Crystallographic texture engineering is a key strategy for enhancing the mechanical properties of polycrystalline magnesium(Mg)alloys.Due to the intrinsic anisotropy of the hexagonal close-packed(HCP)structure,the def...Crystallographic texture engineering is a key strategy for enhancing the mechanical properties of polycrystalline magnesium(Mg)alloys.Due to the intrinsic anisotropy of the hexagonal close-packed(HCP)structure,the deformation behavior of Mg alloys is significantly governed by individual grain deformation and multi-grain interactions,both dictated by crystallographic texture.In the current study,enhanced ductility was achieved in a Mg-Al-Zn-Mn dilute alloy by tailoring a strong basal texture into a transverse-direction-spread elliptical texture through the minor addition of yttrium(Y).Systematic quasi-in-situ electron backscatter diffraction(EBSD)and dislocation/disclination density analyses were performed to examine the microstructural evolution during deformation.We found that disclinations emerge from defect reactions,including dislocation-grain boundary(GB)and twin-GB interactions,which facilitate twinning plasticity and intergranular accommodation in the elliptical-textured alloy,resulting in improved work-hardening capacity and higher ductility(28.5% along the rolling direction and 32.2%along the transverse direction).By introducing disclination analysis to elucidate defect reactions,multi-grain interactions and the associated microstructure-property relationships in polycrystalline metals,our work provides new insights into the design of advanced Mg alloys with enhanced ductility and formability through crystallographic texture engineering.展开更多
Using φ-mapping method and topological current theory, the topological structure and bifurcation ofdisclination lines in two-dimensional liquid crystals are studied. By introducing the strength density and the topolo...Using φ-mapping method and topological current theory, the topological structure and bifurcation ofdisclination lines in two-dimensional liquid crystals are studied. By introducing the strength density and the topologicalcurrent of many disclination lines, the total disclination strength is topologically quantized by the Hopf indices andBrouwer degrees at the singularities of the director field when the Jacobian determinant of director field does not vanish.When the Jacobian determinant vanishes, the origin, annihilation and bifurcation processes of disclination lines arestudied in the neighborhoods of the limit points and bifurcation points, respectively. The branch solutions at the limitpoint and the different directions of all branch curves at the bifurcation point are calculated with the conservation lawof the topological quantum numbers. It is pointed out that a disclination line with a higher strength is unstable and itwill evolve to the lower strength state through the bifurcation process.展开更多
Using mapping method and topological current theory, the topological structure of disclination lines in 2 dimensional liquid crystals is studied. By introducing the strength density and the topological current of m...Using mapping method and topological current theory, the topological structure of disclination lines in 2 dimensional liquid crystals is studied. By introducing the strength density and the topological current of many disclination lines, it is pointed out that the disclination lines are determined by the singulaities of the director field, and topologically quantized by the Hopf indices and Brouwer degrees. Due to the equivalence in physics of the director fields n (x) and n (x) , the Hopf indices can be integers or half integers, representing a generalization of our previous studies of integer Hopf indices.展开更多
In the light of φ-mapping method-and topological current theory, the effect of disclination lines on the free energy density of nematic liquid crystals is studied. It is pointed out that the total Frank free energy d...In the light of φ-mapping method-and topological current theory, the effect of disclination lines on the free energy density of nematic liquid crystals is studied. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclination lines. The other is the saddle-splay energy density, which is shown to be centralized at the disclination lines and to he topologically quantized in the unit of kπ/2 when the Jacobian determinant of the director field does not vanish at the singularities of the director field. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strengthes. When the Jacobian determinant vanishes, the generation, annihilation, intersection, splitting and merging processes of the saddle-splay energy density are detailed in the neighborhoods of the limit points and bifurcation points, respectively. It is shown that the disclination line with high topological quantum number is unstable and will evolve to the low topological quantum number states through the splitting process.展开更多
The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials ...The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the disclination dipole center are also calculated. The influence of the morphology of the blunt crack and the position of the disclination dipole on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases when the wedge disclination dipole approaches the tip of the crack. The effects of the morphology of the blunt crack on the stress intensity factor of the crack and the image force are very significant.展开更多
In this paper, we present an analytical solution of the interaction of the nanotube （NT） with a wedge disclination dipole in nanotube-based composites. The corresponding boundary value problem is solved exactly by u...In this paper, we present an analytical solution of the interaction of the nanotube （NT） with a wedge disclination dipole in nanotube-based composites. The corresponding boundary value problem is solved exactly by using complex potential functions. The explicit expression of the force exerted on disclination dipole is given by using the generalized Peach- Koehler formula. As a numerical illustration, both the equilibrium position and the stability of the disclination dipole are evaluated for different material combinations, relative thickness of an NT, surface/interface effects, and the features of the disclination dipole. The results show that as the thickness of the NT layer increases, the NT has a relatively major role in the force acting on the disclination dipole in the NT-based composite. The cooperative effect of surface/interface stresses and the NT becomes considerable as the increase of NT layer thickness. The equilibrium position may occur, even more than one, due to the influences of the surface/interface stress and the NT thickening. The influences of the surface/interface stresses and the thickness of the NT layer on the force are greatly dependent on the disclination angle.展开更多
The system of a wedge disclination dipole interacting with an internal crack was investigated. By using the complex variable method, the closed form solutions of complex potentials to this problem were presented. The ...The system of a wedge disclination dipole interacting with an internal crack was investigated. By using the complex variable method, the closed form solutions of complex potentials to this problem were presented. The analytic formulae of the physics variables, such as stress intensity factors at the tips of the crack produced by the wedge disclination dipole and the image force acting on disclination dipole center were obtained. The influence of the orientation, the dipole arm and the location of the disclination dipole on the stress intensity factors was discussed in detail. Furthermore, the equilibrium position of the wedge disclination dipole was also examined. It is shown that the shielding or antishielding effect of the wedge disclination to the stress intensity factors is significant when the disclination dipole moves to the crack tips.展开更多
A three-phase composite cylinder model is utilized to study the interaction of a wedge disclination dipole with a coated cylindrical inhomogeneity. The explicit expression of the force acting on the wedge disclination...A three-phase composite cylinder model is utilized to study the interaction of a wedge disclination dipole with a coated cylindrical inhomogeneity. The explicit expression of the force acting on the wedge disclination dipole is calculated. The motilities and the equilibrium po- sitions of the disclination dipole near the coated inhomogeneity are discussed for various material combinations, relative thicknesses of the coating layer and the features of the disclination dipole. The results show that the material properties of the coating layer have a major part to play in alteringi the strengthening effect or toughening effect produced by the coated inhomogeneity.展开更多
The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials ...The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole centre is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force increases （or the attraction force reduces） with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special eases.展开更多
In light of the φ-mapping method, the contribution of disclination lines to the free energy density of 2-dimensional liquid crystals is studied in the single-elastic constant approximation. It is pointed out that, co...In light of the φ-mapping method, the contribution of disclination lines to the free energy density of 2-dimensional liquid crystals is studied in the single-elastic constant approximation. It is pointed out that, compared with the previous theory, the free energy density can be divided into two parts. One is the usual distorted energy density of director field around the disclination lines. The other is the free energy density of the disclination lines themselves which is centralized at the disclination lines and topoligically quantized in a unit of 1/2kπ. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strength. From the method of Lagrangian multipliers, the equilibrium equation and the molecular field of 2-dimensional liquid crystals are also obtained. It is shown that the physical meaning of the Lagrangian multiplier is just the distorted energy density. Key words director field - disclination line - free energy - Lagrangian multiplier PASC2001 64.70.Md - 02.40.-k展开更多
Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,dis...Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,disclinations are introduced into topological nontrivial elastic phononic plates.The deformation of the lattice yielded by disclinations produces a pentagonal core with the local five-fold symmetry.The topological bound states are well localized around the boundaries of the pentagonal cores with and without hollow regions.The topological bound states immunize against the finite sizes and the moderate imperfects of plates,essentially differing from the trivial defect states.The discovery of topological bound states unveils a new horizon in topological mechanics and physics,and it provides a novel platfonn to implement large-scale elastic devices with topologically protected resonances.展开更多
By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are t...By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are topological currents for topological defects in homogeneous equation. The evolution of disclinations is studied, and the branch conditions for generating, annihilating, crossing, splitting and merging of disclinations are given.展开更多
Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of qu...Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.展开更多
Two bowlic cyclotriveratrylene CTV-1 and CTV-2, with different peripheral groups of -OCH3 and -OCH2CH3 for CTV-1 and -OCH3 and -OCH2COOCH3 for CTV-2, respectively, were synthesized by typical trimerization via a multi...Two bowlic cyclotriveratrylene CTV-1 and CTV-2, with different peripheral groups of -OCH3 and -OCH2CH3 for CTV-1 and -OCH3 and -OCH2COOCH3 for CTV-2, respectively, were synthesized by typical trimerization via a multistep sequence from vanillin. Both bowlic CTV molecules were thermotropic liquid crystals, and presented typical grainy textures of the nematic phase and homogeneous texture of the single domain nematic phase. It is of interest to observe the regular and beautiful mosaic-like morphologies after cooling from liquid crystalline phases, which appeared and vanished repeatedly in several circles of cooling and heating. The size of each mosaic was several dozens of micron. In nature, the mosaic-like morphologies are the optical pattern of cracks formed by the shrinking, due to the crystallization of frozen texture of nematic phases. By means of scanning electron microscopy, the mosaic-like morphologies were observed to consist of lamellae, and each mosaic is a rectangular multi-layer lamella, which is composed of packed single-layered lamellae. The fibrils in the diameter of about 1 μm were observed, which are the structural units of lamellae and would be the bundles of the bowlic molecular columns. The mosaic-like morphologies decorate the bowlic molecular columnar nematic phase, therefore, a novel mosaic-like morphologies decoration method was applied to reveal the director distribution of several kinds of point disclinations, such as s = +1(δ =0°and δ =90°) and s = ±1/2, and Nèel domain walls. It was shown that the bowlic molecular columnar nematic phase behaved as normal nematic phases; however, the basic structural units ordered were the bowlic molecular column or the bundles of bowlic molecular column (i.e. fibrils), but not the bowlic molecules themselves. The bowlic molecular columns acted as the rod-like molecules in a normal nematic phase. Therefore, a new term BCN (bowlic columnar nematic phase) is used to describe the anomalous nematic phase in this paper.展开更多
Two decoration techniques, solidification-induced band texture decoration and focal-conic texture decoration, have been established to exhibit the director field of disclinations in a low-molar-mass methacrylate liqui...Two decoration techniques, solidification-induced band texture decoration and focal-conic texture decoration, have been established to exhibit the director field of disclinations in a low-molar-mass methacrylate liquid crystal. The disclinations with strength s=1/2 and s=±1 are observed by the two decoration methods. For the solidification-induced band texture decoration, the molecular orientation is perpendicular to the direction of the band. While for focal-conic texture decoration, it has been proved by the results of IR dichroism that the direction of the director is parallel to the direction of the focal-conic. Therefore, the sketch map of the molecular director filed can be mapped according to the morphological pattern of the solidification-induced band texture or focal-conic texture.展开更多
The observation of disclination cores of high strength S=-2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), dif-fer...The observation of disclination cores of high strength S=-2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), dif-ferential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) prove that the sample exhibits smectic C phase. It is suggested that the formation of the high strength disclination is mainly ascribed to the stronger anchoring of LC molecules on the substrate due to the formation of hydrogen bonds between the pendent hydroxyl of the LC molecule and the substrate.展开更多
A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization...A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.展开更多
Nano-mechanisms of crystal lattice deformation on the interface of dissimilar materials (Cu-Nb), joined by vacuum rolling in solid phase under high temperature (950℃) were studied by means of high resolution electron...Nano-mechanisms of crystal lattice deformation on the interface of dissimilar materials (Cu-Nb), joined by vacuum rolling in solid phase under high temperature (950℃) were studied by means of high resolution electron microscopy. Input of carriers of rotation modes—nano-dipoles of partial disclinations and nano-twist disclinations in the form of double spirals in deformation mechanisms were analyzed. The role of these mechanisms in decrease of shear stability of the interface areas and in production of high-quality rolled metal is discussed.展开更多
The defect structures of s = ±1/2 twist disclinations in twisted nematic and twisted chiral liquid crystals have been investigated within the Landau-de Gennes theory numerically. Our results show that there exist...The defect structures of s = ±1/2 twist disclinations in twisted nematic and twisted chiral liquid crystals have been investigated within the Landau-de Gennes theory numerically. Our results show that there exists eigenvalue exchange across the defect core of both the two models. The defect core is essentially biaxial and never isotropic. The defect centre is uniaxial and is surrounded by a strong biaxial region.展开更多
One fundamental problem of modern physics is the search for a theory of everything able to explain the nature of space-time, what matter is and how matter interacts. There are various propositions, as Grand Unified Th...One fundamental problem of modern physics is the search for a theory of everything able to explain the nature of space-time, what matter is and how matter interacts. There are various propositions, as Grand Unified Theory, Quantum Gravity, Supersymmetry, String and Superstring Theories, and M-Theory. However, none of them is able to consistently explain at the present and same time electromagnetism, relativity, gravitation, quantum physics and observed elementary particles. In this paper, one summarizes the content of a new book, published in English [2] and in French [3], in which it is suggested that Universe could be a massive elastic 3D-lattice, and that fundamental building blocks of Ordinary Matter could consist of topological singularities of this lattice, namely diverse dislocation loops and disclination loops. For an isotropic elastic lattice obeying Newton’s law, with specific assumptions on its elastic properties, one obtains the result that the behaviours of this lattice and of its topological defects display “all” known physics, unifying electromagnetism, relativity, gravitation and quantum physics, and resolving some longstanding questions of modern cosmology. Moreover, studying lattices with axial symmetries, represented by “colored” cubic 3D-lattices, one has identified a lattice structure whose topological defect loops coincide with the complex zoology of elementary particles, which could open a very promising field of research. Here, only main steps and principal results of the new theory are presented and discussed, without showing the mathematical concepts and developments contained in the book.展开更多
基金Financial supports from The National Natural Science Foundation of China (Nos. U22A20109, 52171116 and 52334010)Partial financial support came from The Program for the Central University Youth Innovation TeamThe Fundamental Research Funds for the Central Universities, JLU.
文摘Crystallographic texture engineering is a key strategy for enhancing the mechanical properties of polycrystalline magnesium(Mg)alloys.Due to the intrinsic anisotropy of the hexagonal close-packed(HCP)structure,the deformation behavior of Mg alloys is significantly governed by individual grain deformation and multi-grain interactions,both dictated by crystallographic texture.In the current study,enhanced ductility was achieved in a Mg-Al-Zn-Mn dilute alloy by tailoring a strong basal texture into a transverse-direction-spread elliptical texture through the minor addition of yttrium(Y).Systematic quasi-in-situ electron backscatter diffraction(EBSD)and dislocation/disclination density analyses were performed to examine the microstructural evolution during deformation.We found that disclinations emerge from defect reactions,including dislocation-grain boundary(GB)and twin-GB interactions,which facilitate twinning plasticity and intergranular accommodation in the elliptical-textured alloy,resulting in improved work-hardening capacity and higher ductility(28.5% along the rolling direction and 32.2%along the transverse direction).By introducing disclination analysis to elucidate defect reactions,multi-grain interactions and the associated microstructure-property relationships in polycrystalline metals,our work provides new insights into the design of advanced Mg alloys with enhanced ductility and formability through crystallographic texture engineering.
文摘Using φ-mapping method and topological current theory, the topological structure and bifurcation ofdisclination lines in two-dimensional liquid crystals are studied. By introducing the strength density and the topologicalcurrent of many disclination lines, the total disclination strength is topologically quantized by the Hopf indices andBrouwer degrees at the singularities of the director field when the Jacobian determinant of director field does not vanish.When the Jacobian determinant vanishes, the origin, annihilation and bifurcation processes of disclination lines arestudied in the neighborhoods of the limit points and bifurcation points, respectively. The branch solutions at the limitpoint and the different directions of all branch curves at the bifurcation point are calculated with the conservation lawof the topological quantum numbers. It is pointed out that a disclination line with a higher strength is unstable and itwill evolve to the lower strength state through the bifurcation process.
文摘Using mapping method and topological current theory, the topological structure of disclination lines in 2 dimensional liquid crystals is studied. By introducing the strength density and the topological current of many disclination lines, it is pointed out that the disclination lines are determined by the singulaities of the director field, and topologically quantized by the Hopf indices and Brouwer degrees. Due to the equivalence in physics of the director fields n (x) and n (x) , the Hopf indices can be integers or half integers, representing a generalization of our previous studies of integer Hopf indices.
基金Natural Science Foundation of Shanghai Municipal Committee of Science and Technology，国家自然科学基金，Shanghai Municipal Committee of Science and Technology
文摘In the light of φ-mapping method-and topological current theory, the effect of disclination lines on the free energy density of nematic liquid crystals is studied. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclination lines. The other is the saddle-splay energy density, which is shown to be centralized at the disclination lines and to he topologically quantized in the unit of kπ/2 when the Jacobian determinant of the director field does not vanish at the singularities of the director field. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strengthes. When the Jacobian determinant vanishes, the generation, annihilation, intersection, splitting and merging processes of the saddle-splay energy density are detailed in the neighborhoods of the limit points and bifurcation points, respectively. It is shown that the disclination line with high topological quantum number is unstable and will evolve to the low topological quantum number states through the splitting process.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10872065 and 50801025)the Natural Science Foundation of Hunan Province of China (Grant No. 09JJ4003)the Hunan Provincial Innovation Foundation for Postgraduate,China (Grant No. CX2009B067)
文摘The interaction between a wedge disclination dipole and a crack emanating from a semi-elliptic hole is investigated. Utilising the complex variable method, the closed form solutions are derived for complex potentials and stress fields. The stress intensity factor at the tip of the crack and the image force acting on the disclination dipole center are also calculated. The influence of the morphology of the blunt crack and the position of the disclination dipole on the shielding effect to the crack and the image force is examined in detail. The results indicate that the shielding or anti-shielding effect to the stress intensity factor increases when the wedge disclination dipole approaches the tip of the crack. The effects of the morphology of the blunt crack on the stress intensity factor of the crack and the image force are very significant.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11172094 and 11172095)the Program for New Century Excellent Talents in University of Ministry of Education of China(Grant No.NCET-11-0122)the Hunan Provincial Natural Science Foundation for Creative Research Groups,China(Grant No.12JJ7001)
文摘In this paper, we present an analytical solution of the interaction of the nanotube （NT） with a wedge disclination dipole in nanotube-based composites. The corresponding boundary value problem is solved exactly by using complex potential functions. The explicit expression of the force exerted on disclination dipole is given by using the generalized Peach- Koehler formula. As a numerical illustration, both the equilibrium position and the stability of the disclination dipole are evaluated for different material combinations, relative thickness of an NT, surface/interface effects, and the features of the disclination dipole. The results show that as the thickness of the NT layer increases, the NT has a relatively major role in the force acting on the disclination dipole in the NT-based composite. The cooperative effect of surface/interface stresses and the NT becomes considerable as the increase of NT layer thickness. The equilibrium position may occur, even more than one, due to the influences of the surface/interface stress and the NT thickening. The influences of the surface/interface stresses and the thickness of the NT layer on the force are greatly dependent on the disclination angle.
基金Project supported by the National Natural Science Foundation of China (No. 10472030)
文摘The system of a wedge disclination dipole interacting with an internal crack was investigated. By using the complex variable method, the closed form solutions of complex potentials to this problem were presented. The analytic formulae of the physics variables, such as stress intensity factors at the tips of the crack produced by the wedge disclination dipole and the image force acting on disclination dipole center were obtained. The influence of the orientation, the dipole arm and the location of the disclination dipole on the stress intensity factors was discussed in detail. Furthermore, the equilibrium position of the wedge disclination dipole was also examined. It is shown that the shielding or antishielding effect of the wedge disclination to the stress intensity factors is significant when the disclination dipole moves to the crack tips.
基金Project supported by the National Natural Science Foundation of China(Nos.11172094 and 11172095)the New Century Excellent Talents in University(NCET-11-0122)Hunan Provincial Natural Science Foundation for Creative Research Groups of China(No.12JJ7001)
文摘A three-phase composite cylinder model is utilized to study the interaction of a wedge disclination dipole with a coated cylindrical inhomogeneity. The explicit expression of the force acting on the wedge disclination dipole is calculated. The motilities and the equilibrium po- sitions of the disclination dipole near the coated inhomogeneity are discussed for various material combinations, relative thicknesses of the coating layer and the features of the disclination dipole. The results show that the material properties of the coating layer have a major part to play in alteringi the strengthening effect or toughening effect produced by the coated inhomogeneity.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10872065 and 50801025)
文摘The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole centre is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force increases （or the attraction force reduces） with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special eases.
文摘In light of the φ-mapping method, the contribution of disclination lines to the free energy density of 2-dimensional liquid crystals is studied in the single-elastic constant approximation. It is pointed out that, compared with the previous theory, the free energy density can be divided into two parts. One is the usual distorted energy density of director field around the disclination lines. The other is the free energy density of the disclination lines themselves which is centralized at the disclination lines and topoligically quantized in a unit of 1/2kπ. The topological quantum numbers are determined by the Hopf indices and Brouwer degrees of the director field at the disclination lines, i.e., the disclination strength. From the method of Lagrangian multipliers, the equilibrium equation and the molecular field of 2-dimensional liquid crystals are also obtained. It is shown that the physical meaning of the Lagrangian multiplier is just the distorted energy density. Key words director field - disclination line - free energy - Lagrangian multiplier PASC2001 64.70.Md - 02.40.-k
基金supported by the National Natural Science Foundation of China(Grant Nos.12072108 and 51621004)Hunan Provincial Natural Science Foundation of China(Grant No.2021JJ40626).
文摘Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,disclinations are introduced into topological nontrivial elastic phononic plates.The deformation of the lattice yielded by disclinations produces a pentagonal core with the local five-fold symmetry.The topological bound states are well localized around the boundaries of the pentagonal cores with and without hollow regions.The topological bound states immunize against the finite sizes and the moderate imperfects of plates,essentially differing from the trivial defect states.The discovery of topological bound states unveils a new horizon in topological mechanics and physics,and it provides a novel platfonn to implement large-scale elastic devices with topologically protected resonances.
基金supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry of Chinathe Interdisciplinary Innovation Research Fund for Young Scholars,Lanzhou University
文摘By using topological current theory, this paper studies the inner topological structure of disclinations during the melting of two-dimensional systems. From two-dimensional elasticity theory, it finds that there are topological currents for topological defects in homogeneous equation. The evolution of disclinations is studied, and the branch conditions for generating, annihilating, crossing, splitting and merging of disclinations are given.
文摘Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.
基金Supported by the National Natural Science Foundation of China (Grant No. 20774077)the Natural Science Foundation of Fujian, China (Grant Nos. E0510003 & E0710025)the Project of Science and Technology of Xiamen, China (Grant No. 3502Z20055013)
文摘Two bowlic cyclotriveratrylene CTV-1 and CTV-2, with different peripheral groups of -OCH3 and -OCH2CH3 for CTV-1 and -OCH3 and -OCH2COOCH3 for CTV-2, respectively, were synthesized by typical trimerization via a multistep sequence from vanillin. Both bowlic CTV molecules were thermotropic liquid crystals, and presented typical grainy textures of the nematic phase and homogeneous texture of the single domain nematic phase. It is of interest to observe the regular and beautiful mosaic-like morphologies after cooling from liquid crystalline phases, which appeared and vanished repeatedly in several circles of cooling and heating. The size of each mosaic was several dozens of micron. In nature, the mosaic-like morphologies are the optical pattern of cracks formed by the shrinking, due to the crystallization of frozen texture of nematic phases. By means of scanning electron microscopy, the mosaic-like morphologies were observed to consist of lamellae, and each mosaic is a rectangular multi-layer lamella, which is composed of packed single-layered lamellae. The fibrils in the diameter of about 1 μm were observed, which are the structural units of lamellae and would be the bundles of the bowlic molecular columns. The mosaic-like morphologies decorate the bowlic molecular columnar nematic phase, therefore, a novel mosaic-like morphologies decoration method was applied to reveal the director distribution of several kinds of point disclinations, such as s = +1(δ =0°and δ =90°) and s = ±1/2, and Nèel domain walls. It was shown that the bowlic molecular columnar nematic phase behaved as normal nematic phases; however, the basic structural units ordered were the bowlic molecular column or the bundles of bowlic molecular column (i.e. fibrils), but not the bowlic molecules themselves. The bowlic molecular columns acted as the rod-like molecules in a normal nematic phase. Therefore, a new term BCN (bowlic columnar nematic phase) is used to describe the anomalous nematic phase in this paper.
基金The work was supported by the National Natural Science Foundation of China ( Grant No. 29925411).
文摘Two decoration techniques, solidification-induced band texture decoration and focal-conic texture decoration, have been established to exhibit the director field of disclinations in a low-molar-mass methacrylate liquid crystal. The disclinations with strength s=1/2 and s=±1 are observed by the two decoration methods. For the solidification-induced band texture decoration, the molecular orientation is perpendicular to the direction of the band. While for focal-conic texture decoration, it has been proved by the results of IR dichroism that the direction of the director is parallel to the direction of the focal-conic. Therefore, the sketch map of the molecular director filed can be mapped according to the morphological pattern of the solidification-induced band texture or focal-conic texture.
基金the National Natural Science Foundation of China (Nos.29874020, 59573029), the Natural Science Foundation of Shandong Province of China and the Science Foundation of Polymer Physics Laboratory, the Chinese Academy of Sciences.
文摘The observation of disclination cores of high strength S=-2, -3, -4, -5, -6, -7, -8 in a smectic C phase of Schiff-base type liquid crystal (LC) is reported. The results of polarizing optical microscope (POM), dif-ferential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) prove that the sample exhibits smectic C phase. It is suggested that the formation of the high strength disclination is mainly ascribed to the stronger anchoring of LC molecules on the substrate due to the formation of hydrogen bonds between the pendent hydroxyl of the LC molecule and the substrate.
基金This project was in part supported by the Hong Kong Research Grants Council(HKUST597/95P&6149/97P)
文摘A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.
文摘Nano-mechanisms of crystal lattice deformation on the interface of dissimilar materials (Cu-Nb), joined by vacuum rolling in solid phase under high temperature (950℃) were studied by means of high resolution electron microscopy. Input of carriers of rotation modes—nano-dipoles of partial disclinations and nano-twist disclinations in the form of double spirals in deformation mechanisms were analyzed. The role of these mechanisms in decrease of shear stability of the interface areas and in production of high-quality rolled metal is discussed.
文摘The defect structures of s = ±1/2 twist disclinations in twisted nematic and twisted chiral liquid crystals have been investigated within the Landau-de Gennes theory numerically. Our results show that there exists eigenvalue exchange across the defect core of both the two models. The defect core is essentially biaxial and never isotropic. The defect centre is uniaxial and is surrounded by a strong biaxial region.
文摘One fundamental problem of modern physics is the search for a theory of everything able to explain the nature of space-time, what matter is and how matter interacts. There are various propositions, as Grand Unified Theory, Quantum Gravity, Supersymmetry, String and Superstring Theories, and M-Theory. However, none of them is able to consistently explain at the present and same time electromagnetism, relativity, gravitation, quantum physics and observed elementary particles. In this paper, one summarizes the content of a new book, published in English [2] and in French [3], in which it is suggested that Universe could be a massive elastic 3D-lattice, and that fundamental building blocks of Ordinary Matter could consist of topological singularities of this lattice, namely diverse dislocation loops and disclination loops. For an isotropic elastic lattice obeying Newton’s law, with specific assumptions on its elastic properties, one obtains the result that the behaviours of this lattice and of its topological defects display “all” known physics, unifying electromagnetism, relativity, gravitation and quantum physics, and resolving some longstanding questions of modern cosmology. Moreover, studying lattices with axial symmetries, represented by “colored” cubic 3D-lattices, one has identified a lattice structure whose topological defect loops coincide with the complex zoology of elementary particles, which could open a very promising field of research. Here, only main steps and principal results of the new theory are presented and discussed, without showing the mathematical concepts and developments contained in the book.
