2018 Vol. 35, No. 12
2018, 35(12): 3235-3246.
doi: 10.13801/j.cnki.fhclxb.20180502.006
Abstract:
Flexible optoelectronics have been well developed due to the flexibility and stretchability. While, new requirements are put forward for the next generation of flexible optoelectronics. Shape memory polymers (SMPs) with controllable shape changing properties and tunable moduli have unique benefits in flexible optoelectronics, which can be utilized as the raw materials or flexible substrates. Shape memory flexible optoelectronics can be not only break through the disadvantages of the traditional rigid inorganic devices, but also can greatly increase the functions and applications. Herein, the sate-of-art progresses of SMP-based flexible optoelectronics, including the SMP substrates, drive methods and basic drive principles as well as the fabrication technologies, are reviewed. Furthermore, this paper elaborates the application of four-dimensional (4D) printing technology in the SMP-based structural electronics. Lastly, the existing problems and further developments of SMP-based flexible optoelectronics are described.
Flexible optoelectronics have been well developed due to the flexibility and stretchability. While, new requirements are put forward for the next generation of flexible optoelectronics. Shape memory polymers (SMPs) with controllable shape changing properties and tunable moduli have unique benefits in flexible optoelectronics, which can be utilized as the raw materials or flexible substrates. Shape memory flexible optoelectronics can be not only break through the disadvantages of the traditional rigid inorganic devices, but also can greatly increase the functions and applications. Herein, the sate-of-art progresses of SMP-based flexible optoelectronics, including the SMP substrates, drive methods and basic drive principles as well as the fabrication technologies, are reviewed. Furthermore, this paper elaborates the application of four-dimensional (4D) printing technology in the SMP-based structural electronics. Lastly, the existing problems and further developments of SMP-based flexible optoelectronics are described.
2018, 35(12): 3247-3252.
doi: 10.13801/j.cnki.fhclxb.20180705.004
Abstract:
Carbon nanotubes(CNTs) were modified by Fe3O4, the dispersibility of CNTs in polyvinylidene fluoride (PVDF) and interfacial adhesion were improved so as to achieve high mechanical properties and electrical properties, better application for sensor, actuator and energy storage with functional performance. Fe3O4-CNTs were prepared by in situ hydrothermal synthesis method. Fe3O4-CNTs/PVDF composites were prepared by the casting process. The structure and crystallization behavior of Fe3O4-CNTs/PVDF composite films were studied by SEM, TEM, XRD and DSC. The mechanical properties, the dielectric properties and breakdown field strength of Fe3O4-CNTs/PVDF composite were studied by DMA and the broadband dielectric spectrometer. The results show that, due to the adding of Fe3O4-CNTs, the crystallinity of the composite is improved and the PVDF β crystal phase is observed for adding Fe3O4-CNTs. The dielectric constant is increased, the increase of dielectric loss is inhibited. The breakdown field strength is increased visibly.
Carbon nanotubes(CNTs) were modified by Fe3O4, the dispersibility of CNTs in polyvinylidene fluoride (PVDF) and interfacial adhesion were improved so as to achieve high mechanical properties and electrical properties, better application for sensor, actuator and energy storage with functional performance. Fe3O4-CNTs were prepared by in situ hydrothermal synthesis method. Fe3O4-CNTs/PVDF composites were prepared by the casting process. The structure and crystallization behavior of Fe3O4-CNTs/PVDF composite films were studied by SEM, TEM, XRD and DSC. The mechanical properties, the dielectric properties and breakdown field strength of Fe3O4-CNTs/PVDF composite were studied by DMA and the broadband dielectric spectrometer. The results show that, due to the adding of Fe3O4-CNTs, the crystallinity of the composite is improved and the PVDF β crystal phase is observed for adding Fe3O4-CNTs. The dielectric constant is increased, the increase of dielectric loss is inhibited. The breakdown field strength is increased visibly.
2018, 35(12): 3253-3260.
doi: 10.13801/j.cnki.fhclxb.20180328.001
Abstract:
To improve the mechanical properties of glass fiber reinforced polyphenylene sulfide(PPS) composite laminate, the rigid composite laminate was prepared by thermo-compression lamination using the flexible glass fiber cloth and PPS nonwovens as reinforcement and matrix. Using the mechanical test, XRD, PLM and SEM, the effects of hot pressing temperature and time, content of glass fiber and silane coupling agents on the mechanical properties, crystallinity and microstructure of the composite laminates were explored. The results show that the tensile strength, flexural strength and notched impact strength of the composite laminate with 50wt% glass fiber cloth are 286.0 MPa, 175.0 MPa and 61.6 MPa, respectively, where the composite laminate is hot-pressed at a temperature of 320℃ for 30 min under a pressure of 30 MPa. It is found that using the silane coupling agent KH560 can significantly improve the mechanical properties of composite laminates. The flexural strength reaches to 394.9 MPa and the flexural modulus reaches to 23.6 GPa. Meanwhile, the inter laminar shear strength and notched impact strength are 16.4 MPa and 81.0 MPa, respectively. The mechanical properties of composite laminate have been greatly improved by optimizing the experimental conditions and using the silane coupling agent to treat the surface of glass fiber.
To improve the mechanical properties of glass fiber reinforced polyphenylene sulfide(PPS) composite laminate, the rigid composite laminate was prepared by thermo-compression lamination using the flexible glass fiber cloth and PPS nonwovens as reinforcement and matrix. Using the mechanical test, XRD, PLM and SEM, the effects of hot pressing temperature and time, content of glass fiber and silane coupling agents on the mechanical properties, crystallinity and microstructure of the composite laminates were explored. The results show that the tensile strength, flexural strength and notched impact strength of the composite laminate with 50wt% glass fiber cloth are 286.0 MPa, 175.0 MPa and 61.6 MPa, respectively, where the composite laminate is hot-pressed at a temperature of 320℃ for 30 min under a pressure of 30 MPa. It is found that using the silane coupling agent KH560 can significantly improve the mechanical properties of composite laminates. The flexural strength reaches to 394.9 MPa and the flexural modulus reaches to 23.6 GPa. Meanwhile, the inter laminar shear strength and notched impact strength are 16.4 MPa and 81.0 MPa, respectively. The mechanical properties of composite laminate have been greatly improved by optimizing the experimental conditions and using the silane coupling agent to treat the surface of glass fiber.
2018, 35(12): 3261-3270.
doi: 10.13801/j.cnki.fhclxb.20180319.002
Abstract:
In order to analyze the failure mechanism and energy-absorbing characteristics of carbon fiber reinforced polymer(CFRP) thin-walled C-channels subject to axial compression, 12 groups of T700/MTM28 CFRP thin-walled C-channels specimens with 3 different layer numbers and 4 different ply orientations were fabricated. The failure modes and load-displacement curves were observed, then the effects of layer number and ply orientation on failure modes and energy-absorbing characteristics were further analyzed by investigating the energy-absorbing characteristics indicator, such as peak load, average load, specific energy absorption, load efficiency. The results show that for specimens with 0° plies, the overall instability occurs so it can not absorb crashing energy. For specimens with 0°/90°, ±45° and 45°/90°/-45°/0°plies, the steady progressive failure and local buckling failure modes are presented. The SEA of C-channel specimens with 45°/90°/-45°/0° plies increases with the layer number increasing and it hence has greater potential for energy-absorbing structure design and application.
In order to analyze the failure mechanism and energy-absorbing characteristics of carbon fiber reinforced polymer(CFRP) thin-walled C-channels subject to axial compression, 12 groups of T700/MTM28 CFRP thin-walled C-channels specimens with 3 different layer numbers and 4 different ply orientations were fabricated. The failure modes and load-displacement curves were observed, then the effects of layer number and ply orientation on failure modes and energy-absorbing characteristics were further analyzed by investigating the energy-absorbing characteristics indicator, such as peak load, average load, specific energy absorption, load efficiency. The results show that for specimens with 0° plies, the overall instability occurs so it can not absorb crashing energy. For specimens with 0°/90°, ±45° and 45°/90°/-45°/0°plies, the steady progressive failure and local buckling failure modes are presented. The SEA of C-channel specimens with 45°/90°/-45°/0° plies increases with the layer number increasing and it hence has greater potential for energy-absorbing structure design and application.
2018, 35(12): 3271-3279.
doi: 10.13801/j.cnki.fhclxb.20180314.001
Abstract:
With the rapid improvement of the industry, the air pollution in our country is increasing seriously. As the exterior walls of the buildings are exposed to the air all year round, the various kinds of pollutants attached to the walls are difficult to remove. Therefore, the protective measures of building walls have attracted more and more attention. In this paper, a self-cleaning coating for building wall protection was proposed, which was mainly the compound of the polydimethylsiloxane (PDMS) and hydrophobic SiO2. The prepared coating was sprayed on the building wall and cured at room temperature to form a self-cleaning coating. Through the analysis of the combination mechanism of the coating and building wall, it shows that the coating has a strong adhesion to the wall. Due to the super-hydrophobic property of the coating, the particulate pollutants and the liquid contaminants attached to the wall are easily cleaned through water flow. Furthermore, the experiments also show that the self-cleaning effect of the coating do not change significantly even after five months in the outdoor environment.
With the rapid improvement of the industry, the air pollution in our country is increasing seriously. As the exterior walls of the buildings are exposed to the air all year round, the various kinds of pollutants attached to the walls are difficult to remove. Therefore, the protective measures of building walls have attracted more and more attention. In this paper, a self-cleaning coating for building wall protection was proposed, which was mainly the compound of the polydimethylsiloxane (PDMS) and hydrophobic SiO2. The prepared coating was sprayed on the building wall and cured at room temperature to form a self-cleaning coating. Through the analysis of the combination mechanism of the coating and building wall, it shows that the coating has a strong adhesion to the wall. Due to the super-hydrophobic property of the coating, the particulate pollutants and the liquid contaminants attached to the wall are easily cleaned through water flow. Furthermore, the experiments also show that the self-cleaning effect of the coating do not change significantly even after five months in the outdoor environment.
2018, 35(12): 3280-3287.
doi: 10.13801/j.cnki.fhclxb.20180115.008
Abstract:
The single-shear tensile tests on carbon fiber reinforced plastic (CFRP) laminates and aluminum alloy(AlMg3) dissimilar materials with different textile structures were carried out to study the impact of clearance on the joining between CFRP laminates and AlMg3. The test results show that the CFRP-AlMg3 single-shear connection structure with the same clearance and dissimilar textile structure when the layers of CFRP laminates are given, the compressive stress of the woven fabric CFRP(WO-CFRP) laminates is about 25% higher than that of the unidirectional CFRP(UD-CFRP) laminates. Little difference occurs between the shear stress of their rivets and that of the CFRP laminate for CFRP-AlMg3 single-shear joining structures with the same textile structure and different clearance. At the same time, the extrusion stress analysis of CFRP-AlMg3 single-shear joining structure of the same clearance and different textile structure was also studied. The extrusion stress of WO-CFRP in each stage is higher than that of UD-CFRP high stress about 20% when the other conditions are given. Finally, the effect of clearance on the single-shear joining structure of CFRP-AlMg3 single rivet was studied. The results show that the CFRP laminate has a greater influence on the shear stress when the clearance is 4% of the rivet diameter. When the clearance between the rivet and the hole wall is increased by 0.1 mm and the displacement is 4% of the diameter of the rivet, the compressive stress on the CFRP laminate is reduced by about 17%, whereas the initial damage stress and failure stress on the CFRP laminate are almost none affect and the shear stress on the rivets and the extrusion stress on the aluminum alloy has almost no effect.
The single-shear tensile tests on carbon fiber reinforced plastic (CFRP) laminates and aluminum alloy(AlMg3) dissimilar materials with different textile structures were carried out to study the impact of clearance on the joining between CFRP laminates and AlMg3. The test results show that the CFRP-AlMg3 single-shear connection structure with the same clearance and dissimilar textile structure when the layers of CFRP laminates are given, the compressive stress of the woven fabric CFRP(WO-CFRP) laminates is about 25% higher than that of the unidirectional CFRP(UD-CFRP) laminates. Little difference occurs between the shear stress of their rivets and that of the CFRP laminate for CFRP-AlMg3 single-shear joining structures with the same textile structure and different clearance. At the same time, the extrusion stress analysis of CFRP-AlMg3 single-shear joining structure of the same clearance and different textile structure was also studied. The extrusion stress of WO-CFRP in each stage is higher than that of UD-CFRP high stress about 20% when the other conditions are given. Finally, the effect of clearance on the single-shear joining structure of CFRP-AlMg3 single rivet was studied. The results show that the CFRP laminate has a greater influence on the shear stress when the clearance is 4% of the rivet diameter. When the clearance between the rivet and the hole wall is increased by 0.1 mm and the displacement is 4% of the diameter of the rivet, the compressive stress on the CFRP laminate is reduced by about 17%, whereas the initial damage stress and failure stress on the CFRP laminate are almost none affect and the shear stress on the rivets and the extrusion stress on the aluminum alloy has almost no effect.
2018, 35(12): 3288-3297.
doi: 10.13801/j.cnki.fhclxb.20180319.001
Abstract:
7781/CYCOM 7701 fiberglass/epoxy fabric prepreg was used to fabricate the composite lamina test specimens in medium temperature curing process. These test specimens were categorized into three groups, respectively corresponding to three types of environmental condition of testing:cold temperature dry(CTD), room temperature dry(RTD) and elevated temperature wet (ETW). Under the three types of test environmental condition, the composite lamina mechanical properties of tension, compression, shear, bearing and pull-through were tested. Meanwhile the mechanical properties difference between warp and fill direction of the composite, the existence of notch and impact damage, were properly considered in the test. Based on the test results, the effect of hygro-thermal condition on typical mechanical properties of 7781/CYCOM 7701 fiberglass/epoxy composite lamina was studied. Study indicates:Taking RTD condition as baseline, it rises in CTD condition but descends in ETW condition for each type of strength property. Of these, tensile strength descends 18% to 25%, compressive strength descends 10% to 40%, shear strength descends about 30% to 50%, bearing strength descends about 20%, and pull-through strength descends about 30% in ETW condition; Temperature and moisture absorption condition have a minor effect on tensile and compressive modulus, which is about 10% or below. But they have a major effect on Poisson's ratio and shear modulus. Taking RTD condition as baseline, it descends about 30% and 50% respectively for Poisson's ratio and shear modulus in ETW condition.
7781/CYCOM 7701 fiberglass/epoxy fabric prepreg was used to fabricate the composite lamina test specimens in medium temperature curing process. These test specimens were categorized into three groups, respectively corresponding to three types of environmental condition of testing:cold temperature dry(CTD), room temperature dry(RTD) and elevated temperature wet (ETW). Under the three types of test environmental condition, the composite lamina mechanical properties of tension, compression, shear, bearing and pull-through were tested. Meanwhile the mechanical properties difference between warp and fill direction of the composite, the existence of notch and impact damage, were properly considered in the test. Based on the test results, the effect of hygro-thermal condition on typical mechanical properties of 7781/CYCOM 7701 fiberglass/epoxy composite lamina was studied. Study indicates:Taking RTD condition as baseline, it rises in CTD condition but descends in ETW condition for each type of strength property. Of these, tensile strength descends 18% to 25%, compressive strength descends 10% to 40%, shear strength descends about 30% to 50%, bearing strength descends about 20%, and pull-through strength descends about 30% in ETW condition; Temperature and moisture absorption condition have a minor effect on tensile and compressive modulus, which is about 10% or below. But they have a major effect on Poisson's ratio and shear modulus. Taking RTD condition as baseline, it descends about 30% and 50% respectively for Poisson's ratio and shear modulus in ETW condition.
2018, 35(12): 3298-3303.
doi: 10.13801/j.cnki.fhclxb.20180319.005
Abstract:
Current studies show that nature hail is less dense and tougher than clear ice, and cotton fibers are required to add to the simulated hail ice during the hail impact test on aeronautic structure saccording to ASTM F320-10, so as to accurately recurrent the mechanism properties of nature hail. To obtain the natural hail impact damage on composite skins, cotton fibers reinforced simulated hail ice impact tests on the rigid surface and composite panels were tested with the 80 mm caliber gas gun. The results show almost no influence of the freezing temperature on impact load peak. The elastic module and break strength of the simulated hail ice are of distinct enhancement, with the addition of cotton fibers. Delamination areas of composite panels are impacted by cotton-simulated hail ice vary with the velocity and stacking sequences, while no delamination is found for clear-simulated hail ice.
Current studies show that nature hail is less dense and tougher than clear ice, and cotton fibers are required to add to the simulated hail ice during the hail impact test on aeronautic structure saccording to ASTM F320-10, so as to accurately recurrent the mechanism properties of nature hail. To obtain the natural hail impact damage on composite skins, cotton fibers reinforced simulated hail ice impact tests on the rigid surface and composite panels were tested with the 80 mm caliber gas gun. The results show almost no influence of the freezing temperature on impact load peak. The elastic module and break strength of the simulated hail ice are of distinct enhancement, with the addition of cotton fibers. Delamination areas of composite panels are impacted by cotton-simulated hail ice vary with the velocity and stacking sequences, while no delamination is found for clear-simulated hail ice.
2018, 35(12): 3304-3312.
doi: 10.13801/j.cnki.fhclxb.20180207.002
Abstract:
The accelerated aging test in lab and natural exposure test on ship in the marine environment for G827/3234 composite were carried out.By using the universal testing machine, optical microscope, SEM, DMA, FTIR and so on, the surface and fracture morphology, mechanical property and composition of G827/3234 composite were observed and measured before and after aging.The regression analysis method for the strength median curve of G827/3234 under the natural aging condition was improved, and the equivalent accelerated relationship between the accelerated aging and natural aging was obtained based on the strength retention rate and it was verified. The results show that, after one month of accelerated aging, the flexural strength and flexural modulus of G827/3234 composite are decreased by 1.43% and 4.45%, the decline of interlaminar shear strength is 8.80%, the anti-fatigue property is essentially the same, the glass transition temperature is decreased by 6.2℃, the in ternal friction increases and the storage modulus is decreased by about 5 GPa.The mechanism in the accelerated aging and the strength median equation in the natural aging under the marine environment are given out.The equivalent coefficient of accelerated aging to natural aging is 4.52.The aging mechanism of the two are basically the same and the coefficient is proved to be effective and available.
The accelerated aging test in lab and natural exposure test on ship in the marine environment for G827/3234 composite were carried out.By using the universal testing machine, optical microscope, SEM, DMA, FTIR and so on, the surface and fracture morphology, mechanical property and composition of G827/3234 composite were observed and measured before and after aging.The regression analysis method for the strength median curve of G827/3234 under the natural aging condition was improved, and the equivalent accelerated relationship between the accelerated aging and natural aging was obtained based on the strength retention rate and it was verified. The results show that, after one month of accelerated aging, the flexural strength and flexural modulus of G827/3234 composite are decreased by 1.43% and 4.45%, the decline of interlaminar shear strength is 8.80%, the anti-fatigue property is essentially the same, the glass transition temperature is decreased by 6.2℃, the in ternal friction increases and the storage modulus is decreased by about 5 GPa.The mechanism in the accelerated aging and the strength median equation in the natural aging under the marine environment are given out.The equivalent coefficient of accelerated aging to natural aging is 4.52.The aging mechanism of the two are basically the same and the coefficient is proved to be effective and available.
2018, 35(12): 3313-3323.
doi: 10.13801/j.cnki.fhclxb.20180319.004
Abstract:
In order to investigate the influences of depth of steel fiber reinforced concrete layer, steel fiber volume fraction and ratio of basalt fiber reinforced polymer(BFRP) bars on flexural capacity of high-strength concrete beams reinforced with BFRP bars and steel fiber, 11 specimens were cast and tested. The results indicate that there are 3 failure modes of high-strength concrete beams reinforced with BFRP bars and steel fiber:concrete crush, BFRP bars rupture and balance failure. The steel fiber reinforced concrete layer and steel fiber volume fraction have various influences on flexural capacity of specimens. When the BFRP reinforcement ratio is 0.77%, with the addition of steel fiber (the volume fraction was 1.0%), the flexural capacity can be increased by 22.7%; for the specimen with steel fiber volume fraction of 1.0% and steel fiber reinforced concrete layer of 0.57 times of the total depth of beam, the flexural capacity is 86.7% of that of the fully steel fiber reinforced specimen. Increasing BFRP reinforcement ratio is an effective way to improve the flexural capacity of BFRP bar and steel fiber reinforced beams, the flexural capacity of the specimen with BFRP reinforcement ratio of 1.65% is 39.4% higher than that of the specimen with BFRP reinforcement ratio of 0.56%. Based on the experimental and theoretical analysis, a calculating method, which can be used for evaluating the failure mode and flexural capacity of high-strength concrete beams reinforced with BFRP bars and steel fiber, was proposed. The calculated values have good agreement with test results.
In order to investigate the influences of depth of steel fiber reinforced concrete layer, steel fiber volume fraction and ratio of basalt fiber reinforced polymer(BFRP) bars on flexural capacity of high-strength concrete beams reinforced with BFRP bars and steel fiber, 11 specimens were cast and tested. The results indicate that there are 3 failure modes of high-strength concrete beams reinforced with BFRP bars and steel fiber:concrete crush, BFRP bars rupture and balance failure. The steel fiber reinforced concrete layer and steel fiber volume fraction have various influences on flexural capacity of specimens. When the BFRP reinforcement ratio is 0.77%, with the addition of steel fiber (the volume fraction was 1.0%), the flexural capacity can be increased by 22.7%; for the specimen with steel fiber volume fraction of 1.0% and steel fiber reinforced concrete layer of 0.57 times of the total depth of beam, the flexural capacity is 86.7% of that of the fully steel fiber reinforced specimen. Increasing BFRP reinforcement ratio is an effective way to improve the flexural capacity of BFRP bar and steel fiber reinforced beams, the flexural capacity of the specimen with BFRP reinforcement ratio of 1.65% is 39.4% higher than that of the specimen with BFRP reinforcement ratio of 0.56%. Based on the experimental and theoretical analysis, a calculating method, which can be used for evaluating the failure mode and flexural capacity of high-strength concrete beams reinforced with BFRP bars and steel fiber, was proposed. The calculated values have good agreement with test results.
2018, 35(12): 3324-3330.
doi: 10.13801/j.cnki.fhclxb.20180209.005
Abstract:
Glass fiber reinforced plastic (GFRP) thin-walled tubes have excellent erosion resistant capability and highly feasible design ability, and thus have been shown broad applications in oil and construction industrials. In this paper, we utilized Hopkinson pressure bar(SHPB) system to explore the impact resistance, deformation and failure mode, and dynamic response of GFRP thin-walled tube with different wall thicknesses and shapes. Experimental results prove that the circular tubes possess higher dynamic compression modulus and better impact resistance while the square tubes exhibit more superior energy absorption property. In addition, those performances can be improved with thicker wall. Compared to other traditional aluminum alloy tubes, GFRP tubes show better energy absorption capability. Overall, this study provides significant insights for structural optimization of GFRP tubes and design guidelines on engineer applications.
Glass fiber reinforced plastic (GFRP) thin-walled tubes have excellent erosion resistant capability and highly feasible design ability, and thus have been shown broad applications in oil and construction industrials. In this paper, we utilized Hopkinson pressure bar(SHPB) system to explore the impact resistance, deformation and failure mode, and dynamic response of GFRP thin-walled tube with different wall thicknesses and shapes. Experimental results prove that the circular tubes possess higher dynamic compression modulus and better impact resistance while the square tubes exhibit more superior energy absorption property. In addition, those performances can be improved with thicker wall. Compared to other traditional aluminum alloy tubes, GFRP tubes show better energy absorption capability. Overall, this study provides significant insights for structural optimization of GFRP tubes and design guidelines on engineer applications.
2018, 35(12): 3331-3341.
doi: 10.13801/j.cnki.fhclxb.20180206.001
Abstract:
The shear performance of the concrete cable ducts reinforced with glass fiber reinforced polymer (GFRP) bars was investigated. An appropriate calculation and design method was proposed based on the different countries' design codes. The crack growth mode, the distributions of the strain on the cross sections and the load-deflection curves were obtained by the shearing test on several small and full size specimens. The failure mechanism was revealed. The experimental results show that the shear bearing capacity increases with the increase of area-stirrup ratio and the longitudinal reinforcement ratio. The effect of stirrup on the shear bearing capacity can be neglected if the stirrup ratio is too small. The specimens still have relatively high shear bearing capacity under a small reinforcement ratio of longitudinal reinforcement. The proposed formula can preferably fulfill the requirements of security and economy for designing or fabricating the concrete cable ducts.
The shear performance of the concrete cable ducts reinforced with glass fiber reinforced polymer (GFRP) bars was investigated. An appropriate calculation and design method was proposed based on the different countries' design codes. The crack growth mode, the distributions of the strain on the cross sections and the load-deflection curves were obtained by the shearing test on several small and full size specimens. The failure mechanism was revealed. The experimental results show that the shear bearing capacity increases with the increase of area-stirrup ratio and the longitudinal reinforcement ratio. The effect of stirrup on the shear bearing capacity can be neglected if the stirrup ratio is too small. The specimens still have relatively high shear bearing capacity under a small reinforcement ratio of longitudinal reinforcement. The proposed formula can preferably fulfill the requirements of security and economy for designing or fabricating the concrete cable ducts.
2018, 35(12): 3342-3349.
doi: 10.13801/j.cnki.fhclxb.20180207.004
Abstract:
The resin flow in composite and metal stitched sandwich structure during resin transfer molding (RTM) process was simulated. First, the permeability of fabric and holes of stitched sandwich structure was obtained respectively through the experiment and numerical calculation. Then, the two-dimensional and three-dimensional simplified models that can reflect the flow in holes were established to simulate the resin flow in RTM process. The influence of different process parameters on molding process was discussed. Finally, a molding experiment was made to verify the simulation results. When the ratio of the suture diameter to the hole diameter is within 0.3-0.8, the permeability of the holes decreases with the increasing diameter of the suture. The difference between the permeability of the fabric and the holes is two orders of magnitude. Dry spots are easily produced in holes, so the inlets and outlets should be set to ensure the resin flow through the holes from one side of the core layer to the other side. The area with no defects increases with the increasing injection pressure and decreases with the increasing holes pacing and thickness of the core layer. The unidirectional slotting along each row of holes on core layer can improve the infiltration quality in the holes. When the inlet is a line, the flow of the resin is good. And when the inlet is a point, setting the inlet to the corner can reduce the dry spots on the surface.
The resin flow in composite and metal stitched sandwich structure during resin transfer molding (RTM) process was simulated. First, the permeability of fabric and holes of stitched sandwich structure was obtained respectively through the experiment and numerical calculation. Then, the two-dimensional and three-dimensional simplified models that can reflect the flow in holes were established to simulate the resin flow in RTM process. The influence of different process parameters on molding process was discussed. Finally, a molding experiment was made to verify the simulation results. When the ratio of the suture diameter to the hole diameter is within 0.3-0.8, the permeability of the holes decreases with the increasing diameter of the suture. The difference between the permeability of the fabric and the holes is two orders of magnitude. Dry spots are easily produced in holes, so the inlets and outlets should be set to ensure the resin flow through the holes from one side of the core layer to the other side. The area with no defects increases with the increasing injection pressure and decreases with the increasing holes pacing and thickness of the core layer. The unidirectional slotting along each row of holes on core layer can improve the infiltration quality in the holes. When the inlet is a line, the flow of the resin is good. And when the inlet is a point, setting the inlet to the corner can reduce the dry spots on the surface.
2018, 35(12): 3350-3359.
doi: 10.13801/j.cnki.fhclxb.20180211.003
Abstract:
To obtain the mesoscopic model of composites, an approach on parameter identification of composite components with high accuracy was proposed. Based on the finite element model of micro unidirectional carbon reinforced polymer composite (CFRP), the sensitivity matrix of static displacements with respect to elastic parameters of composite components was formulated and the objective function was defined as the 2-norm of differences between the measured and calculated data on displacements. In order to overcome the problem caused by the magnitude differences between identified variables, the relative sensitivity was chosen to improve the precision and efficiency of parameter identification. The fiber uniform distributed composite plane model and fiber random distributed 3D model were employed respectively to verify the validity and accuracy of the components parameter identification methods. In addition, the influences of number of measuring points and measurement errors on the parameter identification method were revealed. Results show that the identification method of components parameters of composite materials in the presented study is stable considering the influences of number of measuring points and measurement errors.
To obtain the mesoscopic model of composites, an approach on parameter identification of composite components with high accuracy was proposed. Based on the finite element model of micro unidirectional carbon reinforced polymer composite (CFRP), the sensitivity matrix of static displacements with respect to elastic parameters of composite components was formulated and the objective function was defined as the 2-norm of differences between the measured and calculated data on displacements. In order to overcome the problem caused by the magnitude differences between identified variables, the relative sensitivity was chosen to improve the precision and efficiency of parameter identification. The fiber uniform distributed composite plane model and fiber random distributed 3D model were employed respectively to verify the validity and accuracy of the components parameter identification methods. In addition, the influences of number of measuring points and measurement errors on the parameter identification method were revealed. Results show that the identification method of components parameters of composite materials in the presented study is stable considering the influences of number of measuring points and measurement errors.
2018, 35(12): 3360-3367.
doi: 10.13801/j.cnki.fhclxb.20180315.001
Abstract:
Hole edge stress is an important basis for strength check in composite joints design, and bolt-hole clearance has obvious influence on it. For the single-lap joint structure of quasi isotropic laminated plates, the elastic foundation shear beam model was adopted and the analytical solution of the shank deflection was derived. The distribution of the bearing load along the thickness direction of the laminates was given. On this basis, the Persson model of the bearing stress distribution at the hole edge was extended to the three-dimensional case, the stress distribution and the stress concentration factor at the hole edge were obtained. The theoretical results were verified by the three-dimensional detailed finite element method. Finally, the influence of the clearance, laminates thickness and external load on stress concentration factor was analyzed by theoretical method.
Hole edge stress is an important basis for strength check in composite joints design, and bolt-hole clearance has obvious influence on it. For the single-lap joint structure of quasi isotropic laminated plates, the elastic foundation shear beam model was adopted and the analytical solution of the shank deflection was derived. The distribution of the bearing load along the thickness direction of the laminates was given. On this basis, the Persson model of the bearing stress distribution at the hole edge was extended to the three-dimensional case, the stress distribution and the stress concentration factor at the hole edge were obtained. The theoretical results were verified by the three-dimensional detailed finite element method. Finally, the influence of the clearance, laminates thickness and external load on stress concentration factor was analyzed by theoretical method.
2018, 35(12): 3368-3376.
doi: 10.13801/j.cnki.fhclxb.20180317.001
Abstract:
The carbon fiber composite laminates were manufactured in different curing pressures by autoclave process. The relationship between the ultrasonic phased array C scanning image and the defects of microstructure was analyzed, and the correlations among curing pressure, voids and mechanical properties were studied. The results indicate that ultrasonic C scanning image can be used to characterize the content of voids. In this experiment condition, the curing pressure increases from 0 MPa to 0.6 MPa, the porosity decreases by 96.7%, and the tensile strength(TS) and interlaminar shear strength(ILSS) increase by 56.1% and 68.8%, respectively. On this basis, the C scanning images of composite laminate in different curing pressures were processed, and the forming quality index was defined. Thus, the quantitative characterization of voids based on C scanning images was realized. Finally, through mathematical fitting of the results of voids detection, mechanical properties test and image quantitative evaluation, a mathematical model(CPDMP model) among curing pressure-defects-mechanical properties based on image processing was established. In addition, the forming quality index threshold of 81%, the acceptable porosity of more than 1.1% and the corresponding curing pressure of more than 0.35 MPa were presented.
The carbon fiber composite laminates were manufactured in different curing pressures by autoclave process. The relationship between the ultrasonic phased array C scanning image and the defects of microstructure was analyzed, and the correlations among curing pressure, voids and mechanical properties were studied. The results indicate that ultrasonic C scanning image can be used to characterize the content of voids. In this experiment condition, the curing pressure increases from 0 MPa to 0.6 MPa, the porosity decreases by 96.7%, and the tensile strength(TS) and interlaminar shear strength(ILSS) increase by 56.1% and 68.8%, respectively. On this basis, the C scanning images of composite laminate in different curing pressures were processed, and the forming quality index was defined. Thus, the quantitative characterization of voids based on C scanning images was realized. Finally, through mathematical fitting of the results of voids detection, mechanical properties test and image quantitative evaluation, a mathematical model(CPDMP model) among curing pressure-defects-mechanical properties based on image processing was established. In addition, the forming quality index threshold of 81%, the acceptable porosity of more than 1.1% and the corresponding curing pressure of more than 0.35 MPa were presented.
2018, 35(12): 3377-3385.
doi: 10.13801/j.cnki.fhclxb.20180408.002
Abstract:
Bolted repair is a preferable repair method in damaged composite structure, especially in battle damage repair. However, the repair design process is complex, and it is difficult to meet the need for rapid sizing. A parametrical modeling and analysis tool was developed for design of composite bolted repair with penetrating damage, using VB.NET combined with p-version finite element method. The tool allows the user to create the joint geometry through a menu-driven interface and then to generate a customized mesh. Boundary conditions, bolt pattern, bolt diameter, applied load and material properties could also be set. The model was solved automatically, and based on the analysis results, the load transfer ratio, bolt load and the stress around the critical hole are offered by the analysis tool. Finite fracture mechanics model is used to predict the failure load and failure mode of the repaired joints. A case study was shown to demonstrate the usefulness of the tool.
Bolted repair is a preferable repair method in damaged composite structure, especially in battle damage repair. However, the repair design process is complex, and it is difficult to meet the need for rapid sizing. A parametrical modeling and analysis tool was developed for design of composite bolted repair with penetrating damage, using VB.NET combined with p-version finite element method. The tool allows the user to create the joint geometry through a menu-driven interface and then to generate a customized mesh. Boundary conditions, bolt pattern, bolt diameter, applied load and material properties could also be set. The model was solved automatically, and based on the analysis results, the load transfer ratio, bolt load and the stress around the critical hole are offered by the analysis tool. Finite fracture mechanics model is used to predict the failure load and failure mode of the repaired joints. A case study was shown to demonstrate the usefulness of the tool.
2018, 35(12): 3386-3392.
doi: 10.13801/j.cnki.fhclxb.20180319.006
Abstract:
A dual-scale unsaturated flow model was established by introducing the sink function, and the finite element/control volume method was employed to simulate numerically 2-dimensional radial flow in liquid composite molding(LCM) processes under the conditions of constant pressure and constant flow. The pressure distribution and time-varying resin flow front were obtained and compared with the results of theoretical prediction of single-scale model. The simulation results show that during unsaturated flow process, pressure and pressure gradient drop significantly in the unsaturated region; the length of unsaturated region increases firstly and thenkeeps constant, when the saturated flow front reaches the exit, the length begins to decrease; when there is a difference in permeability of two principal direction, the length of unsaturation region in the direction of higher permeability is longer and the time to completely infiltrate the fabric depends on the smaller permeability. The research results have significance to reasonably predict the pressure distribution and the infiltration of the fiber preform in the resin filling process.
A dual-scale unsaturated flow model was established by introducing the sink function, and the finite element/control volume method was employed to simulate numerically 2-dimensional radial flow in liquid composite molding(LCM) processes under the conditions of constant pressure and constant flow. The pressure distribution and time-varying resin flow front were obtained and compared with the results of theoretical prediction of single-scale model. The simulation results show that during unsaturated flow process, pressure and pressure gradient drop significantly in the unsaturated region; the length of unsaturated region increases firstly and thenkeeps constant, when the saturated flow front reaches the exit, the length begins to decrease; when there is a difference in permeability of two principal direction, the length of unsaturation region in the direction of higher permeability is longer and the time to completely infiltrate the fabric depends on the smaller permeability. The research results have significance to reasonably predict the pressure distribution and the infiltration of the fiber preform in the resin filling process.
2018, 35(12): 3393-3399.
doi: 10.13801/j.cnki.fhclxb.20180328.002
Abstract:
Using phenolic resin as binding agent, samples with sintered alumina (100wt%), fused corundum (100wt%) and sintered alumina (50wt%) mixed with fused corundum (50wt%) were prepared, respectively, then the samples were sintered at 1 500℃ and 1 600℃ under flowing nitrogen, respectively. Sintered samples were characterized by XRD, SEM and EDAS. The results show that γ-AlON(Al5O6N) and 12H polytype(Al6O3N4) form in samples sintered at 1 500℃, while γ-AlON(Al5O6N), 21R polytype(Al7O3N5) and 16H polytype(Al8O3N6) form in samples sintered at 1 600℃. The content of AlON increases remarkably in samples sintered at 1 600℃ compared with samples sintered at 1 500℃. At the same sintering temperature, AlON contents in samples prepared with sintered alumina (50wt%) mixed with fused corundum (50wt%), fused corundum (100wt%) and sintered alumina (100wt%) decrease inturn. The formation mechanism of AlON was studied and the reaction model of alumina powder and carbonis was presented.
Using phenolic resin as binding agent, samples with sintered alumina (100wt%), fused corundum (100wt%) and sintered alumina (50wt%) mixed with fused corundum (50wt%) were prepared, respectively, then the samples were sintered at 1 500℃ and 1 600℃ under flowing nitrogen, respectively. Sintered samples were characterized by XRD, SEM and EDAS. The results show that γ-AlON(Al5O6N) and 12H polytype(Al6O3N4) form in samples sintered at 1 500℃, while γ-AlON(Al5O6N), 21R polytype(Al7O3N5) and 16H polytype(Al8O3N6) form in samples sintered at 1 600℃. The content of AlON increases remarkably in samples sintered at 1 600℃ compared with samples sintered at 1 500℃. At the same sintering temperature, AlON contents in samples prepared with sintered alumina (50wt%) mixed with fused corundum (50wt%), fused corundum (100wt%) and sintered alumina (100wt%) decrease inturn. The formation mechanism of AlON was studied and the reaction model of alumina powder and carbonis was presented.
2018, 35(12): 3400-3406.
doi: 10.13801/j.cnki.fhclxb.20180209.003
Abstract:
The slippage stress of micro-interface was analyzed by the microstructure and two-scale interface characteristics in two-scale interface multiphase ceramics. First, the micro-average stress field of the two-scale interface multiphase ceramics was calculated based on the macroscopic, mesoscopic and nanoscopic elastic properties of multiphase ceramics. Interfacial strain model was proposed on the basis of continuity of displacement and stress in nano-interface, and then, the displacement function of fiber and matrix in the vicinity of nano-interface was calculated. Considering the proportional relationship between interfacial strain and interfacial elastic modulus, shear stress under the conditions of external load transfer to the micro-interface was calculated according to nano-interface properties and fiber distribution. At last, combined with yield shear stress of multiphase ceramics which was determined by the indentation test of multiphase ceramics, the theoretical formula of micro-interface slippage stress of multiphase ceramics was obtained. The quantitative results show that the smaller the interfacial elastic modulus and interfacial Poisson's ratio, the easier the interface is to slip, and the easier the plastic deformation of multiphase ceramics.
The slippage stress of micro-interface was analyzed by the microstructure and two-scale interface characteristics in two-scale interface multiphase ceramics. First, the micro-average stress field of the two-scale interface multiphase ceramics was calculated based on the macroscopic, mesoscopic and nanoscopic elastic properties of multiphase ceramics. Interfacial strain model was proposed on the basis of continuity of displacement and stress in nano-interface, and then, the displacement function of fiber and matrix in the vicinity of nano-interface was calculated. Considering the proportional relationship between interfacial strain and interfacial elastic modulus, shear stress under the conditions of external load transfer to the micro-interface was calculated according to nano-interface properties and fiber distribution. At last, combined with yield shear stress of multiphase ceramics which was determined by the indentation test of multiphase ceramics, the theoretical formula of micro-interface slippage stress of multiphase ceramics was obtained. The quantitative results show that the smaller the interfacial elastic modulus and interfacial Poisson's ratio, the easier the interface is to slip, and the easier the plastic deformation of multiphase ceramics.
2018, 35(12): 3407-3414.
doi: 10.13801/j.cnki.fhclxb.20180319.007
Abstract:
The high-cycle bending fatigue experiment of composite cantilever beam was designed by employing the first-order bending resonance phenomenon. Based on the study of the local fatigue damage model and cycle jump technique, the Matlab-based semi-analytical algorithm for high-cycle bending fatigue analysis of the composite cantilever beam was developed to substitute for traditional metal fatigue theory. On the other hand, on the basis of UMAT subroutine, the fatigue damage model and cycle jump technology were successfully applied in the commercial software ABAQUS. The semi-analytical method and the finite element method were separately employed to analyze the progressive damage accumulation and failure process for the high-cycle bending fatigue, out of which high-cycle bending fatigue life was predicted. The numerical results are in agreement with the experimental data.
The high-cycle bending fatigue experiment of composite cantilever beam was designed by employing the first-order bending resonance phenomenon. Based on the study of the local fatigue damage model and cycle jump technique, the Matlab-based semi-analytical algorithm for high-cycle bending fatigue analysis of the composite cantilever beam was developed to substitute for traditional metal fatigue theory. On the other hand, on the basis of UMAT subroutine, the fatigue damage model and cycle jump technology were successfully applied in the commercial software ABAQUS. The semi-analytical method and the finite element method were separately employed to analyze the progressive damage accumulation and failure process for the high-cycle bending fatigue, out of which high-cycle bending fatigue life was predicted. The numerical results are in agreement with the experimental data.
2018, 35(12): 3415-3422.
doi: 10.13801/j.cnki.fhclxb.20180322.001
Abstract:
The stress transfer through the multilayer interphase in ceramic matrix composites was simulated by finite element method. The microstructure of ceramic matrix composites(CMCs) was modeled by a cylinder unit-cell, the sub-layers of interphase were created according to their real thickness within the model. The interfaces between interphase sub-layers, interphase and fibers, interphase and matrix were all assumed to be bonded perfectly. Different material properties were defined for interphase sub-layers, and the axis-symmetry finite element method was applied to analysis the stress. After all, a simulation method for stress transfer through the multilayer interphase was developed. The simulation results for stress transfer within pyolytic carbon(PyC) interphase of different thickness, interphase of different constituents (PyC and SiC), and interphase of different structure ((PyC/SiC) and (SiC/PyC)) were compared. It can be seen from the distribution of stress along fiber and radial direction that the stress transfer and failure mode of interphase in CMCs can be controlled and optimized by rational allocation of the structure, constituent and thickness of multilayer interphase.
The stress transfer through the multilayer interphase in ceramic matrix composites was simulated by finite element method. The microstructure of ceramic matrix composites(CMCs) was modeled by a cylinder unit-cell, the sub-layers of interphase were created according to their real thickness within the model. The interfaces between interphase sub-layers, interphase and fibers, interphase and matrix were all assumed to be bonded perfectly. Different material properties were defined for interphase sub-layers, and the axis-symmetry finite element method was applied to analysis the stress. After all, a simulation method for stress transfer through the multilayer interphase was developed. The simulation results for stress transfer within pyolytic carbon(PyC) interphase of different thickness, interphase of different constituents (PyC and SiC), and interphase of different structure ((PyC/SiC) and (SiC/PyC)) were compared. It can be seen from the distribution of stress along fiber and radial direction that the stress transfer and failure mode of interphase in CMCs can be controlled and optimized by rational allocation of the structure, constituent and thickness of multilayer interphase.
2018, 35(12): 3423-3432.
doi: 10.13801/j.cnki.fhclxb.20180209.002
Abstract:
Based on the meso-structure of 2D braided C/SiC composites, two micromechanical models were presented to simulate the progressive damage behavior of 2D braided C/SiC composites that subjected to off-axial tension. The equivalent elastic constants and strength of the carbon fiber/pyrolytic carbon interface/SiC matrix model were calculated by the finite element method and then applied to the yarn/SiC matrix model. The Tsai-Wu failure criteria that considers different damage modes was utilized to set up the progressive damage model, and the stress-strain relation of 2D braided C/SiC composites was simulated. The damage model explains the damage evolution of 2D braided C/SiC composites tows in the complex stress state. The numerical results accurately capture the experimental data, which demonstrates the validity of the proposed analytical model. And this model provides a method to predict the mechanical properties of 2D braided C/SiC composites.
Based on the meso-structure of 2D braided C/SiC composites, two micromechanical models were presented to simulate the progressive damage behavior of 2D braided C/SiC composites that subjected to off-axial tension. The equivalent elastic constants and strength of the carbon fiber/pyrolytic carbon interface/SiC matrix model were calculated by the finite element method and then applied to the yarn/SiC matrix model. The Tsai-Wu failure criteria that considers different damage modes was utilized to set up the progressive damage model, and the stress-strain relation of 2D braided C/SiC composites was simulated. The damage model explains the damage evolution of 2D braided C/SiC composites tows in the complex stress state. The numerical results accurately capture the experimental data, which demonstrates the validity of the proposed analytical model. And this model provides a method to predict the mechanical properties of 2D braided C/SiC composites.
2018, 35(12): 3433-3440.
doi: 10.13801/j.cnki.fhclxb.20180209.001
Abstract:
Basalt fibers (BF) were modified by physical coating method with three different surfactants. The surface functional groups, hydrophilicity and micro-morphology of raw BF and as-prepared modified basalt fibers (MBF) were characterized by FTIR spectra, optical contact angle analysis and SEM, respectively.Furthermore, the immobilization rate and residual immobilization rate of BF and MBF samples were calculated and biofilm development of BF and MBF were observed by optical microscope and SEM to assess the effects on the immobilization effect of MBF. The results show that the hydrophilicity and dispersion of MBF are efficiently improved in water. Among the modified basalt fibers, the modified basalt fiber modified with hexadecyl trimethyl ammonium chloride (CTAC) (MBF-C) has optimal hydrophilicity and dispersion. The contact angle decreases from 133.57° (BF) to 62.52° (MBF-C). The microorganism immobilization test results illustrate that all three modifications are conductive to increase the microorganism loading and adhesion strength of BF. In addition, the MBF-C possesses an optimal immobilization effect that the immobilization rate and residual immobilization rate reach up to 256.25% and 41.28%, respectively.
Basalt fibers (BF) were modified by physical coating method with three different surfactants. The surface functional groups, hydrophilicity and micro-morphology of raw BF and as-prepared modified basalt fibers (MBF) were characterized by FTIR spectra, optical contact angle analysis and SEM, respectively.Furthermore, the immobilization rate and residual immobilization rate of BF and MBF samples were calculated and biofilm development of BF and MBF were observed by optical microscope and SEM to assess the effects on the immobilization effect of MBF. The results show that the hydrophilicity and dispersion of MBF are efficiently improved in water. Among the modified basalt fibers, the modified basalt fiber modified with hexadecyl trimethyl ammonium chloride (CTAC) (MBF-C) has optimal hydrophilicity and dispersion. The contact angle decreases from 133.57° (BF) to 62.52° (MBF-C). The microorganism immobilization test results illustrate that all three modifications are conductive to increase the microorganism loading and adhesion strength of BF. In addition, the MBF-C possesses an optimal immobilization effect that the immobilization rate and residual immobilization rate reach up to 256.25% and 41.28%, respectively.
2018, 35(12): 3441-3449.
doi: 10.13801/j.cnki.fhclxb.20180516.003
Abstract:
The effects of replacement ratio of recycled brick aggregate (RBA), fiber volume content and fiber types on the compressive strength and elastic modulus of steel-polyolefin hybrid fiber reinforced recycled brick aggregates concrete (HF/RBAC) were investigated through compressive strength and modulus test. According to the XRD and X-CT image of RBA, the reaction theory of active components of RBA with cement hydration products and the energy balance, the failure mechanism and fiber reinforced mechanism of HF/RBAC were investigated. The results show that, when all of natural aggregate(NA) was replaced by RBA, the percentage decrements in the cubic compressive strength, prism compressive strength and elastic modulus of HF/RBAC are found to be 36.72%, 24.95% and 43.53%, respectively. When the value of volume content of steel-polyolefin hybrid fiber is 1.5%, the percentage increments in the cubic compressive strength, prism compressive strength and elastic modulus of HF/RBAC are found to be 20.51%, 30.33% and 35.84%, respectively. Finally, the calculation method of compressive strength and elastic modulus of HF/RBAC was proposed. It had taken into account some factors, such as the crushed values, replacement ratio of recycled brick aggregate, the fiber volume content and fiber type.
The effects of replacement ratio of recycled brick aggregate (RBA), fiber volume content and fiber types on the compressive strength and elastic modulus of steel-polyolefin hybrid fiber reinforced recycled brick aggregates concrete (HF/RBAC) were investigated through compressive strength and modulus test. According to the XRD and X-CT image of RBA, the reaction theory of active components of RBA with cement hydration products and the energy balance, the failure mechanism and fiber reinforced mechanism of HF/RBAC were investigated. The results show that, when all of natural aggregate(NA) was replaced by RBA, the percentage decrements in the cubic compressive strength, prism compressive strength and elastic modulus of HF/RBAC are found to be 36.72%, 24.95% and 43.53%, respectively. When the value of volume content of steel-polyolefin hybrid fiber is 1.5%, the percentage increments in the cubic compressive strength, prism compressive strength and elastic modulus of HF/RBAC are found to be 20.51%, 30.33% and 35.84%, respectively. Finally, the calculation method of compressive strength and elastic modulus of HF/RBAC was proposed. It had taken into account some factors, such as the crushed values, replacement ratio of recycled brick aggregate, the fiber volume content and fiber type.
2018, 35(12): 3450-3457.
doi: 10.13801/j.cnki.fhclxb.20180209.006
Abstract:
Agar films, κ-carrageenan films and their blend films were prepared by thermal casting method, and 0.8%(0.8 g/100 g total dry matter) TiO2 powders were added into the blend films to obtain TiO2/agar-κ-carrageenan composite films. The four kinds films were tested by SEM, XRD, mechanical properties, light transmittance, opacity and resistance to water. The results show that the mechanical properties, light transmittance, opacity and resistance to water of agar-κ-carrageenan films are between agar films and κ-carrageenan films. Agar and κ-carrageenan have the good blending and the intermolecular forces are formed in the blend films. The tensile strength of TiO2/agar-κ-carrageenan composite films is 45.44 MPa which is higher than that of the other three films and increases 46.30% compared with the tensile strength (31.06 MPa) of agar-κ-carrageenan films. But the breaking elongation is 15.73% which is smaller than that of the other three films. The strong interaction forces are formed between matrix molecule of composite films and TiO2. So the tensile strength of the composite films is enhanced. At the same wavelength, the light transmittance of TiO2/agar-κ-carrageenan composite films is the lowest. In the ultraviolet region of 200-400 nm, the light transmittance of TiO2/agar-κ-carrageenan composite films is obviously lower than that of the other three films. TiO2/agar-κ-carrageenan composite films have a significant shielding effect on UV light. But at the 600 nm wavelength, the opacity of TiO2/agar-κ-carrageenan composite films is 0.96 which is the highest of the four films. The resistance to water of TiO2/agar-κ-carrageenan composite films is higher than agar-κ-carrageenan films.
Agar films, κ-carrageenan films and their blend films were prepared by thermal casting method, and 0.8%(0.8 g/100 g total dry matter) TiO2 powders were added into the blend films to obtain TiO2/agar-κ-carrageenan composite films. The four kinds films were tested by SEM, XRD, mechanical properties, light transmittance, opacity and resistance to water. The results show that the mechanical properties, light transmittance, opacity and resistance to water of agar-κ-carrageenan films are between agar films and κ-carrageenan films. Agar and κ-carrageenan have the good blending and the intermolecular forces are formed in the blend films. The tensile strength of TiO2/agar-κ-carrageenan composite films is 45.44 MPa which is higher than that of the other three films and increases 46.30% compared with the tensile strength (31.06 MPa) of agar-κ-carrageenan films. But the breaking elongation is 15.73% which is smaller than that of the other three films. The strong interaction forces are formed between matrix molecule of composite films and TiO2. So the tensile strength of the composite films is enhanced. At the same wavelength, the light transmittance of TiO2/agar-κ-carrageenan composite films is the lowest. In the ultraviolet region of 200-400 nm, the light transmittance of TiO2/agar-κ-carrageenan composite films is obviously lower than that of the other three films. TiO2/agar-κ-carrageenan composite films have a significant shielding effect on UV light. But at the 600 nm wavelength, the opacity of TiO2/agar-κ-carrageenan composite films is 0.96 which is the highest of the four films. The resistance to water of TiO2/agar-κ-carrageenan composite films is higher than agar-κ-carrageenan films.
2018, 35(12): 3458-3465.
doi: 10.13801/j.cnki.fhclxb.20180211.001
Abstract:
The experimental study on the bond properties of glass fiber reinforced polymer (GFRP) bars and coral concrete, carbon fiber reinforced plomer (CFRP) bars and coral concrete under sea water immersion at 30℃ was carried out. The characteristics of bond slip curves, failure modes and bond strength of fiber reinforced polymer(FRP) bars-coral concrete were analyzed. The results show that the mechanical properties and adhesive properties of FRP bars decrease in different degrees after immersion in seawater. With the increase of soaking time, the porosity between surface resin and fiber increases evidently, the phenomenon of debonding occurrs gradually, and the fiber itself is that of GFRP bars. The ultimate bond strength of FRP bars-coral concrete shows a trend to increase at first and then decreases and the later falling rate gradually becomes smaller. The failure modes of some GFRP bars-coral concrete specimens gradually change into bar fracture from pull-out. Increasing the cover thickness of coral concrete could reduce the erosion of the sea water to the FRP bars effectively, and helps to maintain the bond performance of the GFRP bars-coral concrete.
The experimental study on the bond properties of glass fiber reinforced polymer (GFRP) bars and coral concrete, carbon fiber reinforced plomer (CFRP) bars and coral concrete under sea water immersion at 30℃ was carried out. The characteristics of bond slip curves, failure modes and bond strength of fiber reinforced polymer(FRP) bars-coral concrete were analyzed. The results show that the mechanical properties and adhesive properties of FRP bars decrease in different degrees after immersion in seawater. With the increase of soaking time, the porosity between surface resin and fiber increases evidently, the phenomenon of debonding occurrs gradually, and the fiber itself is that of GFRP bars. The ultimate bond strength of FRP bars-coral concrete shows a trend to increase at first and then decreases and the later falling rate gradually becomes smaller. The failure modes of some GFRP bars-coral concrete specimens gradually change into bar fracture from pull-out. Increasing the cover thickness of coral concrete could reduce the erosion of the sea water to the FRP bars effectively, and helps to maintain the bond performance of the GFRP bars-coral concrete.
2018, 35(12): 3466-3473.
doi: 10.13801/j.cnki.fhclxb.20180316.005
Abstract:
The La/Hβ-Al2O3 composite materials were prepared by method of lanthanum ion-exchange and used to improve the low-temperature etherification activity of light gasoline. The physical chemical properties of composite materials were characterized by a series of analytical methods, such as XRD, XRF, BET, FTIR, NH3-TPD, PyIR and FETEM-EDX. The results of XRD, XRF, BET and FTIR show that introduction of a small amount of lanthanum ions has no obvious effect on the crystalline phase and skeleton structure of the composite materials, on the contrary, moderate lanthanum ion exchange has the effect of pore-enlarging. The analysis results of NH3-TPD and PyIR show that acid content and acid strength of the composite materials have been weakened, but the introduction of lanthanum ions can form a new Brønsted acid site, which increases the ratio of medium strong acid and the amount of Brønsted acid sites. The results of FETEM-EDX analysis confirm that the lanthanum species are mainly present in the Hβ molecular sieve of composite materials. The evaluation results of etherification activity of this composite material show that the method of lanthanum ion-exchange can improve the light gasoline etherification activity of composite catalyst, in which the sample 0.1 La/Hβ-Al2O3 shows the best activity, and the yield of methyl tertiary amyl ether is up to 58.13%. The 300 h life test results show that it has good stability and reproducibility.
The La/Hβ-Al2O3 composite materials were prepared by method of lanthanum ion-exchange and used to improve the low-temperature etherification activity of light gasoline. The physical chemical properties of composite materials were characterized by a series of analytical methods, such as XRD, XRF, BET, FTIR, NH3-TPD, PyIR and FETEM-EDX. The results of XRD, XRF, BET and FTIR show that introduction of a small amount of lanthanum ions has no obvious effect on the crystalline phase and skeleton structure of the composite materials, on the contrary, moderate lanthanum ion exchange has the effect of pore-enlarging. The analysis results of NH3-TPD and PyIR show that acid content and acid strength of the composite materials have been weakened, but the introduction of lanthanum ions can form a new Brønsted acid site, which increases the ratio of medium strong acid and the amount of Brønsted acid sites. The results of FETEM-EDX analysis confirm that the lanthanum species are mainly present in the Hβ molecular sieve of composite materials. The evaluation results of etherification activity of this composite material show that the method of lanthanum ion-exchange can improve the light gasoline etherification activity of composite catalyst, in which the sample 0.1 La/Hβ-Al2O3 shows the best activity, and the yield of methyl tertiary amyl ether is up to 58.13%. The 300 h life test results show that it has good stability and reproducibility.
2018, 35(12): 3474-3486.
doi: 10.13801/j.cnki.fhclxb.20180209.004
Abstract:
A Mode-Ⅲ crack inclined to an imperfect interface in piezoelectric phase of a bi-layered magnetoelectric composite was studied. A coupled interfacial imperfection model was proposed to characterize the imperfect interface. Fourier integral transform was applied to reduce the condition on the crack surface to a singular integral equation, which can be numerically solved by Lobatto-Chebyshev collection method for the stress intensity factor(SIF). The effects of the interfacial imperfection parameters, material constants, layer thickness, inclined angle, distance between crack tip-a and interface on SIF were systematically discussed. Several conclusions are yielded:the mechanical imperfection can enhance the SIF independently, while the magnetic or electric imperfection can reduce the SIF only through its coupling with the mechanical imperfection; the coupling of mechanical-magneto or mechanical-electro imperfection can reduce the SIF, but the magneto-electro imperfection coupling does not affect SIF in any case; the SIF can be reduced by changing material constants, such as increasing the shear moduli of piezomagnetic layer, decreasing the shear moduli and dielectric coefficient or increasing the piezoelectric coefficient of piezoelectric layer; the variation of SIF versus inclined angle or distance between crack tip-a and interface can be influenced by interfacial imperfection; increasing the thickness of piezomagnetic or piezoelectric layer can reduce the SIF in a finite interval.
A Mode-Ⅲ crack inclined to an imperfect interface in piezoelectric phase of a bi-layered magnetoelectric composite was studied. A coupled interfacial imperfection model was proposed to characterize the imperfect interface. Fourier integral transform was applied to reduce the condition on the crack surface to a singular integral equation, which can be numerically solved by Lobatto-Chebyshev collection method for the stress intensity factor(SIF). The effects of the interfacial imperfection parameters, material constants, layer thickness, inclined angle, distance between crack tip-a and interface on SIF were systematically discussed. Several conclusions are yielded:the mechanical imperfection can enhance the SIF independently, while the magnetic or electric imperfection can reduce the SIF only through its coupling with the mechanical imperfection; the coupling of mechanical-magneto or mechanical-electro imperfection can reduce the SIF, but the magneto-electro imperfection coupling does not affect SIF in any case; the SIF can be reduced by changing material constants, such as increasing the shear moduli of piezomagnetic layer, decreasing the shear moduli and dielectric coefficient or increasing the piezoelectric coefficient of piezoelectric layer; the variation of SIF versus inclined angle or distance between crack tip-a and interface can be influenced by interfacial imperfection; increasing the thickness of piezomagnetic or piezoelectric layer can reduce the SIF in a finite interval.
2018, 35(12): 3487-3499.
doi: 10.13801/j.cnki.fhclxb.20180319.003
Abstract:
Rubber powder compatibility with different source matrix asphalts was studied based on the rheological theory.Using dynamic shear rheometer, the different matrix asphalts and rubber asphalts were tested by conventional dynamic shear rheological test, such as strain scanning, temperature scanning and frequency scanning.The viscoelastic properties of rubber asphalt were evaluated from the factors such as the phase angle, composite modulus and rutting factors, and the influence of the four components on the rubber asphalt viscoelastic properties was qualitative.Based on the indices such as the residual deformation, elastic energy-storage, elastic ratio and composite elastic modulus, the effects of modifying agent on the modification and viscoelastic properties of rubber asphalt were analyzed using the hysteresis loop back test specimen.The correlation was obtained by using grey correlation mathematical analysis method.The results show that rheological theory is an effective method for studying the compatibility of rubber powder and substrate asphalt.The influence of the four components of asphalt on the viscoelastic properties of rubber asphalt was evaluated from the energy angle, and the effect of asphalt on the residual strain of rubber asphalt is significant; The colloidal components can influence the elastic storage energy and dissipation of rubber asphalt, and the fragrances have the least impact; The asphaltenes have the greatest influence on the rubber asphalt elastic ratio parameters; The aromatic content increases the composite modulus of rubber asphalt.
Rubber powder compatibility with different source matrix asphalts was studied based on the rheological theory.Using dynamic shear rheometer, the different matrix asphalts and rubber asphalts were tested by conventional dynamic shear rheological test, such as strain scanning, temperature scanning and frequency scanning.The viscoelastic properties of rubber asphalt were evaluated from the factors such as the phase angle, composite modulus and rutting factors, and the influence of the four components on the rubber asphalt viscoelastic properties was qualitative.Based on the indices such as the residual deformation, elastic energy-storage, elastic ratio and composite elastic modulus, the effects of modifying agent on the modification and viscoelastic properties of rubber asphalt were analyzed using the hysteresis loop back test specimen.The correlation was obtained by using grey correlation mathematical analysis method.The results show that rheological theory is an effective method for studying the compatibility of rubber powder and substrate asphalt.The influence of the four components of asphalt on the viscoelastic properties of rubber asphalt was evaluated from the energy angle, and the effect of asphalt on the residual strain of rubber asphalt is significant; The colloidal components can influence the elastic storage energy and dissipation of rubber asphalt, and the fragrances have the least impact; The asphaltenes have the greatest influence on the rubber asphalt elastic ratio parameters; The aromatic content increases the composite modulus of rubber asphalt.
2018, 35(12): 3500-3507.
doi: 10.13801/j.cnki.fhclxb.20180409.002
Abstract:
Composite dry-fiber wound reinforced structure could be used to solve the problems of the poor impact resistance and failure of resin under the low temperature of filament winding resin matrix composite structure. In the process of filament winding for dry-fiber reinforced structure, the overlap and compression of the fiber bundle resulting in different thicknesses of dry-fiber wound reinforced layers have an effect on the stability of the winding pattern. The variation in the thickness and distribution law of dry-fiber wound reinforced layers based geodesic were studied winding to make sure the winding pattern stable. The influence of yarn width, pore size and core structure etc on the thickness variation of the dry-fiber reinforced layers was analyzed. The mathematical model of the dry-fiber wound reinforced structure was updated one by one considering the variation of the thickness of the mould. Then the winding trajectory was calculated and the geodesic winding pattern was acquired. Finally, the winding experiment of the dry-fiber wound reinforced layers was carried out taking vessel as example. The thickness of the reinforced layers obtained by theoretical simulation is accurate. The winding pattern is stable, the phenomenon of slipping of fiber doesn't exist. The feasibility of the calculation method of fiber thickness and winding trajectory and the correctness of simulation of dry-fiber reinforced layers thickness are verified.
Composite dry-fiber wound reinforced structure could be used to solve the problems of the poor impact resistance and failure of resin under the low temperature of filament winding resin matrix composite structure. In the process of filament winding for dry-fiber reinforced structure, the overlap and compression of the fiber bundle resulting in different thicknesses of dry-fiber wound reinforced layers have an effect on the stability of the winding pattern. The variation in the thickness and distribution law of dry-fiber wound reinforced layers based geodesic were studied winding to make sure the winding pattern stable. The influence of yarn width, pore size and core structure etc on the thickness variation of the dry-fiber reinforced layers was analyzed. The mathematical model of the dry-fiber wound reinforced structure was updated one by one considering the variation of the thickness of the mould. Then the winding trajectory was calculated and the geodesic winding pattern was acquired. Finally, the winding experiment of the dry-fiber wound reinforced layers was carried out taking vessel as example. The thickness of the reinforced layers obtained by theoretical simulation is accurate. The winding pattern is stable, the phenomenon of slipping of fiber doesn't exist. The feasibility of the calculation method of fiber thickness and winding trajectory and the correctness of simulation of dry-fiber reinforced layers thickness are verified.
2018, 35(12): 3508-3516.
doi: 10.13801/j.cnki.fhclxb.20180211.002
Abstract:
The visco-hyperelastic constitutive models of hydroxyl-terminated polybutadiene (HTPB) inhibitor were studied to describe the tensile mechanical properties accurately under finite deformation. Visco-hyperelastic constitutive model with rate related function and parallel constitutive model were built respectively, and the first model was multiplicatively combined by hyper-elastic model and rate related function, while the latter model was parallelly formed by hyper-elastic model and viscoelastic model containing damage factor. In order to fit the model parameters by the test data, the single-step relaxation test, multi-step relaxation test and uniaxial tensile test at various rates of HTPB inhibitor were undertaken. The results show that HTPB inhibitor is extremely sensitive to strain rate and has a great elongation, reflecting the obvious visco-hyperelasticity. Both of the models are able to predict the tensile mechanical properties of HTPB inhibitor in a large deformation range, meanwhile the model with rate related function can describe the mechanical properties more precisely, which is of great military significance.
The visco-hyperelastic constitutive models of hydroxyl-terminated polybutadiene (HTPB) inhibitor were studied to describe the tensile mechanical properties accurately under finite deformation. Visco-hyperelastic constitutive model with rate related function and parallel constitutive model were built respectively, and the first model was multiplicatively combined by hyper-elastic model and rate related function, while the latter model was parallelly formed by hyper-elastic model and viscoelastic model containing damage factor. In order to fit the model parameters by the test data, the single-step relaxation test, multi-step relaxation test and uniaxial tensile test at various rates of HTPB inhibitor were undertaken. The results show that HTPB inhibitor is extremely sensitive to strain rate and has a great elongation, reflecting the obvious visco-hyperelasticity. Both of the models are able to predict the tensile mechanical properties of HTPB inhibitor in a large deformation range, meanwhile the model with rate related function can describe the mechanical properties more precisely, which is of great military significance.
2018, 35(12): 3517-3525.
doi: 10.13801/j.cnki.fhclxb.20180320.001
Abstract:
A lattice-reinforced sandwich structure with cavities was presented, which had prospects of the integration of both mechanical and acoustic properties. In order to predict the equivalent modulus of lattice-reinforced core materials with cavities, a multi-level equivalent micromechanical mathematical model was built, which was made up of cavities, lattice reinforcements and foam matrices. With the reinforcements and cavities distributing periodically in the core, the representative unit of the equivalent model was established. Based on the Mori-Tanaka method, the single-phase inclusion equivalent was performed twice and the equivalent modulus of lattice-reinforced core materials with cavities were obtained which agree well with the experimental results and those determined using the FEM method. The numerical simulation was then conducted via the ANSYS code package to obtain the bending deformations and the natural frequencies of both the actual model and the equivalent mode, and the equivalent modulus of the core was used as the material parameter of the core of the equivalent model. The simulation results conform highly with each other and the relative errors of both the bending deformation displacements and the natural frequencies at low frequency are less than 2%, which satisfy the precision requirement in engineering.On this premise, further research was conducted to investigate the effects of reinforcements and cavities volume ratio on the equivalent modulus of the core. The results indicate that the above method can predict equivalent modulus of lattice-reinforced core materials with cavities accurately and quickly with a clear mathematical mode and simple formulas.
A lattice-reinforced sandwich structure with cavities was presented, which had prospects of the integration of both mechanical and acoustic properties. In order to predict the equivalent modulus of lattice-reinforced core materials with cavities, a multi-level equivalent micromechanical mathematical model was built, which was made up of cavities, lattice reinforcements and foam matrices. With the reinforcements and cavities distributing periodically in the core, the representative unit of the equivalent model was established. Based on the Mori-Tanaka method, the single-phase inclusion equivalent was performed twice and the equivalent modulus of lattice-reinforced core materials with cavities were obtained which agree well with the experimental results and those determined using the FEM method. The numerical simulation was then conducted via the ANSYS code package to obtain the bending deformations and the natural frequencies of both the actual model and the equivalent mode, and the equivalent modulus of the core was used as the material parameter of the core of the equivalent model. The simulation results conform highly with each other and the relative errors of both the bending deformation displacements and the natural frequencies at low frequency are less than 2%, which satisfy the precision requirement in engineering.On this premise, further research was conducted to investigate the effects of reinforcements and cavities volume ratio on the equivalent modulus of the core. The results indicate that the above method can predict equivalent modulus of lattice-reinforced core materials with cavities accurately and quickly with a clear mathematical mode and simple formulas.
2018, 35(12): 3526-3533.
doi: 10.13801/j.cnki.fhclxb.20180402.001
Abstract:
Reinforced concrete structures are widely used in civil engineering, but chloride-induced corrosion is one of the major factors that seriously deteriorate the durability of reinforced concrete structures. Thus, many numerical models have been developed to study the ion transport of cement-based material in the previous papers. However, most of these models could not consider the interactions between ions in the pore solution and cement hydrate. Based on the transport essential process of chloride in cement-based materials, this research presents a multi-species ionic transport model for cement-based materials coupling ion-cement hydrate interactions. Firstly, both the surface complexation model and the phase-equilibrium model were used to simulate the ion-cement hydrate thermodynamic interactions. Moreover, operator splitting algorithm was employed to solve the finite element numerical model of Nernst-Planck equation that coupling the ion-cement hydrate interactions, and then the variations of the content of each phase in cement hydrate, the porosity and the concentration of free ion in pore solution were discussed. Finally, the multi-species ionic transport numerical model was preliminarily verified by the experimental data published in the previous paper.
Reinforced concrete structures are widely used in civil engineering, but chloride-induced corrosion is one of the major factors that seriously deteriorate the durability of reinforced concrete structures. Thus, many numerical models have been developed to study the ion transport of cement-based material in the previous papers. However, most of these models could not consider the interactions between ions in the pore solution and cement hydrate. Based on the transport essential process of chloride in cement-based materials, this research presents a multi-species ionic transport model for cement-based materials coupling ion-cement hydrate interactions. Firstly, both the surface complexation model and the phase-equilibrium model were used to simulate the ion-cement hydrate thermodynamic interactions. Moreover, operator splitting algorithm was employed to solve the finite element numerical model of Nernst-Planck equation that coupling the ion-cement hydrate interactions, and then the variations of the content of each phase in cement hydrate, the porosity and the concentration of free ion in pore solution were discussed. Finally, the multi-species ionic transport numerical model was preliminarily verified by the experimental data published in the previous paper.
2018, 35(12): 3534-3546.
doi: 10.13801/j.cnki.fhclxb.20180316.001
Abstract:
The bond performance between carbon fiber reinforced polymer composites (CFRP) and steel plate is one of the key problems in strengthening steel structure with CFRP. Tensile-shear tests of 17 CFRP lamina-steel plate single-lap specimens were conducted, the mechanical behavior and failure modes of CFRP-steel interface of specimens with different epoxy adhesives and CFRP materials were studied. The influences of adhesive types and CFRP materials on interfacial bond-slip constitutive and shear bearing capacity were analyzed, and the calculation methods of interfacial shear capacity were discussed. Results show that interface failure modes and ultimate bearing capacity are significantly different for specimens with different adhesives or CFRP materials. The failure mode for specimens with Sika 330 and Lica adhesive is the mixed mode of CFRP-adhesive and steel-adhesive interface debonding, and failure modes for specimens with Araldite adhesive, Sika 30 adhesive, and SF (Sika S512/80) lamina are CFRP superficial delamination, adhesive failure, and CFRP deep layer delamination, respectively. The ultimate bearing capacity of Araldite specimen is 1.7~2.9 times of the other specimens. No descending branches are found in bond-slip curves for Sika 330, Araldite, and Lica specimens, which are characterized by brittle fracture of interfaces. However, low descending branches are found in bond-slip curves for Sika 30 and SF specimens, and forewarning signs occur before interfacial failure. The bond-slip constitutive model for the SF specimens can be simplified to trilinear model, while those for the other specimens can be simplified to bilinear models. The ultimate bearing capacity for SF specimens should be represented by Xia-a model, while those for the other specimens can be represented by Xia-b model. The mechanical behavior of the interface is numerically simulated based on cohesive zone model. Results show that the nonlinear mechanical behavior of the interface can be well simulated by the cohesive zone model, the influence of peeling stress on the bond strength of interface is small for these single-lap specimens.
The bond performance between carbon fiber reinforced polymer composites (CFRP) and steel plate is one of the key problems in strengthening steel structure with CFRP. Tensile-shear tests of 17 CFRP lamina-steel plate single-lap specimens were conducted, the mechanical behavior and failure modes of CFRP-steel interface of specimens with different epoxy adhesives and CFRP materials were studied. The influences of adhesive types and CFRP materials on interfacial bond-slip constitutive and shear bearing capacity were analyzed, and the calculation methods of interfacial shear capacity were discussed. Results show that interface failure modes and ultimate bearing capacity are significantly different for specimens with different adhesives or CFRP materials. The failure mode for specimens with Sika 330 and Lica adhesive is the mixed mode of CFRP-adhesive and steel-adhesive interface debonding, and failure modes for specimens with Araldite adhesive, Sika 30 adhesive, and SF (Sika S512/80) lamina are CFRP superficial delamination, adhesive failure, and CFRP deep layer delamination, respectively. The ultimate bearing capacity of Araldite specimen is 1.7~2.9 times of the other specimens. No descending branches are found in bond-slip curves for Sika 330, Araldite, and Lica specimens, which are characterized by brittle fracture of interfaces. However, low descending branches are found in bond-slip curves for Sika 30 and SF specimens, and forewarning signs occur before interfacial failure. The bond-slip constitutive model for the SF specimens can be simplified to trilinear model, while those for the other specimens can be simplified to bilinear models. The ultimate bearing capacity for SF specimens should be represented by Xia-a model, while those for the other specimens can be represented by Xia-b model. The mechanical behavior of the interface is numerically simulated based on cohesive zone model. Results show that the nonlinear mechanical behavior of the interface can be well simulated by the cohesive zone model, the influence of peeling stress on the bond strength of interface is small for these single-lap specimens.
