap ΔE(S1,S2) between the lowest singlet excited states and not by the large amino twist angle. Similarly, the larger ΔE(S1,S2) of mMMD as compared with MMD is held responsible for its smaller ICT efficiency (no reaction in n-hexane).

Circular Differential Scattering of Single Chiral Self-Assembled Gold Nanorod Dimers

Circular dichroism spectroscopy is essential for structural characterization of proteins and chiral nanomaterials. Chiral structures from plasmonic materials have extraordinary strong circular dichroism effects compared to their molecular counterparts. While being extensively investigated, the comprehensive account of circular dichroism effects consistent with other plasmonic phenomena is still missing. Here we investigated the circular differential scattering of a simple chiral plasmonic system, a twisted side-by-side Au nanorod dimer, using single-particle circular dichroism spectroscopy complimented with electromagnetic simulations. This approach enabled us to quantify the effects of structural symmetry breaking, namely, size-mismatch between the constituent Au nanorods and large twist angles on the resulting circular differential scattering spectrum. Our results demonstrate that, if only scattering is considered as measured by dark-field spectroscopy, a homodimer of Au nanorods with similar sizes prod...

Ferrocenyl–Bipyridinium Cations and Their Platinum Complexes Related to Viologens – Preparation, Redox Properties, and Crystal Structures

N-R1-N′-R2-4,4′-Bipyridinium and N-R1-4,4′-bipyridinium salts containing ferrocenyl substituents were prepared as donor–acceptor compounds (R1 = ferrocenyl, ferrocenylphenyl; R2 = ferrocenyl, ferrocenylphenyl, phenyl, methyl). Platinum(II)-bridged diferrocene compounds were prepared by using the N-R1-4,4′-bipyridinium ligands. These compounds display multistage redox properties. The redox potentials of the ferrocenyl and bipyridinium moieties in these compounds are independently affected by molecular modifications, which indicates that conjugation between the donor and acceptor moieties is less effective. Single-crystal X-ray diffraction analyses revealed large twist angles between the two moieties in the solid state. The compounds exhibit broad charge-transfer absorption bands in the range 450–800 nm. No electronic communication was observed between the terminal ferrocenes in the diferrocene complexes.

Fast falling time of fringe-field-switching negative dielectric anisotropy liquid crystal achieved by inserting vertical walls.

We report a simulation result in which we obtained a faster falling time of the fringe-field-switching negative dielectric anisotropy liquid crystal (n-FFS) by segregating the subpixel area with vertical walls. By inserting walls near both edges of the interdigitated electrodes, the transmittance (TR) between the walls was increased by a large twist angle of the liquid crystal. The falling time of the n-FFS with 12 walls was 10.5 ms, about 50% less than the n-FFS without a wall (21.3 ms). The maximum TR (TR(max)) of the proposed n-FFS was 26.1%, which was slightly smaller than the TR(max) of the n-FFS without walls (27.8%) but still larger than the FFS with a positive dielectric anisotropy liquid crystal (p-FFS).

J1910203 開断面部材を利用したモーフィング翼に関する研究 : 日本機械学会指定テンプレートファイル利用について

We propose a new morphing wing concept for wing twist using a specially designed spar consisting of two pipes. One pipe is a thick closed-section member that carries bending moments. The other pipe is the shape variable member and has open and closed sections. The combination of open and closed sections is designed to achieve an objective disribution of twist angles. The ends of the two pipes are connected at the wing tip side and the other ends are connected to the airplane body or motor, providing a torque at the wing root side. According to this mechanism, the wing tip side has a larger twist angle than the wing root side. We established a theoretical formula describing the twist angle of the spar that combines the open and closed section members. The feasibility of the theoretical formula was demonstrated thorough numerical simulations using finite element analyses.

Fabrication of p-i-n solar cells utilizing ZnInON by RF magnetron sputtering

ABSTRACTWe succeeded in photovoltaic power generation of p-i-n solar cells utilizing epitaxial ZnInON film with a wide band gap of 3.1 eV as the intrinsic layer, suitable for a top cell of tandem solar cells. The solar cell shows a high open circuit voltage (Voc) of 1.68 V under solar simulator light irradiation of 3.2 mW/cm2. The solar cell performance becomes worse under 100 mW/cm2, which is mainly attributed to the leakage current caused by crystal defects and grain boundaries. X-ray diffraction analysis reveals that the ZnInON film has rather large tilt and twist angles and a high dislocation density of 7.62×1010 cm-2. Such low crystallinity is a bottleneck for high performance of the solar cells. Our results demonstrate a potential of epitaxial ZnInON films as an intrinsic layer of wide band gap p-i-n solar cells with a high Voc.

An Analytical Investigation of the Trapeze Effect Acting on a Thin Flexible Ribbon

This paper systematically explores the extensional–torsional coupling due to the trapeze effect acting on a thin flexible ribbon subjected to combined tension and torsion. Kinematic relationships as well as expressions for the restoring torque associated with this effect are analytically derived. Additionally, the locus of points about which the cross sections of a twisted ribbon under tension rotate is derived. These points, called torsional centers, are found to be coincident with the centroids of the axial stress field at each station along the ribbon. More generally, it is shown that when a flexible slender member is in tension, combined transverse forces must act at the centroid of the axial stress field to produce pure bending and no twist. As a result, the elastic axis (EA) of the member shifts from the locus of shear centers to the locus of centroids of the axial stress field. A numerical model is developed to investigate the effect of the position of the EA on the prediction of steady-state deformations and natural frequencies of a rotating ribbon with tip mass. By assuming the EA to be the locus of the shear centers, the tip twist is overpredicted by a factor of 2 for small twist angles, and up to 2.5 for large twist deformations. In addition, assuming the EA to be the locus of shear centers results in an error of up to 60% in the predicted natural frequencies at large twist angles.

Power law type Poynting effect and non-homogeneous radial deformation in the boundary-value problem of torsion of a nonlinear elastic cylinder

The boundary value problem of torsion of a solid cylinder is analyzed for a class of hyperelastic materials that exhibit the power law type dependence of the strain energy density on the magnitude of the deformation gradient. The Saint Venant hypotheses are generalized by including the non-homogeneous longitudinal and radial deformations. A nonlinear variational problem with respect to the function of the radial/surface deformation, the function of the longitudinal deformation, the normalized torque and the normalized axial force is formulated. The asymptotic analytical solutions are obtained for the hard device torsion and for large angles of twist. They illustrate the power law type dependencies of the axial force and the reaction torque on the angle of twist with the exponents p and p−1, respectively. For Treloar (neo-Hookean) materials with p = 2, the classical results can be obtained. The finite element analysis of the hard device torsion is performed by MATLAB. The results indicate that for a homogeneous class of materials and large angles of twist non-homogeneous radial/surface deformation can be observed.

Raman mapping investigation of chemical vapor deposition-fabricated twisted bilayer graphene with irregular grains.

Bilayer graphene as a prototype of two-dimensional stacked material has recently attracted great attention. The twist angle between graphene layers adds another dimension to control its properties. In this study, we used Raman mapping to investigate the twist angle dependence of properties of twisted bilayer graphene (TBG) with irregular grains that was fabricated by chemical vapor deposition (CVD). Different Raman parameters including intensity, width, and position of G and 2D peaks were used to distinguish TBG with different twist angles. The statistical results from Raman imaging on the distribution of twist angle are consistent with the results from selected area election diffraction (SAED). Finally, the Raman peak at approximately 1347 cm(-1) for TBG with a large twist angle was assigned to the D-like peak, although it has similar excitation energy dependence of frequency as the defect-induced D peak. Theoretical calculation further confirmed that vacancy-like defect is not favored in the formation energy for TBG with a large twist angle as compared to monolayer graphene or TBG with other twist angles. These results will help to advance the understanding of TBG properties, especially for CVD samples with irregular grains.

Modeling of the Large Torsional Deformation of an Extremely Flexible Rotor in Hover

This paper describes the refined modeling of the large torsional deformation of extremely flexible rotor blades with negligible structural stiffness. Equations of motion including flap bending and torsion, specifically tailored toward unconventional blades with a tip mass and experiencing large elastic twist angles, are derived using the extended Hamilton’s principle. In particular, the foreshortening of the twisted blade arising from the trapeze effect (also called bifilar effect) is explicitly included. Quasi-steady aerodynamic forces are calculated using the blade element momentum theory. The nonlinear coupled equations of motion are solved using a finite-element method. The analysis is used to predict the thrust as well as the spanwise distribution of flap bending and twist of an 18-in.-diam rotor with extremely flexible blades rotating at 1200 rpm at various collective pitch angles. These predictions are correlated with the measurement of loads obtained using a load cell, and the measurement of the deformation obtained using a noncontact optical technique called digital image correlation. It is found experimentally and analytically that tip twist angles in the range of 10 to 40 deg, depending on the blade design, are attained. This torsional deformation is dictated by the combined action of the propeller moment and the trapeze effect. A detailed explanation of the contribution of the trapeze effect to the equations of motion is presented, and it is shown that omitting the axial foreshortening due to the trapeze effect leads to a 50% error in the computation of blade-tip twist.

In-flight rotorcraft blade elastic twist sensor

A novel sensor network for measuring rotorcraft blade elastic twist in flight using an expansion of strain gage theory is proposed and demonstrated. The embedded sensor has negligible weight, small power draw, high bandwidth (≥100 kHz), works in the high centrifugal force environment of the rotating blade and does not disturb the blade airflow or structure. The sensor network can also be used to measure lead–lag and flap bending. The blade is idealized as an Euler–Bernoulli beam in bending and a rod in torsion. The theory is rigorously derived from first principles and shows that a sawtooth shaped sensor will measure twist directly without any numerical integration. The network is modeled computationally for a blade undergoing arbitrary torsional and bending moments. The model shows the twist sensor is not affected by arbitrary loading or noise or local structural discontinuities. The twist sensor is then embedded in a Mach scale rotor blade. The elastic twist measurement from the sensor exactly matched the actual twist angle on the benchtop for small (±0.08°), moderate (±0.3°) and large (±2.5°) elastic twist angles over a 4.6 in span (16% of total span). For the large twist deflections, the blade also had flap bending deflections of ±0.34 in (±7% of span).

Molecular dynamics simulation of effect of tilt angle on mechanical property of magnesium bicrystals

The effects of grain boundary on the deformation behavior of magnesium bicrystals under tensile loading are investigated using molecular dynamics simulation method. Deformation mechanisms of both asymmetric and symmetric magnesium bicrystals are studied. The results show that the twist angle could exert a significant influence on the flow stress in the plastic stage. It is found that the plastic property of symmetric magnesium bicrystal is much better than that of asymmetric counterpart. In addition, for bicrystalline metal with large twist angle, its plastic response is better than that with small angle, owing to the dislocation nucleation activity in the grain boundary region.

Twisted Intramolecular Charge Transfer State for Long-Wavelength Thermally Activated Delayed Fluorescence

Emission wavelength tuning of thermally activated delayed fluorescence from green to orange in solid state films is demonstrated. Emission tuning occurs by stabilization of the intramolecular charge transfer state between a phenoxazine (PXZ) donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor unit separated by a large twist angle. The emission wavelengths of mono-, bis-, and tri-PXZ-substituted TRZ exhibit a gradual red shift while maintaining a small energy gap between the singlet and triplet excited states. An organic light-emitting diode containing a tri-PXZ-TRZ emitter exhibited a maximum external quantum efficiency of 13.3 ± 0.5% with yellow-orange emission.

Torsional Shear Tests on Laminated Veneer Lumber Using a Universal-Type Test Machine

AbstractThis paper presents a study in which a universal-type test machine was configured to apply torsion load-to-failure to estimate the orthotropic shear strengths of full-size laminated veneer lumber (LVL). The objective of the study is to provide insight and detail to a lesser known torsion test setup, while at the same time estimating the torsional shear strength of 1.9E eastern species LVL, hitherto unknown. It was found that at large angles of twist of approximately 23° or more, the test apparatus experienced slippage at the bearings and had the potential to become unstable due to high lateral forces. This was not an obstacle for calculating the shear strength of LVL in this study, as it is a relatively noncompliant material, but likely would be an issue for more compliant materials. The mean in-plane and through-thickness plane shear strengths of 1.9E eastern species LVL were estimated to be in the range of 7.2–11.2 MPa and 5.9–7.3 MPa, respectively.

Importance of Secondary Interactions in Twisted Doubly Hydrogen Bonded Complexes

Three model hydrogen bond arrays that form complexes with large twist angles between their heterocyclic rings were synthesized differing only in the sequence of their hydrogen bond donors and acceptors. The complementary and self-complementary association of the arrays to form complexes was studied computationally and in solution. The analysis reveals the significant impact secondary interactions have on complex stability in such an arrangement despite the very different topology in comparison to typical planar arrays.

Evidence for Interlayer Coupling and Moiré Periodic Potentials in Twisted Bilayer Graphene

We report a study of the valence band dispersion of twisted bilayer graphene using angle-resolved photoemission spectroscopy and ab initio calculations. We observe two noninteracting cones near the Dirac crossing energy and the emergence of van Hove singularities where the cones overlap for large twist angles (>5°). Besides the expected interaction between the Dirac cones, minigaps appeared at the Brillouin zone boundaries of the moiré superlattice formed by the misorientation of the two graphene layers. We attribute the emergence of these minigaps to a periodic potential induced by the moiré. These anticrossing features point to coupling between the two graphene sheets, mediated by moiré periodic potentials.

Micropolar hyper‐elastoplasticity: constitutive model, consistent linearization, and simulation of 3D scale effects

SUMMARYA computational model for micropolar hyperelastic‐based finite elastoplasticity that incorporates isotropic hardening is developed. The basic concepts of the non‐linear micropolar kinematic framework are reviewed, and a thermodynamically consistent constitutive model that features Neo‐Hooke‐type elasticity and generalized von Mises plasticity is described. The integration of the constitutive initial value problem is carried out by means of an elastic‐predictor/plastic‐corrector algorithm, which retains plastic incompressibility. The solution procedure is developed carefully and described in detail. The consistent material tangent is derived. The micropolar constitutive model is implemented in an implicit finite element framework. The numerical example of a notched cylindrical bar subjected to large axial displacements and large twist angles is presented. The results of the finite element simulations demonstrate (i) that the methodology is capable of capturing the size effect in three‐dimensional elastoplastic solids in the finite strain regime, (ii) that the formulation possesses a regularizing effect in the presence of strain localization, and (iii) that asymptotically quadratic convergence rates of the Newton–Raphson procedure are achieved. Throughout this paper, effort is made to present the developments as a direct extension of standard finite deformation computational plasticity. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Polyoxometalates Paneling through {Mo2O2S2} Coordination: Cation-Directed Conformations and Chemistry of a Supramolecular Hexameric Scaffold

The chemical system based on the [Mo(2)O(2)S(2)(OH(2))(6)](2+) aqua cation (noted L) and the trivacant [AsW(9)O(33)](9-) polyoxometalate (noted POM) has been investigated. Depending upon the ionic strength and the nature of the alkali cations, these complementary components assemble to yield three different architectures derived as hexamer (1), tetramer (2), and dimer (3). This series of clusters displays the same stoichiometry {POM(6)L(9)}(36-), {POM(4)L(6)}(24-), and {POM(2)L(3)}(12-) for 1, 2, and 3, respectively, and their conditions of formation differ mainly by the nature and the concentration of the alkali cation (from Li to Cs). Structural characterizations of 1 reveal a large hexameric supramolecular scaffold (about 25 Å in diameter), which encloses a large internal hole (about 200 Å(3)) filled by water molecules and alkali cations (Na(+) or K(+)). The hexameric scaffold 1 exhibits a rare flexibility property evidenced in the solid state by two distinct conformations, either eclipsed (1a) or staggered-off (1b). Both conformations appear clearly separated by a large twist angle (~40°) and depend mainly on the composition of the internal hole. Structure of anion 2 shows a tetrahedral arrangement where the four POM units and the six connecting {Mo(2)O(2)S(2)} linkers are located at the corners and at the edges, respectively. The structure of anion 3 corresponds to the simplest arrangement, described as a dimeric association of two POM units linked by three {Mo(2)S(2)O(2)} pillars. Stability of the hexameric scaffold has been investigated in solution by (183)W and (39)K NMR and by UV-vis, showing that stability of 1 depends strongly on the proportion of potassium ions, which interfere through host-guest exchange. Density functional methodology (DFT) has been applied to compute the geometries and energies of dimer (3), tetramer (2) and hexamer (1) based on {AsW(9)O(33)} (POM) and {Mo(2)O(2)S(2)} (L) units. Calculations tend to show that internal cations act as "glue" to maintain the POM units connected through the conformationally inward-directed {Mo(2)O(2)S(2)} linkers.