2000 Vol. 17, No. 3
2000, 17(3): 1-5.
Abstract:
The yarn architecture of three dimensional (3 D) braided preforms produced by the four step 1×1 braiding technique has been studied by means of a control volume method in conjunction with experimental investigation. According to the movement traces of yarn carriers on the braiding machine bed, a preform was divided into three regions, i.e. interior, surface and corner, and four kinds of local unit cells were identified for it. Based on the assumption of the braiding yarns with the elliptical cross section and the introduction of the yarn packing factor, the relations between the braiding parameters were derived. Finally, the predictions of the thickness and the fiber volume fraction of preforms have shown good agreement with experimental results.
The yarn architecture of three dimensional (3 D) braided preforms produced by the four step 1×1 braiding technique has been studied by means of a control volume method in conjunction with experimental investigation. According to the movement traces of yarn carriers on the braiding machine bed, a preform was divided into three regions, i.e. interior, surface and corner, and four kinds of local unit cells were identified for it. Based on the assumption of the braiding yarns with the elliptical cross section and the introduction of the yarn packing factor, the relations between the braiding parameters were derived. Finally, the predictions of the thickness and the fiber volume fraction of preforms have shown good agreement with experimental results.
2000, 17(3): 6-10.
Abstract:
The influence of silane coupling agents and grafting modification of polypropylene (PP) matrix on the mechanical properties of continuous glass fibre reinforced polypropylene (CGFRPPs) was studied. The interfacial chemical action and interfacial adhesion in the silanized GF/modified PP were also investigated using FTIR and SEM. The results showed that there is chemical action between the modified PP blended with maleic anhydride grafting PP (MAH g PP) and the silanized GF, which obviously increases the interfacial adhesion and mechanical properties of the composites, and silane coupling agents of different kinds make not much difference to the mechanical properties of GF/PP composites with grafting PP in the matrix.In addition, it was found that improvement of MAH g PP on the mechanical properties of CGFRPPs is superior to that of acrylic acid grafting PP.
The influence of silane coupling agents and grafting modification of polypropylene (PP) matrix on the mechanical properties of continuous glass fibre reinforced polypropylene (CGFRPPs) was studied. The interfacial chemical action and interfacial adhesion in the silanized GF/modified PP were also investigated using FTIR and SEM. The results showed that there is chemical action between the modified PP blended with maleic anhydride grafting PP (MAH g PP) and the silanized GF, which obviously increases the interfacial adhesion and mechanical properties of the composites, and silane coupling agents of different kinds make not much difference to the mechanical properties of GF/PP composites with grafting PP in the matrix.In addition, it was found that improvement of MAH g PP on the mechanical properties of CGFRPPs is superior to that of acrylic acid grafting PP.
2000, 17(3): 11-14.
Abstract:
Thermal cold fatigue of glass mat reinforced polypropylene has been studied by measuring the flexural property and dynamic mechanical property of the composites and the interfacial shear strength of the single filament specimen after thermal cold cycling treatment in different ranges of temperature. The results show that thermal cold cycle leads to the interfacial failure and reduction in mechanical properties. The interfacial failure due to thermal stress will increase with increasing the range of temperature and the number of cycles. Under the same conditions, the interfacial failure of composites differs for different relaxation of the thermal stress of interfaces.
Thermal cold fatigue of glass mat reinforced polypropylene has been studied by measuring the flexural property and dynamic mechanical property of the composites and the interfacial shear strength of the single filament specimen after thermal cold cycling treatment in different ranges of temperature. The results show that thermal cold cycle leads to the interfacial failure and reduction in mechanical properties. The interfacial failure due to thermal stress will increase with increasing the range of temperature and the number of cycles. Under the same conditions, the interfacial failure of composites differs for different relaxation of the thermal stress of interfaces.
2000, 17(3): 15-19.
Abstract:
The surface of F-12 fiber is modified by plasma grafting a kind of macromolecule grafting coupling agent. Based on the analysis of the modified surface of fiber by ESCA, the effects of molecular weight and concentration of grafting coupling agent on the transverse tensile strength are investigated, and the modification mechanism is analyzed according to fracture of transverse tensile. Results show that the grafting modification of grafting coupling agent can effectively improve the interfacial bond properties of F-12/ epoxy composite, and therefore increases the interlaminar shear strength and transverse tensile strength thereof.
The surface of F-12 fiber is modified by plasma grafting a kind of macromolecule grafting coupling agent. Based on the analysis of the modified surface of fiber by ESCA, the effects of molecular weight and concentration of grafting coupling agent on the transverse tensile strength are investigated, and the modification mechanism is analyzed according to fracture of transverse tensile. Results show that the grafting modification of grafting coupling agent can effectively improve the interfacial bond properties of F-12/ epoxy composite, and therefore increases the interlaminar shear strength and transverse tensile strength thereof.
2000, 17(3): 20-23.
Abstract:
The anodic oxidation surface treatment of carbon fibers in 3-D braided preform was studied. The effects of treatment parameters on the properties of 3-D braided carbon fibers composites were examined in terms of interfacial strength, impact strength and compressive strength, and the fracture of the composites was characterized by SEM. The results indicate the method can treat the surface of carbon fibers not only in the outer layer region but also in the inner region of the braided materials. Moreover, the interfacial strength of the 3-D braided carbon fiber/phenolic resin has been improved obviously and the integrated property of composites has also been improved.
The anodic oxidation surface treatment of carbon fibers in 3-D braided preform was studied. The effects of treatment parameters on the properties of 3-D braided carbon fibers composites were examined in terms of interfacial strength, impact strength and compressive strength, and the fracture of the composites was characterized by SEM. The results indicate the method can treat the surface of carbon fibers not only in the outer layer region but also in the inner region of the braided materials. Moreover, the interfacial strength of the 3-D braided carbon fiber/phenolic resin has been improved obviously and the integrated property of composites has also been improved.
2000, 17(3): 24-27.
Abstract:
The carbonyl iron/cobalt phthalocyanine composites were obtained while the solution of carbonyl iron and cobalt phthalocyanine (CoPc) mixing into DMF was backflowing for 3 hours at 114 ~120℃ composite in situ . Composite particles were analyzed using XRD, SEM, TG and DTA. The result shows that the composition and structure of the Fe/CoPc composites are different using various methods of synthesis. The lower the concentration of carbonyl iron decomposing and forming Fe particles, the smaller the average diameter of composites. The surface of the Fe/CoPc composites is covered completely by CoPc, they are almost regular spherical shape and their diameter is of 1.20μm±0.10 μm when the mass content of CoPc in the backflow solution is above 6.7%. Density of the composites is cut down to 3.664 g/cm3 and anti oxygenation of ultramarinen Fe particles in the composites is advanced obviously.
The carbonyl iron/cobalt phthalocyanine composites were obtained while the solution of carbonyl iron and cobalt phthalocyanine (CoPc) mixing into DMF was backflowing for 3 hours at 114 ~120℃ composite in situ . Composite particles were analyzed using XRD, SEM, TG and DTA. The result shows that the composition and structure of the Fe/CoPc composites are different using various methods of synthesis. The lower the concentration of carbonyl iron decomposing and forming Fe particles, the smaller the average diameter of composites. The surface of the Fe/CoPc composites is covered completely by CoPc, they are almost regular spherical shape and their diameter is of 1.20μm±0.10 μm when the mass content of CoPc in the backflow solution is above 6.7%. Density of the composites is cut down to 3.664 g/cm3 and anti oxygenation of ultramarinen Fe particles in the composites is advanced obviously.
2000, 17(3): 28-32.
Abstract:
A special apparatus was constructed by modifying capillary rheometer to study polymer melt flow behavior through fiber beds. One dimension constant pressure flow experiments were carried out to measure the transverse permeability of two glass fiber mats in both unsaturated and saturated flow using PP melt as permeant. The effect of mat architecture on permeability was investigated including mat porosity, fiber diameter and needles. Furthermore, selection of impregnation parameters in GMT melt impregnation was discussed according to the experimental results.
A special apparatus was constructed by modifying capillary rheometer to study polymer melt flow behavior through fiber beds. One dimension constant pressure flow experiments were carried out to measure the transverse permeability of two glass fiber mats in both unsaturated and saturated flow using PP melt as permeant. The effect of mat architecture on permeability was investigated including mat porosity, fiber diameter and needles. Furthermore, selection of impregnation parameters in GMT melt impregnation was discussed according to the experimental results.
2000, 17(3): 33-37.
Abstract:
It is difficult to insure the quality of composites for the reason that there are complicated processes during curing process of composites. The intelligent systems of in time monitoring the cure process need advanced sensors though they are effective ways of elevating the quality of composites. In this paper, a new sort of fiber optic sensor was designed, and the variation of refractive index of resin surrounding the embedded fiber optic was observed by measuring the speckle spatial spectrum at the end face of the fiber optic. The resin cure experiment results measured by the fiber optic sensor were given. This sort of fiber optic sensor was found to be able to detect the gel point, the end point and the lowest point of viscosity of resin matrix. This fiber optic sensor system is sensitive to detect the cure process of composite curing in autoclave and can be used in the intelligent system of in time monitoring the curing process of composites for the reason of precision, simplicity and reliability.
It is difficult to insure the quality of composites for the reason that there are complicated processes during curing process of composites. The intelligent systems of in time monitoring the cure process need advanced sensors though they are effective ways of elevating the quality of composites. In this paper, a new sort of fiber optic sensor was designed, and the variation of refractive index of resin surrounding the embedded fiber optic was observed by measuring the speckle spatial spectrum at the end face of the fiber optic. The resin cure experiment results measured by the fiber optic sensor were given. This sort of fiber optic sensor was found to be able to detect the gel point, the end point and the lowest point of viscosity of resin matrix. This fiber optic sensor system is sensitive to detect the cure process of composite curing in autoclave and can be used in the intelligent system of in time monitoring the curing process of composites for the reason of precision, simplicity and reliability.
2000, 17(3): 38-41.
Abstract:
Residual stress in viscoelastic resin matrix composite laminates at room temperature can keep varying during a long period of time. The characteristic can be reflected by the curvature variation of unsymmetrical laminates. A curvature variation test of unsymmetrical laminate was conducted and the test results indicate that the curvature and residual stress can finally tend to a stable state. Based on the test results, a revised ply stiffness matrix corresponding to the final stable state is deduced by means of a micromechanics model and the calculation method appropriate for the large deformation of composite laminates. The revised stiffness matrix can be used to predict the final stable state of the residual stress and deformation of composite laminates with different stacking sequences, and then determine the variation scope of residual stress. Tests of different laminates for verifying the effect of revised stiffness matrix were also conducted and the test results quite agree with the prediction.
Residual stress in viscoelastic resin matrix composite laminates at room temperature can keep varying during a long period of time. The characteristic can be reflected by the curvature variation of unsymmetrical laminates. A curvature variation test of unsymmetrical laminate was conducted and the test results indicate that the curvature and residual stress can finally tend to a stable state. Based on the test results, a revised ply stiffness matrix corresponding to the final stable state is deduced by means of a micromechanics model and the calculation method appropriate for the large deformation of composite laminates. The revised stiffness matrix can be used to predict the final stable state of the residual stress and deformation of composite laminates with different stacking sequences, and then determine the variation scope of residual stress. Tests of different laminates for verifying the effect of revised stiffness matrix were also conducted and the test results quite agree with the prediction.
2000, 17(3): 42-45.
Abstract:
According to the shear lag model and the actual distribution of whisker in composites, the bearing stress factors of matrix in composites was analyzed. By using the principle of X ray stress measurement, the bearing stress factors of matrix in composites was measured. The calculation result shows that the bearing stress factors of matrix in squeeze casting and extruded vol.20%SiC W/6061Al composites were 0.783 and 0.569, respectively. The experimental result confirmed that the bearing stress factors of matrix in two kinds of composites were 0.742 and 0.557, respectively. The bearing stress factor of matrix in composites from experiment was close to that from calculation.
According to the shear lag model and the actual distribution of whisker in composites, the bearing stress factors of matrix in composites was analyzed. By using the principle of X ray stress measurement, the bearing stress factors of matrix in composites was measured. The calculation result shows that the bearing stress factors of matrix in squeeze casting and extruded vol.20%SiC W/6061Al composites were 0.783 and 0.569, respectively. The experimental result confirmed that the bearing stress factors of matrix in two kinds of composites were 0.742 and 0.557, respectively. The bearing stress factor of matrix in composites from experiment was close to that from calculation.
2000, 17(3): 46-50.
Abstract:
Investigation on the interface reactions and matrix alloying of WCP/Fe-C composites was performed by centrifugal casting a hollow cylinder with composite structure and measuring macrostructures and X ray diffraction analysis and SEM micrography with EDS analysis. In the present work condition, the cylinder, dimensioned by outer diameter 167 mm and inner diameter 87 mm and highness 67 mm, consists of WCP/Fe-C composites surface layer with 16～20 mm heavy cross section and Fe C alloy matrix core. Results show that the surface of CTC particles was partially dissolved by Fe containing melt,even divided.The fine short stick like crystallites, being WC and W 2C primary phase before eutectic, are in situ separated near to the surface of CTC particles. Far from the CTC particles, some separated, fine particle and web WC, W 2C,Fe 3W 3C Fe 4W 2C,Cr 7C 3 and Fe 3C carbide crystallites, are distributed on the matrix of WCP/Fe-C composite. Fe C alloy matrix of the hollow composite cylinder is alloyed in different levels, due to the partial dissolve and diffusion of CTC particles.
Investigation on the interface reactions and matrix alloying of WCP/Fe-C composites was performed by centrifugal casting a hollow cylinder with composite structure and measuring macrostructures and X ray diffraction analysis and SEM micrography with EDS analysis. In the present work condition, the cylinder, dimensioned by outer diameter 167 mm and inner diameter 87 mm and highness 67 mm, consists of WCP/Fe-C composites surface layer with 16～20 mm heavy cross section and Fe C alloy matrix core. Results show that the surface of CTC particles was partially dissolved by Fe containing melt,even divided.The fine short stick like crystallites, being WC and W 2C primary phase before eutectic, are in situ separated near to the surface of CTC particles. Far from the CTC particles, some separated, fine particle and web WC, W 2C,Fe 3W 3C Fe 4W 2C,Cr 7C 3 and Fe 3C carbide crystallites, are distributed on the matrix of WCP/Fe-C composite. Fe C alloy matrix of the hollow composite cylinder is alloyed in different levels, due to the partial dissolve and diffusion of CTC particles.
2000, 17(3): 51-54.
Abstract:
In order to fabricate in situ TiCP/Fe composites under air condition by the synthesis of TiC in Fe-Ti-C melt, the effects of three kinds of covering agents on the oxidization ratio of element Ti in the melt were studied, and the microstructures and mechanical properties of the prepared composites were also analyzed. The results show that the developed mixed salts type covering agent can be used to produce in situ TiCP/Fe composites under air condition, in which the TiCParticles exhibit finer size and homogeneous distribution in the matrix structure, resulting in the composites, especially the quenched composites, to have higher properties.
In order to fabricate in situ TiCP/Fe composites under air condition by the synthesis of TiC in Fe-Ti-C melt, the effects of three kinds of covering agents on the oxidization ratio of element Ti in the melt were studied, and the microstructures and mechanical properties of the prepared composites were also analyzed. The results show that the developed mixed salts type covering agent can be used to produce in situ TiCP/Fe composites under air condition, in which the TiCParticles exhibit finer size and homogeneous distribution in the matrix structure, resulting in the composites, especially the quenched composites, to have higher properties.
2000, 17(3): 55-58.
Abstract:
The forming process and preventive measures of detrimental Fe3C and Fe2Ti in the microstructures of in situ processed TiC P/Fe composites have been studied. The results show that the above two harmful phases form during the solidification of Fe-Ti-C melt, and are related to the Ti content of austenite. The measures of Cu, Ni microalloying and inoculating for the melt can not only promote the synthesis of TiC particles in the melt, but also prevent effectively the harmful phases from precipitating during solidification. As a result, the properties of the composite have been improved
The forming process and preventive measures of detrimental Fe3C and Fe2Ti in the microstructures of in situ processed TiC P/Fe composites have been studied. The results show that the above two harmful phases form during the solidification of Fe-Ti-C melt, and are related to the Ti content of austenite. The measures of Cu, Ni microalloying and inoculating for the melt can not only promote the synthesis of TiC particles in the melt, but also prevent effectively the harmful phases from precipitating during solidification. As a result, the properties of the composite have been improved
2000, 17(3): 59-62.
Abstract:
Through untold centuries of evolutionary development, the insect exoskeleton has become a highly optimized structure suited to a variety of demanding duties. In this study, the structure of the exoskeleton of the insect was investigated for structural characteristics that may prove beneficial to advanced composite efforts. The arrangements of plies discovered in insect exoskeleton were applied to the biomimetic design and synthesis of the glass fiber reinforced epoxy composites. It was shown experimentally that the fracture toughness and the intensity of biomimetic plies are higher those that of conventional ones.
Through untold centuries of evolutionary development, the insect exoskeleton has become a highly optimized structure suited to a variety of demanding duties. In this study, the structure of the exoskeleton of the insect was investigated for structural characteristics that may prove beneficial to advanced composite efforts. The arrangements of plies discovered in insect exoskeleton were applied to the biomimetic design and synthesis of the glass fiber reinforced epoxy composites. It was shown experimentally that the fracture toughness and the intensity of biomimetic plies are higher those that of conventional ones.
2000, 17(3): 63-68.
Abstract:
Measuring apparatus and data processing method of dielectric permittivity at high voltage have been set up. Dependence of dielectric permittivity on electric field for thick PZT/P(VDF TrFE) and PT/P(VDF TrFE) 0-3 ferroelectric composite films has been investigated. The dielectric permittivity increases obviously with the increase of applied field for the composite with the volume fraction of ceramic φ more than 0.3. Maxwell Garnett equation can only be used to predict permittivity of the composite when φ is less than 0.1. Bruggeman equation is suitable for the prediction of dielectric permittivity of composite under low electric field (<1 MV/m). For the dependence of dielectric permittivity on electric field, good agreement is found between the measured permittivity and the prediction of Yamada model with the change of parameter L z, which indicates that L z is determined by dimension of the component, grain shape and static interaction among the grains.
Measuring apparatus and data processing method of dielectric permittivity at high voltage have been set up. Dependence of dielectric permittivity on electric field for thick PZT/P(VDF TrFE) and PT/P(VDF TrFE) 0-3 ferroelectric composite films has been investigated. The dielectric permittivity increases obviously with the increase of applied field for the composite with the volume fraction of ceramic φ more than 0.3. Maxwell Garnett equation can only be used to predict permittivity of the composite when φ is less than 0.1. Bruggeman equation is suitable for the prediction of dielectric permittivity of composite under low electric field (<1 MV/m). For the dependence of dielectric permittivity on electric field, good agreement is found between the measured permittivity and the prediction of Yamada model with the change of parameter L z, which indicates that L z is determined by dimension of the component, grain shape and static interaction among the grains.
2000, 17(3): 69-72.
Abstract:
The combustion regularity of B2O3-Al-C system was investigated and the reaction activation energy of B2O3-Al-C system was determined by the equation of wave speed, through which the transformation SHS diagram of the reaction combustion model was established. Through the numerical simulation, the temperature field of the spiral combustion model was obtained. Combined with experimental results, the formation mechanism of the spiral combustion model occurring under the conditions of actual reaction parameters was analyzed.
The combustion regularity of B2O3-Al-C system was investigated and the reaction activation energy of B2O3-Al-C system was determined by the equation of wave speed, through which the transformation SHS diagram of the reaction combustion model was established. Through the numerical simulation, the temperature field of the spiral combustion model was obtained. Combined with experimental results, the formation mechanism of the spiral combustion model occurring under the conditions of actual reaction parameters was analyzed.
2000, 17(3): 73-77.
Abstract:
Constitutive relationships for composites are investigated in micromechanics. The stress tensor and the strain tensor are decomposed into two orthogonal complementary parts, viz the in-plane part and out-of-plane part, respectively. According to the fact that the in-plane part of strain tensor and the out-of-plane part of stress tensor are continuous across a perfect interface, continuity at a perfect interface between phases is rigorously satisfied, and the interactions between phases are correctly considered. Under these conditions the effective elastic tensor of an n-phase stratified media is analyzed as a whole. Furthermore, the analytical solutions of effective elastic properties of statistically transversely isotropic medium and statistically isotropic medium are obtained from the point of view of statistical averaging. The present theoretical results are in good agreement with related theoretical and experimental results for a two-phase alloy system WC-Co.
Constitutive relationships for composites are investigated in micromechanics. The stress tensor and the strain tensor are decomposed into two orthogonal complementary parts, viz the in-plane part and out-of-plane part, respectively. According to the fact that the in-plane part of strain tensor and the out-of-plane part of stress tensor are continuous across a perfect interface, continuity at a perfect interface between phases is rigorously satisfied, and the interactions between phases are correctly considered. Under these conditions the effective elastic tensor of an n-phase stratified media is analyzed as a whole. Furthermore, the analytical solutions of effective elastic properties of statistically transversely isotropic medium and statistically isotropic medium are obtained from the point of view of statistical averaging. The present theoretical results are in good agreement with related theoretical and experimental results for a two-phase alloy system WC-Co.
2000, 17(3): 78-82.
Abstract:
The scope of application of the path independence of J integral in bimaterial with a crack, which is parallel or vertical or inclined to the interface, is discussed in this paper. According to the conservative law of J integral for the bimaterials with a crack paralleling the interface, a hypothesis about independence of the values of the type Ⅰ fracture strain energy release rate(SERR) from the location of the crack paralleling and closely near the interface is forwarded. And it is verified with finite element method(FFM). A schematic model for a skew crack being near the bimaterial interface is provided. The variation law of SERR with the Dundur's parameters and the angle θ between the interface and the crack surface is calculated by FEM. A method for calculating the stress intensity factor through the SERR for a skew crack near the interface is also given in the paper.
The scope of application of the path independence of J integral in bimaterial with a crack, which is parallel or vertical or inclined to the interface, is discussed in this paper. According to the conservative law of J integral for the bimaterials with a crack paralleling the interface, a hypothesis about independence of the values of the type Ⅰ fracture strain energy release rate(SERR) from the location of the crack paralleling and closely near the interface is forwarded. And it is verified with finite element method(FFM). A schematic model for a skew crack being near the bimaterial interface is provided. The variation law of SERR with the Dundur's parameters and the angle θ between the interface and the crack surface is calculated by FEM. A method for calculating the stress intensity factor through the SERR for a skew crack near the interface is also given in the paper.
2000, 17(3): 83-86.
Abstract:
In this paper, it is pointed out that under both plane stress and plane strain deformation conditions, the constitutive and equilibrium equations in the plane of isotropy of a transversely isotropic body can be expressed in a form identical to that for an isotropic body. This equivalence is implemented through the introduction of a mixed constant containing the Poisson ratios of the transversely isotropic medium. The introduction of this constant eliminates an inconsistency that appeared in the literature on the solution of transversely isotropic bodies. The use of this constant also facilitates consideration of transverse isotropy of the constituents of unidirectional fibre reinforced composite materials.
In this paper, it is pointed out that under both plane stress and plane strain deformation conditions, the constitutive and equilibrium equations in the plane of isotropy of a transversely isotropic body can be expressed in a form identical to that for an isotropic body. This equivalence is implemented through the introduction of a mixed constant containing the Poisson ratios of the transversely isotropic medium. The introduction of this constant eliminates an inconsistency that appeared in the literature on the solution of transversely isotropic bodies. The use of this constant also facilitates consideration of transverse isotropy of the constituents of unidirectional fibre reinforced composite materials.
2000, 17(3): 87-91.
Abstract:
Under the assumption of the existence of an equivalent column which has the same failure behavior as the composite shells following axial impact, the failure of the shells was reduced to a one dimensional problem. An equivalent law was introduced in this paper. By means of the elastic dynamics theory, a simplified impact load was obtained, and then the dynamic radial displacements of the cylindrical shells were determined.
Under the assumption of the existence of an equivalent column which has the same failure behavior as the composite shells following axial impact, the failure of the shells was reduced to a one dimensional problem. An equivalent law was introduced in this paper. By means of the elastic dynamics theory, a simplified impact load was obtained, and then the dynamic radial displacements of the cylindrical shells were determined.
2000, 17(3): 92-95.
Abstract:
A method of equivalent analysis for dynamics and statics behavior of honeycomb sandwich plates is obtained by using low-order shear deformation theory. Equivalent modulus and equivalent density of an equivalent plate are given by means of this method. The difficulty is eliminated that dynamics and statics behavior of honeycomb sandwich plates can not be solved directly by using universal finite element programs such as well known NASTRAN. Results of analytic demonstration show that the equivalent method has a better accuracy of approximation.
A method of equivalent analysis for dynamics and statics behavior of honeycomb sandwich plates is obtained by using low-order shear deformation theory. Equivalent modulus and equivalent density of an equivalent plate are given by means of this method. The difficulty is eliminated that dynamics and statics behavior of honeycomb sandwich plates can not be solved directly by using universal finite element programs such as well known NASTRAN. Results of analytic demonstration show that the equivalent method has a better accuracy of approximation.
2000, 17(3): 96-102.
Abstract:
A higher order shear deformation theory based on global local displacement hypothesis is proposed.This theory fully satisfies the geometric and stress continuity conditions at interfaces and free shear traction conditions on the top and bottom surfaces.It is found that a so called global local superposition technique could be used for expressing the laminate theories in an explicit manner to retain the advantage of numerical efficiency.Based on the superposition technique,the individual terms are identified.It is concluded that not only the completeness of the terms,but also the inclusion of as many terms as possible, are important to a laminate theory.A three nodes triangular element based on this theory is also proposed.The numerical examples show that the higher order shear deformation theory can describe accurately the shear deformation and this displacement element can calculate accurately not only the global displacements but also the interlayer shear stresses.
A higher order shear deformation theory based on global local displacement hypothesis is proposed.This theory fully satisfies the geometric and stress continuity conditions at interfaces and free shear traction conditions on the top and bottom surfaces.It is found that a so called global local superposition technique could be used for expressing the laminate theories in an explicit manner to retain the advantage of numerical efficiency.Based on the superposition technique,the individual terms are identified.It is concluded that not only the completeness of the terms,but also the inclusion of as many terms as possible, are important to a laminate theory.A three nodes triangular element based on this theory is also proposed.The numerical examples show that the higher order shear deformation theory can describe accurately the shear deformation and this displacement element can calculate accurately not only the global displacements but also the interlayer shear stresses.
2000, 17(3): 103-106.
Abstract:
The inverse problems in Hamilton and Gurtin Calculus of Variations for coupled dynamic piezoelectric media were studied. Several kinds of Hamilton type and Gurtin type variational principles and generalized variational principles for piezoelectric media were established by using the VI method. The results can provide the criterion for the dynamic Finite Element Method analysis model for the transversely isotropic piezoelectric media.
The inverse problems in Hamilton and Gurtin Calculus of Variations for coupled dynamic piezoelectric media were studied. Several kinds of Hamilton type and Gurtin type variational principles and generalized variational principles for piezoelectric media were established by using the VI method. The results can provide the criterion for the dynamic Finite Element Method analysis model for the transversely isotropic piezoelectric media.
2000, 17(3): 107-112.
Abstract:
The dynamic stress concentration and the scattering of SH wave by intermixion and crack are studied by means of Green's function. In order to solve the problem, the first important work is to construct a suitable Green's function, which is the solution of displacement field for elastic half space with intermixion and crack by out plane harmonic line source loading at horizontal surface. The integral equation for determining the unknown forces about the problem can be transformed into algebraic equation and solved numerically. So the dynamic stress concentration factor (DSCF) of crack may be determined. The influence of intermixion on crack DSCF is discussed emphatically, numerical results and discussion are given, so a kind of useful reference for engineering design is provided.
The dynamic stress concentration and the scattering of SH wave by intermixion and crack are studied by means of Green's function. In order to solve the problem, the first important work is to construct a suitable Green's function, which is the solution of displacement field for elastic half space with intermixion and crack by out plane harmonic line source loading at horizontal surface. The integral equation for determining the unknown forces about the problem can be transformed into algebraic equation and solved numerically. So the dynamic stress concentration factor (DSCF) of crack may be determined. The influence of intermixion on crack DSCF is discussed emphatically, numerical results and discussion are given, so a kind of useful reference for engineering design is provided.
2000, 17(3): 113-115.
Abstract:
The conditions of the entry of solid particles the melt and influence factors on it were discussed. The thermodynamic condition of a solid particle entering the melt was established, which illustrated that the condition of a particle completely entering the melt spontaneously is zero contact angle and an energy barrier must be overcome even if the contact angle is less than π/2. The critical particle size, equation of work and kinetic condition needed for particles to completely enter the melt were also obtained.
The conditions of the entry of solid particles the melt and influence factors on it were discussed. The thermodynamic condition of a solid particle entering the melt was established, which illustrated that the condition of a particle completely entering the melt spontaneously is zero contact angle and an energy barrier must be overcome even if the contact angle is less than π/2. The critical particle size, equation of work and kinetic condition needed for particles to completely enter the melt were also obtained.
2000, 17(3): 116-119.
Abstract:
The technology of chemical vapor deposition has been used for the depositing layer treatment on the surface of alumina particle, and their properties were also studied, including the oxidation resistant under high temp., the adhesion strength of depositing film, and the influence on the interface adhesion strength between particles and metal matrix. The results show that the interface wettability has been increased and the interface construction has been improved because of the Ni depositing layer oxided; the adhesion strength of depositing film is high; the interface adhesion strength between alumina particles and metal matrix is remarkably increased, 6 times higher than that of undepositing's, and interface of the composite is crackless.
The technology of chemical vapor deposition has been used for the depositing layer treatment on the surface of alumina particle, and their properties were also studied, including the oxidation resistant under high temp., the adhesion strength of depositing film, and the influence on the interface adhesion strength between particles and metal matrix. The results show that the interface wettability has been increased and the interface construction has been improved because of the Ni depositing layer oxided; the adhesion strength of depositing film is high; the interface adhesion strength between alumina particles and metal matrix is remarkably increased, 6 times higher than that of undepositing's, and interface of the composite is crackless.
2000, 17(3): 120-123.
Abstract:
In order to study some stochastic character problems of the composite laminated shell, the author has considered the stochastic characters including the ply angle, ply thickness and material constant, and in Taylor series, the expansions in Taylor series for stress-strain matrix, stiffiness matrix and displacement vector have been employed. Taking from their quadric approximate formulae, the definite solution, primary sensitivity and secondary sensitivity of the response are obtained by means of the quadric perturbation scheme. Then according to the statistical theory and reliability theory, the expected value, variance, coefficient of variation and reliability are given, so as to realize the stochastic finite element analysis of laminate shells.
In order to study some stochastic character problems of the composite laminated shell, the author has considered the stochastic characters including the ply angle, ply thickness and material constant, and in Taylor series, the expansions in Taylor series for stress-strain matrix, stiffiness matrix and displacement vector have been employed. Taking from their quadric approximate formulae, the definite solution, primary sensitivity and secondary sensitivity of the response are obtained by means of the quadric perturbation scheme. Then according to the statistical theory and reliability theory, the expected value, variance, coefficient of variation and reliability are given, so as to realize the stochastic finite element analysis of laminate shells.
