2018 Vol. 35, No. 10
2018, 35(10): 2601-2611.
doi: 10.13801/j.cnki.fhclxb.20171127.001
Abstract:
In order to study the feasibility and formability of the carbon fiber/epoxy composite laminates by rolling proces, it was prepared based on different process and curing scheme. The bending performance and the hot stamping properties of the laminate were analyzed by the three point bending test and stamping experiment. The microstructure of the sample section was observed. Finally, it was compared with the autoclave process. The results show that the comprehensive performance of the laminate obtained by 80℃ pre-curing-rolling-post-curing process is better than those of rolling-curing and curing-rolling process. Under the condition of reduction 0.4 mm, the maximum bending strength and modulus of the laminate increase by 23.8% and 17.4%, respectively, than that of the natural curing samples. Furthermore, the bending strength and modulus are higher than those of the autoclave process. On the stamping process, the reduction and preheating temperature have a significant effect on the forming of the sample. The reasonable reduction can improve the formability and elevated temperature is favorable for the sample formation, however, the higher temperature results in destruction of the specimen and the wrinkle increasing. The main damage area is the punch radius profile at the bottom of the sample, wrinkling along the latitude and longitude direction with fiber into a 45° angle area obvious. The difference of the process has a significant effect on the interlayer combination. Compared with the natural curing, the mechanical properties of the composites are improved after rolling. It provides reference for the recombination of carbon fiber reinforced plastic composite with metal material by rolling process.
In order to study the feasibility and formability of the carbon fiber/epoxy composite laminates by rolling proces, it was prepared based on different process and curing scheme. The bending performance and the hot stamping properties of the laminate were analyzed by the three point bending test and stamping experiment. The microstructure of the sample section was observed. Finally, it was compared with the autoclave process. The results show that the comprehensive performance of the laminate obtained by 80℃ pre-curing-rolling-post-curing process is better than those of rolling-curing and curing-rolling process. Under the condition of reduction 0.4 mm, the maximum bending strength and modulus of the laminate increase by 23.8% and 17.4%, respectively, than that of the natural curing samples. Furthermore, the bending strength and modulus are higher than those of the autoclave process. On the stamping process, the reduction and preheating temperature have a significant effect on the forming of the sample. The reasonable reduction can improve the formability and elevated temperature is favorable for the sample formation, however, the higher temperature results in destruction of the specimen and the wrinkle increasing. The main damage area is the punch radius profile at the bottom of the sample, wrinkling along the latitude and longitude direction with fiber into a 45° angle area obvious. The difference of the process has a significant effect on the interlayer combination. Compared with the natural curing, the mechanical properties of the composites are improved after rolling. It provides reference for the recombination of carbon fiber reinforced plastic composite with metal material by rolling process.
2018, 35(10): 2612-2623.
doi: 10.13801/j.cnki.fhclxb.20171130.001
Abstract:
Polypyrrole (PPy) was in-situ polymerized on the surface of biological template-cellulose nanofibers (CNFs) to form the CNF-PPy complexes, which further were uniformly dispersed into natural rubber (NR) elastomeric matrix to prepare CNF-PPy/NR conductive elastomers with high flexibility. The results show that CNFs can assist PPy to form a three-dimensional network structure in NR matrix, improve the mechanical properties and electrical conductivity of elastomers, and reduce the percolation threshold effectively. When adding 5% CNF(rubber mass as 100) and 20%PPy, the tensile strength of CNF-PPy/NR is (8.97±0.92) MPa, which is about 1.56 times of PPy/NR and 9.54 times of pure NR, respectively, and the conductivity is up to (0.134±0.063) S/m; At 0.3 A/g current density, the specific capacitance can reach 96 F/g, and it can still maintain its initial value of 72% in the cycle of charge and discharge 1 200 times with 1.0 A/g current density. The conductive elastomer exhibits good mechanical and electrical properties, which is expected to be applied in the field of flexible organic electronic devices.
Polypyrrole (PPy) was in-situ polymerized on the surface of biological template-cellulose nanofibers (CNFs) to form the CNF-PPy complexes, which further were uniformly dispersed into natural rubber (NR) elastomeric matrix to prepare CNF-PPy/NR conductive elastomers with high flexibility. The results show that CNFs can assist PPy to form a three-dimensional network structure in NR matrix, improve the mechanical properties and electrical conductivity of elastomers, and reduce the percolation threshold effectively. When adding 5% CNF(rubber mass as 100) and 20%PPy, the tensile strength of CNF-PPy/NR is (8.97±0.92) MPa, which is about 1.56 times of PPy/NR and 9.54 times of pure NR, respectively, and the conductivity is up to (0.134±0.063) S/m; At 0.3 A/g current density, the specific capacitance can reach 96 F/g, and it can still maintain its initial value of 72% in the cycle of charge and discharge 1 200 times with 1.0 A/g current density. The conductive elastomer exhibits good mechanical and electrical properties, which is expected to be applied in the field of flexible organic electronic devices.
2018, 35(10): 2624-2631.
doi: 10.13801/j.cnki.fhclxb.20171214.002
Abstract:
The photoinduced charge carrier dynamics is one of the important factors that affect the photocatalytic performace of semiconductor composites. In this work, tin oxides nano-particles were successfully fabricated by one-step solvent thermal method using SnCl2·2H2O as raw material and NaOH as precipitant. The fabricated samples were characterized by SEM, XRD, TEM and Uv-Vis spectra. The results show that about 10-20 nm particles size SnO-SnO2 composites and about 10 nm tetragonal SnO2 particles can be obtained by adjusting the reaction condition. Photocatalytic degradation performance of the above two nano-materials has been evaluated by using Rhodamine (RhB) as the degradation agent. The degradation time of RhB can be reduced by 50% by using nano SnO-SnO2 composites as photocatalyst compared with pure nano SnO2 particles. For further studying the mechanism for this result, transient surface photovoltage (TSPV) technique has been carried out to understand the photoinduced charge carrier dynamics of the resulting materials. The corresponding results show that the photoinduced charge carrier separation has been enhanced, the surface recombination of photoinduced charge carrier has been reduced, and the lifetime of photoinduced charge carrier on the material surface is prolonged by building the nano SnO-SnO2 composites. Finally, the consequent photocatalystic performance is enhanced.
The photoinduced charge carrier dynamics is one of the important factors that affect the photocatalytic performace of semiconductor composites. In this work, tin oxides nano-particles were successfully fabricated by one-step solvent thermal method using SnCl2·2H2O as raw material and NaOH as precipitant. The fabricated samples were characterized by SEM, XRD, TEM and Uv-Vis spectra. The results show that about 10-20 nm particles size SnO-SnO2 composites and about 10 nm tetragonal SnO2 particles can be obtained by adjusting the reaction condition. Photocatalytic degradation performance of the above two nano-materials has been evaluated by using Rhodamine (RhB) as the degradation agent. The degradation time of RhB can be reduced by 50% by using nano SnO-SnO2 composites as photocatalyst compared with pure nano SnO2 particles. For further studying the mechanism for this result, transient surface photovoltage (TSPV) technique has been carried out to understand the photoinduced charge carrier dynamics of the resulting materials. The corresponding results show that the photoinduced charge carrier separation has been enhanced, the surface recombination of photoinduced charge carrier has been reduced, and the lifetime of photoinduced charge carrier on the material surface is prolonged by building the nano SnO-SnO2 composites. Finally, the consequent photocatalystic performance is enhanced.
2018, 35(10): 2632-2639.
doi: 10.13801/j.cnki.fhclxb.20171218.001
Abstract:
Polyamic acid(PAA) spinning solution was fabricated by using benzophenone-3,3',4,4'-tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether as raw materials, and the polyimide(PI) fiber membranes were prepared by high-pressure electrospinning and thermal imidization. Then, lithium ethylene-vinyl alcohol copolymer sulfate(EVOH-SO3Li)/PI li-ion battery separator composites were prepared by introduction of EVOH-SO3Li fiber on both sides of PI membranes surface through high-pressure electrospinning and heating pressure treatment. The performance of EVOH-SO3Li/PI li-ion battery separator composite was characterized by FTIR, SEM, universal tensile tester, contact angle meter and IM6 electrochemical workstation. The results show that EVOH-SO3Li/PI separator has a clear three-dimensional network structure. Compared with PI separator, the absorption rate and tensile strength of modified EVOH-SO3Li/PI separator composites increase to 521% and 12.83 MPa although the porosity reduces. The excellent thermal shrinkage rate, closed-cell at high temperature and electrochemical performance were exhibited. Then, the electrochemical window increases from 5.5 V to 5.8 V, the bulk resistance decreases from 360 Ω to 315 Ω, and the ion conductivity increases from 2.416×10-3 S/cm to 3.672×10-3 S/cm.
Polyamic acid(PAA) spinning solution was fabricated by using benzophenone-3,3',4,4'-tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether as raw materials, and the polyimide(PI) fiber membranes were prepared by high-pressure electrospinning and thermal imidization. Then, lithium ethylene-vinyl alcohol copolymer sulfate(EVOH-SO3Li)/PI li-ion battery separator composites were prepared by introduction of EVOH-SO3Li fiber on both sides of PI membranes surface through high-pressure electrospinning and heating pressure treatment. The performance of EVOH-SO3Li/PI li-ion battery separator composite was characterized by FTIR, SEM, universal tensile tester, contact angle meter and IM6 electrochemical workstation. The results show that EVOH-SO3Li/PI separator has a clear three-dimensional network structure. Compared with PI separator, the absorption rate and tensile strength of modified EVOH-SO3Li/PI separator composites increase to 521% and 12.83 MPa although the porosity reduces. The excellent thermal shrinkage rate, closed-cell at high temperature and electrochemical performance were exhibited. Then, the electrochemical window increases from 5.5 V to 5.8 V, the bulk resistance decreases from 360 Ω to 315 Ω, and the ion conductivity increases from 2.416×10-3 S/cm to 3.672×10-3 S/cm.
2018, 35(10): 2640-2650.
doi: 10.13801/j.cnki.fhclxb.20180115.006
Abstract:
In order to research the rapid prototyping of fiber reinforced composite parts and accelerate large-scale industrial mass production of composite parts, glass fiber/polypropylene composite laminate was selected to be the experimental object. First, the deep drawing test of glass fiber reinforced thermoplastic resin composite (GFRTP), the outer surface fiber orientation of the sheet and in the long axis direction of 0° and 90° at different temperatures were carried out by using the deep drawing mold. Metallographic specimens were prepared by microstructure observation under a light microscope. The molding of the specimen and the different drawing force-stroke curve were analyzed. The shallow drawing test of the GFRTP along the fiber direction of sheet surface and the direction of the long axis of the mold 0°, 45° and 90° at different temperatures was carried out. Tensile properties were tested at room temperature using the molded test piece. The tensile failure and the specific mechanical properties were compared and analyzed. The results show that, between room temperature of 25℃ and the base resin melting temperature of 165℃, the ultimate drawing depth of the plate increases with the increase of the temperature, and the maximum drawing force decreases.In the range of the selected test temperature, the formability of the specimen at 85℃ is better and the specimen at 0° is better than the specimen at 90°. The temperature does not improve the wrinkle of the specimen.The tensile mechanical properties of the specimen are greatly affected by the direction of the laying fiber of the specimen, and it is very important to prevent the occurrence of defects such as wrinkles.
In order to research the rapid prototyping of fiber reinforced composite parts and accelerate large-scale industrial mass production of composite parts, glass fiber/polypropylene composite laminate was selected to be the experimental object. First, the deep drawing test of glass fiber reinforced thermoplastic resin composite (GFRTP), the outer surface fiber orientation of the sheet and in the long axis direction of 0° and 90° at different temperatures were carried out by using the deep drawing mold. Metallographic specimens were prepared by microstructure observation under a light microscope. The molding of the specimen and the different drawing force-stroke curve were analyzed. The shallow drawing test of the GFRTP along the fiber direction of sheet surface and the direction of the long axis of the mold 0°, 45° and 90° at different temperatures was carried out. Tensile properties were tested at room temperature using the molded test piece. The tensile failure and the specific mechanical properties were compared and analyzed. The results show that, between room temperature of 25℃ and the base resin melting temperature of 165℃, the ultimate drawing depth of the plate increases with the increase of the temperature, and the maximum drawing force decreases.In the range of the selected test temperature, the formability of the specimen at 85℃ is better and the specimen at 0° is better than the specimen at 90°. The temperature does not improve the wrinkle of the specimen.The tensile mechanical properties of the specimen are greatly affected by the direction of the laying fiber of the specimen, and it is very important to prevent the occurrence of defects such as wrinkles.
2018, 35(10): 2651-2657.
doi: 10.13801/j.cnki.fhclxb.20180524.001
Abstract:
The nano-hydroxyapatite (HA) was prepared by coprecipitation method, and the surface was modified by grafting silane coupling agent KH560. Then, the HA/polyether ether ketone (PEEK) composites with 10wt% as-synthesized or surface-modified HA were prepared by hot-press moulding procedure. The effects of different HA on the structure, dynamic mechanical and tribological properties of the composites were investigated. The HA/PEEK composites were characterized by XRD, FTIR, FESEM, tensile test, DMA and friction test. The results show that silane coupling agent KH560 is grafted onto the surface of HA, and the crystal structure of as-synthesized and surface-unmodified HA shows no distinct change. In addition, the addition of different HA into PEEK matrix has almost no influence on the crystal structure of PEEK. Besides, the modified HA is homogeneously dispersed in PEEK matrix. Compared with pure PEEK, the PEEK with the addition of 10wt% surface-modified HA is improved in the storage modulus and glass transition temperature by about 55.56% and 3.6℃, respectively, and reduced in the scratching depth by about 31.1%. Therefore, the thermodynamic and tribological properties of the composites are greatly improved. The tensile strength of surface-modified HA/PEEK composites is 68.33 MPa, which can match well with the strength requirement of human bones.
The nano-hydroxyapatite (HA) was prepared by coprecipitation method, and the surface was modified by grafting silane coupling agent KH560. Then, the HA/polyether ether ketone (PEEK) composites with 10wt% as-synthesized or surface-modified HA were prepared by hot-press moulding procedure. The effects of different HA on the structure, dynamic mechanical and tribological properties of the composites were investigated. The HA/PEEK composites were characterized by XRD, FTIR, FESEM, tensile test, DMA and friction test. The results show that silane coupling agent KH560 is grafted onto the surface of HA, and the crystal structure of as-synthesized and surface-unmodified HA shows no distinct change. In addition, the addition of different HA into PEEK matrix has almost no influence on the crystal structure of PEEK. Besides, the modified HA is homogeneously dispersed in PEEK matrix. Compared with pure PEEK, the PEEK with the addition of 10wt% surface-modified HA is improved in the storage modulus and glass transition temperature by about 55.56% and 3.6℃, respectively, and reduced in the scratching depth by about 31.1%. Therefore, the thermodynamic and tribological properties of the composites are greatly improved. The tensile strength of surface-modified HA/PEEK composites is 68.33 MPa, which can match well with the strength requirement of human bones.
2018, 35(10): 2658-2664.
doi: 10.13801/j.cnki.fhclxb.20171115.009
Abstract:
Using the cloth of glass fiber and nonwovens of polyphenylene sulfide (PPS) as reinforcement and matrix, the glass fiber cloth/PPS nonwoven composite boards were prepared by hot pressing which were put in the oven for heat treatment. The mechanical properties, crystallinity, type and size of grain and micro morphology of glass fiber cloth/PPS nonwoven composite boards were tested and characterized by Instron, XRD, polarizing microscope(PLM) and SEM. The results show that the bending strength, flexural modulus and notched impact strength of the composite board are obviously improved with the increase of the temperature and time of heat treatment. When the temperature of heat treatment is 220℃ and the time of heat treatment is 2 h, the mechanical properties of the composite board are the best. The bending strength, flexural modulus and notched impact strength are 285.7 MPa, 7.8 GPa and 85.0 MPa, respectively, increased by 63.2%, 469.0% and 37.8%, compared with those without heat treatment. The micro morphologies of the glass fiber cloth/PPS nonwoven composite boards show that the interfacial adhesion has been greatly improved.
Using the cloth of glass fiber and nonwovens of polyphenylene sulfide (PPS) as reinforcement and matrix, the glass fiber cloth/PPS nonwoven composite boards were prepared by hot pressing which were put in the oven for heat treatment. The mechanical properties, crystallinity, type and size of grain and micro morphology of glass fiber cloth/PPS nonwoven composite boards were tested and characterized by Instron, XRD, polarizing microscope(PLM) and SEM. The results show that the bending strength, flexural modulus and notched impact strength of the composite board are obviously improved with the increase of the temperature and time of heat treatment. When the temperature of heat treatment is 220℃ and the time of heat treatment is 2 h, the mechanical properties of the composite board are the best. The bending strength, flexural modulus and notched impact strength are 285.7 MPa, 7.8 GPa and 85.0 MPa, respectively, increased by 63.2%, 469.0% and 37.8%, compared with those without heat treatment. The micro morphologies of the glass fiber cloth/PPS nonwoven composite boards show that the interfacial adhesion has been greatly improved.
2018, 35(10): 2665-2677.
doi: 10.13801/j.cnki.fhclxb.20171120.002
Abstract:
The complex forming process of the composite material leads to low manufacturing precision. Assembly gap will be created between the mating surfaces due to the deviation of composite parts. Gap-filling needs to be taken when the thickness of gap exceeds a certain extent. Based on a simplified assembly model, the effect of liquid shim on strain and stress of composite assembly structure with bolt pre-tightening force was studied by means of experiment and finite element analysis. The surface strain under two conditions was compared to analyze the deformation of composite parts, including forced assembly situation and gap-filling situation with liquid shim. The strength ratio was calculated by extracting stress component of element integral points. And the effect of liquid shim on stress of composite assembly structure based on strength ratio was obtained. The primary conclusions are as follows:The area on composite near the edge of the assembly gap is affected by the assembly gap more greatly during forced assembly, while the impact of gap on middle section is relatively small because assembly gap disappears in this area under the clamping force. Liquid shim is helpful to improve the strain state of danger zone near the edge of the assembly gap, but the strain of the compression zone contacting with bolt head which located in middle section of composite is increased due to introduction of liquid shim. Overall, liquid shim makes the strain distribution more uniform. When the assembly gap thickness is more than 0.7 mm, the effect of liquid shim that enhances the strength ratio of the component shows obvious downward trend with the increase of assembly gap thickness.
The complex forming process of the composite material leads to low manufacturing precision. Assembly gap will be created between the mating surfaces due to the deviation of composite parts. Gap-filling needs to be taken when the thickness of gap exceeds a certain extent. Based on a simplified assembly model, the effect of liquid shim on strain and stress of composite assembly structure with bolt pre-tightening force was studied by means of experiment and finite element analysis. The surface strain under two conditions was compared to analyze the deformation of composite parts, including forced assembly situation and gap-filling situation with liquid shim. The strength ratio was calculated by extracting stress component of element integral points. And the effect of liquid shim on stress of composite assembly structure based on strength ratio was obtained. The primary conclusions are as follows:The area on composite near the edge of the assembly gap is affected by the assembly gap more greatly during forced assembly, while the impact of gap on middle section is relatively small because assembly gap disappears in this area under the clamping force. Liquid shim is helpful to improve the strain state of danger zone near the edge of the assembly gap, but the strain of the compression zone contacting with bolt head which located in middle section of composite is increased due to introduction of liquid shim. Overall, liquid shim makes the strain distribution more uniform. When the assembly gap thickness is more than 0.7 mm, the effect of liquid shim that enhances the strength ratio of the component shows obvious downward trend with the increase of assembly gap thickness.
2018, 35(10): 2678-2688.
doi: 10.13801/j.cnki.fhclxb.20171127.002
Abstract:
In order to obtain a new way of connection between composite material and aluminum-alloy, the tooth connection between GFRP tube and aluminum-alloy tube with filament winding was proposed. The tensile experiments on two-group specimens of the tooth connect between GFRP tube and aluminum alloy tubes were conducted. The failure model, load-displacement relationship and load-axial strain relationship were documented during the loading process. The failure mechanism of the tooth connection between GFRP tube and aluminum-alloy tube subject to tension was numerically explored. The results show that the failure model for specimen of the connection is one-by-one shear failure of GFRP tube teeth, the failure process appears the ductility feature and larger axial displacement, and the average ultimate tensile stress of GFRP tube is 213.22 MPa; the connection carries the axial force through interlaminar shear of the teeth, the teeth of GFRP tube is the weak part when the connection was stressed and different teeth endure different load distribution; the failure of teeth originate from the angular point of the root of teeth.
In order to obtain a new way of connection between composite material and aluminum-alloy, the tooth connection between GFRP tube and aluminum-alloy tube with filament winding was proposed. The tensile experiments on two-group specimens of the tooth connect between GFRP tube and aluminum alloy tubes were conducted. The failure model, load-displacement relationship and load-axial strain relationship were documented during the loading process. The failure mechanism of the tooth connection between GFRP tube and aluminum-alloy tube subject to tension was numerically explored. The results show that the failure model for specimen of the connection is one-by-one shear failure of GFRP tube teeth, the failure process appears the ductility feature and larger axial displacement, and the average ultimate tensile stress of GFRP tube is 213.22 MPa; the connection carries the axial force through interlaminar shear of the teeth, the teeth of GFRP tube is the weak part when the connection was stressed and different teeth endure different load distribution; the failure of teeth originate from the angular point of the root of teeth.
2018, 35(10): 2689-2697.
doi: 10.13801/j.cnki.fhclxb.20171108.003
Abstract:
The purpose of this paper was to investigate the stiffener impact damage and its effect on compression after impact (CAI) behavior of T-stiffened composite panels. For single T-stringer stiffened panels, low-velocity impact was conducted on the stiffener with a drop hammer over the panel at five energy levels. The impact experiments reveal that, the panel dent is almost invisible after stiffener impact. Besides, before the impact energy reaches the threshold value, there is no damage occurring in the stiffener and stiffener-panel is not debonding either. However, once the impact energy exceeds the threshold value, the stiffener will be damaged under bending tensile stress, meanwhile the stiffener-panel will debond severely. Compression tests were performed on intact and damaged specimens. The tests show that, when no damage is induced in the stiffener, the low velocity impact has little effect on buckling behavior of the stiffened panel while the failure load is reduced slightly. However, after the stiffener is damaged by impact, the stiffener will unload due to the damage growth during the compression process. The unloading of stiffener can weaken the support for the panel and thus decreases the panel buckling load, which can dramatically reduce the load carrying capacity of the stiffened panel.
The purpose of this paper was to investigate the stiffener impact damage and its effect on compression after impact (CAI) behavior of T-stiffened composite panels. For single T-stringer stiffened panels, low-velocity impact was conducted on the stiffener with a drop hammer over the panel at five energy levels. The impact experiments reveal that, the panel dent is almost invisible after stiffener impact. Besides, before the impact energy reaches the threshold value, there is no damage occurring in the stiffener and stiffener-panel is not debonding either. However, once the impact energy exceeds the threshold value, the stiffener will be damaged under bending tensile stress, meanwhile the stiffener-panel will debond severely. Compression tests were performed on intact and damaged specimens. The tests show that, when no damage is induced in the stiffener, the low velocity impact has little effect on buckling behavior of the stiffened panel while the failure load is reduced slightly. However, after the stiffener is damaged by impact, the stiffener will unload due to the damage growth during the compression process. The unloading of stiffener can weaken the support for the panel and thus decreases the panel buckling load, which can dramatically reduce the load carrying capacity of the stiffened panel.
2018, 35(10): 2698-2705.
doi: 10.13801/j.cnki.fhclxb.20171220.001
Abstract:
The high efficiency load transferred scarf joints have been applied widely in composite junctions and repairs. However, the damage resistance and damage tolerance were not considered in aircraft structure design. The mechanical and fracture properties of composite scarf repair under low velocity impact were investigated. In the bonded zone, different impact locations were set to found the most sensitive location. Then at this position the variation of impact energy was studied. Low impact energy level and high energy level studies imply that the central position has the lowest impact resistance. Impact responses of impact load reveal that four typical phases exist during impact procedure. The impact load has double peak forces phenomenon. The first peak keeps constant while the second one rises with the increase of impact energy. From the failure investigating on the central section, it is found that there are two damage modes of the composites laminates and the adhesive. Composite damage contains the matrix crack on 90ånd 45° plies and the delamination between 0° and 90° plies. Adhesive damage appears at the backside of specimen opposite to the impact location. Further study of simulation reveals the whole impact behavior of the composite scarf repair. The composite damage leads to impact load dropping at PhaseⅡ, and adhesive damage causes the impact load dropping again at the beginning of phase Ⅳ.
The high efficiency load transferred scarf joints have been applied widely in composite junctions and repairs. However, the damage resistance and damage tolerance were not considered in aircraft structure design. The mechanical and fracture properties of composite scarf repair under low velocity impact were investigated. In the bonded zone, different impact locations were set to found the most sensitive location. Then at this position the variation of impact energy was studied. Low impact energy level and high energy level studies imply that the central position has the lowest impact resistance. Impact responses of impact load reveal that four typical phases exist during impact procedure. The impact load has double peak forces phenomenon. The first peak keeps constant while the second one rises with the increase of impact energy. From the failure investigating on the central section, it is found that there are two damage modes of the composites laminates and the adhesive. Composite damage contains the matrix crack on 90ånd 45° plies and the delamination between 0° and 90° plies. Adhesive damage appears at the backside of specimen opposite to the impact location. Further study of simulation reveals the whole impact behavior of the composite scarf repair. The composite damage leads to impact load dropping at PhaseⅡ, and adhesive damage causes the impact load dropping again at the beginning of phase Ⅳ.
2018, 35(10): 2706-2714.
doi: 10.13801/j.cnki.fhclxb.20171228.002
Abstract:
In order to investigate the fatigue behaviors of 3D woven composites under tension-compression cyclic loading, fatigue tests which had a stress ratio of R=-1 were conducted. Under different loading levels, weft and warp fatigue tests were conducted. The hysteresis loops and curves of residual stiffness ratio via fatigue life were obtained. It is implicated that the fatigued damage progress of 3D woven composites under tension-compression cyclic loading mainly contains three stages:the failure of matrix, transverse crack propagation inside the yarns and the fracture of yarns occur in sequence. The crush and debonding of matrix, the avulsion of yarns which is perpendicular to the loading direction and the fracture of yarn which is along the loading direction are major failure modes. The fitted tension-compression fatigue S-N curves were also obtained, which can be applied in engineering to estimate fatigue life of this type of material. Both fatigue life in low and high stress region show small variance. The fitting S-N curves have good linearity in the double logarithm coordinate.
In order to investigate the fatigue behaviors of 3D woven composites under tension-compression cyclic loading, fatigue tests which had a stress ratio of R=-1 were conducted. Under different loading levels, weft and warp fatigue tests were conducted. The hysteresis loops and curves of residual stiffness ratio via fatigue life were obtained. It is implicated that the fatigued damage progress of 3D woven composites under tension-compression cyclic loading mainly contains three stages:the failure of matrix, transverse crack propagation inside the yarns and the fracture of yarns occur in sequence. The crush and debonding of matrix, the avulsion of yarns which is perpendicular to the loading direction and the fracture of yarn which is along the loading direction are major failure modes. The fitted tension-compression fatigue S-N curves were also obtained, which can be applied in engineering to estimate fatigue life of this type of material. Both fatigue life in low and high stress region show small variance. The fitting S-N curves have good linearity in the double logarithm coordinate.
2018, 35(10): 2715-2722.
doi: 10.13801/j.cnki.fhclxb.20180209.007
Abstract:
Using MTS-810 material testing machine, Zwick-HTM5020 high speed tensile testing machine and split Hopkinson tension bar (SHTB) apparatus, combined with digital image correlation method, the tensile mechanical properties of the E glass fiber reinforced epoxy resin composites were studied systematically in the range of strain rates of 10-3-2 400 s-1.The stress-strain curves under different strain rates were obtained, and the influences of strain rate on tensile strength and fracture strain were investigated. The fracture morphology of the tensile specimen was analyzed, and the dependence of fracture mechanism on the strain rate was explored. The results reveal that the normalized tensile strength increases linearly with the logarithm of strain rate, while the normalized fracture strain decreases linearly with the log strain rate. Fractography shows that the main fracture mode of the specimen is shear fracture along 45° direction at low strain rate. With the increasing of strain rate, the fracture mode gradually transforms shear fracture to axial tensile fracture. At high strain rate, it is observed that a large number of glass fibers are broken, and the epoxy resin matrix has serious fragmentation phenomenon, which reflects the strong restraint effect between the epoxy resin matrix and the glass fiber.
Using MTS-810 material testing machine, Zwick-HTM5020 high speed tensile testing machine and split Hopkinson tension bar (SHTB) apparatus, combined with digital image correlation method, the tensile mechanical properties of the E glass fiber reinforced epoxy resin composites were studied systematically in the range of strain rates of 10-3-2 400 s-1.The stress-strain curves under different strain rates were obtained, and the influences of strain rate on tensile strength and fracture strain were investigated. The fracture morphology of the tensile specimen was analyzed, and the dependence of fracture mechanism on the strain rate was explored. The results reveal that the normalized tensile strength increases linearly with the logarithm of strain rate, while the normalized fracture strain decreases linearly with the log strain rate. Fractography shows that the main fracture mode of the specimen is shear fracture along 45° direction at low strain rate. With the increasing of strain rate, the fracture mode gradually transforms shear fracture to axial tensile fracture. At high strain rate, it is observed that a large number of glass fibers are broken, and the epoxy resin matrix has serious fragmentation phenomenon, which reflects the strong restraint effect between the epoxy resin matrix and the glass fiber.
2018, 35(10): 2723-2729.
doi: 10.13801/j.cnki.fhclxb.20171128.007
Abstract:
A modified Arcan fixture was used in this paper to study the damage of notched fiber reinforced compo-sites under complex loading.Notched carbon-fiber reinforced composite specimens([-45/90/45/0]s) were tested under combined tension and shear loading by stretching along 30°direction.The development of cracking in the surface ply of the laminates was measured by the digital image correlation method (DICM), and obvious splitting phenomena is observed at the notch tips. Afterwards a 3D laminate model was developed by finite element software ABAQUS. To capture the true stress concentration at the notch tips, cohesive contact zones were introduced in the model to simulate the splitting in each ply.In order to clarify the effect of rotational degree of freedom at the loading ends on the failure mechanisms and strengths of the laminates, two different boundary conditions were studied, i.e. constraining or relaxing the rotational degree of freedom.The result shows that the direction of resultant force dominates the failure mechanisms and strengths of the laminates. The simulation results with relaxed rotational degree of freedom are in good agreement with the experiments.
A modified Arcan fixture was used in this paper to study the damage of notched fiber reinforced compo-sites under complex loading.Notched carbon-fiber reinforced composite specimens([-45/90/45/0]s) were tested under combined tension and shear loading by stretching along 30°direction.The development of cracking in the surface ply of the laminates was measured by the digital image correlation method (DICM), and obvious splitting phenomena is observed at the notch tips. Afterwards a 3D laminate model was developed by finite element software ABAQUS. To capture the true stress concentration at the notch tips, cohesive contact zones were introduced in the model to simulate the splitting in each ply.In order to clarify the effect of rotational degree of freedom at the loading ends on the failure mechanisms and strengths of the laminates, two different boundary conditions were studied, i.e. constraining or relaxing the rotational degree of freedom.The result shows that the direction of resultant force dominates the failure mechanisms and strengths of the laminates. The simulation results with relaxed rotational degree of freedom are in good agreement with the experiments.
2018, 35(10): 2730-2744.
doi: 10.13801/j.cnki.fhclxb.20171206.005
Abstract:
Experiments and simulations were carried out in this paper to investigate the lightning protection performance of carbon fiber reinforced polymer(CFRP) sprayed with aluminum particles. Results of lightning strike process(LSP) observation, damage test and ultrasonic C-scan show that direct effects of lightning strike can cause obvious external damages to unprotected CFRPs, and Joule heating effect will sustain after lightning current injected into the structure to cause more serious internal damages. Lightning tests implemented to CFRPs with aluminum particles sprayed all top surface show that aluminum coating can significantly reduce the damage area caused by lightning strike on top surface of CFRP, and the thicker the coating is, the better the LSP effect is. Based on experimental results, coupled thermal-electrical analysis models of unprotected CFRP, CFRP with fully sprayed and cruciform aluminum coating were built with temperature dependent material properties, and then testified by comparing with the experimental results. After that, protection performance of sprayed aluminum coating under idealized lightning current component A was discussed with the analysis model. Results show that the percentage of damage area of CFRP and the percentage of mass increase of the structure is optimized at the thickness of 0.19 mm for fully sprayed aluminum coating, and the branch for lightning conduction should be wider than 20 mm for cruciform aluminum coating, while the other branch can be minimized as needed.
Experiments and simulations were carried out in this paper to investigate the lightning protection performance of carbon fiber reinforced polymer(CFRP) sprayed with aluminum particles. Results of lightning strike process(LSP) observation, damage test and ultrasonic C-scan show that direct effects of lightning strike can cause obvious external damages to unprotected CFRPs, and Joule heating effect will sustain after lightning current injected into the structure to cause more serious internal damages. Lightning tests implemented to CFRPs with aluminum particles sprayed all top surface show that aluminum coating can significantly reduce the damage area caused by lightning strike on top surface of CFRP, and the thicker the coating is, the better the LSP effect is. Based on experimental results, coupled thermal-electrical analysis models of unprotected CFRP, CFRP with fully sprayed and cruciform aluminum coating were built with temperature dependent material properties, and then testified by comparing with the experimental results. After that, protection performance of sprayed aluminum coating under idealized lightning current component A was discussed with the analysis model. Results show that the percentage of damage area of CFRP and the percentage of mass increase of the structure is optimized at the thickness of 0.19 mm for fully sprayed aluminum coating, and the branch for lightning conduction should be wider than 20 mm for cruciform aluminum coating, while the other branch can be minimized as needed.
2018, 35(10): 2745-2752.
doi: 10.13801/j.cnki.fhclxb.20180115.007
Abstract:
In this paper, the finite element method was used to simulate and analyze the tensile properties of several pre-molded lap composites with different lamination sequences respectively. The corresponding joggle-lap joint samples were prepared by using domestic carbon fiber and rapid curing epoxy resin. The tensile properties of the lap were tested, and the results of finite element calculation were verified. The calculated results obtained by finite element method are basically consistent with the experimental results. It's found that there are two different failure modes of the preform lap joints with different stacking sequence. The interlaminar peel strength and the flexual property of the plate both determine the failure mode and tensile performance.The weaker damages first, resulting in the failure of the sample. In the preform lap joint, the closer the 0° ply lay to the lap face, the more obvious the influence on lap bonding performance is, and the lap strength performs better. And different relative angle between the fiber layers leads to different stiffnesses distinction. The bigger the difference is, the weaker the joint performs.
In this paper, the finite element method was used to simulate and analyze the tensile properties of several pre-molded lap composites with different lamination sequences respectively. The corresponding joggle-lap joint samples were prepared by using domestic carbon fiber and rapid curing epoxy resin. The tensile properties of the lap were tested, and the results of finite element calculation were verified. The calculated results obtained by finite element method are basically consistent with the experimental results. It's found that there are two different failure modes of the preform lap joints with different stacking sequence. The interlaminar peel strength and the flexual property of the plate both determine the failure mode and tensile performance.The weaker damages first, resulting in the failure of the sample. In the preform lap joint, the closer the 0° ply lay to the lap face, the more obvious the influence on lap bonding performance is, and the lap strength performs better. And different relative angle between the fiber layers leads to different stiffnesses distinction. The bigger the difference is, the weaker the joint performs.
2018, 35(10): 2753-2759.
doi: 10.13801/j.cnki.fhclxb.20180105.001
Abstract:
The void distribution of carbon fibre reinforced plastics (CFRP) has an important effect on its mechanical properties. Focusing on this problem, recurrence quantification analysis (RQA) of ultrasonic back-scatter signals was proposed to characterize void size and position distribution. Three groups of CFRP models with spherical voids were established, in which each model had different void position distribution. The void diameters D ranged from 26 μm to 70 μm, and the distance d of voids was 0.21 mm, 0.14 mm and 0.09 mm, respectively. Based on these models, the back-scatter signals were analyzed by RQA method. The simulated study shows that, recurrence rate PRR decreases with D increasing when the void position distribution is the same. If the void size distribution is the same, PRR increases with d decreasing. The PRR of models with d=0.09 mm are always higher than the other two groups. There is significant difference in PRR between d=0.14 mm and d=0.21 mm models when D<50 μm. But the difference is small when D ≥ 50 μm. The results demonstrate that there is difference in PRR on different void distributions, PRR can be used to characterize different void distributions in CFRP.
The void distribution of carbon fibre reinforced plastics (CFRP) has an important effect on its mechanical properties. Focusing on this problem, recurrence quantification analysis (RQA) of ultrasonic back-scatter signals was proposed to characterize void size and position distribution. Three groups of CFRP models with spherical voids were established, in which each model had different void position distribution. The void diameters D ranged from 26 μm to 70 μm, and the distance d of voids was 0.21 mm, 0.14 mm and 0.09 mm, respectively. Based on these models, the back-scatter signals were analyzed by RQA method. The simulated study shows that, recurrence rate PRR decreases with D increasing when the void position distribution is the same. If the void size distribution is the same, PRR increases with d decreasing. The PRR of models with d=0.09 mm are always higher than the other two groups. There is significant difference in PRR between d=0.14 mm and d=0.21 mm models when D<50 μm. But the difference is small when D ≥ 50 μm. The results demonstrate that there is difference in PRR on different void distributions, PRR can be used to characterize different void distributions in CFRP.
2018, 35(10): 2760-2767.
doi: 10.13801/j.cnki.fhclxb.20171219.001
Abstract:
The properties of single-lap adhesive joint of composite/metal plates were experimentally and theoretically studied. The finite element model of the single-lap adhesive bonded structures consisting of a three-dimensional braided composite plate and a steel plate was established. Based on cohesive zone model and Hashin failure criteria, the damages of the adhesive layer and braided composite were simulated. The results show that the critical load and failure displacement as well as the damage modes of the bonding structure are all in good agreement with the experimental results which verifies the validity of the numerical model. Based on this numerical model, the effects of the thickness and bonding length of the adhesive layer on the critical load and the failure displacement of the adhesive bonded structure were studied. Based on the obtained results, a new type of connection structure was proposed. It is demonstrated that this new connection structure remarkably improves the tensile and bending strengths compared with the original single-lap adhesive bonded structure.
The properties of single-lap adhesive joint of composite/metal plates were experimentally and theoretically studied. The finite element model of the single-lap adhesive bonded structures consisting of a three-dimensional braided composite plate and a steel plate was established. Based on cohesive zone model and Hashin failure criteria, the damages of the adhesive layer and braided composite were simulated. The results show that the critical load and failure displacement as well as the damage modes of the bonding structure are all in good agreement with the experimental results which verifies the validity of the numerical model. Based on this numerical model, the effects of the thickness and bonding length of the adhesive layer on the critical load and the failure displacement of the adhesive bonded structure were studied. Based on the obtained results, a new type of connection structure was proposed. It is demonstrated that this new connection structure remarkably improves the tensile and bending strengths compared with the original single-lap adhesive bonded structure.
2018, 35(10): 2768-2776.
doi: 10.13801/j.cnki.fhclxb.20180207.001
Abstract:
A mathematical model for stiffness reduction of circular composite laminate with delaminations after low velocity impact based on spring-mass model was presented. Plate was divided into a delaminated portion of central disk and an undamaged portion of annulus plate. Bending theory and classical lamination theory were used to obtain the displacement of the plate to compute the stiffness. A FE model for laminate with delaminations on ABAQUS was established to validate the analytical model. Drop weight impact test was conducted and C-scan results was used to calculate the stiffness. The reduction result was used in spring-mass model predicting the contact force history. Comparisons of FE simulation and experiment test results show good agreement of the stiffness reduction and the prediction of contact force history. This analytical method can be applied to low velocity impact analysis with delamination damage.
A mathematical model for stiffness reduction of circular composite laminate with delaminations after low velocity impact based on spring-mass model was presented. Plate was divided into a delaminated portion of central disk and an undamaged portion of annulus plate. Bending theory and classical lamination theory were used to obtain the displacement of the plate to compute the stiffness. A FE model for laminate with delaminations on ABAQUS was established to validate the analytical model. Drop weight impact test was conducted and C-scan results was used to calculate the stiffness. The reduction result was used in spring-mass model predicting the contact force history. Comparisons of FE simulation and experiment test results show good agreement of the stiffness reduction and the prediction of contact force history. This analytical method can be applied to low velocity impact analysis with delamination damage.
2018, 35(10): 2777-2785.
doi: 10.13801/j.cnki.fhclxb.20180202.001
Abstract:
To reduce the thermal deformation, the carbon fiber reinforced polymer(CFRP) circular cell honeycomb core was proposed and designed. The external shear modulus of the core, which plays an important role in calculating the thermal deformation of the sandwich structure based on Reissner theory or ABAQUS software, was discussed in present study. The analytical result of external shear modulus was given based on energy equivalent theory from the stress and strain. Taking the usual lay-up made of T300/epoxy for example, the finite element solution of core calculated by ABAQUS software was compared with the theoretical one, which demonstrates that the maximum error is 10.4%. Using core with (±45°)2 layup and made of T300/epoxy, the double-shear test was carried out. It proves that the error between the experimental and the theoretical solution is 24.1%, which is close to the error of honeycomb core in previous study. The final finite element analysis shows that the 24.1% error has less effect on the mechanical characteristics of whole sandwich structure. Accordingly, analytical expressions for external shear modulus are of great value for engineering application. All the analysis can help for the design of the CFRP circular cell honeycomb core in the future.
To reduce the thermal deformation, the carbon fiber reinforced polymer(CFRP) circular cell honeycomb core was proposed and designed. The external shear modulus of the core, which plays an important role in calculating the thermal deformation of the sandwich structure based on Reissner theory or ABAQUS software, was discussed in present study. The analytical result of external shear modulus was given based on energy equivalent theory from the stress and strain. Taking the usual lay-up made of T300/epoxy for example, the finite element solution of core calculated by ABAQUS software was compared with the theoretical one, which demonstrates that the maximum error is 10.4%. Using core with (±45°)2 layup and made of T300/epoxy, the double-shear test was carried out. It proves that the error between the experimental and the theoretical solution is 24.1%, which is close to the error of honeycomb core in previous study. The final finite element analysis shows that the 24.1% error has less effect on the mechanical characteristics of whole sandwich structure. Accordingly, analytical expressions for external shear modulus are of great value for engineering application. All the analysis can help for the design of the CFRP circular cell honeycomb core in the future.
2018, 35(10): 2786-2792.
doi: 10.13801/j.cnki.fhclxb.20171219.002
Abstract:
Carbon/phenolic composite had been widely used as thermal protection system (TPS). Thus, in order to predict the ablation behavior of the carbon/phenolic composite, a mathematical model was proposed in this paper, which was based on the energy-and mass-conservation principles as well as on the thermal decomposition equation. The ablation process was simulated from the perspective of the fiber and matrix components. The thermal properties during ablation were calculated, and a moving boundary was implemented to consider the recession of the ablation surface. The temperature distribution, density, thermal properties, linear ablation rate and mass loss of the carbon/phenolic composite were predicted. The results show that the ablation of the carbon/phenolic composite is a highly nonlinear process of interaction of various factors. During ablation, the composite material has an uneven temperature distribution and the attenuation of the density on the ablative surface is the largest. In addition, the mass loss and mass loss rate almost increase linearly. The ablation behavior of the fiber and matrix is obviously different. Therefore, in order to provide more accurate reference and basis for the design of thermal protection materials, it is necessary to predict their ablation behavior respectively.
Carbon/phenolic composite had been widely used as thermal protection system (TPS). Thus, in order to predict the ablation behavior of the carbon/phenolic composite, a mathematical model was proposed in this paper, which was based on the energy-and mass-conservation principles as well as on the thermal decomposition equation. The ablation process was simulated from the perspective of the fiber and matrix components. The thermal properties during ablation were calculated, and a moving boundary was implemented to consider the recession of the ablation surface. The temperature distribution, density, thermal properties, linear ablation rate and mass loss of the carbon/phenolic composite were predicted. The results show that the ablation of the carbon/phenolic composite is a highly nonlinear process of interaction of various factors. During ablation, the composite material has an uneven temperature distribution and the attenuation of the density on the ablative surface is the largest. In addition, the mass loss and mass loss rate almost increase linearly. The ablation behavior of the fiber and matrix is obviously different. Therefore, in order to provide more accurate reference and basis for the design of thermal protection materials, it is necessary to predict their ablation behavior respectively.
2018, 35(10): 2793-2803.
doi: 10.13801/j.cnki.fhclxb.20180119.001
Abstract:
Fiber bundle reinforced polymer composites(FBC) and unidirectional laminates demonstrate similar failure features in the standard Iosipescu shear tests. However, a considerable difference is observed between the measured shear strengths of the two kinds of specimens. In this paper, three types of FBC and unidirectional laminates were prepared using two kinds of carbon fibers and epoxy resins. The shear strength of FBC and unidirectional laminates were compared to explore the underlying mechanisms resulting in the different shear strength. It is found through the analysis of the interfacial stress field between fiber bundle and matrix using the interface element method that the interfacial stress state in FBC specimen is a coupling of tensile stress and shear stress, whereas the interface in unidirectional laminate specimen is in an ideal shear stress state. This difference makes the FBC fail at lower shear stress level. In this paper, a strength model was proposed to bridge the shear strength of FBC and unidirectional laminates using Yamada-Sun strength theory. The experimental verification shows that the shear strengths of the unidirectional laminate predicted by the proposed model reach a good agreement with the measured values, with the relative deviation of about 10%. This study provides an effective method to predict or evaluate the interlaminar shear strength of unidirectional laminates based on the tests of FBC with relatively simple sample preparation procedure.
Fiber bundle reinforced polymer composites(FBC) and unidirectional laminates demonstrate similar failure features in the standard Iosipescu shear tests. However, a considerable difference is observed between the measured shear strengths of the two kinds of specimens. In this paper, three types of FBC and unidirectional laminates were prepared using two kinds of carbon fibers and epoxy resins. The shear strength of FBC and unidirectional laminates were compared to explore the underlying mechanisms resulting in the different shear strength. It is found through the analysis of the interfacial stress field between fiber bundle and matrix using the interface element method that the interfacial stress state in FBC specimen is a coupling of tensile stress and shear stress, whereas the interface in unidirectional laminate specimen is in an ideal shear stress state. This difference makes the FBC fail at lower shear stress level. In this paper, a strength model was proposed to bridge the shear strength of FBC and unidirectional laminates using Yamada-Sun strength theory. The experimental verification shows that the shear strengths of the unidirectional laminate predicted by the proposed model reach a good agreement with the measured values, with the relative deviation of about 10%. This study provides an effective method to predict or evaluate the interlaminar shear strength of unidirectional laminates based on the tests of FBC with relatively simple sample preparation procedure.
2018, 35(10): 2804-2812.
doi: 10.13801/j.cnki.fhclxb.20171227.002
Abstract:
A novel model for buckling analysis of carbon nanotube-reinforced functionally gradedplates (CNTs/FGP) was presented based on a re-modified couple stress theory. The equilibrium equations and relevant boundary conditions were derived from principle of minimum potential energy in conjunction with the first-order shear deformation theory. A simply supported CNTs/FGP was taken as illustrative example and analytically solved. The effects of material scale parameters, volume fraction and distributional patterns of the CNTs on the critical buckling load were investigated. The numerical results indicate that the critical buckling loads predicted by the present model are always higher than those by the classical macroscopic theory, and the differences of the two theories gradually increase with decreasing of the plate's geometric size; a small amount of CNTs can tangibly enhance the critical buckling load; the patterns of CNTs in matrix have conspicuous influences on the critical buckling load, which should be considered in engineering design.
A novel model for buckling analysis of carbon nanotube-reinforced functionally gradedplates (CNTs/FGP) was presented based on a re-modified couple stress theory. The equilibrium equations and relevant boundary conditions were derived from principle of minimum potential energy in conjunction with the first-order shear deformation theory. A simply supported CNTs/FGP was taken as illustrative example and analytically solved. The effects of material scale parameters, volume fraction and distributional patterns of the CNTs on the critical buckling load were investigated. The numerical results indicate that the critical buckling loads predicted by the present model are always higher than those by the classical macroscopic theory, and the differences of the two theories gradually increase with decreasing of the plate's geometric size; a small amount of CNTs can tangibly enhance the critical buckling load; the patterns of CNTs in matrix have conspicuous influences on the critical buckling load, which should be considered in engineering design.
2018, 35(10): 2813-2822.
doi: 10.13801/j.cnki.fhclxb.20171214.001
Abstract:
An identification method of loss factors of fiber/resin composite under thermal environment was presented. Firstly, the composite thin plate test-specimen of such material was taken as an example, and its vibration responses under thermal environment were theoretically solved based on the complex modulus method. Then, a laser scanning frame model of composite thin plate was established, and on the basis of the vibration responses obtained by laser scanning and complex modulus method, the relative error function of the responses was constructed by the least square method, so that the loss factors in the different fiber directions under thermal environment can be identified. Next, the identification principle of loss factors of fiber/resin composite under thermal environment was illustrated, and a reasonable and standard identification procedure was summarized. Finally, a vibration testing system of composite thin plate under thermal environment based on laser scanning technique was set up, and TC500 carbon fiber/resin composite thin plate was taken as a research object. The first 4 resonant responses were measured from the room temperature to 300℃, and consequently the loss factors were identified by the 1st resonant response data. It is found that when it raises from the room temperature to 300℃, the loss factors of fiber/resin composite material will increase gradually. In addition, the corresponding loss factor data at 100℃ was substituted into the theoretical model, and the 2nd, 3rd and 4th resonant response results were theoretically obtained at this temperature. By comparing these theoretical results with the experimental results, the relative errors are within the range of 1.4%-13.8%, so the effectiveness and practicability of such identification method have been verified.
An identification method of loss factors of fiber/resin composite under thermal environment was presented. Firstly, the composite thin plate test-specimen of such material was taken as an example, and its vibration responses under thermal environment were theoretically solved based on the complex modulus method. Then, a laser scanning frame model of composite thin plate was established, and on the basis of the vibration responses obtained by laser scanning and complex modulus method, the relative error function of the responses was constructed by the least square method, so that the loss factors in the different fiber directions under thermal environment can be identified. Next, the identification principle of loss factors of fiber/resin composite under thermal environment was illustrated, and a reasonable and standard identification procedure was summarized. Finally, a vibration testing system of composite thin plate under thermal environment based on laser scanning technique was set up, and TC500 carbon fiber/resin composite thin plate was taken as a research object. The first 4 resonant responses were measured from the room temperature to 300℃, and consequently the loss factors were identified by the 1st resonant response data. It is found that when it raises from the room temperature to 300℃, the loss factors of fiber/resin composite material will increase gradually. In addition, the corresponding loss factor data at 100℃ was substituted into the theoretical model, and the 2nd, 3rd and 4th resonant response results were theoretically obtained at this temperature. By comparing these theoretical results with the experimental results, the relative errors are within the range of 1.4%-13.8%, so the effectiveness and practicability of such identification method have been verified.
2018, 35(10): 2823-2831.
doi: 10.13801/j.cnki.fhclxb.20171115.001
Abstract:
The coating plays an important role in the surface modification of the fiber and adjusting the interface residual stress, which has a great influence on the macro performance. In order to accurately predict the effective properties and local field distributions of coating-fiber reinforced magneto-electro-elastic (MEE) materials under a multi field environment, a homogenized micromechanical model was established based on variational asymptotic method. Starting from the total electromagnetic enthalpy of inhomogeneous continuous media, the micromechanical model of multi physics field was converted to the minimization of total electromagnetic enthalpy under confined conditions by using the characteristics that the microscale of the material is much smaller than the macroscopic scale. In order to analyze the general microstructure of intelligent materials in engineering applications, the finite element method was used to implement the numerical simulation of the model. By comparing with the result of finite element analysis, the results show that the model can accurately predict the multiphysics behavior of coating-fiber reinforced MEE materials. The coatings with different thickness and stiffness have a great influence on the stress concentration and effective properties. Meanwhile, many interesting electro-magnetic interaction phenomenen are revealed, which are useful for the performance prediction and optimization of coating-fiber reinforced MEE materials.
The coating plays an important role in the surface modification of the fiber and adjusting the interface residual stress, which has a great influence on the macro performance. In order to accurately predict the effective properties and local field distributions of coating-fiber reinforced magneto-electro-elastic (MEE) materials under a multi field environment, a homogenized micromechanical model was established based on variational asymptotic method. Starting from the total electromagnetic enthalpy of inhomogeneous continuous media, the micromechanical model of multi physics field was converted to the minimization of total electromagnetic enthalpy under confined conditions by using the characteristics that the microscale of the material is much smaller than the macroscopic scale. In order to analyze the general microstructure of intelligent materials in engineering applications, the finite element method was used to implement the numerical simulation of the model. By comparing with the result of finite element analysis, the results show that the model can accurately predict the multiphysics behavior of coating-fiber reinforced MEE materials. The coatings with different thickness and stiffness have a great influence on the stress concentration and effective properties. Meanwhile, many interesting electro-magnetic interaction phenomenen are revealed, which are useful for the performance prediction and optimization of coating-fiber reinforced MEE materials.
2018, 35(10): 2832-2840.
doi: 10.13801/j.cnki.fhclxb.20180208.001
Abstract:
TiC/Ti3SiC2 composite material was prepared by infiltration sintering technology, the investigation was conducted on a HST-100 pin-on-disc friction and wear testing machine in the speed range of 60-90 m/s. The results show that the friction and wear behavior of TiC/Ti3SiC2 is closely related with the sliding speed and TiC content against HSLA80 pairs. When the sliding speed is slower than 80 m/s, the worn surface characterized by groove-ridge, Pan furrows and their combined to pography, uniform oxidation film (FeTiO3 and Fe2.35Ti0.65O4) will be formed on the surface, and the main wear mechanisms are abrasive wear, oxidation wear and adhesive wear. However, When the sliding speed is faster than 80 m/s, the worn surface characterized by isolated peak pattern, discontinuous and non-uniform oxidation film is formed. Wear mechanism is mainiy arc oxidation. Under the same experiment conditions, the coefficient of friction increases and the wear rate decreases with the content increase of TiC content.
TiC/Ti3SiC2 composite material was prepared by infiltration sintering technology, the investigation was conducted on a HST-100 pin-on-disc friction and wear testing machine in the speed range of 60-90 m/s. The results show that the friction and wear behavior of TiC/Ti3SiC2 is closely related with the sliding speed and TiC content against HSLA80 pairs. When the sliding speed is slower than 80 m/s, the worn surface characterized by groove-ridge, Pan furrows and their combined to pography, uniform oxidation film (FeTiO3 and Fe2.35Ti0.65O4) will be formed on the surface, and the main wear mechanisms are abrasive wear, oxidation wear and adhesive wear. However, When the sliding speed is faster than 80 m/s, the worn surface characterized by isolated peak pattern, discontinuous and non-uniform oxidation film is formed. Wear mechanism is mainiy arc oxidation. Under the same experiment conditions, the coefficient of friction increases and the wear rate decreases with the content increase of TiC content.
2018, 35(10): 2841-2850.
doi: 10.13801/j.cnki.fhclxb.20171227.005
Abstract:
The crack distribution and self-healing characteristics of engineered geopolymer composites using metakaolin and fly ash (PVA/MK-FA EGC) at various pre-loadings of 1%, 2% and 3% under air and wet/dry conditioning cycles were investigated at age of 3 days, 7 days and 28 days. The results show that PVA/MK-FA EGC combines the advantages of traditional engineered cementitious composite(ECC) and geopolymer, exhibiting obvious multiple cracking pattern and a strain-hardening behavior. The crack spacing is in the range of 2-5 mm and the maximum residual crack width is below 25 μm, which provide more favorable conditions for self-healing. After self-healing under different environments, number of crack decreases significantly. The ultimate tensile strain can exceed 3.8%, and both ultimate tensile strain and tensile strength capacity of the majority specimens at reloading are higher than the control specimens. Air conditioning can favor the self-healing of the PVA/MK-FA EGC materials. The surface of the particles in the crack is covered with geopolymeric gel, which may enhance the bond of fiber and matrix, resulting in the recovery of the mechanical properties.
The crack distribution and self-healing characteristics of engineered geopolymer composites using metakaolin and fly ash (PVA/MK-FA EGC) at various pre-loadings of 1%, 2% and 3% under air and wet/dry conditioning cycles were investigated at age of 3 days, 7 days and 28 days. The results show that PVA/MK-FA EGC combines the advantages of traditional engineered cementitious composite(ECC) and geopolymer, exhibiting obvious multiple cracking pattern and a strain-hardening behavior. The crack spacing is in the range of 2-5 mm and the maximum residual crack width is below 25 μm, which provide more favorable conditions for self-healing. After self-healing under different environments, number of crack decreases significantly. The ultimate tensile strain can exceed 3.8%, and both ultimate tensile strain and tensile strength capacity of the majority specimens at reloading are higher than the control specimens. Air conditioning can favor the self-healing of the PVA/MK-FA EGC materials. The surface of the particles in the crack is covered with geopolymeric gel, which may enhance the bond of fiber and matrix, resulting in the recovery of the mechanical properties.
2018, 35(10): 2851-2859.
doi: 10.13801/j.cnki.fhclxb.20180119.002
Abstract:
During the long-term natural evolution, the scales of teleost fish become ultra-thin and lightweight and have a good flexibility as well. In order to reveal the structure and mechanism of scales, two scales of fish (cyprinus carpio, carassius auratus) from New Zealand were studied in this paper. Firstly, the surface morphology, cross-section and hierarchical structure of two fish scales were investigated. Then, uniaxial tensile tests were conducted. The results show that the surface morphologies of two scales are various from different location of scales, while two scales are both consist of outer hard bony layer and inner soft collagen layer. For cyprinus carpio scales, through a quasi-linear region from the stress-strain curves, the stress of samples softens slightly before reaching the first peak stress, after which the stress drops to zero. While the stress of carassius auratus scales increases through a quastic-linear region, and then reaches the peak, lastly drops to zero gradually. Comparing the mechanical parameters between cyprinus carpio scales and carassius auratus scales, it's suggested that the tensile strength of carassius auratus scales is superior to that of cyprinus carpio scales. However, the ductility of cyprinus carpio scales has a prior ductility than the carassius auratus scales.
During the long-term natural evolution, the scales of teleost fish become ultra-thin and lightweight and have a good flexibility as well. In order to reveal the structure and mechanism of scales, two scales of fish (cyprinus carpio, carassius auratus) from New Zealand were studied in this paper. Firstly, the surface morphology, cross-section and hierarchical structure of two fish scales were investigated. Then, uniaxial tensile tests were conducted. The results show that the surface morphologies of two scales are various from different location of scales, while two scales are both consist of outer hard bony layer and inner soft collagen layer. For cyprinus carpio scales, through a quasi-linear region from the stress-strain curves, the stress of samples softens slightly before reaching the first peak stress, after which the stress drops to zero. While the stress of carassius auratus scales increases through a quastic-linear region, and then reaches the peak, lastly drops to zero gradually. Comparing the mechanical parameters between cyprinus carpio scales and carassius auratus scales, it's suggested that the tensile strength of carassius auratus scales is superior to that of cyprinus carpio scales. However, the ductility of cyprinus carpio scales has a prior ductility than the carassius auratus scales.
2018, 35(10): 2860-2870.
doi: 10.13801/j.cnki.fhclxb.20180124.001
Abstract:
To study the micro mechanical behavior of steel fiber reinforced reactive powder concrete (SF/RPC) composite material under flexural loads, 10 experimental beams were fabricated and tested. Based on the acoustic emission technique, the acoustic emission signals and waveforms during the test were collected by using the broadband sensors. The acoustic emission parameters of SF/RPC material were analyzed, and the waveform spectrum was studied deeply on the basis of the signal processing of the waveform. The acoustic emission velocity of the SF/RPC material was measured by emitting and receiving signals between the sensors. The acoustic emission characteristics of normal concrete(NC) material were explored for comparison. The results show that the accumulate number of hits is much larger than that of NC beam under the same load, and the acoustic emission activity is higher than that of NC. The acoustic emission characteristic parameters of prestressed SF/RPC are obviously different from NC beam. The average acoustic emission hits proportion of SF/RPC for the short rise time period (<30 μs) is 64.2%, while the proportion of NC is 51.2%. The frequency domain characteristics of SF/RPC material are also significantly different from those of NC material. Before the load, the average wave velocity of SF/RPC is 4 342.8 mm/s, while the velocity of NC is 2 337.7 mm/s. The acoustic emission damage parameter (bI) value is calculated based on the Gutenberg-Richter theory. The relationship between bI value and the damage fracture process of prestressed SF/RPC was explored. This study provides experimental basis for the effective identification of the acoustic emission characteristics of SF/RPC material.
To study the micro mechanical behavior of steel fiber reinforced reactive powder concrete (SF/RPC) composite material under flexural loads, 10 experimental beams were fabricated and tested. Based on the acoustic emission technique, the acoustic emission signals and waveforms during the test were collected by using the broadband sensors. The acoustic emission parameters of SF/RPC material were analyzed, and the waveform spectrum was studied deeply on the basis of the signal processing of the waveform. The acoustic emission velocity of the SF/RPC material was measured by emitting and receiving signals between the sensors. The acoustic emission characteristics of normal concrete(NC) material were explored for comparison. The results show that the accumulate number of hits is much larger than that of NC beam under the same load, and the acoustic emission activity is higher than that of NC. The acoustic emission characteristic parameters of prestressed SF/RPC are obviously different from NC beam. The average acoustic emission hits proportion of SF/RPC for the short rise time period (<30 μs) is 64.2%, while the proportion of NC is 51.2%. The frequency domain characteristics of SF/RPC material are also significantly different from those of NC material. Before the load, the average wave velocity of SF/RPC is 4 342.8 mm/s, while the velocity of NC is 2 337.7 mm/s. The acoustic emission damage parameter (bI) value is calculated based on the Gutenberg-Richter theory. The relationship between bI value and the damage fracture process of prestressed SF/RPC was explored. This study provides experimental basis for the effective identification of the acoustic emission characteristics of SF/RPC material.
2018, 35(10): 2871-2879.
doi: 10.13801/j.cnki.fhclxb.20171228.001
Abstract:
Low temperature performance of asphalt pavement is one of the main indicator of asphalt pavement design in cold areas, the existing single modified asphalt in low-temperature performance does not meet the requirements of PG technical specifications for asphalt pavement in cold areas. In this project, on the basis of PG test and evaluation results to common road asphalt in low-temperature performance of Heilongjiang province, the composite modified asphalt was researched and developed in order to meet the requirements of low temperature performance of asphalt pavement in cold regions in Heilongjiang province. The research contents include:determination of PG zone and PGm-n standard of asphalt pavement in Heilongjiang province, PG performance evaluation of road asphalt in Heilongjiang province, research and development and performance evaluation of composite modified asphalt. The research results show that the road asphalt in Heilongjiang province meets the requirements of PGm-n technology standards in high temperature performance, but does not meet the PGm-n standards in low temperature performance. The composite modified asphalt meets or nears the PGm-n standard in low temperature performance of road asphalt in Heilongjiang province. The research results have some theoretical and practical value to improve the low temperature performance of asphalt pavement in Heilongjiang province.
Low temperature performance of asphalt pavement is one of the main indicator of asphalt pavement design in cold areas, the existing single modified asphalt in low-temperature performance does not meet the requirements of PG technical specifications for asphalt pavement in cold areas. In this project, on the basis of PG test and evaluation results to common road asphalt in low-temperature performance of Heilongjiang province, the composite modified asphalt was researched and developed in order to meet the requirements of low temperature performance of asphalt pavement in cold regions in Heilongjiang province. The research contents include:determination of PG zone and PGm-n standard of asphalt pavement in Heilongjiang province, PG performance evaluation of road asphalt in Heilongjiang province, research and development and performance evaluation of composite modified asphalt. The research results show that the road asphalt in Heilongjiang province meets the requirements of PGm-n technology standards in high temperature performance, but does not meet the PGm-n standards in low temperature performance. The composite modified asphalt meets or nears the PGm-n standard in low temperature performance of road asphalt in Heilongjiang province. The research results have some theoretical and practical value to improve the low temperature performance of asphalt pavement in Heilongjiang province.
2018, 35(10): 2880-2888.
doi: 10.13801/j.cnki.fhclxb.20171213.001
Abstract:
Comparing with optical thermography, vibrothermography(VT) is a new technique.However, the heat generation mechanism of VT has not yet come to an agreement among scholars. The VT of debondings in nonmetallic composite structures was studied focusing on viscoelastic heat.Taking the VT of debonding in aluminum-cork composite structures as an example, the temperature rise patterns on the defects were analyzed by using numerical simulation and experiment. The theoretical results are consistent with the experimental results, and it illustrates that the viscoelastic heat of the nonmetallic material is the leading factor of heat generation at debonding.The conclusion provides a theoretical basis for the VT of debondings in metal-nonmetal composite structures, and delaminations in polymer composite materials.
Comparing with optical thermography, vibrothermography(VT) is a new technique.However, the heat generation mechanism of VT has not yet come to an agreement among scholars. The VT of debondings in nonmetallic composite structures was studied focusing on viscoelastic heat.Taking the VT of debonding in aluminum-cork composite structures as an example, the temperature rise patterns on the defects were analyzed by using numerical simulation and experiment. The theoretical results are consistent with the experimental results, and it illustrates that the viscoelastic heat of the nonmetallic material is the leading factor of heat generation at debonding.The conclusion provides a theoretical basis for the VT of debondings in metal-nonmetal composite structures, and delaminations in polymer composite materials.
2018, 35(10): 2889-2896.
doi: 10.13801/j.cnki.fhclxb.20171227.003
Abstract:
An experimental study of temperature-dependent mechanical behavior of acrylonitrile butadiene styrene (ABS) was performed at a range of temperatures (243 K, 263 K, 296 K, 333 K, 353 K, 383 K) under uniaxial tension condition. In this temperature range, ABS was in the glass state and glass transition region. The results show that the yield stress and ultimate tensile stress decrease linearly but Young's modulus decreases nonlinearly with the increase of temperature. The material parameters of the model at different temperature were obtained by using a sim-flow optimization tool. The temperature-dependent two-layer viscoplasticity constitutive model was established. This constitutive model can predict the stress-strain curve of ABS well at different temperatures between 243 K and 383 K.
An experimental study of temperature-dependent mechanical behavior of acrylonitrile butadiene styrene (ABS) was performed at a range of temperatures (243 K, 263 K, 296 K, 333 K, 353 K, 383 K) under uniaxial tension condition. In this temperature range, ABS was in the glass state and glass transition region. The results show that the yield stress and ultimate tensile stress decrease linearly but Young's modulus decreases nonlinearly with the increase of temperature. The material parameters of the model at different temperature were obtained by using a sim-flow optimization tool. The temperature-dependent two-layer viscoplasticity constitutive model was established. This constitutive model can predict the stress-strain curve of ABS well at different temperatures between 243 K and 383 K.
2018, 35(10): 2897-2905.
doi: 10.13801/j.cnki.fhclxb.20171231.001
Abstract:
A peridynamic model for envelope material was established based on peridynamic theory. First, the basic theory of peridynamic and the major property of envelope material were illustrated. The material was scattered into particles, and based on a classic peridynamic model of composites, the components of constitutive force and strain energy density of each particle were analyzed under a unique condition of intertexture. The constitutive function and peridynamic parameter were divaricated thus completed the model. Emulation of mechanical property was conducted using dynamic relaxation method. The results show a correspondent stress state under tension with an alternative numerical result. The tensile modulus and the load-strain curve are in accordance with the lab results.
A peridynamic model for envelope material was established based on peridynamic theory. First, the basic theory of peridynamic and the major property of envelope material were illustrated. The material was scattered into particles, and based on a classic peridynamic model of composites, the components of constitutive force and strain energy density of each particle were analyzed under a unique condition of intertexture. The constitutive function and peridynamic parameter were divaricated thus completed the model. Emulation of mechanical property was conducted using dynamic relaxation method. The results show a correspondent stress state under tension with an alternative numerical result. The tensile modulus and the load-strain curve are in accordance with the lab results.
2018, 35(10): 2906-2918.
doi: 10.13801/j.cnki.fhclxb.20171128.006
Abstract:
According to the relationship between interface dilation and mode Ⅱfracture energy, a new way of constructing traction-separation law with dilation was presented. The method, by first assuming the mode Ⅱ traction-separation relationship, and then deriving the interface dilation, was easier to apply. Defining four damage variables based on the interface separation and fracture energy, traction-separation laws with dilation considering damage effects were further given. This enables the model to simulate not only the monotonic loading problems but also reversed loading problems. In addition, interface tangential bonding strength, normal separation, and friction effect under interfacial pressure were discussed respectively, which led to corresponding computing methods or recommended value. Finally, an example of traction-separation law with dilation considering damage was proposed. Utilizing finite element method, interface pressure, mixed mode effect, unloading and reloading behavior, and effects of contact penalty stiffness on normal separation were investigated thoroughly.
According to the relationship between interface dilation and mode Ⅱfracture energy, a new way of constructing traction-separation law with dilation was presented. The method, by first assuming the mode Ⅱ traction-separation relationship, and then deriving the interface dilation, was easier to apply. Defining four damage variables based on the interface separation and fracture energy, traction-separation laws with dilation considering damage effects were further given. This enables the model to simulate not only the monotonic loading problems but also reversed loading problems. In addition, interface tangential bonding strength, normal separation, and friction effect under interfacial pressure were discussed respectively, which led to corresponding computing methods or recommended value. Finally, an example of traction-separation law with dilation considering damage was proposed. Utilizing finite element method, interface pressure, mixed mode effect, unloading and reloading behavior, and effects of contact penalty stiffness on normal separation were investigated thoroughly.
