1996 Vol. 13, No. 1
1996, 13(1): 1-8.
Abstract:
By using the split Hopkinson pressure bar technique,impact tests were carried out on fully clamped three-point bending laminated beam specimens made from continuous glass fiber and carbon fiber reinforced polyphenylene sulfide (PPS) of three types of lay-up constructions.The paper focuses research interests on scanning electronic microscopic (SEM)investigation of the impact failure morphology with the aim of providing phenomenological background for working out a new model which would describe more rationally the dynamic response behaviour during transverse impact,as well understanding comprehensively the dominant failure patterns at high strain rate.The results show that the laminate fracture morphology resulting from the given experimental conditions possesses distinct feature for every laminate and is a function of both material characteristics and lay-up constructions.Fiber/matrix interfacial bonding exerts important influence on the microcracking mechanism.
By using the split Hopkinson pressure bar technique,impact tests were carried out on fully clamped three-point bending laminated beam specimens made from continuous glass fiber and carbon fiber reinforced polyphenylene sulfide (PPS) of three types of lay-up constructions.The paper focuses research interests on scanning electronic microscopic (SEM)investigation of the impact failure morphology with the aim of providing phenomenological background for working out a new model which would describe more rationally the dynamic response behaviour during transverse impact,as well understanding comprehensively the dominant failure patterns at high strain rate.The results show that the laminate fracture morphology resulting from the given experimental conditions possesses distinct feature for every laminate and is a function of both material characteristics and lay-up constructions.Fiber/matrix interfacial bonding exerts important influence on the microcracking mechanism.
1996, 13(1): 9-13.
Abstract:
This paper mainly investigates the influences of epoxy resins oligomer molecular weight on the electrical,mechanical,and thermal properties of the cured compound of bisphenol-A type epoxy resins system catalysed by tertiary amine (BDMA) accelerator and cured by anhydride (MeTHPA) curing agent.The results indicated that the strong effect of epoxy resins oligomer molecular weight on the cured compound properties,and the clear regularity of this effect.
This paper mainly investigates the influences of epoxy resins oligomer molecular weight on the electrical,mechanical,and thermal properties of the cured compound of bisphenol-A type epoxy resins system catalysed by tertiary amine (BDMA) accelerator and cured by anhydride (MeTHPA) curing agent.The results indicated that the strong effect of epoxy resins oligomer molecular weight on the cured compound properties,and the clear regularity of this effect.
1996, 13(1): 14-18.
Abstract:
Based on the free volume theory and the experimental results,the contributions of the components to Tg of the network were analysed.To determine the effect of curing agent,the fracture toughness of epoxy network,cured by DDS was investigated.The experimental results showed that KIc of epoxy network cured by DDS was much tougher than the corresponding network cured by BF3MEA.According to the above analysis,the network of matrix was deliberately designed,in order to improve the interlaminar toughness of composite without the degradation of its high temperature performance,and the feasibility of this method was confirmed by the experimental data.
Based on the free volume theory and the experimental results,the contributions of the components to Tg of the network were analysed.To determine the effect of curing agent,the fracture toughness of epoxy network,cured by DDS was investigated.The experimental results showed that KIc of epoxy network cured by DDS was much tougher than the corresponding network cured by BF3MEA.According to the above analysis,the network of matrix was deliberately designed,in order to improve the interlaminar toughness of composite without the degradation of its high temperature performance,and the feasibility of this method was confirmed by the experimental data.
1996, 13(1): 19-24.
Abstract:
The dielectric and pyroelectric properties of TGS.PVDF composite material films are analyzed in theory.The relationship between these two properties and thicknesses of samples,as well as volume ratios of components and sizes of TGS crystal grains,is given experimentally.The pyroelectric effect is distinguished from the depolarization effect so that the correct pyroelectric coefficients of TGS·PVDF composite films are obtained.
The dielectric and pyroelectric properties of TGS.PVDF composite material films are analyzed in theory.The relationship between these two properties and thicknesses of samples,as well as volume ratios of components and sizes of TGS crystal grains,is given experimentally.The pyroelectric effect is distinguished from the depolarization effect so that the correct pyroelectric coefficients of TGS·PVDF composite films are obtained.
1996, 13(1): 25-29.
Abstract:
Samples of glass fiber S2-epoxy (JF-43)prepreg were exposed to 45℃ for different periods up to 56 days.They were analyzed in depth using various techniques to determine the extent of the chemical changes occuring.The physicochemical techniques used were infrared spectroscopy(IR),thermal analysis (differential scanning calorimetry and chermogravimetric analysis),steric exclusion chromatography.All showed evidence of significant changes,the most sensitive one being the infrared spectroscopy.IR test showed that the number of unreacted epoxy groups decreases steadily at a rate of 6.3% per day during the initial 14 days,which is similar to volatile content of resin (4.4%) and insoluble matter content of resin(4.6).The heat of polymerization of resin,measured by thermal analysis,decreased by 14.3% per day from its initial value during the initial 14 days.
Samples of glass fiber S2-epoxy (JF-43)prepreg were exposed to 45℃ for different periods up to 56 days.They were analyzed in depth using various techniques to determine the extent of the chemical changes occuring.The physicochemical techniques used were infrared spectroscopy(IR),thermal analysis (differential scanning calorimetry and chermogravimetric analysis),steric exclusion chromatography.All showed evidence of significant changes,the most sensitive one being the infrared spectroscopy.IR test showed that the number of unreacted epoxy groups decreases steadily at a rate of 6.3% per day during the initial 14 days,which is similar to volatile content of resin (4.4%) and insoluble matter content of resin(4.6).The heat of polymerization of resin,measured by thermal analysis,decreased by 14.3% per day from its initial value during the initial 14 days.
1996, 13(1): 30-34.
Abstract:
SHS+HP method was used for fabricating IMCs reinforced with TiB2 ceramic particles.XRD,SEM and Image analysis were used for studying the microstructure of samples.The results show that SHS process is specially suitable for IMCs reinforced by particles.The average grain size of TiB2 in TiB2/NiAl composites is about 0.8μcm,The porosity of the composites is less than 1.0%.
SHS+HP method was used for fabricating IMCs reinforced with TiB2 ceramic particles.XRD,SEM and Image analysis were used for studying the microstructure of samples.The results show that SHS process is specially suitable for IMCs reinforced by particles.The average grain size of TiB2 in TiB2/NiAl composites is about 0.8μcm,The porosity of the composites is less than 1.0%.
1996, 13(1): 35-39.
Abstract:
Abstract The 27% vol-SiCw/6061A1 composite was fabricated by squeeze casting method.The aging dynamic process of the 27% ovol-SiCw/6061A1 composite was studied at 170℃,and double aging peaks were found in the aging dynamic curves of the composite.The results of DSC analysis showed that the precipitation temperature of β' and β phase in the composite decreased by 56℃ and 76℃,respectively as compared with that in the 6061A1 alloy,from which the effects of the SiC whiskers on the precipitation processes of the composite were discussed.It is concluded that the double aging peaks resulted from the transformation of the precipitation from G.P.zones to β' phase,and this conclusion was further proved by TEM observation of the morphology of the precipitations in the 27% ovol-SiCw/6061A1 composite.
Abstract The 27% vol-SiCw/6061A1 composite was fabricated by squeeze casting method.The aging dynamic process of the 27% ovol-SiCw/6061A1 composite was studied at 170℃,and double aging peaks were found in the aging dynamic curves of the composite.The results of DSC analysis showed that the precipitation temperature of β' and β phase in the composite decreased by 56℃ and 76℃,respectively as compared with that in the 6061A1 alloy,from which the effects of the SiC whiskers on the precipitation processes of the composite were discussed.It is concluded that the double aging peaks resulted from the transformation of the precipitation from G.P.zones to β' phase,and this conclusion was further proved by TEM observation of the morphology of the precipitations in the 27% ovol-SiCw/6061A1 composite.
1996, 13(1): 40-45.
Abstract:
Compocasting is used widely to produce SiCP/Al composites.However it always leads to some problems in the final composites,such as bad wettability between SiC and Al alloy,high porosity,oxide inclusion and clusters of particles.In this paper,a new method to produce SiCP/Al composites has been tried,which is termed inter-composite dilution method.The results show that lO%vol and 15vo1%SiCp/A;composites fabricated by this method have higher tensile strength than those of SiCP/Al prepared by compocasting method.Meanwhile the porosity of SiCP/Al we made declines obviously.It was found by using X-rays diffraction analysis and TEM that there was no reaction between SiC particle and A1 matrix.The results indicate that the method is successful and practical.The processing parameters are reasonable.
Compocasting is used widely to produce SiCP/Al composites.However it always leads to some problems in the final composites,such as bad wettability between SiC and Al alloy,high porosity,oxide inclusion and clusters of particles.In this paper,a new method to produce SiCP/Al composites has been tried,which is termed inter-composite dilution method.The results show that lO%vol and 15vo1%SiCp/A;composites fabricated by this method have higher tensile strength than those of SiCP/Al prepared by compocasting method.Meanwhile the porosity of SiCP/Al we made declines obviously.It was found by using X-rays diffraction analysis and TEM that there was no reaction between SiC particle and A1 matrix.The results indicate that the method is successful and practical.The processing parameters are reasonable.
1996, 13(1): 48-49.
Abstract:
The wetting angle between aluminum and γ-alumina has been calculated in this paper by using nucleation theory.It is found that the wetting angle between aluminum and γ-alumina is between 30° and 50°,i.e.30°
The wetting angle between aluminum and γ-alumina has been calculated in this paper by using nucleation theory.It is found that the wetting angle between aluminum and γ-alumina is between 30° and 50°,i.e.30°
1996, 13(1): 50-54.
Abstract:
The interface reaction process,interface composition and structure between Cr clading and cBN at 600-1000℃ were studied by DTA,XRD,SEM and EPMA.The composition,structure and properties of vitrified bond-Cr clad cBN composite material during firing are discussed.Test results show that interface reaction between Cr clading and cBN occurs above 600℃ through reaction diffusion,and the epitaxial CrN and CrB2 form on the cBN surface above 600℃ and 800℃ separately.The Cr clading and epitaxial compound film cBN on surface of cBN improve the adhesion between the cBN grit and the bond,preventing grit from corrosion during firing.
The interface reaction process,interface composition and structure between Cr clading and cBN at 600-1000℃ were studied by DTA,XRD,SEM and EPMA.The composition,structure and properties of vitrified bond-Cr clad cBN composite material during firing are discussed.Test results show that interface reaction between Cr clading and cBN occurs above 600℃ through reaction diffusion,and the epitaxial CrN and CrB2 form on the cBN surface above 600℃ and 800℃ separately.The Cr clading and epitaxial compound film cBN on surface of cBN improve the adhesion between the cBN grit and the bond,preventing grit from corrosion during firing.
1996, 13(1): 55-59.
Abstract:
Alpha-silicon nitride whiskers and crystalline pillars were produced by amorphous silicon nitride ultrafine powders.The study includes the effect of growth temperature on the defect of whiskers.The results show that the integrity of obtained crystal has related to the growth temperature when whiskers are growing.The relatively integral crystal can only be obtained in a certain range of temperature(1430℃±30 ℃).The growth temperature too high or too low may cause imperfection of the growing crystal and the whiskers with many defects.If the temperature continues to go up,crystalline grain will appear in the whiskers which will become crystalline pillar afterwards.
Alpha-silicon nitride whiskers and crystalline pillars were produced by amorphous silicon nitride ultrafine powders.The study includes the effect of growth temperature on the defect of whiskers.The results show that the integrity of obtained crystal has related to the growth temperature when whiskers are growing.The relatively integral crystal can only be obtained in a certain range of temperature(1430℃±30 ℃).The growth temperature too high or too low may cause imperfection of the growing crystal and the whiskers with many defects.If the temperature continues to go up,crystalline grain will appear in the whiskers which will become crystalline pillar afterwards.
1996, 13(1): 60-65.
Abstract:
According to the mean theory,a shape modified model is set up for the effective medium theory,and the shape-modified Maxwell-Garnett theory and Bruggeman theory are given.Also discussed is the effect of small particle shape on the effective dielectric function.
According to the mean theory,a shape modified model is set up for the effective medium theory,and the shape-modified Maxwell-Garnett theory and Bruggeman theory are given.Also discussed is the effect of small particle shape on the effective dielectric function.
1996, 13(1): 66-71.
Abstract:
The carbon fiber reinforced aluminium composite material was fabricated by means of vacuum pressure infiltration to study the effects on the infiltration and on the properties of the SiC particles hybridized in carbon fibers.The tensile and bending properties were determined and the microstructure and fractography were investigated by the SEM.It was demonstrated that the SiCP hybridized in fibers can separate the clustered fibers and prevent the contact of fibers to provide a better fiber distribution,which is beneficial to infiltration and composite material properties.Optimum properties have been shown in the material made up of sol-gel SiC coating fibers along with SiCP hybridizing.
The carbon fiber reinforced aluminium composite material was fabricated by means of vacuum pressure infiltration to study the effects on the infiltration and on the properties of the SiC particles hybridized in carbon fibers.The tensile and bending properties were determined and the microstructure and fractography were investigated by the SEM.It was demonstrated that the SiCP hybridized in fibers can separate the clustered fibers and prevent the contact of fibers to provide a better fiber distribution,which is beneficial to infiltration and composite material properties.Optimum properties have been shown in the material made up of sol-gel SiC coating fibers along with SiCP hybridizing.
1996, 13(1): 72-77.
Abstract:
In this paper,mechanical model of FRP was analyzed.Acoustic emission (AE) technique and tensile test of latitudinal fiber for toughness matrix were studied.The results show that the major cause of permeability-seepage on corrosion resistant FRP is its lower breaking elongation rate.When loaded and stressed,the product can result in low matrix stress crack and gradually stretch.The crack was aggravated by the stress concentration of matrix region and was verified by the AE technique.The authors consider it necessary that the matrix elongation rate be among 3-6% in the laminated structure of FRP.
In this paper,mechanical model of FRP was analyzed.Acoustic emission (AE) technique and tensile test of latitudinal fiber for toughness matrix were studied.The results show that the major cause of permeability-seepage on corrosion resistant FRP is its lower breaking elongation rate.When loaded and stressed,the product can result in low matrix stress crack and gradually stretch.The crack was aggravated by the stress concentration of matrix region and was verified by the AE technique.The authors consider it necessary that the matrix elongation rate be among 3-6% in the laminated structure of FRP.
1996, 13(1): 78-85.
Abstract:
The homogenization method is used to predict the thermal conductivity of unidirectional fiber reinforced composites.A prediction expression of the thermal conductivity in the direction along the fiber is given by means of this method.Based on the method,using finite element technique,the data results of the thermal conductivity in the direction normal to the fiber are obtained.On the basis of the results obtained,the dependence of the thermal conductivity of composites on the fiber volume fraction is given in curves.The effects of the volume fraction,cross section shape of fibers and their distributing array in the matrix,and the relative conductivity of the fiber and matrix,on the thermal conductivity of composites are analyzed.Observing the random distribution of the fiber in the matrix,the effect of the relative position between fibers on the thermal conductivity of composites is also studied,and it is pointed out that the change of this position may induce anisotropy of composites.It is found that the influence of the matrix property on the conductivity of composites is more important than that of the fiber's property.Comparison with the results of other theoreticl methods and experiments implies that the method proposed is effective.
The homogenization method is used to predict the thermal conductivity of unidirectional fiber reinforced composites.A prediction expression of the thermal conductivity in the direction along the fiber is given by means of this method.Based on the method,using finite element technique,the data results of the thermal conductivity in the direction normal to the fiber are obtained.On the basis of the results obtained,the dependence of the thermal conductivity of composites on the fiber volume fraction is given in curves.The effects of the volume fraction,cross section shape of fibers and their distributing array in the matrix,and the relative conductivity of the fiber and matrix,on the thermal conductivity of composites are analyzed.Observing the random distribution of the fiber in the matrix,the effect of the relative position between fibers on the thermal conductivity of composites is also studied,and it is pointed out that the change of this position may induce anisotropy of composites.It is found that the influence of the matrix property on the conductivity of composites is more important than that of the fiber's property.Comparison with the results of other theoreticl methods and experiments implies that the method proposed is effective.
1996, 13(1): 86-90.
Abstract:
The mechanical behavior in damage zones around crack-tips for carbon fiber aluminium laminates (CALL) hybrid composites was studied by moue interferometry.The strain distributions in the zones around the double-edge crack-tips for longitudinal and transversal specimens were obtained under the tensile loading.The morphology of damaged sections was observed by use of scanning electron microscope and the damage characteristics were analysed for these specimens.
The mechanical behavior in damage zones around crack-tips for carbon fiber aluminium laminates (CALL) hybrid composites was studied by moue interferometry.The strain distributions in the zones around the double-edge crack-tips for longitudinal and transversal specimens were obtained under the tensile loading.The morphology of damaged sections was observed by use of scanning electron microscope and the damage characteristics were analysed for these specimens.
1996, 13(1): 91-96.
Abstract:
Interlayer(or interphase) fracture constitutes an important issue of the micromechanics of composite materials.The present paper studies the fracture behavior of a crack penetrating vertically to an interlayer where the stiffness varies monotonically from one material phase to another material phase.Analytical estimate and full-scaled FEM calculation both indicate that the crack-tip stress intensity factor increases when a crack penetrates the interlayer from the soft material side,and decreases when a crack penetratesthe interlayer from the stiff material side of the bimaterial.
Interlayer(or interphase) fracture constitutes an important issue of the micromechanics of composite materials.The present paper studies the fracture behavior of a crack penetrating vertically to an interlayer where the stiffness varies monotonically from one material phase to another material phase.Analytical estimate and full-scaled FEM calculation both indicate that the crack-tip stress intensity factor increases when a crack penetrates the interlayer from the soft material side,and decreases when a crack penetratesthe interlayer from the stiff material side of the bimaterial.
1996, 13(1): 101-104.
Abstract:
The fatigue life and working noise of composite rolling bearings newly developed were tested and analysed in this paper.The results show that the composite rolling bearings have good property to reduce working noise and,when compared with plastic rolling bearings,their load capacity is largely increased.
The fatigue life and working noise of composite rolling bearings newly developed were tested and analysed in this paper.The results show that the composite rolling bearings have good property to reduce working noise and,when compared with plastic rolling bearings,their load capacity is largely increased.
1996, 13(1): 105-110.
Abstract:
This paper deals with residual stresses and deformations of composite laminates during cooling down stage of curing process.The numerical results slyow that the nonlinearity of thermal physical and mechanical properties is important to predict residual stresses and deformations of composite laminates.The coupling effect between stress and change rate of mechanical properties with temperature must be taken into account in the residual stress and deformation analysis.
This paper deals with residual stresses and deformations of composite laminates during cooling down stage of curing process.The numerical results slyow that the nonlinearity of thermal physical and mechanical properties is important to predict residual stresses and deformations of composite laminates.The coupling effect between stress and change rate of mechanical properties with temperature must be taken into account in the residual stress and deformation analysis.
1996, 13(1): 111-117.
Abstract:
Based on the basic equations of elasticity,the theory of Hamiltonian systems in elasticity is achieved.Combined with the finite element method,the semi-analytical numerical method presented can be used to analyze thick composite laminates with arbitrary boundary conditions and geometrical shapes.
Based on the basic equations of elasticity,the theory of Hamiltonian systems in elasticity is achieved.Combined with the finite element method,the semi-analytical numerical method presented can be used to analyze thick composite laminates with arbitrary boundary conditions and geometrical shapes.
1996, 13(1): 118-122.
Abstract:
Free vibration of composite laminated thick plates with clamped edges is investigated by employing a set of characteristic orthogonal polynomials in Rayleigh-Ritz method.The solutions in this paper are compared with the results existing in the literature,and good agreement is obtained.The effects of various parameters and boundary conditions of laminated plates on the fundamental frequencies are studied.
Free vibration of composite laminated thick plates with clamped edges is investigated by employing a set of characteristic orthogonal polynomials in Rayleigh-Ritz method.The solutions in this paper are compared with the results existing in the literature,and good agreement is obtained.The effects of various parameters and boundary conditions of laminated plates on the fundamental frequencies are studied.
1996, 13(1): 123-126.
Abstract:
Tensile pre-strain was applied to the Aluminium-Aramid Laminates to modify the interlaminar xesidual stresses.The relationship between residual stresses in aluminium and the pre-strain was analysed.The residual stresses in aluminium of several kinds of pre-strain laminates were measured by means of outer layer corrosion.The influences of prestrain on tensile and fatigue properties of the laminates were also studied.
Tensile pre-strain was applied to the Aluminium-Aramid Laminates to modify the interlaminar xesidual stresses.The relationship between residual stresses in aluminium and the pre-strain was analysed.The residual stresses in aluminium of several kinds of pre-strain laminates were measured by means of outer layer corrosion.The influences of prestrain on tensile and fatigue properties of the laminates were also studied.
