2019 Vol. 36, No. 4
2019, 36(4): 771-783.
doi: 10.13801/j.cnki.fhclxb.20181018.002
Abstract:
Fiber reinforced thermoplastic composites (CFRTPs) are highly attractive in the fields of aerospace, automobile, and etc. due to their ease of fabrication, good recyclability and excellent mechanical properties. With the development of nanotechnology, it was found that nanomaterials, such as carbon nanotube, graphene and inorganic nanoparticles are effective to enhance the mechanical properties of CFRTPs. The recent development in the fabrication of nano-modified CFRTPs and their mechanical properties were reviewed in this paper. The two techniques for nano-modification of CFRTPs, including directly dispersing nanoparticles into thermoplastic matrix and modification of fibers with nanoparticles, were introduced. The effects of nanoparticle introduction on the mechanical properties including interfacial bonding properties, tensile/flexure properties, dynamic mechanical properties and impact properties of CFRTPs were analyzed. Finally, the challenges and outlook for nano-modification of CFRTPs were outlined.
Fiber reinforced thermoplastic composites (CFRTPs) are highly attractive in the fields of aerospace, automobile, and etc. due to their ease of fabrication, good recyclability and excellent mechanical properties. With the development of nanotechnology, it was found that nanomaterials, such as carbon nanotube, graphene and inorganic nanoparticles are effective to enhance the mechanical properties of CFRTPs. The recent development in the fabrication of nano-modified CFRTPs and their mechanical properties were reviewed in this paper. The two techniques for nano-modification of CFRTPs, including directly dispersing nanoparticles into thermoplastic matrix and modification of fibers with nanoparticles, were introduced. The effects of nanoparticle introduction on the mechanical properties including interfacial bonding properties, tensile/flexure properties, dynamic mechanical properties and impact properties of CFRTPs were analyzed. Finally, the challenges and outlook for nano-modification of CFRTPs were outlined.
2019, 36(4): 784-794.
doi: 10.13801/j.cnki.fhclxb.20190102.001
Abstract:
In-situ consolidation technology of continuous fiber reinforced thermoplastic matrix composites which means the parts manufacturing can be completed simultaneously could be achieved by auto fiber placement(AFP) machine with the cost decrease of more than 50%.Due to its high efficiency and low consumption, the in-situ consolidation technology is considered to have wide application prospects in aviation field. The research and application of thermoplastic composite in-situ consolidation technology in aviation field at home and abroad were investigated. The current level of materials, equipment and process control on in-situ consolidation technology has been analyzed combined with the typical application of the technology. Meanwhile, the latest development trend of in-situ consolidation technology was also being stated.
In-situ consolidation technology of continuous fiber reinforced thermoplastic matrix composites which means the parts manufacturing can be completed simultaneously could be achieved by auto fiber placement(AFP) machine with the cost decrease of more than 50%.Due to its high efficiency and low consumption, the in-situ consolidation technology is considered to have wide application prospects in aviation field. The research and application of thermoplastic composite in-situ consolidation technology in aviation field at home and abroad were investigated. The current level of materials, equipment and process control on in-situ consolidation technology has been analyzed combined with the typical application of the technology. Meanwhile, the latest development trend of in-situ consolidation technology was also being stated.
2019, 36(4): 795-800.
doi: 10.13801/j.cnki.fhclxb.20180529.001
Abstract:
Space ultrahigh frequency remote sensing reflectors (above 600 GHz in operating frequency range) will cause thermal deformation problems due to non-uniform spatial temperature changes during orbital operation. In order to ensure the electrical performance of the reflecting surface, the space ultrahigh frequency remote sensing reflector requires the surface accuracy of the reflecting surface to have a root mean square of r ≤ 10 μm. Therefore, a novel single-panel grid structure reflector was innovatively proposed, and the thermal deformation analysis of the reflector was performed using finite element analysis software. The influence of different structural parameters of the reflector on the thermal deformation of the reflector was studied, and the structural parameters of the reflector were optimized based on the principle of low thermal deformation. The optimized results still couldn't meet the surface accuracy requirements of space ultrahigh frequency remote sensing reflectors. Therefore, a zero-expansion composite with coefficient of thermal expansion α ≤ 0.5×10-7℃-1 was designed and manufactured. The zero-expansion composite is combined with carbon fiber reinforced polymer composites (CFRP) and Kevlar fiber fabric interlaced and layered in a certain ratio. By adjusting the ratio of reflecting surface laminates, the thermal deformation of the reflecting surface can be reduced to 7.94 μm to meet the surface accuracy requirements of ultrahigh frequency remote sensing reflector.
Space ultrahigh frequency remote sensing reflectors (above 600 GHz in operating frequency range) will cause thermal deformation problems due to non-uniform spatial temperature changes during orbital operation. In order to ensure the electrical performance of the reflecting surface, the space ultrahigh frequency remote sensing reflector requires the surface accuracy of the reflecting surface to have a root mean square of r ≤ 10 μm. Therefore, a novel single-panel grid structure reflector was innovatively proposed, and the thermal deformation analysis of the reflector was performed using finite element analysis software. The influence of different structural parameters of the reflector on the thermal deformation of the reflector was studied, and the structural parameters of the reflector were optimized based on the principle of low thermal deformation. The optimized results still couldn't meet the surface accuracy requirements of space ultrahigh frequency remote sensing reflectors. Therefore, a zero-expansion composite with coefficient of thermal expansion α ≤ 0.5×10-7℃-1 was designed and manufactured. The zero-expansion composite is combined with carbon fiber reinforced polymer composites (CFRP) and Kevlar fiber fabric interlaced and layered in a certain ratio. By adjusting the ratio of reflecting surface laminates, the thermal deformation of the reflecting surface can be reduced to 7.94 μm to meet the surface accuracy requirements of ultrahigh frequency remote sensing reflector.
2019, 36(4): 801-810.
doi: 10.13801/j.cnki.fhclxb.20180608.001
Abstract:
The silicon dioxide/low density polyethylene (SiO2/LDPE) nanocomposites were developed by filling SiO2 nanoparticles into LDPE matrix with melt-blending preparing method to investigate nano-modification method and correlated mechanism for insulation performance improvement of LDPE. The micro-morphology and dispersivity of SiO2 nanofillers composite in LDPE matrix were characterized by scanning electron microscopy (SEM). The differential scanning calorimetry (DSC) and polarizing microscope (PLM) were employed to testify the effects of SiO2 nanofillers on the crystallinity and crystal morphology of LDPE matrix. The trap energy level and density were tested by thermal stimulated current (TSC), combining the Weibull statistics of electric breakdown strength to investigate insulation breakdown performance and attributed mechanism. The nano-SiO2 filling rate can change the crystallinity of composites, while the change will increase the intrinsic structural defects and trap density of LDPE matrix. At the same time, filling nano-SiO2 particles can introduce deeper trap levels than the intrinsic traps of LDPE matrix. Therefore, the most efficient inhibition to electric breakdown process by trapping charge carriers with largest energy, and thus the maximum breakdown strength are obtained for 3wt% filling rate of SiO2/LDPE nanocomposites. In comparison with 60 nm SiO2 nanoparticles, the 30 nm SiO2 nanoparticles with larger specific surface area filled into LDPE render higher dielectric permittivity from SiO2-LDPE interface polarization, indicating the more efficient enhancement for electric breakdown strength by higher-density deep traps at larger-area nano-interfaces. Based on dielectric double-layer theory, the reliable models of electron capture and interface structure were put forward so as to reasonably represent the microscopic trap characteristics and macroscopic electric breakdown mechanism of SiO2/LDPE nanocomposites.
The silicon dioxide/low density polyethylene (SiO2/LDPE) nanocomposites were developed by filling SiO2 nanoparticles into LDPE matrix with melt-blending preparing method to investigate nano-modification method and correlated mechanism for insulation performance improvement of LDPE. The micro-morphology and dispersivity of SiO2 nanofillers composite in LDPE matrix were characterized by scanning electron microscopy (SEM). The differential scanning calorimetry (DSC) and polarizing microscope (PLM) were employed to testify the effects of SiO2 nanofillers on the crystallinity and crystal morphology of LDPE matrix. The trap energy level and density were tested by thermal stimulated current (TSC), combining the Weibull statistics of electric breakdown strength to investigate insulation breakdown performance and attributed mechanism. The nano-SiO2 filling rate can change the crystallinity of composites, while the change will increase the intrinsic structural defects and trap density of LDPE matrix. At the same time, filling nano-SiO2 particles can introduce deeper trap levels than the intrinsic traps of LDPE matrix. Therefore, the most efficient inhibition to electric breakdown process by trapping charge carriers with largest energy, and thus the maximum breakdown strength are obtained for 3wt% filling rate of SiO2/LDPE nanocomposites. In comparison with 60 nm SiO2 nanoparticles, the 30 nm SiO2 nanoparticles with larger specific surface area filled into LDPE render higher dielectric permittivity from SiO2-LDPE interface polarization, indicating the more efficient enhancement for electric breakdown strength by higher-density deep traps at larger-area nano-interfaces. Based on dielectric double-layer theory, the reliable models of electron capture and interface structure were put forward so as to reasonably represent the microscopic trap characteristics and macroscopic electric breakdown mechanism of SiO2/LDPE nanocomposites.
2019, 36(4): 811-825.
doi: 10.13801/j.cnki.fhclxb.20180419.001
Abstract:
The stiffened panel of the typical aerospace carbon fiber reinforced polymer composite structure was studied by analyzing the characteristics of the U3160 unidirectional fabric organization structure. The compression response of the fiber bundle was theoretically modeled according to the compression deformation state of the fiber bundle. Based on the fiber bundle compression model, the thickness change responses of the U3160 unidirectional fabric preform with the 0°/45°/90°/-45°stacking sequence under the influence of compressive stress were forecasted. The permeability model of the fabric preform under the effect of compression stress was formed. Based on the fabric compression model, the equivalent permeability model of fiber bundle was established. According to the tensor theory, the equivalent permeability model of the 0°, ±45° and 90° ply fabric was established respectively. By using the series-parallel relationship of permeable media, the comprehensive characterization model of permeability in each characteristic zone of stiffened panel was established. Based on the PAM-RTM flow simulation software, the permeability of the partition zone was defined, the flowing behavior of resin in the stiffened-panel fabric preforms was simulated during the filling process, the technological parameters was optimized to determine the final filling program, and the models of stiffened panel were made to carry out the molding experiment to verify the rationality of filling program. The work provides the theoretical basis for the successful production, which can be used to finally guide the practice.
The stiffened panel of the typical aerospace carbon fiber reinforced polymer composite structure was studied by analyzing the characteristics of the U3160 unidirectional fabric organization structure. The compression response of the fiber bundle was theoretically modeled according to the compression deformation state of the fiber bundle. Based on the fiber bundle compression model, the thickness change responses of the U3160 unidirectional fabric preform with the 0°/45°/90°/-45°stacking sequence under the influence of compressive stress were forecasted. The permeability model of the fabric preform under the effect of compression stress was formed. Based on the fabric compression model, the equivalent permeability model of fiber bundle was established. According to the tensor theory, the equivalent permeability model of the 0°, ±45° and 90° ply fabric was established respectively. By using the series-parallel relationship of permeable media, the comprehensive characterization model of permeability in each characteristic zone of stiffened panel was established. Based on the PAM-RTM flow simulation software, the permeability of the partition zone was defined, the flowing behavior of resin in the stiffened-panel fabric preforms was simulated during the filling process, the technological parameters was optimized to determine the final filling program, and the models of stiffened panel were made to carry out the molding experiment to verify the rationality of filling program. The work provides the theoretical basis for the successful production, which can be used to finally guide the practice.
2019, 36(4): 826-836.
doi: 10.13801/j.cnki.fhclxb.20180516.001
Abstract:
The experiments of carbon fabrics and glass fiber fabrics under both dry and wet conditions were conducted for exploring the compression characteristic. By using the viscoelastic theory model, the viscoelastic curves and viscoelastic model parameters of the compression, stress relaxation and rebound stages under the two aforementioned conditions were analyzed. The deformation mechanism at three compression stages of the yarn was analyzed, and the corresponding explanations for these differences were presented. The results show that the forming thickness of wet fabrics is slightly larger than dry fabrics when the same maximum forming pressure is loaded at the compression stage. The compression time of wet fabrics is shorter than that of dry fabrics, and the yarn specification is much smaller. Besides, the difference of the time is not obvious. The time constant at the compression stage for wet fabrics is less than the corresponding value for dry fabrics. At the stress relaxation and rebound stage, a small amount of media penetrates into the fabric gaps, while the change process of the fabrics is basically the same. The forming thickness difference and rebound thickness difference under the two conditions are very close. Correspondingly, the rebound thickness of wet fabrics is finally slightly larger than that of dry fabrics. The time constants of stress relaxation and rebound are basically the same. These results provide important guidance for the forming process of fiber reinforced resin matrix composites.
The experiments of carbon fabrics and glass fiber fabrics under both dry and wet conditions were conducted for exploring the compression characteristic. By using the viscoelastic theory model, the viscoelastic curves and viscoelastic model parameters of the compression, stress relaxation and rebound stages under the two aforementioned conditions were analyzed. The deformation mechanism at three compression stages of the yarn was analyzed, and the corresponding explanations for these differences were presented. The results show that the forming thickness of wet fabrics is slightly larger than dry fabrics when the same maximum forming pressure is loaded at the compression stage. The compression time of wet fabrics is shorter than that of dry fabrics, and the yarn specification is much smaller. Besides, the difference of the time is not obvious. The time constant at the compression stage for wet fabrics is less than the corresponding value for dry fabrics. At the stress relaxation and rebound stage, a small amount of media penetrates into the fabric gaps, while the change process of the fabrics is basically the same. The forming thickness difference and rebound thickness difference under the two conditions are very close. Correspondingly, the rebound thickness of wet fabrics is finally slightly larger than that of dry fabrics. The time constants of stress relaxation and rebound are basically the same. These results provide important guidance for the forming process of fiber reinforced resin matrix composites.
2019, 36(4): 837-847.
doi: 10.13801/j.cnki.fhclxb.20180611.002
Abstract:
In this paper, the steel core projectile was used to penetrate interlaminar hybrid composite armor plate to explore the bulletproof performance and bulletproof mechanism. The types of hybrid reinforcement with unidirectional (UD) structure were ultra high molecular weight polyethylene (UHMWPE) fiber and para-aromatic polyamide fiber, whereas the resin was one of waterborne polyurethane (WPU) and epoxy resin (EP). The effects of hybrid ratio, strike face and resin matrix on ballistic properties were discussed. Also, the fracture morphologies were observed by the stereomicroscopy. Moreover, the failure mechanisms of hybrid composite subjected to the ballistic impact were analyzed. The results show that the bulletproof performance of hybrid composite armor plate is superior to that of the single fiber reinforced composite armor plate, and the bulletproof performance of WPU is superior to that of EP. Furthermore, when UHMWPE fiber composite works as strike face, the bulletproof performance is better. Finally, it can be concluded that the tensile deformation of fiber and the delamination are the major ways of the absorbing energy under the ballistic impact by the steel-core bullet.
In this paper, the steel core projectile was used to penetrate interlaminar hybrid composite armor plate to explore the bulletproof performance and bulletproof mechanism. The types of hybrid reinforcement with unidirectional (UD) structure were ultra high molecular weight polyethylene (UHMWPE) fiber and para-aromatic polyamide fiber, whereas the resin was one of waterborne polyurethane (WPU) and epoxy resin (EP). The effects of hybrid ratio, strike face and resin matrix on ballistic properties were discussed. Also, the fracture morphologies were observed by the stereomicroscopy. Moreover, the failure mechanisms of hybrid composite subjected to the ballistic impact were analyzed. The results show that the bulletproof performance of hybrid composite armor plate is superior to that of the single fiber reinforced composite armor plate, and the bulletproof performance of WPU is superior to that of EP. Furthermore, when UHMWPE fiber composite works as strike face, the bulletproof performance is better. Finally, it can be concluded that the tensile deformation of fiber and the delamination are the major ways of the absorbing energy under the ballistic impact by the steel-core bullet.
2019, 36(4): 848-859.
doi: 10.13801/j.cnki.fhclxb.20180522.001
Abstract:
The maintenance of the expansion joints in concrete deck slabs is one of the most serious problems in current bridge engineering. One of the alternatives is the use of link slab in a jointless bridge, which connects the adjacent bridge deck slabs at the pier, forming a continuous slab across the bridge spans. Based on the good corrosion resistance of carbon fiber reinforced polymer (CFRP) and high ductility of engineered cementitious composites(ECC), the CFRP reinforced ECC link slabs were proposed in this study and the behaviour of this novel link slab were investigated through a series of experimental test. The load-displacement response, crack distribution, strain, and deformation of CFRP soft grid, CFRP bar and ECC link slabs were compared to investigate the behaviour of the test link slabs. The experimental results show that all the ECC test link slabs can satisfy the requirements of deformation and cracking. It is found that using CFRP grid results in the damage in the interface of the link slab. Therefore, the multi-cracking behaviour of the ECC link slab is reduced, which has negative effect on the behaviour of ECC link slab. Compared with the other test link slabs, CFRP bars has a significant effect on the ECC link slab. The deformation capacity is significantly enhanced. The cracks are evenly distributed with small crack width. As a result, the global structural performance of ECC link slabs is improved.
The maintenance of the expansion joints in concrete deck slabs is one of the most serious problems in current bridge engineering. One of the alternatives is the use of link slab in a jointless bridge, which connects the adjacent bridge deck slabs at the pier, forming a continuous slab across the bridge spans. Based on the good corrosion resistance of carbon fiber reinforced polymer (CFRP) and high ductility of engineered cementitious composites(ECC), the CFRP reinforced ECC link slabs were proposed in this study and the behaviour of this novel link slab were investigated through a series of experimental test. The load-displacement response, crack distribution, strain, and deformation of CFRP soft grid, CFRP bar and ECC link slabs were compared to investigate the behaviour of the test link slabs. The experimental results show that all the ECC test link slabs can satisfy the requirements of deformation and cracking. It is found that using CFRP grid results in the damage in the interface of the link slab. Therefore, the multi-cracking behaviour of the ECC link slab is reduced, which has negative effect on the behaviour of ECC link slab. Compared with the other test link slabs, CFRP bars has a significant effect on the ECC link slab. The deformation capacity is significantly enhanced. The cracks are evenly distributed with small crack width. As a result, the global structural performance of ECC link slabs is improved.
2019, 36(4): 860-870.
doi: 10.13801/j.cnki.fhclxb.20180517.002
Abstract:
Strength prediction of a laminate with a hole generally depends on a characteristic length of the hole which is not only related to the properties of its constituent materials but also depends on the laminate lay-up and the hole diameter. In this paper, a new method based on linear elastic fracture mechanics was proposed to predict the tensile strength of a symmetric laminate with hole, which only needs the fracture toughness of a cross-ply composite plate and the tensile strength of the un-notched laminate, and which can significantly reduce the requirement on composite data. In this method, the characteristic length was first expressed as a function of the fracture toughness and the un-notched tensile strength of the laminate. Then, the fracture toughness of a 0° ply (i.e. unidirectional laminate) was determined by a compact tension test on the cross-ply laminate[90/0]8s and the virtual crack closure technique. Further, the fracture toughness of laminates with arbitrary symmetric lay-up angles can be calculated from that of the 0° ply. Tensile tests on T300/7901 notched laminates with lay-ups of[0/±45/90]2s and[0/±30/±60/90]s have been done in this work. Three kinds of hole diameters, i.e. 3 mm, 6 mm and 9 mm, were assigned for each of the laminates. The theoretical predictions for the tensile strengths are in good agreement with the measured values. The maximum difference is 15.2%, which is acceptable in engineering applications.
Strength prediction of a laminate with a hole generally depends on a characteristic length of the hole which is not only related to the properties of its constituent materials but also depends on the laminate lay-up and the hole diameter. In this paper, a new method based on linear elastic fracture mechanics was proposed to predict the tensile strength of a symmetric laminate with hole, which only needs the fracture toughness of a cross-ply composite plate and the tensile strength of the un-notched laminate, and which can significantly reduce the requirement on composite data. In this method, the characteristic length was first expressed as a function of the fracture toughness and the un-notched tensile strength of the laminate. Then, the fracture toughness of a 0° ply (i.e. unidirectional laminate) was determined by a compact tension test on the cross-ply laminate[90/0]8s and the virtual crack closure technique. Further, the fracture toughness of laminates with arbitrary symmetric lay-up angles can be calculated from that of the 0° ply. Tensile tests on T300/7901 notched laminates with lay-ups of[0/±45/90]2s and[0/±30/±60/90]s have been done in this work. Three kinds of hole diameters, i.e. 3 mm, 6 mm and 9 mm, were assigned for each of the laminates. The theoretical predictions for the tensile strengths are in good agreement with the measured values. The maximum difference is 15.2%, which is acceptable in engineering applications.
2019, 36(4): 871-880.
doi: 10.13801/j.cnki.fhclxb.20180601.001
Abstract:
An extended GIM (group interaction modelling) method was developed by considering the influence of conversion on the cohesive energy and the degrees of freedom of epoxy resin system, which can predict the relation between conversion and material properties of epoxy resin. The epoxy resin composed of epoxy EPON862 and curing agent DETDA was used as an example for validation of the extended GIM method. It is found that the extended GIM method not only accurately predicts the material properties of fully cured EPON862/DETDA system, including glass transition temperature, volume shrinkage, coefficient of thermal expansion and elastic modulus, but also well captures the trend of these material properties changing with the conversion throughout curing process. And good agreement is found by comparing predicted results with that obtained from the molecular dynamics (MD) simulation and experiments. As combined with curing kinetics, this extended GIM method is capable of providing accurate material properties as the input parameters for modelling the shrinkage strain and residual stress throughout the curing process of epoxy resin.
An extended GIM (group interaction modelling) method was developed by considering the influence of conversion on the cohesive energy and the degrees of freedom of epoxy resin system, which can predict the relation between conversion and material properties of epoxy resin. The epoxy resin composed of epoxy EPON862 and curing agent DETDA was used as an example for validation of the extended GIM method. It is found that the extended GIM method not only accurately predicts the material properties of fully cured EPON862/DETDA system, including glass transition temperature, volume shrinkage, coefficient of thermal expansion and elastic modulus, but also well captures the trend of these material properties changing with the conversion throughout curing process. And good agreement is found by comparing predicted results with that obtained from the molecular dynamics (MD) simulation and experiments. As combined with curing kinetics, this extended GIM method is capable of providing accurate material properties as the input parameters for modelling the shrinkage strain and residual stress throughout the curing process of epoxy resin.
2019, 36(4): 881-891.
doi: 10.13801/j.cnki.fhclxb.20180620.001
Abstract:
Local connection pull-out failure of composite foam sandwich plate were experimentally studied, the failure mode failure load and the influence of panel on joint were analyzed. Numerical analysis was carried out by using ABAQUS finite element software. Simulation results verified the reliability of the model by comparing with the experimental results, The failure mode and internal structure parameters influence on joint destruction were prognosticated and analyzed. The progressive failure in the foam core and the debonding of the adhesive layer between the panel and the foam core were studied. The results show that the crack is generated on the edge foam of foam sandwich plate pre-buried bolt connection structure sealant, and extends to the middle part. When the middle region is all cracked, the cracks at the two ends extend upward along the direction of 45°. The cracking area of the adhesive layer is curved in a shape of curved strip, distributes on both sides of the bolt fastener, and in the width direction of the panel, the cracked area runs through both sides. When maximum depth of embedded parts increases, failure load is also increased. Subcritical failure load and maximum failure load do not change obviously when diameters of embedded parts increase, but the biggest failure displacement reduces.
Local connection pull-out failure of composite foam sandwich plate were experimentally studied, the failure mode failure load and the influence of panel on joint were analyzed. Numerical analysis was carried out by using ABAQUS finite element software. Simulation results verified the reliability of the model by comparing with the experimental results, The failure mode and internal structure parameters influence on joint destruction were prognosticated and analyzed. The progressive failure in the foam core and the debonding of the adhesive layer between the panel and the foam core were studied. The results show that the crack is generated on the edge foam of foam sandwich plate pre-buried bolt connection structure sealant, and extends to the middle part. When the middle region is all cracked, the cracks at the two ends extend upward along the direction of 45°. The cracking area of the adhesive layer is curved in a shape of curved strip, distributes on both sides of the bolt fastener, and in the width direction of the panel, the cracked area runs through both sides. When maximum depth of embedded parts increases, failure load is also increased. Subcritical failure load and maximum failure load do not change obviously when diameters of embedded parts increase, but the biggest failure displacement reduces.
2019, 36(4): 892-904.
doi: 10.13801/j.cnki.fhclxb.20180703.001
Abstract:
Through theoretical derived and finite element simulation, the vibration characteristic of delaminated plain woven fabric glass fiber/epoxy composite laminate with four sides clamped and one side clamped under hygrothermal environment were studied. This paper studies the relationship between delamination angle, delamination location and vibration characteristic. Based on the first order shearing deformation theory of Mindlin and Hamilton principle, the formula of hygrothermal constitutive equation and the natural frequency of laminated plates was derived, considering the hygrothermal stress, mass effect and the equivalence between moisture and temperature. Using user material subroutine (UMAT) interface with the finite element software ABAQUS, the corresponding interface program was compiled and a series of delaminated model under hygrothermal environment were established. It is found that the simulation results are in good agreement with literature experimental value. Results show that delamination makes vibration frequency decrease intensify under hygrothermal environment. Increasing delamination angle can cause the decline of frequency value, and the larger delamination angle, the larger decline frequency. The influence of moisture is more serious than that of temperature on vibration characteristic. The hygrothermal effect can cause the order of the base frequency decline and intensify the local resonance phenomenon. Surface delamination and middle delamination can cause modal change, but there is little difference.
Through theoretical derived and finite element simulation, the vibration characteristic of delaminated plain woven fabric glass fiber/epoxy composite laminate with four sides clamped and one side clamped under hygrothermal environment were studied. This paper studies the relationship between delamination angle, delamination location and vibration characteristic. Based on the first order shearing deformation theory of Mindlin and Hamilton principle, the formula of hygrothermal constitutive equation and the natural frequency of laminated plates was derived, considering the hygrothermal stress, mass effect and the equivalence between moisture and temperature. Using user material subroutine (UMAT) interface with the finite element software ABAQUS, the corresponding interface program was compiled and a series of delaminated model under hygrothermal environment were established. It is found that the simulation results are in good agreement with literature experimental value. Results show that delamination makes vibration frequency decrease intensify under hygrothermal environment. Increasing delamination angle can cause the decline of frequency value, and the larger delamination angle, the larger decline frequency. The influence of moisture is more serious than that of temperature on vibration characteristic. The hygrothermal effect can cause the order of the base frequency decline and intensify the local resonance phenomenon. Surface delamination and middle delamination can cause modal change, but there is little difference.
2019, 36(4): 905-913.
doi: 10.13801/j.cnki.fhclxb.20180827.001
Abstract:
SiBCN ceramic shows excellent thermal stability, oxidation resistance and crystallization resistance. The oxidation behavior of SiBCN ceramics, derived from pyrolysis of polymeric precursor, was studied at 1 200℃ and 1 400℃ in air atmosphere. XPS was used to characterize the chemical bonding of SiBCN ceramic before and after oxidation experiments. XRD and SEM were employed to analyze the phase composition and microstructure of SiBCN ceramic before and after oxidation experiments. The oxidation kinetics was studied by measuring the thickness of oxide layers via SEM. The results show that, after oxidation experiments, dense protective oxide layers form on the surface of SiBCN ceramic to prevent further oxidation. And the diffusion of oxidant through the oxide layers is the rate-controlling process. The oxide layers thickness of SiBCN ceramic growth at 1 200 and 1 400℃ in air can be approximated by a parabolic rate law with rate constants of 0.0224 μm2/h and 0.1045 μm2/h, respectively. Which was thinner than SiC ceramic with rate constants of 0.0449 μm2/h and 0.1288 μm2/h, respectively. The BN(C) structure and the formed of dense SiOxNy layers made SiBCN ceramic have excellent oxidation resistance.
SiBCN ceramic shows excellent thermal stability, oxidation resistance and crystallization resistance. The oxidation behavior of SiBCN ceramics, derived from pyrolysis of polymeric precursor, was studied at 1 200℃ and 1 400℃ in air atmosphere. XPS was used to characterize the chemical bonding of SiBCN ceramic before and after oxidation experiments. XRD and SEM were employed to analyze the phase composition and microstructure of SiBCN ceramic before and after oxidation experiments. The oxidation kinetics was studied by measuring the thickness of oxide layers via SEM. The results show that, after oxidation experiments, dense protective oxide layers form on the surface of SiBCN ceramic to prevent further oxidation. And the diffusion of oxidant through the oxide layers is the rate-controlling process. The oxide layers thickness of SiBCN ceramic growth at 1 200 and 1 400℃ in air can be approximated by a parabolic rate law with rate constants of 0.0224 μm2/h and 0.1045 μm2/h, respectively. Which was thinner than SiC ceramic with rate constants of 0.0449 μm2/h and 0.1288 μm2/h, respectively. The BN(C) structure and the formed of dense SiOxNy layers made SiBCN ceramic have excellent oxidation resistance.
2019, 36(4): 914-920.
doi: 10.13801/j.cnki.fhclxb.20180530.001
Abstract:
TiO2 nanowires were prepared on F-dopet tin oxide(FTO) by hydrothermal method. Then WO3 nanowires were prepared on TiO2 nanowires by hydrothermal method to obtain WO3/TiO2 composite films. The electrochromic properties of WO3/TiO2 composite films were studied by cyclic voltammetry (CV), chronoamperometry (CA) and chronocharging (CC). The response time of the coloring and bleaching state of the film was tested by UV spectrophotometer.Through the above tests, the parameters such as cycle stability, light modulation, coloring efficiency and switching time (Y and X) were calculated. The results show that the electrochromic properties of WO3/TiO2 composite films are obviously improved. The reversibility of WO3/TiO2 composite films increases by 6%, and the coloring efficiency increases by 40.96 cm2/C.
TiO2 nanowires were prepared on F-dopet tin oxide(FTO) by hydrothermal method. Then WO3 nanowires were prepared on TiO2 nanowires by hydrothermal method to obtain WO3/TiO2 composite films. The electrochromic properties of WO3/TiO2 composite films were studied by cyclic voltammetry (CV), chronoamperometry (CA) and chronocharging (CC). The response time of the coloring and bleaching state of the film was tested by UV spectrophotometer.Through the above tests, the parameters such as cycle stability, light modulation, coloring efficiency and switching time (Y and X) were calculated. The results show that the electrochromic properties of WO3/TiO2 composite films are obviously improved. The reversibility of WO3/TiO2 composite films increases by 6%, and the coloring efficiency increases by 40.96 cm2/C.
2019, 36(4): 921-926.
doi: 10.13801/j.cnki.fhclxb.20180608.002
Abstract:
The tightening characteristic of threaded fasteners made of C/C composite under the conditions of no locking adhesive (non-glue coating) and plastering the locking adhesive (glue coating) were investigated. The experiments were done to investigate the correspondence between tightening torques and clamping force of C/C composite threaded fasteners under two conditions, meanwhile, both friction coefficients of thread and bearing-surfaces were analyzed. The results indicate that the clamping force of the glue coating state will be increased by 20%-82% more than that of non-adhesive state under the same tightening torque. Under the glue coating state, the curve of clamping force with tightening torque shows a good linear relationship. And for the non glue coating and glue coating states, the average friction coefficients of thread and bearing-surfaces for the non glue coating bolts are 0.41, 0.35 and 0.59, 0.41, respectively. There is a slight difference between two conditions about the allocation ratio of torque components.
The tightening characteristic of threaded fasteners made of C/C composite under the conditions of no locking adhesive (non-glue coating) and plastering the locking adhesive (glue coating) were investigated. The experiments were done to investigate the correspondence between tightening torques and clamping force of C/C composite threaded fasteners under two conditions, meanwhile, both friction coefficients of thread and bearing-surfaces were analyzed. The results indicate that the clamping force of the glue coating state will be increased by 20%-82% more than that of non-adhesive state under the same tightening torque. Under the glue coating state, the curve of clamping force with tightening torque shows a good linear relationship. And for the non glue coating and glue coating states, the average friction coefficients of thread and bearing-surfaces for the non glue coating bolts are 0.41, 0.35 and 0.59, 0.41, respectively. There is a slight difference between two conditions about the allocation ratio of torque components.
2019, 36(4): 927-937.
doi: 10.13801/j.cnki.fhclxb.20180416.005
Abstract:
The pure Al and 6061Al matrix composites with 31%B4C particle sizes of 6.5-39.5 μm were respectively prepared by powder metallurgy. The microstructure and mechanical properties of composites were tested. The results show that the B4C particles were uniformly distributed in the matrix of all composites, and the densities reached above 99%. For pure Al matrix composites, with the increase of particle size, the densities and ductility increase gradually, and the strength decreases gradually. For 6061Al matrix composites, the densities increase slightly with the increase of particle size, and its strength and ductility are affected by the particle size and the hot-pressing temperature. When hot-pressing temperature is 610℃, the interface reaction is serious. With the increase of B4C particle size, the strength decreases first and then increases, while the ductility increases first and then decreases. When hot-pressing temperature is 580℃, the interface reaction is slight. The strength decreases gradually, and the ductility gradually increased gradually. The particle size, interface reaction and matrix material affect the mechanical properties of B4C reinforced aluminum matrix composites.
The pure Al and 6061Al matrix composites with 31%B4C particle sizes of 6.5-39.5 μm were respectively prepared by powder metallurgy. The microstructure and mechanical properties of composites were tested. The results show that the B4C particles were uniformly distributed in the matrix of all composites, and the densities reached above 99%. For pure Al matrix composites, with the increase of particle size, the densities and ductility increase gradually, and the strength decreases gradually. For 6061Al matrix composites, the densities increase slightly with the increase of particle size, and its strength and ductility are affected by the particle size and the hot-pressing temperature. When hot-pressing temperature is 610℃, the interface reaction is serious. With the increase of B4C particle size, the strength decreases first and then increases, while the ductility increases first and then decreases. When hot-pressing temperature is 580℃, the interface reaction is slight. The strength decreases gradually, and the ductility gradually increased gradually. The particle size, interface reaction and matrix material affect the mechanical properties of B4C reinforced aluminum matrix composites.
2019, 36(4): 938-945.
doi: 10.13801/j.cnki.fhclxb.20180614.002
Abstract:
In this paper, the film cracking and propagation of Zinc film/2Cr13 steel substrate system were investigated from experiments and numerical simulations. The crack initiation threshold of Zinc film was detected by the three-point bending test with the acoustic emission technique and the film fracture toughness was calculated. The extended finite element method was adopted to analyze the crack propagation of Zinc film under the three-point bending, and the load-displacement curve simulated by extended finite element method(XFEM) is consistent with the experimental result. Simulation results show that the stress peak occurs in the area of the film crack tip, and the crack propagates when the stress reaches the critical stress of the damage criterion. Meanwhile, the dimensionless energy release rate of period film cracks under various factors was analyzed. It is found that for the same film thickness, when the film crack on a semi-infinite substrate reaches a stable state, the greater the film stiffness is, the greater the substrate thickness and the crack thickness are.
In this paper, the film cracking and propagation of Zinc film/2Cr13 steel substrate system were investigated from experiments and numerical simulations. The crack initiation threshold of Zinc film was detected by the three-point bending test with the acoustic emission technique and the film fracture toughness was calculated. The extended finite element method was adopted to analyze the crack propagation of Zinc film under the three-point bending, and the load-displacement curve simulated by extended finite element method(XFEM) is consistent with the experimental result. Simulation results show that the stress peak occurs in the area of the film crack tip, and the crack propagates when the stress reaches the critical stress of the damage criterion. Meanwhile, the dimensionless energy release rate of period film cracks under various factors was analyzed. It is found that for the same film thickness, when the film crack on a semi-infinite substrate reaches a stable state, the greater the film stiffness is, the greater the substrate thickness and the crack thickness are.
Molecular dynamics simulation on mechanical properties ofnano self-similar hierarchical honeycomb Al
2019, 36(4): 946-953.
doi: 10.13801/j.cnki.fhclxb.20180517.001
Abstract:
Molecular dynamic (MD) simulations were used to investigate the mechanical behavior (elastic moduli and compressive strength) of self-similar hierarchical honeycomb aluminum (SSHHA) subjected to in-plane and out-of-plane compressive loadings. The influence of relative density, hierarchy order, and length ratio on mechanical properties of SSHHA were especially investigated. The MD results show that, both the in-plane and out-of-plane elastic moduli of SSHHA decrease with the decrease of relative density. A modified Gibson model was proposed to consider the surface effect in nano SSHHA, which shows a good agreement with the MD results. Moreover, by comparing the deformation mechanism of the SSHHA with different orders, it is found that, the mechanical properties can be optimized in the hierarchical structures by connecting a hexagon at the angular point of the 1st honeycomb structure. Compared to the 1st order honeycombs, more dislocations are generated in the 2nd and 3th honeycomb structures under compression loadings, resulting in greater energy absorption capacity. The results also indicate that, in the case where the relative density and length ratio are constant, the 2nd nano SSHHA has the best comprehensive mechanical properties. In other words, the mechanical behavior of nano SSHHA cannot be infinitely enhanced by increasing the number of orders. In the end, the MD results show that, in the case where the relative density is constant, when the length ratios are 0.3 and 0.4 respectively, the 2nd SSHHA has the best in-plane and out-plane mechanical properties, respectively. This study is helpful for the optimal design of SSHHA with enhanced performance.
Molecular dynamic (MD) simulations were used to investigate the mechanical behavior (elastic moduli and compressive strength) of self-similar hierarchical honeycomb aluminum (SSHHA) subjected to in-plane and out-of-plane compressive loadings. The influence of relative density, hierarchy order, and length ratio on mechanical properties of SSHHA were especially investigated. The MD results show that, both the in-plane and out-of-plane elastic moduli of SSHHA decrease with the decrease of relative density. A modified Gibson model was proposed to consider the surface effect in nano SSHHA, which shows a good agreement with the MD results. Moreover, by comparing the deformation mechanism of the SSHHA with different orders, it is found that, the mechanical properties can be optimized in the hierarchical structures by connecting a hexagon at the angular point of the 1st honeycomb structure. Compared to the 1st order honeycombs, more dislocations are generated in the 2nd and 3th honeycomb structures under compression loadings, resulting in greater energy absorption capacity. The results also indicate that, in the case where the relative density and length ratio are constant, the 2nd nano SSHHA has the best comprehensive mechanical properties. In other words, the mechanical behavior of nano SSHHA cannot be infinitely enhanced by increasing the number of orders. In the end, the MD results show that, in the case where the relative density is constant, when the length ratios are 0.3 and 0.4 respectively, the 2nd SSHHA has the best in-plane and out-plane mechanical properties, respectively. This study is helpful for the optimal design of SSHHA with enhanced performance.
2019, 36(4): 954-963.
doi: 10.13801/j.cnki.fhclxb.20180705.002
Abstract:
In order to investigate the biaxial flexural properties of glass fiber meshes in concrete slabs and the reinforcing effects of hybrid use of steel fiber and fiber mesh, the alkali resistance test and two-way slab bending test were carried out. The possible replacement of conventional steel mesh by composed use of glass fiber mesh and steel fibers has been investigated. The results show that the corrosion resistance of the alkali-resistant glass fiber is better than that of the C-glass fiber. Ultimate load of concrete slabs can be improved 59% with addition of alkali-resistant glass fiber mesh. Hybrid use of steel fiber and glass fiber mesh shows significant positive synthetic effect, and ultimate load and toughness of concrete slabs can be improved significantly, and failure mode of the concrete slabs changes from brittle pattern into a ductile one. The conventional steel mesh with constructive steel ratio (0.2%) can be replaced by the hybrid use of alkali-resistant glass fiber mesh and steel fibers with fiber content of 30 kg/m3.
In order to investigate the biaxial flexural properties of glass fiber meshes in concrete slabs and the reinforcing effects of hybrid use of steel fiber and fiber mesh, the alkali resistance test and two-way slab bending test were carried out. The possible replacement of conventional steel mesh by composed use of glass fiber mesh and steel fibers has been investigated. The results show that the corrosion resistance of the alkali-resistant glass fiber is better than that of the C-glass fiber. Ultimate load of concrete slabs can be improved 59% with addition of alkali-resistant glass fiber mesh. Hybrid use of steel fiber and glass fiber mesh shows significant positive synthetic effect, and ultimate load and toughness of concrete slabs can be improved significantly, and failure mode of the concrete slabs changes from brittle pattern into a ductile one. The conventional steel mesh with constructive steel ratio (0.2%) can be replaced by the hybrid use of alkali-resistant glass fiber mesh and steel fibers with fiber content of 30 kg/m3.
2019, 36(4): 964-971.
doi: 10.13801/j.cnki.fhclxb.20180522.002
Abstract:
To investigate the effect of liquid-wetting on their microstructure and determine their structural stability to capillary tension, nano-porous thermal insulating materials were directly immersed in absolute alcohol or deionized water, and then they were dried under room temperature and atmospheric pressure. The microstructure of the materials was characterized by nitrogen adsorption-desorption, SEM and optical microscope, and the gas pressure dependence of their gaseous thermal conductivity was described by Kaganer model with two different pore sizes. The results indicate that the skeleton particle diameter and the pore size are not affected by wetting with alcohol. However, the interfacial area between adjacent skeleton particles increases and the pore size either increases or decreases via water wetting. For the alcohol-wetted material, two different equivalent pore sizes derived from its gaseous thermal conductivity are 70 nm and 300 nm and their contributions to the total porosity are about 82% and 18%, respectively. In case of the water-wetted material, two different equivalent pore sizes deduced from its gaseous thermal conductivity are 30 nm and 60 μm and their contributions to the total porosity are about 58% and 42%, respectively.
To investigate the effect of liquid-wetting on their microstructure and determine their structural stability to capillary tension, nano-porous thermal insulating materials were directly immersed in absolute alcohol or deionized water, and then they were dried under room temperature and atmospheric pressure. The microstructure of the materials was characterized by nitrogen adsorption-desorption, SEM and optical microscope, and the gas pressure dependence of their gaseous thermal conductivity was described by Kaganer model with two different pore sizes. The results indicate that the skeleton particle diameter and the pore size are not affected by wetting with alcohol. However, the interfacial area between adjacent skeleton particles increases and the pore size either increases or decreases via water wetting. For the alcohol-wetted material, two different equivalent pore sizes derived from its gaseous thermal conductivity are 70 nm and 300 nm and their contributions to the total porosity are about 82% and 18%, respectively. In case of the water-wetted material, two different equivalent pore sizes deduced from its gaseous thermal conductivity are 30 nm and 60 μm and their contributions to the total porosity are about 58% and 42%, respectively.
2019, 36(4): 972-981.
doi: 10.13801/j.cnki.fhclxb.20180516.002
Abstract:
Using guava-like polyacrylate-3-(methacryloyloxy) propyltrimethoxysilane modified silica (PAcr MPS-SiO2) grafted composite particles as the dispersion phase, and polymethylmethacrylate (PMMA) resin as the continuous phase, their mixture was melt blended in a HAKKA torque rheometer, in order to investigate the dispersion and orientation behavior of the grafted composite particles with different crosslinking structures under various melt shear conditions. It is found that due to the induced effect provided by the strong shear force in the melt-mixed field, and also the restraint effect provided by the widespread grafting cross-linking structure formed with SiO2 particles as the cross-linking point and the grafted polymer chain as the linking line in PAcr-MPS-SiO2 particles, the guava-like composite particles are likely to be oriented and rearranged. They can be in turn deformed into sphere, ellipsoid, rod-shaped, microfibril and other oriented morphologies without large-scale tear dissociation, and finally in-situ formed a fibrous orientation structure with a large aspect ratio in the polymer matrix. The degree of orientation of the composite particles and the grafted SiO2 clusters inside could both be controlled within a certain range, by adjusting the degree of crosslinking of the PAcr-MPS-SiO2 composite particles from changing the degree of MPS modification on the silica surface, or by adjusting the shear strength of the melt shear field from changing the screw speed. When the gel fraction of the composite particles is 40%, the mixture temperature is 180℃, the screw speed fixed at 65 r/min and the blending time of 12 minutes, an ordered alongside oriented structure with an average aspect ratio of 11.8 can be obtained. Accordingly, we would believe this study could open a new pathway to in-situ construct and effiviently regulate one-dimensional orientation structure in polymer matrix.
Using guava-like polyacrylate-3-(methacryloyloxy) propyltrimethoxysilane modified silica (PAcr MPS-SiO2) grafted composite particles as the dispersion phase, and polymethylmethacrylate (PMMA) resin as the continuous phase, their mixture was melt blended in a HAKKA torque rheometer, in order to investigate the dispersion and orientation behavior of the grafted composite particles with different crosslinking structures under various melt shear conditions. It is found that due to the induced effect provided by the strong shear force in the melt-mixed field, and also the restraint effect provided by the widespread grafting cross-linking structure formed with SiO2 particles as the cross-linking point and the grafted polymer chain as the linking line in PAcr-MPS-SiO2 particles, the guava-like composite particles are likely to be oriented and rearranged. They can be in turn deformed into sphere, ellipsoid, rod-shaped, microfibril and other oriented morphologies without large-scale tear dissociation, and finally in-situ formed a fibrous orientation structure with a large aspect ratio in the polymer matrix. The degree of orientation of the composite particles and the grafted SiO2 clusters inside could both be controlled within a certain range, by adjusting the degree of crosslinking of the PAcr-MPS-SiO2 composite particles from changing the degree of MPS modification on the silica surface, or by adjusting the shear strength of the melt shear field from changing the screw speed. When the gel fraction of the composite particles is 40%, the mixture temperature is 180℃, the screw speed fixed at 65 r/min and the blending time of 12 minutes, an ordered alongside oriented structure with an average aspect ratio of 11.8 can be obtained. Accordingly, we would believe this study could open a new pathway to in-situ construct and effiviently regulate one-dimensional orientation structure in polymer matrix.
2019, 36(4): 982-992.
Abstract:
By using tetraethyl orthosilicate (TEOS), epoxide resin (E51), styrene (St), et al. as the main materials, a kind of porous silica shell microcapsules (PSSM) were synthesized through in-polymerization in the core and hydrolysis-polycondensation for forming the shell. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to characterize the morphology, chemical composition and core shell ratio of the synthesized PSSM. Influences of PSSM on the impermeability and pore structure of hardened cement mortar via alternating current impedance spectroscopy technique (ACI) and mercury intrusion porosimetry (MIP) were studied after the hardened cement mortar samples were preloaded by 80% their compressive strength loads and cured including water curing or dry-wet cycling curing. The characterization results prove that the obtained product presents core-shell structured microcapsules with size of 10-100 μm, in which poly-siloxane forms porous shell and liquid form epoxy resin held by a polystyrene network composes the core. The mass ratio of the core to shell is 1.54. Compare with the blank samples without preloading-curing treatment, connected pore solution resistance RCH and diffusion resistance coefficient σ of the preloading-curing treated blank samples decrease and their porosities increase, which suggests that the preloading treatment leads to the formation of micro-cracks in the specimen and the following curing does not result in full healing of the formed micro-cracks. On the other hand, for those sample containing 8% PSSM, RCH and σ of the preloading-curing treated samples are even higher than those of the non-treated samples. This phenomenon is attributed to the micro-cracks formation due to the preloading treatment allows invasion of water into the body of the mortar specimens during the following water immersion. Thus, the PSSM that is incorporated into the mortar samples contributes to crack healing by leakage of the epoxy resin from the core through the intact or broken porous shell and the subsequent curing reaction with the curing agent located in cement matrix. The above mentioned results provide a clear proof of concept for such self-healing microcapsules.
By using tetraethyl orthosilicate (TEOS), epoxide resin (E51), styrene (St), et al. as the main materials, a kind of porous silica shell microcapsules (PSSM) were synthesized through in-polymerization in the core and hydrolysis-polycondensation for forming the shell. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to characterize the morphology, chemical composition and core shell ratio of the synthesized PSSM. Influences of PSSM on the impermeability and pore structure of hardened cement mortar via alternating current impedance spectroscopy technique (ACI) and mercury intrusion porosimetry (MIP) were studied after the hardened cement mortar samples were preloaded by 80% their compressive strength loads and cured including water curing or dry-wet cycling curing. The characterization results prove that the obtained product presents core-shell structured microcapsules with size of 10-100 μm, in which poly-siloxane forms porous shell and liquid form epoxy resin held by a polystyrene network composes the core. The mass ratio of the core to shell is 1.54. Compare with the blank samples without preloading-curing treatment, connected pore solution resistance RCH and diffusion resistance coefficient σ of the preloading-curing treated blank samples decrease and their porosities increase, which suggests that the preloading treatment leads to the formation of micro-cracks in the specimen and the following curing does not result in full healing of the formed micro-cracks. On the other hand, for those sample containing 8% PSSM, RCH and σ of the preloading-curing treated samples are even higher than those of the non-treated samples. This phenomenon is attributed to the micro-cracks formation due to the preloading treatment allows invasion of water into the body of the mortar specimens during the following water immersion. Thus, the PSSM that is incorporated into the mortar samples contributes to crack healing by leakage of the epoxy resin from the core through the intact or broken porous shell and the subsequent curing reaction with the curing agent located in cement matrix. The above mentioned results provide a clear proof of concept for such self-healing microcapsules.
2019, 36(4): 993-1000.
doi: 10.13801/j.cnki.fhclxb.20180619.001
Abstract:
In order to explore the mechanical properties of self-compacting lightweight aggregate concrete under biaxial loading, the three axis test machine was used to carry out biaxial compression-compression and biaxial tension-compression. The stress-strain curve and its failure form under different working conditions were obtained. The peak stress and peak strain of the stress-strain curve were extracted, and the ordinary concrete and the lightweight aggregate concrete in the related literature were obtained. The biaxial mechanical properties of self-compacting lightweight aggregate concrete was compared with research results of ordinary concrete and the lightweight aggregate concrete. The results show that the specimen mainly presents the shear failure mode when the lateral pressure is low, and the specimen is split when the lateral stress is high. Under the condition of biaxial tension-compression, the specimen is mainly splitting failure, which is independent of lateral stress. With the increase of lateral pressure stress, the main compressive stress of the self-compacting lightweight aggregate concrete is obviously higher than that without lateral stress, the maximum increasing of peak stress is 68.08%, and the main tensile stress gradually decreases with the increase of lateral pressure stress, and the maximum decrease is 62.35%. Using the Kupfer biaxial stress failure criterion, it is proved that the influence of the lateral stress on the self-compacting lightweight aggregate concrete is more conservative. At the same time, the failure criterion of the self-compacting lightweight aggregate concrete biaxial mechanical properties was proposed based on Kupfer. The failure criterion equation has good applicability.
In order to explore the mechanical properties of self-compacting lightweight aggregate concrete under biaxial loading, the three axis test machine was used to carry out biaxial compression-compression and biaxial tension-compression. The stress-strain curve and its failure form under different working conditions were obtained. The peak stress and peak strain of the stress-strain curve were extracted, and the ordinary concrete and the lightweight aggregate concrete in the related literature were obtained. The biaxial mechanical properties of self-compacting lightweight aggregate concrete was compared with research results of ordinary concrete and the lightweight aggregate concrete. The results show that the specimen mainly presents the shear failure mode when the lateral pressure is low, and the specimen is split when the lateral stress is high. Under the condition of biaxial tension-compression, the specimen is mainly splitting failure, which is independent of lateral stress. With the increase of lateral pressure stress, the main compressive stress of the self-compacting lightweight aggregate concrete is obviously higher than that without lateral stress, the maximum increasing of peak stress is 68.08%, and the main tensile stress gradually decreases with the increase of lateral pressure stress, and the maximum decrease is 62.35%. Using the Kupfer biaxial stress failure criterion, it is proved that the influence of the lateral stress on the self-compacting lightweight aggregate concrete is more conservative. At the same time, the failure criterion of the self-compacting lightweight aggregate concrete biaxial mechanical properties was proposed based on Kupfer. The failure criterion equation has good applicability.
2019, 36(4): 1001-1007.
doi: 10.13801/j.cnki.fhclxb.20180614.001
Abstract:
In order to consider both the thermal stress accumulation and relaxation effects of asphalt concrete (AC) during the process of temperature drop, and determine the critical cracking temperature, the low temperature shrinkage coefficient tests were conducted on AC specimens, and the tensile strength and creep compliance were determined from indirect tensile tests. The Prony series representation of relaxation modulus was obtained from the theoretical relationship. The thermal stress was computed according to the Boltzmann superposition principle. Thermal stresses induced at several of temperature drop rates were analyzed and the critical cracking temperatures (CCT) were determined based on the tensile strength curve. The calculation results were verified. The results show that this approach can take both the stress accumulation and relaxation into consideration, and better represent the low temperature cracking characteristic of AC. The calculation results are similar to that obtained from thermal stress restrained specimen test (TSRST). This approach can apply to both uniform temperatures drop and continuous drop in the field. The rate of thermal stress accumulation increases with decreasing temperature or increasing drop rate. The CCT increases with increasing drop rate.
In order to consider both the thermal stress accumulation and relaxation effects of asphalt concrete (AC) during the process of temperature drop, and determine the critical cracking temperature, the low temperature shrinkage coefficient tests were conducted on AC specimens, and the tensile strength and creep compliance were determined from indirect tensile tests. The Prony series representation of relaxation modulus was obtained from the theoretical relationship. The thermal stress was computed according to the Boltzmann superposition principle. Thermal stresses induced at several of temperature drop rates were analyzed and the critical cracking temperatures (CCT) were determined based on the tensile strength curve. The calculation results were verified. The results show that this approach can take both the stress accumulation and relaxation into consideration, and better represent the low temperature cracking characteristic of AC. The calculation results are similar to that obtained from thermal stress restrained specimen test (TSRST). This approach can apply to both uniform temperatures drop and continuous drop in the field. The rate of thermal stress accumulation increases with decreasing temperature or increasing drop rate. The CCT increases with increasing drop rate.
2019, 36(4): 1008-1016.
doi: 10.13801/j.cnki.fhclxb.20180716.001
Abstract:
The pore structure and surface morphology of rubber powder treated by hydrogen peroxide(H2O2) solution and high temperature performance of crumb rubber modified asphalt prepared from crumb rubber treated by three different proportions of H2O2 solution on the crumb rubber surface modification were studied. The pore structure, micro-morphology of the rubber powder and the viscosity, viscoelasticity of the rubber asphalt were analyzed by the adsorption-desorption experiments, scanning electron microscope test, rotational viscosity test and dynamic shear rheological test. The results show that the average pore size of the rubber powder after treatment with H2O2 solution is significantly smaller, and the pore volume and pore area of the pores change in a certain pattern. With the increase of the proportion of H2O2 solution, the contact surface between the particles increases, the floccule and pores of the powder increase, and the interface degree between the powder and the asphalt is strengthened. In the asphalt, the solubility of the rubber hydrocarbon and release of the carbon black particles of the rubber powder increase, and the mechanical properties such as the strength, elasticity and wear resistance of the rubber powder decrease. As a result, the elasticity, viscosity and high-temperature rutting resistance of the rubber asphalt decrease.
The pore structure and surface morphology of rubber powder treated by hydrogen peroxide(H2O2) solution and high temperature performance of crumb rubber modified asphalt prepared from crumb rubber treated by three different proportions of H2O2 solution on the crumb rubber surface modification were studied. The pore structure, micro-morphology of the rubber powder and the viscosity, viscoelasticity of the rubber asphalt were analyzed by the adsorption-desorption experiments, scanning electron microscope test, rotational viscosity test and dynamic shear rheological test. The results show that the average pore size of the rubber powder after treatment with H2O2 solution is significantly smaller, and the pore volume and pore area of the pores change in a certain pattern. With the increase of the proportion of H2O2 solution, the contact surface between the particles increases, the floccule and pores of the powder increase, and the interface degree between the powder and the asphalt is strengthened. In the asphalt, the solubility of the rubber hydrocarbon and release of the carbon black particles of the rubber powder increase, and the mechanical properties such as the strength, elasticity and wear resistance of the rubber powder decrease. As a result, the elasticity, viscosity and high-temperature rutting resistance of the rubber asphalt decrease.
2019, 36(4): 1017-1028.
doi: 10.13801/j.cnki.fhclxb.20180626.003
Abstract:
Functionally graded material (FGM) disk subjected to thermal load was investigated based on thermally coupled theory. According to the theory of FGM construction and the axisymmetric characteristic of the disk, the full field distribution of its mechanical properties was obtained. The temperature distribution of the disk was deduced and analyzed by the functionally constructed method and the thermally coupled conduction equation, respectively. Thermally coupled constitutive relations combined with the temperature distribution were established, and their material constants were determined due to the principle of mechanical properties of thermoelastic materials under the two dimensional condition. The displacement governing equations of different FGM structural form disk in different temperature distribution were solved using the differential quadrature method(DQM). The results reveal that thermally coupled constitutive relations can be degenerated to Hooke's laws at room temperature. The error of radial displacement of the disk under classical thermoelastic theory and thermally coupled theory can reach 41.7%. The results of thermally coupled theory change with temperature nonlinearly, and this change trend is also reflected in a large number of scientific experiments. The thermoelastic field in a disk is significantly influenced by temperature change of the outer surface in a disk, angular speed, and temperature distribution.
Functionally graded material (FGM) disk subjected to thermal load was investigated based on thermally coupled theory. According to the theory of FGM construction and the axisymmetric characteristic of the disk, the full field distribution of its mechanical properties was obtained. The temperature distribution of the disk was deduced and analyzed by the functionally constructed method and the thermally coupled conduction equation, respectively. Thermally coupled constitutive relations combined with the temperature distribution were established, and their material constants were determined due to the principle of mechanical properties of thermoelastic materials under the two dimensional condition. The displacement governing equations of different FGM structural form disk in different temperature distribution were solved using the differential quadrature method(DQM). The results reveal that thermally coupled constitutive relations can be degenerated to Hooke's laws at room temperature. The error of radial displacement of the disk under classical thermoelastic theory and thermally coupled theory can reach 41.7%. The results of thermally coupled theory change with temperature nonlinearly, and this change trend is also reflected in a large number of scientific experiments. The thermoelastic field in a disk is significantly influenced by temperature change of the outer surface in a disk, angular speed, and temperature distribution.
2019, 36(4): 1029-1035.
doi: 10.13801/j.cnki.fhclxb.20180626.002
Abstract:
In order to effectively analyze the properties of sandwich beams, a multi-scale variational asymptotic model was established based on the variational asymptotic method. Firstly, the geometrical nonlinear equations of the original 3D sandwich beam were established based on the concept of rotation tensor decomposition. By using the characteristics of slender and heterogeneous, the anisotropy and heterogeneity problems of sandwich beams were strictly decomposed into 1D nonlinear analysis along the beam reference line at the macroscopic level and unit cell constitutive analysis at the microscopic level. Based on the principle of minimum potential energy, the effective stiffness and fluctuation function solution were obtained by minimizing the variational leading items in the strain energy functional, and substituted into the 1D model of beam to perform the global response analysis. Then, the resulting global response and fluctuation function solution were used to recover the local fields. Due to the variational characteristics, the constructed multiscale model can be easily numerical implemented by finite element method. The example results of three kinds of sandwich beams show that the global displacements and local stress fields obtained by the constructed model are in good agreement with the 3D finite element method, but the computational cost and modeling workload are significantly reduced, which provides a simple way for the structural designer to evaluate the performance of the sandwich beams at the initial design stage.
In order to effectively analyze the properties of sandwich beams, a multi-scale variational asymptotic model was established based on the variational asymptotic method. Firstly, the geometrical nonlinear equations of the original 3D sandwich beam were established based on the concept of rotation tensor decomposition. By using the characteristics of slender and heterogeneous, the anisotropy and heterogeneity problems of sandwich beams were strictly decomposed into 1D nonlinear analysis along the beam reference line at the macroscopic level and unit cell constitutive analysis at the microscopic level. Based on the principle of minimum potential energy, the effective stiffness and fluctuation function solution were obtained by minimizing the variational leading items in the strain energy functional, and substituted into the 1D model of beam to perform the global response analysis. Then, the resulting global response and fluctuation function solution were used to recover the local fields. Due to the variational characteristics, the constructed multiscale model can be easily numerical implemented by finite element method. The example results of three kinds of sandwich beams show that the global displacements and local stress fields obtained by the constructed model are in good agreement with the 3D finite element method, but the computational cost and modeling workload are significantly reduced, which provides a simple way for the structural designer to evaluate the performance of the sandwich beams at the initial design stage.
2019, 36(4): 1036-1044.
doi: 10.13801/j.cnki.fhclxb.20180613.001
Abstract:
The bending performance of bamboo scrimber beams strengthened with fiber reinforced polymer composites (FRP) was analyzed by finite element software ABAQUS. The finite element simulation results are coincident with the experimental results, and the load-displacement curves are consistent and the cross-section strain development process is basically similar. The finite element prediction of bearing capacity has a good accuracy. When the load of 70 kN is applied, the errors of the strain of the cross section is within 13.96%. The maximum error of the predicted bearing capacity is 9.04%. The FRP reinforcement realizes the stress redistribution for bamboo beams and the performance of bamboo in the compression zone may be developed with more efficiency. Moreover, the influences of the aspect ratio, the number of the FRP layers and the FRP type on the bending performance of bamboo beams were investigated by parametric analysis. The increase of the number of FRP layers has a significant improvement effect on the ultimate bearing capacity and cross-sectional stiffness of the bamboo scrimber beams. With a given number of FRP layers and FRP type, the increment of ultimate bearing capacity and cross-sectional stiffness increases as the height of the cross-section reduces, and the enhancement effect of CFRP is better than that of the BFRP with the same cross-sectional height and the same number of FRP layers.
The bending performance of bamboo scrimber beams strengthened with fiber reinforced polymer composites (FRP) was analyzed by finite element software ABAQUS. The finite element simulation results are coincident with the experimental results, and the load-displacement curves are consistent and the cross-section strain development process is basically similar. The finite element prediction of bearing capacity has a good accuracy. When the load of 70 kN is applied, the errors of the strain of the cross section is within 13.96%. The maximum error of the predicted bearing capacity is 9.04%. The FRP reinforcement realizes the stress redistribution for bamboo beams and the performance of bamboo in the compression zone may be developed with more efficiency. Moreover, the influences of the aspect ratio, the number of the FRP layers and the FRP type on the bending performance of bamboo beams were investigated by parametric analysis. The increase of the number of FRP layers has a significant improvement effect on the ultimate bearing capacity and cross-sectional stiffness of the bamboo scrimber beams. With a given number of FRP layers and FRP type, the increment of ultimate bearing capacity and cross-sectional stiffness increases as the height of the cross-section reduces, and the enhancement effect of CFRP is better than that of the BFRP with the same cross-sectional height and the same number of FRP layers.
2019, 36(4): 1045-1051.
doi: 10.13801/j.cnki.fhclxb.20180530.002
Abstract:
In order to reveal the potential application in aeronautic and astronautic engineering, the lattice sandwich plate subjected to in-plane compression was focused on and its mechanical behaviors were studied. Based on the failure modes including Euler buckling, shear buckling, face dimpling, face wrinkling and face crushing, a minimum mass optimization method was proposed for the lattice sandwich plate, where six optimization variables were considered, including the panel thickness, the length of rod, the size of rod cross-section, the inclined angle of rod and the wideness ratio of cell. The experimental specimens of the lattice sandwich plate were fabricated based on selective laser melting(SLM) additive manufacturing process. Then, finite element method was validated by comparison with the experimental results, and the error is less than 10%. Finally, both the initial and the optimal designs were analyzed by finite element method. Numerical results show that the optimal design can reduce 16.6% of the mass under the identical compression load, which proves the availability of the optimization method. Moreover, the consistency between the experiments and numerical result proves that additive manufacturing can be used to fabricate the lattice sandwich structure with stable mechanical properties.
In order to reveal the potential application in aeronautic and astronautic engineering, the lattice sandwich plate subjected to in-plane compression was focused on and its mechanical behaviors were studied. Based on the failure modes including Euler buckling, shear buckling, face dimpling, face wrinkling and face crushing, a minimum mass optimization method was proposed for the lattice sandwich plate, where six optimization variables were considered, including the panel thickness, the length of rod, the size of rod cross-section, the inclined angle of rod and the wideness ratio of cell. The experimental specimens of the lattice sandwich plate were fabricated based on selective laser melting(SLM) additive manufacturing process. Then, finite element method was validated by comparison with the experimental results, and the error is less than 10%. Finally, both the initial and the optimal designs were analyzed by finite element method. Numerical results show that the optimal design can reduce 16.6% of the mass under the identical compression load, which proves the availability of the optimization method. Moreover, the consistency between the experiments and numerical result proves that additive manufacturing can be used to fabricate the lattice sandwich structure with stable mechanical properties.
2019, 36(4): 1052-1061.
doi: 10.13801/j.cnki.fhclxb.20180626.004
Abstract:
By designing curvilinear fiber trajectory, composite rotary shell with variable stiffness (VS) has more excellent buckling resistance than straight-fiber shell with constant stiffness (CS). This work studies the influence of ply patterns and geometrical parameters on buckling performance of composite rotary shell under combined loads. Firstly, directional arc of the cross section of rotary shell was used to describe the linear variation of fiber angle, and based on this, a parametric finite element model of VS rotary shell was established. Secondly, for the purpose of achieving the maximum buckling capacity, the fiber trajectory of the composite rotary shell was optimized by combining the sequence quadratic response surface method (SRSM) with the rotary shell model. Finally, effects of ply patterns and geometrical parameters on both the cylindrical shells with bending-torsion load and the elliptical cylindrical shells with axial compression-bending-torque load were studied. It is found that the buckling capacity of VS composite cylindrical shell increases with the increase of the proportion of bending moment, and this is better than the quasi-isotropic (QI) cylindrical shells. However, when the torsional moment is the dominant factor, the buckling performance of the optimized CS cylindrical shell shows more advantages. The buckling performance of the elliptical VS cylindrical shell with smaller ratio of radius is obviously better than that of the QI cylindrical shell under different loads. The closer the cross-section is to a circle, the weaker the improvement of the buckling performance of the elliptical cylindrical shell by the curvilinear fiber.
By designing curvilinear fiber trajectory, composite rotary shell with variable stiffness (VS) has more excellent buckling resistance than straight-fiber shell with constant stiffness (CS). This work studies the influence of ply patterns and geometrical parameters on buckling performance of composite rotary shell under combined loads. Firstly, directional arc of the cross section of rotary shell was used to describe the linear variation of fiber angle, and based on this, a parametric finite element model of VS rotary shell was established. Secondly, for the purpose of achieving the maximum buckling capacity, the fiber trajectory of the composite rotary shell was optimized by combining the sequence quadratic response surface method (SRSM) with the rotary shell model. Finally, effects of ply patterns and geometrical parameters on both the cylindrical shells with bending-torsion load and the elliptical cylindrical shells with axial compression-bending-torque load were studied. It is found that the buckling capacity of VS composite cylindrical shell increases with the increase of the proportion of bending moment, and this is better than the quasi-isotropic (QI) cylindrical shells. However, when the torsional moment is the dominant factor, the buckling performance of the optimized CS cylindrical shell shows more advantages. The buckling performance of the elliptical VS cylindrical shell with smaller ratio of radius is obviously better than that of the QI cylindrical shell under different loads. The closer the cross-section is to a circle, the weaker the improvement of the buckling performance of the elliptical cylindrical shell by the curvilinear fiber.
