2001 Vol. 18, No. 3
2001, 18(3): 1-4.
Abstract:
Nano-technology is a new preparing method of material. In this paper, the structure character of nanoparticles is briefly mentioned. And the mechanism and character of five kinds of nanocomposites preparing technologies as well as properties of nanocomposites are introduced. Also the future of polymer-nanocomposites is prospected.
Nano-technology is a new preparing method of material. In this paper, the structure character of nanoparticles is briefly mentioned. And the mechanism and character of five kinds of nanocomposites preparing technologies as well as properties of nanocomposites are introduced. Also the future of polymer-nanocomposites is prospected.
2001, 18(3): 5-9.
Abstract:
Polymer-Layered Silicate(PLS) nanocomposite is a new kind of composite material,which has superior properties,and is in the frontier of material science. In this paper,the authors firstly review the structure and the modification of layered silicate,in which the kind of intercalation agent and the cation exchange capacity (CEC) are key influence factors of preparing PLS nanocomposites,and then focus on the preparation process of PLS nanocomposites,microstructure and its characters, while the main preparation process is intercalation complex including intercalation polymerization and polymer intercalation. Finally,according to the development,properties and application of PLS nanocomposites,the authors give some development and research progress of PLS nanocomposites.
Polymer-Layered Silicate(PLS) nanocomposite is a new kind of composite material,which has superior properties,and is in the frontier of material science. In this paper,the authors firstly review the structure and the modification of layered silicate,in which the kind of intercalation agent and the cation exchange capacity (CEC) are key influence factors of preparing PLS nanocomposites,and then focus on the preparation process of PLS nanocomposites,microstructure and its characters, while the main preparation process is intercalation complex including intercalation polymerization and polymer intercalation. Finally,according to the development,properties and application of PLS nanocomposites,the authors give some development and research progress of PLS nanocomposites.
2001, 18(3): 10-13.
Abstract:
The influence of composition on the curing kinetic parameter, electrical, mechanical, thermal properties and the glass transition temperature (Tg) of epoxy and cyanate ester co-curing system catalyzed by transition metal acetylacetone(MT(atat)<em>n) was studied by means of DSC,dielectric and dynamic mechanical methods in this paper. The results showed that the reactive activation energy (Ea) and frequency factor (A) of the co-curing is found to increase with enhanced concentrations of cyanate of the co-curing system. The glass transition temperature (Tg) and thermal stability of the cyanate and epoxy cured system is found to increase with enhanced concentrations of cyanate in the same cured condition; addition of the cyanate will decrease the loss factor, and dielectrical value as well.
The influence of composition on the curing kinetic parameter, electrical, mechanical, thermal properties and the glass transition temperature (Tg) of epoxy and cyanate ester co-curing system catalyzed by transition metal acetylacetone(MT(atat)<em>n) was studied by means of DSC,dielectric and dynamic mechanical methods in this paper. The results showed that the reactive activation energy (Ea) and frequency factor (A) of the co-curing is found to increase with enhanced concentrations of cyanate of the co-curing system. The glass transition temperature (Tg) and thermal stability of the cyanate and epoxy cured system is found to increase with enhanced concentrations of cyanate in the same cured condition; addition of the cyanate will decrease the loss factor, and dielectrical value as well.
2001, 18(3): 14-17.
Abstract:
Magnetorheological fluid (MRF) has drawn much attention due to its powerful shearing stress. The yield stress of MRF is about ten times greater than that of electrorheological fluid (ERF). But a projecting question is the subsidence of particles as a result of gravity for magnetorheological fluid. Fe particles have been prepared with microemulsion, and being coated by protein, polymeric protein-Fe particles have been obtained. The preparation of MRF, and XRD,TEM,IR analysis of surface structure for protein-Fe have been reported in the paper. The magnetorheological, temperature effects and subsidence stability have been investigated also on MRF of protein-Fe. The results show that the protein-Fe is a complex particle composition from crystal α-Fe and non-crystal protein. The magnetorheological fluid has good magnetorheological effect, and its subsidence stability is excellent compared with the single carbonyl iron.
Magnetorheological fluid (MRF) has drawn much attention due to its powerful shearing stress. The yield stress of MRF is about ten times greater than that of electrorheological fluid (ERF). But a projecting question is the subsidence of particles as a result of gravity for magnetorheological fluid. Fe particles have been prepared with microemulsion, and being coated by protein, polymeric protein-Fe particles have been obtained. The preparation of MRF, and XRD,TEM,IR analysis of surface structure for protein-Fe have been reported in the paper. The magnetorheological, temperature effects and subsidence stability have been investigated also on MRF of protein-Fe. The results show that the protein-Fe is a complex particle composition from crystal α-Fe and non-crystal protein. The magnetorheological fluid has good magnetorheological effect, and its subsidence stability is excellent compared with the single carbonyl iron.
2001, 18(3): 18-21.
Abstract:
The study of the resistivity temperature dependence of polyethylene-carbon-black composites mixed with different concentrations of carbon fiber is reported. Carbon fibers provide charge transport over large distances, whereas carbon blacks not only provide charge transport over relatively small distances but also improve the interfiber contacts through carbon black particle bridges. Incorporation of carbon fibers into polyethylene-carbon black composites can substantially improve the conductivity level of these systems. Only charge transport over relatively small distances is affected by the increasing temperature before PTC transition. Through black particles bridging neighbouring carbon fibers, carbon fiber conductive network can compensate for somewhat conductivity losses resulting from the increasing interparticle distances of carbon black. Resistivity of composites before PTC transition is thus more and more insensitive to temperature change due to the increase of carbon fiber loading. However, in the temperature range of polyethylene melting point, charge transports over large and small distances are both destroyed in the composites. In this case resistivity increases drastically, giving rise to an extremely large PTC anomaly effect. So the positive temperature coefficient of resistance (PTC) effects become stronger, and the PTC transition temperature is increased as concentration of carbon fiber in polyethylene-carbon-black composite.
The study of the resistivity temperature dependence of polyethylene-carbon-black composites mixed with different concentrations of carbon fiber is reported. Carbon fibers provide charge transport over large distances, whereas carbon blacks not only provide charge transport over relatively small distances but also improve the interfiber contacts through carbon black particle bridges. Incorporation of carbon fibers into polyethylene-carbon black composites can substantially improve the conductivity level of these systems. Only charge transport over relatively small distances is affected by the increasing temperature before PTC transition. Through black particles bridging neighbouring carbon fibers, carbon fiber conductive network can compensate for somewhat conductivity losses resulting from the increasing interparticle distances of carbon black. Resistivity of composites before PTC transition is thus more and more insensitive to temperature change due to the increase of carbon fiber loading. However, in the temperature range of polyethylene melting point, charge transports over large and small distances are both destroyed in the composites. In this case resistivity increases drastically, giving rise to an extremely large PTC anomaly effect. So the positive temperature coefficient of resistance (PTC) effects become stronger, and the PTC transition temperature is increased as concentration of carbon fiber in polyethylene-carbon-black composite.
2001, 18(3): 22-25.
Abstract:
PEO/Li<em>xV2-δO4-δ nanocomposite was prepared by the solution intercalation method. Powder X-ray diffraction, differential scanning calorimetry and infrared spectrum analysis show that PEO chains intercalate Li<em>xV2-δO4-δ galleries and expand the lattice lamella by 0.42 nm. The movement ability of PEO is also restricted.
PEO/Li<em>xV2-δO4-δ nanocomposite was prepared by the solution intercalation method. Powder X-ray diffraction, differential scanning calorimetry and infrared spectrum analysis show that PEO chains intercalate Li<em>xV2-δO4-δ galleries and expand the lattice lamella by 0.42 nm. The movement ability of PEO is also restricted.
2001, 18(3): 26-29.
Abstract:
Some treatment methods such as blasting, phosphate-fluofide, hydrogen peroxide alkaline solution oxidation were used as surface activation of Ti alloy, and the effect of coupling agent was investigated. SEM and XPS analysis and mechanical properties test of Ti/CFRP showed blasting then coupling agent treatment was a practical surface activation method.
Some treatment methods such as blasting, phosphate-fluofide, hydrogen peroxide alkaline solution oxidation were used as surface activation of Ti alloy, and the effect of coupling agent was investigated. SEM and XPS analysis and mechanical properties test of Ti/CFRP showed blasting then coupling agent treatment was a practical surface activation method.
2001, 18(3): 30-33.
Abstract:
The chemorheological behaviors of bismaleimide resin (QY8911-4) for Resin Transfer Molding (RTM) were studied. A chemorheological model of the resin was developed based on dual-arrhenius equation. The estimated viscosity values of the established model are in good agreement with the experimental ones.The model was used to determine the critical low viscosity windows of the resin system for RTM processes. The optimum processing parameters of QY8911-4 resin for RTM are 100 ℃~110 ℃ at which the viscosity of the resin will be less than 200 cP within 55 minutes. These parameters are essential for the manufacture of structure composites with high fiber content. The longer pot life of the resin also can be obtained with low working temperature between 90 ℃ and 100 ℃, in which the viscosity of the resin can keep less than 800 cP. The developed model is important for processing simulation, parameter optimization and quality control for RTM processes.
The chemorheological behaviors of bismaleimide resin (QY8911-4) for Resin Transfer Molding (RTM) were studied. A chemorheological model of the resin was developed based on dual-arrhenius equation. The estimated viscosity values of the established model are in good agreement with the experimental ones.The model was used to determine the critical low viscosity windows of the resin system for RTM processes. The optimum processing parameters of QY8911-4 resin for RTM are 100 ℃~110 ℃ at which the viscosity of the resin will be less than 200 cP within 55 minutes. These parameters are essential for the manufacture of structure composites with high fiber content. The longer pot life of the resin also can be obtained with low working temperature between 90 ℃ and 100 ℃, in which the viscosity of the resin can keep less than 800 cP. The developed model is important for processing simulation, parameter optimization and quality control for RTM processes.
2001, 18(3): 34-37.
Abstract:
The study of the quantitative contribution of the thermal volume expansion to the positive temperature coefficient (PTC) switch effect of fine particles filled polymer composites in the carbon black-polyethylene(CB-PE) system is reported. The decrease of room temperature resistivity with the increase of CB loading level (CB volume fractions at room temperature) experimentally obtained was fitted by General Effective Medium (GEM) equation in order to establish the mixing rule of the system. A dilution of the CB volume fraction due to the thermal volume expansion of the composites is estimated and "real" CB volume fractions of a certain loading level at different temperatures are thus found. Being treated equivalent to the loading levels, the "real" CB volume fractions at high temperatures are used to replace the volume fraction in the above GEM equation. By using this model, the contribution of thermal expansion of matrix to the jump-like PTC switch transition of the composites is quantitatively estimated. The theory and experiment have proved that the conductive mechanism of abrupt resistivity increase at PTC transition range is equivalent as abrupt resistivity increase at the percolation curve close to the critical volume fraction.
The study of the quantitative contribution of the thermal volume expansion to the positive temperature coefficient (PTC) switch effect of fine particles filled polymer composites in the carbon black-polyethylene(CB-PE) system is reported. The decrease of room temperature resistivity with the increase of CB loading level (CB volume fractions at room temperature) experimentally obtained was fitted by General Effective Medium (GEM) equation in order to establish the mixing rule of the system. A dilution of the CB volume fraction due to the thermal volume expansion of the composites is estimated and "real" CB volume fractions of a certain loading level at different temperatures are thus found. Being treated equivalent to the loading levels, the "real" CB volume fractions at high temperatures are used to replace the volume fraction in the above GEM equation. By using this model, the contribution of thermal expansion of matrix to the jump-like PTC switch transition of the composites is quantitatively estimated. The theory and experiment have proved that the conductive mechanism of abrupt resistivity increase at PTC transition range is equivalent as abrupt resistivity increase at the percolation curve close to the critical volume fraction.
2001, 18(3): 38-42.
Abstract:
The physical and chemical characterization and analysis on the surface of four carbon fibers (T300,T700,T800 and AS4) were performed by SEM, AFM and XPS. Observed by SEM,the surface physical morphology of T300 and T800 was similar, the surface of T700 was glossier and had floccules and the surface of AS4 was most glossy and had larger diameter. More micromorphology of carbon fibers were revealed, the difference on surface state of T300 and T800 were great. Quantitative analysis by XPS, the surface activity of T300,T700 and T800 were materialized on the mechanical property of composites' interface.
The physical and chemical characterization and analysis on the surface of four carbon fibers (T300,T700,T800 and AS4) were performed by SEM, AFM and XPS. Observed by SEM,the surface physical morphology of T300 and T800 was similar, the surface of T700 was glossier and had floccules and the surface of AS4 was most glossy and had larger diameter. More micromorphology of carbon fibers were revealed, the difference on surface state of T300 and T800 were great. Quantitative analysis by XPS, the surface activity of T300,T700 and T800 were materialized on the mechanical property of composites' interface.
2001, 18(3): 43-45.
Abstract:
An electric conductivity model of metal-insulator composites with an interfacial shell is given. And the expression for the effective electric conductivity of a metal-insulator composite with an interfacial shell is presented. Considering the interaction of metal particles, with consideration of the interface layer between two distinct topological structures, a simple self-consistent way is used to improve this expression. The theoretical results on electric conductivity of silver-phenol composites are in good agreement with experimental data.
An electric conductivity model of metal-insulator composites with an interfacial shell is given. And the expression for the effective electric conductivity of a metal-insulator composite with an interfacial shell is presented. Considering the interaction of metal particles, with consideration of the interface layer between two distinct topological structures, a simple self-consistent way is used to improve this expression. The theoretical results on electric conductivity of silver-phenol composites are in good agreement with experimental data.
2001, 18(3): 46-51.
Abstract:
A theoretical model of movement behavior of second phase particles in metal melt in centrifugal field was set up. The factors affecting the movement behavior of the particle were analyzed with this model. The results show that the distance and velocity of the particle moving from inside to outside increase with time in an exponential law. The bigger the particle diameter, the higher the particle density,and the faster the rotation speed of mold, then the longer the distance of particle movement will be. The phenomenon that particle runs after particle exists because of not only the difference of particle diameter but also the difference of particle density during the transport, which is the main reason that particles collide and accumulate and big particles or particles with big density segregate to the specimen outside. To reduce the pursuit, collision, and accumulation of particles during particles movement, it is very important to use the particles with the same diameter and composition. The distance between two particles whose initial positions in the radial direction are different increases gradually with time. For some particles whose space length is the same at a radial straight line, the distances between any two near particles are still equal after particles move for a moment though it is longer than that at the initial position. The gradient distribution of particles in the specimen is induced by the sedimentation of particles from outside to inside the specimen, the increase of viscosity of the metal melt with the temperature decreasing, and the solidification of the metal melt.
A theoretical model of movement behavior of second phase particles in metal melt in centrifugal field was set up. The factors affecting the movement behavior of the particle were analyzed with this model. The results show that the distance and velocity of the particle moving from inside to outside increase with time in an exponential law. The bigger the particle diameter, the higher the particle density,and the faster the rotation speed of mold, then the longer the distance of particle movement will be. The phenomenon that particle runs after particle exists because of not only the difference of particle diameter but also the difference of particle density during the transport, which is the main reason that particles collide and accumulate and big particles or particles with big density segregate to the specimen outside. To reduce the pursuit, collision, and accumulation of particles during particles movement, it is very important to use the particles with the same diameter and composition. The distance between two particles whose initial positions in the radial direction are different increases gradually with time. For some particles whose space length is the same at a radial straight line, the distances between any two near particles are still equal after particles move for a moment though it is longer than that at the initial position. The gradient distribution of particles in the specimen is induced by the sedimentation of particles from outside to inside the specimen, the increase of viscosity of the metal melt with the temperature decreasing, and the solidification of the metal melt.
2001, 18(3): 52-55.
Abstract:
The strengthening effect of Al2O3 microspheres was investigated in an Al-6061 based metal matrix composite. The strength of the material in the solid solution state was significantly increased by the addition of the reinforcement microspheres. This increase in strength corresponds well to the calculation of a dislocation strengthening model using dislocation densities measured from TEM observations. The strain hardening rate of the material in various aging states is also increased by this addition, which can be accounted for by the combination of the dislocation strengthening model and the model of geometrically necessary dislocations in plastically non-homogeneous material proposed by Ashby.
The strengthening effect of Al2O3 microspheres was investigated in an Al-6061 based metal matrix composite. The strength of the material in the solid solution state was significantly increased by the addition of the reinforcement microspheres. This increase in strength corresponds well to the calculation of a dislocation strengthening model using dislocation densities measured from TEM observations. The strain hardening rate of the material in various aging states is also increased by this addition, which can be accounted for by the combination of the dislocation strengthening model and the model of geometrically necessary dislocations in plastically non-homogeneous material proposed by Ashby.
2001, 18(3): 56-59.
Abstract:
Under vacuum condition, with CuO as oxidizer, Al2O3/Cu surficial composites layer can be prepared through internal oxidation of Cu-Al alloy at certain temperatures. At low internal oxidation temperatures, there are more Al2O3 particles on the boundary than in the copper grains. At higher temperatures, Al2O3 particles distribute homogeneously. With the increasing of aluminium content, the depth of the composite layer reduces and the microhardness increases.
Under vacuum condition, with CuO as oxidizer, Al2O3/Cu surficial composites layer can be prepared through internal oxidation of Cu-Al alloy at certain temperatures. At low internal oxidation temperatures, there are more Al2O3 particles on the boundary than in the copper grains. At higher temperatures, Al2O3 particles distribute homogeneously. With the increasing of aluminium content, the depth of the composite layer reduces and the microhardness increases.
2001, 18(3): 60-66.
Abstract:
TiB and TiC reinforced titanium matrix composites have been produced by non-consumable arc-melting technology utilizing the self-propagation high-temperature synthesis reactions between titanium and B4C, graphite. Microstructures have been observed by scanning electron microscopy and transmission electron microscopy. The results show that in situ synthesized reinforcements are distributed uniformly in matrix alloy. TiB grows in short-fibre shape and TiC grows in dendritic, equiaxed shapes. The interfaces between reinforcements and titanium matrix alloy are very clean. There is no any interfacial reaction. However, there are high-density dislocations near TiC particle. Mechanical properties have been improved due to the incorporation of reinforcements. The addition of aluminum element not only strengthens the titanium matrix alloy by solid solution strengthening, but also improves the mechanical properties of composites by refining the reinforcements.
TiB and TiC reinforced titanium matrix composites have been produced by non-consumable arc-melting technology utilizing the self-propagation high-temperature synthesis reactions between titanium and B4C, graphite. Microstructures have been observed by scanning electron microscopy and transmission electron microscopy. The results show that in situ synthesized reinforcements are distributed uniformly in matrix alloy. TiB grows in short-fibre shape and TiC grows in dendritic, equiaxed shapes. The interfaces between reinforcements and titanium matrix alloy are very clean. There is no any interfacial reaction. However, there are high-density dislocations near TiC particle. Mechanical properties have been improved due to the incorporation of reinforcements. The addition of aluminum element not only strengthens the titanium matrix alloy by solid solution strengthening, but also improves the mechanical properties of composites by refining the reinforcements.
2001, 18(3): 67-71.
Abstract:
The fracture mirror method was modified and applied to evaluation of the in-situ strength of fibers in ceramic composites. The most significant modifications include (1) the mirror constant relies on the tensile test of fiber bundles instead of a single fiber test and (2) the gauge length parameter is redefined. Traditionally, the gauge length parameter was considered as mean fiber pull out length. In this study, by analyzing the mechanism of fiber pullout, the parameter was defined as the sum of double pullout length and double ineffective length of the broken fibers and the random parameter was then graded statistically. Based on this method, Weibull parameters and mean in-situ strength of the M40JB fiber embedded in SiC matrix composites produced from polymer precursor were obtained. The experimental results show that the Weibull shape parameters of fabricated fibers and in-situ ones are nearly identical, but the scale parameter of in-situ fiber strength is much lower than that of the fabricated one. That means the flaws position distribution in both fibers does not vary obviously, however, the flaws are deeper in in-situ fiber than in fabricated one and that leads the strength of the former fiber to decrease markedly.
The fracture mirror method was modified and applied to evaluation of the in-situ strength of fibers in ceramic composites. The most significant modifications include (1) the mirror constant relies on the tensile test of fiber bundles instead of a single fiber test and (2) the gauge length parameter is redefined. Traditionally, the gauge length parameter was considered as mean fiber pull out length. In this study, by analyzing the mechanism of fiber pullout, the parameter was defined as the sum of double pullout length and double ineffective length of the broken fibers and the random parameter was then graded statistically. Based on this method, Weibull parameters and mean in-situ strength of the M40JB fiber embedded in SiC matrix composites produced from polymer precursor were obtained. The experimental results show that the Weibull shape parameters of fabricated fibers and in-situ ones are nearly identical, but the scale parameter of in-situ fiber strength is much lower than that of the fabricated one. That means the flaws position distribution in both fibers does not vary obviously, however, the flaws are deeper in in-situ fiber than in fabricated one and that leads the strength of the former fiber to decrease markedly.
2001, 18(3): 72-75.
Abstract:
The properties of three types of fibers reinforced SiC composite materials produced by polymer infiltration were compared and the cause of property differences was exposed via analysis of the microstructure of the materials. It was found that SiC matrix composite material reinforced by Hi-Nicalon fibre had the most preferable properties, uni-directional composite material of this type reached a bending strength of 703.6 MPa, and fracture toughness of 23.1 MPa·m1/2. Composite materials reinforced by JC carbon fibre had preferable properties too, with bending strength of 501.1 MPa, and fracture toughness of 13.8 MPa·m 1/2.
The properties of three types of fibers reinforced SiC composite materials produced by polymer infiltration were compared and the cause of property differences was exposed via analysis of the microstructure of the materials. It was found that SiC matrix composite material reinforced by Hi-Nicalon fibre had the most preferable properties, uni-directional composite material of this type reached a bending strength of 703.6 MPa, and fracture toughness of 23.1 MPa·m1/2. Composite materials reinforced by JC carbon fibre had preferable properties too, with bending strength of 501.1 MPa, and fracture toughness of 13.8 MPa·m 1/2.
2001, 18(3): 76-80.
Abstract:
The advantage and the ablation mechanism of C/C composites are demonstrated. A physical model of mechanical-ablation is established mainly in terms of both the thermoelasticity mechanics and fracture mechanics. Then, the influence of environment and the appearance and disappearance of surface roughness are discussed. The mechanical ablation and thermo-chemical ablation of C/C composites are analyzed. All these make some helpful discussion for thermal protection materials.
The advantage and the ablation mechanism of C/C composites are demonstrated. A physical model of mechanical-ablation is established mainly in terms of both the thermoelasticity mechanics and fracture mechanics. Then, the influence of environment and the appearance and disappearance of surface roughness are discussed. The mechanical ablation and thermo-chemical ablation of C/C composites are analyzed. All these make some helpful discussion for thermal protection materials.
2001, 18(3): 81-84.
Abstract:
M40JB-Cf/SiC and T800-Cf/SiC composite's elevated temperature tensile strengths were tested with spindle-shaped and rectangular specimens. The tensile strength and tensile modulus were got after modifying the spindle-shaped specimen's strain formula. The elevated temperature tensile results showed that M40JB/SiC composite's tensile strength was 374MPa under 1300℃ and 338MPa under 1450℃, the tensile modulus was 134GPa under 1300℃ and 116GPa under 1450℃. Compared with the M40JB-Cf/SiC composites, the T800-Cf/SiC composites' tensile strength was 392MPa under 1300℃, higher than the M40JB-Cf/SiC composites, while the tensile modulus was 115GPa under 1300℃, lower than M40JB-Cf/SiC composite's. From the elevated temperature tensile test results, it was found that the composite tensile strength was correlative with the specimen's failure mode. When the failure happened at the effective part, the tensile strength values were higher than the values when the failure happened at the ineffective part, which were only 250MPa. The tensile stress-strain curves of M40JB-Cf/SiC composites showed non-linear-elastic fracture characters clearly of plastic materials, but the tensile stress-strain curves of T800-Cf/SiC composites were the linear curves.
M40JB-Cf/SiC and T800-Cf/SiC composite's elevated temperature tensile strengths were tested with spindle-shaped and rectangular specimens. The tensile strength and tensile modulus were got after modifying the spindle-shaped specimen's strain formula. The elevated temperature tensile results showed that M40JB/SiC composite's tensile strength was 374MPa under 1300℃ and 338MPa under 1450℃, the tensile modulus was 134GPa under 1300℃ and 116GPa under 1450℃. Compared with the M40JB-Cf/SiC composites, the T800-Cf/SiC composites' tensile strength was 392MPa under 1300℃, higher than the M40JB-Cf/SiC composites, while the tensile modulus was 115GPa under 1300℃, lower than M40JB-Cf/SiC composite's. From the elevated temperature tensile test results, it was found that the composite tensile strength was correlative with the specimen's failure mode. When the failure happened at the effective part, the tensile strength values were higher than the values when the failure happened at the ineffective part, which were only 250MPa. The tensile stress-strain curves of M40JB-Cf/SiC composites showed non-linear-elastic fracture characters clearly of plastic materials, but the tensile stress-strain curves of T800-Cf/SiC composites were the linear curves.
2001, 18(3): 85-90.
Abstract:
This paper presents the results of experimental studies on fiber alignment and its influence on the tensile strength along different directions for fiber reinforced cement fabricated by extrusion technique. It is well known that fibers can be aligned into the desired directions during an extrusion process through a properly designed die and high shear. The fiber alignment, of course, would lead to direction dependency of the tensile properties of GFRC extrudate. The current study investigated such a dependency using the existing extrusion equipment. It is found that when the fiber volume ratio is low, say 1 % of glass fiber, it can be aligned almost in unified direction, i.e. extrusion direction. As a result, the tensile strength of a thin plate along the extrusion direction is much higher than that of along the transverse direction. When the fiber volume ratio is increased to 2 % or 4 %, the fiber volume along the transverse direction is largely increased even though the majority of fiber is still aligned along the extrusion direction. Thus, the tensile strength in the transverse direction is significantly increased. In fact, the tensile strength along the transverse direction is almost the same to that along the extrusion direction when the fiber volume ratio reaches 2 %. Furthermore, the extrusion direction strength of samples did not increase proportionally to the fiber volume ratio. But the toughness and the destroy form have been improved with the fiber volume ratio increasing.
This paper presents the results of experimental studies on fiber alignment and its influence on the tensile strength along different directions for fiber reinforced cement fabricated by extrusion technique. It is well known that fibers can be aligned into the desired directions during an extrusion process through a properly designed die and high shear. The fiber alignment, of course, would lead to direction dependency of the tensile properties of GFRC extrudate. The current study investigated such a dependency using the existing extrusion equipment. It is found that when the fiber volume ratio is low, say 1 % of glass fiber, it can be aligned almost in unified direction, i.e. extrusion direction. As a result, the tensile strength of a thin plate along the extrusion direction is much higher than that of along the transverse direction. When the fiber volume ratio is increased to 2 % or 4 %, the fiber volume along the transverse direction is largely increased even though the majority of fiber is still aligned along the extrusion direction. Thus, the tensile strength in the transverse direction is significantly increased. In fact, the tensile strength along the transverse direction is almost the same to that along the extrusion direction when the fiber volume ratio reaches 2 %. Furthermore, the extrusion direction strength of samples did not increase proportionally to the fiber volume ratio. But the toughness and the destroy form have been improved with the fiber volume ratio increasing.
2001, 18(3): 91-96.
Abstract:
Based on the multiphase composite ceramic tool material Al2O3 reinforced by SiC and (W,Ti)C particles, the magnitude and the distribution of the residual thermal stress are analyzed in detail with the finite element modeling method. The results show that the residual thermal stress in the multiphase composite ceramic tool material is affected noticeably by the distribution unit models, size and distribution forms of the dispersed phases and their volume fractions. Tensile stress fields are found to exist in the matrix together with the compressive stress fields to different extents and in different ranges. The structure of both tensile and compressive stress fields has close relations with the distribution forms of the dispersed SiC and (W,Ti)C particles. The research here denotes that close relations exist between the residual thermal stress and the microstructure and the mechanical property of the composite ceramic tool material.
Based on the multiphase composite ceramic tool material Al2O3 reinforced by SiC and (W,Ti)C particles, the magnitude and the distribution of the residual thermal stress are analyzed in detail with the finite element modeling method. The results show that the residual thermal stress in the multiphase composite ceramic tool material is affected noticeably by the distribution unit models, size and distribution forms of the dispersed phases and their volume fractions. Tensile stress fields are found to exist in the matrix together with the compressive stress fields to different extents and in different ranges. The structure of both tensile and compressive stress fields has close relations with the distribution forms of the dispersed SiC and (W,Ti)C particles. The research here denotes that close relations exist between the residual thermal stress and the microstructure and the mechanical property of the composite ceramic tool material.
2001, 18(3): 97-100.
Abstract:
The three-point test was carried out to test the modulus of rupture of PZT composite laminates. It is evident that the positive electric field can improve the modulus of rupture of PZT composite laminates but the negative one can decrease its modulus of rupture. A setup of in-situ AE measuring system was established to determine the different damage models of PZT composite laminates during the process of loading, and the damage model of PZT composite laminates was also verified by the scanning acoustic microscopic images.
The three-point test was carried out to test the modulus of rupture of PZT composite laminates. It is evident that the positive electric field can improve the modulus of rupture of PZT composite laminates but the negative one can decrease its modulus of rupture. A setup of in-situ AE measuring system was established to determine the different damage models of PZT composite laminates during the process of loading, and the damage model of PZT composite laminates was also verified by the scanning acoustic microscopic images.
2001, 18(3): 101-105.
Abstract:
According to the three-dimensional elastic equilibrium equations and the conditions of interfacial shear slip, a model of interfacial shear slip of laminated composite plates is developed. The shear slip is described by the linear interfacial constitutive relations of transverse shear stresses and in-plane displacement jumps on weakly bonded interfaces. The model takes the same form of displacement field and equilibrium equations as the general two-dimentional plate and shell theories do, but it is relatively simple and very accurate because the shear deformation functions, which account for bonding conditions on the interfaces and the traction boundary conditions on the lateral planes, are introduced. The closed-form solution of simply supported cross-ply plates is obtained. Bending and buckling of laminated plates are considered and the effects of interfacial weakly bonding are discussed. The numerical results are compared with the exact solutions and show the high accuracy of the present model.
According to the three-dimensional elastic equilibrium equations and the conditions of interfacial shear slip, a model of interfacial shear slip of laminated composite plates is developed. The shear slip is described by the linear interfacial constitutive relations of transverse shear stresses and in-plane displacement jumps on weakly bonded interfaces. The model takes the same form of displacement field and equilibrium equations as the general two-dimentional plate and shell theories do, but it is relatively simple and very accurate because the shear deformation functions, which account for bonding conditions on the interfaces and the traction boundary conditions on the lateral planes, are introduced. The closed-form solution of simply supported cross-ply plates is obtained. Bending and buckling of laminated plates are considered and the effects of interfacial weakly bonding are discussed. The numerical results are compared with the exact solutions and show the high accuracy of the present model.
2001, 18(3): 106-110.
Abstract:
The fatigue properties of steel-cord rubber composite under T-T loading are studied in this paper. The effects of maximum stress and frequency on fatigue life are analyzed and the hysteretic loss and the variation of temperature during the cyclic tension are obtained as well. A linear life prediction equation is given in terms of the fatigue-life diagram. The results indicate that the increase in the maximum strain exhibits a three-stage tendency. The two-step experiments demonstrate that this tendency also exists in the fatigue process of defected specimens.
The fatigue properties of steel-cord rubber composite under T-T loading are studied in this paper. The effects of maximum stress and frequency on fatigue life are analyzed and the hysteretic loss and the variation of temperature during the cyclic tension are obtained as well. A linear life prediction equation is given in terms of the fatigue-life diagram. The results indicate that the increase in the maximum strain exhibits a three-stage tendency. The two-step experiments demonstrate that this tendency also exists in the fatigue process of defected specimens.
2001, 18(3): 111-118.
Abstract:
The statistical analysis of the strength data of T300/QY8911, T300/HD03 and T300/QY8911-Ⅱ gives the maximum standard deviation. And it is shown that the strength performance scatter of the unidirectional composite laminate in 0° or 90° stacking sequence is bigger than that of the multidirectional laminates. From the statistical distribution test of the strength performance of T300/QY8911, T300/HD03 and T300/QY8911-Ⅱ, it is also found that the strength performance of these composites follows the log-normal distribution. Then a small sample factor method with high precision for the reliability design of composite strength performance is presented, and is compared with two other methods. The verification results show that this method presented in this paper can give the stable calculation results and is with high calculation precision. Moreover, it can obtain the bigger prediction values than the other methods, and more sufficiently make use of composites, so as to save specimens.
The statistical analysis of the strength data of T300/QY8911, T300/HD03 and T300/QY8911-Ⅱ gives the maximum standard deviation. And it is shown that the strength performance scatter of the unidirectional composite laminate in 0° or 90° stacking sequence is bigger than that of the multidirectional laminates. From the statistical distribution test of the strength performance of T300/QY8911, T300/HD03 and T300/QY8911-Ⅱ, it is also found that the strength performance of these composites follows the log-normal distribution. Then a small sample factor method with high precision for the reliability design of composite strength performance is presented, and is compared with two other methods. The verification results show that this method presented in this paper can give the stable calculation results and is with high calculation precision. Moreover, it can obtain the bigger prediction values than the other methods, and more sufficiently make use of composites, so as to save specimens.
2001, 18(3): 119-123.
Abstract:
Multiweb structures are integral ones composed by upper skin,lower skin and webs. This kind of structure can reduce the height and weight of wings and at the same time,maintain the strength and rigidity. Moreover,the application of composite multiweb structures in modern fighters is becoming an inevitable trend because of the various advantages of this material. To solve the problem of buckling,the theory of nonlinear stability of composite laminates and method of rigidity equivalence are adopted in this article. The relevant constitutive equation and nonlinear stability governing equations are established. At last,the nonlinear equations are solved by numerical computation. The overall and local critical loads of buckling are obtained under various boundary conditions and compressive and shear loads in plane. The validity and effectiveness of the theory and method are demonstrated by comparison with the solutions obtained by the other existent references. They can satisfy absolutely the demands of engineering.
Multiweb structures are integral ones composed by upper skin,lower skin and webs. This kind of structure can reduce the height and weight of wings and at the same time,maintain the strength and rigidity. Moreover,the application of composite multiweb structures in modern fighters is becoming an inevitable trend because of the various advantages of this material. To solve the problem of buckling,the theory of nonlinear stability of composite laminates and method of rigidity equivalence are adopted in this article. The relevant constitutive equation and nonlinear stability governing equations are established. At last,the nonlinear equations are solved by numerical computation. The overall and local critical loads of buckling are obtained under various boundary conditions and compressive and shear loads in plane. The validity and effectiveness of the theory and method are demonstrated by comparison with the solutions obtained by the other existent references. They can satisfy absolutely the demands of engineering.
2001, 18(3): 124-132.
Abstract:
The nonlinear contact problem of composite beams is linearized by an inverse method, that is to say, the loading distribution on the contact zone with the adjustable parameter and the contact width are assumed to be given and the curvature of the cylinder is to be solved. By means of the principle of superposition, the loading state is decomposed into symmetric and antisymmetric ones. The trigonometric series and Legendre series are applied to describe the displacement field of the above two loading states and the principle of minimum potential energy is used to determine the unknown coefficients of the above series. Then the displacement and stress fields of the composite beam are known. The adjustable parameter of loading distribution is used to satisfy the compatibility conditions of displacements along the contact surface. By the way the indentor curvature is determined. Then many families of straight lines passing through the origin of the indentor curvature varying as the loading with different contact zones can be figured out. Based on the above straight lines, the contact zone can be determined from the known indentor curvature and loading. From the computational results, it can be shown that the displacements and stresses converge very well and the distribution of shearing stress obtained from the constitutive equation and from the equilibrium equation agree with each other very well. The distribution of stress of the composite beam has the local effects, and at the place far from local loading the distribution of stress is the same as the results of classical beam theory.
The nonlinear contact problem of composite beams is linearized by an inverse method, that is to say, the loading distribution on the contact zone with the adjustable parameter and the contact width are assumed to be given and the curvature of the cylinder is to be solved. By means of the principle of superposition, the loading state is decomposed into symmetric and antisymmetric ones. The trigonometric series and Legendre series are applied to describe the displacement field of the above two loading states and the principle of minimum potential energy is used to determine the unknown coefficients of the above series. Then the displacement and stress fields of the composite beam are known. The adjustable parameter of loading distribution is used to satisfy the compatibility conditions of displacements along the contact surface. By the way the indentor curvature is determined. Then many families of straight lines passing through the origin of the indentor curvature varying as the loading with different contact zones can be figured out. Based on the above straight lines, the contact zone can be determined from the known indentor curvature and loading. From the computational results, it can be shown that the displacements and stresses converge very well and the distribution of shearing stress obtained from the constitutive equation and from the equilibrium equation agree with each other very well. The distribution of stress of the composite beam has the local effects, and at the place far from local loading the distribution of stress is the same as the results of classical beam theory.
2001, 18(3): 133-139.
Abstract:
The delamination or breakage around the body turn up section point in radial truck tires usually occurs, which affects enormously their endurance. In this paper, the FEA of tire structures is used to analyze in detail the stress analysis parameters in the critical regions in radial truck tires with different body turn up heights and based on these, the body turn up heights are screened.
The delamination or breakage around the body turn up section point in radial truck tires usually occurs, which affects enormously their endurance. In this paper, the FEA of tire structures is used to analyze in detail the stress analysis parameters in the critical regions in radial truck tires with different body turn up heights and based on these, the body turn up heights are screened.
