2001 Vol. 18, No. 2
2001, 18(2): 1-3.
Abstract:
Poly (Penton) is a novel kind of polymer that is studied and developed in recent years. It has many prominent properties, such as high melting point and crystallinity, low water absorption and air permeability, excellent chemical corrosion resistance and abrasion resistance. But its notched impact strength and tensile strength are quite low. The mechanical properties of PCE/POM、PCE/EVA、PCE/POM/EVA blends were studied and compared. It was found that EVA was effective compatibilizer for PCE/POM blends and POM was effective reinforcer for PCE/EVA blends. So the method was considered as a good way to develop the high-strengthened and high-toughened PCE blends.
Poly (Penton) is a novel kind of polymer that is studied and developed in recent years. It has many prominent properties, such as high melting point and crystallinity, low water absorption and air permeability, excellent chemical corrosion resistance and abrasion resistance. But its notched impact strength and tensile strength are quite low. The mechanical properties of PCE/POM、PCE/EVA、PCE/POM/EVA blends were studied and compared. It was found that EVA was effective compatibilizer for PCE/POM blends and POM was effective reinforcer for PCE/EVA blends. So the method was considered as a good way to develop the high-strengthened and high-toughened PCE blends.
2001, 18(2): 4-7.
Abstract:
To prepare rubber compound with excellent properties, such as tensile strength, tear strength, hot tear strength and striking heat resistance property, a study was made on micro-fiber of EPDM/PA. It was the first time to find that after some parts of carbon black were replaced by ternary-nylon-copolymer(nylon6/66/1010=20/10/70), mechanical properties of this compound vulcanized by peroxide, especially hot tear could be improved magnificently, while the composite keeping striking heat resistance property. SEM shows that disperse particles could be changed into micro-fibers through some special treatment. Micro-fibers are disorderly oriented in one plane which is vertical to the direction of vulcanization's tension. Only a few micro-fibers become irregular through vulcanizing. Physical test reveals that elongations at break along the lengthways direction are larger than elongations at break along the vertical direction, which is contradictionary to the law of short fiber rubber composite. The reason for it was explained.
To prepare rubber compound with excellent properties, such as tensile strength, tear strength, hot tear strength and striking heat resistance property, a study was made on micro-fiber of EPDM/PA. It was the first time to find that after some parts of carbon black were replaced by ternary-nylon-copolymer(nylon6/66/1010=20/10/70), mechanical properties of this compound vulcanized by peroxide, especially hot tear could be improved magnificently, while the composite keeping striking heat resistance property. SEM shows that disperse particles could be changed into micro-fibers through some special treatment. Micro-fibers are disorderly oriented in one plane which is vertical to the direction of vulcanization's tension. Only a few micro-fibers become irregular through vulcanizing. Physical test reveals that elongations at break along the lengthways direction are larger than elongations at break along the vertical direction, which is contradictionary to the law of short fiber rubber composite. The reason for it was explained.
2001, 18(2): 9-12.
Abstract:
A computer image analysis technique is used to study the fiber tows' cross-section (FTC) in 3-D braided composites. The results indicate that FTC in the center, side and corner of 3-D braided composites is different. The changing period of cross section areas is related to the pitch length.
A computer image analysis technique is used to study the fiber tows' cross-section (FTC) in 3-D braided composites. The results indicate that FTC in the center, side and corner of 3-D braided composites is different. The changing period of cross section areas is related to the pitch length.
2001, 18(2): 14-17.
Abstract:
Conductive ABS resin composites filled with general pitch-based carbon fibers were fabricated by hot-press moulding after raw materials were preblended through a single screw extruder. The composite resistivity decreases with fibers content going up. And the electrical current displays non-linear dependence on the external voltage acted on composites and the resistance of composites varies down with the raise of voltage, which implies that the composites don't meet Ohm's Law. When fibers fraction increases, the linearity between current and voltage goes up correspondingly. For the sample containing fillers of 40 wt%, its resistance remains constant and it satisfies Ohm's Law very well. It is interesting that the high voltage can result in the permanent reduction of composite resistance. And the voltage, which makes the permanent reduction of composites resistance, goes up with the increase of fillers loading. Moreover, the linearity of current and voltage rises after composites were treated by high voltage. All these phenomena can be explained by quantum tunneling model the results of this paper provide a new method for improving the conductivity and stability to varied voltage of composites.
Conductive ABS resin composites filled with general pitch-based carbon fibers were fabricated by hot-press moulding after raw materials were preblended through a single screw extruder. The composite resistivity decreases with fibers content going up. And the electrical current displays non-linear dependence on the external voltage acted on composites and the resistance of composites varies down with the raise of voltage, which implies that the composites don't meet Ohm's Law. When fibers fraction increases, the linearity between current and voltage goes up correspondingly. For the sample containing fillers of 40 wt%, its resistance remains constant and it satisfies Ohm's Law very well. It is interesting that the high voltage can result in the permanent reduction of composite resistance. And the voltage, which makes the permanent reduction of composites resistance, goes up with the increase of fillers loading. Moreover, the linearity of current and voltage rises after composites were treated by high voltage. All these phenomena can be explained by quantum tunneling model the results of this paper provide a new method for improving the conductivity and stability to varied voltage of composites.
2001, 18(2): 18-21.
Abstract:
This paper investigated the pore structure and pore size distributions of some porous clay composites by using N2 adsorption at low temperature(77K) and discussed the influences of different crosslinking agents on its pore structure and pore size distribution. The results show that the synthesis conditions of porous clays, especially, the hydrolysed process of crosslinking agents, play a very important role in the influences in pore structure and pore size distributions of porous clays.
This paper investigated the pore structure and pore size distributions of some porous clay composites by using N2 adsorption at low temperature(77K) and discussed the influences of different crosslinking agents on its pore structure and pore size distribution. The results show that the synthesis conditions of porous clays, especially, the hydrolysed process of crosslinking agents, play a very important role in the influences in pore structure and pore size distributions of porous clays.
2001, 18(2): 22-26.
Abstract:
Hydroxyapatite particles were modified by 3-(trimethoxysilyl) propyl methacrylate (A-174) and polyacrylic acid (PAA) in aqueous solutions respectively. Poly(DL-lactide)/hydroxyapatite(PDLLA/HA) composites were prepared by solution-dispersion compounding and composites rods with diameter 3.2 mm were achieved by oriented molding. Results showed that the glass transition temperature of PDLLA in composites and the bending strength of the composites were increased because of enhancement of the interfacial bonding of the composites.
Hydroxyapatite particles were modified by 3-(trimethoxysilyl) propyl methacrylate (A-174) and polyacrylic acid (PAA) in aqueous solutions respectively. Poly(DL-lactide)/hydroxyapatite(PDLLA/HA) composites were prepared by solution-dispersion compounding and composites rods with diameter 3.2 mm were achieved by oriented molding. Results showed that the glass transition temperature of PDLLA in composites and the bending strength of the composites were increased because of enhancement of the interfacial bonding of the composites.
2001, 18(2): 27-31.
Abstract:
A self-referenced optical fiber cure sensor is proposed to in-situ monitor the cure of epoxy resins. The sensor is fabricated by cleaving a multimode step index optical fiber whose core is of refractive index 1.558, the cleaved end is used to infer the refractive index of the epoxy during cure. The refractive index of the fiber core serves as a reference to calibrate the zero bias and sensitivity of the sensor. As the refractive index of the epoxy system increases with the extent of cure, it will equal the refractive index of the fiber core at a cure extent and then the calibration can be done. Thus, in the later parts of the cure, the sensor can provide quantitative information about cure reaction. When monitoring the cure of composites, the sensors embedded in different part of the structure can be normalized to a common scale such that the real-time comparison of each sensor's output becomes possible. The validity and feasibility of the proposed sensor have been confirmed in the cure monitoring experiments on an epoxy system.
A self-referenced optical fiber cure sensor is proposed to in-situ monitor the cure of epoxy resins. The sensor is fabricated by cleaving a multimode step index optical fiber whose core is of refractive index 1.558, the cleaved end is used to infer the refractive index of the epoxy during cure. The refractive index of the fiber core serves as a reference to calibrate the zero bias and sensitivity of the sensor. As the refractive index of the epoxy system increases with the extent of cure, it will equal the refractive index of the fiber core at a cure extent and then the calibration can be done. Thus, in the later parts of the cure, the sensor can provide quantitative information about cure reaction. When monitoring the cure of composites, the sensors embedded in different part of the structure can be normalized to a common scale such that the real-time comparison of each sensor's output becomes possible. The validity and feasibility of the proposed sensor have been confirmed in the cure monitoring experiments on an epoxy system.
2001, 18(2): 32-36.
Abstract:
The fatigue behaviour of continuous-glass-fibre-mat reinforced polypropylene composites (GMT-PPs) with different interfacial adhesion is investigated by dynamic fatigue tests. The results show that the effect of the interfacial adhesion on the fatigue performance of GMT-PPs is obvious and the improved interfacial adhesion results in an improved fatigue performance. Through the observation of SEM, it is found that the failure modes are different in static tension and dynamic tension for GMT-PPs with strong interfaces. The failure mode of the former is the matrix failure, while that of the latter is the interfacial debonding failure, which means that fatigue loading has a more damaging effect on the interfacial adhesion than on the polymeric matrix. The stronger the interfacial adhesion, the more difficult the interfacial debonding, thus GMT-PPs with well interfacial adhesion has the better the fatigue performance.
The fatigue behaviour of continuous-glass-fibre-mat reinforced polypropylene composites (GMT-PPs) with different interfacial adhesion is investigated by dynamic fatigue tests. The results show that the effect of the interfacial adhesion on the fatigue performance of GMT-PPs is obvious and the improved interfacial adhesion results in an improved fatigue performance. Through the observation of SEM, it is found that the failure modes are different in static tension and dynamic tension for GMT-PPs with strong interfaces. The failure mode of the former is the matrix failure, while that of the latter is the interfacial debonding failure, which means that fatigue loading has a more damaging effect on the interfacial adhesion than on the polymeric matrix. The stronger the interfacial adhesion, the more difficult the interfacial debonding, thus GMT-PPs with well interfacial adhesion has the better the fatigue performance.
2001, 18(2): 36-40.
Abstract:
Using an impregnation and pultrusion device developed at our laboratory, long glass fiber reinforced polypropylene pellets for injection molding were produced. Composites samples were molded with the pellets by a conventional injection machine. Factors affecting the impact toughness were studied by Charpy test. The impact toughness increased with the addition of grafted polypropylene at first, but it decreased slowly when the grafted polypropylene addition exceeded 5 %. Nevertheless, higher impact toughness was obtained with longer pellets and/or wider runner. As to molded planar samples, the impact toughness varied depending on the position where the sample was cut. Annealing was an effective method to improve the impact toughness.
Using an impregnation and pultrusion device developed at our laboratory, long glass fiber reinforced polypropylene pellets for injection molding were produced. Composites samples were molded with the pellets by a conventional injection machine. Factors affecting the impact toughness were studied by Charpy test. The impact toughness increased with the addition of grafted polypropylene at first, but it decreased slowly when the grafted polypropylene addition exceeded 5 %. Nevertheless, higher impact toughness was obtained with longer pellets and/or wider runner. As to molded planar samples, the impact toughness varied depending on the position where the sample was cut. Annealing was an effective method to improve the impact toughness.
2001, 18(2): 41-45.
Abstract:
Using an impregnation/pultrusion device developed at our laboratory, long glass fiber reinforced polypropylene (LGFRP) pellets were produced. Composites parts were injection molded with the pellets by a conventional injection machine. Factors affecting the tensile strength of the parts were studied. Polypropylene grafted with maleic anhydride (PP-MAH) as surface-modifier was very efficient to improve the tensile strength. The tensile strength reached a maximum value for a grafted PP-MAH content of 0.3 % of PP. The better the glass fiber in pellets was impregnated, the higher the strength would be. The tensile strength of the parts molded with 10 mm long pellets was lower than those with 5 mm or 15 mm long pellets. Annealing was an efficient way to improve the tensile strength.
Using an impregnation/pultrusion device developed at our laboratory, long glass fiber reinforced polypropylene (LGFRP) pellets were produced. Composites parts were injection molded with the pellets by a conventional injection machine. Factors affecting the tensile strength of the parts were studied. Polypropylene grafted with maleic anhydride (PP-MAH) as surface-modifier was very efficient to improve the tensile strength. The tensile strength reached a maximum value for a grafted PP-MAH content of 0.3 % of PP. The better the glass fiber in pellets was impregnated, the higher the strength would be. The tensile strength of the parts molded with 10 mm long pellets was lower than those with 5 mm or 15 mm long pellets. Annealing was an efficient way to improve the tensile strength.
2001, 18(2): 46-49.
Abstract:
In this paper, the influence of temperature on the tensile strength of the ultra-high molecular weight polyethylene (UHMWPE) fiber strands which reinforce the UD75 composites is analyzed. The variation of ballistic absorption energy as well as the adhesive bonding force between layers, the thickness and density of laminates of UD75 composites with molding pressures is studied. The results show that the tensile strength of the UHMWPE fiber strands is greatly decreased when the temperature is higher than 123 ℃, and the ballistic absorption energy is up to the highest value when the molding pressure is about 12.5 MPa. The study results would be valuable for the proper preparation and optimum design of composite armors.
In this paper, the influence of temperature on the tensile strength of the ultra-high molecular weight polyethylene (UHMWPE) fiber strands which reinforce the UD75 composites is analyzed. The variation of ballistic absorption energy as well as the adhesive bonding force between layers, the thickness and density of laminates of UD75 composites with molding pressures is studied. The results show that the tensile strength of the UHMWPE fiber strands is greatly decreased when the temperature is higher than 123 ℃, and the ballistic absorption energy is up to the highest value when the molding pressure is about 12.5 MPa. The study results would be valuable for the proper preparation and optimum design of composite armors.
2001, 18(2): 50-53.
Abstract:
The tribological characteristics of carbon fiber/Aramid pulp reinforced modified phenolic were investigated in this paper. The influence of the component on properties was found. Simultaneously, testing results showed that this hybrid composite has excellent tribological performance.
The tribological characteristics of carbon fiber/Aramid pulp reinforced modified phenolic were investigated in this paper. The influence of the component on properties was found. Simultaneously, testing results showed that this hybrid composite has excellent tribological performance.
2001, 18(2): 54-56.
Abstract:
The use of electron beams to initiate polymerization reactions is an area on which much interest has focused. The curing of vinyl monomers such as acrylates and maleimides by means of high energy electron beam irradiation normally proceeds via a free-radical mechanism. While e-beam-induced polymerization of epoxy resins proceeds via a cationic mechanism in the presence of an appropriate photoinitiator. This work investigated the synthesis of new maleimide,aromatic imide monomers,active PMR polyamide acid and silaceous acrylates containing vinyl groups. The cure activity of these vinyl monomers was conducted, so as the epoxy resins. The results suggested that the potential curability exists in the active groups and the structure of the chain.
The use of electron beams to initiate polymerization reactions is an area on which much interest has focused. The curing of vinyl monomers such as acrylates and maleimides by means of high energy electron beam irradiation normally proceeds via a free-radical mechanism. While e-beam-induced polymerization of epoxy resins proceeds via a cationic mechanism in the presence of an appropriate photoinitiator. This work investigated the synthesis of new maleimide,aromatic imide monomers,active PMR polyamide acid and silaceous acrylates containing vinyl groups. The cure activity of these vinyl monomers was conducted, so as the epoxy resins. The results suggested that the potential curability exists in the active groups and the structure of the chain.
2001, 18(2): 57-60.
Abstract:
To fine weave & pierced C/C composites, at fiber/matrix and fiber bundle/matrix two different level interfaces, the push-out test results are obtained using in situ interfacial strength testing instrument. Then using an interface spring element model, the finite element computer simulation methods are employed to simulate the fiber and fiber bundle push-out test processes. The analysis program is written and the interface shearing strengths of different level interfaces are obtained.
To fine weave & pierced C/C composites, at fiber/matrix and fiber bundle/matrix two different level interfaces, the push-out test results are obtained using in situ interfacial strength testing instrument. Then using an interface spring element model, the finite element computer simulation methods are employed to simulate the fiber and fiber bundle push-out test processes. The analysis program is written and the interface shearing strengths of different level interfaces are obtained.
2001, 18(2): 61-64.
Abstract:
Based on previous work, abrasive wear resistance of Al2O3/steel composites with different Al2O3 particle volume fraction (VOF) at 900℃ was investigated. It can be got from the experimental results that a suitable particle volume fraction is important to protect the metal matrix from wear at elevated temperature. The less the particle VOF, the poorer the abrasive wear of the composites due to bulk matrix easily worn off by grits. The more the particle VOF, however, the poorer the abrasive wear of the composites, too. The reason is that Al2O 3 particles are easily dug out by grits during wearing. When the particle VOF is 39%, the wear resistance of test composites is excellent.
Based on previous work, abrasive wear resistance of Al2O3/steel composites with different Al2O3 particle volume fraction (VOF) at 900℃ was investigated. It can be got from the experimental results that a suitable particle volume fraction is important to protect the metal matrix from wear at elevated temperature. The less the particle VOF, the poorer the abrasive wear of the composites due to bulk matrix easily worn off by grits. The more the particle VOF, however, the poorer the abrasive wear of the composites, too. The reason is that Al2O 3 particles are easily dug out by grits during wearing. When the particle VOF is 39%, the wear resistance of test composites is excellent.
2001, 18(2): 65-69.
Abstract:
The microstructure of TiC-Fe cermets prepared by SHS/PHIP was studied. A thin diffusion layer was found between Fe and TiC. As the Fe content was increased, the thickness of diffusion layer and particle size of TiC were decreased, and the combustion reaction became incomplete since some of the lath structure consisting mainly of C were found in Fe-binder phase of TiC-40Fe. There exists a little of precipitate phase of Fe2Ti in Fe-binder phase. A great deal of dislocation were observed in TiC grains.
The microstructure of TiC-Fe cermets prepared by SHS/PHIP was studied. A thin diffusion layer was found between Fe and TiC. As the Fe content was increased, the thickness of diffusion layer and particle size of TiC were decreased, and the combustion reaction became incomplete since some of the lath structure consisting mainly of C were found in Fe-binder phase of TiC-40Fe. There exists a little of precipitate phase of Fe2Ti in Fe-binder phase. A great deal of dislocation were observed in TiC grains.
2001, 18(2): 70-74.
Abstract:
The influence of Fe content on the properties of TiC-Al2O3/Fe composites prepared by SHS/PHIP was studied. The results show that the TiC-Al2O3/Fe cermets prepared by SHS/PHIP possess high mechanical properties such as well-improved flexural strength and fracture toughness owing to the addition of Fe, and highly special stiffness. The TiC-Al2O3 ceramic exhibits the typical brittle fracture behavior. However, the TiC-Al2O3/Fe cermets exhibit obvious characteristic of tough fracture with Fe content increasing.
The influence of Fe content on the properties of TiC-Al2O3/Fe composites prepared by SHS/PHIP was studied. The results show that the TiC-Al2O3/Fe cermets prepared by SHS/PHIP possess high mechanical properties such as well-improved flexural strength and fracture toughness owing to the addition of Fe, and highly special stiffness. The TiC-Al2O3 ceramic exhibits the typical brittle fracture behavior. However, the TiC-Al2O3/Fe cermets exhibit obvious characteristic of tough fracture with Fe content increasing.
2001, 18(2): 75-80.
Abstract:
Different distribution of temperature field affects movement and distribution of particles in a centrifugal acceleration field. To accurately describe the distribution of particles, it is necessary to simulate the temperature field in the centrifugal acceleration field under current experiment conditions. In this paper, the solidification process of self-hardening sand centrifugal casting is simulated in the 2-D cylindrical coordinate by adopting the finite difference method and using MathCad 7.0 for the first time. The influences of rotational speed, pouring temperatures, mould temperatures and mould types on temperature distribution are studied. Numerical analysis shows that solidification process of casting with self-hardening sand and iron cover is not similar to the directional solidification from outer to inner: the upper and lower surfaces of casting firstly solidify, and then solidification front moves to the middle. This study also indicates that solidification speed of casting increases with an increase in rotational speed and thermal diffusivity of casting mould, or increases with a decrease in mould temperature and pouring temperature. The influence of mould temperature on the temperature field is the largest, the influence of rotational speed is the second, and that of pouring temperature the least.
Different distribution of temperature field affects movement and distribution of particles in a centrifugal acceleration field. To accurately describe the distribution of particles, it is necessary to simulate the temperature field in the centrifugal acceleration field under current experiment conditions. In this paper, the solidification process of self-hardening sand centrifugal casting is simulated in the 2-D cylindrical coordinate by adopting the finite difference method and using MathCad 7.0 for the first time. The influences of rotational speed, pouring temperatures, mould temperatures and mould types on temperature distribution are studied. Numerical analysis shows that solidification process of casting with self-hardening sand and iron cover is not similar to the directional solidification from outer to inner: the upper and lower surfaces of casting firstly solidify, and then solidification front moves to the middle. This study also indicates that solidification speed of casting increases with an increase in rotational speed and thermal diffusivity of casting mould, or increases with a decrease in mould temperature and pouring temperature. The influence of mould temperature on the temperature field is the largest, the influence of rotational speed is the second, and that of pouring temperature the least.
2001, 18(2): 81-84.
Abstract:
In this article, the complex process of phthalocyanine nickel with Fe3O4 nanoparticles has been analyzed, the complex mechanism and the structure model for NiPc-Fe3O4 nanoparticles composite have been studied. For the complexes mechanism of NiPc with Fe3O4 nanoparticles, first, there are complex between NiPc and all Fe3O4 nanoparticles. Then, Fe3O4 nanoparticles accumulate together to form the accumulators; NiPc have the function of cohering Fe3O4 nanoparticles. A considerable number of NiPc combine with Fe3O4 nanoparticles and on the surface of the accumulators to form NiPc-Fe3O4 nanoparticles composite. All the processes above take place spontaneously. Inside the NiPc-Fe3O4 nanoparticles complex, Fe3O4 nanoparticles accumulate together without order, on the surface of composite, NiPc form a molecular dispersion layer. The threshold of the molecular dispersion layer is 0.06 g/g(Fe3O4).
In this article, the complex process of phthalocyanine nickel with Fe3O4 nanoparticles has been analyzed, the complex mechanism and the structure model for NiPc-Fe3O4 nanoparticles composite have been studied. For the complexes mechanism of NiPc with Fe3O4 nanoparticles, first, there are complex between NiPc and all Fe3O4 nanoparticles. Then, Fe3O4 nanoparticles accumulate together to form the accumulators; NiPc have the function of cohering Fe3O4 nanoparticles. A considerable number of NiPc combine with Fe3O4 nanoparticles and on the surface of the accumulators to form NiPc-Fe3O4 nanoparticles composite. All the processes above take place spontaneously. Inside the NiPc-Fe3O4 nanoparticles complex, Fe3O4 nanoparticles accumulate together without order, on the surface of composite, NiPc form a molecular dispersion layer. The threshold of the molecular dispersion layer is 0.06 g/g(Fe3O4).
2001, 18(2): 85-88.
Abstract:
Effects of through-thickness stitching on Mode II interlaminar fracture toughness(GII) and modes of delamination of composite laminates were investigated by performing end-notched flexure(ENF) tests. Vertical displacement of loading point and crack shear displacement(CSD) between upper and lower crack surfaces at the end of ENF specimens were measured. Different stitch yarns and stitch densities were considered. The addition of stitching was found to decrease the initiation interlaminar fracture toughness GIIi, but can effectively suppress the growth of delamination.
Effects of through-thickness stitching on Mode II interlaminar fracture toughness(GII) and modes of delamination of composite laminates were investigated by performing end-notched flexure(ENF) tests. Vertical displacement of loading point and crack shear displacement(CSD) between upper and lower crack surfaces at the end of ENF specimens were measured. Different stitch yarns and stitch densities were considered. The addition of stitching was found to decrease the initiation interlaminar fracture toughness GIIi, but can effectively suppress the growth of delamination.
2001, 18(2): 90-93.
Abstract:
The bending problem of thin film/substrate composite subjected to thermal load is studied. The relation between the thermal expansion coefficient of conductive thin films, temperature and deformation of specimen surfaces is derived in this paper. Based on the findings, a method for measuring the thermal expansion coefficient of conductive thin films is developed. The thermal expansion coefficient of conductive thin films has been measured by applying the method in a thermal bend test.
The bending problem of thin film/substrate composite subjected to thermal load is studied. The relation between the thermal expansion coefficient of conductive thin films, temperature and deformation of specimen surfaces is derived in this paper. Based on the findings, a method for measuring the thermal expansion coefficient of conductive thin films is developed. The thermal expansion coefficient of conductive thin films has been measured by applying the method in a thermal bend test.
2001, 18(2): 93-96.
Abstract:
The district climate was described as year-accumulative-temperature, year-accumulative-temperature equivalence, year-accumulative-humidity, year-accumulative-humidity equivalence, year-accumulative-UV(ultra-violet) irradiant and year-accumulative-UV irradiant equivalence in this paper. These parameters were used to calculate atmospheric aging and in-service aging among different districts. The equivalence relationship between the accelerated aging environment and the atmospheric aging environment was created in this paper, and some examples were cited in illustrating the equivalence relationship.
The district climate was described as year-accumulative-temperature, year-accumulative-temperature equivalence, year-accumulative-humidity, year-accumulative-humidity equivalence, year-accumulative-UV(ultra-violet) irradiant and year-accumulative-UV irradiant equivalence in this paper. These parameters were used to calculate atmospheric aging and in-service aging among different districts. The equivalence relationship between the accelerated aging environment and the atmospheric aging environment was created in this paper, and some examples were cited in illustrating the equivalence relationship.
2001, 18(2): 97-101.
Abstract:
A continuous model for determining the buckling strains of stitched laminates including arbitrary embedded delamination is developed. The analysis allows stitched laminates to have a multiple number of delminations of various shapes and sizes, and at any locations. The method treats the discontinuous laminates as a body without delamination but with a force system added at a number of discrete points in the delaminated region so as to make the net interfacial tractions to vanish at these points. Hence, the procedure solves problems of delaminated stitched laminates directly as a continuous system. Numerical results accounting for the effects of location of stitches in the delamination region, stitching density, and equivalent stiffness coefficient of stitching thread on buckling strains are presented.
A continuous model for determining the buckling strains of stitched laminates including arbitrary embedded delamination is developed. The analysis allows stitched laminates to have a multiple number of delminations of various shapes and sizes, and at any locations. The method treats the discontinuous laminates as a body without delamination but with a force system added at a number of discrete points in the delaminated region so as to make the net interfacial tractions to vanish at these points. Hence, the procedure solves problems of delaminated stitched laminates directly as a continuous system. Numerical results accounting for the effects of location of stitches in the delamination region, stitching density, and equivalent stiffness coefficient of stitching thread on buckling strains are presented.
2001, 18(2): 102-108.
Abstract:
The transverse loading state of a laminate with elliptical delaminations is decomposed by means of the principle of superposition, so the problem of delamination can be reduced to the analysis of the additional displacements and stresses caused by the additional shear loading acting on the delamination surfaces, and thus a simple mechanics model of the delamination area is established. The laminate sections parallel to the coordinate planes can be regarded as laminated beams with delaminations, the displacements of which can be expressed by the analytical solutions of the additional displacements in the above beams. In this way, the additional displacement fields satisfying the displacement boundary condition of the delamination area can be established. Finally, a closed form solution of additional displacements is obtained by the principle of minimum potential energy. The above results are compared with the convergent solutions obtained by the method of trigonometric series. It shows that the deflections acquired from two different ways agree with each other very well and are greater than the in plane displacements by 1~2 order of magnitude.
The transverse loading state of a laminate with elliptical delaminations is decomposed by means of the principle of superposition, so the problem of delamination can be reduced to the analysis of the additional displacements and stresses caused by the additional shear loading acting on the delamination surfaces, and thus a simple mechanics model of the delamination area is established. The laminate sections parallel to the coordinate planes can be regarded as laminated beams with delaminations, the displacements of which can be expressed by the analytical solutions of the additional displacements in the above beams. In this way, the additional displacement fields satisfying the displacement boundary condition of the delamination area can be established. Finally, a closed form solution of additional displacements is obtained by the principle of minimum potential energy. The above results are compared with the convergent solutions obtained by the method of trigonometric series. It shows that the deflections acquired from two different ways agree with each other very well and are greater than the in plane displacements by 1~2 order of magnitude.
2001, 18(2): 109-113.
Abstract:
A prediction of the elastic property and strength of woven composites was established. Corresponding experimental studies were completed. The effects of various structural and geometrical parameters on the properties of woven composites were studied systematically. Fabric micro-structural parameter determination for optimizing the elastic properties of woven composites was provided. A code with user-friendly interface has been developed to provide an efficient calculation tool in selecting the best fabric reinforcement for structural composites. Tensile and compressive strength after impact, residual fatigue strength and fatigue life were evaluated experimentally. A finite element analysis coupled with failure criteria was developed to predict the impact threshold energy of the composites. Equations of predicting the fatigue life for woven composites were provided. Comparison of experimental data with the prediction results shows good agreement, thus confirming the usefulness of the predictions.
A prediction of the elastic property and strength of woven composites was established. Corresponding experimental studies were completed. The effects of various structural and geometrical parameters on the properties of woven composites were studied systematically. Fabric micro-structural parameter determination for optimizing the elastic properties of woven composites was provided. A code with user-friendly interface has been developed to provide an efficient calculation tool in selecting the best fabric reinforcement for structural composites. Tensile and compressive strength after impact, residual fatigue strength and fatigue life were evaluated experimentally. A finite element analysis coupled with failure criteria was developed to predict the impact threshold energy of the composites. Equations of predicting the fatigue life for woven composites were provided. Comparison of experimental data with the prediction results shows good agreement, thus confirming the usefulness of the predictions.
2001, 18(2): 114-117.
Abstract:
The modulus of SMAs varied with the stage of phase transformation and it brought large recovery stress of restrained recovery. By laying Shape Memory Alloys(SMAs) wires in the composite material laminate,the property of the composite laminate was improved and strengthened. Besides, bending and torsion of the laminate can be found and governed.How to calculate the mechanics behavior correctly is the base of shape control and design and applying of shape memory alloy composite material structures.The nonlinear finite element analysis of the composite laminate includes the thermodynamic behavior and large deformation recovery of the SMAs wires,and by comparing the experimental result with the analytical result, some significant conclusion was obtained.
The modulus of SMAs varied with the stage of phase transformation and it brought large recovery stress of restrained recovery. By laying Shape Memory Alloys(SMAs) wires in the composite material laminate,the property of the composite laminate was improved and strengthened. Besides, bending and torsion of the laminate can be found and governed.How to calculate the mechanics behavior correctly is the base of shape control and design and applying of shape memory alloy composite material structures.The nonlinear finite element analysis of the composite laminate includes the thermodynamic behavior and large deformation recovery of the SMAs wires,and by comparing the experimental result with the analytical result, some significant conclusion was obtained.
2001, 18(2): 118-123.
Abstract:
A new method for calculating viscoelastic damping and energy loss of fiber composites is presented. Firstly, on the scale of lamina, the energy dissipation formula is obtained by using a damping matrix and the theory of linear anisotropic viscoelasticity. Then on the scale of laminate, an effective damping(loss) matrix is obtained by using an equivalent energy theory (including stored energy and dissipated energy). In terms of the effective damping matrix, the energy loss and specific damping of the laminate can be calculated by using the effective stress and effective strain. The key point is the derivation of the effective damping matrix, which is a function of damping coefficients, volume fraction, and stiffness coefficients of each lamina and the effective stiffness coefficients of the laminate. In this way, the energy loss of fiber composites under arbitrary loading can be computed, which is very important in the numerical analysis for viscoelastic material and structures. In the end, several numerical examples are given to show the reasonability of the model.
A new method for calculating viscoelastic damping and energy loss of fiber composites is presented. Firstly, on the scale of lamina, the energy dissipation formula is obtained by using a damping matrix and the theory of linear anisotropic viscoelasticity. Then on the scale of laminate, an effective damping(loss) matrix is obtained by using an equivalent energy theory (including stored energy and dissipated energy). In terms of the effective damping matrix, the energy loss and specific damping of the laminate can be calculated by using the effective stress and effective strain. The key point is the derivation of the effective damping matrix, which is a function of damping coefficients, volume fraction, and stiffness coefficients of each lamina and the effective stiffness coefficients of the laminate. In this way, the energy loss of fiber composites under arbitrary loading can be computed, which is very important in the numerical analysis for viscoelastic material and structures. In the end, several numerical examples are given to show the reasonability of the model.
2001, 18(2): 124-127.
Abstract:
In this paper, the formulation of the design optimization problem of materials with specific elastic properties is investigated. A shape optimization method is used to determine the microstructure shape of composite materials composed of two phases (a material phase and a void phase) in order to design composite materials with specific elastic properties, such as with zero Poisson's ratio. Microstructure topology is limited to honeycombed skeleton structure in a unit cell as this is the most easily manufactured. The optimal goal is to minimize the square of the differences between the components of effective elastic tensor and the desired (given) values of these components. The effective behavior of composite materials is evaluated by use of a finite element based numerical homogenization procedure. As an example, the design of materials with zero Poisson's ratio shows the procedure.
In this paper, the formulation of the design optimization problem of materials with specific elastic properties is investigated. A shape optimization method is used to determine the microstructure shape of composite materials composed of two phases (a material phase and a void phase) in order to design composite materials with specific elastic properties, such as with zero Poisson's ratio. Microstructure topology is limited to honeycombed skeleton structure in a unit cell as this is the most easily manufactured. The optimal goal is to minimize the square of the differences between the components of effective elastic tensor and the desired (given) values of these components. The effective behavior of composite materials is evaluated by use of a finite element based numerical homogenization procedure. As an example, the design of materials with zero Poisson's ratio shows the procedure.
