2001 Vol. 18, No. 4
2001, 18(4): 1-5.
Abstract:
Carbon nanotubes (CNTs) possess significant advantages such as super-strong mechanical properties, very high aspect ratio, high chemical and thermal stability and unique electrical conductivity. CNTs are hence considered as the ultimate type for the novel composites. The development of the composites with CNTs was reviewed. Ni-based-CNTs composite coating was prepared by electroless plating, which had amorphous microstructure and exhibited much higher wear resistance over traditional composite coating. The advantages of composite plating to prepare metal-based CNTs were further discussed. In addition, a conducting polymer polyaniline-CNTs composite was synthesized by in situ chemical polymerization, which can be used as electrode material for rechargeable batteries and electrochemical supercapacitors.
Carbon nanotubes (CNTs) possess significant advantages such as super-strong mechanical properties, very high aspect ratio, high chemical and thermal stability and unique electrical conductivity. CNTs are hence considered as the ultimate type for the novel composites. The development of the composites with CNTs was reviewed. Ni-based-CNTs composite coating was prepared by electroless plating, which had amorphous microstructure and exhibited much higher wear resistance over traditional composite coating. The advantages of composite plating to prepare metal-based CNTs were further discussed. In addition, a conducting polymer polyaniline-CNTs composite was synthesized by in situ chemical polymerization, which can be used as electrode material for rechargeable batteries and electrochemical supercapacitors.
2001, 18(4): 6-10.
Abstract:
The microstructure, dynamic visco elasticity, thermal expansion property and mechanical property of easy recycling PP/LCP composites are discussed in this paper. Not only the LCP is not dissolved into PP phase, but also two phases of PP and LCP possess good bonding strength because there were differences in the thermal expansion coefficient between the PP and LCP phases. When the addition content of LCP was less than 40 %, a reinforcement phase with LCP as fiber situatied in PP matrix was formed and distributed in the flow direction. When the addition content of LCP was more than 60 %, the ductile and strength properties would decrease due to the existence of PP phase.
The microstructure, dynamic visco elasticity, thermal expansion property and mechanical property of easy recycling PP/LCP composites are discussed in this paper. Not only the LCP is not dissolved into PP phase, but also two phases of PP and LCP possess good bonding strength because there were differences in the thermal expansion coefficient between the PP and LCP phases. When the addition content of LCP was less than 40 %, a reinforcement phase with LCP as fiber situatied in PP matrix was formed and distributed in the flow direction. When the addition content of LCP was more than 60 %, the ductile and strength properties would decrease due to the existence of PP phase.
2001, 18(4): 11-16.
Abstract:
To meet the need for geometric data in finite element investigation, a study on the corner microstructure of three-dimensional(3-D) 4-directional rectangular composite preforms braided by 4-step 1∶1 procedure is made, and a accurate geometry model of the structure is developed. The vector method is used to deduce some mathematic expressions of, the axis of yarn(fiber bundle) at fabric corner, the contact curves at which a yarn at fabric corner touches with one at fabric interior & one at fabric corner, and etc. These formulas supply the geometric parameters of corner microstructure, which are useful to graphic emulation and mechanical analysis of this material.
To meet the need for geometric data in finite element investigation, a study on the corner microstructure of three-dimensional(3-D) 4-directional rectangular composite preforms braided by 4-step 1∶1 procedure is made, and a accurate geometry model of the structure is developed. The vector method is used to deduce some mathematic expressions of, the axis of yarn(fiber bundle) at fabric corner, the contact curves at which a yarn at fabric corner touches with one at fabric interior & one at fabric corner, and etc. These formulas supply the geometric parameters of corner microstructure, which are useful to graphic emulation and mechanical analysis of this material.
2001, 18(4): 17-22.
Abstract:
RTM process is considered as an affordable and environmental friendly manufacture technology for the advanced composites. One of the major difficulties of RTM applications is related with complex resin flow behavior during mould filling. A mold filling simulation tool, named BHRTM-2, was developed based on numerical models of RTM process and FEM/CV method. BHRTM-2 was developed in windows environment and a powerful snapping function was also provided, which let an operator easily determine the injection and vent locations. The automatically mashing function for complex plate shape part was also featured. The pressure field, resin flow front, filling time and dry spot of mold filling can be predicted with the simulation tool. The theoretical and experimental verifications of the mold filling simulation were well illustrated and case studies were also given in the research. The research will provide an affordable and user friendly simulation tool for RTM process.
RTM process is considered as an affordable and environmental friendly manufacture technology for the advanced composites. One of the major difficulties of RTM applications is related with complex resin flow behavior during mould filling. A mold filling simulation tool, named BHRTM-2, was developed based on numerical models of RTM process and FEM/CV method. BHRTM-2 was developed in windows environment and a powerful snapping function was also provided, which let an operator easily determine the injection and vent locations. The automatically mashing function for complex plate shape part was also featured. The pressure field, resin flow front, filling time and dry spot of mold filling can be predicted with the simulation tool. The theoretical and experimental verifications of the mold filling simulation were well illustrated and case studies were also given in the research. The research will provide an affordable and user friendly simulation tool for RTM process.
2001, 18(4): 23-28.
Abstract:
The effect of molding conditions and pretreatment of ramie with alkali or silane on mechanical properties of ramie weave/LLDPE laminate is studied in this paper. The results show that the laminate, molding at 140 ℃ with a pressure of 7.35 MPa, has optimal mechanical properties. In comparison with untreated ramie, the tensile strength is increased from 51.0MPa (untreated) to 102.6, 83.6MPa and 89.8MPa respectively in case the weave used has been pretreated with alkali, KH-550 or A-151; the flexural strength, flexural modulus, total impact energy per unit area and dynamic flexural strength amount to 81.6 MPa, 6.01 GPa, 37.8 kJ/m2 and 106 MPa from 23.1MPa, 1.58 GPa, 30.9 kJ/m2 and 31.1 MPa.
The effect of molding conditions and pretreatment of ramie with alkali or silane on mechanical properties of ramie weave/LLDPE laminate is studied in this paper. The results show that the laminate, molding at 140 ℃ with a pressure of 7.35 MPa, has optimal mechanical properties. In comparison with untreated ramie, the tensile strength is increased from 51.0MPa (untreated) to 102.6, 83.6MPa and 89.8MPa respectively in case the weave used has been pretreated with alkali, KH-550 or A-151; the flexural strength, flexural modulus, total impact energy per unit area and dynamic flexural strength amount to 81.6 MPa, 6.01 GPa, 37.8 kJ/m2 and 106 MPa from 23.1MPa, 1.58 GPa, 30.9 kJ/m2 and 31.1 MPa.
2001, 18(4): 29-33.
Abstract:
Factors in process of UV photo-initiated grafting treatment to UHMWPE fibers woven are discussed. The inter-laminar shear strength (ILSS) of composites was used to characterize the treatment effect. The results show that UV photo-initiated grafting acrylamide is the best. After treatment, the ILSS of composites increased up to 18.85 MPa, almost twice that of untreated. The surface properties and morphologies of UHMWPE fibers before and after treatment were studied by SEM, FTIR and XPS.
Factors in process of UV photo-initiated grafting treatment to UHMWPE fibers woven are discussed. The inter-laminar shear strength (ILSS) of composites was used to characterize the treatment effect. The results show that UV photo-initiated grafting acrylamide is the best. After treatment, the ILSS of composites increased up to 18.85 MPa, almost twice that of untreated. The surface properties and morphologies of UHMWPE fibers before and after treatment were studied by SEM, FTIR and XPS.
2001, 18(4): 34-37.
Abstract:
Anodic oxidation treatment was used to modify the carbon fibers surfaces of 3D woven perform. The effect of the treatment on the ablative property of 3D perform reinforced phenol composites was studied. The results indicated that the method could improve the ablative resistance of the composites. The linear ablative rate of the composites at the test surface and the maximum temperature of the backside of the composites were decreased by 7.2% and 20℃ respectively. Moreover, the pbotographs of the composites which had been ablated were studied by SEM to analyze the effects of the treatment mechanisms on the ablative performance.
Anodic oxidation treatment was used to modify the carbon fibers surfaces of 3D woven perform. The effect of the treatment on the ablative property of 3D perform reinforced phenol composites was studied. The results indicated that the method could improve the ablative resistance of the composites. The linear ablative rate of the composites at the test surface and the maximum temperature of the backside of the composites were decreased by 7.2% and 20℃ respectively. Moreover, the pbotographs of the composites which had been ablated were studied by SEM to analyze the effects of the treatment mechanisms on the ablative performance.
2001, 18(4): 38-41.
Abstract:
To better understand the mechanisms of poor ductility of particulate reinforced Al-matrix composites, tensile deformation at room and liquid nitrogen temperature and notched-specimen bending at room temperature were conducted for (Al2O3)P/6061Al. Deformation and fracture process of the composite was characterized by the following successive events: localized deformation of the matrix, cracking of larger reinforcement particles within the deformation bands, and failure along the localized deformation bands through interaction of further localized straining and promoted cracking. No essential effect of deformation mode, deformation temperature and material condition on the above characteristics was identified. Taking into account the limited beneficial effects of cryogenic temperature and cryogenic treatment on ductility, factors influencing and the potential of improving ductility of particulate reinforced Al-matrix composites were discussed.
To better understand the mechanisms of poor ductility of particulate reinforced Al-matrix composites, tensile deformation at room and liquid nitrogen temperature and notched-specimen bending at room temperature were conducted for (Al2O3)P/6061Al. Deformation and fracture process of the composite was characterized by the following successive events: localized deformation of the matrix, cracking of larger reinforcement particles within the deformation bands, and failure along the localized deformation bands through interaction of further localized straining and promoted cracking. No essential effect of deformation mode, deformation temperature and material condition on the above characteristics was identified. Taking into account the limited beneficial effects of cryogenic temperature and cryogenic treatment on ductility, factors influencing and the potential of improving ductility of particulate reinforced Al-matrix composites were discussed.
2001, 18(4): 42-45.
Abstract:
The interfacial shear strength of SiC fiber reinforced aluminum composite treated with SiC2 was studied by the method of fragmentation and acoustic emission after a certain cycle fatigue loading. The result shows that the pretreatment with fatigue and without fatigue displays a great influence on the stiffness of the test machine which will affect the calculations of fiber strength in composite. The measurement of fiber strength of hot pressed specimens by a dissolving method indicates that the fiber strength does not lose via composite process. The critical length of fiber increases a little after certain cycles of fatigue loading and thus, interfacial shear strength decreases.
The interfacial shear strength of SiC fiber reinforced aluminum composite treated with SiC2 was studied by the method of fragmentation and acoustic emission after a certain cycle fatigue loading. The result shows that the pretreatment with fatigue and without fatigue displays a great influence on the stiffness of the test machine which will affect the calculations of fiber strength in composite. The measurement of fiber strength of hot pressed specimens by a dissolving method indicates that the fiber strength does not lose via composite process. The critical length of fiber increases a little after certain cycles of fatigue loading and thus, interfacial shear strength decreases.
2001, 18(4): 46-49.
Abstract:
Ti-40Al-2B(wt%) alloy was produced successfully by an in-situ method. The microstructure and the phase constitution, especially the morphology of the primary TiB2 of this alloy were investigated by XRD and SEM. The results show that this alloy is composed of TiAl and TiB2. TiB2 mainly exists in the matrix with block primary TiB2 and plate or fine bar shape eutectic TiB2.The primary TiB2 is hexagonal prism morphology. Clear growth steps were observed at the top of the primary TiB2, and the crystal faces were determined to be (0001) and ｛101 - 0｝. Based on the crystal growth theory, it was considered that the growth element of the primary TiB2 is the trigonal prism of six Ti atoms with one B atom at the center, and the primary TiB2 grows mainly in a step growth method. The growth rate of ｛112 - 1｝ faces is the fastest and that of ｛101 - 0｝ is the slowest, which results in a hexagonal prism TiB2 with ｛101 - 0｝ as prismatic faces.
Ti-40Al-2B(wt%) alloy was produced successfully by an in-situ method. The microstructure and the phase constitution, especially the morphology of the primary TiB2 of this alloy were investigated by XRD and SEM. The results show that this alloy is composed of TiAl and TiB2. TiB2 mainly exists in the matrix with block primary TiB2 and plate or fine bar shape eutectic TiB2.The primary TiB2 is hexagonal prism morphology. Clear growth steps were observed at the top of the primary TiB2, and the crystal faces were determined to be (0001) and ｛101 - 0｝. Based on the crystal growth theory, it was considered that the growth element of the primary TiB2 is the trigonal prism of six Ti atoms with one B atom at the center, and the primary TiB2 grows mainly in a step growth method. The growth rate of ｛112 - 1｝ faces is the fastest and that of ｛101 - 0｝ is the slowest, which results in a hexagonal prism TiB2 with ｛101 - 0｝ as prismatic faces.
2001, 18(4): 50-53.
Abstract:
Ti-17Al-1.5B alloy was produced by an in-situ method. The microstructure and the phase constitution of this alloy were investigated by XRD and SEM. The results show that this alloy is composed of Ti3Al and TiB. The coarser and longer primary TiB is highly faceted and exhibits a hollow needle morphology, and the eutectic TiB is fine needle shape. Based on the stability theory of crystal growth, the propagation of the steps on the center of the solid-liquid interface of TiB crystal is stopped due to very large diffusional under-cooling when the solid-liquid interface grows to a critical dimension at [010] direction; therefore, the TiB crystal grows preferentially from the edge of the crystal. Additionally, the growth rate at [010] direction of TiB crystal is very fast because of its B27 crystal structure. So it is considered that the inhomogeneity in supersaturation of crystal-liquid interface and B27 crystal structure of TiB resulted its growing with hollow shape when the (010) facet reaches a critical dimension. The eutectic needle TiB is difficult to grow with hollow morphology because of its much smaller cross section.
Ti-17Al-1.5B alloy was produced by an in-situ method. The microstructure and the phase constitution of this alloy were investigated by XRD and SEM. The results show that this alloy is composed of Ti3Al and TiB. The coarser and longer primary TiB is highly faceted and exhibits a hollow needle morphology, and the eutectic TiB is fine needle shape. Based on the stability theory of crystal growth, the propagation of the steps on the center of the solid-liquid interface of TiB crystal is stopped due to very large diffusional under-cooling when the solid-liquid interface grows to a critical dimension at [010] direction; therefore, the TiB crystal grows preferentially from the edge of the crystal. Additionally, the growth rate at [010] direction of TiB crystal is very fast because of its B27 crystal structure. So it is considered that the inhomogeneity in supersaturation of crystal-liquid interface and B27 crystal structure of TiB resulted its growing with hollow shape when the (010) facet reaches a critical dimension. The eutectic needle TiB is difficult to grow with hollow morphology because of its much smaller cross section.
2001, 18(4): 54-57.
Abstract:
The mechanisms of tensile fracture and strengthening of aluminium alloy matrix composites reinforced with SiC particles are examined. The results show that fracture evolution entails a process of microvoid nucleation, growth, coalescence (MNG) for the PRMMCs and there exhibit three models of initial fracture in the process: toughness fracture of the matrix, boundary separation and particle break. Experimental analyses show that strengthening effect of the composites depends on the matching relations between the matrix and the boundary strength and it is very difficult to strengthen the composites when yield stress of the matrix goes beyound a certain critical value.
The mechanisms of tensile fracture and strengthening of aluminium alloy matrix composites reinforced with SiC particles are examined. The results show that fracture evolution entails a process of microvoid nucleation, growth, coalescence (MNG) for the PRMMCs and there exhibit three models of initial fracture in the process: toughness fracture of the matrix, boundary separation and particle break. Experimental analyses show that strengthening effect of the composites depends on the matching relations between the matrix and the boundary strength and it is very difficult to strengthen the composites when yield stress of the matrix goes beyound a certain critical value.
2001, 18(4): 58-63.
Abstract:
The microstructure and properties of in situ VCP/steel composite fabricated by casting are investigated, and the formation mechanism of the composite microstructure is also analysed. The results show that in situ VCP /steel composite has low pouring temperature (1723~1773 K) and good cast forming. It is suited to fabricate the in situ composite that demands a large reinforced particle volume fraction. In situ VCP composite contains fine VC particles, which distribute homogeneously in the matrix, and 15 % particle volume. Three types of reinforced VC phases, granular VC from melt, strip eutectic VC, and granular VC separated from matrix, were found in composite microstructure. The composite microstructure stability can be remarkably improved by alloying matrix. After 923 K temperature, the composite can still hold hardness at HRC 60. This property can improve the composite wear-resistance at high temperature.
The microstructure and properties of in situ VCP/steel composite fabricated by casting are investigated, and the formation mechanism of the composite microstructure is also analysed. The results show that in situ VCP /steel composite has low pouring temperature (1723~1773 K) and good cast forming. It is suited to fabricate the in situ composite that demands a large reinforced particle volume fraction. In situ VCP composite contains fine VC particles, which distribute homogeneously in the matrix, and 15 % particle volume. Three types of reinforced VC phases, granular VC from melt, strip eutectic VC, and granular VC separated from matrix, were found in composite microstructure. The composite microstructure stability can be remarkably improved by alloying matrix. After 923 K temperature, the composite can still hold hardness at HRC 60. This property can improve the composite wear-resistance at high temperature.
2001, 18(4): 64-67.
Abstract:
Mechanical properties and the damage evolutions of short fiber reinforced metal matrix composites (MMC) were studied by a meso mechanics model numerically. A phenomenological cohesive interface was formulated to simulate the fiber/matrix interface damage while the Gurson-Tvergaard model was adopted to describe the matrix damage. Attention was focused on the effects of the meso parameters on the damage, strength and toughness of the MMC. The meso parameters considered here include interface strength and fiber's aspectratio. All the computations were made based on the cell model. The investigation revealed that, if the interface is weak, the interface debonding is the main reason causing the MMC's loading capacity decreasing; when the interface strength is strong enough, the fiber tends to break and the ultimate strength of MMC is dominated by the fiber's strength. The dependence of the distribution of the matrix damage on the interface strength was also depicted in this study.
Mechanical properties and the damage evolutions of short fiber reinforced metal matrix composites (MMC) were studied by a meso mechanics model numerically. A phenomenological cohesive interface was formulated to simulate the fiber/matrix interface damage while the Gurson-Tvergaard model was adopted to describe the matrix damage. Attention was focused on the effects of the meso parameters on the damage, strength and toughness of the MMC. The meso parameters considered here include interface strength and fiber's aspectratio. All the computations were made based on the cell model. The investigation revealed that, if the interface is weak, the interface debonding is the main reason causing the MMC's loading capacity decreasing; when the interface strength is strong enough, the fiber tends to break and the ultimate strength of MMC is dominated by the fiber's strength. The dependence of the distribution of the matrix damage on the interface strength was also depicted in this study.
2001, 18(4): 68-71.
Abstract:
In this paper, Cf/SiC was prepared by the process of precursor-infiltration-pyrolysis(PIP) using carbon fiber bundles and polycarbosilane(PCS), and the damage extent of fibers in Cf/SiC was studied. The results show that strongly bonded fiber/matrix interface will come into being because PCS is ready to pyrolyze surrounding the fibers, and the considerable oxygen and impurity hurts the fiber. At the same time, the thermal stress hurts the fiber greatly, which is caused by the imparity of the fiber-matrix coefficients of thermal expansion and considerable bulk-shrink in the process of pyrolysis.
In this paper, Cf/SiC was prepared by the process of precursor-infiltration-pyrolysis(PIP) using carbon fiber bundles and polycarbosilane(PCS), and the damage extent of fibers in Cf/SiC was studied. The results show that strongly bonded fiber/matrix interface will come into being because PCS is ready to pyrolyze surrounding the fibers, and the considerable oxygen and impurity hurts the fiber. At the same time, the thermal stress hurts the fiber greatly, which is caused by the imparity of the fiber-matrix coefficients of thermal expansion and considerable bulk-shrink in the process of pyrolysis.
2001, 18(4): 72-75.
Abstract:
Based on gravitational separation-thermit(G-T) self-propagating high-temperature synthesis(SHS) technique, ceramic-lined composite gun pipes respectively with the base of 20 carbon steel, Cr25Ni20 heat-resisting steel and 1Cr18Ni9Ti stainless steel were produced. It was obtained that interface bonding between metal and ceramics in composite gun pipes was mainly achieved with mechanical combination. In 1Cr18Ni9Ti composite pipes, except for stronger interlocking, solution and infiltration bond type was formed to some extent due to accumulation at the interface and spreading to the ceramic layer of Ti element. After use in industry, the bonding mechanism in 1Cr18Ni9Ti composite pipe had been gradually transferred to diffusion bonding, and tendency of partial interface reaction bonding was presented as results of Ti and C element accumulating at the interface area, intermediate areas between ceramics and metal being widened and TiC new phase in ceramics appearing. While it remained mechanical combination at interface of 20 carbon steel and Cr25Ni20 steel composite pipes.
Based on gravitational separation-thermit(G-T) self-propagating high-temperature synthesis(SHS) technique, ceramic-lined composite gun pipes respectively with the base of 20 carbon steel, Cr25Ni20 heat-resisting steel and 1Cr18Ni9Ti stainless steel were produced. It was obtained that interface bonding between metal and ceramics in composite gun pipes was mainly achieved with mechanical combination. In 1Cr18Ni9Ti composite pipes, except for stronger interlocking, solution and infiltration bond type was formed to some extent due to accumulation at the interface and spreading to the ceramic layer of Ti element. After use in industry, the bonding mechanism in 1Cr18Ni9Ti composite pipe had been gradually transferred to diffusion bonding, and tendency of partial interface reaction bonding was presented as results of Ti and C element accumulating at the interface area, intermediate areas between ceramics and metal being widened and TiC new phase in ceramics appearing. While it remained mechanical combination at interface of 20 carbon steel and Cr25Ni20 steel composite pipes.
2001, 18(4): 76-81.
Abstract:
The crack growth resistance behaviors(R-curve ) of Al2O3-SiCW and Al2O3-TiCP ceramic matrix composites were determined by the indentation-strength method. The properties of the thermal shock resistance of the two materials were also estimated. The relationship between the R-curve and the thermal shock resistance of the materials was discussed. The properties of the thermal shock resistance increased with the increasing steepness of the R-curve gradient. Both materials exhibited rising R-curve behavior and improved thermal shock resistance. The Al2O3-SiCW composite showed better damage tolerance and higher thermal shock resistance than Al2O3-TiCP composites. SEM observation and theoretical analysis indicate that these phenomena can be attributed mainly to the principle toughening mechanism of pull-out and bridging of the SiC whiskers.
The crack growth resistance behaviors(R-curve ) of Al2O3-SiCW and Al2O3-TiCP ceramic matrix composites were determined by the indentation-strength method. The properties of the thermal shock resistance of the two materials were also estimated. The relationship between the R-curve and the thermal shock resistance of the materials was discussed. The properties of the thermal shock resistance increased with the increasing steepness of the R-curve gradient. Both materials exhibited rising R-curve behavior and improved thermal shock resistance. The Al2O3-SiCW composite showed better damage tolerance and higher thermal shock resistance than Al2O3-TiCP composites. SEM observation and theoretical analysis indicate that these phenomena can be attributed mainly to the principle toughening mechanism of pull-out and bridging of the SiC whiskers.
2001, 18(4): 82-86.
Abstract:
Following Loves shell theory, the governing equations of the composite cylindrical shell associated with asymmetric deformation perturbance were obtained. By taking the displacement functions as complex Fourier series at the perturbed state, the perturbed motion equations were deduced to a set of Mathieu equations. Then the critical load and natural frequencies were calculated. Previous studies on dynamic stability of laminated shells had not taken into account the geometric nonlinearity which was considered in the present work. Numerical results showed that the critical load yielded by geometric nonlinearity was about 5 % higher than that given by geometric linearity.
Following Loves shell theory, the governing equations of the composite cylindrical shell associated with asymmetric deformation perturbance were obtained. By taking the displacement functions as complex Fourier series at the perturbed state, the perturbed motion equations were deduced to a set of Mathieu equations. Then the critical load and natural frequencies were calculated. Previous studies on dynamic stability of laminated shells had not taken into account the geometric nonlinearity which was considered in the present work. Numerical results showed that the critical load yielded by geometric nonlinearity was about 5 % higher than that given by geometric linearity.
2001, 18(4): 87-92.
Abstract:
In this paper,a geometric model and a model of physical properties of the system of TiC-Ni functionally graded materials are given obtained from experiment. And with the two models,the influences of gradient exponent on stress intensity factors,strain energy density factors and its initiating angles are analyzed using the finite element method. The stress intensity factor and stress energy density factor of model Ⅰ under distributed load have the minimum values when P is 1.3, but the stress intensity factors and stress energy density factors of model Ⅱ under residual stress field or stable thermal field only have maximum ones. On the other hand, the influences of gradient exponent on fracture initiating angles under residual stress field or stable thermal field are much larger than under the distributed load.
In this paper,a geometric model and a model of physical properties of the system of TiC-Ni functionally graded materials are given obtained from experiment. And with the two models,the influences of gradient exponent on stress intensity factors,strain energy density factors and its initiating angles are analyzed using the finite element method. The stress intensity factor and stress energy density factor of model Ⅰ under distributed load have the minimum values when P is 1.3, but the stress intensity factors and stress energy density factors of model Ⅱ under residual stress field or stable thermal field only have maximum ones. On the other hand, the influences of gradient exponent on fracture initiating angles under residual stress field or stable thermal field are much larger than under the distributed load.
2001, 18(4): 93-97.
Abstract:
This work attempts to find a new homogenization method for the analysis of assemblage of elastic contact bodies. A brief review of existing works for both micro or local analysis level and macro analysis level of the problem is given. The finite element method for the local RVE analysis is presented. An important feature of this work is the quasi-static cohesive frictional contact analysis of RVE, i.e. the local composed of deformable elastic bodies, by means of the parametric quadratic programming principle and its corresponding algorithmic implementation. The work presented in this paper is a fundamental study for the homogenization analysis of the problem.
This work attempts to find a new homogenization method for the analysis of assemblage of elastic contact bodies. A brief review of existing works for both micro or local analysis level and macro analysis level of the problem is given. The finite element method for the local RVE analysis is presented. An important feature of this work is the quasi-static cohesive frictional contact analysis of RVE, i.e. the local composed of deformable elastic bodies, by means of the parametric quadratic programming principle and its corresponding algorithmic implementation. The work presented in this paper is a fundamental study for the homogenization analysis of the problem.
2001, 18(4): 98-102.
Abstract:
Based on the work presented in paper [1], a new homogenisation method for the analysis of assemblage of elastic contact bodies is proposed in this paper. An important feature of this work is to define numerically a homogenised constitutive relationship for the global behaviour of the assemblies in terms of the analysis on the RVE level, and a new consistent homogenisation method is furthermore presented. Numerical example and results are given to demonstrate the validity and efficiency of the new method.
Based on the work presented in paper [1], a new homogenisation method for the analysis of assemblage of elastic contact bodies is proposed in this paper. An important feature of this work is to define numerically a homogenised constitutive relationship for the global behaviour of the assemblies in terms of the analysis on the RVE level, and a new consistent homogenisation method is furthermore presented. Numerical example and results are given to demonstrate the validity and efficiency of the new method.
2001, 18(4): 103-107.
Abstract:
In the paper, von-Karman type orthotropic rectangular plates with two adjacent edges simply supported and the other two adjacent edges clamped are analysed by using Galerkin method.The beam vibration functions are taken as displacement functions that may accurately satisfy the boundary conditions, and have orthogonality property.The governing nonlinear partial differential equations are reduced to an infinite set of systems of nonlinear algebraic equations containing Fourier coefficients which have been solved by linearizing iterative procedures. The series of beam vibration functions are rapidly converged. Only a few items of the series may meet the need of accuracy. Numerical results of deflection and stress are obtained for different composite materials.
In the paper, von-Karman type orthotropic rectangular plates with two adjacent edges simply supported and the other two adjacent edges clamped are analysed by using Galerkin method.The beam vibration functions are taken as displacement functions that may accurately satisfy the boundary conditions, and have orthogonality property.The governing nonlinear partial differential equations are reduced to an infinite set of systems of nonlinear algebraic equations containing Fourier coefficients which have been solved by linearizing iterative procedures. The series of beam vibration functions are rapidly converged. Only a few items of the series may meet the need of accuracy. Numerical results of deflection and stress are obtained for different composite materials.
2001, 18(4): 108-114.
Abstract:
A finite element analysis model of steady rolling tires is developed in this paper. The model includes the geometric nonlinearity due to large deformation, material nonlinearity, incompressibility constraint on deformation of elastomers, the anisotropy of cord-rubber composites, the nonlinear boundary conditions resulting from both tire-rim contact and tire-foundation contact and the tire-foundation contact slip friction in steady rolling. Numerical results show that the model is very reasonable.
A finite element analysis model of steady rolling tires is developed in this paper. The model includes the geometric nonlinearity due to large deformation, material nonlinearity, incompressibility constraint on deformation of elastomers, the anisotropy of cord-rubber composites, the nonlinear boundary conditions resulting from both tire-rim contact and tire-foundation contact and the tire-foundation contact slip friction in steady rolling. Numerical results show that the model is very reasonable.
2001, 18(4): 115-118.
Abstract:
The kinetic mechanism of XD reaction in Al-TiO2-C system was studied in this paper. Result shows that a strong exothermic reaction results in the formation of a high temperature metallurgical micro-region in the sample, which is favorable to synthesis of reinforcing particles TiCp / (Al2O3)P and in matrix alloying. Synthetic reactions take place as different kinetic mechanisms in different periods. There exists a crack of the reactants during the quick reaction period,the cracking was caused by the steep temperature gradient and great thermal stress inside the reactants. The cracking of reactants makes the reaction speed very fast and synthesized particles (Al2O3)P and TiCP very fine.
The kinetic mechanism of XD reaction in Al-TiO2-C system was studied in this paper. Result shows that a strong exothermic reaction results in the formation of a high temperature metallurgical micro-region in the sample, which is favorable to synthesis of reinforcing particles TiCp / (Al2O3)P and in matrix alloying. Synthetic reactions take place as different kinetic mechanisms in different periods. There exists a crack of the reactants during the quick reaction period,the cracking was caused by the steep temperature gradient and great thermal stress inside the reactants. The cracking of reactants makes the reaction speed very fast and synthesized particles (Al2O3)P and TiCP very fine.
2001, 18(4): 119-122.
Abstract:
The fatigue properties of two types of wood (P. Ussurensis and B. Platyphylla) and wood plastic composites were analyzed by three-point bend fracture testing, and fatigue crack propagation models were investigated. Test results show that the maximum stress of wood plastic composites presents a linear relationship with logarithmic fatigue life. Fatigue load increases linearly with enhanced polymer content. For P. Ussurensis, the slope of S-N fatigue curve is influenced by polymer content in wood, and fatigue crack grows along wood fibre. For B. Platyphylla plastic composites (PC>30 wt.%), fatigue crack grows in the shape of 'Z’ along the height of the specimen.
The fatigue properties of two types of wood (P. Ussurensis and B. Platyphylla) and wood plastic composites were analyzed by three-point bend fracture testing, and fatigue crack propagation models were investigated. Test results show that the maximum stress of wood plastic composites presents a linear relationship with logarithmic fatigue life. Fatigue load increases linearly with enhanced polymer content. For P. Ussurensis, the slope of S-N fatigue curve is influenced by polymer content in wood, and fatigue crack grows along wood fibre. For B. Platyphylla plastic composites (PC>30 wt.%), fatigue crack grows in the shape of 'Z’ along the height of the specimen.
2001, 18(4): 123-127.
Abstract:
Laminate repair is a basic research topic of composite repair. Thereinto, patch-bonded repair and flush repair are the two most important methods. In this work, FEM analysis was researched on the above two methods, and the scheme of parameter selection was provided. The research shows that, for most patch-bonded cases, patch thickness should be half of the original laminate, and the overlap length should be about 25 mm. And for most flush repairs, the scarf angle can be 6°. Typical specimens were tested to verify the optimized design parameters. To eliminate the influence of the additional bending and to simulate the actual structure more exactly, the patch-bonded specimens should be designed as two-sided repair. The results of the tests fitted in well with the parameters derived from the theoretical analysis. And the scheme of parameter selection has great significance in directing the engineering practice of composite repair.
Laminate repair is a basic research topic of composite repair. Thereinto, patch-bonded repair and flush repair are the two most important methods. In this work, FEM analysis was researched on the above two methods, and the scheme of parameter selection was provided. The research shows that, for most patch-bonded cases, patch thickness should be half of the original laminate, and the overlap length should be about 25 mm. And for most flush repairs, the scarf angle can be 6°. Typical specimens were tested to verify the optimized design parameters. To eliminate the influence of the additional bending and to simulate the actual structure more exactly, the patch-bonded specimens should be designed as two-sided repair. The results of the tests fitted in well with the parameters derived from the theoretical analysis. And the scheme of parameter selection has great significance in directing the engineering practice of composite repair.
2001, 18(4): 128-132.
Abstract:
The theoretical roughness of machined surface of common metal materials can be calculated using the current formula. However, the machined surface of composites may include a variety of machining defects, and their concave or convex defects may not form directly by the cutting of tool edge. So, the current formula for the calculation of theoretical roughness of conventional metal materials is unsuitable for composites. The machined surface texture and roughness of composites reinforced by fiber are closely-related to the cutting direction. Though the composites reinforced by particles is isotropic, their machined surface textures and roughness are mainly controlled and dominated by the hardness and the volume as well as the size of the reinforcing particle. The interface strength between the reinforce and the matrix, the cutting tool and machining parameters affect the machined surface roughness of composites signally.
The theoretical roughness of machined surface of common metal materials can be calculated using the current formula. However, the machined surface of composites may include a variety of machining defects, and their concave or convex defects may not form directly by the cutting of tool edge. So, the current formula for the calculation of theoretical roughness of conventional metal materials is unsuitable for composites. The machined surface texture and roughness of composites reinforced by fiber are closely-related to the cutting direction. Though the composites reinforced by particles is isotropic, their machined surface textures and roughness are mainly controlled and dominated by the hardness and the volume as well as the size of the reinforcing particle. The interface strength between the reinforce and the matrix, the cutting tool and machining parameters affect the machined surface roughness of composites signally.
2001, 18(4): 133-135.
Abstract:
Joining of alumina ceramics to copper was investigated with a self-made producing device. Studies were focused on temperatures, pressures and interfacial cohesive strength. The highest joining strenth of 15.1 MPa was obtained for the sample under the conditions of 725 ℃ for joining temperature, 7.5 MPa for joining pressure and 300 s for joining time.
Joining of alumina ceramics to copper was investigated with a self-made producing device. Studies were focused on temperatures, pressures and interfacial cohesive strength. The highest joining strenth of 15.1 MPa was obtained for the sample under the conditions of 725 ℃ for joining temperature, 7.5 MPa for joining pressure and 300 s for joining time.
