CONSTITUTIVE RELATION AND STIFFNESS DEGRADATION OF CRACKED ANISOTROPIC COMPOSITE LAMINATES(II)─DETERMINATION OF RESOLVED STIFFNESS AND INVESTIGATION OF STIFFNESS DEGRADATION

The study on properly degradation of damaged,.onlj,osile laminates is extendedto anisotropic laminates with matrix cracking. In (II) of the paper, a solution forpartitioned stiffness is given to complete the constitutive relations developed in (I) Thestiffness degradation in (θ_m/90_n)_s cracked laminates is calculated and the results arediscussed.     

PROPERTY DEGRADATION OF ANISOTROPIC COMPOSITE LAMINATES WITH MATRIX CRACKING (I)-CONSTITUTIVE RELATION DEVELOPING FOR (θ_m/90_n)_s CRACKED LAMINATES BY STIFFNESS PARTITION

The study on property degradation of damaged composite laminates is extendedto anisotropic laminates with matrix cracking. In (I) of the paper, an idea of "stiffnesspatition" is proposed to deal with the puzzle that the in-plane normal response iscoupled with the shear response of the laminates. For (θ_m/90_n.), laminates containingtransversely cracked layers under general in-plane loading, the constitutive relationsare derived and the effective stiffnesses are expressed as the function of crack density.     

PROPERTY DEGRADATION OF ANISOTROPIC COMPOSITELAMINATES WITH MATRIX CRACKING(Ⅰ)──CONSTITUTIVE RELATION DEVELOPING FOR (θ_m/90_n)_s CRACKED LAMINATES BY STIFFNESS PARTITION

I.IntroductionThestudyofconstitutiverelationsforcrackedcompositelaminateisadifficultbutelementaryworkincompositedamagemechanics.Onedistinctiveadvantageofacompositelaminateisitsdesignabilityofmechanicalbehaviorcausedbydifferentlayups,butjustthisfeaturemakesthelaminateanisotropictherebyincreasethecomplicationforanalyingthelaminate,especiallyforacrackedlaminate.Matrixcrackingisadamageformoccurredmoreearlyinloadedlaminates.Itsmacroresponsehasbeenasubjectofextensiveresearchinrecentstudies.Tillnow,…     

SYNTHESIS OF HYDROPHILIC ZnS NANOCRYSTALS AND THEIR APPLICATION IN PHOTOCATALYTIC DEGRADATION OF DYE POLLUTANTS

Hydrophilic ZnS nanocrystals with narrow size distribution were synthesized via homogeneous precipitation using EDTA as stabilizer. The as-synthesized products were characterized with XRD, TEM, HRTEM and UV-Vis spectrum. UV-Vis spectra showed that ZnS nanocrystals exhibited strong quantum-confined effect with a blue shift in the band gap of light absorbance. The photocatalytic activity of these nanocrystals was also investigated for the liquid phase photocatalytic degradation of Basic Violet 5BN (BV5) dye under UV irradiation. It was found that the ZnS nanocrystals had good catalytic activity for photodegradation of BV5.     

DIFFERENCE DISCRETE SYSTEM OF EULER-BEAM WITH ARBITRARY SUPPORTS AND SIGN-OSCILLATORY PROPERTY OF STIFFNESS MATRICES

The difference discrete system of Euler-beam with arbitrary supports was constructed by using the two order central difference formulas. This system is equivalent to the spring-mass-rigidrod model. By using the theory of oscillatory matrix, the sign-oscillatory property of stiffness matrices of this system was proved, and the necessary and sufficient condition for the system to be positive was obtained completely.     

THE MEASUREMENT OF PLASTIC DEFORMATION AND CRACK GROWTH IN CRACKED SPECIMENS BY SAM

In this paper,scanning acoustic microscope(SAM) was used to obtainsome characteristic photographs which explain the mesoscopic information of severalcracked specimens.New results on subsurface information of steel,nickel andaluminium were presented.Plastic deformation and crack initiation were observed andanalysed.The length of crack propagation was measured.SAM is particularly suited tothe study of many mesoscopic phenomena in material science because it can imagemesoscopic subsurface feature without sectioning.It is revealed that SAM has a brightfuture in the field of mesomechanics.     

THE INCREMENT STIFFNESS MATRIX AND TOTAL QUANTUM STIFFNESS IN NONLINEAR ANALYSES

In this paper,the expressions of both increment stiffness matrix and total quantumstiffness matrix in nonlinear analyses are derived in detail.and their relationship isdiscussed in mathematical meaning.The results given in our paper will be of great importance to the ana.yses of nonlinearnumerical and nonlinear stability in finite element methods.     

GREEN＇S FUNCTION AND EFFECTIVE ELASTIC STIFFNESS TENSOR FOR ARBITRARY AGGREGATES OF CUBIC CRYSTALS

A closed but approximate formula of Green‘s function for an arbitrary aggregate of cubic crystallites is given to derive the effective elastic stiffness tensor of the polycrystal. This formula, which includes three elastic constants of single cubic crystal and five texture coefficients,accounts for the effects of the orientation distribution function (ODF) up to terms linear in the texture coefficients. Thus it is expected that our formula would be applicable to arbitrary aggregates with weak texture or to materials such as aluminum whose single crystal has weak anisotropy.Three examples are presented to compare predictions from our formula with those from Nishioka and Lothe‘s formula and Synge‘s contour integral through numerical integration. As an application of Green‘s function, we briefly describe the procedure of deriving the effective elastic stiffness tensor for an orthorhombic aggregate of cubic crystallites. The comparison of the computational results given by the finite element method and our effective elastic stiffness tensor is made by an example.     

WAY TO DETERMINE STIFFNESS FUNCTION OF STRUCTURE

For calculating the stiffness function of a structure, the differential equation of the vibration of the structure was divided into the differential equation on the original stiffness function that was known, and Fredholm integral equation of the first kind on the undetermined stiffness function that was unknown. And the stable solutions of the integral equation, when the smooth factor was equal to zero, was solved by the extrapolation with p smooth factors. So the stiffness function of the structure is obtained. Applied examples show that the method is feasible and effective.     

GREEN’S FUNCTION AND EFFECTIVE ELASTIC STIFFNESS TENSOR FOR ARBITRARY AGGREGATES OF CUBIC CRYSTALS

A closed but approximate formula of Green’s function for an arbitrary aggregate of cubic crystallites is given to derive the e?ective elastic sti?ness tensor of the polycrystal. This formula, which includes three elastic constants of single cubic c…     

AN APPROXIMATE ANALYSIS OF FREQUENCY RESPONSE OF A CRACKED HINGEDHINGED BEAM

A new method based on a modified line-spring model is developed forevaluating the natural frequencies of vibration of a cracked beam.This model inconjunction with the Euler-Bernoulli beam theory,modal analysis and linear elasticfracture mechanics is applied to obtain an approximate characteristic equation of acracked hinged-hinged beam.By solving this equation the natural frequencies aredetermined for different crack lengths in different positions.The results show goodagreement with the solutions through finite element analysis.The present method maybe extended to analyze other cracked complicated structures with various boundaryconditions.     

DAMAGE PROGRESSIVE MODEL OF COMPRESSION OF COMPOSITE LAMINATES AFTER LOW VELOCITY IMPACT

IntroductionCompressivepropertiesofcompositelaminatesafterlowvelocityimpactareoneofthemostseriouscircumstanceswhichmustbetakenintoaccountindamagetolerancedesignofcompositestructures[1].Impactdamagegenerallymanifestsintheformsofdelaminations,matrixcracksandfibrefracture[2 ,3].Sofaralotofresearcheshavebeentakeninlowvelocityimpactbehaviorofcompositelaminatesandtheirpost_impactcompressiveproperties.Compressivefailuremechanismsofcompositelaminatesafterlowvelocityimpacthavenotbeenknownclearly .Ther…     

VARIATIONAL PRINCIPLE OF HYBRID ENERGY AND THE FUNDAMENTALS OF 3-D LAMINATE THEORY—A NEW APPROACH FOR THE ANALYSIS OF INTERLAMINAR STRESSES IN COMPOSITE LAMINATES

This paper discusses the discuntinuity of stresses and strains at interlaminar surfaces of the eomposne laminate and presents a 3-D laminate theory for composite materials. This paper also presents a new type of clastic energy based on the globally continuous variables in laminates, different from the traditional potemial energy and complementary energy. Then. a variational principle corresponding to the 3-D laminate theory is developed. The theory and the principle could be a basis of verifying the 2-D lamimte theory and deterplining the interlaminar stresses mear the free edges.     

ENERGY RELEASE RATE COMPONENTS ANALYSIS OF LAMINATES WITH EMBEDDED DELAMINATION

This paper is the continuation of the authors' previous investigation inwhich the formula of total energy release rate at each point along the delaminationboundary iS derived by using variational method of moving boundary.In the presentpaper,the analytical model is reformed and the individual components of energyrelease rate are derived in the form of plate theory.The circular delaminationembedded in circular laminates is analysed and some conclusions are obtained.     

THE DYNAMIC STIFFNESS MATRIX OF THE FINITE ANNULAR PLATE ELEMENT

The dynamic deformation of harmonic vibration is used as the shape functions of thefinite annular plate element.and some integration difficulties related to the Bessel’sfunctions are solved in this paper.Then the dynamic stiffness matrix of the finite annularplate element is established in closed form and checked by the direct stiffness method.Thepaper has given wide converage for decomposing the dynamic matrix into the power seriesof frequency square.By utilizing the axial symmetry of annular,the modes withdifferent numbers of nodal diameters are separately treated Thus some terse and completeresults are obtained as the.foundation of structural characteristic analysis and dynamicresponse computation.     

A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES

This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching,and to predict the in-plane effective tensile strength of the stitched composite laminates.The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties.A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching.The undistorted region,the fiber distortion region,the resin-rich pocket and the through-thickness reinforcement section are taken into account.The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters,the distortion width and maximum misalignment.It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors,the stitch hole and inhomogeneous fiber content.The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite.The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]_(2s) T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations,showing an acceptable agreement with experimental data.     

DISPERSION OF NANODIAMOND AND ULTRA-FINE POLISHING OF QUARTZ WAFER

Mechanochemical Modification (MCM) of nanodiamond surface with DN-10 was studied in relation to the performance of nanodiamond in polishing quartz wafers. Results show that the modified nanodiamond is more stable in the pH range 8-11. A super smooth surface with an average roughness of 0.214 nm was achieved using a nanodiamond-based slurry regulated by N-(2-hydroxyethyl)ethylenediamine. It is suggested that the principal ultra-fine polishing mechanism of auartz wafer involves atom-level removal under the synergism of chemical and mechanical actions.     

APPLICATION OF THE DIGITAL MOIRE METHOD IN FRACTURE ANALYSIS OF A CRACKED RUBBER SHEET

This paper deals with the mode I crack problem of a cracked rubber sheet under plane stress condition using the delicate digital moire technique. Through the four step phase-shifting method of automated fringe analysis, the displacement fields in the Cartesian coordinate system are given. By the coordinate-transform equation, the radial and circular displacement distributions in the polar coordinate system are obtained. The displacement isoline distributions and displacement vector distributions near the crack tip are discussed. The strain isoline distributions near the crack tip are also analyzed in this paper. Finally, the distribution rules for the mechanical fields near the crack tip are discussed with the sector division method.     

GENERAL SITUATION OF THE PARTICIPATION OF EDITORIAL BOARD MEMBERS OF APPLIED MATHEMATICS AND MECHANICS IN THE 16th.INTERNATIONAL CONGRESS OF THEORETICAL AND APPLIED MECHANICS

The 16th.International Congress of Theoretical and Applied Mechanics(ICTAM),which isheld every four years under the auspices of International Union of Theoretical and AppliedMechanics(IUTAM),was held on Aug.19,1984 Aug.25,1984 in Lyngby Industrial University.Copenhagen.Denmark.35 representatives of the People’s Republic of China participated in this     

BASIC FORMULATION OF STATIC AND DYNAMIC BEHAVIOURS OF SOIL AND OTHER POROUS MEDIA

This paper treats the soil and rock or concrete as a two-phasemedium composed of a solid skeleton and an interstitial fluid.Un-der the unsaturated condition of interstitial fluid,the thirdphase is taken into consideration. In this paper. we consider theconstitutive relation,dynamic and kinematic relations,and also va-rious approximations with their limits of validity.including thoseof most practical engineering situations such as the consolidationproblem and the undrained behaviour. The finite element discreti-zation and the time dependent solution of various classes of soilproblem are also discussed.