2018 Vol. 35, No. 6
2018, 35(6): 1361-1376.
doi: 10.13801/j.cnki.fhclxb.20180327.001
Abstract:
It is inevitable to induce the cure-induced distortions in thermoset composites due to extrinsic processing conditions and intrinsic materials anisotropy. Analytical solution could provide a quick prediction and explain underlying mechanisms of cure-induced distortions in composites, therefore it is increasingly investigated. This paper aimed at introducing the factors and sources giving rise to the cure-induced distortions in thermoset composites, with an emphasis being placed on state-of-art investigation on the analytical solutions of cure-induced distortions in flat and curved composite parts, and analyzing their merits and demerits to offer a direction and reference to the estimate of cure-induced distortions in composites. In the end, the future development of cure-induced distortions in composites was discussed briefly.
It is inevitable to induce the cure-induced distortions in thermoset composites due to extrinsic processing conditions and intrinsic materials anisotropy. Analytical solution could provide a quick prediction and explain underlying mechanisms of cure-induced distortions in composites, therefore it is increasingly investigated. This paper aimed at introducing the factors and sources giving rise to the cure-induced distortions in thermoset composites, with an emphasis being placed on state-of-art investigation on the analytical solutions of cure-induced distortions in flat and curved composite parts, and analyzing their merits and demerits to offer a direction and reference to the estimate of cure-induced distortions in composites. In the end, the future development of cure-induced distortions in composites was discussed briefly.
2018, 35(6): 1377-1385.
doi: 10.13801/j.cnki.fhclxb.20170725.002
Abstract:
1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 3,3',4,4'-oxydiphthalic dianhydride (ODPA) were used as the monomers of polyimide (PI). Using the in-situ amination method, the graphene oxide (GO) was firstly reacted with 6FAPB to obtain the in-situ aminated GO. Then, the in-situ aminated GO was polymerized with ODPA and 6FAPB to obtain the in-situ aminated GO/poly(amic acid) (PAA) solution. After coating of the GO/PAA solution on a clean glass substrate, the in-situ aminated GO/PI composites containing 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% GO (mass fraction) were successfully prepared by thermal imidization. By means of FTIR, XPS, XRD, UV-vis, TGA, TMA, SEM, tension tester and contact angle measurement, the structure and properties of the in-situ aminated GO/PI composites were characterized. These experimental results show that the in-situ aminated GO connects with PI macromolecular chains with chemical bonds, which is helpful for improving the dispersion uniformity of GO in PI matrix and the interaction between GO and PI molecular. The XRD results show that the in-situ aminated GO/PI composites are amorphous. The optical properties of the in-situ aminated GO/PI composite films show a sharp downward trend, while the mechanical and thermal properties increase with the increase of GO loading. When the mass fraction of GO is 1.0wt%, the tensile strength of the in-situ aminated GO/PI composites increases from 64 MPa to 83 MPa, the Young's modulus improves from 1.67 GPa to 2.10 GPa, furthermore, the 10% thermal decomposition temperature also increases from 593℃ to 597℃. However, the glass transition temperature (Tg) of the in-situ aminated GO/PI composites changes slightly. As a result of thermal imidization, most of the oxygen functional groups on the surface of GO disappear, the water uptake of the in-situ aminated GO/PI composites decreases from 0.86% to 0.58%, and the water contact angle enhances from 72.5°of pure PI film to 77.8° of 1.0%GO/PI film.
1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 3,3',4,4'-oxydiphthalic dianhydride (ODPA) were used as the monomers of polyimide (PI). Using the in-situ amination method, the graphene oxide (GO) was firstly reacted with 6FAPB to obtain the in-situ aminated GO. Then, the in-situ aminated GO was polymerized with ODPA and 6FAPB to obtain the in-situ aminated GO/poly(amic acid) (PAA) solution. After coating of the GO/PAA solution on a clean glass substrate, the in-situ aminated GO/PI composites containing 0.05wt%, 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% GO (mass fraction) were successfully prepared by thermal imidization. By means of FTIR, XPS, XRD, UV-vis, TGA, TMA, SEM, tension tester and contact angle measurement, the structure and properties of the in-situ aminated GO/PI composites were characterized. These experimental results show that the in-situ aminated GO connects with PI macromolecular chains with chemical bonds, which is helpful for improving the dispersion uniformity of GO in PI matrix and the interaction between GO and PI molecular. The XRD results show that the in-situ aminated GO/PI composites are amorphous. The optical properties of the in-situ aminated GO/PI composite films show a sharp downward trend, while the mechanical and thermal properties increase with the increase of GO loading. When the mass fraction of GO is 1.0wt%, the tensile strength of the in-situ aminated GO/PI composites increases from 64 MPa to 83 MPa, the Young's modulus improves from 1.67 GPa to 2.10 GPa, furthermore, the 10% thermal decomposition temperature also increases from 593℃ to 597℃. However, the glass transition temperature (Tg) of the in-situ aminated GO/PI composites changes slightly. As a result of thermal imidization, most of the oxygen functional groups on the surface of GO disappear, the water uptake of the in-situ aminated GO/PI composites decreases from 0.86% to 0.58%, and the water contact angle enhances from 72.5°of pure PI film to 77.8° of 1.0%GO/PI film.
2018, 35(6): 1386-1394.
doi: 10.13801/j.cnki.fhclxb.20170725.001
Abstract:
Wheat gluten (WG) reacted with acrylic acid (AA) in the promotion of 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) to produce WG-AA chains. Following, yeast decomposed the starch that existed in WG to produce CO2, which used as pore template to prepare a novel porous WG/poly(sodium acrylic)(PNaA) composite hydrogel(WG/PNaA) via free-radical graft copolymerization of sodium acrylate and WG-AA chains in the aqueous solution. FTIR spectra demonstrate that AA is grafted onto the WG chains, and the composite hydrogel is formed successfully in the presence of cross-linker N,N'-methylene discrylamide (MBA). Field emission SEM (FESEM) also displays that incorporating the proper amount of yeast into the hydrogel matrix can form porous interlinked channels within the composite hydrogel network. The porous WG/PNaA composite hydrogel shows greater equilibrium swelling capacity both in distilled water and in 0.9% NaCl solution, and the Schott's second-order swelling dynamic constant Kis is improved to 5 times compared with non-yeast exited hydrogel. Ritger's semi-empirical equation analysis also confirms that the water transport mechanism of the porous WG/PNaA composite hydrogel is non-Fickian diffusion type (n=0.5642), which means, the porous structure of the composite hydrogel is benefit to the water molecules spread quickly at the beginning swelling. The swelling-deswelling behaviors of the porous WG/PNaA composite hydrogel in distilled water-0.9% NaCl solution and in pH 2.2 and pH 7.4 phosphate buffer solution were assessed and the results show that the composite hydrogel exhibits excellent salt, pH-dependent swelling responsiveness after 5 times repeated swelling, which providing a potential application in the field of drug controlled-release.
Wheat gluten (WG) reacted with acrylic acid (AA) in the promotion of 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) to produce WG-AA chains. Following, yeast decomposed the starch that existed in WG to produce CO2, which used as pore template to prepare a novel porous WG/poly(sodium acrylic)(PNaA) composite hydrogel(WG/PNaA) via free-radical graft copolymerization of sodium acrylate and WG-AA chains in the aqueous solution. FTIR spectra demonstrate that AA is grafted onto the WG chains, and the composite hydrogel is formed successfully in the presence of cross-linker N,N'-methylene discrylamide (MBA). Field emission SEM (FESEM) also displays that incorporating the proper amount of yeast into the hydrogel matrix can form porous interlinked channels within the composite hydrogel network. The porous WG/PNaA composite hydrogel shows greater equilibrium swelling capacity both in distilled water and in 0.9% NaCl solution, and the Schott's second-order swelling dynamic constant Kis is improved to 5 times compared with non-yeast exited hydrogel. Ritger's semi-empirical equation analysis also confirms that the water transport mechanism of the porous WG/PNaA composite hydrogel is non-Fickian diffusion type (n=0.5642), which means, the porous structure of the composite hydrogel is benefit to the water molecules spread quickly at the beginning swelling. The swelling-deswelling behaviors of the porous WG/PNaA composite hydrogel in distilled water-0.9% NaCl solution and in pH 2.2 and pH 7.4 phosphate buffer solution were assessed and the results show that the composite hydrogel exhibits excellent salt, pH-dependent swelling responsiveness after 5 times repeated swelling, which providing a potential application in the field of drug controlled-release.
2018, 35(6): 1395-1401.
doi: 10.13801/j.cnki.fhclxb.20170825.004
Abstract:
The carboxyl carboxyl nitrile rubber (CTBN) and nano-silica (nano SiO2) were used as toughening agents, the copolymer of CTBN and epoxy resin (EP) were prepared as an emulsion by reverse transfer, followed by addition of nano SiO2 for blending. Finally, the curing agent was added to prepare the nano SiO2-CTBN modified water-based EP(nano SiO2-CTBN/WEP) composite by gradient heating. The properties of the nano SiO2-CTBN/WEPcomposite were characterized by an FTIR, SEM, TEM, universal tensile tester and TGA. The results show that:when the CTBN mass fraction is 20%(mass ratio to EP E-51), the prepared CTBN/WEP emulsion exhibites better storage stability. The addition of 3% nano SiO2 in CTBN/WEP resultes in the best effect of toughening. The tensile strength is 14.5 MPa, the elongation at break is 9.1%, the impact strength is 11.3 kJ/m2 and the flexural strength is 22.4 MPa, which increase by 40.1%, 27.4%, 73.9% and 72.7%, respectively, compared with the CTBN/WEP sample without adding of nano SiO2. The initial thermal decomposition temperature of the nano SiO2-CTBN/WEP also increases by nearly 25℃.
The carboxyl carboxyl nitrile rubber (CTBN) and nano-silica (nano SiO2) were used as toughening agents, the copolymer of CTBN and epoxy resin (EP) were prepared as an emulsion by reverse transfer, followed by addition of nano SiO2 for blending. Finally, the curing agent was added to prepare the nano SiO2-CTBN modified water-based EP(nano SiO2-CTBN/WEP) composite by gradient heating. The properties of the nano SiO2-CTBN/WEPcomposite were characterized by an FTIR, SEM, TEM, universal tensile tester and TGA. The results show that:when the CTBN mass fraction is 20%(mass ratio to EP E-51), the prepared CTBN/WEP emulsion exhibites better storage stability. The addition of 3% nano SiO2 in CTBN/WEP resultes in the best effect of toughening. The tensile strength is 14.5 MPa, the elongation at break is 9.1%, the impact strength is 11.3 kJ/m2 and the flexural strength is 22.4 MPa, which increase by 40.1%, 27.4%, 73.9% and 72.7%, respectively, compared with the CTBN/WEP sample without adding of nano SiO2. The initial thermal decomposition temperature of the nano SiO2-CTBN/WEP also increases by nearly 25℃.
2018, 35(6): 1402-1406.
doi: 10.13801/j.cnki.fhclxb.20170623.002
Abstract:
Carbon fiber/poly (lactic acid) (CF/PLA) composites were prepared by using CF as filler. The mass ratio of CF(CF:PLA) were 1%, 3%, 5%, 10% and 15%. Crystallinity and rheological properties of PLA and CF/PLA composites were investigated. The results show that, CF/PLA composites with 1% and 3% CF can improve the overall crystallinity of PLA at cooling process due to the heterogeneous nucleation mechanism. The intensity of XRD diffraction peaks gets stronger. The crystallization temperature and crystallinity respectively of CF/PLA composites increase to 112.5℃ and 30.7%. And the rheological properties are similar to those of pure PLA. When the mass ratio of CF increases to 5%, which is the "percolation threshold", the viscosity of CF/PLA composites gets a sharp rise. The movements of molecular segments are limited, leading a decrease in crystallinity of PLA. When the mass ratio of CF is 15%, the crystallization temperature of CF/PLA composites reduces to 93.1℃ and the crystallinity is only 2.5%.
Carbon fiber/poly (lactic acid) (CF/PLA) composites were prepared by using CF as filler. The mass ratio of CF(CF:PLA) were 1%, 3%, 5%, 10% and 15%. Crystallinity and rheological properties of PLA and CF/PLA composites were investigated. The results show that, CF/PLA composites with 1% and 3% CF can improve the overall crystallinity of PLA at cooling process due to the heterogeneous nucleation mechanism. The intensity of XRD diffraction peaks gets stronger. The crystallization temperature and crystallinity respectively of CF/PLA composites increase to 112.5℃ and 30.7%. And the rheological properties are similar to those of pure PLA. When the mass ratio of CF increases to 5%, which is the "percolation threshold", the viscosity of CF/PLA composites gets a sharp rise. The movements of molecular segments are limited, leading a decrease in crystallinity of PLA. When the mass ratio of CF is 15%, the crystallization temperature of CF/PLA composites reduces to 93.1℃ and the crystallinity is only 2.5%.
2018, 35(6): 1407-1413.
doi: 10.13801/j.cnki.fhclxb.20170727.001
Abstract:
Taking poly(oxypropylene)-polyamines (POP) and cetyltrimethyl ammonium chloride(OTAC) as modifier, modified montmorillonite(POP-MMT and OTAC-MMT) was prepared via cation exchange. 4,4'-diamino diphenyl methane bismaleimide (MBMI), 3,3'-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE) were used to synthesize MBMI-BBA-BBE matrix. POP-MMT/MBMI-BBA-BBE and OTAC-MMT/MBMI-BBA-BBE composites were prepared from MBMI-BBA-BBE, POP-MMT and OTAC-MMT by in-situ polymerization method, respectively.The results of FTIR spectra show that new groups have been introduced into the layers of two kinds of modified montmorillonite and organized successfully. The XRD result reveals that the interlayer spacing of POP-MMT and OTAC-MMT increases compared with sodium montmorillonite(Na-MMT). The SEM images display that the surface of composites is more rough, modified MMT disperses uniformly, crazing and microcrack appear and direct in different directions, and the composites exhibit ductile fracture. The test results of mechanical properties of composites show that the tendency of the bending strength and the impact strength of composites first increase and then decrease, which are higher than that of Na-MMT/MBMI-BBA-BBE and MBMI-BBA-BBE, the mechanical properties increase significantly, especially the effect of OTAC-MMT/MBMI-BBA-BBE is more obvious.
Taking poly(oxypropylene)-polyamines (POP) and cetyltrimethyl ammonium chloride(OTAC) as modifier, modified montmorillonite(POP-MMT and OTAC-MMT) was prepared via cation exchange. 4,4'-diamino diphenyl methane bismaleimide (MBMI), 3,3'-diallyl bisphenol A (BBA) and bisphenol-A diallyl ether (BBE) were used to synthesize MBMI-BBA-BBE matrix. POP-MMT/MBMI-BBA-BBE and OTAC-MMT/MBMI-BBA-BBE composites were prepared from MBMI-BBA-BBE, POP-MMT and OTAC-MMT by in-situ polymerization method, respectively.The results of FTIR spectra show that new groups have been introduced into the layers of two kinds of modified montmorillonite and organized successfully. The XRD result reveals that the interlayer spacing of POP-MMT and OTAC-MMT increases compared with sodium montmorillonite(Na-MMT). The SEM images display that the surface of composites is more rough, modified MMT disperses uniformly, crazing and microcrack appear and direct in different directions, and the composites exhibit ductile fracture. The test results of mechanical properties of composites show that the tendency of the bending strength and the impact strength of composites first increase and then decrease, which are higher than that of Na-MMT/MBMI-BBA-BBE and MBMI-BBA-BBE, the mechanical properties increase significantly, especially the effect of OTAC-MMT/MBMI-BBA-BBE is more obvious.
2018, 35(6): 1414-1420.
doi: 10.13801/j.cnki.fhclxb.20170904.001
Abstract:
In order to investigate the mechanism of the effect of orientation magnetic field on dynamic viscoelasticity of cobalt particles filled magnetorheological elastomer (MRE), cobalt particles were synthesized by a solvothermal method. The XRD and SEM results indicate the spherical cobalt particles have close-packed hexagonal structure with particle size within the range of 1-2 μm. Silicone rubber was used as the matrix to prepare cobalt particles filled MRE. During the curing process, different orientation fields (0 mT, 480 mT and 1 154 mT) were applied to prepare different MRE, and their dynamic viscoelasticity were tested. The results indicate the ordered structure formed by the cobalt particles was enhanced with increasing orientation field. As a result, the storage modulus G ' and the loss modulus G ″ of Co particles filled(MRE) increase with increasing orientation field. However, when the orientation field exceeds a critical value, the ordered becomes stable, and the effect of orientation field on dynamic viscoelasticity of MREs becomes insignificant.
In order to investigate the mechanism of the effect of orientation magnetic field on dynamic viscoelasticity of cobalt particles filled magnetorheological elastomer (MRE), cobalt particles were synthesized by a solvothermal method. The XRD and SEM results indicate the spherical cobalt particles have close-packed hexagonal structure with particle size within the range of 1-2 μm. Silicone rubber was used as the matrix to prepare cobalt particles filled MRE. During the curing process, different orientation fields (0 mT, 480 mT and 1 154 mT) were applied to prepare different MRE, and their dynamic viscoelasticity were tested. The results indicate the ordered structure formed by the cobalt particles was enhanced with increasing orientation field. As a result, the storage modulus G ' and the loss modulus G ″ of Co particles filled(MRE) increase with increasing orientation field. However, when the orientation field exceeds a critical value, the ordered becomes stable, and the effect of orientation field on dynamic viscoelasticity of MREs becomes insignificant.
2018, 35(6): 1421-1427.
doi: 10.13801/j.cnki.fhclxb.20170821.006
Abstract:
The waterborne polyurethane prepolymer (WPUP) encapsulated ZnO particles(ZnO@WPUP) were synthesized by using in-situ emulsion polymerization method. The aramid fibers pretreated by KOH were then secondly treated by modified ZnO emulsion. In addition, aramid/rubber composites modified by ZnO@WPUP were obtained by the vulcanization between aramid fiber and nature rubber.Meanwhile, the influence of ZnO@WPUP on the adhesion property of aramid/rubber composites was analyzed by FTIR, SEM and cord-H-pull test. The results show that WPUP can effectively enhance the dispersing property of ZnO. The roughness and dispersing property of ZnO@WPUP on the surface of aramid fibers increase obviously as the content of WPUP increasing. Thereby the modified ZnO can effectively improve the amount of adhesive rubber on the aramid fibers surface, and the adhesion strength of aramid/rubber composites is enhanced significantly.
The waterborne polyurethane prepolymer (WPUP) encapsulated ZnO particles(ZnO@WPUP) were synthesized by using in-situ emulsion polymerization method. The aramid fibers pretreated by KOH were then secondly treated by modified ZnO emulsion. In addition, aramid/rubber composites modified by ZnO@WPUP were obtained by the vulcanization between aramid fiber and nature rubber.Meanwhile, the influence of ZnO@WPUP on the adhesion property of aramid/rubber composites was analyzed by FTIR, SEM and cord-H-pull test. The results show that WPUP can effectively enhance the dispersing property of ZnO. The roughness and dispersing property of ZnO@WPUP on the surface of aramid fibers increase obviously as the content of WPUP increasing. Thereby the modified ZnO can effectively improve the amount of adhesive rubber on the aramid fibers surface, and the adhesion strength of aramid/rubber composites is enhanced significantly.
2018, 35(6): 1428-1435.
doi: 10.13801/j.cnki.fhclxb.20170905.006
Abstract:
The different solution of rare earth modifier (La, Ce, Pr, Nd and Sm) were used to modify glass fiber (GF) and silica (SiO2), the glass fiber-SiO2/polytetrafluoroethylene (GF-SiO2/PTFE) composites of 55wt% SiO2 and 2wt% GF were mixed by a high-speed dispersion machine and prepared by hot-pressing. The effects of rare earth modifier on the properties of the composites material were investigated, such as the water absorption, the thermal, the dielectric properties, the tensile strength and morphology. The FTIR method was used to investigate the structures of rare earth La, unmodified filler and modified filler. The surface morphology and element were analyzed by SEM and EDS. The results show that rare earth La is superior to other rare earth modifier in promoting the interfacial adhesion between glass fiber and polytetrafluoroethylene (PTFE) and improving the water absorption, the coefficient of thermal expansion, the dielectric properties and tensile properties of the GF-SiO2/PTFE composites due to the stable electronic structure of rare earth La and the strong attraction to the anion.. The dielectric properties of the GF-SiO2/PTFE composites is mainly affected by the content of rare earth La, and the optimum performance of the GF-SiO2/PTFE composites is obtained at 0.3wt% rare earth La content.
The different solution of rare earth modifier (La, Ce, Pr, Nd and Sm) were used to modify glass fiber (GF) and silica (SiO2), the glass fiber-SiO2/polytetrafluoroethylene (GF-SiO2/PTFE) composites of 55wt% SiO2 and 2wt% GF were mixed by a high-speed dispersion machine and prepared by hot-pressing. The effects of rare earth modifier on the properties of the composites material were investigated, such as the water absorption, the thermal, the dielectric properties, the tensile strength and morphology. The FTIR method was used to investigate the structures of rare earth La, unmodified filler and modified filler. The surface morphology and element were analyzed by SEM and EDS. The results show that rare earth La is superior to other rare earth modifier in promoting the interfacial adhesion between glass fiber and polytetrafluoroethylene (PTFE) and improving the water absorption, the coefficient of thermal expansion, the dielectric properties and tensile properties of the GF-SiO2/PTFE composites due to the stable electronic structure of rare earth La and the strong attraction to the anion.. The dielectric properties of the GF-SiO2/PTFE composites is mainly affected by the content of rare earth La, and the optimum performance of the GF-SiO2/PTFE composites is obtained at 0.3wt% rare earth La content.
2018, 35(6): 1436-1442.
doi: 10.13801/j.cnki.fhclxb.20170814.002
Abstract:
In order to evaluate the lighting strike damage degree and characteristics of the carbon fiber/epoxy resin matrix composite material under different aircraft lighting strike zones, three different lighting current combined waveforms (A+B, D+B+C and A+B+C+D) were used to simulate lighting strike experimental research on two kinds of composite specimens with different sizes(Type1 and Type2).Damage was assessed using visual inspection and ultrasonic testing to analyze and evaluate the lighting strike damage degree and characteristics of the composite material on the plane 1A, 2A and 1B lighting zone. Meanwhile, the damage resistance characteristics of the carbon fiber/epoxy resin matrix composite specimens with copper wire mesh were compared to the benchmark values of unprotected specimens under different lighting strike zones. The results show that under different lighting strike zones, the damage modes of the carbon fiber/epoxy resin matrix composite materials caused by lighting current are basically the same, including fiber fracture, matrix ablation and delamination. For the same type of test specimens, most severe lighting damage is in the 1B lighting zone followed by 2A lighting zone, and 1A lighting zone has the least degree of damage. Type1 test specimens with small length-width radio have the less damage degree than the ones with large length-width radio under the same lighting strike zones. 0.25 mm copper wire mesh can effectively protect the carbon fiber/epoxy resin matrix composite material. Type2 protected test specimens have 88.9%, 53.9% and 68.7% damage degree compared to the unprotected ones, which are located in 1A, 2A and 1B lighting zones.
In order to evaluate the lighting strike damage degree and characteristics of the carbon fiber/epoxy resin matrix composite material under different aircraft lighting strike zones, three different lighting current combined waveforms (A+B, D+B+C and A+B+C+D) were used to simulate lighting strike experimental research on two kinds of composite specimens with different sizes(Type1 and Type2).Damage was assessed using visual inspection and ultrasonic testing to analyze and evaluate the lighting strike damage degree and characteristics of the composite material on the plane 1A, 2A and 1B lighting zone. Meanwhile, the damage resistance characteristics of the carbon fiber/epoxy resin matrix composite specimens with copper wire mesh were compared to the benchmark values of unprotected specimens under different lighting strike zones. The results show that under different lighting strike zones, the damage modes of the carbon fiber/epoxy resin matrix composite materials caused by lighting current are basically the same, including fiber fracture, matrix ablation and delamination. For the same type of test specimens, most severe lighting damage is in the 1B lighting zone followed by 2A lighting zone, and 1A lighting zone has the least degree of damage. Type1 test specimens with small length-width radio have the less damage degree than the ones with large length-width radio under the same lighting strike zones. 0.25 mm copper wire mesh can effectively protect the carbon fiber/epoxy resin matrix composite material. Type2 protected test specimens have 88.9%, 53.9% and 68.7% damage degree compared to the unprotected ones, which are located in 1A, 2A and 1B lighting zones.
2018, 35(6): 1443-1451.
doi: 10.13801/j.cnki.fhclxb.20170821.001
Abstract:
Glass fiber reinforced resin composite(GRP) sandwich panels with PVC foam or Balsa wood as core material are widely used in ship construction and ocean engineering. Flexural behaviors of hybrid joints of sandwich panel-steel plate which subjected to static and fatigue loads respectively, were investigated with both numerical and experimental methods. Different parameter sets of hybrid joint specimens were designed and fabricated. Static and fatigue four-point bending experiments were implemented to study the bending strength, stiffness and failure modes of joints. ABAQUS and MSC. Fatigue softwares were also adopted to simulate their failure characteristics. The influences of filler material, geometric length of filler and the inserted length of steel plate on the bending performance of the joint were respectively assessed. The results show that failure occurs near the filler area of joints under bending load, and failure mode mainly depends on different filler parameters. Extending the steel end to filler area can obviously improve bending performance of joint, as well as adopting Balsa wood as filler material. All specimens are failed before 106 cycles in the larger fatigue load case, while in the lower fatigue load case, all the specimens are nearly intact after 106 cycles and their residual strengths are quite close to their static ultimate strength. It is indicated that fatigue cycles with smaller loading amplitudes have little influence on their loading capacities.
Glass fiber reinforced resin composite(GRP) sandwich panels with PVC foam or Balsa wood as core material are widely used in ship construction and ocean engineering. Flexural behaviors of hybrid joints of sandwich panel-steel plate which subjected to static and fatigue loads respectively, were investigated with both numerical and experimental methods. Different parameter sets of hybrid joint specimens were designed and fabricated. Static and fatigue four-point bending experiments were implemented to study the bending strength, stiffness and failure modes of joints. ABAQUS and MSC. Fatigue softwares were also adopted to simulate their failure characteristics. The influences of filler material, geometric length of filler and the inserted length of steel plate on the bending performance of the joint were respectively assessed. The results show that failure occurs near the filler area of joints under bending load, and failure mode mainly depends on different filler parameters. Extending the steel end to filler area can obviously improve bending performance of joint, as well as adopting Balsa wood as filler material. All specimens are failed before 106 cycles in the larger fatigue load case, while in the lower fatigue load case, all the specimens are nearly intact after 106 cycles and their residual strengths are quite close to their static ultimate strength. It is indicated that fatigue cycles with smaller loading amplitudes have little influence on their loading capacities.
2018, 35(6): 1452-1463.
doi: 10.13801/j.cnki.fhclxb.20170821.008
Abstract:
In order to calculate the residual stress of CFRP layers and metal liner for composite cylinders consisting of alternate multi-angle CFRP winding layers and thin-walled metal liner, a superposition algorithm layer by layer for CFRP layers and metal liner residual stress was proposed, reflecting on the thick walled cylinder theory and the elastic superposition theory of orthotropic material, and the effect of removing mandrel was under consideration as well. The influence of the spiral layers winding angle and the thickness of mandrel on the residual stress of CFRP layers and steel liner was analyzed with constant winding tension. The greater the thickness of mandrel, the lower the residual stress of CFRP layers is, but too thick mandrel weakens the enhancement effect of steel liner profiting from winding tension. When the spiral winding angle is in 65°, the residual stress of hoop layers is minimum, and the residual stress of spiral layers and steel liner is maximum. For the enhancement effect for steel liner, the yield loading pressure of steel liner was measured by the acoustic emission characteristics of the steel liner and the strain measurement of composite cylinder outer edge in the loading process based on water-pressure test. The test results were basically consistent with the theoretical prediction values and the validity of the algorithm proposed above was verified. A optimization design ideal of fibra intertwist tension system for composite cylinder with alternate multi-angle winding layers, which withstands an internal pressure load, was proposed to improve the winding quality, based on the hypothesis of equal residual stress in hoop and spiral layers, respectively.
In order to calculate the residual stress of CFRP layers and metal liner for composite cylinders consisting of alternate multi-angle CFRP winding layers and thin-walled metal liner, a superposition algorithm layer by layer for CFRP layers and metal liner residual stress was proposed, reflecting on the thick walled cylinder theory and the elastic superposition theory of orthotropic material, and the effect of removing mandrel was under consideration as well. The influence of the spiral layers winding angle and the thickness of mandrel on the residual stress of CFRP layers and steel liner was analyzed with constant winding tension. The greater the thickness of mandrel, the lower the residual stress of CFRP layers is, but too thick mandrel weakens the enhancement effect of steel liner profiting from winding tension. When the spiral winding angle is in 65°, the residual stress of hoop layers is minimum, and the residual stress of spiral layers and steel liner is maximum. For the enhancement effect for steel liner, the yield loading pressure of steel liner was measured by the acoustic emission characteristics of the steel liner and the strain measurement of composite cylinder outer edge in the loading process based on water-pressure test. The test results were basically consistent with the theoretical prediction values and the validity of the algorithm proposed above was verified. A optimization design ideal of fibra intertwist tension system for composite cylinder with alternate multi-angle winding layers, which withstands an internal pressure load, was proposed to improve the winding quality, based on the hypothesis of equal residual stress in hoop and spiral layers, respectively.
2018, 35(6): 1464-1471.
doi: 10.13801/j.cnki.fhclxb.20170815.001
Abstract:
Four kinds of husk fibers, coconut shell, hazelnut shell, walnut shell and rice husk were used as filler material and polyvinyl chloride as the base material to prepare the husk fiber/polyvinyl chloride composites. Four kinds of husk fibers were analyzed by comprehensive thermal analyzer and FTIR. The creep and wear properties of four kinds of husk fiber/polyvinyl chloride composites were tested. The results show that the cellulose content in rice husk is 43.6%, which is the highest in the four kinds of husk fibers. The rice husk fiber/polyvinyl chloride composites have good interface and mechanical properties, and their compressive, tensile and flexural strength are the highest, which is 43.1 MPa, 23.2 MPa and 46.1 MPa, and increase by 13.7%, 33.3% and 21.0%, respectively, compared with walnut shell fiber/polyvinyl chloride composites of lowest strength. Under the same stress, the creep strain of rice husk fiber/polyvinyl chloride composites is the smallest. Under the same wear conditions, the specific wear rate of rice husk fiber/polyvinyl chloride composites is the smallest, while their friction coefficient is also the smallest.
Four kinds of husk fibers, coconut shell, hazelnut shell, walnut shell and rice husk were used as filler material and polyvinyl chloride as the base material to prepare the husk fiber/polyvinyl chloride composites. Four kinds of husk fibers were analyzed by comprehensive thermal analyzer and FTIR. The creep and wear properties of four kinds of husk fiber/polyvinyl chloride composites were tested. The results show that the cellulose content in rice husk is 43.6%, which is the highest in the four kinds of husk fibers. The rice husk fiber/polyvinyl chloride composites have good interface and mechanical properties, and their compressive, tensile and flexural strength are the highest, which is 43.1 MPa, 23.2 MPa and 46.1 MPa, and increase by 13.7%, 33.3% and 21.0%, respectively, compared with walnut shell fiber/polyvinyl chloride composites of lowest strength. Under the same stress, the creep strain of rice husk fiber/polyvinyl chloride composites is the smallest. Under the same wear conditions, the specific wear rate of rice husk fiber/polyvinyl chloride composites is the smallest, while their friction coefficient is also the smallest.
2018, 35(6): 1472-1480.
doi: 10.13801/j.cnki.fhclxb.20170829.005
Abstract:
The new energy absorption structure of glass fiber/resin composite wound hollow glass microspheres/resin solid ball element had been put forward. In order to investigate the damage evolvement law and energy dissipation mechanism of the element, the numerical analysis model was built by ABAQUS and the experiments were conducted under low-velocity and large-mass impact loading. Comparative analysis of numerical simulation and experimental results show that the key to the crashworthiness design of the structure was the compatibility design of the Poisson' s ratio between the surface and solid buoyant core.The smooth plastic compression damage and shear failure of the solid buoyant core come to occur due to the constraint stress of the composite surface with lower Poisson's ratio. The progressive tensile breaking of the composite surface is caused by transverse expansion deformation of the solid buoyant core and the petal shaped damage appears. The results show that this new structure has good energy dissipation property and provide certain reserve buoyancy.
The new energy absorption structure of glass fiber/resin composite wound hollow glass microspheres/resin solid ball element had been put forward. In order to investigate the damage evolvement law and energy dissipation mechanism of the element, the numerical analysis model was built by ABAQUS and the experiments were conducted under low-velocity and large-mass impact loading. Comparative analysis of numerical simulation and experimental results show that the key to the crashworthiness design of the structure was the compatibility design of the Poisson' s ratio between the surface and solid buoyant core.The smooth plastic compression damage and shear failure of the solid buoyant core come to occur due to the constraint stress of the composite surface with lower Poisson's ratio. The progressive tensile breaking of the composite surface is caused by transverse expansion deformation of the solid buoyant core and the petal shaped damage appears. The results show that this new structure has good energy dissipation property and provide certain reserve buoyancy.
2018, 35(6): 1481-1489.
doi: 10.13801/j.cnki.fhclxb.20170727.004
Abstract:
Using the constructed three-dimensional progressive damage degradation model for composite based on the theory of continuum damage mechanics (CDM), dynamic response and damage performance of composite laminate under the act of lightning strike impact force were analyzed through the platform of ABAQUS software and VUMAT subroutine. Analysis results indicate that under the act of lightning strike impact force, laminate displays oscillatory movement with amplitude decrease, and the work did by lightning strike impact force converts with internal energy and kinetic energy of laminate mutually, and accompanys with the consumed viscous dissipation energy, additionally, it can be expressed as a function of electrical charge and action integral of lightning current. Mechanical impact damage degree of laminate depends on the work due to lightning strike impact force, for the same material, matrix, fiber and delamination damage exist different corresponding critical damage external energy, respectively. When the work did by lightning strike impact force higher than the critical damage energy, laminate will occur corresponding damage form. With the same boundary support condition, the maximum value of fiber, matrix and delamination damage state variables depend on total work did by lightning strike impact force, and have nothing to do with lightning current parameters.
Using the constructed three-dimensional progressive damage degradation model for composite based on the theory of continuum damage mechanics (CDM), dynamic response and damage performance of composite laminate under the act of lightning strike impact force were analyzed through the platform of ABAQUS software and VUMAT subroutine. Analysis results indicate that under the act of lightning strike impact force, laminate displays oscillatory movement with amplitude decrease, and the work did by lightning strike impact force converts with internal energy and kinetic energy of laminate mutually, and accompanys with the consumed viscous dissipation energy, additionally, it can be expressed as a function of electrical charge and action integral of lightning current. Mechanical impact damage degree of laminate depends on the work due to lightning strike impact force, for the same material, matrix, fiber and delamination damage exist different corresponding critical damage external energy, respectively. When the work did by lightning strike impact force higher than the critical damage energy, laminate will occur corresponding damage form. With the same boundary support condition, the maximum value of fiber, matrix and delamination damage state variables depend on total work did by lightning strike impact force, and have nothing to do with lightning current parameters.
2018, 35(6): 1490-1496.
doi: 10.13801/j.cnki.fhclxb.20170630.002
Abstract:
A composite nanoparticle hollow mesoporous SiO2(HMSiO2)@chitosan-graft-polyamidoxime(CTS-g-PAO) was prepared via HMSiO2 through sol-gel method used as CTS coating on HMSiO2 by inverse microemulsion synthesis used as the matrix to graft polyacrylonitrile (PAN), which was transformed to PAO. The component and the structure of the HMSiO2@CTS-g-PAO composite were examined by FTIR and XRD. The morphology and the size of the HMSiO2@CTS-g-PAO were confirmed by SEM and Laser Particle Size Analyzer. The results show that the HMSiO2@CTS-g-PAO is core-shell nanoparticle with the HMSiO2 as the core and the CTS-g-PAO as the shell. K2Cr2O7 solution is used as the Cr target for detecting the adsorption capacity of the prepared HMSiO2@CTS-g-PAO. The results indicate that the adsorption capacity of CrVI is 3.28 mmol/g when the pH of K2Cr2O7 solution is 2 and the concentration of the solution is 91.4 mg/L. Furthermore, the adsorption process is consistent with the pseudo-second-order kinetics and mainly belongs to chemical adsorption.
A composite nanoparticle hollow mesoporous SiO2(HMSiO2)@chitosan-graft-polyamidoxime(CTS-g-PAO) was prepared via HMSiO2 through sol-gel method used as CTS coating on HMSiO2 by inverse microemulsion synthesis used as the matrix to graft polyacrylonitrile (PAN), which was transformed to PAO. The component and the structure of the HMSiO2@CTS-g-PAO composite were examined by FTIR and XRD. The morphology and the size of the HMSiO2@CTS-g-PAO were confirmed by SEM and Laser Particle Size Analyzer. The results show that the HMSiO2@CTS-g-PAO is core-shell nanoparticle with the HMSiO2 as the core and the CTS-g-PAO as the shell. K2Cr2O7 solution is used as the Cr target for detecting the adsorption capacity of the prepared HMSiO2@CTS-g-PAO. The results indicate that the adsorption capacity of CrVI is 3.28 mmol/g when the pH of K2Cr2O7 solution is 2 and the concentration of the solution is 91.4 mg/L. Furthermore, the adsorption process is consistent with the pseudo-second-order kinetics and mainly belongs to chemical adsorption.
2018, 35(6): 1497-1502.
doi: 10.13801/j.cnki.fhclxb.20170901.001
Abstract:
The application of polymer is limited by its relaxations behaviors. The main research of this paper was focused on the effect which the aluminum trihydroxide (ATH) filler has on α relaxation and β relaxation of epoxy composites. And the broadband dielectric spectroscopy technology was applied to investigate such effect in this paper. In our experiments, the test condition was that the broad frequency of broadband dielectric spectroscopy ranged from 0.1 Hz to 2 MHz and the temperature of the broadband dielectric spectroscopy was from-100℃ to 100℃, also the inorganic filler must be the ATH powder with the particle size of 2 μm. The pure epoxy resin and the epoxy resin to which was added different proportion (0%, 20%, 40%, 60%, 80% and 100%) of the fillers were prepared and the dielectric properties of each of them was measured. The results show that, the quantities of the inorganic fillers have little effects on α relaxation but have an obvious and significant effect on β relaxation. With the quantities of the inorganic fillers increasing, the Vogel temperature decreases at first and then increases. On the contrary, the β relaxation apparent activation energy of ATH/epoxy composite increases at first and then decreases.
The application of polymer is limited by its relaxations behaviors. The main research of this paper was focused on the effect which the aluminum trihydroxide (ATH) filler has on α relaxation and β relaxation of epoxy composites. And the broadband dielectric spectroscopy technology was applied to investigate such effect in this paper. In our experiments, the test condition was that the broad frequency of broadband dielectric spectroscopy ranged from 0.1 Hz to 2 MHz and the temperature of the broadband dielectric spectroscopy was from-100℃ to 100℃, also the inorganic filler must be the ATH powder with the particle size of 2 μm. The pure epoxy resin and the epoxy resin to which was added different proportion (0%, 20%, 40%, 60%, 80% and 100%) of the fillers were prepared and the dielectric properties of each of them was measured. The results show that, the quantities of the inorganic fillers have little effects on α relaxation but have an obvious and significant effect on β relaxation. With the quantities of the inorganic fillers increasing, the Vogel temperature decreases at first and then increases. On the contrary, the β relaxation apparent activation energy of ATH/epoxy composite increases at first and then decreases.
2018, 35(6): 1503-1509.
doi: 10.13801/j.cnki.fhclxb.20170824.002
Abstract:
A finite element model of conical projectiles impacting composite laminated plates had been established by using Abaqus software. The reliability of the model was verified by comparing with the existing literature. And the relationship between the residual velocity and the initial velocity of the conical projectile at different angles of incidence, the failure mode of the composite laminated plate and the rules of projectile ricochet were studied. The results show that when the projectile impacts the laminates at 90° and from the critical velocity is larger, the residual velocity of the projectile is linearly related to the initial velocity. Different initial velocities can lead to different damage areas of the laminate and different mechanisms of damage. The smaller the incident angle of the projectile, the thicker the laminate, the more prone to ricochet, and the influence of the angle of incidence and the number of laying layers on the ricochet is given. The study can provide a reference for the design and optimization of various protective equipment.
A finite element model of conical projectiles impacting composite laminated plates had been established by using Abaqus software. The reliability of the model was verified by comparing with the existing literature. And the relationship between the residual velocity and the initial velocity of the conical projectile at different angles of incidence, the failure mode of the composite laminated plate and the rules of projectile ricochet were studied. The results show that when the projectile impacts the laminates at 90° and from the critical velocity is larger, the residual velocity of the projectile is linearly related to the initial velocity. Different initial velocities can lead to different damage areas of the laminate and different mechanisms of damage. The smaller the incident angle of the projectile, the thicker the laminate, the more prone to ricochet, and the influence of the angle of incidence and the number of laying layers on the ricochet is given. The study can provide a reference for the design and optimization of various protective equipment.
2018, 35(6): 1510-1517.
doi: 10.13801/j.cnki.fhclxb.20170824.003
Abstract:
The joint stiffness is an important parameter in the design of composite bolted joints and is influenced largely by the bolt-hole clearance. Aiming at the elastic foundation stiffness kc*, an analytical expression was derived by introducing Liu Cai-Shan's inner cylindrical contact model. This analytical expression can take account of the bolt-hole clearance and it shows that kc* deceases with the increase of clearance. Aiming at the nail-head restraint coefficient kr, an approximate expression was obtained by the strain energy method from a reasonable stress distribution hypothesis. Based on kc* and kr, the analytical solution of the joint stiffness was derived from an elastic foundation beam model. The load-displacement curves of double-lap bolted joints predicted by the analytical method were validated by 3-D detailed FE-models. Finally, the mechanical mechanism of the clearance influence on the joint stiffness was analyzed by finite element method. Moreover, the influences of the clearances form 1-300 μm were given quantitatively by the analytic method.
The joint stiffness is an important parameter in the design of composite bolted joints and is influenced largely by the bolt-hole clearance. Aiming at the elastic foundation stiffness kc*, an analytical expression was derived by introducing Liu Cai-Shan's inner cylindrical contact model. This analytical expression can take account of the bolt-hole clearance and it shows that kc* deceases with the increase of clearance. Aiming at the nail-head restraint coefficient kr, an approximate expression was obtained by the strain energy method from a reasonable stress distribution hypothesis. Based on kc* and kr, the analytical solution of the joint stiffness was derived from an elastic foundation beam model. The load-displacement curves of double-lap bolted joints predicted by the analytical method were validated by 3-D detailed FE-models. Finally, the mechanical mechanism of the clearance influence on the joint stiffness was analyzed by finite element method. Moreover, the influences of the clearances form 1-300 μm were given quantitatively by the analytic method.
2018, 35(6): 1518-1524.
doi: 10.13801/j.cnki.fhclxb.20170713.002
Abstract:
Due to its superior properties, carbon nanotubes (CNTs) have been regarded as a promising reinforcement for the metal matrix composites (MMCs). How to fabricate the MMCs with homogeneous CNTs reinforcement is a hot research field. In the present study, the CNTs reinforced Al composite foams were successfully prepared through a combination of in-situ chemical vapor deposition (CVD), short time ball milling and the space holder method. The effects of ball milling time on the micro morphology, compressive property and energy absorption capacity of the CNTs/Al composite foams were investigated. The results show that with the ball milling time increasing, the microstructure uniformity of the composite foams is improved as a result of the enhanced CNTs dispersion in the Al matrix. Besides, the CNTs are deeply embedded inside the Al matrix after 90 min ball milling. Moreover, compared to the non-ball-milling 3.0wt% CNTs/Al composite foams, when the ball milling time increases to 90 min, the pore wall hardness, yield strength and energy absorption capacity of the composite foams are increased by 67%, 126% and 343%, respectively.
Due to its superior properties, carbon nanotubes (CNTs) have been regarded as a promising reinforcement for the metal matrix composites (MMCs). How to fabricate the MMCs with homogeneous CNTs reinforcement is a hot research field. In the present study, the CNTs reinforced Al composite foams were successfully prepared through a combination of in-situ chemical vapor deposition (CVD), short time ball milling and the space holder method. The effects of ball milling time on the micro morphology, compressive property and energy absorption capacity of the CNTs/Al composite foams were investigated. The results show that with the ball milling time increasing, the microstructure uniformity of the composite foams is improved as a result of the enhanced CNTs dispersion in the Al matrix. Besides, the CNTs are deeply embedded inside the Al matrix after 90 min ball milling. Moreover, compared to the non-ball-milling 3.0wt% CNTs/Al composite foams, when the ball milling time increases to 90 min, the pore wall hardness, yield strength and energy absorption capacity of the composite foams are increased by 67%, 126% and 343%, respectively.
2018, 35(6): 1525-1534.
doi: 10.13801/j.cnki.fhclxb.20170905.005
Abstract:
The dynamic recrystallization behavior of short carbon fiber(CFs)/AZ91D composite and AZ91D Mg alloy was investigated by isothermal compressive experiment at the deformation temperatures from 340℃ to 400℃, strain rates from 0.001 s-1 to 1 s-1 and a maximum true strain of 0.7. The results show that both CFs/AZ91D composites and Mg alloy exhibit an obvious dynamic recrystallization during being compressed at elevated temperature. The addition of CFs greatly promotes the dynamic recrystallization of the matrix alloy in the composite. As a result, the critical strain for dynamic recrystallization is reduced and a finer recrystallized grain structure is obtained in the composite. For the Mg alloy, the variation of volume fraction of dynamic recrystallization with the strain presents the classical "S" mode. For the CFs/AZ91D composites, however, the increase of volume fraction of dynamic recrystallization with the increase of strain exhibits a rapid-slow-stable behavior. The dynamic recrystallization critical strain and kinetics models of CFs/AZ91D composite and Mg alloy were developed according to the experimental results. Based on these models, the difference of the dynamic recrystallization behavior between CFs/AZ91D composite and Mg alloy was analyzed.
The dynamic recrystallization behavior of short carbon fiber(CFs)/AZ91D composite and AZ91D Mg alloy was investigated by isothermal compressive experiment at the deformation temperatures from 340℃ to 400℃, strain rates from 0.001 s-1 to 1 s-1 and a maximum true strain of 0.7. The results show that both CFs/AZ91D composites and Mg alloy exhibit an obvious dynamic recrystallization during being compressed at elevated temperature. The addition of CFs greatly promotes the dynamic recrystallization of the matrix alloy in the composite. As a result, the critical strain for dynamic recrystallization is reduced and a finer recrystallized grain structure is obtained in the composite. For the Mg alloy, the variation of volume fraction of dynamic recrystallization with the strain presents the classical "S" mode. For the CFs/AZ91D composites, however, the increase of volume fraction of dynamic recrystallization with the increase of strain exhibits a rapid-slow-stable behavior. The dynamic recrystallization critical strain and kinetics models of CFs/AZ91D composite and Mg alloy were developed according to the experimental results. Based on these models, the difference of the dynamic recrystallization behavior between CFs/AZ91D composite and Mg alloy was analyzed.
2018, 35(6): 1535-1541.
doi: 10.13801/j.cnki.fhclxb.20170904.002
Abstract:
In order to analyse the influence of composite fiber ratio on the strength and breathability of reinforced silica sol shell for investment casting, the bending strength of the embryo and after baking and breathability of composite fiber reinforced shell samples were studied. Ceramic and nylon composite fibers were used to enhance silica sol shell samples. In the slurry, the volume ratio of the nylon fiber and ceramic fiber respectively were 100:0, 82.7:17.3, 61.5:38.5, 34.7:65.3 and 0:100. The results indicate that when the proportion of nylon fibers changes from 0% to 100% in the complex fibers, the bending strength of the embryo of the shell increases gradually, the overall change of the fired bending strength is not obvious, and the breathability rate has the trend of increasing first and then decreasing. When the volume content of nylon fibers is 82.7%, the breathability rate reachs maximum, which is 5.21. According to the analysis of the fracture morphology and fiber reinforced behavior, the bending strength of the embryo of mold shell is mainly affected by the volume content of fiber and the flexural strength and permeability of the shell after baking are influenced by the volume content of ceramic fiber, the thickness of coating and the number of holes that the nylon fiber left after being burning.
In order to analyse the influence of composite fiber ratio on the strength and breathability of reinforced silica sol shell for investment casting, the bending strength of the embryo and after baking and breathability of composite fiber reinforced shell samples were studied. Ceramic and nylon composite fibers were used to enhance silica sol shell samples. In the slurry, the volume ratio of the nylon fiber and ceramic fiber respectively were 100:0, 82.7:17.3, 61.5:38.5, 34.7:65.3 and 0:100. The results indicate that when the proportion of nylon fibers changes from 0% to 100% in the complex fibers, the bending strength of the embryo of the shell increases gradually, the overall change of the fired bending strength is not obvious, and the breathability rate has the trend of increasing first and then decreasing. When the volume content of nylon fibers is 82.7%, the breathability rate reachs maximum, which is 5.21. According to the analysis of the fracture morphology and fiber reinforced behavior, the bending strength of the embryo of mold shell is mainly affected by the volume content of fiber and the flexural strength and permeability of the shell after baking are influenced by the volume content of ceramic fiber, the thickness of coating and the number of holes that the nylon fiber left after being burning.
2018, 35(6): 1542-1548.
doi: 10.13801/j.cnki.fhclxb.20170825.002
Abstract:
The hexadecanol (H)-palmitic acid (PA)-lauric acid (LA)@(Ce-La-TiO2) photocatalytic-heat-mositure composites were prepared experimentally by the sol-gel method and the vacuum adsorption method, with the Ce-La-TiO2 hollow microspheres as the carrier material and H-PA-LA as the phase change material separately. The light response property, heat property, mositure property, composition and microstructure were tested and characterized by UV-Vis, XRD, DSC, DVS and SEM, respectively. The results show that the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites present as uniform spheres, with small particle size and good dispersion, which promotes the coordinated effect of La ions and Ce ions. When the mass ratio of Ce(NO3)3·6H2O to La(NO3)3·6H2O is 1:1, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites can obtain the optimal light response property. When the mass ratio of H-PA-LA to Ce-La-TiO2 hollow microspheres is 1:2, H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites show the best heat property. When the vacuum degree of vacuum drying oven is 0.07 MPa, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites show the optimal moisture property.
The hexadecanol (H)-palmitic acid (PA)-lauric acid (LA)@(Ce-La-TiO2) photocatalytic-heat-mositure composites were prepared experimentally by the sol-gel method and the vacuum adsorption method, with the Ce-La-TiO2 hollow microspheres as the carrier material and H-PA-LA as the phase change material separately. The light response property, heat property, mositure property, composition and microstructure were tested and characterized by UV-Vis, XRD, DSC, DVS and SEM, respectively. The results show that the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites present as uniform spheres, with small particle size and good dispersion, which promotes the coordinated effect of La ions and Ce ions. When the mass ratio of Ce(NO3)3·6H2O to La(NO3)3·6H2O is 1:1, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites can obtain the optimal light response property. When the mass ratio of H-PA-LA to Ce-La-TiO2 hollow microspheres is 1:2, H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites show the best heat property. When the vacuum degree of vacuum drying oven is 0.07 MPa, the H-PA-LA@(Ce-La-TiO2) photocatalytic-heat-mositure composites show the optimal moisture property.
2018, 35(6): 1549-1557.
doi: 10.13801/j.cnki.fhclxb.20180111.001
Abstract:
A magnetic microspheres (Calcium Alginate@Fe3O4/Biochar) was prepared using calcium alginate (CA) encapsulated biochar (BC) and Fe3O4 as the green adsorbent for Co(Ⅱ) removal from aqueous solution. The effects of the initial Co(NO3)2 concentration, initial pH value of Co(Ⅱ) solution and equilibrium contact time were investigated on CA@Fe3O4/BC. The isothermal thermodynamic datas of the CA@Fe3O4/BC conformed to the Langmuir model. The maximum adsorption capacity of the CA@Fe3O4/BC from the Langmuir equation is 16.23 mg·g-1 at pH=6. It appears a synergistic effect between biochar and Fe3O4 in CA, which enhances the maximum adsorption capacity of Co(Ⅱ) ion. The presence of the magnetic particles in magnetic microsphere allows easy isolation of the material from aqueous solutions by using a magnet. The adsorptions of Co(Ⅱ) by the CA@Fe3O4/BC are in good agreement with pseudo-second-order kinetic. The mechanism studies for Co (Ⅱ) removal by the CA@Fe3O4/BC show that the nature of Co(Ⅱ) abstraction takes place through the ion exchange between Ca(Ⅱ) and Co(Ⅱ) as well as the formation of coordination complex.
A magnetic microspheres (Calcium Alginate@Fe3O4/Biochar) was prepared using calcium alginate (CA) encapsulated biochar (BC) and Fe3O4 as the green adsorbent for Co(Ⅱ) removal from aqueous solution. The effects of the initial Co(NO3)2 concentration, initial pH value of Co(Ⅱ) solution and equilibrium contact time were investigated on CA@Fe3O4/BC. The isothermal thermodynamic datas of the CA@Fe3O4/BC conformed to the Langmuir model. The maximum adsorption capacity of the CA@Fe3O4/BC from the Langmuir equation is 16.23 mg·g-1 at pH=6. It appears a synergistic effect between biochar and Fe3O4 in CA, which enhances the maximum adsorption capacity of Co(Ⅱ) ion. The presence of the magnetic particles in magnetic microsphere allows easy isolation of the material from aqueous solutions by using a magnet. The adsorptions of Co(Ⅱ) by the CA@Fe3O4/BC are in good agreement with pseudo-second-order kinetic. The mechanism studies for Co (Ⅱ) removal by the CA@Fe3O4/BC show that the nature of Co(Ⅱ) abstraction takes place through the ion exchange between Ca(Ⅱ) and Co(Ⅱ) as well as the formation of coordination complex.
2018, 35(6): 1558-1565.
doi: 10.13801/j.cnki.fhclxb.20171012.002
Abstract:
Using illite as carrier and dicyandiamide (C2H4 N4) as g-C3N4 precursor, a novel visible light responding g-C3N4/illite photocatalytic composite was prepared through chemical impregnation combined with thermal polymerization technique. The microstructure, interface and optical properties of the obtained photo-catalytic composites were characterized by XRD、FESEM、AFM、UV-Vis、BET and PL. In addition, using ciprofloxacin (CIP) as the target pollutant, the photo-catalytic activity of photo-catalytic composite was evaluated under visible light. The results indicate that the as-synthesized g-C3N4/illite sample exhibits significantly enhanced photocatalytic activity under visible-light irradiation, whose reaction constant rate is almost 11.26 times that of the pure g-C3N4. The g-C3N4 nanosheets are firmly attached on the surface of illite, which could effectively inhibit the recombination of photogenerated carriers and then further improve the adsorption capacity and photoactivity of g-C3N4 photocatalyst.
Using illite as carrier and dicyandiamide (C2H4 N4) as g-C3N4 precursor, a novel visible light responding g-C3N4/illite photocatalytic composite was prepared through chemical impregnation combined with thermal polymerization technique. The microstructure, interface and optical properties of the obtained photo-catalytic composites were characterized by XRD、FESEM、AFM、UV-Vis、BET and PL. In addition, using ciprofloxacin (CIP) as the target pollutant, the photo-catalytic activity of photo-catalytic composite was evaluated under visible light. The results indicate that the as-synthesized g-C3N4/illite sample exhibits significantly enhanced photocatalytic activity under visible-light irradiation, whose reaction constant rate is almost 11.26 times that of the pure g-C3N4. The g-C3N4 nanosheets are firmly attached on the surface of illite, which could effectively inhibit the recombination of photogenerated carriers and then further improve the adsorption capacity and photoactivity of g-C3N4 photocatalyst.
2018, 35(6): 1566-1573.
doi: 10.13801/j.cnki.fhclxb.20170905.003
Abstract:
With plastering gypsum as the matrix, phase change and humidity storage fibers were mixed with plastering gypsum to prepare phase change and humidity storage fibers/gypsum composite. Basic performance, humidity storage humidity controlling performance, phase change temperature controlling performance and durability performance of phase change and humidity storage fibers/gypsum composite were tested and analyzed. Structural composition and microstructure of phase change and humidity storage fibers/gypsum composite were analyzed by FTIR and SEM. The results show that phase change and humidity storage fibers with mass content of 40.0wt% can provide the best performance and good durability performance of phase change and humidity storage fibers/gypsum composite. The standard diffusion degree of water consumption is 0.70, initial setting time is 40 min, final setting time is 55 min, bulk density is 1 005.56 kg/m3, tensile connection strength is 0.10 MPa and compressive strength is 2.55 MPa. Equilibrium moisture content is 0.0395-0.0935 g·g-1 in relative humidity 40%-65%. Cooling time is 100 s form 35℃ to 20℃ with clear phase change platform. After the cycling test, the moisture absorption performance decline of phase change and humidity storage fibers/gypsum composite is less than 10%, phase change and temperature controlling performance decline is less than 5%.
With plastering gypsum as the matrix, phase change and humidity storage fibers were mixed with plastering gypsum to prepare phase change and humidity storage fibers/gypsum composite. Basic performance, humidity storage humidity controlling performance, phase change temperature controlling performance and durability performance of phase change and humidity storage fibers/gypsum composite were tested and analyzed. Structural composition and microstructure of phase change and humidity storage fibers/gypsum composite were analyzed by FTIR and SEM. The results show that phase change and humidity storage fibers with mass content of 40.0wt% can provide the best performance and good durability performance of phase change and humidity storage fibers/gypsum composite. The standard diffusion degree of water consumption is 0.70, initial setting time is 40 min, final setting time is 55 min, bulk density is 1 005.56 kg/m3, tensile connection strength is 0.10 MPa and compressive strength is 2.55 MPa. Equilibrium moisture content is 0.0395-0.0935 g·g-1 in relative humidity 40%-65%. Cooling time is 100 s form 35℃ to 20℃ with clear phase change platform. After the cycling test, the moisture absorption performance decline of phase change and humidity storage fibers/gypsum composite is less than 10%, phase change and temperature controlling performance decline is less than 5%.
2018, 35(6): 1574-1581.
doi: 10.13801/j.cnki.fhclxb.20170714.002
Abstract:
A highly transparent carboxymethyl cellulose (CMC)/cellulose fiber composite film based on cellulose fibers and CMC was rapidly prepared by a combination of paper making method and impregnation, aiming to replace current rigid, non-biodegradable substrates for electronic devices. The optical transmittance of composite films as function of the mass ratio of CMC to northern wood fibers and the influence of the CMC molecular weight on the mechanical properties were investigated.The effect of fiber species (northern wood fiber, eucalyptus wood fiber, manila hemp fiber, bagasse fiber) on the mechanical properties of highly transparent CMC/cellulose fiber composite films was also studied. The results show that the CMC/northern wood fiber composite film exhibits a light transmittance of 90%, a tensile strength of 111 MPa, and a folding endurance up to 2 526 times when the mass ratio of CMC (molecular weight:700 000)to softwood fibers is 7:3. This biodegradable, mechanically flexible, strong, and highly transparent CMC/cellulose fiber composite film shows the potential to be used in the fabrication of next generation flexible and green electronic devices as a substrate to maintain the sustainability of human's society.
A highly transparent carboxymethyl cellulose (CMC)/cellulose fiber composite film based on cellulose fibers and CMC was rapidly prepared by a combination of paper making method and impregnation, aiming to replace current rigid, non-biodegradable substrates for electronic devices. The optical transmittance of composite films as function of the mass ratio of CMC to northern wood fibers and the influence of the CMC molecular weight on the mechanical properties were investigated.The effect of fiber species (northern wood fiber, eucalyptus wood fiber, manila hemp fiber, bagasse fiber) on the mechanical properties of highly transparent CMC/cellulose fiber composite films was also studied. The results show that the CMC/northern wood fiber composite film exhibits a light transmittance of 90%, a tensile strength of 111 MPa, and a folding endurance up to 2 526 times when the mass ratio of CMC (molecular weight:700 000)to softwood fibers is 7:3. This biodegradable, mechanically flexible, strong, and highly transparent CMC/cellulose fiber composite film shows the potential to be used in the fabrication of next generation flexible and green electronic devices as a substrate to maintain the sustainability of human's society.
2018, 35(6): 1582-1589.
doi: 10.13801/j.cnki.fhclxb.20170824.005
Abstract:
RHF(Rice husk fiber, RHF) was added into cement as reinforced materials to prepare RHF/cement composites.The effect of particle size on the dispersion properties of RHF in cement matrix was studied. And take the particle size and mass ratio of RHF to cement as factors, the density, flexural strength, water content, water absorption and thermal conductivity of RHF/cement composite as response value, the mathematical model was established using the response surface method, the molding process of RHF/cement composites was optimized. The results show that the smaller particle size of RHF, the better dispersion of RHF in cement, the dispersion coefficient reaches the maximum value of 0.981 when particle size is 150 μm.The response surface model analysis shows that the RHF/cement composite achieves optimal when particle size is 150 μm and mass ratio is 3%, under this process, the density, flexural strength, water content, water absorption and thermal conductivity of RHF/cement reach 1 559 kg/m3, 9.38 MPa, 7.05%, 16.71%, and 0.50W/(m·K), respectively, which are all up to JC/T 411-2007.
RHF(Rice husk fiber, RHF) was added into cement as reinforced materials to prepare RHF/cement composites.The effect of particle size on the dispersion properties of RHF in cement matrix was studied. And take the particle size and mass ratio of RHF to cement as factors, the density, flexural strength, water content, water absorption and thermal conductivity of RHF/cement composite as response value, the mathematical model was established using the response surface method, the molding process of RHF/cement composites was optimized. The results show that the smaller particle size of RHF, the better dispersion of RHF in cement, the dispersion coefficient reaches the maximum value of 0.981 when particle size is 150 μm.The response surface model analysis shows that the RHF/cement composite achieves optimal when particle size is 150 μm and mass ratio is 3%, under this process, the density, flexural strength, water content, water absorption and thermal conductivity of RHF/cement reach 1 559 kg/m3, 9.38 MPa, 7.05%, 16.71%, and 0.50W/(m·K), respectively, which are all up to JC/T 411-2007.
2018, 35(6): 1590-1598.
doi: 10.13801/j.cnki.fhclxb.20180207.003
Abstract:
In order to study the application of recycled aggregate in water permeable concrete, two series of researches on the recycled aggregate concrete made from waste pavement concrete were designed to study the influence of the proportion of recycled aggregates in recycled pervious concrete(RPC). That is, the recycled aggregates with particle size of 9.5-19.0 mm replaced the same size natural aggregate by 0%, 25%, 50%, 75% and 100% (standard) quality, respectively(series1). And RPC was designed by two kinds of particle size aggregates with 4.75-9.5 mm, 9.5-19.0 mm according to the ratio of 0:1, 1:1, 1:2, 2:1, 2:3 and 3:2(series 2).With this basis, its physical, mechanical, water permeability and their relationship were analyzed, and the reasonable rate of recycled aggregate and double particle size ratio were obtained. In the 1:1 and 2:1 blending can get better strength and water permeability. The pore distribution characteristics and trends were analyzed by the image processing of the cutting test block, and the plane porosity, equivalent pore size and water permeability coefficient were correlated. The results show that the number and area of cross-section pores play a key role in the permeable capacity of recycled pervious concrete.
In order to study the application of recycled aggregate in water permeable concrete, two series of researches on the recycled aggregate concrete made from waste pavement concrete were designed to study the influence of the proportion of recycled aggregates in recycled pervious concrete(RPC). That is, the recycled aggregates with particle size of 9.5-19.0 mm replaced the same size natural aggregate by 0%, 25%, 50%, 75% and 100% (standard) quality, respectively(series1). And RPC was designed by two kinds of particle size aggregates with 4.75-9.5 mm, 9.5-19.0 mm according to the ratio of 0:1, 1:1, 1:2, 2:1, 2:3 and 3:2(series 2).With this basis, its physical, mechanical, water permeability and their relationship were analyzed, and the reasonable rate of recycled aggregate and double particle size ratio were obtained. In the 1:1 and 2:1 blending can get better strength and water permeability. The pore distribution characteristics and trends were analyzed by the image processing of the cutting test block, and the plane porosity, equivalent pore size and water permeability coefficient were correlated. The results show that the number and area of cross-section pores play a key role in the permeable capacity of recycled pervious concrete.
2018, 35(6): 1599-1608.
doi: 10.13801/j.cnki.fhclxb.20170821.009
Abstract:
To explore the steel fiber which can improve the fire resistance of ultra-high-performance concrete (UHPC), explosive spalling behavior of different types of steel fiber (three types of normal steel fiber and two types of recycled steel fiber from waste tire) reinforced UHPC and plain UHPC exposed to high temperature up to 800℃ were experimentally investigated in this paper, and fracture energies of these concretes were also tested. All of plain UHPC specimens encounter severe explosive spalling. Steel fiber significantly alleviates the explosive spalling of UHPC but cannot avoid the occurrence of explosive spalling. UHPC incorporating normally available commercial steel fiber with hooked-end (35 mm long and 0.55 mm in diameter) exhibits the best resistance to explosive spalling, and the second is the UHPC incorporating recycled steel fiber without attached rubber. This suggests that the characteristics of steel fiber affect the explosive spalling of steel fiber reinforced UHPC significantly. The steel fiber which has a large distribution density or that without a large distribution density but can make concrete have high toughness (fracture energy), is more appropriate to be utilized in UHPC structures with high fire resistance requirements.
To explore the steel fiber which can improve the fire resistance of ultra-high-performance concrete (UHPC), explosive spalling behavior of different types of steel fiber (three types of normal steel fiber and two types of recycled steel fiber from waste tire) reinforced UHPC and plain UHPC exposed to high temperature up to 800℃ were experimentally investigated in this paper, and fracture energies of these concretes were also tested. All of plain UHPC specimens encounter severe explosive spalling. Steel fiber significantly alleviates the explosive spalling of UHPC but cannot avoid the occurrence of explosive spalling. UHPC incorporating normally available commercial steel fiber with hooked-end (35 mm long and 0.55 mm in diameter) exhibits the best resistance to explosive spalling, and the second is the UHPC incorporating recycled steel fiber without attached rubber. This suggests that the characteristics of steel fiber affect the explosive spalling of steel fiber reinforced UHPC significantly. The steel fiber which has a large distribution density or that without a large distribution density but can make concrete have high toughness (fracture energy), is more appropriate to be utilized in UHPC structures with high fire resistance requirements.
2018, 35(6): 1609-1618.
doi: 10.13801/j.cnki.fhclxb.20170801.002
Abstract:
Cement-based material is a strain-rate-sensitivity material, understanding of the strain rate effect on the mechanical properties and deformation of cement-based materials fully can ensure safe design of concrete structures with enhanced performance. The micro creep of hardened cement pastes under different strain rates were investigated by performing continuous stiffness measurement. The (water to cement) w/c ratios of hardened cement pastes were 0.3, 0.4, and 0.5. The maximum indentation depth during the CSM was set as 30 μm and the applied strain rates were 0.01 s-1, 0.05 s-1, 0.1 s-1, and 0.5 s-1. The results show that a unique hvp-P-ε relationship is found for hardened cement paste under the strain rates ranging between 0.01s-1 and 0.5 s-1 at microscale. This is analogous to the unique εvp-σ-ε relationship for clays. The hvp-P-ε relationship can be simply described by two sets of curves:the PN/PN0.05-ε curve and the normalized hvp-P/(PN/PN0.05) curve. These two curves can be used to predict the hvp-P curves of cement pastes under any constant strain rate during the loading stage. This finding preliminary confirms the applicability of the isotache approach to characterize the time-dependent deformation of cement pastes at microscale.
Cement-based material is a strain-rate-sensitivity material, understanding of the strain rate effect on the mechanical properties and deformation of cement-based materials fully can ensure safe design of concrete structures with enhanced performance. The micro creep of hardened cement pastes under different strain rates were investigated by performing continuous stiffness measurement. The (water to cement) w/c ratios of hardened cement pastes were 0.3, 0.4, and 0.5. The maximum indentation depth during the CSM was set as 30 μm and the applied strain rates were 0.01 s-1, 0.05 s-1, 0.1 s-1, and 0.5 s-1. The results show that a unique hvp-P-ε relationship is found for hardened cement paste under the strain rates ranging between 0.01s-1 and 0.5 s-1 at microscale. This is analogous to the unique εvp-σ-ε relationship for clays. The hvp-P-ε relationship can be simply described by two sets of curves:the PN/PN0.05-ε curve and the normalized hvp-P/(PN/PN0.05) curve. These two curves can be used to predict the hvp-P curves of cement pastes under any constant strain rate during the loading stage. This finding preliminary confirms the applicability of the isotache approach to characterize the time-dependent deformation of cement pastes at microscale.
2018, 35(6): 1619-1628.
doi: 10.13801/j.cnki.fhclxb.20170808.006
Abstract:
In order to study the effect of aging on microstructure and fatigue properties of modified asphalt, the asphalt routine index test, the Dynamic Shear Rheometer(DSR) test and the AFM test were used to analyse penetration, ductility, softening point, fatigue performance and microstructure of styrene-butadiene-styrene tri-block copolymer(SBS) modified asphalt and rubber powder modified asphalt from the macro and micro perspective before and after aging.The results show that with the deepening of aging, the hardness of modified asphalt increases and the high temperature performance also improves, whlie the temperature sensitivity becomes lower and the low temperature crack resistance becomes worse. The anti-aging properties of rubber modified asphalt are better than that of SBS modified asphalt according to the comprehensive analysis of penetration ratio, ductility ratio and softening point ratio.With the decrease of temperature, the increase of frequency and the deepening of aging, the anti-fatigue performance of two modified asphalt is deteriorated. The microstructure observation results show that SBS modified asphalt has "bee-like structure" and the volume and height of "bee-like structure" increase after aging, but their numbers decrease.There is no "bee-like structure" in the rubber powder modified asphalt, it is due to some reactions like swelling, desulfurization and degradation occured in the blending process of asphalt and rubber powder that restricted the "bee-like structure" formation, and few changes occur in the roughness and the height of rubber powder modified asphalt surface after aging. Rubber powder modified asphalt has better fatigue resistance, aging resistance and high temperature performance than that of SBS modified asphalt.
In order to study the effect of aging on microstructure and fatigue properties of modified asphalt, the asphalt routine index test, the Dynamic Shear Rheometer(DSR) test and the AFM test were used to analyse penetration, ductility, softening point, fatigue performance and microstructure of styrene-butadiene-styrene tri-block copolymer(SBS) modified asphalt and rubber powder modified asphalt from the macro and micro perspective before and after aging.The results show that with the deepening of aging, the hardness of modified asphalt increases and the high temperature performance also improves, whlie the temperature sensitivity becomes lower and the low temperature crack resistance becomes worse. The anti-aging properties of rubber modified asphalt are better than that of SBS modified asphalt according to the comprehensive analysis of penetration ratio, ductility ratio and softening point ratio.With the decrease of temperature, the increase of frequency and the deepening of aging, the anti-fatigue performance of two modified asphalt is deteriorated. The microstructure observation results show that SBS modified asphalt has "bee-like structure" and the volume and height of "bee-like structure" increase after aging, but their numbers decrease.There is no "bee-like structure" in the rubber powder modified asphalt, it is due to some reactions like swelling, desulfurization and degradation occured in the blending process of asphalt and rubber powder that restricted the "bee-like structure" formation, and few changes occur in the roughness and the height of rubber powder modified asphalt surface after aging. Rubber powder modified asphalt has better fatigue resistance, aging resistance and high temperature performance than that of SBS modified asphalt.
2018, 35(6): 1629-1635.
doi: 10.13801/j.cnki.fhclxb.20170727.005
Abstract:
To study the effects of sand content on dynamic compression strength and energy absorption characteristics of cemented silty clay, dynamic compression tests on cemented silty clay with different sand contents were conducted using Φ 50 mm split Hopkinson pressure bar (SHPB) apparatus under 0.4 MPa impact pressure. The results show that the dynamic stress-strain curve of plain cemented silty clay (without sand) can be divided into three stages of elastic deformation, yield-hardening and failure. With the increase of sand content, there is an ideal plastic stage occurring on dynamic stress-strain curve but not obvious for yield stage gradually. In addition, the dynamic compression strength of silty clay stabilized by cement mortar increases firstly and then decreases with the increasing of sand content. The maximum of dynamic compression strength of silty clay stabilized by cement mortar is 9.56 MPa at sand content of 10%, which results in 9.79% increase compared with plain cement-soil. The absorbed energy of silty clay stabilized by cement mortar increases with the increase of dynamic compression strength, which shows an approximate exponential relation.
To study the effects of sand content on dynamic compression strength and energy absorption characteristics of cemented silty clay, dynamic compression tests on cemented silty clay with different sand contents were conducted using Φ 50 mm split Hopkinson pressure bar (SHPB) apparatus under 0.4 MPa impact pressure. The results show that the dynamic stress-strain curve of plain cemented silty clay (without sand) can be divided into three stages of elastic deformation, yield-hardening and failure. With the increase of sand content, there is an ideal plastic stage occurring on dynamic stress-strain curve but not obvious for yield stage gradually. In addition, the dynamic compression strength of silty clay stabilized by cement mortar increases firstly and then decreases with the increasing of sand content. The maximum of dynamic compression strength of silty clay stabilized by cement mortar is 9.56 MPa at sand content of 10%, which results in 9.79% increase compared with plain cement-soil. The absorbed energy of silty clay stabilized by cement mortar increases with the increase of dynamic compression strength, which shows an approximate exponential relation.
2018, 35(6): 1636-1645.
doi: 10.13801/j.cnki.fhclxb.20170920.001
Abstract:
The mechanical properties of biomaterials are closely related to their structural design in nature. The flexible biological materials mostly are designed as hierarchical structure that has the unique feature of gradient, which makes the materials have good deformation capacity as well as toughness. In this paper, the concept of bioinspired flexible structural elements was put forward that based on the basic elements of engineering structural design. The bionic elements were divided into line elements, beam elements, column elements, plate and shell elements, thin film elements and composite elements according to the geometrical morphology. The design system of bioinspired flexible structure was developed from the point of view of system theory. The design criterion of flexible bionic structure was summarized. A novel bionic functionally gradient plate was design based on the gradient structure of fish scale. The normalized-dimensionless natural frequencies of functionally graded plate were computed by the finite element method, the results show that the functionally graded plate, inspired by the structure of fish scale, has the characteristics of flexibility and stiffness softening. Finally, the natural function of flexible biomimetic methods is discussed in detail, including imitation design, combinatorial design and matching design.
The mechanical properties of biomaterials are closely related to their structural design in nature. The flexible biological materials mostly are designed as hierarchical structure that has the unique feature of gradient, which makes the materials have good deformation capacity as well as toughness. In this paper, the concept of bioinspired flexible structural elements was put forward that based on the basic elements of engineering structural design. The bionic elements were divided into line elements, beam elements, column elements, plate and shell elements, thin film elements and composite elements according to the geometrical morphology. The design system of bioinspired flexible structure was developed from the point of view of system theory. The design criterion of flexible bionic structure was summarized. A novel bionic functionally gradient plate was design based on the gradient structure of fish scale. The normalized-dimensionless natural frequencies of functionally graded plate were computed by the finite element method, the results show that the functionally graded plate, inspired by the structure of fish scale, has the characteristics of flexibility and stiffness softening. Finally, the natural function of flexible biomimetic methods is discussed in detail, including imitation design, combinatorial design and matching design.
2018, 35(6): 1646-1651.
doi: 10.13801/j.cnki.fhclxb.20170824.001
Abstract:
Short fiber reinforced ethylene propylene diene monomer(EPDM) film material is a new type of thermal insulation and structural materials, which is applied in the cladding of solid rocket motor with low density, ablative resistance and good mechanical properties. In order to establish a general criterion for rate dependent anisotropy in quasi-static conditions, rate dependent function and rate intensity factor methods were introduced to extend Tsai-Hill strength criterion, which was used to predict the tensile strength in different off-axis directions. Studies show that axial strength and shear strength increase with the strain rate. Compared with rate intensity factor method, Tsai-Hill strength criterion based on rate dependent function method has higher prediction accuracy. Meanwhile, the prediction error of rate intensity factor method has strong relations with selection of reference rate and function expression of rate intensity factor.
Short fiber reinforced ethylene propylene diene monomer(EPDM) film material is a new type of thermal insulation and structural materials, which is applied in the cladding of solid rocket motor with low density, ablative resistance and good mechanical properties. In order to establish a general criterion for rate dependent anisotropy in quasi-static conditions, rate dependent function and rate intensity factor methods were introduced to extend Tsai-Hill strength criterion, which was used to predict the tensile strength in different off-axis directions. Studies show that axial strength and shear strength increase with the strain rate. Compared with rate intensity factor method, Tsai-Hill strength criterion based on rate dependent function method has higher prediction accuracy. Meanwhile, the prediction error of rate intensity factor method has strong relations with selection of reference rate and function expression of rate intensity factor.
2018, 35(6): 1652-1660.
doi: 10.13801/j.cnki.fhclxb.20171018.001
Abstract:
Liquid diffusion welding method was used to prepare metallurgical bonding aluminum foam sandwich. The bonding interfacial microstructure was observed by optical microscope (OM) and SEM. Under the effect of ultrasonic vibration, the bonding seam is uniform and continuous. The ZnAl eutectic dendrite structure forms on the surfaces of Al foam core and Al sheet substrates. Furthermore, obvious erosion behavior can be seen on the bonding surfaces as ZnAl alloy filler melted. EDS line scan results show that the mutual diffusion of the main elements Zn and Al across the interface is extensive. All these characteristics imply that the oxide film on the substrates is destroyed and sound bonding achieves. Three point bending fatigue test was employed to the sandwich structure fatigue behavior. Comparing with the adhesive aluminum foam sandwich, the fatigue life (S-N) curves indicate that the metallurgical bonding samples have a better fatigue performance, and their fatigue limits are 3 058 N and 2 829 N respectively. Under the same load, the metallurgical bonding sample has much longer fatigue life than the adhesive sample. And the fatigue fracture mode for these two types samples are completely different in two ways, the failure mode for adhesive sample is shear debonding, but no debonding occurred for metallurgical bonding sample, which indicates that failure mode of metallurgical bonding sample due to foam core shear.
Liquid diffusion welding method was used to prepare metallurgical bonding aluminum foam sandwich. The bonding interfacial microstructure was observed by optical microscope (OM) and SEM. Under the effect of ultrasonic vibration, the bonding seam is uniform and continuous. The ZnAl eutectic dendrite structure forms on the surfaces of Al foam core and Al sheet substrates. Furthermore, obvious erosion behavior can be seen on the bonding surfaces as ZnAl alloy filler melted. EDS line scan results show that the mutual diffusion of the main elements Zn and Al across the interface is extensive. All these characteristics imply that the oxide film on the substrates is destroyed and sound bonding achieves. Three point bending fatigue test was employed to the sandwich structure fatigue behavior. Comparing with the adhesive aluminum foam sandwich, the fatigue life (S-N) curves indicate that the metallurgical bonding samples have a better fatigue performance, and their fatigue limits are 3 058 N and 2 829 N respectively. Under the same load, the metallurgical bonding sample has much longer fatigue life than the adhesive sample. And the fatigue fracture mode for these two types samples are completely different in two ways, the failure mode for adhesive sample is shear debonding, but no debonding occurred for metallurgical bonding sample, which indicates that failure mode of metallurgical bonding sample due to foam core shear.
2018, 35(6): 1661-1673.
doi: 10.13801/j.cnki.fhclxb.20170831.001
Abstract:
The finite-element model of three-dimensional steel fiber reinforced ultra-high performance concrete (SF/UHPC) cylindrical specimen was developed on the mesoscopic level by utilizing LS-DYNA, and the mechanical properties and crack development of which under axial compression were numerically simulated. Based on the verification of the validity and rationality of above-mentioned mesoscopic numerical model, the effects of steel fiber volume fraction, aspect ratio, shape and size on compressive strength, toughness and failure mode of SF/UHPC were studied emphatically. Finally, the formula for predicting the compressive strength of SF/UHPC was fitted according to the simulation results. The results indicate that the developed mesoscopic model in this paper for simulating SF/UHPC can well characterize the static performance and damage mechanism of concrete under uniaxial compression stress, and the fitting formula can also predict the compressive strength of SF/UHPC.
The finite-element model of three-dimensional steel fiber reinforced ultra-high performance concrete (SF/UHPC) cylindrical specimen was developed on the mesoscopic level by utilizing LS-DYNA, and the mechanical properties and crack development of which under axial compression were numerically simulated. Based on the verification of the validity and rationality of above-mentioned mesoscopic numerical model, the effects of steel fiber volume fraction, aspect ratio, shape and size on compressive strength, toughness and failure mode of SF/UHPC were studied emphatically. Finally, the formula for predicting the compressive strength of SF/UHPC was fitted according to the simulation results. The results indicate that the developed mesoscopic model in this paper for simulating SF/UHPC can well characterize the static performance and damage mechanism of concrete under uniaxial compression stress, and the fitting formula can also predict the compressive strength of SF/UHPC.
2018, 35(6): 1674-1682.
doi: 10.13801/j.cnki.fhclxb.20170807.002
Abstract:
In order to investigate the friction mechanism and wear law of diamond-like carbon (DLC) film, the DLC film was firstly prepared in the method of melting crystal carbon at high temperature and quenching it at rapid speeds based on molecular dynamics simulations. A hemispherical indenter was then used to perform friction behavior on the DLC surface. The prepared film has the density of 2.72 g·cm-3, with sp2 and sp3 hybridization fraction of 37.1% and 60.4% respectively. The friction results show that the wear rate increases linearly with the load under 120 nN and this is in agreement with Archard's wear law. Whereas, the wear rate decreases with the friction velocity because of the effects of velocity on stress distribution and cutting depth. If Si atoms are embedded into the film as inclusion and the inclusion content increases from 0% to 25%, the wear rate will firstly decline and then rise. Finally a wear model among inclusion content, friction velocity and wear rate is established according to the wear datum under a certain load of 50 nN, with the relative error less than 10% to simulation results. The wear model indicates that the minimum wear rate occurs when the film has the Si content of 7.2% with a constant load and friction velocity. The wear model provides an efficient and convenient method for predicting inclusion content on line.
In order to investigate the friction mechanism and wear law of diamond-like carbon (DLC) film, the DLC film was firstly prepared in the method of melting crystal carbon at high temperature and quenching it at rapid speeds based on molecular dynamics simulations. A hemispherical indenter was then used to perform friction behavior on the DLC surface. The prepared film has the density of 2.72 g·cm-3, with sp2 and sp3 hybridization fraction of 37.1% and 60.4% respectively. The friction results show that the wear rate increases linearly with the load under 120 nN and this is in agreement with Archard's wear law. Whereas, the wear rate decreases with the friction velocity because of the effects of velocity on stress distribution and cutting depth. If Si atoms are embedded into the film as inclusion and the inclusion content increases from 0% to 25%, the wear rate will firstly decline and then rise. Finally a wear model among inclusion content, friction velocity and wear rate is established according to the wear datum under a certain load of 50 nN, with the relative error less than 10% to simulation results. The wear model indicates that the minimum wear rate occurs when the film has the Si content of 7.2% with a constant load and friction velocity. The wear model provides an efficient and convenient method for predicting inclusion content on line.
