1996 Vol. 13, No. 2
1996, 13(2): 1-8.
Abstract:
The electrical properties of ABS resin filled with carbon fibers,mixed by solvent, two-roll mill and brabender were studied in this paper.The relationship between the fiber content and the resistivity of the composites was obtained and its conductive mechanism was analyzed.By comparing the results it was shown that the aspect ratio of carbon fibers plays an important role in the resistivity of the composites.Other factors such as fiber distribution in the composites also have some effects on it.Shielding effects of these composites were obtained by theoretical calculation.
The electrical properties of ABS resin filled with carbon fibers,mixed by solvent, two-roll mill and brabender were studied in this paper.The relationship between the fiber content and the resistivity of the composites was obtained and its conductive mechanism was analyzed.By comparing the results it was shown that the aspect ratio of carbon fibers plays an important role in the resistivity of the composites.Other factors such as fiber distribution in the composites also have some effects on it.Shielding effects of these composites were obtained by theoretical calculation.
1996, 13(2): 9-16.
Abstract:
The appearance or intensity increasing of new absorption bands and the disappearance or intensity lowering of original absorption bands might be expected to run parallel to the synthesis and curing reactions of the modified epoxy resin.Fourier transform infra-red analysis is used to obtasn useful information on chemical changes.This paper is primarily concerned to explain the changes of the frequencies and intensities of IR absorption bands for assessing the reaction mechanisms.
The appearance or intensity increasing of new absorption bands and the disappearance or intensity lowering of original absorption bands might be expected to run parallel to the synthesis and curing reactions of the modified epoxy resin.Fourier transform infra-red analysis is used to obtasn useful information on chemical changes.This paper is primarily concerned to explain the changes of the frequencies and intensities of IR absorption bands for assessing the reaction mechanisms.
1996, 13(2): 17-21.
Abstract:
This paper elaborates the micro-structural shape and the stretch destructive mechanism of the rigid polyurethane foam plastics reinforced by the glass fibres,and probes preliminarily into the optimum length of the strengthening glass fibres.
This paper elaborates the micro-structural shape and the stretch destructive mechanism of the rigid polyurethane foam plastics reinforced by the glass fibres,and probes preliminarily into the optimum length of the strengthening glass fibres.
1996, 13(2): 22-27.
Abstract:
The effects of surface treatment and weight loading of glass-fiber on mechanical and thermal properties of fiber reinforced PVC composite (GFRPVC)were studied.The GF/PVC interface and its effect on the properties of GFRPVC were also investigated using SEM.It was found that GFRPVC composite (30wt% of G.F.) had flexure strength of 190MPa,a flexure modulus of 8.90GPa,a tensile strength of 110MPa,a tensile modulus of 8.8GPa,a notched Izod impact strength of 140J/m,a thermal expansion coefficient of 2.23 (×10-5)℃-1,and HDT of 84℃.Compared with 96MPa, 2.9GPa,54MPa,2.60GPa,37.6J/m,3.12(×10-5)℃-1,78℃ for RPVC, respectively.
The effects of surface treatment and weight loading of glass-fiber on mechanical and thermal properties of fiber reinforced PVC composite (GFRPVC)were studied.The GF/PVC interface and its effect on the properties of GFRPVC were also investigated using SEM.It was found that GFRPVC composite (30wt% of G.F.) had flexure strength of 190MPa,a flexure modulus of 8.90GPa,a tensile strength of 110MPa,a tensile modulus of 8.8GPa,a notched Izod impact strength of 140J/m,a thermal expansion coefficient of 2.23 (×10-5)℃-1,and HDT of 84℃.Compared with 96MPa, 2.9GPa,54MPa,2.60GPa,37.6J/m,3.12(×10-5)℃-1,78℃ for RPVC, respectively.
1996, 13(2): 28-32.
Abstract:
Sa mples of glass fiber (S2 )-epoxy (JF-43) composite prepreg were exposed to 45℃,25℃,5℃ respectively and about 50 percent relative humidity for different periods up to 196 days.They were analyzed in depth using infrared spectroscopy (IR) and other chemical analysis in order to determine the extent of the chemical changes occurring and to study the relationship between chemical changes and temperatures of aging.All showed evidence of significant changes.The temperature of aging had a significant effect on prepreg chemical changes such as epoxy group content,insoluble content and so on.The same samples,which were exposed to 25℃ and about 50 percent relative humidity for different periods up to 77 days, were determined using IR and mechanical property instrument.A linear relationship could be discerned between epoxy group content and laminate mechanical properties such as flexural properties and tensile properties at a confidence level of 99 percent by linear regression to the data.The cured degree calculated from the epoxy index of prepreg would be used as a parameter of quality control.The quality index concerning the importance of monitoring the aging by physicochemical methods was discussed.
Sa mples of glass fiber (S2 )-epoxy (JF-43) composite prepreg were exposed to 45℃,25℃,5℃ respectively and about 50 percent relative humidity for different periods up to 196 days.They were analyzed in depth using infrared spectroscopy (IR) and other chemical analysis in order to determine the extent of the chemical changes occurring and to study the relationship between chemical changes and temperatures of aging.All showed evidence of significant changes.The temperature of aging had a significant effect on prepreg chemical changes such as epoxy group content,insoluble content and so on.The same samples,which were exposed to 25℃ and about 50 percent relative humidity for different periods up to 77 days, were determined using IR and mechanical property instrument.A linear relationship could be discerned between epoxy group content and laminate mechanical properties such as flexural properties and tensile properties at a confidence level of 99 percent by linear regression to the data.The cured degree calculated from the epoxy index of prepreg would be used as a parameter of quality control.The quality index concerning the importance of monitoring the aging by physicochemical methods was discussed.
1996, 13(2): 33-37.
Abstract:
The mechanical performance of SiCp/2024 composite,after pre-charged with hydrogen and during the dynamical cathodic hydrogen-charging,is studied by the slow strain rate tension technique.The fractographs are examined.The hydrogen content of the composite,alter charged with hydrogen under several usually employed charging conditions,is determined.It is revealed that strong cathodic polarization deteriorates the mechanical performance for the reason of alkaline corrosion caused by the polarization.This deterioration has nothing to do with hydrogen embrittlement.The results lead to a new conclusion,that under the present test conditions,the composite suffers neither hydrogen embrittlement nor irreversible hydrogen damage.This is related to the fail in hydrogen-chaging.
The mechanical performance of SiCp/2024 composite,after pre-charged with hydrogen and during the dynamical cathodic hydrogen-charging,is studied by the slow strain rate tension technique.The fractographs are examined.The hydrogen content of the composite,alter charged with hydrogen under several usually employed charging conditions,is determined.It is revealed that strong cathodic polarization deteriorates the mechanical performance for the reason of alkaline corrosion caused by the polarization.This deterioration has nothing to do with hydrogen embrittlement.The results lead to a new conclusion,that under the present test conditions,the composite suffers neither hydrogen embrittlement nor irreversible hydrogen damage.This is related to the fail in hydrogen-chaging.
1996, 13(2): 38-41.
Abstract:
Interfacial reactions have been investigated in Titanium-based matrix composites.It has been found that there is a non-stoichiometric interface formed around each TiC particle.The relation between heat treatment and interfacial layer width is also discussed.
Interfacial reactions have been investigated in Titanium-based matrix composites.It has been found that there is a non-stoichiometric interface formed around each TiC particle.The relation between heat treatment and interfacial layer width is also discussed.
1996, 13(2): 42-47.
Abstract:
In this paper,inner-oxidizing of Cu-0.31% Al alloy wateratomized powder and Cu-Al2O3 composite made from the powder was studied.The material was manufactured using powder metallurgy processing and its main properties are as follows:σb=608MPa,HV=1529MPa,resistivity=2.2μΩ·cm, density=8.8g/cm3.
In this paper,inner-oxidizing of Cu-0.31% Al alloy wateratomized powder and Cu-Al2O3 composite made from the powder was studied.The material was manufactured using powder metallurgy processing and its main properties are as follows:σb=608MPa,HV=1529MPa,resistivity=2.2μΩ·cm, density=8.8g/cm3.
1996, 13(2): 48-52.
Abstract:
In order to improve oxidation-resistance of diamond grit,interface reaction process, composition and structure between Ti,Mo and W coating and diamonds are studied by XRD,SEM,DAT and TGA.Influence of Ti,Mo and W coating on oxidation of diamonds is investigated.Test results show that reactions between Ti,Mo and W coating and diamonds occur separately above 600,650 and 650℃.Corresponding epitaxial TiC,Mo2C+MoC and W2C+WC films grow on diamonds surface reaction diffusion process.These high oxidation resistant carbides films prevent diamonds from oxidation.The diamonds with Ti, Mo and W coating oxidate in air separately above 958,871 and 880℃.After these diamonds with coatings are treated in vacuum with carbon,oxidation temperature of diamonds with Ti,Mo and W coatings are separately 1024,977 and 986℃.
In order to improve oxidation-resistance of diamond grit,interface reaction process, composition and structure between Ti,Mo and W coating and diamonds are studied by XRD,SEM,DAT and TGA.Influence of Ti,Mo and W coating on oxidation of diamonds is investigated.Test results show that reactions between Ti,Mo and W coating and diamonds occur separately above 600,650 and 650℃.Corresponding epitaxial TiC,Mo2C+MoC and W2C+WC films grow on diamonds surface reaction diffusion process.These high oxidation resistant carbides films prevent diamonds from oxidation.The diamonds with Ti, Mo and W coating oxidate in air separately above 958,871 and 880℃.After these diamonds with coatings are treated in vacuum with carbon,oxidation temperature of diamonds with Ti,Mo and W coatings are separately 1024,977 and 986℃.
1996, 13(2): 53-59.
Abstract:
We review some recent developments in the electrochemical synthetic methods of Graphite Intercalation Compounds,and its probability; we also carry out discussions on the various properties of this materials,while the drawbacks of this method in the current industrial production are presented and the possible ways of solving are proposed.
We review some recent developments in the electrochemical synthetic methods of Graphite Intercalation Compounds,and its probability; we also carry out discussions on the various properties of this materials,while the drawbacks of this method in the current industrial production are presented and the possible ways of solving are proposed.
1996, 13(2): 60-64.
Abstract:
Alpha-silicon nitride whiskers were prepared by the"in-situ" growth of ultrafine amorphous silicon nitride powders.The experiment was carried out at 1400~1450℃ for 1~4 hours.When the experiment was conducted in the atmosphere of nitrogen with high purity,the nitrogen content,oxygen content and chlorine content in alpha-silicon nitride whiskers obtained were 32%-34%,8%~6% and~0.1%,respectively.A lot of defects were detected in the whisker.However,when the experiment was completed in an atmosphere of ammonia, the content of nitrogen,oxygen and chlorine in the whiskers changed to 39%,1% and 0.01%,respectively,where nearly "defect-free" in the whisker was detected.
Alpha-silicon nitride whiskers were prepared by the"in-situ" growth of ultrafine amorphous silicon nitride powders.The experiment was carried out at 1400~1450℃ for 1~4 hours.When the experiment was conducted in the atmosphere of nitrogen with high purity,the nitrogen content,oxygen content and chlorine content in alpha-silicon nitride whiskers obtained were 32%-34%,8%~6% and~0.1%,respectively.A lot of defects were detected in the whisker.However,when the experiment was completed in an atmosphere of ammonia, the content of nitrogen,oxygen and chlorine in the whiskers changed to 39%,1% and 0.01%,respectively,where nearly "defect-free" in the whisker was detected.
1996, 13(2): 65-70.
Abstract:
Using Kelvin's solutions and the concepts of finite-part integral,a set of hypersingular integral equations to solve the inclusion problems in two dimension elasticity is derived,and its numerical method is then proposed by combining the finite-part integral method with the boundary element method.Finally,several examples are carried out,and the numerical results of the stress intensity factors are obtained.
Using Kelvin's solutions and the concepts of finite-part integral,a set of hypersingular integral equations to solve the inclusion problems in two dimension elasticity is derived,and its numerical method is then proposed by combining the finite-part integral method with the boundary element method.Finally,several examples are carried out,and the numerical results of the stress intensity factors are obtained.
1996, 13(2): 71-75.
Abstract:
BEM is a kind of numerical method developing rapidly.Some problems about the application of plane orthotropic boundary elements to moregeneral composite laminates are studied in this paper.They include the equivalent single plate of laminate,the off-axis fundamental solution,the analytic calculation of influence coefficients of straight high-order boundary elements,and the expression of stresses at any interior point.The examples show that the results of BEM are consistent with the analytic solutions and the results of FEM.
BEM is a kind of numerical method developing rapidly.Some problems about the application of plane orthotropic boundary elements to moregeneral composite laminates are studied in this paper.They include the equivalent single plate of laminate,the off-axis fundamental solution,the analytic calculation of influence coefficients of straight high-order boundary elements,and the expression of stresses at any interior point.The examples show that the results of BEM are consistent with the analytic solutions and the results of FEM.
1996, 13(2): 76-83.
Abstract:
In the research of the limit strength of laminates under combined loading,a new tensorial strength criterion and a combined strength theory of laminates based on the basic strength and optimal experimental strength of laminates are proposed.With a newly developed Degradated Ply Stiffness Theory and "Uniform Degradated Stiffness Coefficient" from experiments,the last ply failure (LPF) is predicted.Moreover,the Degradated Tensorial Strength Criterion of laminates is established.The criterion has the advantages of using lamina property,with the help of uniform degradated stiffness coefficients,to predict the ultimate loading capacity of any laminates under multiaxial loadings.It shows that the correlation between the experimental results of a series of typical laminates,in both plates and tubes,under multiaxial loading,and the theoretical predictions is reasonable.The presented criteria and the engineering methods of strength design are believed to be valuable and to be of practical significance in structural design.
In the research of the limit strength of laminates under combined loading,a new tensorial strength criterion and a combined strength theory of laminates based on the basic strength and optimal experimental strength of laminates are proposed.With a newly developed Degradated Ply Stiffness Theory and "Uniform Degradated Stiffness Coefficient" from experiments,the last ply failure (LPF) is predicted.Moreover,the Degradated Tensorial Strength Criterion of laminates is established.The criterion has the advantages of using lamina property,with the help of uniform degradated stiffness coefficients,to predict the ultimate loading capacity of any laminates under multiaxial loadings.It shows that the correlation between the experimental results of a series of typical laminates,in both plates and tubes,under multiaxial loading,and the theoretical predictions is reasonable.The presented criteria and the engineering methods of strength design are believed to be valuable and to be of practical significance in structural design.
1996, 13(2): 84-88.
Abstract:
The cause of fiber bridging and its effect on the mode I interlaminar fracture toughness GIC are discussed and the method of isolated plies for overcoming the effect of fiber bridging is put forward in this paper.By changing the ply design of specimens,the possibility of fiber nesting is reduced to the lowest level.The calculation by FEM shows that the use of isolated plies does not change the distribution and concentration of stress in the tip of the interlaminated crack.The calculation of flexural rigidity of the specimens shows that if the ply angle of the isolated plies is ±10°~±20°,the flex-torsion coupling of specimens will be reduced to a minimum.The feasibility of this method is proved by experimental data.
The cause of fiber bridging and its effect on the mode I interlaminar fracture toughness GIC are discussed and the method of isolated plies for overcoming the effect of fiber bridging is put forward in this paper.By changing the ply design of specimens,the possibility of fiber nesting is reduced to the lowest level.The calculation by FEM shows that the use of isolated plies does not change the distribution and concentration of stress in the tip of the interlaminated crack.The calculation of flexural rigidity of the specimens shows that if the ply angle of the isolated plies is ±10°~±20°,the flex-torsion coupling of specimens will be reduced to a minimum.The feasibility of this method is proved by experimental data.
1996, 13(2): 89-93.
Abstract:
The steady thermo-elasto-plastic behavior of ceramic-metal functionally gradient materials(FGMs) was investigated by considering an Al2O3/Ni gradient material.The inelastic properties of the gradient interlayers were first evaluated using mean-field micromechanics and elasto-plastic self-consistent micromechanics method,and then an elastoplastic finite element model was used to calculate the thermal stress in the material The results show that the thermo-elasto-plastic behavior exerts significant influences on the thermal stress relaxation characteristics of the FGMs.
The steady thermo-elasto-plastic behavior of ceramic-metal functionally gradient materials(FGMs) was investigated by considering an Al2O3/Ni gradient material.The inelastic properties of the gradient interlayers were first evaluated using mean-field micromechanics and elasto-plastic self-consistent micromechanics method,and then an elastoplastic finite element model was used to calculate the thermal stress in the material The results show that the thermo-elasto-plastic behavior exerts significant influences on the thermal stress relaxation characteristics of the FGMs.
1996, 13(2): 94-97.
Abstract:
The Bauschinger effect of whisker-reinforced-metal matrix composite materials is researched with the modified equivalent inclusion theory by the authors.The influences of the loading sequence and whisker content on the Bauschinger effect are discussed.The theoretical model in this paper can simulate the Bauschinger effect numerically.
The Bauschinger effect of whisker-reinforced-metal matrix composite materials is researched with the modified equivalent inclusion theory by the authors.The influences of the loading sequence and whisker content on the Bauschinger effect are discussed.The theoretical model in this paper can simulate the Bauschinger effect numerically.
1996, 13(2): 98-104.
Abstract:
This paper proposes a BEM computation model to calculate the transverse effective moduli and Poisson's ratios of unidirectional fiber reinforced composites.The computation results of ν12,ν32,ν13 and ν23, are in good agreement with the experimental results.The E2,E3 for carbon-fiber reinforced composites coincide with the experimental results excellently.However,for glass-fiber reinforced epoxy composite,the computation results of E2,E3 are about 10-25 percent lower.For the latter,it is guessed that there may exist remarkable interlayer effect,which was not considered in the computation process.
This paper proposes a BEM computation model to calculate the transverse effective moduli and Poisson's ratios of unidirectional fiber reinforced composites.The computation results of ν12,ν32,ν13 and ν23, are in good agreement with the experimental results.The E2,E3 for carbon-fiber reinforced composites coincide with the experimental results excellently.However,for glass-fiber reinforced epoxy composite,the computation results of E2,E3 are about 10-25 percent lower.For the latter,it is guessed that there may exist remarkable interlayer effect,which was not considered in the computation process.
1996, 13(2): 105-109.
Abstract:
A new displacement model of free vibrations,including effects of normal stress, normal strain and transverse shear deformation,is developed in this paper.The new model solutions are compared with the YNS theory solutions using Rayleigh-Ritz method for free vibrations,and the effects of transverse normal stress and normal strain on the fundamental frequencies of free vibrations of composite laminated plates with simply-supported edges are obtained.
A new displacement model of free vibrations,including effects of normal stress, normal strain and transverse shear deformation,is developed in this paper.The new model solutions are compared with the YNS theory solutions using Rayleigh-Ritz method for free vibrations,and the effects of transverse normal stress and normal strain on the fundamental frequencies of free vibrations of composite laminated plates with simply-supported edges are obtained.
1996, 13(2): 110-116.
Abstract:
In this paper,design methods for the gas pipeline structure of composites are introduced 6y combining the reliability theory and grey system theory with optimization ,and taking account of influences of white,grey and random factors on the oil or gas pipeline design.A relation between soil temperature and the central depth of a buried pipe is deduced from a grey mathematical model GM(11).A method for selection of the best from transfergas formulas is also introduced in terms of the grey relative ratio.
In this paper,design methods for the gas pipeline structure of composites are introduced 6y combining the reliability theory and grey system theory with optimization ,and taking account of influences of white,grey and random factors on the oil or gas pipeline design.A relation between soil temperature and the central depth of a buried pipe is deduced from a grey mathematical model GM(11).A method for selection of the best from transfergas formulas is also introduced in terms of the grey relative ratio.
1996, 13(2): 117-123.
Abstract:
Dynamic characteristic of uniaxially-reinforced composite cantilever sheet was analyzed by the finite difference method in terms of the bend vibration theory of sheet.Static characteristic of the square sheet was determined,as concentrated forces were applied to its four corners.The dynamic (static) measurement of elastic constants in uniaxially-reinforced composite has been presented.As compared with the usual measurement,it has the advantages of simplicity,rapidity,high accuracy and good repetition.
Dynamic characteristic of uniaxially-reinforced composite cantilever sheet was analyzed by the finite difference method in terms of the bend vibration theory of sheet.Static characteristic of the square sheet was determined,as concentrated forces were applied to its four corners.The dynamic (static) measurement of elastic constants in uniaxially-reinforced composite has been presented.As compared with the usual measurement,it has the advantages of simplicity,rapidity,high accuracy and good repetition.
1996, 13(2): 124-130.
Abstract:
Typical damage states in unnotched [02/±452/902]s composite laminate were studied by experimental observation,and the stiffness reduction rate caused by damages was measured in the laminate.Two 3-1} mechanical models in which transverse crack and delamination with transverse crack developing are put forward,and the stiffness redumion of the laminate is calculated by the model, and is in agreement with the experiment.The results show that the transverse crack and delamination are the major damage modes of the laminate,and the damage development of delamination is a main and stable process,and markedly leads to the decrease in stiffness of the laminate.
Typical damage states in unnotched [02/±452/902]s composite laminate were studied by experimental observation,and the stiffness reduction rate caused by damages was measured in the laminate.Two 3-1} mechanical models in which transverse crack and delamination with transverse crack developing are put forward,and the stiffness redumion of the laminate is calculated by the model, and is in agreement with the experiment.The results show that the transverse crack and delamination are the major damage modes of the laminate,and the damage development of delamination is a main and stable process,and markedly leads to the decrease in stiffness of the laminate.
