2016 Vol. 33, No. 4
2016, 33(4): 689-703.
doi: 10.13801/j.cnki.fhclxb.20160122.003
Abstract:
Carbon nanotubes(CNTs), due to their extremely high mechanical performance, excellent electrical and thermal properties, have been regarded as ideally reinforcement phase of composites. CNTs reinforced metal matrix composites have become a very important research area. However, due to the issues of the compatibility between CNTs and metal matrix, the difficulty to control dispersion of reinforcement in spatial and the high ampacity but relatively low conductivity of CNTs, the electrical properties of CNTs reinforced metal matrix composites do not show significantly enhancement and the electrical and mechanical properties are difficult to be balanced, the overall research is still in infancy. We discuss the research status of CNTs reinforced metal matrix composites from the aspects of pretreatment, processing method and mechanism of electrical conduction, as well as the outlook for the future development trend in this area.
Carbon nanotubes(CNTs), due to their extremely high mechanical performance, excellent electrical and thermal properties, have been regarded as ideally reinforcement phase of composites. CNTs reinforced metal matrix composites have become a very important research area. However, due to the issues of the compatibility between CNTs and metal matrix, the difficulty to control dispersion of reinforcement in spatial and the high ampacity but relatively low conductivity of CNTs, the electrical properties of CNTs reinforced metal matrix composites do not show significantly enhancement and the electrical and mechanical properties are difficult to be balanced, the overall research is still in infancy. We discuss the research status of CNTs reinforced metal matrix composites from the aspects of pretreatment, processing method and mechanism of electrical conduction, as well as the outlook for the future development trend in this area.
2016, 33(4): 704-713.
doi: 10.13801/j.cnki.fhclxb.20150723.001
Abstract:
In order to improve the interfacial strength between Kevlar fibers and composite matrix, LiCl ethanol solution was used to treat Kevlar fibers by certain time. Then, the surface chemical composition, micromorphology, tensile strength of single filament for LiCl treated Kevlar fibers and interface properties of Kevlar fibers/epoxy resin composites etc. were tested and analyzed. The results show that after using LiCl ethanol solution treating Kevlar fibers, the content of nitrogen containing functional groups on Kevlar fiber surface increases. After the treatment, there are some etched grooves appear on the Kevlar fiber surface and the surface roughness increases, thus the adhesion property between Kevlar fibers and epoxy resin matrix enhances, which makes the interlaminar shear strength of Kevlar fibers/epoxy resin composites increases from 21.75 MPa before treatment to 37.98 MPa. The optimum treatment time is 3-4 h, while the unnecessary extend of treatment time will lead to the decrease for the tensile strength of single filament for Kevlar fiber and the interlaminar shear strength of composites. The conclusions obtained proves that using LiCl to treat Kevlar fibers is an effective method for surface modification.
In order to improve the interfacial strength between Kevlar fibers and composite matrix, LiCl ethanol solution was used to treat Kevlar fibers by certain time. Then, the surface chemical composition, micromorphology, tensile strength of single filament for LiCl treated Kevlar fibers and interface properties of Kevlar fibers/epoxy resin composites etc. were tested and analyzed. The results show that after using LiCl ethanol solution treating Kevlar fibers, the content of nitrogen containing functional groups on Kevlar fiber surface increases. After the treatment, there are some etched grooves appear on the Kevlar fiber surface and the surface roughness increases, thus the adhesion property between Kevlar fibers and epoxy resin matrix enhances, which makes the interlaminar shear strength of Kevlar fibers/epoxy resin composites increases from 21.75 MPa before treatment to 37.98 MPa. The optimum treatment time is 3-4 h, while the unnecessary extend of treatment time will lead to the decrease for the tensile strength of single filament for Kevlar fiber and the interlaminar shear strength of composites. The conclusions obtained proves that using LiCl to treat Kevlar fibers is an effective method for surface modification.
2016, 33(4): 714-722.
doi: 10.13801/j.cnki.fhclxb.20150803.001
Abstract:
In order to develop the composite film with better force sensitive characteristic, nano Fe50Ni50 powders whose particle size was about 100 nm were prepared by liquid phase reduction method firstly, and the nano powders were mixed and dispersed with butyl rubber(IIR) by liquid phase mixing dispersing method. Then, the nano Fe50Ni50 powders/IIR composite films whose powders were well dispersed and content was 65wt% were obtained by mechanical mixing and pressing. Finally, the force-sensing characteristics of nano Fe50Ni50 powders/IIR composite films were investigated under the conditions of continuous uploading/downloading speed was 0.10 mm/min and test frequency was 1 kHz. The results show that liquid phase mixing dispersing method can make the Fe50Ni50 powders achieve uniform dispersion effect at nano-scale in the composite films. When compressive stress is 0.20-0.90 MPa, the thicker the film is, the larger its standard deviation is, and the worse the force sensitivity stability is. With compressive stress increasing, impedance of the film which thickness is 185μm decreases linearly approximately during uploading period, and force sensitive degree is stable in range of 40-60, the standard deviation is about 1-2. The conclusions obtained show that the prepared film has excellent force sensitive characteristic when the compressive stress is 0.20-0.90 MPa.
In order to develop the composite film with better force sensitive characteristic, nano Fe50Ni50 powders whose particle size was about 100 nm were prepared by liquid phase reduction method firstly, and the nano powders were mixed and dispersed with butyl rubber(IIR) by liquid phase mixing dispersing method. Then, the nano Fe50Ni50 powders/IIR composite films whose powders were well dispersed and content was 65wt% were obtained by mechanical mixing and pressing. Finally, the force-sensing characteristics of nano Fe50Ni50 powders/IIR composite films were investigated under the conditions of continuous uploading/downloading speed was 0.10 mm/min and test frequency was 1 kHz. The results show that liquid phase mixing dispersing method can make the Fe50Ni50 powders achieve uniform dispersion effect at nano-scale in the composite films. When compressive stress is 0.20-0.90 MPa, the thicker the film is, the larger its standard deviation is, and the worse the force sensitivity stability is. With compressive stress increasing, impedance of the film which thickness is 185μm decreases linearly approximately during uploading period, and force sensitive degree is stable in range of 40-60, the standard deviation is about 1-2. The conclusions obtained show that the prepared film has excellent force sensitive characteristic when the compressive stress is 0.20-0.90 MPa.
2016, 33(4): 723-731.
doi: 10.13801/j.cnki.fhclxb.20150911.004
Abstract:
In order to develop a new type epoxy gel coat to meet the requirements of aeronautical environment, the impact toughness and impact fracture morphologies of epoxy gel coats modified with different molecular weights and different amounts of polyethylene glycol(PEG) at room temperature were investigated. Then, the crack properties of PEG modified epoxy gel coat under thermal shock(-50℃/30 min+90℃/30 min) were mainly investigated by using a simple thermal shock specimen model, and it was verified by analyzing the changing tendencies of thermal expansion and storage modulus etc. The results show that the impact strength of 5wt% PEG-1000 modified epoxy gel coat is enhanced by 31.8% comparing with that of unmodified epoxy gel coat, which reaches the highest value of 4.97 kJ·m-2. More obvious plastic deformation morphologies appear on the impact fracture surfaces of PEG-1000 and PEG-2000 modified epoxy gel coats, and the impact toughness of gel coats increases. The macroscopic initial crack property of 15wt% PEG-400 modified epoxy gel coat under thermal shock reaches the best, average initial crack needs conducting 10.4 cycles. The properties of crack extension resistance for modified epoxy gel coat are basically improved with the increase of PEG molecular weight and content. However, the crack width will be amplified with the increase of PEG molecular weight.
In order to develop a new type epoxy gel coat to meet the requirements of aeronautical environment, the impact toughness and impact fracture morphologies of epoxy gel coats modified with different molecular weights and different amounts of polyethylene glycol(PEG) at room temperature were investigated. Then, the crack properties of PEG modified epoxy gel coat under thermal shock(-50℃/30 min+90℃/30 min) were mainly investigated by using a simple thermal shock specimen model, and it was verified by analyzing the changing tendencies of thermal expansion and storage modulus etc. The results show that the impact strength of 5wt% PEG-1000 modified epoxy gel coat is enhanced by 31.8% comparing with that of unmodified epoxy gel coat, which reaches the highest value of 4.97 kJ·m-2. More obvious plastic deformation morphologies appear on the impact fracture surfaces of PEG-1000 and PEG-2000 modified epoxy gel coats, and the impact toughness of gel coats increases. The macroscopic initial crack property of 15wt% PEG-400 modified epoxy gel coat under thermal shock reaches the best, average initial crack needs conducting 10.4 cycles. The properties of crack extension resistance for modified epoxy gel coat are basically improved with the increase of PEG molecular weight and content. However, the crack width will be amplified with the increase of PEG molecular weight.
2016, 33(4): 732-740.
doi: 10.13801/j.cnki.fhclxb.20150921.002
Abstract:
The digital speckle correlation method(DSCM) was taken to conduct a mesoscopic-level characterization on crack initiation and propagation patterns in semi-circular shaped hot-mix asphalt(HMA) specimens that were aged by ultraviolet lights and under tension-bending test. Vic-3D analysis software was employed to calculate the whole field displacement and strain, and displacement and strain fields of specimen rapturing process were obtained. The results show that, based on the comparison among asphalt mortar under ultraviolent lights, aggregate and the strain field along horizontal direction, the interphase is the weakest part of the hot-mix asphalt and it is more prone to producing crack. Further analysis of curve of strain along horizontal direction changing with load on HMA cracking time better reveals the time difference in initiating HMA micro-cracks and macro-cracks, and ultraviolet aging can noticeably shorten the interface initiating cracks time in HMA specimens. At the same time, upon receiving same ultraviolet aging, crumb rubber(CR) modified HMA has better cracking resistance and load-bearing capacity than styrene butadiene styrene(SBS) modified HMA based on comparing the patterns of load changing with displacement between CR modified HMA and SBS modified HMA specimens.
The digital speckle correlation method(DSCM) was taken to conduct a mesoscopic-level characterization on crack initiation and propagation patterns in semi-circular shaped hot-mix asphalt(HMA) specimens that were aged by ultraviolet lights and under tension-bending test. Vic-3D analysis software was employed to calculate the whole field displacement and strain, and displacement and strain fields of specimen rapturing process were obtained. The results show that, based on the comparison among asphalt mortar under ultraviolent lights, aggregate and the strain field along horizontal direction, the interphase is the weakest part of the hot-mix asphalt and it is more prone to producing crack. Further analysis of curve of strain along horizontal direction changing with load on HMA cracking time better reveals the time difference in initiating HMA micro-cracks and macro-cracks, and ultraviolet aging can noticeably shorten the interface initiating cracks time in HMA specimens. At the same time, upon receiving same ultraviolet aging, crumb rubber(CR) modified HMA has better cracking resistance and load-bearing capacity than styrene butadiene styrene(SBS) modified HMA based on comparing the patterns of load changing with displacement between CR modified HMA and SBS modified HMA specimens.
2016, 33(4): 741-748.
doi: 10.13801/j.cnki.fhclxb.20151225.001
Abstract:
The viscosity-temperature and viscosity-time characteristic curves of high-temperature resistant glycidylamine epoxy system were measured by the rotational rheometer to investigate the chemorheological characteristics of the resin system. Daul Arrhenius model and engineering viscosity model were established compared with each other to analyze the isothermal viscosity characteristic curves of the resin system. Then a second-order exponential viscosity model was proposed to predict the viscosity change law of the resin system. The results show that the prediction accuracy and applicability of the second-order exponential viscosity model are better than Daul Arrhenius model and engineering viscosity model. The predicted viscosity is in a good agreement with the experimental data. This phenomenological formula of viscosity versus temperature and time can be used to predict the processing window of the resin system conveniently and accurately, and point out the technology problems in the engineering applications.
The viscosity-temperature and viscosity-time characteristic curves of high-temperature resistant glycidylamine epoxy system were measured by the rotational rheometer to investigate the chemorheological characteristics of the resin system. Daul Arrhenius model and engineering viscosity model were established compared with each other to analyze the isothermal viscosity characteristic curves of the resin system. Then a second-order exponential viscosity model was proposed to predict the viscosity change law of the resin system. The results show that the prediction accuracy and applicability of the second-order exponential viscosity model are better than Daul Arrhenius model and engineering viscosity model. The predicted viscosity is in a good agreement with the experimental data. This phenomenological formula of viscosity versus temperature and time can be used to predict the processing window of the resin system conveniently and accurately, and point out the technology problems in the engineering applications.
2016, 33(4): 749-757.
doi: 10.13801/j.cnki.fhclxb.20151211.001
Abstract:
The antistatic and heat-resistant carbon fiber(CF)-aluminum nitride(AlN)/poly ether ether ketone(PEEK) composites were prepared by compression molding, in which PEEK was used as matrix resin, CF and AlN were used as fillers. The antistatic, thermal and mechanical properties of CF-AlN/PEEK composites were characterized by high resistance meter, thermal conductivity instrument, thermo-gravimetric, differential scanning calorimetry and SEM. The effect of cooling rate on properties of composites and the effect of heat post-treatment on mechanical properties were also discussed. The results show that CF-AlN/PEEK composites have better properties when the mass fractions of CF and AlN are both 10% and surface resistivity is 108 Ω which improves 6 magnitude than that of PEEK. The thermal conductivity coefficient and initial decomposition temperature are 0.418 W·(m·K)-1 and 573℃ respectively.The tensile strength increases by 40.4%. The lower the cooling rate is, the higher the melting point of composites have. Heat post-treatment could affect mechanical properties of CF-AlN/PEEK composites. Tensile strength can reach 146 MPa at 270℃ after heat treating 2 h, which indicates that processing temperature is one of the factors that influences properties of composite in process of production.
The antistatic and heat-resistant carbon fiber(CF)-aluminum nitride(AlN)/poly ether ether ketone(PEEK) composites were prepared by compression molding, in which PEEK was used as matrix resin, CF and AlN were used as fillers. The antistatic, thermal and mechanical properties of CF-AlN/PEEK composites were characterized by high resistance meter, thermal conductivity instrument, thermo-gravimetric, differential scanning calorimetry and SEM. The effect of cooling rate on properties of composites and the effect of heat post-treatment on mechanical properties were also discussed. The results show that CF-AlN/PEEK composites have better properties when the mass fractions of CF and AlN are both 10% and surface resistivity is 108 Ω which improves 6 magnitude than that of PEEK. The thermal conductivity coefficient and initial decomposition temperature are 0.418 W·(m·K)-1 and 573℃ respectively.The tensile strength increases by 40.4%. The lower the cooling rate is, the higher the melting point of composites have. Heat post-treatment could affect mechanical properties of CF-AlN/PEEK composites. Tensile strength can reach 146 MPa at 270℃ after heat treating 2 h, which indicates that processing temperature is one of the factors that influences properties of composite in process of production.
2016, 33(4): 758-767.
doi: 10.13801/j.cnki.fhclxb.20150907.003
Abstract:
Carbon fiber reinforced plastic(CFRP) are made up of fiber, resin and interface at the mesoscopic level. The essence of cutting process is a evolution process of material failure at mesoscopic level and chips formation at macro level. To reveal the mesoscopic failure of materials in cutting CFRP, a mesoscopic finite element model was built in cutting CFRP, which consists of fiber, matrix, interface constituent phases instead of using the traditional equivalent homogeneous modeling method. Different constituent phases not only based on their respective material constitutive, but also failure and evolution criterion were considered in order to simulate failure of materials. The processes of fiber/matrix fracture, interface break and evolution can be simulated actually from mesoscopic perspective in cutting process of CFRP unidirectional laminates of different fiber orientations. The simulation results show that the mesoscopic failure of CFRP materials differs at different fiber orientations. The destruction form at the fiber orientation of 0åre mainly interface cracking and fiber bending. At the fiber orientations of 45°/90°, fiber and matrix are crushed by cutting tool immersed in workpiece. At the fiber orientation of 135°, the destruction form is mainly fiber bending fracture, and fracture often exists below the machined surface. The validity of the simulation results is verified by the experimental micro on-line observation method.
Carbon fiber reinforced plastic(CFRP) are made up of fiber, resin and interface at the mesoscopic level. The essence of cutting process is a evolution process of material failure at mesoscopic level and chips formation at macro level. To reveal the mesoscopic failure of materials in cutting CFRP, a mesoscopic finite element model was built in cutting CFRP, which consists of fiber, matrix, interface constituent phases instead of using the traditional equivalent homogeneous modeling method. Different constituent phases not only based on their respective material constitutive, but also failure and evolution criterion were considered in order to simulate failure of materials. The processes of fiber/matrix fracture, interface break and evolution can be simulated actually from mesoscopic perspective in cutting process of CFRP unidirectional laminates of different fiber orientations. The simulation results show that the mesoscopic failure of CFRP materials differs at different fiber orientations. The destruction form at the fiber orientation of 0åre mainly interface cracking and fiber bending. At the fiber orientations of 45°/90°, fiber and matrix are crushed by cutting tool immersed in workpiece. At the fiber orientation of 135°, the destruction form is mainly fiber bending fracture, and fracture often exists below the machined surface. The validity of the simulation results is verified by the experimental micro on-line observation method.
2016, 33(4): 768-778.
doi: 10.13801/j.cnki.fhclxb.20150911.002
Abstract:
Two key problems in structural durability design for mechanically fastened carbon fiber reinforced epoxy composite joints:temperature-time dependent behavior for viscoelastic preload relaxation and prediction method for its long time performance were investigated. Preload relaxation prediction model was developed on basis of the creep total-strain theory. 36 h constant temperature durability tests show that the relaxation rate of preload for joints is faster with the greater initial preload and higher temperature; relaxation rate of composite joints is much greater than that of metallic joints; preload relaxation mainly behaves as the material creep process. Compared to the short-term test results, it shows that the model can well predict the relaxation for different temperatures, preloads and joint materials, which also provides a basis for extrapolation method of determining test data.
Two key problems in structural durability design for mechanically fastened carbon fiber reinforced epoxy composite joints:temperature-time dependent behavior for viscoelastic preload relaxation and prediction method for its long time performance were investigated. Preload relaxation prediction model was developed on basis of the creep total-strain theory. 36 h constant temperature durability tests show that the relaxation rate of preload for joints is faster with the greater initial preload and higher temperature; relaxation rate of composite joints is much greater than that of metallic joints; preload relaxation mainly behaves as the material creep process. Compared to the short-term test results, it shows that the model can well predict the relaxation for different temperatures, preloads and joint materials, which also provides a basis for extrapolation method of determining test data.
2016, 33(4): 779-787.
doi: 10.13801/j.cnki.fhclxb.20150723.003
Abstract:
The oxidized carbon fibers(OCF) were prepared via surface oxidation treatment of carbon fibers(CF) in concentrated H2SO4/concentrated HNO3 blend acid, and then OCF were modified by silane coupling agent γ-methacryloxypropyl trimethoxy silane(KH-570), to obtain the KH-570 grafting modified carbon fibers(KCF), which were subsequently applied to ethylene-vinyl acetate copolymer(EVA) foamed composites. The surface modified characteristics, the structures and properties of carbon fiber/EVA composites were investigated by FTIR, XPS, Raman, FESEM and electronic universal testing machine etc. The result shows that both oxidation and grafting reaction can increase the content of active functional groups and roughness on surface of carbon fiber, which can improve the compatibility between carbon fibers and EVA matrix, leading to improvement on physical properties of carbon fiber/EVA foamed composites. Under the same conditions, the KH-570 grafting modified carbon fiber/EVA foamed composites have superior physical properties.
The oxidized carbon fibers(OCF) were prepared via surface oxidation treatment of carbon fibers(CF) in concentrated H2SO4/concentrated HNO3 blend acid, and then OCF were modified by silane coupling agent γ-methacryloxypropyl trimethoxy silane(KH-570), to obtain the KH-570 grafting modified carbon fibers(KCF), which were subsequently applied to ethylene-vinyl acetate copolymer(EVA) foamed composites. The surface modified characteristics, the structures and properties of carbon fiber/EVA composites were investigated by FTIR, XPS, Raman, FESEM and electronic universal testing machine etc. The result shows that both oxidation and grafting reaction can increase the content of active functional groups and roughness on surface of carbon fiber, which can improve the compatibility between carbon fibers and EVA matrix, leading to improvement on physical properties of carbon fiber/EVA foamed composites. Under the same conditions, the KH-570 grafting modified carbon fiber/EVA foamed composites have superior physical properties.
2016, 33(4): 788-796.
doi: 10.13801/j.cnki.fhclxb.20150901.001
Abstract:
In order to investigate the effects of ultrasonic vibration-assisted grinding on cutting force and surface quality of carbon fiber reinforced plastics(CFRP), cutting force model of ultrasonic vibration-assisted grinding was proposed. Theoretical analysis and test verification of trajectory of abrasive particle, the effect of sharped cutting edge, maximum undeformed chip thickness were conducted. The result shows that the cutting force is smaller and the surface quality is better in ultrasonic vibration-assisted grinding than in conventional grinding. The cutting force increases by 44.7% in ultrasonic vibration-assisted grinding when the per-tooth feed rises to 8μm/z from 4μm/z. Meanwhile it is 84.9% in conventional grinding. The cutting force increases by 187.8% in ultrasonic vibration-assisted grinding, which is lower than that in the conventional grinding of 209%, when the cutting depth is high up to 400μm from 200μm. Under the same processing parameters, the resin smearing, surface groove and fiber pull-out substantially decrease in ultrasonic vibration-assisted grinding compared with conventional grinding.
In order to investigate the effects of ultrasonic vibration-assisted grinding on cutting force and surface quality of carbon fiber reinforced plastics(CFRP), cutting force model of ultrasonic vibration-assisted grinding was proposed. Theoretical analysis and test verification of trajectory of abrasive particle, the effect of sharped cutting edge, maximum undeformed chip thickness were conducted. The result shows that the cutting force is smaller and the surface quality is better in ultrasonic vibration-assisted grinding than in conventional grinding. The cutting force increases by 44.7% in ultrasonic vibration-assisted grinding when the per-tooth feed rises to 8μm/z from 4μm/z. Meanwhile it is 84.9% in conventional grinding. The cutting force increases by 187.8% in ultrasonic vibration-assisted grinding, which is lower than that in the conventional grinding of 209%, when the cutting depth is high up to 400μm from 200μm. Under the same processing parameters, the resin smearing, surface groove and fiber pull-out substantially decrease in ultrasonic vibration-assisted grinding compared with conventional grinding.
2016, 33(4): 797-805.
doi: 10.13801/j.cnki.fhclxb.20150901.002
Abstract:
Selective adsorbent resin comprising of bentonite/sodium lignosulfonate graft-polymerized with acrylamide and maleic anhydride(Ben/LS-g-AM-co-MAH) was prepared by free radical graft solution copolymerization method by using sodium lignosulfonate(LS), acrylamide(AM) and maleic anhydride(MAH) as raw materials, bentonite as inorganic filler, potassium peroxydisulfate(KPS) as initiator, N, N'-methylene-bis-acrylamide(NMBA) as crosslinker. The as-prepared adsorbent resin was characterized by elemental analysis(EA), specific surface area and pore size analysis(BET), FTIR, nuclear magnetic resonance spectrum(13C NMR), XRD, SEM-EDS and XPS. The results show that there are a large number of acrylamide and carboxyl groups in the structure of Ben/LS-g-AM-co-MAH and the adsorbent resin possesses high adsorption capacity and selectivity to Pb2+ in Pb2+/Cu2+ binary solution.
Selective adsorbent resin comprising of bentonite/sodium lignosulfonate graft-polymerized with acrylamide and maleic anhydride(Ben/LS-g-AM-co-MAH) was prepared by free radical graft solution copolymerization method by using sodium lignosulfonate(LS), acrylamide(AM) and maleic anhydride(MAH) as raw materials, bentonite as inorganic filler, potassium peroxydisulfate(KPS) as initiator, N, N'-methylene-bis-acrylamide(NMBA) as crosslinker. The as-prepared adsorbent resin was characterized by elemental analysis(EA), specific surface area and pore size analysis(BET), FTIR, nuclear magnetic resonance spectrum(13C NMR), XRD, SEM-EDS and XPS. The results show that there are a large number of acrylamide and carboxyl groups in the structure of Ben/LS-g-AM-co-MAH and the adsorbent resin possesses high adsorption capacity and selectivity to Pb2+ in Pb2+/Cu2+ binary solution.
2016, 33(4): 806-813.
doi: 10.13801/j.cnki.fhclxb.20151013.003
Abstract:
Aiming at the quite uneven load distributions in the multiple bolts and premature failure at the most highly loaded induced by the brittle nature of composites, the clearance between the bolt and its corresponding hole was adjusted to improve the unequal load distribution. Firstly, bolt-hole clearances was chosen as the design variable and a quadratic programming optimization model of load distribution for multi-bolt joint based upon spring-mass model was built. Then, the optimization model was solved by using interior point method and the global optimum solution of the optimization model was obtained. At last, as an example, the bolt-hole clearances of composite mechanical joint with 5 bolts were optimized. The calculation results obtained were compared with the prediction results from finite element model. It shows that model optimization results agree well with finite element results. After optimization, the maximum bolt load proportion decrease dramatically from 41.1% to 20%. The model can be used effectively and accurately in uniform design of load distributions for multi-bolt composite joints.
Aiming at the quite uneven load distributions in the multiple bolts and premature failure at the most highly loaded induced by the brittle nature of composites, the clearance between the bolt and its corresponding hole was adjusted to improve the unequal load distribution. Firstly, bolt-hole clearances was chosen as the design variable and a quadratic programming optimization model of load distribution for multi-bolt joint based upon spring-mass model was built. Then, the optimization model was solved by using interior point method and the global optimum solution of the optimization model was obtained. At last, as an example, the bolt-hole clearances of composite mechanical joint with 5 bolts were optimized. The calculation results obtained were compared with the prediction results from finite element model. It shows that model optimization results agree well with finite element results. After optimization, the maximum bolt load proportion decrease dramatically from 41.1% to 20%. The model can be used effectively and accurately in uniform design of load distributions for multi-bolt composite joints.
2016, 33(4): 814-820.
doi: 10.13801/j.cnki.fhclxb.20150914.001
Abstract:
Lithium zinc ferrite(Li0.435Zn0.195Fe2.37O4, LZFO) was prepared by sol-gel method and interfacial polymerization method was used to prepare pure polyaniline(PANI) and PANI nanofibers/LZFO composites. The phase, structure and microwave absorption property of the materials were analyzed and characterized by SEM, XRD, FTIR and vector network analyzer(PNA). The results show that the samples are PANI, LZFO and different ratio of PANI nanofibers/LZFO composites. In the range of 2-18 GHz, PANI nanofibers/LZFO composites emerge two bands corresponding to electromagnetic wave reflection loss below -10 dB. The PANI nanofibers enhance the wave-absorbing property and widen the wave-absorbing band of PANI nanofibers/LZFO composites compared with PANI and LZFO. When the mass fraction of PANI nanofibers for PANI nanofibers/LZFO composites is 10%, the composites get the best comprehensive wave-absorbing properties. The peak of absorption could reach -33.8 dB and the bands corresponding to electromagnetic wave reflection loss below -10 dB lay in 2.5-5.5 GHz and 14.5-16.5 GHz. While the PANI and LZFO only emerge one band corresponding to electromagnetic wave reflection loss below -10 dB. Therefore, the electromagnetic parameter is adjusted and the microwave absorption property improves through grafting PANI nanofibers with ferrite.
Lithium zinc ferrite(Li0.435Zn0.195Fe2.37O4, LZFO) was prepared by sol-gel method and interfacial polymerization method was used to prepare pure polyaniline(PANI) and PANI nanofibers/LZFO composites. The phase, structure and microwave absorption property of the materials were analyzed and characterized by SEM, XRD, FTIR and vector network analyzer(PNA). The results show that the samples are PANI, LZFO and different ratio of PANI nanofibers/LZFO composites. In the range of 2-18 GHz, PANI nanofibers/LZFO composites emerge two bands corresponding to electromagnetic wave reflection loss below -10 dB. The PANI nanofibers enhance the wave-absorbing property and widen the wave-absorbing band of PANI nanofibers/LZFO composites compared with PANI and LZFO. When the mass fraction of PANI nanofibers for PANI nanofibers/LZFO composites is 10%, the composites get the best comprehensive wave-absorbing properties. The peak of absorption could reach -33.8 dB and the bands corresponding to electromagnetic wave reflection loss below -10 dB lay in 2.5-5.5 GHz and 14.5-16.5 GHz. While the PANI and LZFO only emerge one band corresponding to electromagnetic wave reflection loss below -10 dB. Therefore, the electromagnetic parameter is adjusted and the microwave absorption property improves through grafting PANI nanofibers with ferrite.
2016, 33(4): 821-826.
doi: 10.13801/j.cnki.fhclxb.20150921.003
Abstract:
Monodisperse ZrO2 sub micrometer with diameters of about 230 nm were prepared firstly via sol-gel method using zirconium tetrabutoxide as raw material. Then, ZrO2 was treated as precursor, the Sn2+ ions were physically adsorbed on the surface of the ZrO2 with the addition of a small amount of AgNO3. The raw material seeds were loaded on the surface of the ZrO2 via reduction of Ag+ to Ag0. With the addition of formaldehyde, core-shell nano Ag@ZrO2 composites were synthesized. Finally, the as-prepared ZrO2 and Ag@ZrO2 were characterized by TEM, XRD and UV-Vis, and their antibacterial properties against Staphylococcus aureus(S.aureus) and Escherichia coli(E.coli) were also studied. The results indicate that the antibacterial rates against S.aureus and E.coli of the Ag@ZrO2 is 95.5% and 99.0%, respectively, when the Ag concentration is 0.6 mg/mL. Therefore, the Ag@ZrO2 can be used in daily life and medical practice as ideal antibacterial material.
Monodisperse ZrO2 sub micrometer with diameters of about 230 nm were prepared firstly via sol-gel method using zirconium tetrabutoxide as raw material. Then, ZrO2 was treated as precursor, the Sn2+ ions were physically adsorbed on the surface of the ZrO2 with the addition of a small amount of AgNO3. The raw material seeds were loaded on the surface of the ZrO2 via reduction of Ag+ to Ag0. With the addition of formaldehyde, core-shell nano Ag@ZrO2 composites were synthesized. Finally, the as-prepared ZrO2 and Ag@ZrO2 were characterized by TEM, XRD and UV-Vis, and their antibacterial properties against Staphylococcus aureus(S.aureus) and Escherichia coli(E.coli) were also studied. The results indicate that the antibacterial rates against S.aureus and E.coli of the Ag@ZrO2 is 95.5% and 99.0%, respectively, when the Ag concentration is 0.6 mg/mL. Therefore, the Ag@ZrO2 can be used in daily life and medical practice as ideal antibacterial material.
2016, 33(4): 827-832.
doi: 10.13801/j.cnki.fhclxb.20150907.002
Abstract:
The stress-strain behavior for needled C/SiC composites was studied under static tensile loading at room temperature. A unit-cell model to predict the stress-strain properties for needled C/SiC composites was presented based on the representative volume element which was chosen according to the microstructure by micro CT technology reconstruction. Based on the interfacial friction model which is capable of stress-strain calculation of unidirectional fiber reinforced C/SiC composites under arbitrary loading/unloading procedure, the stress-strain response of unidirectional fiber bundle layer can be calculated from the properties of material mesoscopic constituents. By substituting the stress-strain response of unidirectional fiber bundle layer into the unit-cell model, the stress-strain response of the entire needled C/SiC composites can be obtained by finite element methods. By performing static tensile test of needled C/SiC composites, the predicted stress-strain responses match well with the test results.
The stress-strain behavior for needled C/SiC composites was studied under static tensile loading at room temperature. A unit-cell model to predict the stress-strain properties for needled C/SiC composites was presented based on the representative volume element which was chosen according to the microstructure by micro CT technology reconstruction. Based on the interfacial friction model which is capable of stress-strain calculation of unidirectional fiber reinforced C/SiC composites under arbitrary loading/unloading procedure, the stress-strain response of unidirectional fiber bundle layer can be calculated from the properties of material mesoscopic constituents. By substituting the stress-strain response of unidirectional fiber bundle layer into the unit-cell model, the stress-strain response of the entire needled C/SiC composites can be obtained by finite element methods. By performing static tensile test of needled C/SiC composites, the predicted stress-strain responses match well with the test results.
2016, 33(4): 833-840.
doi: 10.13801/j.cnki.fhclxb.20150715.001
Abstract:
Porous TiB2-TiC composites were produced by self-propagating high-temperature synthesis method, with Ti, B4C and SiC whiskers(SiCw) as raw materials. The effects of SiCw content on phases, microstructures, porosity and compressive strength of TiB2-TiC composites were studied. The results show that the composites are mainly composed of poor boron phases TiB and Ti3B4, TiC and a little TiB2 when there is no SiCw added. After adding SiCw into 5Ti+B4C system, the poor boron phases TiB and Ti3B4 decrease and even disappear, while the content of rich boron phase TiB2 and TiC increase. With the increasing of SiCw content, the porosity of composites gradually increases from 38.46% to 52.78%. When the content of SiCw is less than 1.0, the compressive strength of porous TiB2-TiC composites improves significantly with the increasing of SiCw content and reaches to the maximum value of 56.04 MPa when the content of SiCw is 1.0. A part of Ti is consumed by reacting with SiCw to form TiC, Ti3SiC2 and TiSi2 phases, so less Ti is remaining to react with B4C. This promotes the formation of rich boron phase TiB2 and TiC. Moreover some of the granular TiC or lamellar Ti3SiC2 grow around the surface of SiCw, which is beneficial to improve the bonding strength of SiCw and TiB2-TiC matrix, and the effect of SiCw reinforcement.
Porous TiB2-TiC composites were produced by self-propagating high-temperature synthesis method, with Ti, B4C and SiC whiskers(SiCw) as raw materials. The effects of SiCw content on phases, microstructures, porosity and compressive strength of TiB2-TiC composites were studied. The results show that the composites are mainly composed of poor boron phases TiB and Ti3B4, TiC and a little TiB2 when there is no SiCw added. After adding SiCw into 5Ti+B4C system, the poor boron phases TiB and Ti3B4 decrease and even disappear, while the content of rich boron phase TiB2 and TiC increase. With the increasing of SiCw content, the porosity of composites gradually increases from 38.46% to 52.78%. When the content of SiCw is less than 1.0, the compressive strength of porous TiB2-TiC composites improves significantly with the increasing of SiCw content and reaches to the maximum value of 56.04 MPa when the content of SiCw is 1.0. A part of Ti is consumed by reacting with SiCw to form TiC, Ti3SiC2 and TiSi2 phases, so less Ti is remaining to react with B4C. This promotes the formation of rich boron phase TiB2 and TiC. Moreover some of the granular TiC or lamellar Ti3SiC2 grow around the surface of SiCw, which is beneficial to improve the bonding strength of SiCw and TiB2-TiC matrix, and the effect of SiCw reinforcement.
2016, 33(4): 841-851.
doi: 10.13801/j.cnki.fhclxb.20151010.002
Abstract:
Under fatigue loading of fiber-reinforced ceramic matrix composites(CMCs), the fatigue hysteresis phenomenon appears as the fiber slipping repeatedly relative to matrix in the interface debonded region. The area of the hysteresis loops, i.e., the hysteresis dissipated energy, can be used to monitor the damage evolution in fiber-reinforced CMCs under fatigue loading. An approach to predict the fatigue life of fiber-reinforced CMCs has been developed based on the hysteresis dissipated energy. The hysteresis loops models considering fiber failure has been developed. The relationships between the hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter, stress-strain hysteresis loops and fatigue damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding, interface wear and fiber failure, have been established. The effects of fatigue peak stress, fatigue stress ratio and fiber volume content on the fatigue life S-N curve, hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter as functions of cycle number have been investigated for fiber-reinforced CMCs. The fatigue life decreases with increasing fatigue peak stress, and increases with increasing fiber volume content; the hysteresis dissipated energy increases with increasing fatigue peak stress, and decreases with increasing stress ratio and fiber volume content; and hysteresis dissipated energy-based damage parameter decreases with increasing fiber volume content.
Under fatigue loading of fiber-reinforced ceramic matrix composites(CMCs), the fatigue hysteresis phenomenon appears as the fiber slipping repeatedly relative to matrix in the interface debonded region. The area of the hysteresis loops, i.e., the hysteresis dissipated energy, can be used to monitor the damage evolution in fiber-reinforced CMCs under fatigue loading. An approach to predict the fatigue life of fiber-reinforced CMCs has been developed based on the hysteresis dissipated energy. The hysteresis loops models considering fiber failure has been developed. The relationships between the hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter, stress-strain hysteresis loops and fatigue damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding, interface wear and fiber failure, have been established. The effects of fatigue peak stress, fatigue stress ratio and fiber volume content on the fatigue life S-N curve, hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter as functions of cycle number have been investigated for fiber-reinforced CMCs. The fatigue life decreases with increasing fatigue peak stress, and increases with increasing fiber volume content; the hysteresis dissipated energy increases with increasing fatigue peak stress, and decreases with increasing stress ratio and fiber volume content; and hysteresis dissipated energy-based damage parameter decreases with increasing fiber volume content.
2016, 33(4): 852-858.
doi: 10.13801/j.cnki.fhclxb.20150915.001
Abstract:
In order to improve the strength of calcium phosphate cements(CPCs), graphene oxide(GO) in nano-sheet form was composited with CPCs. CPCs whose amount ratio of substance for α-Ca3(PO4)2, CaHPO4 and CaCO4 was 1:1:1 were used as solid phase, the aqueous dispersions of GO with different concentrations were used as solidification liquids, both of them were mixed according to certain powder/liquid ratio, set and solidified, thus the GO/CPCs were prepared firstly. Then, the effect of GO additive amount on the mechanical strength of GO/CPCs was discussed. The setting time, degradation rate after immersion in simulated body fluid and pH of extract liquids were measured, the phase was tested by XRD, and the micromorphology was observed by SEM. The results show that GO additive amount has remarkable effect on compressive strength of CPCs, the optimum additive amount is 0.0500wt%. With the aging time increasing, all of the compressive strength of CPCs with different GO additive amounts improves significantly, especially in the earlier stage. Comparing to the control group without the addition of GO, after aging for 2 h and 24 h, the compressive strength of 0.0500wt% GO/CPCs increase by 200% and 67%, respectively. The degradation rate of GO/CPCs in simulated body fluid increases, and pH of extract liquid decreases. GO/CPCs can obtain more hydroxyapatite phase in the corresponding period of hydration reaction, and the grains are well-aligned, regular and fine. The conclusions obtained indicate that the addition of GO can improve the compressive strength of CPCs significantly.
In order to improve the strength of calcium phosphate cements(CPCs), graphene oxide(GO) in nano-sheet form was composited with CPCs. CPCs whose amount ratio of substance for α-Ca3(PO4)2, CaHPO4 and CaCO4 was 1:1:1 were used as solid phase, the aqueous dispersions of GO with different concentrations were used as solidification liquids, both of them were mixed according to certain powder/liquid ratio, set and solidified, thus the GO/CPCs were prepared firstly. Then, the effect of GO additive amount on the mechanical strength of GO/CPCs was discussed. The setting time, degradation rate after immersion in simulated body fluid and pH of extract liquids were measured, the phase was tested by XRD, and the micromorphology was observed by SEM. The results show that GO additive amount has remarkable effect on compressive strength of CPCs, the optimum additive amount is 0.0500wt%. With the aging time increasing, all of the compressive strength of CPCs with different GO additive amounts improves significantly, especially in the earlier stage. Comparing to the control group without the addition of GO, after aging for 2 h and 24 h, the compressive strength of 0.0500wt% GO/CPCs increase by 200% and 67%, respectively. The degradation rate of GO/CPCs in simulated body fluid increases, and pH of extract liquid decreases. GO/CPCs can obtain more hydroxyapatite phase in the corresponding period of hydration reaction, and the grains are well-aligned, regular and fine. The conclusions obtained indicate that the addition of GO can improve the compressive strength of CPCs significantly.
2016, 33(4): 859-865.
doi: 10.13801/j.cnki.fhclxb.20151008.002
Abstract:
In order to fabricate the hydroxyapatite(HA) composite coating which is more excellent in aspects of mechanical properties and bioactivity, HA-SrCO3-SiO2 composite coatings were fabricated firstly using electrophoretic deposition method aided with high temperature sintering by adding binary osteogenesis trace element compounds SrCO3 and SiO2, and using chitosan as porogen. Then, the composite coatings were tested and characterized by FTIR, XRD, SEM, EDS, universal material testing machine and electrochemical workstation, and the bioactivity of HA-SrCO3-SiO2 composite coatings was evaluated by immersion and cultivation in simulated body fluid of 1.5 times ionic concentration. The results show that the bonding strength between HA-SrCO3-SiO2 composite coating and substrate reaches 28.6 MPa. After immersion and cultivation in simulated body fluid for 7 d, the surface of composite coating is completely covered by carbonated hydroxyapatite, which indicates that the composite coating possesses better bioactivity than those of single osteogenesis trace element compound doped composite coating and pure HA coating. The conclusions obtained show that the prepared HA-SrCO3-SiO2 composite coatings would be developed as a brand generation of the artificial bone replacement material.
In order to fabricate the hydroxyapatite(HA) composite coating which is more excellent in aspects of mechanical properties and bioactivity, HA-SrCO3-SiO2 composite coatings were fabricated firstly using electrophoretic deposition method aided with high temperature sintering by adding binary osteogenesis trace element compounds SrCO3 and SiO2, and using chitosan as porogen. Then, the composite coatings were tested and characterized by FTIR, XRD, SEM, EDS, universal material testing machine and electrochemical workstation, and the bioactivity of HA-SrCO3-SiO2 composite coatings was evaluated by immersion and cultivation in simulated body fluid of 1.5 times ionic concentration. The results show that the bonding strength between HA-SrCO3-SiO2 composite coating and substrate reaches 28.6 MPa. After immersion and cultivation in simulated body fluid for 7 d, the surface of composite coating is completely covered by carbonated hydroxyapatite, which indicates that the composite coating possesses better bioactivity than those of single osteogenesis trace element compound doped composite coating and pure HA coating. The conclusions obtained show that the prepared HA-SrCO3-SiO2 composite coatings would be developed as a brand generation of the artificial bone replacement material.
2016, 33(4): 866-874.
doi: 10.13801/j.cnki.fhclxb.20160102.002
Abstract:
The waste polyester/cotton(P/C) blended fabric and waste polyester(PE) fabric were used to reinforce the cement based permeable concrete brick. The effects of fabric content and size on the compressive property, permeability and water retention property of composite permeable brick(CPB) were investigated. The results show that with increasing of fabric additive volume fraction, the compressive strength, compression toughness index and absorbed energy of CPB first increase and then decrease, and the permeability coefficient and water retention coefficient increase; with increasing of fabric size, the compressive strength, permeability coefficient and water retention coefficient of CPB decrease, the compression toughness index increases and absorbed energy has little change; when the added amount of fabric and fiber with equal mass are smaller, compared with CPB reinforced with waste fabric, the compressive strength of CPB reinforced with recycled fiber is lower but the compression toughness index, absorbed energy and permeability coefficient are bigger; when fabric additive volume fraction ≤2%, the compressive strength of CPB reinforced with P/C fabric(PC-CPB) is better than that of CPB reinforced with polyester fabric(P-CPB), the permeability coefficient and water retention coefficient of PC-CPB are close to those of P-CPB, but when fabric additive volume fraction >2% the results are contrary, and the compression toughness index, absorbed energy of PC-CPB are always better than those of P-CPB; CPB reinforced with 2% fabric additive volume fraction 3 mm×3 mm P/C fabric has the compressive strength 28.20 MPa, absorbed energy 1097.55 N·m, permeability coefficient 0.267 mm/s, water retention coefficient 43.40 g/cm2, which are raised by 21.8%, 55.8%, 115.3% and 33.3% respectively compared with the ordinary permeable brick.
The waste polyester/cotton(P/C) blended fabric and waste polyester(PE) fabric were used to reinforce the cement based permeable concrete brick. The effects of fabric content and size on the compressive property, permeability and water retention property of composite permeable brick(CPB) were investigated. The results show that with increasing of fabric additive volume fraction, the compressive strength, compression toughness index and absorbed energy of CPB first increase and then decrease, and the permeability coefficient and water retention coefficient increase; with increasing of fabric size, the compressive strength, permeability coefficient and water retention coefficient of CPB decrease, the compression toughness index increases and absorbed energy has little change; when the added amount of fabric and fiber with equal mass are smaller, compared with CPB reinforced with waste fabric, the compressive strength of CPB reinforced with recycled fiber is lower but the compression toughness index, absorbed energy and permeability coefficient are bigger; when fabric additive volume fraction ≤2%, the compressive strength of CPB reinforced with P/C fabric(PC-CPB) is better than that of CPB reinforced with polyester fabric(P-CPB), the permeability coefficient and water retention coefficient of PC-CPB are close to those of P-CPB, but when fabric additive volume fraction >2% the results are contrary, and the compression toughness index, absorbed energy of PC-CPB are always better than those of P-CPB; CPB reinforced with 2% fabric additive volume fraction 3 mm×3 mm P/C fabric has the compressive strength 28.20 MPa, absorbed energy 1097.55 N·m, permeability coefficient 0.267 mm/s, water retention coefficient 43.40 g/cm2, which are raised by 21.8%, 55.8%, 115.3% and 33.3% respectively compared with the ordinary permeable brick.
2016, 33(4): 875-883.
doi: 10.13801/j.cnki.fhclxb.20151109.001
Abstract:
Using Ti(OC4H9)4 as raw material, CO(NH2)2 as N source, La(NO3)3·6H2O as La source, the N and La co-doped nano TiO2/tourmaline composites were synthesized via ultrasonic assisted sol-gel method. The structure and performance of composites were characterized by XRD, UV-Vis, SEM-EDS and XPS. The photocatalytic activity and recycling performance of N and La co-doped nano TiO2/tourmaline composites were evaluated with 2, 4, 6-trinitrotoluene as target pollutant. The results show that TiO2 grain sizes refine more and light abstraction width expands to visible region by the synergetic effect of N and La co-doped, and tourmaline loaded. N and La co-doped nano TiO2/tourmaline composites have good photocatalytic activity and recycling performance.The removal effect of 2, 4, 6-trinitrotoluene is good under the condition of simulating visible light irradiation.
Using Ti(OC4H9)4 as raw material, CO(NH2)2 as N source, La(NO3)3·6H2O as La source, the N and La co-doped nano TiO2/tourmaline composites were synthesized via ultrasonic assisted sol-gel method. The structure and performance of composites were characterized by XRD, UV-Vis, SEM-EDS and XPS. The photocatalytic activity and recycling performance of N and La co-doped nano TiO2/tourmaline composites were evaluated with 2, 4, 6-trinitrotoluene as target pollutant. The results show that TiO2 grain sizes refine more and light abstraction width expands to visible region by the synergetic effect of N and La co-doped, and tourmaline loaded. N and La co-doped nano TiO2/tourmaline composites have good photocatalytic activity and recycling performance.The removal effect of 2, 4, 6-trinitrotoluene is good under the condition of simulating visible light irradiation.
2016, 33(4): 884-892.
doi: 10.13801/j.cnki.fhclxb.20150709.003
Abstract:
Test investigation enforcing bearing load was occupied on GLARE36/5 laminates. The bearing damage progressive and ultimate failure modes of GLARE laminates were observed using ultrasonic C-scan, fracture macro photography and scanning electron microscope. Results indicate that the bearing damage of GLARE laminates initially occurred as plastic deformation of aluminium alloy, while in the stage of damage extension, delamination in layer appears and develops due to larger plastic deformation of aluminium alloy and bearing normal stress is mainly carried by 0°fiber. After the buckling and fracture of fiber in 0°ply, the matrix damage and delamination progress rapidly. Finally, bearing failure of the laminates occurres. Bearing progressive damage numerical model was developed, in which bearing failure in GLARE laminates were classified as in-ply failure and inter-ply failure, modelled with Hashin criteria in strain form and cohesive element approach respectively, while considering metal plasticity. This model was used to predict the locations where in-ply damage and delamination occur firstly, the progression of damage, final failure modes and failure loads. The calculation results are in good agreement with test results, meaning that the calculation method is able to simulate the progressive damage of GLARE laminates under bearing load effectively.
Test investigation enforcing bearing load was occupied on GLARE36/5 laminates. The bearing damage progressive and ultimate failure modes of GLARE laminates were observed using ultrasonic C-scan, fracture macro photography and scanning electron microscope. Results indicate that the bearing damage of GLARE laminates initially occurred as plastic deformation of aluminium alloy, while in the stage of damage extension, delamination in layer appears and develops due to larger plastic deformation of aluminium alloy and bearing normal stress is mainly carried by 0°fiber. After the buckling and fracture of fiber in 0°ply, the matrix damage and delamination progress rapidly. Finally, bearing failure of the laminates occurres. Bearing progressive damage numerical model was developed, in which bearing failure in GLARE laminates were classified as in-ply failure and inter-ply failure, modelled with Hashin criteria in strain form and cohesive element approach respectively, while considering metal plasticity. This model was used to predict the locations where in-ply damage and delamination occur firstly, the progression of damage, final failure modes and failure loads. The calculation results are in good agreement with test results, meaning that the calculation method is able to simulate the progressive damage of GLARE laminates under bearing load effectively.
2016, 33(4): 893-901.
doi: 10.13801/j.cnki.fhclxb.20150824.002
Abstract:
In order to determine effects of rib support on axial compression behaviors of composite stiffened panels, composite stiffened panels with I shape and hat shape cross-section without and with rib support were investigated experimentally and numerically. In axial compression tests, strain gauge and Moiré interferometry were used to monitor timely the buckling load and buckling modes of specimens, fracture section was observed aimed to analyze the fracture mechanism of structural damage. Based on the software of ABAQUS, a finite element model was developed to simulate the buckling and post-buckling progress of the stiffened panels, then the damage mechanism of stiffened panels was further analyzed by stress distribution evolution on the buckled antinode line and node line. The calculated results are coordinated with the testing results very well. The results indicate that the rib support has changed buckling mode but no impact on the buckling load for stiffened panels with different types of stiffener. The collapse load has a slight difference between with the rib support and without the support on the node line for the stiffened panels with I shape stringer, while that of the former panels has increased by 26.2% than the latter panels for the stiffened panels with hat shape stringer which the rib support was located on the antinode line. Stress distribution concentrates into interface between the stiffener and skin on the antinode line, high stress will induce interface debond, which will lead to collapse of structures concentrating on the antinode line.
In order to determine effects of rib support on axial compression behaviors of composite stiffened panels, composite stiffened panels with I shape and hat shape cross-section without and with rib support were investigated experimentally and numerically. In axial compression tests, strain gauge and Moiré interferometry were used to monitor timely the buckling load and buckling modes of specimens, fracture section was observed aimed to analyze the fracture mechanism of structural damage. Based on the software of ABAQUS, a finite element model was developed to simulate the buckling and post-buckling progress of the stiffened panels, then the damage mechanism of stiffened panels was further analyzed by stress distribution evolution on the buckled antinode line and node line. The calculated results are coordinated with the testing results very well. The results indicate that the rib support has changed buckling mode but no impact on the buckling load for stiffened panels with different types of stiffener. The collapse load has a slight difference between with the rib support and without the support on the node line for the stiffened panels with I shape stringer, while that of the former panels has increased by 26.2% than the latter panels for the stiffened panels with hat shape stringer which the rib support was located on the antinode line. Stress distribution concentrates into interface between the stiffener and skin on the antinode line, high stress will induce interface debond, which will lead to collapse of structures concentrating on the antinode line.
2016, 33(4): 902-909.
doi: 10.13801/j.cnki.fhclxb.20150729.002
Abstract:
The deformation of composite parts during curing process is one of the key technique problems. Analytical calculation model and finite element simulation model were proposed to predict the curing deformation of composite parts by introducing a shear layer between the tool and composite part. The shear modulus of the shear layer was used to measure the interaction between the tool and composite part during curing process. The value of shear modulus was obtained by comparing with experimental data. Based on the proposed curing deformation model, the results were compared with experimental results in reference. Results show that the proposed model has good reliability. Meanwhile, a three dimensional finite element simulation model, which took part anisotropy of materials, chemical shrinkage and interaction between the tool and composite part in molding process into account, was also established for L-shaped composite part. Simulation results show that by introducing tool interaction, we could accurately predict curing deformations for L-shaped part.
The deformation of composite parts during curing process is one of the key technique problems. Analytical calculation model and finite element simulation model were proposed to predict the curing deformation of composite parts by introducing a shear layer between the tool and composite part. The shear modulus of the shear layer was used to measure the interaction between the tool and composite part during curing process. The value of shear modulus was obtained by comparing with experimental data. Based on the proposed curing deformation model, the results were compared with experimental results in reference. Results show that the proposed model has good reliability. Meanwhile, a three dimensional finite element simulation model, which took part anisotropy of materials, chemical shrinkage and interaction between the tool and composite part in molding process into account, was also established for L-shaped composite part. Simulation results show that by introducing tool interaction, we could accurately predict curing deformations for L-shaped part.
2016, 33(4): 910-920.
doi: 10.13801/j.cnki.fhclxb.20151010.001
Abstract:
Honeycomb sandwich plate with negative Poisson's ratio is a special composite structure, whose dynamic behavior has not yet been studied. We applied Reddy's shear plate theory to do a free flexural vibration analysis of honeycomb sandwich plate with negative Poisson's ratio simply supported on opposite edges. Honeycomb core that consists of concave hexagon cellular element can be taken as an orthotropic layer. Equivalent elastic parameters of core were derived from the revised Gibson formula. From concrete example, we conclude that the classical sandwich plate theory and one order shear plate theory were not applicable to the vibration analysis of honeycomb sandwich plate. With Reddy's shear plate theory, we studied the influence of plate thickness of honeycomb sandwich plate, core plate, and angle of cellular element on flexural vibration frequency. Besides the above, a related curve chart was drawn. Results show that for honeycomb sandwich plate with negative Poisson's ratio simply supported on opposite edges, the natural frequency parameter increases with the ratio of plate thickness if ratio of plate thickness is less than a certain value. However, if the ratio of plate thickness was more than this value, the increase of natural frequency parameter behaves a complex variation with the increase of ratio of plate thickness. The conclusion derived from this paper provides a theoretical ground and numerical reference for the design and practical application of honeycomb sandwich plate.
Honeycomb sandwich plate with negative Poisson's ratio is a special composite structure, whose dynamic behavior has not yet been studied. We applied Reddy's shear plate theory to do a free flexural vibration analysis of honeycomb sandwich plate with negative Poisson's ratio simply supported on opposite edges. Honeycomb core that consists of concave hexagon cellular element can be taken as an orthotropic layer. Equivalent elastic parameters of core were derived from the revised Gibson formula. From concrete example, we conclude that the classical sandwich plate theory and one order shear plate theory were not applicable to the vibration analysis of honeycomb sandwich plate. With Reddy's shear plate theory, we studied the influence of plate thickness of honeycomb sandwich plate, core plate, and angle of cellular element on flexural vibration frequency. Besides the above, a related curve chart was drawn. Results show that for honeycomb sandwich plate with negative Poisson's ratio simply supported on opposite edges, the natural frequency parameter increases with the ratio of plate thickness if ratio of plate thickness is less than a certain value. However, if the ratio of plate thickness was more than this value, the increase of natural frequency parameter behaves a complex variation with the increase of ratio of plate thickness. The conclusion derived from this paper provides a theoretical ground and numerical reference for the design and practical application of honeycomb sandwich plate.
2016, 33(4): 921-928.
doi: 10.13801/j.cnki.fhclxb.20150911.003
Abstract:
In order to improve the anti-penetration capacity of lightweight composite armors, metal lattice truss cored sandwich protective structures filled with ceramic rods internally and packaged by epoxy resin hybridized with short cut glass fibers were proposed. First, the anti-penetration capacity for projectile of metal lattice truss cored sandwich protective structures filled with ceramic rods was investigated by ballistic impact experiments. Then, considering failure mode and energy absorption efficiency, the anti-penetration mechanism of the sandwich protective structures was synthetically analyzed. The results show that the main failure modes of metal lattice truss cored sandwich protective structures filled with ceramic rods consist the tensile failure of metal lattice truss structure and hybrid fillers, the fracture of ceramic rods, the local shear failure of front sheet and rear sheet, and the overall bending deformation of rear sheet. In the penetration process of spherical projectile, the anti-penetration capacity of protective structures is significantly improved for the large plastic deformation and shear cavity of metal lattice truss, the fracture failure of ceramic rods and epoxy resin, and the macro-bending deformation of front sheet. The conclusions obtained can provide some references for the protective design of new lightweight composite armors.
In order to improve the anti-penetration capacity of lightweight composite armors, metal lattice truss cored sandwich protective structures filled with ceramic rods internally and packaged by epoxy resin hybridized with short cut glass fibers were proposed. First, the anti-penetration capacity for projectile of metal lattice truss cored sandwich protective structures filled with ceramic rods was investigated by ballistic impact experiments. Then, considering failure mode and energy absorption efficiency, the anti-penetration mechanism of the sandwich protective structures was synthetically analyzed. The results show that the main failure modes of metal lattice truss cored sandwich protective structures filled with ceramic rods consist the tensile failure of metal lattice truss structure and hybrid fillers, the fracture of ceramic rods, the local shear failure of front sheet and rear sheet, and the overall bending deformation of rear sheet. In the penetration process of spherical projectile, the anti-penetration capacity of protective structures is significantly improved for the large plastic deformation and shear cavity of metal lattice truss, the fracture failure of ceramic rods and epoxy resin, and the macro-bending deformation of front sheet. The conclusions obtained can provide some references for the protective design of new lightweight composite armors.
2016, 33(4): 929-938.
doi: 10.13801/j.cnki.fhclxb.20151013.002
Abstract:
In order to solve the fracture parameters of piezoelectric materials with cracks under the electromechanical coupling effect accurately and effectively, Cell-Based smoothed extended finite element method for piezoelectric materials containing cracks was put forward firstly by introducing complex potential function method, extended finite element method and smooth gradient technology into the problem of fracture mechanics for piezoelectric materials with cracks. Then, the intensity factors of piezoelectric materials with center cracks were simulated, and the simulated results were compared with the calculated results of extended finite element method and finite element method. The results of numerical examples show that Cell-Based smoothed extended finite element method has both the characteristics of extended finite element method and smoothed finite element method, not only the element meshes and crack surface are independent of each other, but also unnecessary to divide the element at crack tip precisely, at the same time, Cell-Based smoothed extended finite element method also has advantage such as the shape function is simple and does not require derivative, the mesh quality requirements are low and the solution precision is high, etc. The conclusions obtained show that Cell-Based smoothed extended finite element method is an effective numerical method for fracture analysis of piezoelectric materials.
In order to solve the fracture parameters of piezoelectric materials with cracks under the electromechanical coupling effect accurately and effectively, Cell-Based smoothed extended finite element method for piezoelectric materials containing cracks was put forward firstly by introducing complex potential function method, extended finite element method and smooth gradient technology into the problem of fracture mechanics for piezoelectric materials with cracks. Then, the intensity factors of piezoelectric materials with center cracks were simulated, and the simulated results were compared with the calculated results of extended finite element method and finite element method. The results of numerical examples show that Cell-Based smoothed extended finite element method has both the characteristics of extended finite element method and smoothed finite element method, not only the element meshes and crack surface are independent of each other, but also unnecessary to divide the element at crack tip precisely, at the same time, Cell-Based smoothed extended finite element method also has advantage such as the shape function is simple and does not require derivative, the mesh quality requirements are low and the solution precision is high, etc. The conclusions obtained show that Cell-Based smoothed extended finite element method is an effective numerical method for fracture analysis of piezoelectric materials.
2016, 33(4): 939-946.
doi: 10.13801/j.cnki.fhclxb.20151012.002
Abstract:
With poplar particles and inorganic adhesive as main raw materials, inorganic poplar particleboard was prepared by cold pressing technology. The effect of different adhesive consumption and density on physical and mechanical properties of inorganic poplar particleboard was studied. XRD and SEM were used to analyze influencing mechanism of inorganic poplar particleboard's properties with different adhesive consumption and densities. At the same time, the fire retardancy and smoke suppression characteristics of inorganic poplar particleboard were tested by CONE. The results show that, on one hand, modulus of rupture(MOR) and modulus of elasticity(MOE) of inorganic poplar particleboard firstly increase and then decrease with the increase of adhesive consumption, meanwhile, internal bond(IB) increases gradually and 24 h thickness swelling(TS) decreases gradually. MOR and MOE reach the maximum at 21.5 MPa and 4360 MPa respectively when adhesive consumption is 57%; and IB and 24 h TS reach the maximum of 2.61 MPa and the minimum of 3.36% respectively when adhesive consumption is 65%. With the increase of adhesive consumption, heat release rate(HRR) decreases, peak time of HRR postpones, total heat release(THR) and total smoke production(TSP) decreases. On the other hand, with the increase of density, MOR and MOE increase gradually, IB firstly increases and then decreases which is contrary with 24 h TS. IB and 24 h TS reach the maximum and minimum of 3.54 MPa and 3.99% respectively when the density of inorganic poplar particleboard is 1.1 g/cm3.
With poplar particles and inorganic adhesive as main raw materials, inorganic poplar particleboard was prepared by cold pressing technology. The effect of different adhesive consumption and density on physical and mechanical properties of inorganic poplar particleboard was studied. XRD and SEM were used to analyze influencing mechanism of inorganic poplar particleboard's properties with different adhesive consumption and densities. At the same time, the fire retardancy and smoke suppression characteristics of inorganic poplar particleboard were tested by CONE. The results show that, on one hand, modulus of rupture(MOR) and modulus of elasticity(MOE) of inorganic poplar particleboard firstly increase and then decrease with the increase of adhesive consumption, meanwhile, internal bond(IB) increases gradually and 24 h thickness swelling(TS) decreases gradually. MOR and MOE reach the maximum at 21.5 MPa and 4360 MPa respectively when adhesive consumption is 57%; and IB and 24 h TS reach the maximum of 2.61 MPa and the minimum of 3.36% respectively when adhesive consumption is 65%. With the increase of adhesive consumption, heat release rate(HRR) decreases, peak time of HRR postpones, total heat release(THR) and total smoke production(TSP) decreases. On the other hand, with the increase of density, MOR and MOE increase gradually, IB firstly increases and then decreases which is contrary with 24 h TS. IB and 24 h TS reach the maximum and minimum of 3.54 MPa and 3.99% respectively when the density of inorganic poplar particleboard is 1.1 g/cm3.
2016, 33(4): 947-953.
doi: 10.13801/j.cnki.fhclxb.20150930.001
Abstract:
The anisotropy produced by the different properties of fluid and solid phase in saturated rock and soil-like porous materials and heterogeneity of porous microstructures made the calculation of micro mechanics properties very complex. In order to accurately predict the effective elastic properties and micro stress-strain fields of rock and soil-like materials, the energy functional and corresponding porous elastic constitutive relations were built based on the Biot porous elastic media theory. The energy variational functional is then asymptotically expended to series of approximate functional by taking advantage of the small ratio of micro scale to macro scale. With the fluctuation functions of field variables as unknown variables, the analytical solutions to the fluctuation functions can be obtained by solving the minimum problem(stationary value problem) of approximate functionals. Thus, a micromechanical model is established, which is as close as possible to the real physical and engineering problem. The developed micromechanical model is numerically implemented through the finite element technology. The examples of porous material show that the accuracy of micromechanical properties calculated by the developed model is much better than the classical homogenization theory, in which the fluid material is regarded as solid material with high Poisson's ratio; especially the local stress-strain fields distribution can be accurately recovered, laying a solid foundation for the analysis of damage and local fracture.
The anisotropy produced by the different properties of fluid and solid phase in saturated rock and soil-like porous materials and heterogeneity of porous microstructures made the calculation of micro mechanics properties very complex. In order to accurately predict the effective elastic properties and micro stress-strain fields of rock and soil-like materials, the energy functional and corresponding porous elastic constitutive relations were built based on the Biot porous elastic media theory. The energy variational functional is then asymptotically expended to series of approximate functional by taking advantage of the small ratio of micro scale to macro scale. With the fluctuation functions of field variables as unknown variables, the analytical solutions to the fluctuation functions can be obtained by solving the minimum problem(stationary value problem) of approximate functionals. Thus, a micromechanical model is established, which is as close as possible to the real physical and engineering problem. The developed micromechanical model is numerically implemented through the finite element technology. The examples of porous material show that the accuracy of micromechanical properties calculated by the developed model is much better than the classical homogenization theory, in which the fluid material is regarded as solid material with high Poisson's ratio; especially the local stress-strain fields distribution can be accurately recovered, laying a solid foundation for the analysis of damage and local fracture.
