Effects Of Anisotropic Coupling Research Articles

Symmetry-driven anisotropic coupling effect in antiferromagnetic topological insulator: Mechanism for a quantum anomalous Hall state with a high Chern number

Symmetry-driven anisotropic coupling effect in antiferromagnetic topological insulator: Mechanism for a quantum anomalous Hall state with a high Chern number

A new set of explicit solutions for postbuckling behaviour of anisotropic shear deformable laminated cylindrical shells with general imperfection distribution and thermal loading

Thermal postbuckling analysis is presented for shear-deformable anisotropic laminated cylindrical shell with general imperfection distribution under several typical temperature fields are analyzed, including uniform temperature, tent-like linear distribution, axial and circumferential quadratic parabolic temperature fields over the shell surface and through the shell thickness. On this basis, the general temperature distribution can be obtained based on the three-dimensional steady-state heat transfer equation. At the same time, based on the high order shear deformation theory including anisotropic coupling effect, geometrically nonlinear large deflection displacement-strain relationship, the general initial geometric imperfections obtained by measurement and analytical means are introduced, and the thermal buckling equilibrium differential equation of anisotropic shear deformable laminated cylindrical shell with initial imperfections is established. A two-step perturbation-Galerkin integral method is used to obtain explicit solutions for the path development direction of post-thermal buckling equilibrium. The results of parameter analysis show that the material properties and temperature dependence, temperature distribution, lay-up and geometric parameters such as radius-to-thickness ratio have important effects on the thermal buckling load and postbuckling equilibrium path. The present method provides an effective theoretical prediction and analysis method for the design of the carrying capacity of submarine pipelines.

New Materials for Sports Equipment Made of Anisotropic Fiber-reinforced Plastics with Stiffness Related Coupling Effect

Fiber-reinforced plastics (FRP) are often used in sporting goods to increase their lightweight degree. Symmetric laminate are mostly used because of the complex deformation effects of asymmetric multi-layer Structures (MLS), which are also hard to handle in the complete production process. In the board sports industry almost all products are made out of symmetric biaxial or triaxial glass fiber fabrics to increase the stiffness and strength of the sandwich composites. Carbon fiber-reinforced plastics (CFRP) are used to reduce the high performance products’ weight. FRP are also well suited to integrate additional functions. An uncommon way for such integration is the use of the material intrinsic anisotropic coupling effects of asymmetric MLS. Based on these deformation effects of FRP an all-new snowboard with the so-called anisotropic layer design technology (A.L.D.-tech) was developed at the Institute for Structure Lightweight, Technische Universität Chemnitz. In this product the anisotropic coupling effects are used for implementing a riding specific deformation of the snowboard to increase the customer value. At present, the spin-off silbaerg TM Snowboards uses three different levels of the A.L.D.-tech for the worldwide first serial products with such coupling effects; snowboards made of glass and carbon fiber reinforced sandwich structures. By varying the fabric material and the lay-up of the A.L.D.-tech MLS, different characteristics of the riding specific deformation are adjustable. For developing and computing this all-new type of board sport product the researchers used a numerical approach using a Finite Element Method (FEM) software solution provided by ANSYS. The model based on the Classical Laminate Theory (CLT) and focuses also the failure assessment by using Cuntze's failure criteria [1]. The ABD-Matrix of the CLT provides a good tool to visualize the different deformation effects of asymmetric MLS, which depends on the disc-plate problem. Due to this an A.L.D.-tech MLS with an unusual bending-curvature or bending-torsion coupling was developed, verified and launched into the market. This paper contains the description of different fabric material and lay-up combinations to adjust the grade of the anisotropic coupling of the snowboard as well as the integration of stitched sensors to measure the deformation while riding the snowboard. The comparison between numerical solution and experimental verification tests confirm the accuracy of the numerical model.

Effects of disoriented grains on the elastic constants of directionally solidified superalloys

Two models, namely, coaxial and non-coaxial, are proposed to estimate the elastic constants of directionally solidified superalloys, which behave like transversely isotropic materials and require five independent elastic constants. Coaxial model considers each grain as an individual and obtains the averaged values. Because of the longitudinal grain structure, three independent constants are carried over from original cubic single crystal and the other two are obtainable through the averaging process. For each disoriented direction in the non-coaxial model, a lumped grain, which behaves like a transverse isotropy is proposed. By assuming the disoriented angle follows Weibull distribution, non-coaxial model obtains the expectations of compliances from probability consideration. Disoriented effect could be simulated through the parameters of Weibull distribution. Experimental off-axis Young's modulus data are compared with numerical predictions by both models. Excellent agreement is observed between coaxial model and 90° off-axis experimental data. However, the coaxial model over predicts the 45° off-axis Young's modulus, because anisotropic coupling effect is very strong in the real off-axis specimens. As non-coaxial model considers the disoriented effect, excellent agreement is observed between non-coaxial model and 45° off-axis experiment data. Disoriented grain consideration reduces the anisotropic coupling effect and predicts better to the real off-axis specimens.

Mechanical coupling in single crystal silicon for MEMS design

There is an active interest in the development of microelectromechanical systems (MEMS) devices using single crystal silicon. Single crystal silicon is known to display anisotropic mechanical properties and several papers have been presented that deal explicitly with various aspects arising from the anisotropy. In this paper we develop comprehensive expressions and graphs to allow for the easy determination of anisotropic coupling effects in beam and plate structures with a particular emphasis upon (100) and (111) wafers. Further, through the use of illustrative examples, we highlight practical issues in modeling single crystal MEMS devices with special attention to the ability of beam and plate models to accurately capture three-dimensional (3-D) behavior.

High-field transport of electrons and radiative effects using coupled force-balance and Fokker-Planck equations beyond the relaxation-time approximation

The dynamics of a many-electron system under both dc and infrared fields is separated into a center-of-mass and a relative motion. The first-order force-balance equation is employed for the slow center-of-mass motion of electrons, and the Fokker-Planck equation is used for the ultrafast relative scattering motion of degenerate electrons. This approach allows us to include the anisotropic energy-relaxation process which has been neglected in the energy-balance equation in the past. It also leads us to include the anisotropic coupling to the incident infrared field with different polarizations. Based on this model, the transport of electrons is explored under strong dc and infrared fields by going beyond the relaxation-time approximation. The anisotropic dependence of the electron distribution function on the parallel and perpendicular kinetic energies of electrons is displayed with respect to the dc field direction, and the effect of anisotropic coupling to an incident infrared field with polarizations parallel and perpendicular to the applied dc electric field is shown. The heating of electrons is more accurately described beyond the energy-balance equation with the inclusion of an anisotropic coupling to the infrared field. The drift velocity of electrons is found to increase with the amplitude of the infrared field due to a suppressed momentum-relaxation process (or frictional force) under parallel polarization but decreases with the amplitude due to an enhanced momentum-relaxation process under perpendicular polarization.

Anisotropic effects in the compression buckling of laminated composite cylindrical shells

This paper addresses two aspects of buckling relevant to design. The first describes the preliminary experimental results that validate the presence of a newly reported spiral buckling mode; whilst the second concerned the effects of extension/twist anisotropy on the buckling loads of cylindrical shells under compression. The influence of designing laminates with antisymmetric lay-ups in comparison with a symmetrical lay-up is also investigated. Antisymmetric quasi-isotropic laminates, based on 0, 90 and ±45° angles produces greater buckling loads than the equivalent symmetric lay-up. Whilst all anisotropic coupling effects appear to lower the buckling loads, a laminate that is 48 plies thick is necessary to eliminate them in thin-walled shells. Such a laminate is at least 6 mm thick. Many designs require thinner laminates, and in so doing, mitigate the need for guidelines on efficient anisotropic lay-ups. Neglecting the effect of prebuckling deformation, it is found that extension/twist coupling is less deleterious than flexural/twist coupling in this respect. Therefore, antisymmetric laminates appear preferable for initial buckling of quasi-isotropic laminates.

Exact analysis of cascaded second-order nonlinearity in rotated Ti:LiNbO3 Couplers

The effects of anisotropic coupling on the nonlinear behavior of different LiNbO3 waveguides and couplers employing cascaded second-order nonlinearity are analyzed and the importance of leaky mode effect is shown. A set of practical coupling structures made of both symmetric and asymmetric waveguides is investigated and their performance is compared. The home-made computer-code, based on coupled wave theory and anisotropic mode propagation in the complex domain, allows an exact electromagnetic investigation of devices, taking into account both guided and leaky propagation in structures which exhibit losses, the generated second harmonic wave having leaky nature. As an example, for the well-investigated slab three layer waveguide, by taking into account the leaky nature of the generated second harmonic, the modal mismatch Δβ = 333 m−1 is obtained at the azimuthal angle θm ≅ 61.9∘ (between the crystal optical c-axis and the propagation direction) while the angle found via the conventional approach is θm ≅ 63.5∘. Moreover, the calculated second harmonic wave exhibits an attenuation equal to 7.44 × 10−1dB/cm that strongly influences the whole cascaded second-order phenomenon. The simulation results, for those structures in which it is possible to neglect the hybrid and leaky nature of the propagation modes, are compared with the literature data and an excellent agreement is found.

Shear Correction Factors for Thin-Walled Composite Boxbeam Considering Nonclassical Behaviors

In this study, shear correction factor for thin-walled composite boxbeam is investigated with considering the anisotropic coupling effects in its laminated walls parallel to the external shear load. We first consider a generally orthotropic laminated beam whose cross section is rectangular. The beam does in-plane shear deformation by the applied shear force, so that there arises the effect of extension-shear coupling which does not arise in the conventionally studied out-of-plane shear deformation. The shear correction factor is defined by the energy considerations with taking into account the coupling effect. Then the procedures are extended to the case of laminated thin-walled boxbeam, where the coupling plays a significant role due to the geometric characteristics of boxbeam. The shear correction factors for the representative boxbeams which are the core structural components of modern composite helicopter rotor blade are presented with the change of their laminate sequences.

Crack-tip dislocations and fracture behavior in Ni 3Al and Ni 3Si

The ideal Griffith energies and the critical stress intensity factors for three cleavage modes are determined from the calculated elastic constants and surface energies. The propensity for crack tip deformation is estimated on the basis of the calculated antiphase boundary (APD), complex stacking fault and superlattice intrinsic stacking fault energies and the anisotropic coupling effect on dislocation mobility, i.e. non-Schmid effects. It is shown that while the calculated Griffith energy of Ni 3 Si is larger than that of Ni 3Al, dislocation emission from a crack tip is easier and dislocation mobility is higher in Ni 3Al than in Ni 3Si. When a crack is loaded in a mixed mode (K I + K III), emission of a super-Shockley partial from the crack trailing extended SISF is predicted and confirmed by in situ straining transmission electron microscopy observations of Ni 3Al.

Deformation twinning in h.c.p. metals and alloys

Abstract The important role of deformation twinning in plastic deformation of h.c.p. metals and alloys is emphasized and the twin nucleation mechanisms are examined. A bifurcated homogeneous nucleation model is presented on the basis of the classical nucleation theory, the shape bifurcation theory and the elastic inclusion model. The activation energy for twin formation depends most sensitively on the twin-boundary energy. The structures and energies of (1122) and (1011) coherent twin boundaries are obtained by atomistic simulations using the Lennard-Jones potential for a model h.c.p. metal. The anisotropic coupling effect of normal stresses on twin disolocation mobility is determined over a wide temperature range (0-1200 K). The available experimental data on titanium and zirconium are consistent with the prediction from the proposed nucleation model and the temperature-dependent mobility of twin dislocations. Alloying effects on twinning and future research areas are discussed.

Theory of Upper Critical Field of Superconducting Alloys

The investigation is carried out of the upper critical field H c 2 of a superconducting alloy in the case where an appreciable variation of the transition temperature T c is observed on alloying. It is assumed that the density of states is not a smooth function of energy at and near the Fermi level and that the BCS coupling parameter is anisotropic. It turns out that the shift of Fermi level on alloying does not modify the expression for H c 2 usually employed if one interprets T c and Fermi velocity in the expression as those of the alloy. It is also discussed that a recent investigation by Teichler on the effect of anisotropic coupling ignores an important term. For the case of Nb–Ta system, it becomes clear that the shift of Fermi level is small enough so that Fermi velocity remains constant even though there exists a large variation in T c with alloying. Qualitative discussions are given on the effect of anisotropic coupling, and it turns out that more detailed experimental investigations are needed t...