2014 Vol. 31, No. 1
2014, 31(1): 1-8.
Abstract:
The magnetic composites were prepared by mixing bisphenols A WSR-615 and glycidyl amine AG-80 epoxy resins and a high content of Fe-Si magnetic particles using hot-pressing process. The glass transition temperature and impact property of the epoxy resins and the impact strength and magnetization of the composites were investigated as a function of Fe-Si content and temperature. It is shown that the impact strength and the magnetization of Fe-Si/epoxy composites increase with increasing the Fe-Si content and are enhanced from 4.03 kJ/m2 and 162.07 emu/g to 7.16 kJ/m2 and 175.04 emu/g at 54 vol% to 66 vol% Fe-Si particles. The impact strength and magnetization of the composites are very lightly sensitive to the temperature change from-60 ℃ to 140 ℃, which is desired for practical applications requiring that the mechanical and magnetic properties are stable as the temperature changes.
The magnetic composites were prepared by mixing bisphenols A WSR-615 and glycidyl amine AG-80 epoxy resins and a high content of Fe-Si magnetic particles using hot-pressing process. The glass transition temperature and impact property of the epoxy resins and the impact strength and magnetization of the composites were investigated as a function of Fe-Si content and temperature. It is shown that the impact strength and the magnetization of Fe-Si/epoxy composites increase with increasing the Fe-Si content and are enhanced from 4.03 kJ/m2 and 162.07 emu/g to 7.16 kJ/m2 and 175.04 emu/g at 54 vol% to 66 vol% Fe-Si particles. The impact strength and magnetization of the composites are very lightly sensitive to the temperature change from-60 ℃ to 140 ℃, which is desired for practical applications requiring that the mechanical and magnetic properties are stable as the temperature changes.
2014, 31(1): 9-17.
Abstract:
Burr and spalling damages introduced by drilling have great influence on the assembling accuracy of carbon/epoxy(C/EP) composite components. In order to investigate the formation mechanisms of burr and spalling, scratching experiment was adopted to study the fracture and removal process of C/EP composites cutting with different fiber orientations. Chips and scratching grooves were observed by FEI Quanta 200 environmental SEM. Results show that when scratching direction is perpendicular to fiber orientation, scratching force is the largest and spalling is prone to appear. When the angle between scratching direction and fiber orientation is 30°, 45°, and 60°, the fibers on the left side of groove yield towards the left, bend and fracture in the zigzag shape, otherwise they form burr damage. While the fibers on the right side of groove bend in a large deformation and fracture homogenously, are not easy to form burr. Theoretical analyses and scratching experimental results show: burr is prone to appear in the region where the included angle between fiber orientation and cutting speed direction is acute. Hole exit edge is smooth in the region where the included angle between fiber orientation and cutting speed direction is obtuse. Spalling is prone to appear where fiber orientation is perpendicular to cutting speed direction. The above distribution is in accordance with the experimental results.
Burr and spalling damages introduced by drilling have great influence on the assembling accuracy of carbon/epoxy(C/EP) composite components. In order to investigate the formation mechanisms of burr and spalling, scratching experiment was adopted to study the fracture and removal process of C/EP composites cutting with different fiber orientations. Chips and scratching grooves were observed by FEI Quanta 200 environmental SEM. Results show that when scratching direction is perpendicular to fiber orientation, scratching force is the largest and spalling is prone to appear. When the angle between scratching direction and fiber orientation is 30°, 45°, and 60°, the fibers on the left side of groove yield towards the left, bend and fracture in the zigzag shape, otherwise they form burr damage. While the fibers on the right side of groove bend in a large deformation and fracture homogenously, are not easy to form burr. Theoretical analyses and scratching experimental results show: burr is prone to appear in the region where the included angle between fiber orientation and cutting speed direction is acute. Hole exit edge is smooth in the region where the included angle between fiber orientation and cutting speed direction is obtuse. Spalling is prone to appear where fiber orientation is perpendicular to cutting speed direction. The above distribution is in accordance with the experimental results.
2014, 31(1): 18-25.
Abstract:
An effective method was established for damage analysis of composite laminated plate. Improved Chang/Chang failure criterion including all kinds of damage forms was used to model in-plate damage. TIEBREAK contact equivalent of Mixed-Mode cohesive zone model was used for modeling the regions between two layers. From composite thin-walled structure design requirement, three parameters of stacking sequence affecting impact damage resistance under low energy impact were studied with the numerical method, i.e, interface angel, ply orientation and ply grouping. After general study of the effects of stacking sequence on the impact resistance, some design guidelines to improve the impact damage resistance of composite plates were given, and the stacking sequence of a composite laminated plate was redesigned according to the guidelines. The finite element analysis shows that the guidelines are feasible and valid.
An effective method was established for damage analysis of composite laminated plate. Improved Chang/Chang failure criterion including all kinds of damage forms was used to model in-plate damage. TIEBREAK contact equivalent of Mixed-Mode cohesive zone model was used for modeling the regions between two layers. From composite thin-walled structure design requirement, three parameters of stacking sequence affecting impact damage resistance under low energy impact were studied with the numerical method, i.e, interface angel, ply orientation and ply grouping. After general study of the effects of stacking sequence on the impact resistance, some design guidelines to improve the impact damage resistance of composite plates were given, and the stacking sequence of a composite laminated plate was redesigned according to the guidelines. The finite element analysis shows that the guidelines are feasible and valid.
2014, 31(1): 26-32.
Abstract:
From the sensitivity of the fibre Bragg grating (FBG) center wavelength changing with strain changes on the surface of carbon fibre reinforced plastics (CFRP) composite, the correlation between the tensile rate of the FBG wavelength and the fracture status was investigated during the stretching process and the strain wave response characteristics of the specimen surface, that is, the elastic modulus of CFRP tensile specimens decreases with the increasing of the internal damage, and stabilizes before the appearance of the stress relaxation in the specimen, at which the strain response of acoustic emission received on the surface of the fracture area is slightly greater than the one in other areas. By combining FBG with the CFRP fracture monitoring, a CFRP fracture monitoring method based on the FBG has been proposed. The method coupling sensing probe directly with specimen has achieved the absolute monitoring of CFRP fracture state.
From the sensitivity of the fibre Bragg grating (FBG) center wavelength changing with strain changes on the surface of carbon fibre reinforced plastics (CFRP) composite, the correlation between the tensile rate of the FBG wavelength and the fracture status was investigated during the stretching process and the strain wave response characteristics of the specimen surface, that is, the elastic modulus of CFRP tensile specimens decreases with the increasing of the internal damage, and stabilizes before the appearance of the stress relaxation in the specimen, at which the strain response of acoustic emission received on the surface of the fracture area is slightly greater than the one in other areas. By combining FBG with the CFRP fracture monitoring, a CFRP fracture monitoring method based on the FBG has been proposed. The method coupling sensing probe directly with specimen has achieved the absolute monitoring of CFRP fracture state.
2014, 31(1): 33-39.
Abstract:
The time dependent characteristics of stress intensity factors (SIFs) and strain energy release rate for mode Ⅰ cracks in polymeric graded materials with arbitrary distribution of volume content of constituent materials under creep loading were investigated. The effective relaxation modulus was predicted based on Mori-Tanaka approach. In Laplace transform domain, the fracture parameters were determined by applying graded finite element method and virture crack closure technique, and their correspondent quantities in physical space were obtained with numerical Laplace inversion. The polymeric graded plate strips with edge crack parallel to graded direction were analyzed, and both far field homogeneous tension and three-point bending were considered respectively. The numerical results show that the strain energy release rate increases with time elapsed and its variation range is dependent on the volume fraction of viscoelastic constituent, and the intensity of stress field near crack tip varies with time due to stress redistribution originating from heterogeneous viscoelasic behaviour of graded materials. The SIFs increase with time when crack is located on the side with less volume content of viscoelastic constituent, and decrease on the contrary. The time-dependent variation range of SIFs is influenced by both the distribution of volume fraction of constituents and loading mode, and reaches the maximum value for the linear distribution of volume fraction. The increase or decrease of SIFs will speed or abate the damage in the process zone near crack tip. These results suggest that it is necessary to adopt both SIFs and strain energy release rate to control the time delayed fracture in polymeric graded materials.
The time dependent characteristics of stress intensity factors (SIFs) and strain energy release rate for mode Ⅰ cracks in polymeric graded materials with arbitrary distribution of volume content of constituent materials under creep loading were investigated. The effective relaxation modulus was predicted based on Mori-Tanaka approach. In Laplace transform domain, the fracture parameters were determined by applying graded finite element method and virture crack closure technique, and their correspondent quantities in physical space were obtained with numerical Laplace inversion. The polymeric graded plate strips with edge crack parallel to graded direction were analyzed, and both far field homogeneous tension and three-point bending were considered respectively. The numerical results show that the strain energy release rate increases with time elapsed and its variation range is dependent on the volume fraction of viscoelastic constituent, and the intensity of stress field near crack tip varies with time due to stress redistribution originating from heterogeneous viscoelasic behaviour of graded materials. The SIFs increase with time when crack is located on the side with less volume content of viscoelastic constituent, and decrease on the contrary. The time-dependent variation range of SIFs is influenced by both the distribution of volume fraction of constituents and loading mode, and reaches the maximum value for the linear distribution of volume fraction. The increase or decrease of SIFs will speed or abate the damage in the process zone near crack tip. These results suggest that it is necessary to adopt both SIFs and strain energy release rate to control the time delayed fracture in polymeric graded materials.
2014, 31(1): 40-48.
Abstract:
The bonding mechanism of adjacent plies during the tap laying process was discussed, and the bonding process was modeled as squeezing flow of resin patch under parallel plate. It is pointed out that when the viscosity of resin is constant, the bonding capability will become stronger when infiltration effect of the interface becomes better. The calculation formula of the infiltration effect was deduced by using fluid mechanics theory. Influence of main processing parameters (layup pressure, layup velocity, etc.) on infiltration effect and bonding capability was analyzed. The peel force was used to quantify the bonding capability of the ply. A series of experiments were carried out on the automated tape laying platform. It is shown that the bonding capability will become weaker as the layup velocity increases, and become stronger as layup pressure, mould temperature and roller radius increase. This law conforms to the calculation formula of the infiltration effect.
The bonding mechanism of adjacent plies during the tap laying process was discussed, and the bonding process was modeled as squeezing flow of resin patch under parallel plate. It is pointed out that when the viscosity of resin is constant, the bonding capability will become stronger when infiltration effect of the interface becomes better. The calculation formula of the infiltration effect was deduced by using fluid mechanics theory. Influence of main processing parameters (layup pressure, layup velocity, etc.) on infiltration effect and bonding capability was analyzed. The peel force was used to quantify the bonding capability of the ply. A series of experiments were carried out on the automated tape laying platform. It is shown that the bonding capability will become weaker as the layup velocity increases, and become stronger as layup pressure, mould temperature and roller radius increase. This law conforms to the calculation formula of the infiltration effect.
2014, 31(1): 49-58.
Abstract:
In the view of investigating the sensitive degree of filling time and resin flow front shape to the material and processing parameters during liquid composite molding (LCM) processes, the sensitivity analysis method was introduced to study the resin infiltration process, in which both edge effect and curing reaction were considered. The mathematical relationships of the key physical parameters such as fluid pressure sensitivity and flow rate sensitivity were deduced, and then the filling time sensitivity equation and resin flow front shape sensitivity equation that represents the probability of defects formation were also established. Finally, the coupling method for calculating various parameters and the technical route of sensitivity analysis were designed. On these bases, a simulation program was self-developed to analyze the influencing degree of the key material and processing parameters on the development of resin flow patterns. The simulation results show that under constant injection pressure conditions, elevating the resin injection temperature is the most effective method to raise the production efficiency, and the decrease of edge permeability is the best way to improve the resin flow front shape and the resin infiltration result.
In the view of investigating the sensitive degree of filling time and resin flow front shape to the material and processing parameters during liquid composite molding (LCM) processes, the sensitivity analysis method was introduced to study the resin infiltration process, in which both edge effect and curing reaction were considered. The mathematical relationships of the key physical parameters such as fluid pressure sensitivity and flow rate sensitivity were deduced, and then the filling time sensitivity equation and resin flow front shape sensitivity equation that represents the probability of defects formation were also established. Finally, the coupling method for calculating various parameters and the technical route of sensitivity analysis were designed. On these bases, a simulation program was self-developed to analyze the influencing degree of the key material and processing parameters on the development of resin flow patterns. The simulation results show that under constant injection pressure conditions, elevating the resin injection temperature is the most effective method to raise the production efficiency, and the decrease of edge permeability is the best way to improve the resin flow front shape and the resin infiltration result.
2014, 31(1): 59-65.
Abstract:
The silk sericin/Poly(isopropylacrylamide-lithium magnesium silicate hydrate) (SS/Poly(NIPAm-LMSH)) nano composite hydrogels with high swelling ratios and rapid responsibility, via semi-interpenetrating network and in-situ radical polymerization, were prepared by introducing SS with good bio-compatibility and high water absorption into Poly(NIPAm-LMSH) nano composite hydrogel network. The effects of SS content on the pore morphology, swelling behavior, crystal structure, compatibility and stability of the resulting hydrogels were investigated. The results show that the SS/Poly(NIPAm-LMSH) hydrogels after freeze-drying present porous structure with large pore size 20-30 μm and thinner pore walls 1-4 μm. With increasing SS content, the pore shape turns to elongated and layered structure from polyhedral structure. Compared to pure Poly(NIPAm-LMSH) hydrogels in equilibrium swelling state, the addition of SS increases the swelling ratios, belonging to non-Fickian diffusion at the beginning of swelling process, and water was expelled 90% from the hydrogel matrix within 10 min at 37 ℃. The sericin in the hydrogels shows good compatibility and Tg at 141-144 ℃. The maximum thermal decomposition temperature of SS/Poly(NIPAm-LMSH) nanocomposite hydrogels is 365-373 ℃, and the mass remaining ratios increase with the addition of sericin content.
The silk sericin/Poly(isopropylacrylamide-lithium magnesium silicate hydrate) (SS/Poly(NIPAm-LMSH)) nano composite hydrogels with high swelling ratios and rapid responsibility, via semi-interpenetrating network and in-situ radical polymerization, were prepared by introducing SS with good bio-compatibility and high water absorption into Poly(NIPAm-LMSH) nano composite hydrogel network. The effects of SS content on the pore morphology, swelling behavior, crystal structure, compatibility and stability of the resulting hydrogels were investigated. The results show that the SS/Poly(NIPAm-LMSH) hydrogels after freeze-drying present porous structure with large pore size 20-30 μm and thinner pore walls 1-4 μm. With increasing SS content, the pore shape turns to elongated and layered structure from polyhedral structure. Compared to pure Poly(NIPAm-LMSH) hydrogels in equilibrium swelling state, the addition of SS increases the swelling ratios, belonging to non-Fickian diffusion at the beginning of swelling process, and water was expelled 90% from the hydrogel matrix within 10 min at 37 ℃. The sericin in the hydrogels shows good compatibility and Tg at 141-144 ℃. The maximum thermal decomposition temperature of SS/Poly(NIPAm-LMSH) nanocomposite hydrogels is 365-373 ℃, and the mass remaining ratios increase with the addition of sericin content.
2014, 31(1): 66-72.
Abstract:
By controlling the on-line thermal stress of Polyacrylonitrile [P(AN/IA)] at 180 ℃ according to the feature of thermal properties and aggregation structure of PAN binary copolymer[P(AN/IA)], the pre-treated PAN fibers have been continuously stabilized and carbonized to obtain the corresponding stabilized PAN fibers and carbon fibers. The acquired samples were then researched by DSC, FTIR, and WAXD. The analysis results showed that the appropriate thermal stress relaxation treatment of received PAN binary copolymer fibers could improve the tensile strength of resulting carbon fibers. The orientation degree of quasi-crystal areas in PAN fibers has been enhanced with the raise of thermal stress at 180 ℃; however, the activation energy of cyclization reaction for pre-treatment fibers significantly increased and relative cyclization index for pre-oxidized fibers gradually decreased, the interlayer size of corresponding carbon fibers were initially decreased and then increased, while the crystallite size showed the opposite tendency. The mechanical properties of carbon fibers including tensile strength and tensile modulus showed a strong dependence on the thermal stress relaxation treatment of PAN fibers at 180 ℃. Comprehensive study results show that the binary copolymer [P(AN/IA)] with appropriate thermal stress relaxation treatment could transformed into carbon fibers with superior structure parameters and mechanical properities.
By controlling the on-line thermal stress of Polyacrylonitrile [P(AN/IA)] at 180 ℃ according to the feature of thermal properties and aggregation structure of PAN binary copolymer[P(AN/IA)], the pre-treated PAN fibers have been continuously stabilized and carbonized to obtain the corresponding stabilized PAN fibers and carbon fibers. The acquired samples were then researched by DSC, FTIR, and WAXD. The analysis results showed that the appropriate thermal stress relaxation treatment of received PAN binary copolymer fibers could improve the tensile strength of resulting carbon fibers. The orientation degree of quasi-crystal areas in PAN fibers has been enhanced with the raise of thermal stress at 180 ℃; however, the activation energy of cyclization reaction for pre-treatment fibers significantly increased and relative cyclization index for pre-oxidized fibers gradually decreased, the interlayer size of corresponding carbon fibers were initially decreased and then increased, while the crystallite size showed the opposite tendency. The mechanical properties of carbon fibers including tensile strength and tensile modulus showed a strong dependence on the thermal stress relaxation treatment of PAN fibers at 180 ℃. Comprehensive study results show that the binary copolymer [P(AN/IA)] with appropriate thermal stress relaxation treatment could transformed into carbon fibers with superior structure parameters and mechanical properities.
2014, 31(1): 73-80.
Abstract:
A special spoke-wheel cryogenic support structure was introduced, with the experimental study of its thermal and mechanical performance of different materials and different spoke quantity and cross-section shape. The study included thermal conductivity experimental measurements of both polyether-ether-ketone (PEEK) and glass fiber reinforced plastic (GRP) material, thermal resistance measurements and the mechanical tensile failure tests of a variety of support wheels which have different structural forms of PEEK and GRP. The various experimental results were analyzed and compared, with the measurement error analysis. The results show that, when the temperature is below 200K, the thermal conductivity of the PEEK material is less than that of the GRP material, but they are almost the same above 200K. The thermal resistance of the support wheel decreases with the increase of the number of spokes and the spoke cross-sectional area, and the measured thermal resistance is a comprehensive result of the solid thermal conduction and thermal radiation. The mechanical performance of the support wheel is improved by the increase of the number of spokes and the spoke cross-sectional area, and the load bearing capability of the support of the GRP material is larger in the radial direction than in the axial direction, while that of the PEEK material is nearly same in both directions. That is mainly due to the anisotropic properties of GRP material. Eventually, the support wheel of PEEK material with 6 ribbed spokes is the best choice by integrating thermal and mechanical performance test results.
A special spoke-wheel cryogenic support structure was introduced, with the experimental study of its thermal and mechanical performance of different materials and different spoke quantity and cross-section shape. The study included thermal conductivity experimental measurements of both polyether-ether-ketone (PEEK) and glass fiber reinforced plastic (GRP) material, thermal resistance measurements and the mechanical tensile failure tests of a variety of support wheels which have different structural forms of PEEK and GRP. The various experimental results were analyzed and compared, with the measurement error analysis. The results show that, when the temperature is below 200K, the thermal conductivity of the PEEK material is less than that of the GRP material, but they are almost the same above 200K. The thermal resistance of the support wheel decreases with the increase of the number of spokes and the spoke cross-sectional area, and the measured thermal resistance is a comprehensive result of the solid thermal conduction and thermal radiation. The mechanical performance of the support wheel is improved by the increase of the number of spokes and the spoke cross-sectional area, and the load bearing capability of the support of the GRP material is larger in the radial direction than in the axial direction, while that of the PEEK material is nearly same in both directions. That is mainly due to the anisotropic properties of GRP material. Eventually, the support wheel of PEEK material with 6 ribbed spokes is the best choice by integrating thermal and mechanical performance test results.
2014, 31(1): 81-87.
Abstract:
The aniline-strontium titanyl oxalate (aniline-SrTi(C2O4)2) particles were prepared by a precipitation method. FTIR patterns show that aniline has been added to the surface of the SrTi(C2O4)2 particles. XRD patterns indicate that the particles are amorphous structure with a little of crystallization. The morphology of the particles was observed by SEM, the results of which indicate that with the increase of the molar ratio of aniline toTi atoms, naniline/nTi, the smorphology of aniline-SrTi(C2O4)2 particles change from approximate globular (naniline/nTi =0) to a polyhedron shape (naniline/nTi =2), and then a mixure consists of rod and cluster shaped particles (naniline/nTi =3). The electrorheological (ER) fluids were prepared with 66.7% mass fraction of aniline-SrTi(C2O4)2 particles with different aniline contentand tested. The experimental results indicate that the ER fluid prepared by the particles with a molar ratio of naniline/nTi =2 present the largest field-induced shear stress, yield stress and leak current density. The aniline controls the particle morphology during the preparation of the particles, and acts as polar molecules in the ER fluids system. The influence of the aniline on properties of the ER fluids is a combined effect of the two roles.
The aniline-strontium titanyl oxalate (aniline-SrTi(C2O4)2) particles were prepared by a precipitation method. FTIR patterns show that aniline has been added to the surface of the SrTi(C2O4)2 particles. XRD patterns indicate that the particles are amorphous structure with a little of crystallization. The morphology of the particles was observed by SEM, the results of which indicate that with the increase of the molar ratio of aniline toTi atoms, naniline/nTi, the smorphology of aniline-SrTi(C2O4)2 particles change from approximate globular (naniline/nTi =0) to a polyhedron shape (naniline/nTi =2), and then a mixure consists of rod and cluster shaped particles (naniline/nTi =3). The electrorheological (ER) fluids were prepared with 66.7% mass fraction of aniline-SrTi(C2O4)2 particles with different aniline contentand tested. The experimental results indicate that the ER fluid prepared by the particles with a molar ratio of naniline/nTi =2 present the largest field-induced shear stress, yield stress and leak current density. The aniline controls the particle morphology during the preparation of the particles, and acts as polar molecules in the ER fluids system. The influence of the aniline on properties of the ER fluids is a combined effect of the two roles.
2014, 31(1): 88-92.
Abstract:
Fe73.5Cu1Nb3Si13.5B9 soft magnetic powder/silicone rubber composites with different powder contents are prepared by mechanical blending and precise cast pressure hot forming method, using ternary block copolymerization silicone rubber as the matrices and Fe73.5Cu1Nb3Si13.5B9 soft magnetic powder as functional filler particles. The percolation characters of the composite are deeply studied through alternating current impedance, direct current resistance and the interaction degree of particles and particle with silicone rubber. It is shown that the flexible stress sensitive composite presents remarkable double percolation character of alternating-current impedance and it is also found that the alternating current impedance in "the first percolation area" is caused by the particle tunnel transition and "the second percolation area" depends on the contact resistance of Fe73.5Cu1Nb3Si13.5B9 particle chains.
Fe73.5Cu1Nb3Si13.5B9 soft magnetic powder/silicone rubber composites with different powder contents are prepared by mechanical blending and precise cast pressure hot forming method, using ternary block copolymerization silicone rubber as the matrices and Fe73.5Cu1Nb3Si13.5B9 soft magnetic powder as functional filler particles. The percolation characters of the composite are deeply studied through alternating current impedance, direct current resistance and the interaction degree of particles and particle with silicone rubber. It is shown that the flexible stress sensitive composite presents remarkable double percolation character of alternating-current impedance and it is also found that the alternating current impedance in "the first percolation area" is caused by the particle tunnel transition and "the second percolation area" depends on the contact resistance of Fe73.5Cu1Nb3Si13.5B9 particle chains.
2014, 31(1): 93-100.
Abstract:
A vermiculite/poly(acrylic acid) (VMT/PAA) superabsorbent composite is prepared in aqueous solution by a simple one-step using glow-discharge electrolysis plasma (GDEP) induced graft copolymerization of acrylic acid (AA) and vermiculite(VMT), in which N,N'-methylenebisacrylamide (MBA) is used as a crosslinker. The structure of the resulting product is characterized by FTIR and XRD. A mechanism for synthesis of vermiculite/poly(acrylic acid) superabsorbent composite is proposed and the swelling kinetics in distilled water is systematically investigated. The influences of various pH values and salts solutions on the equilibrium swelling ratio are preliminarily studied. The results show that the swelling kinetics follows the pseudo-second-order swelling kinetics model. The vermiculite/poly(acrylic acid) superabsorbent composite is responsive to pH and salts, and it has excellent on-off switching behavior as reversible swelling and deswelling. In addition, the equilibrium swelling ratio of univalent cation salt solution is higher than that of bivalent cation salt solution.
A vermiculite/poly(acrylic acid) (VMT/PAA) superabsorbent composite is prepared in aqueous solution by a simple one-step using glow-discharge electrolysis plasma (GDEP) induced graft copolymerization of acrylic acid (AA) and vermiculite(VMT), in which N,N'-methylenebisacrylamide (MBA) is used as a crosslinker. The structure of the resulting product is characterized by FTIR and XRD. A mechanism for synthesis of vermiculite/poly(acrylic acid) superabsorbent composite is proposed and the swelling kinetics in distilled water is systematically investigated. The influences of various pH values and salts solutions on the equilibrium swelling ratio are preliminarily studied. The results show that the swelling kinetics follows the pseudo-second-order swelling kinetics model. The vermiculite/poly(acrylic acid) superabsorbent composite is responsive to pH and salts, and it has excellent on-off switching behavior as reversible swelling and deswelling. In addition, the equilibrium swelling ratio of univalent cation salt solution is higher than that of bivalent cation salt solution.
2014, 31(1): 101-106.
Abstract:
During fabricating curved composite laminate, frictional slipping processes in prepreg stack and between prepreg and mold occur. The slipping degree has significant effect on the manufacturing quality of composite. In this paper, a testing device was established to evaluate the frictional slipping behavior of prepreg systems. By means of this equipment, the frictional resistances of carbon fiber/epoxy prepreg and prepreg and prepreg and tool materials, including steel, aluminum and rubber, under different processing parameters were analyzed. The experimeantal results indicate that the change of temperature can alter the frictional mechanism in prepreg stack, while the variation of exteral pressure does not change the frictional mechanism in prepreg stack. High temperature and low external pressure decrease the frictional resistance in prepreg stack, and further the slipping behavior. In addition, the surface roughness of tool material has great effect on the frictional slipping property between prepreg and tool, and the frictional resistance is influenced by the temperature rather than the external pressure.
During fabricating curved composite laminate, frictional slipping processes in prepreg stack and between prepreg and mold occur. The slipping degree has significant effect on the manufacturing quality of composite. In this paper, a testing device was established to evaluate the frictional slipping behavior of prepreg systems. By means of this equipment, the frictional resistances of carbon fiber/epoxy prepreg and prepreg and prepreg and tool materials, including steel, aluminum and rubber, under different processing parameters were analyzed. The experimeantal results indicate that the change of temperature can alter the frictional mechanism in prepreg stack, while the variation of exteral pressure does not change the frictional mechanism in prepreg stack. High temperature and low external pressure decrease the frictional resistance in prepreg stack, and further the slipping behavior. In addition, the surface roughness of tool material has great effect on the frictional slipping property between prepreg and tool, and the frictional resistance is influenced by the temperature rather than the external pressure.
2014, 31(1): 107-111.
Abstract:
Using the mass ratio of ethylene-vinyl acetate to starch, glycerol content and NaHCO3 content as the input parameters, the tensile strength and resilience as the output parameters, a 3-layer BP (back propagation) neural network were established. The extrusion foaming orthogonal experiment result of the starch were taken as sample to forecast the properties of starch foaming materials. The results show that the BP neural network could accurately predict the properties. Meanwhile, the resilience of foaming material increases with the increase of glycerol content, while the tensile strength decreases with the glycerol content's increasing. When the mass fraction of NaHCO3 is 3%, the tensile strength reaches its minimum. The results provide information for improving the properties and expanding the application scope of the biomass foaming material.
Using the mass ratio of ethylene-vinyl acetate to starch, glycerol content and NaHCO3 content as the input parameters, the tensile strength and resilience as the output parameters, a 3-layer BP (back propagation) neural network were established. The extrusion foaming orthogonal experiment result of the starch were taken as sample to forecast the properties of starch foaming materials. The results show that the BP neural network could accurately predict the properties. Meanwhile, the resilience of foaming material increases with the increase of glycerol content, while the tensile strength decreases with the glycerol content's increasing. When the mass fraction of NaHCO3 is 3%, the tensile strength reaches its minimum. The results provide information for improving the properties and expanding the application scope of the biomass foaming material.
2014, 31(1): 112-117.
Abstract:
P(3HB-co-4HB)-PLA blend and glass fiber(GF) treated by hydrochloric acid or coupling agent were selected as the matrix and the reinforced material respectively to prepare GF/P(3HB-co-4HB)-PLA composites via melt blending in order to improve its mechanical properties and dimensional stability and enlarge its application fields. Fourier transform infrared spectroscopy(FTIR), scanning electron microscope(SEM), thermo gravimetric analyzer(TGA) and universal testing instrument etc. were used to investigate the influence of the surface treatment methods of GF on the mechanical and thermal properties, dimensional stability and fracture surface of the composites. The results show that the comprehensive properties of P(3HB-co-4HB)-PLA blends have been enhanced obviously by adding the surface-modified GF. The GF surface grafted with coupling agent can be homodispersed in the P(3HB-co-4HB)-PLA matrix to obtain better interfacial bonding. The tensile strength, flexural strength, notched impact strength and hardness of the composites with 20%(mass fraction) of GF modified by coupling agent increase by 29.38%, 20.32%, 41.38% and 15.31% respectively. The initial decomposition temperature(IDT) and vicat softening temperature(VST) of the composites increase by 6.64 ℃ and 10.7 ℃ respectively. The dimensional stability of the composites in the length direction increase by 32.47% and 33.70% respectively at room temperature or 60 ℃ for 60 d.
P(3HB-co-4HB)-PLA blend and glass fiber(GF) treated by hydrochloric acid or coupling agent were selected as the matrix and the reinforced material respectively to prepare GF/P(3HB-co-4HB)-PLA composites via melt blending in order to improve its mechanical properties and dimensional stability and enlarge its application fields. Fourier transform infrared spectroscopy(FTIR), scanning electron microscope(SEM), thermo gravimetric analyzer(TGA) and universal testing instrument etc. were used to investigate the influence of the surface treatment methods of GF on the mechanical and thermal properties, dimensional stability and fracture surface of the composites. The results show that the comprehensive properties of P(3HB-co-4HB)-PLA blends have been enhanced obviously by adding the surface-modified GF. The GF surface grafted with coupling agent can be homodispersed in the P(3HB-co-4HB)-PLA matrix to obtain better interfacial bonding. The tensile strength, flexural strength, notched impact strength and hardness of the composites with 20%(mass fraction) of GF modified by coupling agent increase by 29.38%, 20.32%, 41.38% and 15.31% respectively. The initial decomposition temperature(IDT) and vicat softening temperature(VST) of the composites increase by 6.64 ℃ and 10.7 ℃ respectively. The dimensional stability of the composites in the length direction increase by 32.47% and 33.70% respectively at room temperature or 60 ℃ for 60 d.
2014, 31(1): 118-124.
Abstract:
The structural, electronic and magnetic properties of Co10 nanowire encapsulated inside (12,0) boron nitride nanotube (BNNT) were investigated by the first-principles calculations. A approximate regular triangle cross section shape is formed for outer (12,0) BNNT in the relaxed geometry structure of Co10/BNNT(12,0) system. Binding energy analysis shows that the combining processes of Co10/BNNT(12,0) system is exothermic, and therefore the Co10 nanowire can be encapsulated into semiconducting (12,0) BNNT and form a stable hybrid structure. The charges are transferred from Co10 nanowire to more electronegative BNNT, and the formed Co-N bonds have polar covalent bond characteristics. The magnetic moment of Co10/BNNT(12,0) system is smaller than that of the freestanding Co10 nanowire. The stable Co10/BNNT(12,0) system exhibit higher magnetic moment and half-metal character implying which can be useful for a wide variety of next-generation magnetic data storage and spintronics devices.
The structural, electronic and magnetic properties of Co10 nanowire encapsulated inside (12,0) boron nitride nanotube (BNNT) were investigated by the first-principles calculations. A approximate regular triangle cross section shape is formed for outer (12,0) BNNT in the relaxed geometry structure of Co10/BNNT(12,0) system. Binding energy analysis shows that the combining processes of Co10/BNNT(12,0) system is exothermic, and therefore the Co10 nanowire can be encapsulated into semiconducting (12,0) BNNT and form a stable hybrid structure. The charges are transferred from Co10 nanowire to more electronegative BNNT, and the formed Co-N bonds have polar covalent bond characteristics. The magnetic moment of Co10/BNNT(12,0) system is smaller than that of the freestanding Co10 nanowire. The stable Co10/BNNT(12,0) system exhibit higher magnetic moment and half-metal character implying which can be useful for a wide variety of next-generation magnetic data storage and spintronics devices.
2014, 31(1): 125-132.
Abstract:
The wood fibres (WF) were esterified with maleic anhydride (MA) in a mixing chamber. Then the esterified WF (EWF), HDPE and dicumyl peroxide (DCP) were compounded to prepare EWF/HDPE composites through reactive extrusion. The mechanical properties and microstructures of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), mechanical test, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC). The results show that, the ester group is successfully introduced onto the WF via the dry process. In comparison with the WF/HDPE composite without compatibilization, EWF/HDPE composites by reactive extrusion show an increase of 112% and 36% in tensile and impact strength respectively. A significantly improved interfacial adhesion, an increase in the crystalline size and crystallinity, but a slight decrease in thermo-stability are also observed for the reactively extruded composites. The mechanism of the reactive extrusion is discussed. It is suggested that the increase in mechanical properties of the composites is mainly contributed to the compatibilization by reactive extrusion, rather than alterations in the crystal structure of HDPE matrix.
The wood fibres (WF) were esterified with maleic anhydride (MA) in a mixing chamber. Then the esterified WF (EWF), HDPE and dicumyl peroxide (DCP) were compounded to prepare EWF/HDPE composites through reactive extrusion. The mechanical properties and microstructures of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), mechanical test, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC). The results show that, the ester group is successfully introduced onto the WF via the dry process. In comparison with the WF/HDPE composite without compatibilization, EWF/HDPE composites by reactive extrusion show an increase of 112% and 36% in tensile and impact strength respectively. A significantly improved interfacial adhesion, an increase in the crystalline size and crystallinity, but a slight decrease in thermo-stability are also observed for the reactively extruded composites. The mechanism of the reactive extrusion is discussed. It is suggested that the increase in mechanical properties of the composites is mainly contributed to the compatibilization by reactive extrusion, rather than alterations in the crystal structure of HDPE matrix.
2014, 31(1): 133-139.
Abstract:
Standard specimens of microcapsule-basalt fiber/cement composite materials were prepared with cement, basalt fiber and microcapsule, designed with epoxy resin as cores and urea-formaldehyde resins (UF) as shells. Effects of fiber contents, fiber length, microcapsule mass fractions, water-cement ratio, and the curing duration were studied to the flexural strength and compressive strength of the composites. The best proportion of mechanical properties of self-healing composite was chosen by orthogonal design experiments. Results show the flexural strength rises with the increase of fiber contents. However, the compressive strength rises with the decrease of fiber contents. With the rising of fiber length, the flexural strength increases slightly while the compressive strength decreases slightly. The flexural strength rises at first and then reduces with the increase of flexural strength, while the compressive strength reduces. Both the flexural strength and the compressive strength rise with the increase of the curing duration. Composites can be repaired by self-healing microcapsule spontaneously after damages. The healing and recovery rate of flexural strength is 117% and 103%.The healing rate and recovery rate of compressive strength is 71% and 97%.
Standard specimens of microcapsule-basalt fiber/cement composite materials were prepared with cement, basalt fiber and microcapsule, designed with epoxy resin as cores and urea-formaldehyde resins (UF) as shells. Effects of fiber contents, fiber length, microcapsule mass fractions, water-cement ratio, and the curing duration were studied to the flexural strength and compressive strength of the composites. The best proportion of mechanical properties of self-healing composite was chosen by orthogonal design experiments. Results show the flexural strength rises with the increase of fiber contents. However, the compressive strength rises with the decrease of fiber contents. With the rising of fiber length, the flexural strength increases slightly while the compressive strength decreases slightly. The flexural strength rises at first and then reduces with the increase of flexural strength, while the compressive strength reduces. Both the flexural strength and the compressive strength rise with the increase of the curing duration. Composites can be repaired by self-healing microcapsule spontaneously after damages. The healing and recovery rate of flexural strength is 117% and 103%.The healing rate and recovery rate of compressive strength is 71% and 97%.
2014, 31(1): 140-145.
Abstract:
The influences of the modified polypropylene (PP) fiber and the hybrid ratio and hybrid effect of PP fiber and aramid fiber on the mechanical properties of cement-based composites were investigated. The physical models of the interface layer of fiber and cement mortar were built in order to describe the fiber reinforced mechanism of the cement mortar. The experiments show that the modified PP fiber improves the earlier flexural strength of cement mortar obviously, and the mixture of PP fiber and aramid fiber increases the later flexural strength of cement mortar significantly. The 3 days and 28 days flexural strength of the cement mortar, which reinforced by the mixture of 0.56% volume fraction of PP fiber and 0.24% volume fraction of aramid fiber, are increased by 18.48% and 31.17% compared to its ordinary cement mortar, respectively, and its 3 days and 28 days compressive strength are increased by 7.16% and 5.19%, respectively.
The influences of the modified polypropylene (PP) fiber and the hybrid ratio and hybrid effect of PP fiber and aramid fiber on the mechanical properties of cement-based composites were investigated. The physical models of the interface layer of fiber and cement mortar were built in order to describe the fiber reinforced mechanism of the cement mortar. The experiments show that the modified PP fiber improves the earlier flexural strength of cement mortar obviously, and the mixture of PP fiber and aramid fiber increases the later flexural strength of cement mortar significantly. The 3 days and 28 days flexural strength of the cement mortar, which reinforced by the mixture of 0.56% volume fraction of PP fiber and 0.24% volume fraction of aramid fiber, are increased by 18.48% and 31.17% compared to its ordinary cement mortar, respectively, and its 3 days and 28 days compressive strength are increased by 7.16% and 5.19%, respectively.
2014, 31(1): 146-151.
Abstract:
The Ni-BaTiO3/polyvinylidene fluoride (Ni-BaTiO3/PVDF) and Ag-BaTiO3/PVDF three-component composites were prepared to improve the breakdown strength of the composites, in which Ni and Ag metal nano-particles were used as the third phase. The effects of addition, particle size and type of metals on the breakdown strengths of the composites were studied. The experimental results show that all breakdown strengths of Ni-BaTiO3/PVDF and Ag-BaTiO3/PVDF three-component composites increase firstly and then decline with the increase of Ni or Ag addition. And all composites give comparative dielectric constants than those without metals addition and each has maximum breakdown strength over the range of metal addition. For same type metal of Ni, addition with smaller size of Ni is better for enhancing the breakdown strength of the composites. Moreover with the same particle size and addition, Ni-BaTiO3/PVDF composites show better breakdown performance. The breakdown strength of Ni(50 nm)-BaTiO3/PVDF nanocomposite with 1.90% volume fraction of Ni reaches up to 200 kV/mm and its energy density is about five times of BaTiO3/PVDF composite. The Coulomb blockade effect is employed to explain the dielectric breakdown strengths under high electric field of such kind of composties.
The Ni-BaTiO3/polyvinylidene fluoride (Ni-BaTiO3/PVDF) and Ag-BaTiO3/PVDF three-component composites were prepared to improve the breakdown strength of the composites, in which Ni and Ag metal nano-particles were used as the third phase. The effects of addition, particle size and type of metals on the breakdown strengths of the composites were studied. The experimental results show that all breakdown strengths of Ni-BaTiO3/PVDF and Ag-BaTiO3/PVDF three-component composites increase firstly and then decline with the increase of Ni or Ag addition. And all composites give comparative dielectric constants than those without metals addition and each has maximum breakdown strength over the range of metal addition. For same type metal of Ni, addition with smaller size of Ni is better for enhancing the breakdown strength of the composites. Moreover with the same particle size and addition, Ni-BaTiO3/PVDF composites show better breakdown performance. The breakdown strength of Ni(50 nm)-BaTiO3/PVDF nanocomposite with 1.90% volume fraction of Ni reaches up to 200 kV/mm and its energy density is about five times of BaTiO3/PVDF composite. The Coulomb blockade effect is employed to explain the dielectric breakdown strengths under high electric field of such kind of composties.
2014, 31(1): 152-157.
Abstract:
The elastic properties and deformation mechanisms of graphene/Cu composites were studied by using molecular dynamics method, with combination of embedded atom method (EAM), reactive empirical bonding order (REBO) potential and Morse potential together. Young's moduli of the composites with different volume fraction of graphene were obtained as a linear function of the volume friction of graphene, which is consistent with the prediction by Halpin-Tsai model. In addition, the yield stress of the composites can also be improved by the graphene. Based on the comparison of the initial crack propagation in single-crystalline Cu and graphene/Cu composites, it is found that the addition of graphene is beneficial to inhibit crack propagation. Slipping along the graphene surface explains the deformation mechanism of the composites, and the results indicate graphene can dramatically improve the plastic deformation capability of the composites.
The elastic properties and deformation mechanisms of graphene/Cu composites were studied by using molecular dynamics method, with combination of embedded atom method (EAM), reactive empirical bonding order (REBO) potential and Morse potential together. Young's moduli of the composites with different volume fraction of graphene were obtained as a linear function of the volume friction of graphene, which is consistent with the prediction by Halpin-Tsai model. In addition, the yield stress of the composites can also be improved by the graphene. Based on the comparison of the initial crack propagation in single-crystalline Cu and graphene/Cu composites, it is found that the addition of graphene is beneficial to inhibit crack propagation. Slipping along the graphene surface explains the deformation mechanism of the composites, and the results indicate graphene can dramatically improve the plastic deformation capability of the composites.
2014, 31(1): 158-165.
Abstract:
A Fe3O4/chitosan magnetic composite particle loading riboflavin used as model of drug is prepared through a co-precipitation process in situ. The chemical component, morphology and magnetic property were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. The results show that the diameter of a typical Fe3O4/chitosan composite particle is about 40 nm and the distribution is uniform, the average magnetic response time is 52 s, and the strength of saturation magnetization is 3.313 2 A·m2·kg-1. The drug content (mass fraction), the drug loading efficiency and the in vitro release profiles under simulated gastric fluid, simulated intestinal fluid, saline, glucose solution using in medicine and redistilled water were investigated using UV/Vis spectrophotometry, respectively. The results show that the drug content is about 9.9%, the drug loading efficiency reaches 70.8%, and the Fe3O4/chitosan composite particle displays an excellent drug controlled release behavior under the experimental conditions of the simulated intestinal fluid. Less than 16.06% of the drug is released from composite particle after 10 h but up to 52.18% after 60 h.
A Fe3O4/chitosan magnetic composite particle loading riboflavin used as model of drug is prepared through a co-precipitation process in situ. The chemical component, morphology and magnetic property were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. The results show that the diameter of a typical Fe3O4/chitosan composite particle is about 40 nm and the distribution is uniform, the average magnetic response time is 52 s, and the strength of saturation magnetization is 3.313 2 A·m2·kg-1. The drug content (mass fraction), the drug loading efficiency and the in vitro release profiles under simulated gastric fluid, simulated intestinal fluid, saline, glucose solution using in medicine and redistilled water were investigated using UV/Vis spectrophotometry, respectively. The results show that the drug content is about 9.9%, the drug loading efficiency reaches 70.8%, and the Fe3O4/chitosan composite particle displays an excellent drug controlled release behavior under the experimental conditions of the simulated intestinal fluid. Less than 16.06% of the drug is released from composite particle after 10 h but up to 52.18% after 60 h.
2014, 31(1): 166-170.
Abstract:
Nano-sized polyhedral oligomeric silsesquioxane-TriSilanol cyclohexyl (POSS) particulates reinforced Sn-3.5Ag composite solder joint could improve mechanical reliability. The 3% fraction of POSS reinforcement is the best weight fraction. The welding characterization of POSS reinforcement in 3% POSS/Sn-Ag composite solder was analyzed through differential scanning calorimeter (DSC) analysis based on former experimental results in this paper. Results indicate that the welding temperature of 3% POSS/Sn-Ag composite solder is similar to that of Sn-3.5Ag eutectic solder, so 3% POSS/Sn-Ag composite solder has acceptable processing property. In addition, according to DSC analysis, 3% POSS/Sn-Ag composite solder has higher activation energy. It demonstrates that POSS reinforcements might be present in the Sn boundaries.
Nano-sized polyhedral oligomeric silsesquioxane-TriSilanol cyclohexyl (POSS) particulates reinforced Sn-3.5Ag composite solder joint could improve mechanical reliability. The 3% fraction of POSS reinforcement is the best weight fraction. The welding characterization of POSS reinforcement in 3% POSS/Sn-Ag composite solder was analyzed through differential scanning calorimeter (DSC) analysis based on former experimental results in this paper. Results indicate that the welding temperature of 3% POSS/Sn-Ag composite solder is similar to that of Sn-3.5Ag eutectic solder, so 3% POSS/Sn-Ag composite solder has acceptable processing property. In addition, according to DSC analysis, 3% POSS/Sn-Ag composite solder has higher activation energy. It demonstrates that POSS reinforcements might be present in the Sn boundaries.
2014, 31(1): 171-178.
Abstract:
A mesoscale model of void-containing composites was built by DIGIMAT/FE, which includes three phases (fiber, resin and void) and effectively reflects the real microstructure and mesoscale material properties of the composites. Ultrasonic excitation was loaded into the model by ABAQUS/EXPLICIT for finite element analysis (FEA). Acoustic propagation process was extracted to build a relationship between ultrasonic attenuation coefficient and porosity of unidirectional continuous fiber reinforced composites. Taking T800/epoxy composite as an example, the effect of void size on the numerical prediction of ultrasonic attenuation was studied, and the accuracy of the FEA model was verified by making a comparison between the numerical and analytical predictions. The simulation method will be an effective guidance for experimental process, and a theoretical basis for reducing porosity to increase the service performance of composites.
A mesoscale model of void-containing composites was built by DIGIMAT/FE, which includes three phases (fiber, resin and void) and effectively reflects the real microstructure and mesoscale material properties of the composites. Ultrasonic excitation was loaded into the model by ABAQUS/EXPLICIT for finite element analysis (FEA). Acoustic propagation process was extracted to build a relationship between ultrasonic attenuation coefficient and porosity of unidirectional continuous fiber reinforced composites. Taking T800/epoxy composite as an example, the effect of void size on the numerical prediction of ultrasonic attenuation was studied, and the accuracy of the FEA model was verified by making a comparison between the numerical and analytical predictions. The simulation method will be an effective guidance for experimental process, and a theoretical basis for reducing porosity to increase the service performance of composites.
2014, 31(1): 179-186.
Abstract:
Based on the meso-structure of 3D full five-directional (Q5D) braided composites, a nonlinear finite element model with interface phase was presented to simulate the damage and failure of Q5D braided composites under unidirectional tension by introducing the interfacial phase element. The failure criteria proposed by Linde and Von-Mises criteria were considered for initial damage prediction of yarns and matrix. Quads failure criteria was adopted to identify the onset of debonding of the interface phase. The progressive damage of Q5D braided composites with interface phase was studied subjected to longitudinal tensile loading, and ultimate strength of the sample was obtained. The damage mechanisms were revealed in the simulation process and the changing characteristics of mechanical behaviors of braided composites with the interfacial properties were described. The results show that the numerical simulation results are in a good agreement with experimental results, which validate the effectiveness of the model and provide a basis for the analysis of mechanical properties and optimization design of structures.
Based on the meso-structure of 3D full five-directional (Q5D) braided composites, a nonlinear finite element model with interface phase was presented to simulate the damage and failure of Q5D braided composites under unidirectional tension by introducing the interfacial phase element. The failure criteria proposed by Linde and Von-Mises criteria were considered for initial damage prediction of yarns and matrix. Quads failure criteria was adopted to identify the onset of debonding of the interface phase. The progressive damage of Q5D braided composites with interface phase was studied subjected to longitudinal tensile loading, and ultimate strength of the sample was obtained. The damage mechanisms were revealed in the simulation process and the changing characteristics of mechanical behaviors of braided composites with the interfacial properties were described. The results show that the numerical simulation results are in a good agreement with experimental results, which validate the effectiveness of the model and provide a basis for the analysis of mechanical properties and optimization design of structures.
2014, 31(1): 187-193.
Abstract:
Finite element model(FEM) of the embedded co-cured perforated damping layer composite structure (ECPDLCS)was developed, and the improved mode strain energy method to predict the mode loss factor was presented. The FEM simulation results were verified by experiment data, which indicates the method and model proposed by this paper was valid. The valid model and method was employed to investigate the effects of the damping layer thickness, punch diameter and spacing on the mode loss factor and natural frequency of the embedded co-cured perforated damping layer composite structure. The impact of punch diameter and spacing on dynamics characteristics in the same damping layer area ratio was also explored. The result shows that the increasing of damping layer thickness and reducing of diameter and/or spacing can enhance mode loss factor, however the mode frequency is decreased. Under the same damping layer area ratio, the mode loss factor is rose and the mode frequency is decreased with the increasing of diameter and spacing. The conclusion is very important for the theoretical prediction of the dynamics characteristics of the ECPDLCS.
Finite element model(FEM) of the embedded co-cured perforated damping layer composite structure (ECPDLCS)was developed, and the improved mode strain energy method to predict the mode loss factor was presented. The FEM simulation results were verified by experiment data, which indicates the method and model proposed by this paper was valid. The valid model and method was employed to investigate the effects of the damping layer thickness, punch diameter and spacing on the mode loss factor and natural frequency of the embedded co-cured perforated damping layer composite structure. The impact of punch diameter and spacing on dynamics characteristics in the same damping layer area ratio was also explored. The result shows that the increasing of damping layer thickness and reducing of diameter and/or spacing can enhance mode loss factor, however the mode frequency is decreased. Under the same damping layer area ratio, the mode loss factor is rose and the mode frequency is decreased with the increasing of diameter and spacing. The conclusion is very important for the theoretical prediction of the dynamics characteristics of the ECPDLCS.
2014, 31(1): 194-199.
Abstract:
The optimization design of composite strut-braced wings with aeroelastic constraint was conducted by using the genetic-gradient hybrid algorithm, and a comparison between the strut-braced wing configuration and conventional configuration was also presented. The objective was to minimize the structural mass subject to the constraints of deformation at wingtip, buckling and flutter speed. The composite layups and structural parameters of strut were designed in the case of critical load conditions. The influences of strut locations on optimal designs were investigated. The results indicate that the material in the bending direction can be dramatically reduced by using the composite strut-braced wing, which has an obvious advantage in reducing structural mass. The structural mass, buckling and distribution of torsion stiffness can be significantly affected by the strut location. The buckling failure of strut should be taken into account in the structural design of composite strut-braced wing.
The optimization design of composite strut-braced wings with aeroelastic constraint was conducted by using the genetic-gradient hybrid algorithm, and a comparison between the strut-braced wing configuration and conventional configuration was also presented. The objective was to minimize the structural mass subject to the constraints of deformation at wingtip, buckling and flutter speed. The composite layups and structural parameters of strut were designed in the case of critical load conditions. The influences of strut locations on optimal designs were investigated. The results indicate that the material in the bending direction can be dramatically reduced by using the composite strut-braced wing, which has an obvious advantage in reducing structural mass. The structural mass, buckling and distribution of torsion stiffness can be significantly affected by the strut location. The buckling failure of strut should be taken into account in the structural design of composite strut-braced wing.
2014, 31(1): 200-206.
Abstract:
Drop hammer low-velocity impact(LVI) tests on composite stiffened panel were carried out. Impact support bracket was designed based on specimen configuration, and effect of bracket pitch on impact damage was studied. Impact tests with the same energy on three typical positions of specimen were carried out to obtain the damage appearance. Compressive tests were conducted and test results of damaged specimens and undamaged ones were compared to analysis the effect of impact position on the compressive performance of the structure. Test results show that, with the same impact energy, the smaller the bracket pitch is, the severer the impact damage is. With the same impact energy of 50 J, damage on the stiffener skin is almost invisible, and damage on the skin between stiffeners is clearly visible, while impact on stiffener edge skin can result in debonding of the stiffener flange. Impact damage can slightly reduce the buckling load of the structure. The impact damage on the skin between stiffeners or on the stiffener skin has little effect on the compressive performance, while impact on stiffener edge skin can induce local buckling of damaged skin, and it has a notable effect on the failure pattern as well as the ultimate strength of the structure.
Drop hammer low-velocity impact(LVI) tests on composite stiffened panel were carried out. Impact support bracket was designed based on specimen configuration, and effect of bracket pitch on impact damage was studied. Impact tests with the same energy on three typical positions of specimen were carried out to obtain the damage appearance. Compressive tests were conducted and test results of damaged specimens and undamaged ones were compared to analysis the effect of impact position on the compressive performance of the structure. Test results show that, with the same impact energy, the smaller the bracket pitch is, the severer the impact damage is. With the same impact energy of 50 J, damage on the stiffener skin is almost invisible, and damage on the skin between stiffeners is clearly visible, while impact on stiffener edge skin can result in debonding of the stiffener flange. Impact damage can slightly reduce the buckling load of the structure. The impact damage on the skin between stiffeners or on the stiffener skin has little effect on the compressive performance, while impact on stiffener edge skin can induce local buckling of damaged skin, and it has a notable effect on the failure pattern as well as the ultimate strength of the structure.
2014, 31(1): 207-212.
Abstract:
Based on the elastic foundation beam model, the bilinear cohesive constitutive relation was introduced through the relationship between the deflection and the relative displacement, unified description of interface damage state through the interface damage factor was used, and the damage cohesive zone was taken into account in the crack tip and the general solutions of each segment of double cantilever beam(DCB) specimen were found. The integral constant was solved with the continuity boundary conditions, and the load-displacement curve was obtained with of crack length and the cohesive zone range as the variables, thus DCB specimen crack propagation process was obtained. To verify presented theoretical analysis, in which the nonlinear phenomenon after elastic segment and the effect of the three cohesive parameters were considered simultaneously, some comparisons were made with the existing theoretical results. The effect of three interface parameters on the DCB specimen load-displacement curve was investigated, and the results provide the basis for the selection of interface parameters. The relationship between interface parameters and cohesive zone length was given.
Based on the elastic foundation beam model, the bilinear cohesive constitutive relation was introduced through the relationship between the deflection and the relative displacement, unified description of interface damage state through the interface damage factor was used, and the damage cohesive zone was taken into account in the crack tip and the general solutions of each segment of double cantilever beam(DCB) specimen were found. The integral constant was solved with the continuity boundary conditions, and the load-displacement curve was obtained with of crack length and the cohesive zone range as the variables, thus DCB specimen crack propagation process was obtained. To verify presented theoretical analysis, in which the nonlinear phenomenon after elastic segment and the effect of the three cohesive parameters were considered simultaneously, some comparisons were made with the existing theoretical results. The effect of three interface parameters on the DCB specimen load-displacement curve was investigated, and the results provide the basis for the selection of interface parameters. The relationship between interface parameters and cohesive zone length was given.
2014, 31(1): 213-219.
Abstract:
Three dimensional finite element model of composite fastener was established based on Abaqus to predict the thread load distribution of composite fasteners. In order to simulate the real situation, the nut was placed on an elastic foundation and the tension-compression modulus asymmetry of C or SiC matrix composites was considered by Abaqus users' subroutine USDFLD. Furthermore, Yamamoto's method for the metal threaded connections was empirically extended to the connections by C or SiC matrix composites with special consideration of the anisotropy and tension-compression modulus asymmetry. The effectiveness of the extended Yamamoto's method (EYM) was validated by finite element method (FEM) for different materials and different geometry parameters. The results show that the load distribution of composite fasteners is usually more uniform than that of the metal fasteners. In addition, the nonuniformity of load distribution increases with the pitch-to-diameter ratio, but the relative rotation of bolt and nut almost have no effect on the load distribution.
Three dimensional finite element model of composite fastener was established based on Abaqus to predict the thread load distribution of composite fasteners. In order to simulate the real situation, the nut was placed on an elastic foundation and the tension-compression modulus asymmetry of C or SiC matrix composites was considered by Abaqus users' subroutine USDFLD. Furthermore, Yamamoto's method for the metal threaded connections was empirically extended to the connections by C or SiC matrix composites with special consideration of the anisotropy and tension-compression modulus asymmetry. The effectiveness of the extended Yamamoto's method (EYM) was validated by finite element method (FEM) for different materials and different geometry parameters. The results show that the load distribution of composite fasteners is usually more uniform than that of the metal fasteners. In addition, the nonuniformity of load distribution increases with the pitch-to-diameter ratio, but the relative rotation of bolt and nut almost have no effect on the load distribution.
2014, 31(1): 220-226.
Abstract:
In this paper, a modified virtual crack closure technique proposed by author had been used to analyze the interface fracture of jointed area in multi-material components under a combined thermal and mechanical loading. Firstly, through the fracture analysis of a single leg bending (SLB) model which was established with a rubber sandwich under the different thermal loading, the rubber sandwich's influence on the energy release rate as well as each component was studied. Then, the interface fracture of typical multi-material cylindrical shell skirts composed by composite-rubber-metal under a combined thermal and mechanical loading, which had a heat flux boundary, was analyzed. It shows that the energy release rate of the interface crack gradually increases as the temperature rises. Lastly, the effect of the position of delamination and the thickness of the rubber on the energy release rate of each interface was discussed. It can be seen that there is a size effect between rubber thickness and interface toughness.
In this paper, a modified virtual crack closure technique proposed by author had been used to analyze the interface fracture of jointed area in multi-material components under a combined thermal and mechanical loading. Firstly, through the fracture analysis of a single leg bending (SLB) model which was established with a rubber sandwich under the different thermal loading, the rubber sandwich's influence on the energy release rate as well as each component was studied. Then, the interface fracture of typical multi-material cylindrical shell skirts composed by composite-rubber-metal under a combined thermal and mechanical loading, which had a heat flux boundary, was analyzed. It shows that the energy release rate of the interface crack gradually increases as the temperature rises. Lastly, the effect of the position of delamination and the thickness of the rubber on the energy release rate of each interface was discussed. It can be seen that there is a size effect between rubber thickness and interface toughness.
2014, 31(1): 227-233.
Abstract:
The composite flat woven preform deformation during the draping process was analyzed, and several fundamental assumptions were proposed for draping simulation. Based on the existing fishnet algorithms, a surface information based improved fishnet algorithm (SIB fishnet algorithm) was proposed. In this algorithm, geometry information of the surface such as tangent vector and normal curvature is used to determine the position of the current node. The use of the geometry information simplifies the mapping calculation and improves the computational accuracy. Surface-surface intersection algorithm needed for the SIB-fishnet algorithm was also studied in this paper. The draping simulation results of sphere and saddle surface generated by different algorithms were compared to verify the accuracy and stability of the SIB fishnet algorithm.
The composite flat woven preform deformation during the draping process was analyzed, and several fundamental assumptions were proposed for draping simulation. Based on the existing fishnet algorithms, a surface information based improved fishnet algorithm (SIB fishnet algorithm) was proposed. In this algorithm, geometry information of the surface such as tangent vector and normal curvature is used to determine the position of the current node. The use of the geometry information simplifies the mapping calculation and improves the computational accuracy. Surface-surface intersection algorithm needed for the SIB-fishnet algorithm was also studied in this paper. The draping simulation results of sphere and saddle surface generated by different algorithms were compared to verify the accuracy and stability of the SIB fishnet algorithm.
2014, 31(1): 234-240.
Abstract:
Based upon the large deflection equation of anisotropic composite panels, an analytical method for the buckling under in-plane bending load of orthotropic composite laminates has been presented by utilizing Ritz method and the principle of minimum potential energy. Moreover, a stress analysis method for the buckling of composite laminates under bending-shear combination loads was presented as well. The result by the present method was compared with that by the finite element method (FEM). The result by both the present method and FEM agree very well. The expression for the present method is clear and concise, which is easy to be applied in engineering practices.
Based upon the large deflection equation of anisotropic composite panels, an analytical method for the buckling under in-plane bending load of orthotropic composite laminates has been presented by utilizing Ritz method and the principle of minimum potential energy. Moreover, a stress analysis method for the buckling of composite laminates under bending-shear combination loads was presented as well. The result by the present method was compared with that by the finite element method (FEM). The result by both the present method and FEM agree very well. The expression for the present method is clear and concise, which is easy to be applied in engineering practices.
2014, 31(1): 241-247.
Abstract:
The fracture behavior of four non-symmetric radial cracks originating from a circular hole in piezoelectric composite materials subjected to remotely uniform in-plane electric loading and anti-plane mechanical loading was studied in this paper. The problem was transformed using the complex variable method and a new mapping function into Cauchy integral equations. By solving the Cauchy integral equations, the analytical solutions of electric and elastic fields and field intensity factors near the crack tip were obtained under the electrically impermeable and permeable assumptions. Several known results were the special cases of the present results and new models used for simulating more practical defects in piezoelectric composite materials were derived as well, such as three radial cracks originating from a circular hole, semi-circular hole with an edge crack originating from a semi-infinite plane and a semi-infinite plane with an edge crack. A well agreement of the analytical solutions with the finite element results shows the accuracy and efficiency of the present method. Numerical examples are provided graphically to show the effects of the geometrical parameters on the field intensity factors.
The fracture behavior of four non-symmetric radial cracks originating from a circular hole in piezoelectric composite materials subjected to remotely uniform in-plane electric loading and anti-plane mechanical loading was studied in this paper. The problem was transformed using the complex variable method and a new mapping function into Cauchy integral equations. By solving the Cauchy integral equations, the analytical solutions of electric and elastic fields and field intensity factors near the crack tip were obtained under the electrically impermeable and permeable assumptions. Several known results were the special cases of the present results and new models used for simulating more practical defects in piezoelectric composite materials were derived as well, such as three radial cracks originating from a circular hole, semi-circular hole with an edge crack originating from a semi-infinite plane and a semi-infinite plane with an edge crack. A well agreement of the analytical solutions with the finite element results shows the accuracy and efficiency of the present method. Numerical examples are provided graphically to show the effects of the geometrical parameters on the field intensity factors.
2014, 31(1): 248-253.
Abstract:
Carbon fiber reinforced polymer (CFRP) tendons applied in the bridge engineering are generally sustained with cyclic load, which may bring degradation of the tendons' mechanical properties. The initial mechanical properties of CFRP tendons were tested through static load testing firstly. Then the effect of cyclic load on elastic modulus, relaxation and tensile strength of CFRP tendons under every stage was investigated through fatigue tests. The results show that the elastic modulus of the tendons under ultimate tensile state is about 5% higher than initial condition. Therefore, when the deformation of CFRP tendons has a significant impact on internal force of structure, the nonlinear problem of CFRP material is strongly recommended to be considered during structure designing stage. Two million times of normal service cyclic loading has little effect on elastic modulus, relaxation and tensile strength of CFRP tendons. Under the cycle loading with the stress range of 4.3% of ultimate tensile strength, the tensile strength of CFRP tendons increases by 1.2%. However, when the stress range reaches to 7%, there is no significant change in tensile strength compared with that under the initial condition.
Carbon fiber reinforced polymer (CFRP) tendons applied in the bridge engineering are generally sustained with cyclic load, which may bring degradation of the tendons' mechanical properties. The initial mechanical properties of CFRP tendons were tested through static load testing firstly. Then the effect of cyclic load on elastic modulus, relaxation and tensile strength of CFRP tendons under every stage was investigated through fatigue tests. The results show that the elastic modulus of the tendons under ultimate tensile state is about 5% higher than initial condition. Therefore, when the deformation of CFRP tendons has a significant impact on internal force of structure, the nonlinear problem of CFRP material is strongly recommended to be considered during structure designing stage. Two million times of normal service cyclic loading has little effect on elastic modulus, relaxation and tensile strength of CFRP tendons. Under the cycle loading with the stress range of 4.3% of ultimate tensile strength, the tensile strength of CFRP tendons increases by 1.2%. However, when the stress range reaches to 7%, there is no significant change in tensile strength compared with that under the initial condition.
