2019 Vol. 36, No. 5
2019, 36(5): 1063-1073.
doi: 10.13801/j.cnki.fhclxb.20180703.003
Abstract:
Glass fiber reinforced polymer (GFRP) composites had been applied in more and more anti-floating construction with their advantages such as high tensile strength, resistance to corrosion, low electromagnetic properties and so on, but the researched about their properties after bending are insufficient. To find the mechanical properties of bending GFRP composite anti-floating anchor, the paper studied the anchorage performance of straight and bended GFRP composite anchor bolt on the basis of a full-scale pullout test consisted of 8 surface sticky sand GFRP composite anti-floating anchors and 8 thread steel anti-floating anchors. The results show that the curved GFRP composites are unfavorable for improving the ultimate bearing capacity, and the longer with the bending length, the lower the ultimate bearing capacity is. However, bending treatment can effectively limit the displacement of the anchor bolt in the bottom plate, and the longer with the bending length, the more obvious the limiting effect shows. Increasing the anchorage length can effectively limit the displacement and improve the bearing capacity of the anchor bolts. The paper also introduces anti-floating anchor bending effect coefficient and puts forward the question which needs to be researched in the future based on the discussion of the influence about the anchorage properties of anchor bolts after bending.
Glass fiber reinforced polymer (GFRP) composites had been applied in more and more anti-floating construction with their advantages such as high tensile strength, resistance to corrosion, low electromagnetic properties and so on, but the researched about their properties after bending are insufficient. To find the mechanical properties of bending GFRP composite anti-floating anchor, the paper studied the anchorage performance of straight and bended GFRP composite anchor bolt on the basis of a full-scale pullout test consisted of 8 surface sticky sand GFRP composite anti-floating anchors and 8 thread steel anti-floating anchors. The results show that the curved GFRP composites are unfavorable for improving the ultimate bearing capacity, and the longer with the bending length, the lower the ultimate bearing capacity is. However, bending treatment can effectively limit the displacement of the anchor bolt in the bottom plate, and the longer with the bending length, the more obvious the limiting effect shows. Increasing the anchorage length can effectively limit the displacement and improve the bearing capacity of the anchor bolts. The paper also introduces anti-floating anchor bending effect coefficient and puts forward the question which needs to be researched in the future based on the discussion of the influence about the anchorage properties of anchor bolts after bending.
2019, 36(5): 1074-1082.
doi: 10.13801/j.cnki.fhclxb.20180724.002
Abstract:
Continuous glass fiber/polypropylene (GF/PP) composite corrugated sandwich panels with different laminates were prepared in this paper. The effects of different panels and core materials on the mechanical properties of corrugated sandwich panels were studied, including flat compression and bending properties. The results show that under the same panel, increase the thickness of the core board can greatly increase the overall flat-pressure performance of the sandwich panel. Under the same board, the method of laminating the panel has certain influence on the flat pressure performance of the sandwich panel. The corrugated sandwich panel with 0° and 90° layers has the highest flatwise compression modulus of 59.55 MPa, while the overall flatwise compression properties of those panels with the same layers cannot be increased significantly by only increasing panel thickness. The panel lay-up method has a great influence on the bending performance. The corrugated sandwich plates with 0° outer layer have the highest transverse bending modulus of 783.66 MPa, while the corrugated sandwich plate with 90° outer layer have the highest longitudinal flexural modulus of 732.09 MPa. However, for the panels with the single layers(0° or 90° layers), the bending property along a certain direction of sandwich panel will be a short board.
Continuous glass fiber/polypropylene (GF/PP) composite corrugated sandwich panels with different laminates were prepared in this paper. The effects of different panels and core materials on the mechanical properties of corrugated sandwich panels were studied, including flat compression and bending properties. The results show that under the same panel, increase the thickness of the core board can greatly increase the overall flat-pressure performance of the sandwich panel. Under the same board, the method of laminating the panel has certain influence on the flat pressure performance of the sandwich panel. The corrugated sandwich panel with 0° and 90° layers has the highest flatwise compression modulus of 59.55 MPa, while the overall flatwise compression properties of those panels with the same layers cannot be increased significantly by only increasing panel thickness. The panel lay-up method has a great influence on the bending performance. The corrugated sandwich plates with 0° outer layer have the highest transverse bending modulus of 783.66 MPa, while the corrugated sandwich plate with 90° outer layer have the highest longitudinal flexural modulus of 732.09 MPa. However, for the panels with the single layers(0° or 90° layers), the bending property along a certain direction of sandwich panel will be a short board.
2019, 36(5): 1083-1091.
doi: 10.13801/j.cnki.fhclxb.20180821.002
Abstract:
The thermoplastic resin polyaryletherketone with cardo (PEK-C) films of three different thicknesses (about 1 μm, 10 μm, 30 μm) were prepared by dip-coating method. Hot pressing technology was employed to obtain the film interleaved carbon fiber/epoxy composite laminates. The mode I interlaminar fracture toughness (GIC), compressive after impact (CAI), interlaminar shear strength and flexural properties were tested to investigate the effect of PEK-C film and film thickness on the mechanical properties of carbon fiber/epoxy composites. The microstructure was observed by SEM and the phase structure was scanned by AFM. The results show that GIC, CAI and interlaminar shear strength increase for the carbon fiber/epoxy composite laminates with PEK-C films of different thickness. GIC and shear strength are increased maximally at a film thickness of 10 μm, which are increased by 157.17% and 17.57%, respectively. CAI is the largest at a film thickness of 30 μm, reaching 186.67 MPa due to the fact that PEK-C and epoxy resin form a dual-phase structure during the hot pressing curing process, improving the toughness of the material. The flexural strength and flexural modulus of carbon fiber/epoxy composite laminates decrease with the increase of the film thickness, from 1 551 MPa, 106 GPa without films to 965 MPa, 79 GPa at the film thickness of 30 μm due to the diffusion of PEK-C resin into the epoxy resin, which reduces the fiber volume fraction and material stiffness.
The thermoplastic resin polyaryletherketone with cardo (PEK-C) films of three different thicknesses (about 1 μm, 10 μm, 30 μm) were prepared by dip-coating method. Hot pressing technology was employed to obtain the film interleaved carbon fiber/epoxy composite laminates. The mode I interlaminar fracture toughness (GIC), compressive after impact (CAI), interlaminar shear strength and flexural properties were tested to investigate the effect of PEK-C film and film thickness on the mechanical properties of carbon fiber/epoxy composites. The microstructure was observed by SEM and the phase structure was scanned by AFM. The results show that GIC, CAI and interlaminar shear strength increase for the carbon fiber/epoxy composite laminates with PEK-C films of different thickness. GIC and shear strength are increased maximally at a film thickness of 10 μm, which are increased by 157.17% and 17.57%, respectively. CAI is the largest at a film thickness of 30 μm, reaching 186.67 MPa due to the fact that PEK-C and epoxy resin form a dual-phase structure during the hot pressing curing process, improving the toughness of the material. The flexural strength and flexural modulus of carbon fiber/epoxy composite laminates decrease with the increase of the film thickness, from 1 551 MPa, 106 GPa without films to 965 MPa, 79 GPa at the film thickness of 30 μm due to the diffusion of PEK-C resin into the epoxy resin, which reduces the fiber volume fraction and material stiffness.
2019, 36(5): 1092-1100.
doi: 10.13801/j.cnki.fhclxb.20180612.001
Abstract:
A new family of tooth plate-glass fiber/polyurethane (TP-GF/PU) foam core sandwich beams consisted of TP-GF facesheets and a PU foam core were studied, in which tooth plates were connected with foam core through tooth nails. TP-GF/PU foam core sandwich beams were fabricated by a vacuum-assisted resin infusion process. The aim of this article is to investigate the impact response and impact damage of TP-GF/PU foam core sandwich beams with various foam densities and fiber thickness under low velocity impact tests. Double cantilever tests were also conducted to investigate the interfacial properties of TP-GF/PU foam core sandwich beams. An analytical model was used to calculate the strain energy release rate of TP-GF/PU foam core sandwich beams. The test results show that, under the energy impact of 22 J, 33 J and 44 J, the maximum contact force of the sandwich beam with a density of 150 kg/m3 is 31.2%, 48.6% and 33.3% higher than that of the ordinary sandwich beams, respectively. The absorbed energy is 17.2%, 11.3%, 15.5% higher than that of the ordinary sandwich beams, respectively. The maximum contact force increased with the increase of foam core density and impact energy. The main damage modes for TP-GF/PU with low foam density are face sheet bending. The strain energy release rate of TP-GF/PU specimen increase with the increase of the foam density.
A new family of tooth plate-glass fiber/polyurethane (TP-GF/PU) foam core sandwich beams consisted of TP-GF facesheets and a PU foam core were studied, in which tooth plates were connected with foam core through tooth nails. TP-GF/PU foam core sandwich beams were fabricated by a vacuum-assisted resin infusion process. The aim of this article is to investigate the impact response and impact damage of TP-GF/PU foam core sandwich beams with various foam densities and fiber thickness under low velocity impact tests. Double cantilever tests were also conducted to investigate the interfacial properties of TP-GF/PU foam core sandwich beams. An analytical model was used to calculate the strain energy release rate of TP-GF/PU foam core sandwich beams. The test results show that, under the energy impact of 22 J, 33 J and 44 J, the maximum contact force of the sandwich beam with a density of 150 kg/m3 is 31.2%, 48.6% and 33.3% higher than that of the ordinary sandwich beams, respectively. The absorbed energy is 17.2%, 11.3%, 15.5% higher than that of the ordinary sandwich beams, respectively. The maximum contact force increased with the increase of foam core density and impact energy. The main damage modes for TP-GF/PU with low foam density are face sheet bending. The strain energy release rate of TP-GF/PU specimen increase with the increase of the foam density.
2019, 36(5): 1101-1113.
doi: 10.13801/j.cnki.fhclxb.20180703.002
Abstract:
To reveal the effects of manufacturing induced thermal residual stress(TRS) on the transverse tensile response prediction of carbon fiber reinforced epoxy composites, a representative volume element (RVE) generation method based on the random perturbation method was developed and RVE models which are more similar to the real microstructure were established. With periodical boundary conditions and the constitutive models of the constituents (fiber, matrix and interface), the thermal residual stress and progressive damage response of the models can be predicted under the thermal and mechanical loading conditions respectively. From the results, it can be found that the manufacturing process induces compressive stress in the matrix between two adjacent fibers and tensile stress around the voids along the loading direction. For the RVE models without voids, it is the interface debonding that contributes to the crack initiation and the thermal residual stress between two adjacent fibers increases the predicted strengths. The crack of the RVE models with voids all initiates from the matrix around the void and the manufacturing induced residual tensile stress around the void along the loading direction would contribute to the decrease of the predicted strengths from RVE models with voids. For the RVE models with different void sizes, with the increase of the void size, the failure strength decreases, and the thermal residual stress weakens the effects of void size on strength reduction. For the RVE models containing elliptical voids with different aspect ratios, the thermal residual stress would enhance the effects of aspect ratio on the strength reduction.
To reveal the effects of manufacturing induced thermal residual stress(TRS) on the transverse tensile response prediction of carbon fiber reinforced epoxy composites, a representative volume element (RVE) generation method based on the random perturbation method was developed and RVE models which are more similar to the real microstructure were established. With periodical boundary conditions and the constitutive models of the constituents (fiber, matrix and interface), the thermal residual stress and progressive damage response of the models can be predicted under the thermal and mechanical loading conditions respectively. From the results, it can be found that the manufacturing process induces compressive stress in the matrix between two adjacent fibers and tensile stress around the voids along the loading direction. For the RVE models without voids, it is the interface debonding that contributes to the crack initiation and the thermal residual stress between two adjacent fibers increases the predicted strengths. The crack of the RVE models with voids all initiates from the matrix around the void and the manufacturing induced residual tensile stress around the void along the loading direction would contribute to the decrease of the predicted strengths from RVE models with voids. For the RVE models with different void sizes, with the increase of the void size, the failure strength decreases, and the thermal residual stress weakens the effects of void size on strength reduction. For the RVE models containing elliptical voids with different aspect ratios, the thermal residual stress would enhance the effects of aspect ratio on the strength reduction.
2019, 36(5): 1114-1123.
doi: 10.13801/j.cnki.fhclxb.20180725.001
Abstract:
In this paper, based on continuous damage mechanics and cohesive element model, the internal and interlaminar damage of carbon fiber reinforced polymer (CFRP) composite laminates with different impact locations and patch layers under low velocity impact load were numerically analyzed in ABAQUS, and the results were compared with the experimental results. Five kinds of repaired structures corresponding to the relative impact location of 0 mm, 10 mm, 20 mm, 30 mm and 40 mm were selected. The impact force and impact energy of the repaired structure during the low velocity impact were obtained from numerical and experimental approach. By keeping the monolayer thickness unchanged, the layer number of the used patches increased from 1 layer to 5 layers, and the low velocity impact response of repaired structures was obtained numerically and experimentally. The results show that when the impactor contacts repaired structures, it causes damage to the patch, but the patch definitely improves the impact resistance of the damaged parent laminates. When the impact point is closer to the damage hole of the repaired structure, the more serious the damage of the structure is caused by the impact. Moreover, the increase of the layer number within the patch design improves the impact resistance of the repaired structure. An optimum layer number is 2 obtained by optimizing the layer number, and the corresponding delamination area is reduced by 19.9% compared with damaged parent laminate without repair.
In this paper, based on continuous damage mechanics and cohesive element model, the internal and interlaminar damage of carbon fiber reinforced polymer (CFRP) composite laminates with different impact locations and patch layers under low velocity impact load were numerically analyzed in ABAQUS, and the results were compared with the experimental results. Five kinds of repaired structures corresponding to the relative impact location of 0 mm, 10 mm, 20 mm, 30 mm and 40 mm were selected. The impact force and impact energy of the repaired structure during the low velocity impact were obtained from numerical and experimental approach. By keeping the monolayer thickness unchanged, the layer number of the used patches increased from 1 layer to 5 layers, and the low velocity impact response of repaired structures was obtained numerically and experimentally. The results show that when the impactor contacts repaired structures, it causes damage to the patch, but the patch definitely improves the impact resistance of the damaged parent laminates. When the impact point is closer to the damage hole of the repaired structure, the more serious the damage of the structure is caused by the impact. Moreover, the increase of the layer number within the patch design improves the impact resistance of the repaired structure. An optimum layer number is 2 obtained by optimizing the layer number, and the corresponding delamination area is reduced by 19.9% compared with damaged parent laminate without repair.
2019, 36(5): 1124-1131.
doi: 10.13801/j.cnki.fhclxb.20180726.001
Abstract:
To provide a reference for the safety design and application of carbon fiber reinforced polymer (CFRP) composites adhesive structure, the fatigue life characteristics and residual strength of adhesively bonded CFRP composite-aluminum alloy butt joint were studied. The special fixture was designed to complete the production and solidification of the joints, and the tensile and shear quasi-static failure strength were tested. On the basis, the fatigue life under different stress levels was tested. The residual strength of the joint under specific load levels after different cycles was obtained and the failure modes are observed and analyzed. The results show that the fatigue stress-number of cycle (S-N) curve of adhesive joints accords with linear function on the single logarithmic coordinate. With the increase of alternating load cycles, the residual strength of the joint decreases, first slowly and then quickly. The decrease is more obvious under the larger load level. The failure modes of joint also changed which from slight fiber tear of CFRP composite transformer into local interfacial failure. Combined with the initial failure criterion obtained by experiment and the fatigue degradation factor, the cohesive zone model is used to simulate the strength attenuation of the adhesive joint under alternating load, and the results show that the model can predict the residual strength of the joint under alternating load effectively.
To provide a reference for the safety design and application of carbon fiber reinforced polymer (CFRP) composites adhesive structure, the fatigue life characteristics and residual strength of adhesively bonded CFRP composite-aluminum alloy butt joint were studied. The special fixture was designed to complete the production and solidification of the joints, and the tensile and shear quasi-static failure strength were tested. On the basis, the fatigue life under different stress levels was tested. The residual strength of the joint under specific load levels after different cycles was obtained and the failure modes are observed and analyzed. The results show that the fatigue stress-number of cycle (S-N) curve of adhesive joints accords with linear function on the single logarithmic coordinate. With the increase of alternating load cycles, the residual strength of the joint decreases, first slowly and then quickly. The decrease is more obvious under the larger load level. The failure modes of joint also changed which from slight fiber tear of CFRP composite transformer into local interfacial failure. Combined with the initial failure criterion obtained by experiment and the fatigue degradation factor, the cohesive zone model is used to simulate the strength attenuation of the adhesive joint under alternating load, and the results show that the model can predict the residual strength of the joint under alternating load effectively.
2019, 36(5): 1132-1142.
doi: 10.13801/j.cnki.fhclxb.20180716.004
Abstract:
This paper presents a substitution model based on stiffness equivalence to study the delamination buckling in T300/QY8911 carbon fiber reinforced polymer composite, delaminated laminates. The delaminated laminate contains a buried through-width delamination. Exact model was introduced in which the nonlinear contact effect between sub-laminates above and beneath the delamination was included. It is found from exact analysis that the sub-laminates above and beneath the delamination undergo identical global deflection. Based on such observation an equivalent substitution model which is perfect is proposed to replace the delaminated portion of the laminate. The substitute model has the same geometric size and is stacked in the same sequence as that of the delaminated portion. Further observation of the deflection modes also suggests that the stiffness of the substitute model is taken as the sum of the stiffness of the two portions above and beneath the delamination. Using the equivalent substitution model the delaminated laminate is divided into three sub-laminates, each of which is delamination-free. Governing equations for the buckling of the delaminated laminate were established and were solved by considering the boundary conditions at the ends and the continuity conditions at the delamination fronts. Analytical solutions of the buckling load are obtained for different delamination size and depth. The efficiency and accuracy of the presented model was confirmed by comparing with the exact results and ABAQUS predictions, both showing a good agreement with those from presented model. The model presented herein greatly simplifies the tedious derivation and saves the calculations, thus is in favor of engineers to conveniently and effectively estimate the degradation of the mechanical performances caused by the delamination. More importantly, the deep mechanical mechanism can be effectively extended to evaluate the nonlinear mechanical properties of laminates containing multiple delamination yet providing a powerful technical support for structural design and mechanics analysis of advanced composites.
This paper presents a substitution model based on stiffness equivalence to study the delamination buckling in T300/QY8911 carbon fiber reinforced polymer composite, delaminated laminates. The delaminated laminate contains a buried through-width delamination. Exact model was introduced in which the nonlinear contact effect between sub-laminates above and beneath the delamination was included. It is found from exact analysis that the sub-laminates above and beneath the delamination undergo identical global deflection. Based on such observation an equivalent substitution model which is perfect is proposed to replace the delaminated portion of the laminate. The substitute model has the same geometric size and is stacked in the same sequence as that of the delaminated portion. Further observation of the deflection modes also suggests that the stiffness of the substitute model is taken as the sum of the stiffness of the two portions above and beneath the delamination. Using the equivalent substitution model the delaminated laminate is divided into three sub-laminates, each of which is delamination-free. Governing equations for the buckling of the delaminated laminate were established and were solved by considering the boundary conditions at the ends and the continuity conditions at the delamination fronts. Analytical solutions of the buckling load are obtained for different delamination size and depth. The efficiency and accuracy of the presented model was confirmed by comparing with the exact results and ABAQUS predictions, both showing a good agreement with those from presented model. The model presented herein greatly simplifies the tedious derivation and saves the calculations, thus is in favor of engineers to conveniently and effectively estimate the degradation of the mechanical performances caused by the delamination. More importantly, the deep mechanical mechanism can be effectively extended to evaluate the nonlinear mechanical properties of laminates containing multiple delamination yet providing a powerful technical support for structural design and mechanics analysis of advanced composites.
2019, 36(5): 1143-1150.
doi: 10.13801/j.cnki.fhclxb.20180821.003
Abstract:
The Filament winding with tension (force winding) can be used for superimposing a compressive radial stress field onto the tensile field caused by high-speed rotation to prevent radial delamination and unmatched deformation. The fiber winding process is assumed as continuous superposition of pre-tensioned composite thin rings, and the mechanical model of force filament winding is proposed on the basis of anisotropic composite elastic theory and isotropic thick-walled cylinder elastic theory. The radial and circumferential stresses of winding layers and the deformations of mandrel with winding layer number were obtained. The mechanical analytical model was verified by the test. The stress saturation is found in the high tension filament winding by the test and also proved by the analytical solutions. The two relevant key parameters for stress distribution in the force winding, the ratio of hoop stiffness to radial stiffness Eθ/Er and the fiber tension T(r) are identified and discussed. The present and analysis approaches are critical to the successful design, analysis and implementation of filament force winding.
The Filament winding with tension (force winding) can be used for superimposing a compressive radial stress field onto the tensile field caused by high-speed rotation to prevent radial delamination and unmatched deformation. The fiber winding process is assumed as continuous superposition of pre-tensioned composite thin rings, and the mechanical model of force filament winding is proposed on the basis of anisotropic composite elastic theory and isotropic thick-walled cylinder elastic theory. The radial and circumferential stresses of winding layers and the deformations of mandrel with winding layer number were obtained. The mechanical analytical model was verified by the test. The stress saturation is found in the high tension filament winding by the test and also proved by the analytical solutions. The two relevant key parameters for stress distribution in the force winding, the ratio of hoop stiffness to radial stiffness Eθ/Er and the fiber tension T(r) are identified and discussed. The present and analysis approaches are critical to the successful design, analysis and implementation of filament force winding.
2019, 36(5): 1151-1158.
doi: 10.13801/j.cnki.fhclxb.20180625.001
Abstract:
Thermal residual phenomena occurrs in carbon fiber reinforced polymer (CFRP) composite laminates by 3D printing due to the material mismatch among layers and the gradient cooling during printing, and affects the forming quality. Instead of the simple assumption of synchronous cooling, the concept of gradient cooling was introduced to characterize real manufacturing processes. The analytical solutions of thermal residual deformations and stresses of cross-ply composite plates and beams were established. To characterize time-dependent forming and cooling processes during 3D printing, a through-thickness cooling gradient was considered in each layer forming turn. The thermal residual responses in each turn were deduced. The total thermal residual deformations and stresses were obtained in an accumulative way. Four gradient cooling models were summarized to cover various 3D printing techniques. The accuracy and reliability of the present solutions are proved in the example of CFRP composite by 3D printing. It is illustrated that the assumption of synchronous cooling would lead to big errors. Thermal residual level is proportional to the cooling gradient. The effects of ply-up patterns on thermal residual responses are discussed. This work provides reliable methods to optimize structures and techniques and decrease thermal residual level of CFRP composites in 3D printing.
Thermal residual phenomena occurrs in carbon fiber reinforced polymer (CFRP) composite laminates by 3D printing due to the material mismatch among layers and the gradient cooling during printing, and affects the forming quality. Instead of the simple assumption of synchronous cooling, the concept of gradient cooling was introduced to characterize real manufacturing processes. The analytical solutions of thermal residual deformations and stresses of cross-ply composite plates and beams were established. To characterize time-dependent forming and cooling processes during 3D printing, a through-thickness cooling gradient was considered in each layer forming turn. The thermal residual responses in each turn were deduced. The total thermal residual deformations and stresses were obtained in an accumulative way. Four gradient cooling models were summarized to cover various 3D printing techniques. The accuracy and reliability of the present solutions are proved in the example of CFRP composite by 3D printing. It is illustrated that the assumption of synchronous cooling would lead to big errors. Thermal residual level is proportional to the cooling gradient. The effects of ply-up patterns on thermal residual responses are discussed. This work provides reliable methods to optimize structures and techniques and decrease thermal residual level of CFRP composites in 3D printing.
2019, 36(5): 1159-1168.
doi: 10.13801/j.cnki.fhclxb.20180911.005
Abstract:
In order to obtain the exact solution for the vibration and sound radiation of composite sandwich cylindrical shell, the shell was divided into several thin layers in the thickness direction, the state space equation was established for each thin layer based on three-dimensional elastic theory and state space technique and the transfer matrix of transversal displacement and stress was built considering the continuous condition of displacement and stress. The fluid load on the outer surface and the point excitation on the inner surface were expanded by Fourier series and introduced into the state space equation, the exact elastic solution of underwater vibration and sound radiation of composite sandwich shell was obtained. In contrast to the results by finite element simulation and that from the previous literature, present theoretical model is more accurate than the approximate two-dimensional shell theories. The effect of ply angle, thickness distribution of face and core and loss factor on vibration and sound radiation were further investigated. The results show that in the frequency range below the ring frequency the peak's number of sound power changes as the parabolic curve, and in the middle and high frequency bands above the ring frequency the peak's number of sound power increases first and tends to be gentle, and then continues to increase. With the increasing of core's loss factor, the peak value of sound radiation power gradually decreases, as well as the extent of decline.
In order to obtain the exact solution for the vibration and sound radiation of composite sandwich cylindrical shell, the shell was divided into several thin layers in the thickness direction, the state space equation was established for each thin layer based on three-dimensional elastic theory and state space technique and the transfer matrix of transversal displacement and stress was built considering the continuous condition of displacement and stress. The fluid load on the outer surface and the point excitation on the inner surface were expanded by Fourier series and introduced into the state space equation, the exact elastic solution of underwater vibration and sound radiation of composite sandwich shell was obtained. In contrast to the results by finite element simulation and that from the previous literature, present theoretical model is more accurate than the approximate two-dimensional shell theories. The effect of ply angle, thickness distribution of face and core and loss factor on vibration and sound radiation were further investigated. The results show that in the frequency range below the ring frequency the peak's number of sound power changes as the parabolic curve, and in the middle and high frequency bands above the ring frequency the peak's number of sound power increases first and tends to be gentle, and then continues to increase. With the increasing of core's loss factor, the peak value of sound radiation power gradually decreases, as well as the extent of decline.
2019, 36(5): 1169-1178.
doi: 10.13801/j.cnki.fhclxb.20180725.002
Abstract:
In view of the anchor problem of large-tonnage fiber reinforced polymer (FRP) composites cable, basing on previous proposed integral variable stiffness anchor method suitable for multi root and large-diameter FRP composite cables(large-tonnage anchor for short), the essential reason of stress concentration at the loading end of FRP composite cable was analyzed based on the relationship between stress and strain, and the interfacial friction coefficient relationship of cooperative work between the FRP composites and load transfer component was deduced. Based on the principle of work and power, the calculation formula of anchor force for large-tonnage anchor was derived, and the parameter analysis was carried out based on the calculation formula of anchor force. The theoretical derivation results show that the stress concentration at the loading end of FRP composite cable can be caused by load transfer component with equal stiffness, and the large-tonnage anchor basing on load transfer component with variable stiffness can effectively avoids the cut effect of FRP composite cable. The derived interfacial friction coefficient relationship can be used as the basis for judge whether FRP composite cable and load transfer component follow up synchronously. The parameter analysis shows that increasing the anchor length and the cone angle (keeping the thickness of loading end unchanged) is advantageous to design small size and large-tonnage anchor system, while increasing the cone angle (keeping the thickness of free end unchanged) and the thickness of the loading end and the free end simultaneously is disadvantageous to design small size and large-tonnage anchor system.
In view of the anchor problem of large-tonnage fiber reinforced polymer (FRP) composites cable, basing on previous proposed integral variable stiffness anchor method suitable for multi root and large-diameter FRP composite cables(large-tonnage anchor for short), the essential reason of stress concentration at the loading end of FRP composite cable was analyzed based on the relationship between stress and strain, and the interfacial friction coefficient relationship of cooperative work between the FRP composites and load transfer component was deduced. Based on the principle of work and power, the calculation formula of anchor force for large-tonnage anchor was derived, and the parameter analysis was carried out based on the calculation formula of anchor force. The theoretical derivation results show that the stress concentration at the loading end of FRP composite cable can be caused by load transfer component with equal stiffness, and the large-tonnage anchor basing on load transfer component with variable stiffness can effectively avoids the cut effect of FRP composite cable. The derived interfacial friction coefficient relationship can be used as the basis for judge whether FRP composite cable and load transfer component follow up synchronously. The parameter analysis shows that increasing the anchor length and the cone angle (keeping the thickness of loading end unchanged) is advantageous to design small size and large-tonnage anchor system, while increasing the cone angle (keeping the thickness of free end unchanged) and the thickness of the loading end and the free end simultaneously is disadvantageous to design small size and large-tonnage anchor system.
2019, 36(5): 1179-1188.
doi: 10.13801/j.cnki.fhclxb.20180726.002
Abstract:
The mode I interlaminar fracture toughness of composite laminates with epoxy interleaf was studied in the double cantilever beam (DCB) tests. Brittle unstable and stable delaminations were observed in the specimens with and without interleaf respectively. For the unstable crack growth, based on dynamic fracture mechanics, the relation between strain energy release rate and the change of kinetic energy was analyzed. A static simulation method for dynamic crack growth was proposed, which transformed the change of kinetic energy into the change of input fracture toughness (GIC*). GIC* was calculated according to the evolution of fracture resistance in the tests and input into ABAQUS for the simulation of crack growth using virtual crack closure technique (VCCT). A three-dimensional finite element model was constructed to simulate the dynamic delamination growth from crack onset to arrest, and the complex mechanical behavior in the unstable crack growth was studied.
The mode I interlaminar fracture toughness of composite laminates with epoxy interleaf was studied in the double cantilever beam (DCB) tests. Brittle unstable and stable delaminations were observed in the specimens with and without interleaf respectively. For the unstable crack growth, based on dynamic fracture mechanics, the relation between strain energy release rate and the change of kinetic energy was analyzed. A static simulation method for dynamic crack growth was proposed, which transformed the change of kinetic energy into the change of input fracture toughness (GIC*). GIC* was calculated according to the evolution of fracture resistance in the tests and input into ABAQUS for the simulation of crack growth using virtual crack closure technique (VCCT). A three-dimensional finite element model was constructed to simulate the dynamic delamination growth from crack onset to arrest, and the complex mechanical behavior in the unstable crack growth was studied.
2019, 36(5): 1189-1199.
doi: 10.13801/j.cnki.fhclxb.20180626.001
Abstract:
Filament winding pattern design is an important research field in the design of fiber reinforced resin polymer (FRP) composites winding shell and it plays an important role for filament winding products. A complete non-geodesic design method was proposed for unequal polar openings shell or different dome shapes shell based on non-geodesic equations. A model was established to obtain the number of tangent points and roving width by mandrel rotation angle and winding pattern. A FRP composites winding simulation software system was developed based on the winding pattern design method, the simulations of computer graphics and tests for non-geodesic filament winding were realized. The simulation results in every section meets design requirement which do not indicate abnormal phenomena such as winding angle saltation, irregular fiber distribution and heavily fiber overlap. This filament winding software system can help project planner decrease winding pattern trial and error times and lay the foundation for the optimization of winding angle and winding angle sequence.
Filament winding pattern design is an important research field in the design of fiber reinforced resin polymer (FRP) composites winding shell and it plays an important role for filament winding products. A complete non-geodesic design method was proposed for unequal polar openings shell or different dome shapes shell based on non-geodesic equations. A model was established to obtain the number of tangent points and roving width by mandrel rotation angle and winding pattern. A FRP composites winding simulation software system was developed based on the winding pattern design method, the simulations of computer graphics and tests for non-geodesic filament winding were realized. The simulation results in every section meets design requirement which do not indicate abnormal phenomena such as winding angle saltation, irregular fiber distribution and heavily fiber overlap. This filament winding software system can help project planner decrease winding pattern trial and error times and lay the foundation for the optimization of winding angle and winding angle sequence.
2019, 36(5): 1200-1209.
doi: 10.13801/j.cnki.fhclxb.20180713.001
Abstract:
The internal defects in the material structure and their distributions could effectively be identified by using stress wave characteristics. In order to identify the internal defects of the preform by using processing loads that act as a stress wave excitation source, the effect of the processing parameters on the stress wave propagation characteristics in the laying process should be first studied to determine the position of the stress sensor. In this paper, the thermo-mechanical coupling model of the laying process was constructed by using the finite element method (FEM). The relationship between the stress wave characteristic parameters and the processing parameters was analyzed, and the experimental verification was then carried out. In order to explain the effect of the processing parameters on the stress wave characteristics from the perspective of microscopic energy, molecular dynamics (MD) method was used to establish the molecular model of the prepreg interface, and the energy parameters such as total energy, surface energy of fibers, and internal energy of matrix were calculated. Furthermore, the driving energy of stress wave and its contribution ratio under different processing parameters were identified and evaluated to reveal the energy effect mechanism of the processing parameters on the stress wave characteristics. The results show that the lateral waves driven by the internal energy of matrix have a significant relationship with the processing parameters. The effect of the formation of internal defects on the waveform is easy to identify under the different processing parameters. This conclusion could be used as a reference for stress sensor placement.
The internal defects in the material structure and their distributions could effectively be identified by using stress wave characteristics. In order to identify the internal defects of the preform by using processing loads that act as a stress wave excitation source, the effect of the processing parameters on the stress wave propagation characteristics in the laying process should be first studied to determine the position of the stress sensor. In this paper, the thermo-mechanical coupling model of the laying process was constructed by using the finite element method (FEM). The relationship between the stress wave characteristic parameters and the processing parameters was analyzed, and the experimental verification was then carried out. In order to explain the effect of the processing parameters on the stress wave characteristics from the perspective of microscopic energy, molecular dynamics (MD) method was used to establish the molecular model of the prepreg interface, and the energy parameters such as total energy, surface energy of fibers, and internal energy of matrix were calculated. Furthermore, the driving energy of stress wave and its contribution ratio under different processing parameters were identified and evaluated to reveal the energy effect mechanism of the processing parameters on the stress wave characteristics. The results show that the lateral waves driven by the internal energy of matrix have a significant relationship with the processing parameters. The effect of the formation of internal defects on the waveform is easy to identify under the different processing parameters. This conclusion could be used as a reference for stress sensor placement.
2019, 36(5): 1210-1215.
doi: 10.13801/j.cnki.fhclxb.20180725.004
Abstract:
The current ASTM standard for measuring the mode Ⅰ interlaminar fracture toughness of composite requires to measure the crack growth length, which is a very tedious and difficult process for measuring the interlaminar fracture toughness in low temperature environment. To overcome the limitation of measuring the crack growth length, a double compliances method was used to measure the mode Ⅰ interlaminar fracture toughness. The process of this method was nearly the same as that recommended in the ASTM, except avoiding measuring the crack growth length. To verify the accuracy of this method, five double cantilever beam (DCB) specimens made of carbon fiber reinforced epoxy composites were tested at -10℃ environment. The fracture toughness were determined by using the methods recommended by the ASTM standard and the present double compliances method. The result shows that the relative difference of the fracture toughness obtained from the ASTM methods and the double compliances method is within 5%. Therefore, the present paper provides a simple and reliable method for determining the mode Ⅰ interlaminar fracture toughness of composite in the low temperature environment.
The current ASTM standard for measuring the mode Ⅰ interlaminar fracture toughness of composite requires to measure the crack growth length, which is a very tedious and difficult process for measuring the interlaminar fracture toughness in low temperature environment. To overcome the limitation of measuring the crack growth length, a double compliances method was used to measure the mode Ⅰ interlaminar fracture toughness. The process of this method was nearly the same as that recommended in the ASTM, except avoiding measuring the crack growth length. To verify the accuracy of this method, five double cantilever beam (DCB) specimens made of carbon fiber reinforced epoxy composites were tested at -10℃ environment. The fracture toughness were determined by using the methods recommended by the ASTM standard and the present double compliances method. The result shows that the relative difference of the fracture toughness obtained from the ASTM methods and the double compliances method is within 5%. Therefore, the present paper provides a simple and reliable method for determining the mode Ⅰ interlaminar fracture toughness of composite in the low temperature environment.
2019, 36(5): 1216-1225.
doi: 10.13801/j.cnki.fhclxb.20180725.003
Abstract:
In this study, the short-term (15 min) tensile creep behaviors of polypropylene (PP) at different temperature and stress levels were examined by DMA creep model test, followed by the characterization on the long-term tensile creep behavior (10 h) continuous glass fiber reinforced polypropylene composites (CGF/PP) at the different stress levels and fiber orientations. The Burgers viscoelastic model was adopted to simulate the materials creep curves and pertinent model parameters associated with the stress levels and fiber orientations were derived. The results show that, with the rise of loaded stress, the creep compliance and steady-state creep rate of PP and unidirectional CGF/PP laminate both increase significantly, and the creep modulus retention rate decrease obviously, demonstrating that the creep behaviors of CGF/PP under low stress levels is dependent on the viscoelastic properties of PP matrix. The tensile-shear coupling effects occur in the loaded angle from 0° to 90° for the off-axis tension with a stress level of 30%, specifically in the 45° where steady-state creep rate and the creep deformation of composites exhibit maximum values. The derived numerical model by means of four element Burgers viscoelastic model to fit the creep curves in different conditions matches well with the experimental data, with a correlation coefficients of 0.99 between them. The numerical clearly illustrated the stress and fiber orientation dependence for the pertinent model parameters. The numerical formula of model parameters was established. The estimated tensile creep curve in the 0° fiber direction at 10 MPa and the estimated off-axis tensile creep curve in the 45° off-axis fiber direction at 30% of stress level are nearly identical with the experimental curve, showing the reliability of the derived numerical model in this paper.
In this study, the short-term (15 min) tensile creep behaviors of polypropylene (PP) at different temperature and stress levels were examined by DMA creep model test, followed by the characterization on the long-term tensile creep behavior (10 h) continuous glass fiber reinforced polypropylene composites (CGF/PP) at the different stress levels and fiber orientations. The Burgers viscoelastic model was adopted to simulate the materials creep curves and pertinent model parameters associated with the stress levels and fiber orientations were derived. The results show that, with the rise of loaded stress, the creep compliance and steady-state creep rate of PP and unidirectional CGF/PP laminate both increase significantly, and the creep modulus retention rate decrease obviously, demonstrating that the creep behaviors of CGF/PP under low stress levels is dependent on the viscoelastic properties of PP matrix. The tensile-shear coupling effects occur in the loaded angle from 0° to 90° for the off-axis tension with a stress level of 30%, specifically in the 45° where steady-state creep rate and the creep deformation of composites exhibit maximum values. The derived numerical model by means of four element Burgers viscoelastic model to fit the creep curves in different conditions matches well with the experimental data, with a correlation coefficients of 0.99 between them. The numerical clearly illustrated the stress and fiber orientation dependence for the pertinent model parameters. The numerical formula of model parameters was established. The estimated tensile creep curve in the 0° fiber direction at 10 MPa and the estimated off-axis tensile creep curve in the 45° off-axis fiber direction at 30% of stress level are nearly identical with the experimental curve, showing the reliability of the derived numerical model in this paper.
2019, 36(5): 1226-1234.
doi: 10.13801/j.cnki.fhclxb.20180814.001
Abstract:
The numerical model of carbon fiber reinforced polymer (CFRP) composite sandwich plates with square honeycomb cores of different relative densities subjected to water blast is established based on finite element software ABAQUS. The deformation process, core compression characteristics and structure damage and failure modes were analyzed. The numerical results show that the core compression reaches to its peak value when the velocity of the back face sheet drops to the same as the front face sheet. The maximum core compression increases slowly with the peak pressure when the peak pressure is small and then the increasing rate switches to a higher level until the core is nearly completely compressed. The failure modes of the sandwich structures vary with the core relative density and the value of the peak pressure. The carbon fiber reinforced composite sandwich plates outperform the mass-equal laminate plates when subjected to water blast. The research can provide reference to the application of the composite sandwich structure in the protection shields against underwater shock wave loads.
The numerical model of carbon fiber reinforced polymer (CFRP) composite sandwich plates with square honeycomb cores of different relative densities subjected to water blast is established based on finite element software ABAQUS. The deformation process, core compression characteristics and structure damage and failure modes were analyzed. The numerical results show that the core compression reaches to its peak value when the velocity of the back face sheet drops to the same as the front face sheet. The maximum core compression increases slowly with the peak pressure when the peak pressure is small and then the increasing rate switches to a higher level until the core is nearly completely compressed. The failure modes of the sandwich structures vary with the core relative density and the value of the peak pressure. The carbon fiber reinforced composite sandwich plates outperform the mass-equal laminate plates when subjected to water blast. The research can provide reference to the application of the composite sandwich structure in the protection shields against underwater shock wave loads.
2019, 36(5): 1235-1243.
doi: 10.13801/j.cnki.fhclxb.20180706.001
Abstract:
Polycrystalline diamond compact (PDC) bit matrix materials were fabricated by pressureless infiltration method using the cast tungsten carbide powders mixed with nickel powders as the skeleton powders. The effects of the morphologies, particle sizes and content of the cast tungsten carbide powders on the microstructure and mechanical properties of the PDC bit matrix were investigated in detail. The results show that the microstructure and mechanical properties of the prepared PDC bit matrix are significantly affected by the morphologies, particle sizes and content of the cast tungsten carbide powders. In contrast to the traditional cast tungsten carbide, the bit matrix, prepared by using spherical cast tungsten carbide powders with moderate particle size as the skeleton, shows a more homogenous and denser structure and obtained enhanced mechanical properties. The PDC bit matrix, prepared by using spherical cast tungsten carbide powder with particle size of 150-180 μm mixed with 13wt% nickel powders as the skeleton, exhibits better mechanical properties than that of the petroleum industry standard SY/T 5217-2000. Its hardness, impact toughness and bending strength were HRC 34 and 6.7 J/cm2 and 820 MPa, respectively.
Polycrystalline diamond compact (PDC) bit matrix materials were fabricated by pressureless infiltration method using the cast tungsten carbide powders mixed with nickel powders as the skeleton powders. The effects of the morphologies, particle sizes and content of the cast tungsten carbide powders on the microstructure and mechanical properties of the PDC bit matrix were investigated in detail. The results show that the microstructure and mechanical properties of the prepared PDC bit matrix are significantly affected by the morphologies, particle sizes and content of the cast tungsten carbide powders. In contrast to the traditional cast tungsten carbide, the bit matrix, prepared by using spherical cast tungsten carbide powders with moderate particle size as the skeleton, shows a more homogenous and denser structure and obtained enhanced mechanical properties. The PDC bit matrix, prepared by using spherical cast tungsten carbide powder with particle size of 150-180 μm mixed with 13wt% nickel powders as the skeleton, exhibits better mechanical properties than that of the petroleum industry standard SY/T 5217-2000. Its hardness, impact toughness and bending strength were HRC 34 and 6.7 J/cm2 and 820 MPa, respectively.
2019, 36(5): 1244-1253.
doi: 10.13801/j.cnki.fhclxb.20180724.001
Abstract:
In order to study the influence of different cooling and lubrication methods on tool wear in machining SiCP/Al composites, the turning experiments with cooling and lubrication methods including dry, liquid nitrogen (LN2), minimum quantity lubrication (MQL), cutting oil (Oil) and emulsion were carried out, the influences of cooling and lubrication methods on tool boundary wear, tool breakage and flank wear were analyzed. The results show that MQL and LN2 can bring the detached SiC particles away from the cutting zone due to their more effective flushing characteristic, which contributes to the decrease of boundary wear; the application of Oil and Emulsion deteriorates boundary wear intensely because of less flushing ability. The increase in the thermal stress and mechanical shocking applied to the tool and build-up edge shedding will cause the cutting process to be unstable with the application of LN2, resulting in tool breakage at the cutting distance of 1 100 m; when turning with Oil, serious boundary wear can decrease the tool nose size and lead to reducing of intensity of the tool nose, so tool breakage occurs at the cutting distance of 825 m. Flank wear decreases due to MQL's great lubrication permeability and LN2' effective cooling effect. Therefore, MQL possesses good cooling, lubrication and fluid flushing effects and is a better cooling and lubrication method for machining SiCP/Al composites.
In order to study the influence of different cooling and lubrication methods on tool wear in machining SiCP/Al composites, the turning experiments with cooling and lubrication methods including dry, liquid nitrogen (LN2), minimum quantity lubrication (MQL), cutting oil (Oil) and emulsion were carried out, the influences of cooling and lubrication methods on tool boundary wear, tool breakage and flank wear were analyzed. The results show that MQL and LN2 can bring the detached SiC particles away from the cutting zone due to their more effective flushing characteristic, which contributes to the decrease of boundary wear; the application of Oil and Emulsion deteriorates boundary wear intensely because of less flushing ability. The increase in the thermal stress and mechanical shocking applied to the tool and build-up edge shedding will cause the cutting process to be unstable with the application of LN2, resulting in tool breakage at the cutting distance of 1 100 m; when turning with Oil, serious boundary wear can decrease the tool nose size and lead to reducing of intensity of the tool nose, so tool breakage occurs at the cutting distance of 825 m. Flank wear decreases due to MQL's great lubrication permeability and LN2' effective cooling effect. Therefore, MQL possesses good cooling, lubrication and fluid flushing effects and is a better cooling and lubrication method for machining SiCP/Al composites.
2019, 36(5): 1254-1262.
doi: 10.13801/j.cnki.fhclxb.20180901.001
Abstract:
Thermal protection systems and hot structures of hypersonic vehicles include many composite plates. These structures are very sensitive to acoustic loads during cruise or re-entry flights and are destroyed easily. It is a vital challenge for the integrity and the durability of hypersonic vehicle plates. The C/SiC composite testing flat plates with thickness from 1 mm to 3 mm were chosen and many acoustic tests were carried out using a progressive wave tube facility. The four edges of these flat plates were completely fixed using fastening bolts. Responses of acceleration and strain of the C/SiC composite testing plates within 156-165 dB acoustic loads were obtained. The C/SiC composite testing plate with the thickness of 1 mm was destroyed rapidly subjected acoustic load with sound pressure level 168 dB. The failure plate was detected using the infrared nondestructive devices and the fracture surface was observed using SEM, then the failure modes of the testing plate were also achieved. The results are significant to optimum designs and anti-acoustic failure evaluation for high temperature material structures.
Thermal protection systems and hot structures of hypersonic vehicles include many composite plates. These structures are very sensitive to acoustic loads during cruise or re-entry flights and are destroyed easily. It is a vital challenge for the integrity and the durability of hypersonic vehicle plates. The C/SiC composite testing flat plates with thickness from 1 mm to 3 mm were chosen and many acoustic tests were carried out using a progressive wave tube facility. The four edges of these flat plates were completely fixed using fastening bolts. Responses of acceleration and strain of the C/SiC composite testing plates within 156-165 dB acoustic loads were obtained. The C/SiC composite testing plate with the thickness of 1 mm was destroyed rapidly subjected acoustic load with sound pressure level 168 dB. The failure plate was detected using the infrared nondestructive devices and the fracture surface was observed using SEM, then the failure modes of the testing plate were also achieved. The results are significant to optimum designs and anti-acoustic failure evaluation for high temperature material structures.
2019, 36(5): 1263-1274.
doi: 10.13801/j.cnki.fhclxb.20181129.002
Abstract:
Polyvinyl chloride (PVC) was heat-treated in a vacuum at 270℃ to prepare a partly conjugated derivative (CDPVC) through a reaction of remove HCl. The nano TiO2/CDPVC composite was prepared by compounding commercial TiO2 and CDPVC with the mass ratio of 2:1 in a high-energy ball-miller, and was characterized by TEM, XRD, XPS, FTIR, SEM and Raman, et al. The photocatalytic degradation of rhodamine B (Rh B) and the photocatalytic reduction of K2Cr2O7 were used to evaluate the visible photocatalytic activity and stability of the nano TiO2/CDPVC composite. The results show that the structure of Ti-O-C formed by compounding TiO2 and CDPVC in a high-energy ball-miller, which is advantageous to the improvement in both visible-light absorption capacity of the nano TiO2/CDPVC composite and separation efficiency of photogenerated electron/hole pairs. Compared to nano TiO2 and TiO2-CDPVC (an ordinary product after grinding TiO2 and CDPVC), nano TiO2/CDPVC composite exhibits the higher visible-light photocatalytic activity and excellent stability. The visible-light photocatalytic mechanism can be proposed that CDPVC adsorbs photos to produce photogenerated electron-hole pairs, and the photogenerated electrons can be easily injected into the conduction band of TiO2. The photogenerated electrons (eCB-) in CDPVC and conduction band of TiO2 can be captured by oxygen on the surface of the TiO2/CDPVC composite to form·O-2 radicals, and·O-2 radicals can directly degrade rhodamine B molecules even to produce H2O and CO2.
Polyvinyl chloride (PVC) was heat-treated in a vacuum at 270℃ to prepare a partly conjugated derivative (CDPVC) through a reaction of remove HCl. The nano TiO2/CDPVC composite was prepared by compounding commercial TiO2 and CDPVC with the mass ratio of 2:1 in a high-energy ball-miller, and was characterized by TEM, XRD, XPS, FTIR, SEM and Raman, et al. The photocatalytic degradation of rhodamine B (Rh B) and the photocatalytic reduction of K2Cr2O7 were used to evaluate the visible photocatalytic activity and stability of the nano TiO2/CDPVC composite. The results show that the structure of Ti-O-C formed by compounding TiO2 and CDPVC in a high-energy ball-miller, which is advantageous to the improvement in both visible-light absorption capacity of the nano TiO2/CDPVC composite and separation efficiency of photogenerated electron/hole pairs. Compared to nano TiO2 and TiO2-CDPVC (an ordinary product after grinding TiO2 and CDPVC), nano TiO2/CDPVC composite exhibits the higher visible-light photocatalytic activity and excellent stability. The visible-light photocatalytic mechanism can be proposed that CDPVC adsorbs photos to produce photogenerated electron-hole pairs, and the photogenerated electrons can be easily injected into the conduction band of TiO2. The photogenerated electrons (eCB-) in CDPVC and conduction band of TiO2 can be captured by oxygen on the surface of the TiO2/CDPVC composite to form·O-2 radicals, and·O-2 radicals can directly degrade rhodamine B molecules even to produce H2O and CO2.
2019, 36(5): 1275-1283.
doi: 10.13801/j.cnki.fhclxb.20180709.001
Abstract:
Carbon fiber reinforced polymer (CFRP) composite is a new high-performance material with the advantages of light weight, high strength and corrosion resistance. This paper presents the results of experimental studied on the size effect of the eccentric compressive performance of reinforced concrete columns strengthened with CFRP composite sheets. A total of fifteen reinforced concrete columns were designed and tested up to failure under eccentric compressive loads, the columns were geometrically similar to one another. Three factors were taken into consideration in this study, such as the size of column, eccentricity and the layers of CFRP composite sheets. The test results indicate that the failure modes, the relative deflection, the peak strains of CFRP composite and steels are obviously affected by the size of columns. The ultimate load of reinforced concrete columns strengthened with CFRP composite sheets significantly decreases with the eccentricity increases, and the rate of decrease gradually becomes slower with the size increasing. Under the same eccentricity, the safety storage coefficient of reinforced concrete columns strengthened with CFRP composite gradually decreases with the increase of the size.
Carbon fiber reinforced polymer (CFRP) composite is a new high-performance material with the advantages of light weight, high strength and corrosion resistance. This paper presents the results of experimental studied on the size effect of the eccentric compressive performance of reinforced concrete columns strengthened with CFRP composite sheets. A total of fifteen reinforced concrete columns were designed and tested up to failure under eccentric compressive loads, the columns were geometrically similar to one another. Three factors were taken into consideration in this study, such as the size of column, eccentricity and the layers of CFRP composite sheets. The test results indicate that the failure modes, the relative deflection, the peak strains of CFRP composite and steels are obviously affected by the size of columns. The ultimate load of reinforced concrete columns strengthened with CFRP composite sheets significantly decreases with the eccentricity increases, and the rate of decrease gradually becomes slower with the size increasing. Under the same eccentricity, the safety storage coefficient of reinforced concrete columns strengthened with CFRP composite gradually decreases with the increase of the size.
Dynamic response and anti-penetration performance of multi-layered heterogeneous composite structure
2019, 36(5): 1284-1294.
doi: 10.13801/j.cnki.fhclxb.20180716.003
Abstract:
In order to study the dynamic response and anti-penetration performance of multi-layered heterogeneous composite structures, Hopkinson's test equipment was used to perform impact loading on the multilayer composite structures with different material arrangement sequences and aluminum foam cores. The waveforms of the incident wave, reflected wave, and transmitted wave measured by the strain gauges on the incident rod and the transmission rod were used to verify the correctness of the numerical simulation model. Combined with numerical simulation, the influence of different structures on the stress wave propagation characteristics and the stress field distribution of the specimen was studied. According to the characteristics of the dynamic response of composite structures, composite targets were designed and subjected to an anti-penetration test. The plastic deformation characteristics of the target plate and the mechanism of anti-penetration energy dissipation were analyzed. The effect of thickness of aluminum foam sandwich on protection performance was analyzed by numerical simulation. The results show that the armored steel post-composite structure and foam sandwich structure can help to reduce stress concentration and reduce the area of ceramic damage. Aluminum foam cores are too thick to provide support for deformation of the target board and increase resistance to penetration. In the five kinds of aluminum foam thickness h=2 mm, h=5 mm, h=10 mm, h=20 mm and h=30 mm, multi-layer heterogeneous target board with h=10 mm has the best protective performance.
In order to study the dynamic response and anti-penetration performance of multi-layered heterogeneous composite structures, Hopkinson's test equipment was used to perform impact loading on the multilayer composite structures with different material arrangement sequences and aluminum foam cores. The waveforms of the incident wave, reflected wave, and transmitted wave measured by the strain gauges on the incident rod and the transmission rod were used to verify the correctness of the numerical simulation model. Combined with numerical simulation, the influence of different structures on the stress wave propagation characteristics and the stress field distribution of the specimen was studied. According to the characteristics of the dynamic response of composite structures, composite targets were designed and subjected to an anti-penetration test. The plastic deformation characteristics of the target plate and the mechanism of anti-penetration energy dissipation were analyzed. The effect of thickness of aluminum foam sandwich on protection performance was analyzed by numerical simulation. The results show that the armored steel post-composite structure and foam sandwich structure can help to reduce stress concentration and reduce the area of ceramic damage. Aluminum foam cores are too thick to provide support for deformation of the target board and increase resistance to penetration. In the five kinds of aluminum foam thickness h=2 mm, h=5 mm, h=10 mm, h=20 mm and h=30 mm, multi-layer heterogeneous target board with h=10 mm has the best protective performance.
2019, 36(5): 1295-1305.
doi: 10.13801/j.cnki.fhclxb.20180703.004
Abstract:
Ultra-high-performance concrete (UHPC) is a new type of cemetitious composite material with ultra-high strength, ultra-high durability and high toughness. It has received extensive attention in the field of civil engineering at home and broad because of its superior performance and had a broad prospect of engineering application. The uniaxial tensile and compressive stress-strain constitutive model is the premise and foundation for the analysis of mechanical properties of UHPC members. In order to further study mechanical properties of UHPC, this paper summarized different UHPC constitutive models proposed by domestic and foreign scholars, including uniaxial compressive stress-strain relationship, uniaxial tensile stress-strain and stress-crack width relationship, and carries on the classification and comparison. Some similarities and differences of existing models are found, and the reasons for this difference were analyzed. In the last part, some constitutive relations were applied to the finite element analysis software ABAQUS. Numerical simulation of UHPC beam reinforced with high strength steel bars was carried out, and the rationality of some constitutive models was verified by comparison with the experimental results. Some conclusions were put forward. The research results of this paper provide a basis for structural performance study, structural analysis and structural design of UHPC.
Ultra-high-performance concrete (UHPC) is a new type of cemetitious composite material with ultra-high strength, ultra-high durability and high toughness. It has received extensive attention in the field of civil engineering at home and broad because of its superior performance and had a broad prospect of engineering application. The uniaxial tensile and compressive stress-strain constitutive model is the premise and foundation for the analysis of mechanical properties of UHPC members. In order to further study mechanical properties of UHPC, this paper summarized different UHPC constitutive models proposed by domestic and foreign scholars, including uniaxial compressive stress-strain relationship, uniaxial tensile stress-strain and stress-crack width relationship, and carries on the classification and comparison. Some similarities and differences of existing models are found, and the reasons for this difference were analyzed. In the last part, some constitutive relations were applied to the finite element analysis software ABAQUS. Numerical simulation of UHPC beam reinforced with high strength steel bars was carried out, and the rationality of some constitutive models was verified by comparison with the experimental results. Some conclusions were put forward. The research results of this paper provide a basis for structural performance study, structural analysis and structural design of UHPC.
2019, 36(5): 1306-1312.
doi: 10.13801/j.cnki.fhclxb.20180705.003
Abstract:
In order to improve the stress accuracy of thermal elastic composite laminates, the generalized H-R variational principle of elastic material was extended to the generalized H-R variational principle of thermal elastic material based on the symplectic element theory of related references, and the corresponding modified principle was proposed. The parametered symplectic element was established. One of the main advantages of this element is that there is no zeros in the leading diagonal of coefficient matrix compared to the traditional mixed element. Consequently, the stability of the numerical results of finite element linear system of equations is guaranteed. At the same time, the element is symmetric for both the displacement variable and the stress variable, so its corresponding finite element linear system of equations is symmetric and symplectic conservation. Compared with the exact solution, the numerical results show that the accurate order of the generalized displacements and stresses are consistent, and hold high accuracy.
In order to improve the stress accuracy of thermal elastic composite laminates, the generalized H-R variational principle of elastic material was extended to the generalized H-R variational principle of thermal elastic material based on the symplectic element theory of related references, and the corresponding modified principle was proposed. The parametered symplectic element was established. One of the main advantages of this element is that there is no zeros in the leading diagonal of coefficient matrix compared to the traditional mixed element. Consequently, the stability of the numerical results of finite element linear system of equations is guaranteed. At the same time, the element is symmetric for both the displacement variable and the stress variable, so its corresponding finite element linear system of equations is symmetric and symplectic conservation. Compared with the exact solution, the numerical results show that the accurate order of the generalized displacements and stresses are consistent, and hold high accuracy.
2019, 36(5): 1313-1318.
doi: 10.13801/j.cnki.fhclxb.20180818.001
Abstract:
The deformation and instability characteristics of ligaments in chiral honeycomb control the impact resistance of these materials. In this paper, the impact dynamic load coefficient of ligament and the critical pressure of ligament instability in the first stage of in-plane shock buffering were discussed by means of energy method and extremum analysis of functional exponential function, then the analytical expression of the dynamic load coefficient and the critical pressure instability were obtained, and then the internal micro-structural collapse mechanism and the key influencing factors of impact resistance of the chiral honeycomb material were revealed. The results show that the larger the torsion angle of the ligament node ring, which is regarded as the torsion spring, during impact compression deformation, the smaller the dynamic load coefficient of the ligament, while the pressure of instability of the ligament increases with the torsion angle of the node ring. The research methods and results can provide reference for the further research and microstructure design of the impact resistance of chiral honeycomb materials and similar honeycomb materials.
The deformation and instability characteristics of ligaments in chiral honeycomb control the impact resistance of these materials. In this paper, the impact dynamic load coefficient of ligament and the critical pressure of ligament instability in the first stage of in-plane shock buffering were discussed by means of energy method and extremum analysis of functional exponential function, then the analytical expression of the dynamic load coefficient and the critical pressure instability were obtained, and then the internal micro-structural collapse mechanism and the key influencing factors of impact resistance of the chiral honeycomb material were revealed. The results show that the larger the torsion angle of the ligament node ring, which is regarded as the torsion spring, during impact compression deformation, the smaller the dynamic load coefficient of the ligament, while the pressure of instability of the ligament increases with the torsion angle of the node ring. The research methods and results can provide reference for the further research and microstructure design of the impact resistance of chiral honeycomb materials and similar honeycomb materials.
2019, 36(5): 1319-1326.
doi: 10.13801/j.cnki.fhclxb.20180827.003
Abstract:
Differential equation to analyze the vibration problem of a magnetostrictive laminated cantilever with thin-film actuator was derived by Hamilton's variational principle, using the nonlinear constitutive relation of magnetostrictive material. The free vibration and forced vibration of magnetostrictive laminated cantilever with thin-film were analyzed by means of the methods of separation variables and the analytic solution of ordinary differential equations. The numerical example shows that the calculation results of this paper are in good agreement with finite element results, which evidences validity of the theoretical model and solution method, and the effect of the geometric parameters and material parameters on natural frequency of the laminated beam was discussed. The deflection response of beam excited by a periodic input magnetic field was also analyzed, which present the dynamic characteristic of frequency multiplying effect. The deflection response of the cantilever beam excited by a periodic input magnetic field was also analyzed, which presented the double frequency effect of dynamic characteristics.
Differential equation to analyze the vibration problem of a magnetostrictive laminated cantilever with thin-film actuator was derived by Hamilton's variational principle, using the nonlinear constitutive relation of magnetostrictive material. The free vibration and forced vibration of magnetostrictive laminated cantilever with thin-film were analyzed by means of the methods of separation variables and the analytic solution of ordinary differential equations. The numerical example shows that the calculation results of this paper are in good agreement with finite element results, which evidences validity of the theoretical model and solution method, and the effect of the geometric parameters and material parameters on natural frequency of the laminated beam was discussed. The deflection response of beam excited by a periodic input magnetic field was also analyzed, which present the dynamic characteristic of frequency multiplying effect. The deflection response of the cantilever beam excited by a periodic input magnetic field was also analyzed, which presented the double frequency effect of dynamic characteristics.
2019, 36(5): 1327-1334.
doi: 10.13801/j.cnki.fhclxb.20180622.001
Abstract:
To study the correlation between the macroscopic and microscopic properties of the hydroxyl-terminated polybutadiene inhibitor in solid rocket motor, as well as accurately predict the storage life of the material, accelerated aging tests at 50℃, 60℃, 70℃ and 80℃ were carried out. The correlation functions about crosslink density and maximum elongation were built, and logarithmic model, power function model and exponential model were used to study how the crosslink density varied with storage time. The crosslink density was selected to describe the aging properties, and the modified Arrhenius method was chosen to predict the storage life of hydroxyl-terminated polybutadiene inhibitor under room temperature. The results show that the power function model with α=0.3 can describe the variation law of crosslink density well. The apparent activation energy of the aging reaction obtained by modified Arrhenius method has a linear relationship with temperature. Taking the crosslink densities as the failure criterion, which are calculated by linear equation and quadratic polynomial respectively when the maximum elongation decrease of 50%, the estimated storage lifetime of the hydroxyl-terminated polybutadiene inhibitor at 298.15 K are 17.38 years and 16.14 years, identical to that when solved with the maximum elongation. Besides, the predicted lifetime can meet the aging performance requirements of the inhibitor.
To study the correlation between the macroscopic and microscopic properties of the hydroxyl-terminated polybutadiene inhibitor in solid rocket motor, as well as accurately predict the storage life of the material, accelerated aging tests at 50℃, 60℃, 70℃ and 80℃ were carried out. The correlation functions about crosslink density and maximum elongation were built, and logarithmic model, power function model and exponential model were used to study how the crosslink density varied with storage time. The crosslink density was selected to describe the aging properties, and the modified Arrhenius method was chosen to predict the storage life of hydroxyl-terminated polybutadiene inhibitor under room temperature. The results show that the power function model with α=0.3 can describe the variation law of crosslink density well. The apparent activation energy of the aging reaction obtained by modified Arrhenius method has a linear relationship with temperature. Taking the crosslink densities as the failure criterion, which are calculated by linear equation and quadratic polynomial respectively when the maximum elongation decrease of 50%, the estimated storage lifetime of the hydroxyl-terminated polybutadiene inhibitor at 298.15 K are 17.38 years and 16.14 years, identical to that when solved with the maximum elongation. Besides, the predicted lifetime can meet the aging performance requirements of the inhibitor.
2019, 36(5): 1335-1341.
doi: 10.13801/j.cnki.fhclxb.20180827.002
Abstract:
The present work aimed to restrain shuttle effect of lithium-sulfur (Li-S) batteries and improve the cycle performance. Hydroxylated multi-walled carbon nanotube (MWCNTs-OH) was used in the positive electrode to absorb polysulfides for cheking the shuttle effect. The diffusion of polysulphides was prevented from absorbing of hydroxyl groups to them. The utilization of active materials was enhanced.The capacity and cycle performance of lithium-sulfur batteries were greatly improved. The morphology and structure of electrodes were observed by TEM, SEM and EDS. The electrochemical test results show that the initial discharge specific capacity of Li-S batteries with the MWCNTs-OH reaches to 1 281 mAh/g and the coulomb efficiency reaches around 96.7%. The discharge capacity remains 882 mAh/g after 10 cycles. The batteries maintained a discharge specific capacity of 794.2 mAh/g, 712.2 mAh/g and 557.3 mAh/g at the current rate of 0.2 C, 0.5 C and 1 C respectively, showing excellent magnification.
The present work aimed to restrain shuttle effect of lithium-sulfur (Li-S) batteries and improve the cycle performance. Hydroxylated multi-walled carbon nanotube (MWCNTs-OH) was used in the positive electrode to absorb polysulfides for cheking the shuttle effect. The diffusion of polysulphides was prevented from absorbing of hydroxyl groups to them. The utilization of active materials was enhanced.The capacity and cycle performance of lithium-sulfur batteries were greatly improved. The morphology and structure of electrodes were observed by TEM, SEM and EDS. The electrochemical test results show that the initial discharge specific capacity of Li-S batteries with the MWCNTs-OH reaches to 1 281 mAh/g and the coulomb efficiency reaches around 96.7%. The discharge capacity remains 882 mAh/g after 10 cycles. The batteries maintained a discharge specific capacity of 794.2 mAh/g, 712.2 mAh/g and 557.3 mAh/g at the current rate of 0.2 C, 0.5 C and 1 C respectively, showing excellent magnification.
