Significant Anisotropic Behavior Research Articles

Magnetic order in single crystals of Na3Co2SbO6 with a honeycomb arrangement of 3d7Co2+ ions

We have synthesized single crystals of Na$_3$Co$_2$SbO$_6$ and characterized the structure and magnetic order by measuring anisotropic magnetic properties, heat capacity, x-ray and neutron single crystal diffraction. Magnetic properties and specific heat of polycrystalline Na$_3$Co$_2$SbO$_6$ were also measured for comparison. Na$_3$Co$_2$SbO$_6$ crystallizes in a monoclinic structure (space group $C2/m$) with [Co$_2$SbO$_6$]$^{3-}$ layers separated by Na$^+$ ions. The temperature dependence of magnetic susceptibility shows significant anisotropic behavior in the whole temperature range 2\,K-350\,K investigated in this work. An effective moment of about 5.5\,$\mu_B$/Co$^{2+}$ from a Curie-Weiss fitting of the magnetic susceptibility is larger than the spin only value and signals significant orbital contribution. Na$_3$Co$_2$SbO$_6$ single crystal undergoes a transition into a long-range antiferromagnetically ordered state below $T_N$=5\,K. Neutron single crystal diffraction confirmed the zigzag magnetic structure with a propagation vector k\,=\,(0.5, 0.5, 0). The ordered moment is found to be 0.9\,$\mu_B$ at 4\,K and align along the crystallographic \textit{b}-axis. Density functional theory calculations suggest that the experimentally observed zigzag order is energetically competing with the Neel order. It is also found that the covalency between Co $d$ and O $p$ is quite strong and competes with the local spin-orbit coupling, suggesting a $J_{eff}$=1/2 ground state may not be realized in this compound.

Effects of microstructure and internal defects on mechanical anisotropy and asymmetry of selective laser-melted 316L austenitic stainless steel

In this study, the anisotropic and asymmetric mechanical behaviors of 316 L stainless steel processed using selective laser melting, were investigated experimentally and theoretically by performing tension and compression tests along different directions of the sample. Significant anisotropic and asymmetric behaviors were observed due to the effects of microstructure and internal defects. Severe anisotropy in stress level and elongation were found in the tensile behavior, while compression behavior exhibited somewhat different yield strength and strain hardening with loading direction. Finite element simulations based on the real microstructure and microstructural analysis confirmed that pore shape and molten pool boundary are the major reasons for the mechanical anisotropy and asymmetry. This result supports a guideline for designing parts and the scanning directions used in selective laser melting.

Plastic anisotropy and deformation-induced phase transformation of additive manufactured stainless steel

Plastic anisotropy and deformation-induced phase transformation of additively manufactured (AM) stainless steels were investigated via in-situ neutron diffraction, electron backscatter diffraction, metallography, and fractography. Two types of tensile specimens were manufactured: (1) One sample was vertically fabricated with its tensile axis parallel to the z-direction (AM-V), (2) The other sample was horizontally fabricated with its tensile axis perpendicular to the z-direction (AM-H). A commercial 15-5PH stainless steel (CA) was used for comparison. AM steel revealed enhanced yield strength, tensile strength, and uniform elongation over CA, which was mainly due to grain refinement and transformation induced plasticity (TRIP). Different onsets of strain nonlinearity between AM-V and AM-H were closely related to martensitic phase transformation. Stresses estimated from lattice strains measured by neutron diffraction matched well with the applied stress-strain curves. After plastic deformation, voids were formed and congregated near the solidified line where fine grains were populated. Higher dislocation density was observed in the fine grain zone, and lower density was shown in the relatively coarse grain zone. AM steels exhibited significant anisotropic fracture behavior in terms of loading direction. In contrast to isotropic failure for CA and AM-V, AM-H revealed anisotropic failure with elliptical formation of the fracture feature. The fracture surface of AM-H possessed many secondary cracks propagating perpendicular to the building direction. The occurrence of secondary cracks in AM-H resulted in rapid load drop during tensile loading after necking.

Enhanced quasi-isotropic ductility in bi-textured AZ91 Mg alloy processed by up-scaled RD-ECAP processing

In the present work, an up-scaled rotational die equal channel angular pressing (RD-ECAP), which circumvented the limitation of the removing and re-inserting procedure of the conventional ECAP, was developed to make it possible to prepare large scale ECAP billets with dimension of 50 mm × 50 mm × 100 mm, and was successfully applied to an as-cast AZ91 alloy without a prior thermomechanical treatment. Benefiting from the large scale ECAP billet, the anisotropic tensile behavior of the ECAP alloy was examined, and was carefully linked to its microstructure and texture evolution. Our results shown that the large scale AZ91 RD-ECAP alloy exhibited simultaneously improved strength and ductility compared to as-cast alloy, while it possessed significantly anisotropic mechanical behavior. Interestingly, the anisotropy of ductility was nonsignificant, showing dramatically enhanced quasi-isotropic ductility. The improved strength and ductility were ascribed to the significant grain refinement, fine second phase, and texture strengthening. The tensile anisotropy was resulted by the bi-texture which was comprised of four prismatic texture components and three basal texture components. This study clearly highlights the potential for scaling RD-ECAP for an industrial scale implementation, while significant anisotropic mechanic behavior should be paid much attention.

Extreme ultraviolet mask roughness effects in high numerical aperture lithography.

Given the reflective nature of extreme ultraviolet lithography and its extremely short operational wavelength, roughness of the optical surfaces is of significant concern. In particular, roughness in the mask multilayer leads to image plane speckle and ultimately patterned line-edge or line-width variability in the imaging process. Here we consider the implications of this effect for future high numerical aperture (NA) systems that are assumed to require anamorphic magnification projection optics. The results show significant anisotropic behavior at high NA as well as a substantial increase in relative patterned line variability in the shadowed direction when comparing 0.55NA to 0.33NA, despite the assumption of an anamorphic magnification system. The shadowed-direction patterned line variability is 2× larger than for unshadowed lines, and the majority of the increase in variability occurs in the low frequency regime.

Rectangular and Triangular Corrugated Composite Skins

A simple analytical model for the effective stiffness of rectangular and triangular corrugated composites is developed for the symmetrical and unsymmetrical laminates. The stiffness matrices for the corrugated composites were derived. The elongation and effective stiffness in the longitudinal and transverse directions for the rectangular and triangular corrugated composites were calculated and compared. The dimensions of the rectangular and triangular elements for unidirectional and plain woven fabrics made up of E-glass/Epoxy were investigated. The analytical model has been validated by experimental results from bending and tension tests. FEM models were used to predict the characteristics of rectangular and triangularly corrugated composites using ABAQUS. FEM and analytical models results are compared. Load displacement curves in tensile and bending tests are investigated. Four stages of their mechanical behaviour are identified. Finally ultimate strain and anisotropic behaviour of rectangular and triangular corrugated composites are investigated as experimentally. Results from FEM in ABAQUS, experimental findings, and analytical simulations show that corrugated composites laminates can afford larger deformations than their flat counterparts. Those laminates or skins have significant anisotropic behaviour and they are candidates for morphing applications.

In-situ measurement technologies for flow behaviour and contact status of fibre-reinforced thermoplastics during forming with a six degree of freedom press

The paper presents investigations on a forming process, which is implemented in a forming press based on a Stewart platform. In contrast to common forming techniques, this buildup offers not only one but six degrees of freedom. This is of particular interest when it comes to the forming of materials that show significant anisotropic behaviour such as fibre-reinforced plastics. Therefore, an experimental setup is presented to record characteristic variables during the forming process of fibre-reinforced thermoplastics. The contact state is of particular interest for this kind of forming process because it changes continuously in shape and position as the forming process progresses. For this purpose, temperatures at different places in the tool are recorded to provide information about the flow velocity of the material and the contact state between tool and workpiece. This allows the determination of the exact time and position of the contact between material and forming tool as well as the duration of this contact. The results are compared with optical measurements analysed by image processing algorithm and process forces measured by load cells.

An Experimental Study on the Strength Behavior of Compacted Loess under the Principal Stress Axis Rotation

A series of consolidated-undrained tests was carried out on compacted loess with a hollow cylinder torsional shear apparatus to investigate the stress-strain characteristics and the strength behavior of the compacted loess under different stress paths. Two kinds of stress paths were considered in these tests, including directional shear tests with fixed principal stress axes and shear tests under pure principal stress axis rotation. Test results reveal that the stress-strain curves of the compacted loess under these two kinds of stress paths followed a similar trend, in which two shear stages were observed. In the first shear stage, with the increase of the generalized shear stress, the generalized shear strain developed relatively slowly and the specimen of the compacted loess showed a rigid response. With the further increase of the shear stress, an obvious turning point appeared and the second shear stage started. In the second stage, the generalized shear strain began to develop rapidly and the specimen showed a ductile response. The results also reveal that when the directional shear was applied to the specimens of compacted loess under different principal stress directions, there was a large difference in the generalized shear stress - strain curves and the specimens showed significant anisotropic behavior. A compared with the specimens not subjected to the principal stress axis rotation, the specimens subjected to the principal stress axes rotation had remarkably higher strength. In addition, the specimens of the compacted loess had different levels of strength when they were tested at different shear rates. The decrease of the shear rate had a slight influence on the increase of the shear strength of the compacted loess.

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants.

Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair. We tested at least six samples of: 1) fresh autologous porcine pericardium (APP), 2) glutaraldehyde fixed porcine pericardium (GPP), 3) St Jude Medical pericardial patch (SJM), 4) CardioCel patch (CC), 5) PeriGuard (PG), 6) Supple PeriGuard (SPG) and 7) fresh porcine AV leaflets (PC). We introduced efficient displacement-controlled testing protocols and processing, as well as advanced convexity requirements on the strain energy functions used to describe the mechanical response of the materials under loading. The proposed experimental and data processing pipeline allowed for a robust in-plane characterization of all the materials tested, with constants determined for two Fung-like hyperelastic, anisotropic strain energy models. Overall, CC and SPG (respectively PG) patches ranked as the closest mechanical equivalents to young (respectively aged) AV leaflets. Because the native leaflets as well as CC, PG and SPG patches exhibit significant anisotropic behaviors, it is suggested that the fiber and cross-fiber directions of these replacement biomaterials be matched with those of the host AV leaflets. The long-term performance of cusp replacement materials would ideally be evaluated in large animal models for AV disease and cusp repair, and over several months or more. Given the unavailability and impracticality of such models, detailed information on stress-strain behavior, as studied herein, and investigations of durability and valve dynamics will be the best surrogates, as they have been for prosthetic valves. Overall, comparison with Fig. 3 suggests that CC and SPG (respectively PG) patches may be the closest mechanical equivalents to young (respectively aged) AV leaflets. Interestingly, the thicknesses of these materials are close to those reported for porcine and younger human AV leaflets, which may facilitate surgical implantation, by contrast to the thinner APP which has poor handling qualities. Because the native leaflets as well as CC, PG and SPG patches exhibit anisotropic behaviors, from a mechanistic perspective alone, it stands to reason that cardiac surgeons should seek to intraoperatively match the fiber and cross-fiber directions of these replacement biomaterials with those of the repaired AV leaflets.

Long-term mechanical behaviour of skeletal muscle tissue in semi-confined compression experiments

In this study, porcine skeletal muscle tissue was tested until 112 hours post mortem using a semi-confined compression device that induces fascicles to enter one of the states of compression (mode I), tension (mode II), or constant length (mode III). Based on the authors׳ previous studies (Böl et al., 2014, 2015a), the anisotropic mechanical behaviour of the tissue was analysed, with a special focus on the testing time post mortem. The results suggest that the tissue exhibits significant anisotropic behaviour during the first hours of post mortem but that this anisotropy becomes insignificant at later time points. Interestingly, the compressibility of the tissue is more or less unaffected by the testing time. These results are discussed especially with respect to tissue microstructure.

Anisotropic magnetotransport and exotic longitudinal linear magnetoresistance inWTe2crystals

WTe2 semimetal, as a typical layered transition-metal dichalcogenide, has recently attracted much attention due to the extremely large, non-saturating parabolic magnetoresistance in perpendicular field. Here, we report a systematic study of the angular dependence of the magnetoresistance in WTe2 single crystal. The violation of the Kohler rule and a significant anisotropic magnetotransport behavior in different magnetic field directions are observed. Surprisingly, when the applied field is parallel to the tungsten chains of WTe2, an exotic large longitudinal linear magnetoresistance as high as 1200% at 15 T and 2 K is identified. Violation of the Kohler rule in transverse magnetoresistance can be understood based on a dual effect of the excitons formation and thermal activation, while large longitudinal linear magnetoresistance reflects perfectly the scattering and nesting of quasi-1D nature of this balanced hole-electron system. Our work will stimulate studies of such double-carrier correlated material and corresponding quantum physics.

Magnetic and optical anisotropy in the infinite-chains iron oxide Sr2FeO3: A first-principle investigation

We perform first-principles calculations of electronic structure, magnetic structure and linear optical response in Sr2FeO3 based on the density functional theory (DFT) employing the generalized gradient approximation (GGA) plus on-site Coulomb repulsion method. For its special 1D Fe-O chains structure with iron square-planar coordination, the magnetic interaction and linear dielectric function show significant anisotropic behavior. In particular, giant optical anisotropy is found.

High hole mobility InGaSb/AlSb QW field effect transistors grown on Si by molecular beam epitaxy

Growth of InGaSb/AlSb high hole mobility quantum well field effect transistors (QW FETs) on Si substrates with a step-graded GaAsSb metamorphic buffer layer by molecular beam epitaxy is explored. With an optimized growth temperature for the InGaSb/AlSb QW, hole mobility of 770cm2/Vs and 3060cm2/Vs have been achieved at room temperature and 77K, respectively. It is also found that the twins in the samples do not cause significant anisotropic behavior of the InGaSb QW FETs in term of gate direction.

Anisotropic g factors of the tetragonal Cu2+ monomer in Tl-2223 superconductor

The gyromagnetic factors of the Cu2+ monomer in Tl-2223 superconductor are quantitatively investigated from the perturbation formulas of these factors for a 3d9 ion in a tetragonally elongated octahedron. The local tetragonal distortion of the system is attributable to the axial elongation along c axis, corresponding to the five-fold coordinated Cu2+(2) site with almost 30% longer Cu–O bond length for the apical oxygen as compared to the four planar ones. The significant anisotropic behaviors of the EPR spectra perpendicular to and parallel with the ab (CuO2) layers are analyzed on the basis of the local tetragonal elongation.

Tuning Out-of-Plane Spin Polarization Using in-Plane Magnetic Fields in a Quasi-One-Dimensional Quantum Wire Embedded in (110) Plane

We investigate theoretically the combination effect of an in-plane magnetic field and spin-orbit interactions (SOIs) on the spin and charge transport property of a quasi-one-dimensional quantum wire embedded in the (110) crystallographic plane. We find that the oscillations of the conductance induced by the SOIs become more significant and different for the spin-up and spin-down electrons in the presence of the in-plane magnetic field. The conductance exhibits a significant anisotropic behavior and electrons exhibit out-of-plane spin polarization which can be tuned by an in-plane magnetic field. These features offer us an efficient way to control SOI-induced spin transport using in-plane magnetic fields.

Multi-component modelling of human brain tissue: a contribution to the constitutive and computational description of deformation, flow and diffusion processes with application to the invasive drug-delivery problem

Human brain tissue is complex and multi-component in nature. It consists of an anisotropic hyperelastic solid material composed of tissue cells and blood vessel walls. Brain tissue is permeated by two viscous pore liquids, the interstitial fluid and the blood. Both liquids are mobile within the tissue and exhibit a significant anisotropic perfusion behaviour. To model this complex aggregate, the well-founded Theory of Porous Media, a continuum-mechanical approach for the description of multi-component aggregates, is used. To include microscopic information, the model is enhanced by tissue characteristics obtained from medical imaging techniques. Moreover, the model is applied to invasive drug-delivery strategies, i.e. the direct extra-vascular infusion of therapeutic agents. For this purpose, the overall interstitial fluid is treated as a real two-component mixture of a liquid solvent and a dissolved therapeutic solute. Finally, the continuum-mechanical model results in a set of strongly coupled partial differential equations which are spatially discretised using mixed finite elements and solved in a monolithic manner with an implicit Euler time-integration scheme. Numerical examples demonstrate the applicability of the presented model.

Microstructure and mechanical properties of milled fibre/SiC multilayer composites prepared by tape casting and pressureless sintering

In the present work, milled carbon fibre with high mechanical properties was used to reinforce silicon carbide, and Csf/SiC multilayer composites were prepared by tape casting and pressureless sintering. The milled C fibres were firstly dispersed in solvents with the aid of dispersant (Triton X-100) and then mixed with SiC slurry to make green Csf/SiC tapes to limit fibre breakage. The average length of C fibres slightly decreased with the increase of mixing time in the present duration, indicating that mixing the SiC slurry with the fibre-predispersed solution is an effective method for adding fibres with limited breakage. Fibres were homogeneously distributed in the tapes and tended to align fairly well along the tape casting direction. The relative density of the composite containing milled C fibres decreased with the fibre amount. The Csf/SiC multilayer composites demonstrated significant anisotropic shrinkage behaviour in different directions, while the addition of short C fibres hindered the shrinkage in the plane containing the fibres during sintering. Elastic modulus and bending strength decreased with increased porosity, which implies that bending properties are affected more significantly by residual porosity rather than fibres' properties.

Improved age-hardening behavior of Mg–Sn–Mn alloy by addition of Ag and Zn

The effect of 0.5at% Ag and its combination with 0.4at% Zn on the precipitation hardening behavior of Mg–1.5Sn–0.5Mn (at%) alloy have been investigated using hardness measurements and transmission electron microscopy (TEM). The results show that sole addition of Ag can remarkably improve the peak hardness from 58HV to 77HV after ageing at 200°C, which is attributed to the increased number density, the size and so the volume fraction of the Mg2Sn lath precipitates. A combination addition of Ag and Zn further improves the peak-hardness to 83HV and the time to peak hardness has been reduced from 120h to 100h. The joint addition of Ag and Zn both increases the number density and refines the Mg2Sn precipitates. Zn also promotes the Mg2Sn precipitates lying on the non-basal plane of matrix, as well as the blocky Mg54Ag17 phase which has an orientation relationship with α-Mg matrix as (001)ɛ′//(0001)α, [200]ɛ′//[−1−120]α, [0−20]ɛ′//[1−100]α. In the peak-aged Ag modified alloys, Ag atoms are segregated in the Mg2Sn precipitates. Nucleation, growth and coarsening of the Mg2Sn precipitates simultaneously occur as the ageing proceeds. The growth of Mg2Sn precipitates exhibits a significant anisotropic behavior. Addition of Ag can promote the precipitation process during the underage period and retarding the growth of Mg2Sn during the overage period, leading to a more thermal stable microstructure of the Ag and Ag+Zn modified alloys, from which only a small hardness decrease after 700h ageing is detected.

On the plastic anisotropy of an aluminium alloy and its influence on constrained multiaxial flow

The influence of plastic anisotropy on the mechanical behaviour of a rolled aluminium plate under quasi-static loading conditions is studied experimentally and numerically. Material tests in different directions with respect to the rolling direction of the plate were carried out on various specimen shapes providing a wide range of stress states. The Yld2004-18p anisotropic yield function was identified through uniaxial tensile tests, shear tests and upsetting tests. This yield function was found to provide an adequate description of the significant anisotropic behaviour of a high-strength AA7075-T651 plate. Numerical simulations of all the material tests were then performed with an elasto-plastic material model using both the anisotropic and an isotropic version of the yield function. The numerical predictions of the mechanical response for notched tensile tests obtained with the isotropic version of the material model clearly over-estimated the experimental results. Similar results have been reported in the literature on other materials using isotropic constitutive relations. This over-estimation was significantly reduced when using the anisotropic version of the material model, and the reason why plastic anisotropy is so important for an accurate prediction of the notch-strengthening effect is explained. It was also established that the exponent of the yield function Yld2004-18p has a strong influence on the results for the notched tensile tests. When the exponent of the yield surface was assigned a sufficiently high value, an almost perfect fit between the numerical predictions and the experimental results was obtained.

Anisotropic property in interacting quantum wires embedded in (110) plane

We investigate the theoretically combined effect of spin–orbit interactions and Coulomb interaction on the ground state and transport property of a quantum wire oriented along different crystallographic directions in the (110) plane. We find that the electron’s ground state exhibits phase transition among spin density wave, charge density wave, singlet superconductivity and metamagnetism, which can be controlled by changing the crystallographic orientation, the strengths of the spin–orbit interactions and the Coulomb interaction. The ac conductance exhibits a significant anisotropic behavior and a out-of-plane spin polarization which can be tuned by an in-plane electric field.