ANALYSIS OF 2-D THIN STRUCTURES BY THE MESHLESS REGULAR HYBRID BOUNDARY NODE METHOD

Thin structures are generally solved by the Finite Element Method(FEM), using plate or shell finite elements which have manylimitations in applications, such as numerical locking, edge effects,length scaling and the cnvergence problem. Recently, by proposing anew approach to tranting the nearly- singular integrals, Liu et al.developed a BEM to successfully solve thin structures with thethickness-to- length ratios in the micro-or nano-scales. On the otherhand, the meshless Regular Hybrid Boundary Node Method (RHBNM), whichis proposed by the current authors and based on a modified functionaland the Moving Least-Square (MLS) approximation, has very promisingapplications for engineering problems owing To its meshless natureand dimension-reduction advantage, and not involving any singular ornearly-singular Integrals. Test examples show that the RHBNM can alsobe applied readily to thin structures with high accu- Racy withoutany modification.

BEM FOR SIMULATION OF A 2D ELASTIC BODY WITH RANDOMLY DISTRIBUTED CIRCULAR INCLUSIONS

Based on our 2D BEM software THBEM2 which can be applied to thesimulation of an elastic body with randomly distributed identicalcircular holes, a scheme of BEM for the simulation of elastic bodieswith randomly distributed circular inclusions is proposed. Thenumerical examples given show that the bound- ary element method ismore accurate and more effective than the finite element method forsuch a problem. The scheme presented van also be successfully used toestimate the effective elastic properties of composite Materials.

FURTHER IMPROVEMENT ON FUNDAMENTAL SOLUTIONS OF PLANE PROBLEMS FOR ORTHOTROPIC MATERIALS

On the basis of the existing fundamental solutions ofdisplacements, further improvement is made, and then the generalfundamental solutions of both plane elastic and plane plasticproblems for ortho- tropic materials are obtained. Two parametersbased on material constants a_1, a_2 are used to derive the rele-vant expressions in a real variable form. Additionally, an analyticalmethod of solving the singular integral for the internal stresses isintroduced, and the corresponding result are given. If a_1=a_2=1, allthe expres- sions obtained for orthotropy can be reduced to thecorresponding ones for isotropy. Because all these expres- sions andresults can be directly used for both isotropic problems andorthotropic problems, it is convenient to use them in engineeringwith the boundary element method (BEM).

A UNIFIED ENERGY APPROACH TO A CLASS OF MICROMECHANICS MODELS FOR MICROCRACKED SOLIDS

Micromechanics models have been developed For the determination of the elastic moduli of microcracked solids based on different approaches and interpretations, including the dilute or non-interacting solution, the Mori-Tanaka method, the self-consistent method, and the generalized self-consistent method. It is shown in the present study that all these micromechanics models can be unified within an energy-equivalence framework, and that they differ only in the way in which the microcrack opening and sliding displacements are evaluated. Relevance to the differential methods and the verification of these models are discussed.

QUASI-MICROMECHANICAL CONSTITUTIVE THEORY FOR BRITTLE DAMAGED MATERIALS UNDER TENSION

One of fundamental but difficult problems in damage mechanics isthe formulation of the ef- fective constitutive relation ofmicrocrack-weakened brittle o quasi-brittle materials under complexloading, especially when microcrack interaction is taken intoaccount. The combination of phenomenological and mi- cromechanicaldamage mechanics is a promising approach to construction andapplicable damage model with a firm physical foundation.

A new development of Al-Ti-C grain refining master alloys

Al Ti C master alloys have been prepared with a novel production method. A combination of X ray phase analysis, SEM and EDS was used to examine the phases and microstructures of the master alloys. The master alloys have block like Al 3Ti particles and submicron size TiC X with X ranging from 0.49 to 0.78 and show excellent grain refining performance for commercially pure aluminum. Titanium carbides were observed at the crystallization centers in refined castings.

Surface Modification of Nanometer Silica by N, N'-dicyclohexyl- carbodiimide Mediated Amidation

A potentially versatile procedure for surface modification of nanometer silica is illustrated by N, N-dicyclohexylcarbodiimide (DCC) mediated amidation of stearic acid.

COMPLETE EIGEN-SOLUTIONS FOR ANTI-PLANE NOTCHES WITH MULTI-MATERIALS BY SUPER-INVERSE ITERATION

Ln this paper, the super-inverse iterative method is proposed to compute the accurate and complete eigen-solutions for anti-plane cracks/notches with multi-materials, arbitrary opening angles and various surface conditions. Taking the advantage of the knowledge of the variation forms of the eigen-functions, a series of numerical techniques are proposed to simplify the computation and speed up the convergence rare of the inverse iteration. A number of numerical examples are given to demonstrate the excellent accuracy, efficiency and reliability of the proposed approach.

A STUDY OF CRACK CLOSURE IN ELECTRIC-FIELD-INDUCED FATIGUE IN FERROELECTRIC CERAMICS

Considering the influence of the domain switching near the tip of a crack andapplying the idea of multiscale singularity fields in piezoelectric fracture, we have obtained anempirical criterion for the crack closure. Based on the domain switching in the electric yieldregion, referring to Yang's results on the small scale yield model for the electrical fatigue crack,a model of the crack closure during electric-field-induced fatigue is developed to analyze thecrack growth. In terms of the model we have obtained the formula of the rate of the crack growthunder cyclic electric loading. Finally we compare the theoretical predictions with the results givenby Cao and Evans experimentally. It should be pointed out that the model proposed is empirical andneeds to be verified by more experimental results.

THE BOUNDARY LAYER SOLUTIONS OF THE INTERFACE PROBLEM CONSIDERING THE STRAIN GRADIENT

Acoording to the classical elastic theory, there is always adiscontinuity of rotation angle on the interface different materials.This illogic result can be overcome by the strain gradient plasticitytheory. In the light of this theory, there is a group of boundarylayer solutions near the in- terface, which have made importantadjustment of the classical results.

AN ASYMPTOTIC METHOD FOR ANALYZING THE STRESS IN A FUNCTIONALLY GRADIENT MATERIAL LAYER ON A SURFACE OF A STRUCTURAL COMPONENT

A simple and effective method for analyzing the stress distribution in a Functionally Gradient Material(FGM) layer on the su;face of a structural component is proposed in this paper. Generally, the FGM layer is very thin compared with the characteristic length of the structural component, and the nonhomogeneity exists only in the thin layer. Based on these features, by choosing a small parameter I which characterizes the stiffness of the layer relative to the component, and expanding the stresses and displacements on the two sides of the interface according to the parameter lambda, then asymptotically using the continuity conditions of the stresses and displacements on the interface, a decoupling computing process of the coupling control equations of the layer and the structural component is realized. Finally, two examples are given to illustrate the application of the method proposed.

Numerical Simulation of Thermal Stress of Shaped Casting Based on Rheological Model

In order to study the thermal stresses at the mushy zone, a three dimensional rheological model [H]-[H\N]-[N\S] including elastic, visco-elastic and visco-plastic elements was established, its algorithm and codes for finite element method were also developed. A FDM/FEM integrated analysis system of thermal stresses was built based on the integration of this procedure with thermal analysis by finite difference method. A steel sample casting with a hot spot was simulated in order to validate this system, and the calculated and experimental results were in good agreement.

Thermodynamic Aspect in Synthesis of AlN Powders by Carbothermal Reduction and Nitridation Process

A thermodynamical calculation shows that AlN powders were synthesized in the process by the overall reaction Al2O3(s)S+3C(s)+N-2(g)=2AlN(s)+3CO(g) and its minimum reaction temperature T-0=1852 K, if all reactants and products were in standard states. In the practical experiments, AlN phase appeared obviously at only 1300 degrees C, the major reasons are related to the partial pressure of its gaseous product p(co) and the mixed free energy. The synthesis temperature could be towered by either increasing N-2 flow rate or elevating N-2 pressure. On the other hand, as the temperature decreases, the equilibrium constant K-m also reduces, and the reducing rate strongly depends on the temperature: the lower the temperature, the higher the rate.

Spatially Inhomogeneous Gain Modification in Photonic Crystals

The electric and magnetic energy distributions in photonic crystals （PC） are calculated by using the plane wave expansion （PWE） method. Even though the total electric and magnetic energy in each unit cell of photonic crystals are equal to each other, the ratio of electric and magnetic energy densities varies depending on the local position. Based on Fermi＇s golden rule, the optical gain is analysed in the full quantum framework that takes the nonuniform energy density ratio into account. This nonuniform energy density ratio in photonic crystals, defined in an equal form as gain modification factor, leads to spatially inhomogeneous modification of optical gain. Results reported in the paper provide a new perspective for analysing gain characteristics, as well as the lasing properties, in photonic crystals.

3-D NUMERICAL SIMULATION OF FRACTURE PROCESSES IN HETEROGENEOUS BRITTLE MATERIALS

By using the lattice model combined with finite element methods andstatistical techniques, a numerical approach is developed to establish mechanical models ofthree-dimensional heterogeneous brittle materials. A special numerical code is introduced, in whicha lattice model and statistical approaches are used to simulate the initial heterogeneity ofmaterial properties. The size of displacement-load step is adap-tively determined so that only fewelements would fail in each load step. When the tensile principal strain in an element exceeds theultimate strain of this element, the element is considered broken and its Young's modulus is set tobe very low. Some important behaviors of heterogeneous brittle materials are indicated using thiscode. Load-displacement curves and figures of three-dimensional fracture patterns are alsonumerically obtained, which are similar to those observed in laboratory tests.

Persistent Currents in Toroidal Single-wall Carbon Nanotubes

In this paper the persistent currents of ideal toroidal single-wall carbon nanotubes (TSWNTs) are calculated from the tight-binding model and the periodic boundary conditions. The electronic structure and persistent current of a TSWNT strongly depend on its helicity and longitudinal circumference, making the TSWNTs a geometry-sensitive kind of materials. The interatomic carbonic interactions other than pp pi-type are also studied and are found to introduce more steps to the persistent current. The diamagnetic-paramagnetic transitions occur more frequently, and the persistent current depends on the interaction energy values, while the periodicity of magnetic flux preserves.

A NEW METHOD TO DETERMINE THE R-CURVE OF CERAMICS-FRACTURE GRATING METHOD

The etching technique of the single-lined zero-thickness specimen grating is applied to the surface of the SiC fiber toughening Si3N4 ceramic composite specimen. The position of the crack and the crack length during the process of crack extension when the load is applied and gradually increased can be determined by recording the output voltage value of the Wheatstone bridge in which the ceramic specimen with the fracture grating on is located. The crack-growth-resistance(R-curve) of this material is thus obtained.

ANTI-PLANE CRACK MOVING ALONG THE INTERFACE OF DISSIMILAR PIEZOELECTRIC MATERIALS

The problem of an anti-plane Griffith crack moving along the interface of dissimilar piezoelectric materials is solved by using the integral transform technique. It is shown from the result that the intensity factors of anti-plane stress and electric displacement around the crack tip are dependent on the speed of the Griffith crack as well as the material coefficients. When the two piezoelectric materials are identical, the present result will be reduced to the result far the problem of an anti-plane moving Griffith crack in homogeneous piezoelectric materials.

AN INVESTIGATION ON ASYMPTOTIC NEAR-TIP FIELDS OF DYNAMIC CRACK IN AN ELASTIC-PERFECTLY PLASTIC COMPRESSIBLE MATERIAL

The stress and deformation fields near the tip of a mode-I dynamic crack steadily propagating in an elastic-perfectly plastic compressible material are considered under plane strain conditions. Within the framework of infinitesimal displacement gradient theory, the material is characterized by the Von Mises yield criterion and the associated J(2) flow theory of plasticity. Through rigorous mathematical analysis, this paper eliminates the possibilities of elastic unloading and continuous asymptotic fields with singular deformation, and then constructs a fully continuous and bounded asymptotic stress and strain field. It is found that in this solution there exists a parameter phi(0) which cannot be determined by asymptotic analysis but may characterize the effect of the far field. Lastly the variations of continuous stresses, velocities and strains around the crack tip are given numerically for different values of phi(0).

AN ACCELERATION FOR THE EIGENSYSTEM REALIZATION ALGORITHM WITH PARTIAL SINGULAR VALUES DECOMPOSITION

The real-time identification of dynamic parameters is importantfor the control system of spacecraft. The eigensystme realizationalgorithm (ERA) is currently the typical method for such applica-tion. In order to identify the dynamic parameter of spacecraftrapidly and accurately, an accelerated ERA with a partial singularvalues decomposition (PSVD) algorithm is presented. In the PSVD, theHankel matrix is reduced to dual diagonal form first, and thentransformed into a tridiagonal matrix.