2016 Vol. 33, No. 10
2016, 33(10): 2141-2150.
doi: 10.13801/j.cnki.fhclxb.20151223.006
Abstract:
Organoclay/polyethersulfone(PES)-epoxy composites with different organoclay mass fractions were fabricated by solvent method and melting method. The microstructures and mechanical properties of the composites were studied. The toughening mechanisms of composites were revealed. T800H-organoclay/PES-epoxy composite prepreg unidirectional tape was prepared by adding T800H(12K) carbon fiber into organoclay/PES-epoxy composites. Composite unidirectional laminates were prepared with autoclave process. The mode I and mode II interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites were studied. Results show that the interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites and organoclay/PES-epoxy composites incorporated with organoclay mass fraction show similar trends, which supportes the proposed toughening mechanism.
Organoclay/polyethersulfone(PES)-epoxy composites with different organoclay mass fractions were fabricated by solvent method and melting method. The microstructures and mechanical properties of the composites were studied. The toughening mechanisms of composites were revealed. T800H-organoclay/PES-epoxy composite prepreg unidirectional tape was prepared by adding T800H(12K) carbon fiber into organoclay/PES-epoxy composites. Composite unidirectional laminates were prepared with autoclave process. The mode I and mode II interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites were studied. Results show that the interlaminar fracture toughness of T800H-organoclay/PES-epoxy composites and organoclay/PES-epoxy composites incorporated with organoclay mass fraction show similar trends, which supportes the proposed toughening mechanism.
2016, 33(10): 2151-2157.
doi: 10.13801/j.cnki.fhclxb.20151218.001
Abstract:
Temperature and strain in a representative liquid molding epoxy resin were in-situ monitored by Fiber Bragg Grating (FBG) sensors throughout different curing processes and post-curing processes. Curing shrinkage regularity of the resin in different processes was derived from its linear volume variation transformed from the strain evolution in resin. Process parameters of experiential curing and post-curing processes were validated and optimized based on the curing shrinkage. The results show that conversion degree and glass transition temperature of the liquid moldingresin cured at 80℃ are 90% and 85℃ respectively, which are higher than resin cured at 75℃. However, total curing shrinkage of the resin cured at 80℃ is only 5% higher than cured at 75℃. The strain in resin becomes constant after 180 min in isothermal procedure of 120℃ post-curing, which means the resin is cured completely. There is no need to extend the post-curing time.
Temperature and strain in a representative liquid molding epoxy resin were in-situ monitored by Fiber Bragg Grating (FBG) sensors throughout different curing processes and post-curing processes. Curing shrinkage regularity of the resin in different processes was derived from its linear volume variation transformed from the strain evolution in resin. Process parameters of experiential curing and post-curing processes were validated and optimized based on the curing shrinkage. The results show that conversion degree and glass transition temperature of the liquid moldingresin cured at 80℃ are 90% and 85℃ respectively, which are higher than resin cured at 75℃. However, total curing shrinkage of the resin cured at 80℃ is only 5% higher than cured at 75℃. The strain in resin becomes constant after 180 min in isothermal procedure of 120℃ post-curing, which means the resin is cured completely. There is no need to extend the post-curing time.
2016, 33(10): 2158-2165.
doi: 10.13801/j.cnki.fhclxb.20160127.002
Abstract:
Long glass fiber reinforced nylon10T(LGF/PA10T) composites were prepared by melt blending method, and the effects of different thermal-oxidative aging time on the static and dynamic mechanical properties of LGF/PA10T composites were characterized by DSC, DMA, SEM and mechanical properties test, and the activation energy of glass transition of LGF/PA10T composites were calculated. The results indicate that PA10T molecular chains are a little cross-linked in the initial stage of aging, slightly increasing the rigid properties of material, but the molecular chains fracture and the reduction of molecular weight play a vital role in the whole aging process. After aging at 240℃ for 50 d, the tensile strength retention rate, flexural strength retention rate and notch impact strength retention rate of LGF/PA10T composites are 4.9%, 6.3% and 9.4%, respectively. With the increase of aging time, the interfacial interaction between glass fiber and PA10T matrix is weakened, both of the glass transition temperature and damping capacity decrease. The calculation results of activation energy show that thermal-oxidative aging can make the mobility of PA10T molecular chain changed and reduce the thermal stability of LGF/PA10T composites.
Long glass fiber reinforced nylon10T(LGF/PA10T) composites were prepared by melt blending method, and the effects of different thermal-oxidative aging time on the static and dynamic mechanical properties of LGF/PA10T composites were characterized by DSC, DMA, SEM and mechanical properties test, and the activation energy of glass transition of LGF/PA10T composites were calculated. The results indicate that PA10T molecular chains are a little cross-linked in the initial stage of aging, slightly increasing the rigid properties of material, but the molecular chains fracture and the reduction of molecular weight play a vital role in the whole aging process. After aging at 240℃ for 50 d, the tensile strength retention rate, flexural strength retention rate and notch impact strength retention rate of LGF/PA10T composites are 4.9%, 6.3% and 9.4%, respectively. With the increase of aging time, the interfacial interaction between glass fiber and PA10T matrix is weakened, both of the glass transition temperature and damping capacity decrease. The calculation results of activation energy show that thermal-oxidative aging can make the mobility of PA10T molecular chain changed and reduce the thermal stability of LGF/PA10T composites.
2016, 33(10): 2166-2173.
doi: 10.13801/j.cnki.fhclxb.20160129.001
Abstract:
Nano-SiC/low density polyethylene (LDPE) composites with different nano SiC mass fractions (0.5%, 2.0%, 3.0%) were prepared by melt blending method. Effects of nano-SiC particles on dielectric properties of LDPE were studied. Dispersion character of nano-SiC particles was observed by SEM. Space charge distribution character of nano-SiC/LDPE composites under 40 kV/mm field strength was obtained by using pulse electro-acousitc(PEA)method. Thermal simulated current (TSC) was also employed to further identify that nano-SiC can increase the trap density of LDPE. The results show that nano-SiC particles disperse uniformly in LDPE and there is no larger agglomeration. The quantity of injected space charge of nano-SiC/LDPE composites with nano SiC mass fraction of 0.5%, 2.0% and 3.0% are much lower than that of LDPE. After short circuit 600 s, the residual space charge density is much smaller than that of LDPE. The quantity of injected space charge and conductivity of nano-SiC/LDPE composites both reduce with the increase of nano-SiC particles. The nonlinear coefficient of electric field of nano-SiC/LDPE composites with nano SiC mass fraction of 3.0% is 2.6, which is much smaller than that of LDPE of 4.3. TSC curves show that a large number of traps appear in nano-SiC/LDPE composites, which inhibit the transportation of carriers in material, thus hinder the migration and accumulation of space charge.
Nano-SiC/low density polyethylene (LDPE) composites with different nano SiC mass fractions (0.5%, 2.0%, 3.0%) were prepared by melt blending method. Effects of nano-SiC particles on dielectric properties of LDPE were studied. Dispersion character of nano-SiC particles was observed by SEM. Space charge distribution character of nano-SiC/LDPE composites under 40 kV/mm field strength was obtained by using pulse electro-acousitc(PEA)method. Thermal simulated current (TSC) was also employed to further identify that nano-SiC can increase the trap density of LDPE. The results show that nano-SiC particles disperse uniformly in LDPE and there is no larger agglomeration. The quantity of injected space charge of nano-SiC/LDPE composites with nano SiC mass fraction of 0.5%, 2.0% and 3.0% are much lower than that of LDPE. After short circuit 600 s, the residual space charge density is much smaller than that of LDPE. The quantity of injected space charge and conductivity of nano-SiC/LDPE composites both reduce with the increase of nano-SiC particles. The nonlinear coefficient of electric field of nano-SiC/LDPE composites with nano SiC mass fraction of 3.0% is 2.6, which is much smaller than that of LDPE of 4.3. TSC curves show that a large number of traps appear in nano-SiC/LDPE composites, which inhibit the transportation of carriers in material, thus hinder the migration and accumulation of space charge.
2016, 33(10): 2174-2180.
doi: 10.13801/j.cnki.fhclxb.20151218.002
Abstract:
A kind of high-temperature resistant foam composites with relatively integrated structure after pyrolysis was prepared with ZrSi2 particles filling boron-modified phenolic resin. The curing mechanism, high-temperature pyrolytic behaviors, compression performances before and after pyrolysis of foam composites were investigated with respect to ZrSi2 particle mass fraction, and the strengthen mechanism of ZrSi2 particles on pyrolytic products of foam composites was also analyzed. The results show that the introduction of ZrSi2 particles does not affect the curing and crosslinking of boron-modified phenolic resin but induces chemical reactions with pyrolytic volatiles derived from boron-modified phenolic resin, which could increase the char yield and the compressive specific strength of pyrolytic products. When the mass ratio of introduced ZrSi2 particles to boron-modified phenolic reaches 10%, there is the most significant improvement on the char yield and the compressive strength of pyrolytic products. After pyrolysis of ZrSi2/boron-modified phenolic foam, ZrSi2 particles are pinned on the cell walls of pyrolytic products as the secondary phase particles, part of pyrolytic volatiles are absorbed and translated into solid phase products by chemical reaction, and obviously decreased defects increase the mechanical property of pyrolytic products.
A kind of high-temperature resistant foam composites with relatively integrated structure after pyrolysis was prepared with ZrSi2 particles filling boron-modified phenolic resin. The curing mechanism, high-temperature pyrolytic behaviors, compression performances before and after pyrolysis of foam composites were investigated with respect to ZrSi2 particle mass fraction, and the strengthen mechanism of ZrSi2 particles on pyrolytic products of foam composites was also analyzed. The results show that the introduction of ZrSi2 particles does not affect the curing and crosslinking of boron-modified phenolic resin but induces chemical reactions with pyrolytic volatiles derived from boron-modified phenolic resin, which could increase the char yield and the compressive specific strength of pyrolytic products. When the mass ratio of introduced ZrSi2 particles to boron-modified phenolic reaches 10%, there is the most significant improvement on the char yield and the compressive strength of pyrolytic products. After pyrolysis of ZrSi2/boron-modified phenolic foam, ZrSi2 particles are pinned on the cell walls of pyrolytic products as the secondary phase particles, part of pyrolytic volatiles are absorbed and translated into solid phase products by chemical reaction, and obviously decreased defects increase the mechanical property of pyrolytic products.
2016, 33(10): 2181-2186.
doi: 10.13801/j.cnki.fhclxb.20151118.002
Abstract:
Self-made composite adsorbent resins comprising of Bentonite/sodium lignosulfonate graft-polymerized with acrylamide and maleic anhydride (Bentonite/LS-g-AM-co-MAH) were used to investigate the effect of competitive cations and coexisting anions in supporting electrolyte on the adsorption of Pb2+ onto Bentonite/LS-g-AM-co-MAH. The results show that, under the presence of Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Co2+, Zn2+, Cd2+ and Cu2+ in the solution, the removal capacities of Pb2+ reduce and the order of decreasing effect is as follows: Cu2+ > Cd2+ > Zn2+ > Co2+ > Ni2+ > Ca2+ > Mg2+ > K+ > Na+ > Li+. Under the existence of Fe3+ and Al3+ in the solution, the adsorption of Pb2+ decreases at pH=2.0-3.0 and increases at pH=4.0-6.0, and the effect order is Fe3+>Al3+. Coexisting anions NO3-, Cl- and Br- in the solution have negative effect on the Pb2+ adsorption and the decreasing order is Br- > Cl- > NO3-. SO42- and PO43- in the solution have positive effect on the removal of Pb2+ and their effects are quite similar.
Self-made composite adsorbent resins comprising of Bentonite/sodium lignosulfonate graft-polymerized with acrylamide and maleic anhydride (Bentonite/LS-g-AM-co-MAH) were used to investigate the effect of competitive cations and coexisting anions in supporting electrolyte on the adsorption of Pb2+ onto Bentonite/LS-g-AM-co-MAH. The results show that, under the presence of Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Co2+, Zn2+, Cd2+ and Cu2+ in the solution, the removal capacities of Pb2+ reduce and the order of decreasing effect is as follows: Cu2+ > Cd2+ > Zn2+ > Co2+ > Ni2+ > Ca2+ > Mg2+ > K+ > Na+ > Li+. Under the existence of Fe3+ and Al3+ in the solution, the adsorption of Pb2+ decreases at pH=2.0-3.0 and increases at pH=4.0-6.0, and the effect order is Fe3+>Al3+. Coexisting anions NO3-, Cl- and Br- in the solution have negative effect on the Pb2+ adsorption and the decreasing order is Br- > Cl- > NO3-. SO42- and PO43- in the solution have positive effect on the removal of Pb2+ and their effects are quite similar.
2016, 33(10): 2187-2196.
doi: 10.13801/j.cnki.fhclxb.20151217.003
Abstract:
The torsion buckling, failure load and failure modes of the carbon fiber reinforced polymer (CFRP) thin-walled circular tubes were tested and numerical simulated. Three failure modes of the circular tubes under torque were observed in the test, and the characteristics and mechanism of different failure modes were analyzed. Buckling and damage finite element models of the circular tubes were established by ABAQUS considering the factors such as initial imperfection and nonlinear buckling etc. of cylindrical shells. The results show that buckling could induce micro crack produce and propagation on the surface of the circular tubes, and it accelerates failure of the circular tubes. The interlaminar stress of the circular tubes under torque failure process is relatively small, and the interlaminar delamination is mainly caused by the sudden damage of the tube wall. The initial imperfection of the cylindrical shells has a great influence on the buckling and failure loads. The initial imperfection coefficient of the circular tube was determined by comparing the calculation results with test data in this paper, and the numerical simulation results of damage models and test data are consistent, which verifies the effectiveness of the finite element models.
The torsion buckling, failure load and failure modes of the carbon fiber reinforced polymer (CFRP) thin-walled circular tubes were tested and numerical simulated. Three failure modes of the circular tubes under torque were observed in the test, and the characteristics and mechanism of different failure modes were analyzed. Buckling and damage finite element models of the circular tubes were established by ABAQUS considering the factors such as initial imperfection and nonlinear buckling etc. of cylindrical shells. The results show that buckling could induce micro crack produce and propagation on the surface of the circular tubes, and it accelerates failure of the circular tubes. The interlaminar stress of the circular tubes under torque failure process is relatively small, and the interlaminar delamination is mainly caused by the sudden damage of the tube wall. The initial imperfection of the cylindrical shells has a great influence on the buckling and failure loads. The initial imperfection coefficient of the circular tube was determined by comparing the calculation results with test data in this paper, and the numerical simulation results of damage models and test data are consistent, which verifies the effectiveness of the finite element models.
2016, 33(10): 2197-2204.
doi: 10.13801/j.cnki.fhclxb.20160118.002
Abstract:
A micromechanical model was developed for predicting effective hygrothermoelastic properties of composites and local field distributions within the unit cell based on the framework of the variational asymptotic homogenization theory. Starting from the derivation of the hygrothermoelastic free energy functional of composites, the leading variable item in the functional of free energy was asymptotically analyzed by taking advantage of the small ratio of microscale to macroscale. Micromechanical model and the recovery relationships of local field distributions for the hygrothermoelastic problem were obtained and implemented by using finite element method. Comparison with ABAQUS finite element example shows the constructed micromechanical model can predict the effective hygrothermoelastic properties of composites and local field distributions effectively and accurately.
A micromechanical model was developed for predicting effective hygrothermoelastic properties of composites and local field distributions within the unit cell based on the framework of the variational asymptotic homogenization theory. Starting from the derivation of the hygrothermoelastic free energy functional of composites, the leading variable item in the functional of free energy was asymptotically analyzed by taking advantage of the small ratio of microscale to macroscale. Micromechanical model and the recovery relationships of local field distributions for the hygrothermoelastic problem were obtained and implemented by using finite element method. Comparison with ABAQUS finite element example shows the constructed micromechanical model can predict the effective hygrothermoelastic properties of composites and local field distributions effectively and accurately.
2016, 33(10): 2205-2214.
doi: 10.13801/j.cnki.fhclxb.20151217.002
Abstract:
Using glass frits can improve mechanical strength and keep structure integrity of ceramifiable silicone rubber matrix composites after pyrolysis at high temperature. In order to study the effects of composition of glass frits on the high-temperature resistance properties of muscovite/silicone rubber composites, two composites were prepared by using glass frits A and B as fluxing agent, respectively. The mechanical properties, microstructure, thermal decomposition properties and ceramic mechanism of both composites were studied. The results show that tensile strength of muscovite/silicone rubber composites is 3~4 MPa at room temperature, and flexural strength of the samples after pyrolysis is 0.3-4.5 MPa and can keep structure integrity at 600-1 200℃. SEM results reveal that glass frit B is helpful to form a large amount of liquid phase structure, and improve the strength and structure of ceramic layer produced after pyrolysis. TG results show that glass frits can accelerate the decomposition of silicone rubber, so the amount of glass frits should be controlled. XRD results show that adding glass frit B which includes more SiO2 and K2O to muscovite/silicone rubber composites can form an amorphous phase and a potassium aluminum silicate (K2O·Al2O3·6SiO2) during the temperature change and therefore increase the strength of ceramic layer.
Using glass frits can improve mechanical strength and keep structure integrity of ceramifiable silicone rubber matrix composites after pyrolysis at high temperature. In order to study the effects of composition of glass frits on the high-temperature resistance properties of muscovite/silicone rubber composites, two composites were prepared by using glass frits A and B as fluxing agent, respectively. The mechanical properties, microstructure, thermal decomposition properties and ceramic mechanism of both composites were studied. The results show that tensile strength of muscovite/silicone rubber composites is 3~4 MPa at room temperature, and flexural strength of the samples after pyrolysis is 0.3-4.5 MPa and can keep structure integrity at 600-1 200℃. SEM results reveal that glass frit B is helpful to form a large amount of liquid phase structure, and improve the strength and structure of ceramic layer produced after pyrolysis. TG results show that glass frits can accelerate the decomposition of silicone rubber, so the amount of glass frits should be controlled. XRD results show that adding glass frit B which includes more SiO2 and K2O to muscovite/silicone rubber composites can form an amorphous phase and a potassium aluminum silicate (K2O·Al2O3·6SiO2) during the temperature change and therefore increase the strength of ceramic layer.
2016, 33(10): 2215-2222.
doi: 10.13801/j.cnki.fhclxb.20160113.001
Abstract:
The effects of pre-tighten force, tooth length and stress level on static and fatigue performances of carbon fiber reinforced plastics (CFRP) pre-tighten single tooth connector (PTSTC) were investigated by tests. The test results show that the fatigue ultimate load-capacity of CFRP PTSTC reaches to 80%-85% of the static ultimate load-capacity, and comparing with traditional connection methods such as bolt connection etc., the fatigue performance of it has advantages at some degree. The pre-tighten load can improve the static and fatigue performances of CFRP single tooth connector significantly. The static ultimate load-capacity of CFRP PTSTC increases with the tooth-length increasing, but increasing the tooth-length would not necessarily improves the fatigue life of the connector under the same load level, especially, the fatigue life reduces with the tooth-length increases under lower load level. The fatigue crack of PTSTC initiates rapidly during the early loading period, then grows slowly, and propagates sharply again in the last few cycles before fracture. The pre-tighten load can slow down the fatigue damage accumulation rate. The stiffness degeneration during fatigue process of PTSTC is not obviously, which is only 1%-4% in the former 95% of the fatigue life. The pre-tighten load can also slow down the stiffness degeneration rate. The investigation conclusions obtained can provide references for the anti-fatigue design of composite connector.
The effects of pre-tighten force, tooth length and stress level on static and fatigue performances of carbon fiber reinforced plastics (CFRP) pre-tighten single tooth connector (PTSTC) were investigated by tests. The test results show that the fatigue ultimate load-capacity of CFRP PTSTC reaches to 80%-85% of the static ultimate load-capacity, and comparing with traditional connection methods such as bolt connection etc., the fatigue performance of it has advantages at some degree. The pre-tighten load can improve the static and fatigue performances of CFRP single tooth connector significantly. The static ultimate load-capacity of CFRP PTSTC increases with the tooth-length increasing, but increasing the tooth-length would not necessarily improves the fatigue life of the connector under the same load level, especially, the fatigue life reduces with the tooth-length increases under lower load level. The fatigue crack of PTSTC initiates rapidly during the early loading period, then grows slowly, and propagates sharply again in the last few cycles before fracture. The pre-tighten load can slow down the fatigue damage accumulation rate. The stiffness degeneration during fatigue process of PTSTC is not obviously, which is only 1%-4% in the former 95% of the fatigue life. The pre-tighten load can also slow down the stiffness degeneration rate. The investigation conclusions obtained can provide references for the anti-fatigue design of composite connector.
2016, 33(10): 2223-2229.
doi: 10.13801/j.cnki.fhclxb.20160309.002
Abstract:
Temperature field variation rule of carbon fiber reinforced polymer (CFRP) was tested by using electric thermal experimental platform for composites, while revealing the influence mechanism of electric thermal effect on the mechanical properties of CFRP from the interfacial shear strength of monofilament tensile fracture, the short beam shear property and shear fracture etc.The results show that electric thermal effect can increase the overall temperature of CFRP, and reach steady state temperature at about 4 min. CFRP laminate surface temperature is higher with increasing of the current strength, CFRP's surface temperature reaches 151℃ when the current strength is 8 A (0.44 A/mm2); the monofilament tensile and short beam shear strength of the interface with the increasing current strength increase at first and then decrease; when at a low current, the electric thermal effect generates less Joule heat, which can optimize the interface property to improve the interfacial shear strength, when at a high current, the electric thermal effect's Joule heat is much higher, which can produce the irreversible damage such as ablation on interface and reduce the interfacial bonding property.
Temperature field variation rule of carbon fiber reinforced polymer (CFRP) was tested by using electric thermal experimental platform for composites, while revealing the influence mechanism of electric thermal effect on the mechanical properties of CFRP from the interfacial shear strength of monofilament tensile fracture, the short beam shear property and shear fracture etc.The results show that electric thermal effect can increase the overall temperature of CFRP, and reach steady state temperature at about 4 min. CFRP laminate surface temperature is higher with increasing of the current strength, CFRP's surface temperature reaches 151℃ when the current strength is 8 A (0.44 A/mm2); the monofilament tensile and short beam shear strength of the interface with the increasing current strength increase at first and then decrease; when at a low current, the electric thermal effect generates less Joule heat, which can optimize the interface property to improve the interfacial shear strength, when at a high current, the electric thermal effect's Joule heat is much higher, which can produce the irreversible damage such as ablation on interface and reduce the interfacial bonding property.
2016, 33(10): 2230-2236.
doi: 10.13801/j.cnki.fhclxb.20160315.010
Abstract:
Inspired by the suture joint structure in nature, models of composite bionic suture joint structure with different orders of hierarchies were investigated based on the principle of graphic fractal. The law of interfacial damage extension and structural loading mechanism of joint structure were studied using commercial finite element software ABAQUS. The influence of structural interlocking feature, number of teeth and shape of teeth on the structural loading capability of the high-hierarchy suture joint structure was analyzed. The results show that the structural interlocking feature of the high-hierarchy suture joint structure improves structural loading capability significantly and changes the structure damage mechanism. Increasing the number of joint teeth on the unit width properly and changing local feature of joint teeth can reduce stress concentration and improve mechanical property of suture joint structure. The research explains the mechanical principle embodied in the process of evolution for the suture joint structure in nature, and provides new insights for the development of new engineering joint structure.
Inspired by the suture joint structure in nature, models of composite bionic suture joint structure with different orders of hierarchies were investigated based on the principle of graphic fractal. The law of interfacial damage extension and structural loading mechanism of joint structure were studied using commercial finite element software ABAQUS. The influence of structural interlocking feature, number of teeth and shape of teeth on the structural loading capability of the high-hierarchy suture joint structure was analyzed. The results show that the structural interlocking feature of the high-hierarchy suture joint structure improves structural loading capability significantly and changes the structure damage mechanism. Increasing the number of joint teeth on the unit width properly and changing local feature of joint teeth can reduce stress concentration and improve mechanical property of suture joint structure. The research explains the mechanical principle embodied in the process of evolution for the suture joint structure in nature, and provides new insights for the development of new engineering joint structure.
2016, 33(10): 2237-2245.
doi: 10.13801/j.cnki.fhclxb.20160308.005
Abstract:
In order to fabricate Al2O3/Fe composite honeycombs with high-performances, 316L alloy powder, Al2O3 powder and binder were used as raw materials, Al2O3/Fe composite honeycombs were obtained by plasticizing powder extrusion and sintering at 1 200℃ for 2 h in argon atmosphere firstly. Then, the effects of adding Al2O3 on the structures and properties of Al2O3/Fe composite honeycombs were investigated by SEM, XRD and universal testing machine. The results show that metal powder particles bind together to form γ-Fe matrix network structure during sintering process, and Cr2O3 with polygon geometric shape is formed on the surface. Adding a small amount of Al2O3 can inhibit the precipitation of Cr from matrix and reduce the amount of Cr2O3 on the surface, which makes the sintering combination of metal powder particles more compact and the surface of structure more smooth. With Al2O3 content increasing, the bonding capacity for the surface of honeycomb materials with catalytic activity coating enhances, compressive strength of the composite honeycomb increases at first and then decreases, and when Al2O3 content is 5.0wt%, the compressive strength reaches 26 MPa. The conclusions obtained show that the mechanical properties of 5.0wt% Al2O3/Fe composite honeycomb are the best, and the surface paintability is preferable.
In order to fabricate Al2O3/Fe composite honeycombs with high-performances, 316L alloy powder, Al2O3 powder and binder were used as raw materials, Al2O3/Fe composite honeycombs were obtained by plasticizing powder extrusion and sintering at 1 200℃ for 2 h in argon atmosphere firstly. Then, the effects of adding Al2O3 on the structures and properties of Al2O3/Fe composite honeycombs were investigated by SEM, XRD and universal testing machine. The results show that metal powder particles bind together to form γ-Fe matrix network structure during sintering process, and Cr2O3 with polygon geometric shape is formed on the surface. Adding a small amount of Al2O3 can inhibit the precipitation of Cr from matrix and reduce the amount of Cr2O3 on the surface, which makes the sintering combination of metal powder particles more compact and the surface of structure more smooth. With Al2O3 content increasing, the bonding capacity for the surface of honeycomb materials with catalytic activity coating enhances, compressive strength of the composite honeycomb increases at first and then decreases, and when Al2O3 content is 5.0wt%, the compressive strength reaches 26 MPa. The conclusions obtained show that the mechanical properties of 5.0wt% Al2O3/Fe composite honeycomb are the best, and the surface paintability is preferable.
2016, 33(10): 2246-2252.
doi: 10.13801/j.cnki.fhclxb.20160307.001
Abstract:
In order to solve the problems of annular uniform and stable flow distribution for the cladding molten metal in the solid-liquid cast-rolling bonding (SLCRB) process of bimetallic clad pipes, an annular delivery device comprised with three-level annular stepped shunts and the tapered buffer was proposed and designed. Besides, the fluid dynamics model during the steady flow distribution process was established based on the commercial software Fluent. The influence of the delivery device structure and the cast-rolling speed on system flow field was analyzed, and the internal structure and flow distribution conditions of delivery device were presented to obtain a uniform and stable outlet flow field, which was verified by the water model experiment. The results show that it contributes to the uniformly flow distribution if the aspect ratio of the annular delivery device channel is no smaller than 1, and the stream buffer action of the tapered buffer region is crucial. The Pb-Al bimetallic clad pipes with outer diameter of 38 mm and inner diameter of 26 mm was produced successfully at the cast-rolling speed of 1.2 m/min. The thickness of the cladding metal is uniform and the combined effect at the interface is well.
In order to solve the problems of annular uniform and stable flow distribution for the cladding molten metal in the solid-liquid cast-rolling bonding (SLCRB) process of bimetallic clad pipes, an annular delivery device comprised with three-level annular stepped shunts and the tapered buffer was proposed and designed. Besides, the fluid dynamics model during the steady flow distribution process was established based on the commercial software Fluent. The influence of the delivery device structure and the cast-rolling speed on system flow field was analyzed, and the internal structure and flow distribution conditions of delivery device were presented to obtain a uniform and stable outlet flow field, which was verified by the water model experiment. The results show that it contributes to the uniformly flow distribution if the aspect ratio of the annular delivery device channel is no smaller than 1, and the stream buffer action of the tapered buffer region is crucial. The Pb-Al bimetallic clad pipes with outer diameter of 38 mm and inner diameter of 26 mm was produced successfully at the cast-rolling speed of 1.2 m/min. The thickness of the cladding metal is uniform and the combined effect at the interface is well.
2016, 33(10): 2253-2260.
doi: 10.13801/j.cnki.fhclxb.20160112.006
Abstract:
An axisymmetric unit cell model of particle reinforced Al matrix composites was established, and the mechanical behaviors and micro-stress distribution of B4C particles reinforced Al5083 matrix composites were simulated by finite element method. The results show that the simulation result agrees well with the experimental result. The simulated tensile stress of spheroidicity particle reinforced composites is 485 MPa, while the experimental value is 477 MPa, indicating a relative error as low as 1.7%. Particle shapes have a significant influence on the micro-stress field of composites: the sharp edge of cylindrical particle leads to a stress concentration easily, while the spherical particle results in a relatively uniform stress distribution at the interface. Elastic modulus as well as tensile strength of the composites increase with the increase of volume fraction for B4C particle in a certain range. In the case of constant particle volume fraction, when the particles with different aspect ratios are aligned along the load direction, the larger the aspect ratio of particles, the higher the elastic modulus and tensile strength of composites.
An axisymmetric unit cell model of particle reinforced Al matrix composites was established, and the mechanical behaviors and micro-stress distribution of B4C particles reinforced Al5083 matrix composites were simulated by finite element method. The results show that the simulation result agrees well with the experimental result. The simulated tensile stress of spheroidicity particle reinforced composites is 485 MPa, while the experimental value is 477 MPa, indicating a relative error as low as 1.7%. Particle shapes have a significant influence on the micro-stress field of composites: the sharp edge of cylindrical particle leads to a stress concentration easily, while the spherical particle results in a relatively uniform stress distribution at the interface. Elastic modulus as well as tensile strength of the composites increase with the increase of volume fraction for B4C particle in a certain range. In the case of constant particle volume fraction, when the particles with different aspect ratios are aligned along the load direction, the larger the aspect ratio of particles, the higher the elastic modulus and tensile strength of composites.
2016, 33(10): 2261-2269.
doi: 10.13801/j.cnki.fhclxb.20160308.004
Abstract:
The surface of SiCP was Ti-coated via melt salt, and the Ti-coated SiCP/Al2014 composites were fabricated by stir casting method. The effect law of size and volume fraction of Ti-coated SiCP on the microstructure and mechanical properties of SiCP/Al2014 composites were investigated. The results show that the Ti-coated processing could effectively improve the distribution uniformity of Ti-coated SiCP in Al matrix. When the size of Ti-coated SiCP keeps constant, the distribution uniformity of Ti-coated SiCP in Al matrix decreases with increasing volume fraction of SiCP. When volume fraction of SiCP keeps constant, the distribution uniformity of Ti-coated SiCP in Al matrix increases with increasing size of SiCP. When size of SiCP keeps constant, the tensile strength of SiCP/Al2014 composites at room temperature increases first then decreases with increasing volume fraction of particles. The SiCP/Al2014 composites with 4% volume fraction of particles possess the highest tensile strength, i.e., composites containing SiCP with sizes of 5 μm and 10 μm correspond to tensile strength of 524 MPa and 536 MPa, respectively. The tensile strength of SiCP/Al2014 composites at high temperature (493 K) increases with increasing volume fraction of SiCP. SiCP/Al composites with 6% volume fraction of particles possess the highest tensile strength. The composite with 5 μm-SiCP exhibits tensile strength of 308 MPa while that with 10 μm-SiCP exhibits tensile strength of 320 MPa when the volume fraction of particles is 6%.
The surface of SiCP was Ti-coated via melt salt, and the Ti-coated SiCP/Al2014 composites were fabricated by stir casting method. The effect law of size and volume fraction of Ti-coated SiCP on the microstructure and mechanical properties of SiCP/Al2014 composites were investigated. The results show that the Ti-coated processing could effectively improve the distribution uniformity of Ti-coated SiCP in Al matrix. When the size of Ti-coated SiCP keeps constant, the distribution uniformity of Ti-coated SiCP in Al matrix decreases with increasing volume fraction of SiCP. When volume fraction of SiCP keeps constant, the distribution uniformity of Ti-coated SiCP in Al matrix increases with increasing size of SiCP. When size of SiCP keeps constant, the tensile strength of SiCP/Al2014 composites at room temperature increases first then decreases with increasing volume fraction of particles. The SiCP/Al2014 composites with 4% volume fraction of particles possess the highest tensile strength, i.e., composites containing SiCP with sizes of 5 μm and 10 μm correspond to tensile strength of 524 MPa and 536 MPa, respectively. The tensile strength of SiCP/Al2014 composites at high temperature (493 K) increases with increasing volume fraction of SiCP. SiCP/Al composites with 6% volume fraction of particles possess the highest tensile strength. The composite with 5 μm-SiCP exhibits tensile strength of 308 MPa while that with 10 μm-SiCP exhibits tensile strength of 320 MPa when the volume fraction of particles is 6%.
2016, 33(10): 2270-2276.
doi: 10.13801/j.cnki.fhclxb.20160118.001
Abstract:
By combining ultrasonic vibration thermal effects conversion with dynamic boundary conditions imposed, the ultrasonic vibration boundary conditions were made approximation. The residual stress of SiC/316L composite coating with ultrasonic vibration in laser cladding was investigated, and the influence of ultrasonic amplitude and scanning speed on residual stress of composite coating was studied. According to the optimization results, SiC/316L composite coating was prepared by ultrasonic aided laser cladding.The results show that ultrasonic amplitude and scanning speed have significant effects on x-stress, y-stress, shear stress at the interface and von Mises stress on the coating surface. The residual stress relaxation of SiC/316L composite coating is excellent when the ultrasonic amplitude is 10 μm and scanning speed is 10 mm/s. The structure of coating is obvious refinement, and SiC particles is uniform distributed for the ultrasonic cavitation or mechanical effect and acoustic streaming effect.
By combining ultrasonic vibration thermal effects conversion with dynamic boundary conditions imposed, the ultrasonic vibration boundary conditions were made approximation. The residual stress of SiC/316L composite coating with ultrasonic vibration in laser cladding was investigated, and the influence of ultrasonic amplitude and scanning speed on residual stress of composite coating was studied. According to the optimization results, SiC/316L composite coating was prepared by ultrasonic aided laser cladding.The results show that ultrasonic amplitude and scanning speed have significant effects on x-stress, y-stress, shear stress at the interface and von Mises stress on the coating surface. The residual stress relaxation of SiC/316L composite coating is excellent when the ultrasonic amplitude is 10 μm and scanning speed is 10 mm/s. The structure of coating is obvious refinement, and SiC particles is uniform distributed for the ultrasonic cavitation or mechanical effect and acoustic streaming effect.
2016, 33(10): 2277-2289.
doi: 10.13801/j.cnki.fhclxb.20160118.003
Abstract:
Split Hopkinson pressure bar (SHPB) system was used to investigate the dynamic compressive properties of in situ synthesized TiC particles and TiB whisker mixing reinforced titanium matrix composites (TMCs) at the temperature range 293-973 K and the strain rates range 6 000-10 000 s-1. The test results show that the flow stress of TMCs significantly decreases with the temperature increasing when the temperature is in the range of 373-573 K, 673-773 K and 873-973 K. At relatively low temperature (lower than 373 K) and low strain rate (6 000-8 000 s-1), TMCs exhibit a slight strain rate hardening characteristic. However, at high temperature (573 K or higher), TMCs present obvious strain softening feature at all strain rates used and the strain rate softening effect is more significant under higher temperature. The analysis on the failure/fracture mechanisms shows that the combined effect of the adiabatic softening and the behavior of the micro cracks generation and development in the adiabatic shear band (ABS) are the mechanisms for the strain softening. Under high strain rate combined with high strain, micro cracks initiate in the ABS and will cause the rapidly damage or fracture of TMCs on the macro when the ductility of the TMCs is not high enough to suppress or hinder the development of the micro cracks under relative low temperature. Titanium alloy matrix plastic fracture is the main material damage mode but local brittle fracture also presents around the reinforcement phase.
Split Hopkinson pressure bar (SHPB) system was used to investigate the dynamic compressive properties of in situ synthesized TiC particles and TiB whisker mixing reinforced titanium matrix composites (TMCs) at the temperature range 293-973 K and the strain rates range 6 000-10 000 s-1. The test results show that the flow stress of TMCs significantly decreases with the temperature increasing when the temperature is in the range of 373-573 K, 673-773 K and 873-973 K. At relatively low temperature (lower than 373 K) and low strain rate (6 000-8 000 s-1), TMCs exhibit a slight strain rate hardening characteristic. However, at high temperature (573 K or higher), TMCs present obvious strain softening feature at all strain rates used and the strain rate softening effect is more significant under higher temperature. The analysis on the failure/fracture mechanisms shows that the combined effect of the adiabatic softening and the behavior of the micro cracks generation and development in the adiabatic shear band (ABS) are the mechanisms for the strain softening. Under high strain rate combined with high strain, micro cracks initiate in the ABS and will cause the rapidly damage or fracture of TMCs on the macro when the ductility of the TMCs is not high enough to suppress or hinder the development of the micro cracks under relative low temperature. Titanium alloy matrix plastic fracture is the main material damage mode but local brittle fracture also presents around the reinforcement phase.
2016, 33(10): 2290-2296.
doi: 10.13801/j.cnki.fhclxb.20160315.011
Abstract:
Anti oxidation coating technology is one of the most effective ways to solve the high temperature oxidation resistance of carbon/carbon composites. In order to improve the high temperature oxidation resistance of materials above 1 800℃, a SiC/MoSi2/ZrO2 gradient oxidation resistant coating system was fabricated on surface of the carbon/carbon composites by the pack cementation method, slurry method and plasma spraying process. The surface and section morphologies of coating were observed by XRD/EDS, intensity and roughness testing. The total coating system is tested by plasma wind tunnel. Results show that the coating has a compact interfacial bonding strength among matrix, transition layer and high temperature oxidation resistance layer. High temperature oxidation resistance layer has uniform thickness and dense structure. After 600 s plasma wind tunnel oxidation, surface temperature of coating reaches up to 1 850℃. The oxidation mass loss rate is 3.15×10-6 g/(cm2·s). The SiC/MoSi2/ZrO2 gradient oxidation resistant coating system has good antioxidant capacity over 1 800℃.
Anti oxidation coating technology is one of the most effective ways to solve the high temperature oxidation resistance of carbon/carbon composites. In order to improve the high temperature oxidation resistance of materials above 1 800℃, a SiC/MoSi2/ZrO2 gradient oxidation resistant coating system was fabricated on surface of the carbon/carbon composites by the pack cementation method, slurry method and plasma spraying process. The surface and section morphologies of coating were observed by XRD/EDS, intensity and roughness testing. The total coating system is tested by plasma wind tunnel. Results show that the coating has a compact interfacial bonding strength among matrix, transition layer and high temperature oxidation resistance layer. High temperature oxidation resistance layer has uniform thickness and dense structure. After 600 s plasma wind tunnel oxidation, surface temperature of coating reaches up to 1 850℃. The oxidation mass loss rate is 3.15×10-6 g/(cm2·s). The SiC/MoSi2/ZrO2 gradient oxidation resistant coating system has good antioxidant capacity over 1 800℃.
Preparation and dynamic compression properties of Zr-W multifunctional energetic structural material
2016, 33(10): 2297-2303.
doi: 10.13801/j.cnki.fhclxb.20160315.001
Abstract:
The compressive behavior of pressing sintering Zr-W multifunctional energetic structural material was tested at different strain rates by using material testing machine and split Hopkinson pressure bar (SHPB) system. A constant strain rate dynamic loading can be obtained by combination of attaching a strain gauge directly to the sample and employing the pulse shaping technique. Test results show that Zr-W material appears good linear elasticity both under quasi-static and dynamic loading, and its elastic modulus is about 186 GPa, not so sensitive to stain rate effect. The Zr-W material presents high-strength and brittle which is attributed to the W2Zr sintering product phase, and it can fragment, react and rapidly release high amounts of energy under strong impacting load. The results show that the Zr-W material has high energy, and its dynamic failure strain and failure strength increase with the strain rate increasing.
The compressive behavior of pressing sintering Zr-W multifunctional energetic structural material was tested at different strain rates by using material testing machine and split Hopkinson pressure bar (SHPB) system. A constant strain rate dynamic loading can be obtained by combination of attaching a strain gauge directly to the sample and employing the pulse shaping technique. Test results show that Zr-W material appears good linear elasticity both under quasi-static and dynamic loading, and its elastic modulus is about 186 GPa, not so sensitive to stain rate effect. The Zr-W material presents high-strength and brittle which is attributed to the W2Zr sintering product phase, and it can fragment, react and rapidly release high amounts of energy under strong impacting load. The results show that the Zr-W material has high energy, and its dynamic failure strain and failure strength increase with the strain rate increasing.
2016, 33(10): 2304-2311.
doi: 10.13801/j.cnki.fhclxb.20151223.001
Abstract:
In order to solve the application problems of TiO2 such as the poor effective utilization rate for solar energy, high recombination rate of photoinduced electrons and holes, low photocatalytic activity and difficulty in recycle etc., nano Ag-carbon nanotube (CNT)-mixed crystal TiO2 composite fibers were synthesized successfully by electrospinning technology, and the microstructures and constructions of the materials were analyzed in detail by characterization methods such as SEM, XRD, EDS and Raman etc., thus the photocatalytic activities of nano Ag-CNT-mixed crystal TiO2 composite fibers for methylene blue were investigated. The results show that the mixed crystal of anatase- and rutile-TiO2 can not only reduce the band gap, but also slow down the combination and cancellation of photoinduced electrons and holes. The localized surface plasmon resonance of Ag nanoparticles can enhance the light absorption of nano Ag-CNT-mixed crystal TiO2 composite fibers, and CNT can promote the effective segregation of photoinduced electrons and holes. The degradation rate of nano Ag-CNT-mixed crystal TiO2 composite fibers for methylene blue in the first cycle reaches 97.5%, and the degradation rate for methylene blue after 5 catalytic cycles still retains above 90.0%. The conclusions obtained show that the new type nano Ag-CNT-mixed crystal TiO2 composite fiber prepared by electrospinning is a high-activity photocatalyst and is easy to be recycled, which has application prospects for the photo degradation of methylene blue.
In order to solve the application problems of TiO2 such as the poor effective utilization rate for solar energy, high recombination rate of photoinduced electrons and holes, low photocatalytic activity and difficulty in recycle etc., nano Ag-carbon nanotube (CNT)-mixed crystal TiO2 composite fibers were synthesized successfully by electrospinning technology, and the microstructures and constructions of the materials were analyzed in detail by characterization methods such as SEM, XRD, EDS and Raman etc., thus the photocatalytic activities of nano Ag-CNT-mixed crystal TiO2 composite fibers for methylene blue were investigated. The results show that the mixed crystal of anatase- and rutile-TiO2 can not only reduce the band gap, but also slow down the combination and cancellation of photoinduced electrons and holes. The localized surface plasmon resonance of Ag nanoparticles can enhance the light absorption of nano Ag-CNT-mixed crystal TiO2 composite fibers, and CNT can promote the effective segregation of photoinduced electrons and holes. The degradation rate of nano Ag-CNT-mixed crystal TiO2 composite fibers for methylene blue in the first cycle reaches 97.5%, and the degradation rate for methylene blue after 5 catalytic cycles still retains above 90.0%. The conclusions obtained show that the new type nano Ag-CNT-mixed crystal TiO2 composite fiber prepared by electrospinning is a high-activity photocatalyst and is easy to be recycled, which has application prospects for the photo degradation of methylene blue.
2016, 33(10): 2312-2318.
doi: 10.13801/j.cnki.fhclxb.20151230.001
Abstract:
Ultra-high molecular weight polyethylene (UHMW-PE) fiber fabric reinforced-polyethylene (PE) coat flexible composites were taken as research object. Firstly, the cross-section of the composites was polished by ion polishing instrument, and then the microscopic structure of the composites was measured through SEM and optical microscope. In this way, the microscopic geometry parameters of the composites were got. Finally, based on homogenization method and continuum hypothesis, mechanical model of unit cell was set up, and tensile load-strain curve of unit-cell was calculated. The theoretical values were compared with the experimental values. The results show that the tensile load-strain curve obtained by mechanical model of unit-cell of the composites based on multi-dimension method was in good agreement with the tension load-strain curve obtained by experiment. The theoretical model is better able to predict tensile modulus of fiber fabric reinforced flexible composite.
Ultra-high molecular weight polyethylene (UHMW-PE) fiber fabric reinforced-polyethylene (PE) coat flexible composites were taken as research object. Firstly, the cross-section of the composites was polished by ion polishing instrument, and then the microscopic structure of the composites was measured through SEM and optical microscope. In this way, the microscopic geometry parameters of the composites were got. Finally, based on homogenization method and continuum hypothesis, mechanical model of unit cell was set up, and tensile load-strain curve of unit-cell was calculated. The theoretical values were compared with the experimental values. The results show that the tensile load-strain curve obtained by mechanical model of unit-cell of the composites based on multi-dimension method was in good agreement with the tension load-strain curve obtained by experiment. The theoretical model is better able to predict tensile modulus of fiber fabric reinforced flexible composite.
2016, 33(10): 2319-2324.
doi: 10.13801/j.cnki.fhclxb.20160127.001
Abstract:
In order to characterize the anisotropic mechanical behaviors of woven fabric composites precisely, based on fiber reinforced composite continuum medium mechanics theory, an anisotropic hyperelastic constitutive model with biaxial tension coupling of fiber for woven fabric composites was proposed firstly. The unit-volume strain energy in the model was decomposed into the deformation energy of fiber elongation, the compaction deformation energy due to biaxial tension coupling and shear deformation energy due to the change of angels between fibers. Then, determination approach for model parameters was given, and parameters of constitutive model were obtained by fitting the uni-axial tensile, biaxial tensile and picture-frame shear experiment data. Finally, the numerical simulation of biaxial tensile and picture-frame shear experiments was conducted by the model, and the simulation results were contrasted and analyzed with experiment data. The results show that the constitutive model proposed is suitable to characterize the non-linear and anisotropic mechanical behaviors cased by large deformation of woven fabric composites during forming process. The conclusions obtained show that the proposed constitutive model has advantages of simple and useful, and the determination of material parameters is easy, which can lay down the theoretical foundation for the numerical simulation and processing optimization for the forming of woven fabric composites.
In order to characterize the anisotropic mechanical behaviors of woven fabric composites precisely, based on fiber reinforced composite continuum medium mechanics theory, an anisotropic hyperelastic constitutive model with biaxial tension coupling of fiber for woven fabric composites was proposed firstly. The unit-volume strain energy in the model was decomposed into the deformation energy of fiber elongation, the compaction deformation energy due to biaxial tension coupling and shear deformation energy due to the change of angels between fibers. Then, determination approach for model parameters was given, and parameters of constitutive model were obtained by fitting the uni-axial tensile, biaxial tensile and picture-frame shear experiment data. Finally, the numerical simulation of biaxial tensile and picture-frame shear experiments was conducted by the model, and the simulation results were contrasted and analyzed with experiment data. The results show that the constitutive model proposed is suitable to characterize the non-linear and anisotropic mechanical behaviors cased by large deformation of woven fabric composites during forming process. The conclusions obtained show that the proposed constitutive model has advantages of simple and useful, and the determination of material parameters is easy, which can lay down the theoretical foundation for the numerical simulation and processing optimization for the forming of woven fabric composites.
2016, 33(10): 2325-2335.
doi: 10.13801/j.cnki.fhclxb.20160218.001
Abstract:
A new type of square thin-walled steel tube/bamboo plywood composite hollow column with horizontal binding bars (SBCCB) was proposed to solve the issue that the square thin-walled steel tube/bamboo plywood composite hollow column (SBCC) was liable to glue failure under compressive load. Nine SBCCB were used to perform the axial compression tests firstly. The failure modes of SBCCB loaded were investigated, the influences of the cross-sectional size, slenderness ratio and sectional combination mode of SBCCB on the glue failure load and ultimate bearing load of it were analyzed, and the ultimate compressive stress of SBCCB was compared with existing data of SBCC. Then, the calculating formula for the axial compression bearing-capacity of SBCCB was derived through the nonlinear regression analysis. The results indicate that the axial compressive failure damage of SBCCB is primarily the glue failure of bamboo plywood between horizontal binding bars of the end of column and the middle of column the glue failure as well as material broken damage of bamboo plywood. The ultimate bearing capacity is not only related to the cross-sectional size and slenderness ratio, but also affected by the sectional combination mode. By setting horizontal binding bars, the glue failure binding can be suppressed effectively, the ultimate failure mode changes, and the ultimate carrying capacity improves significantly. Compared with the ultimate compressive stress of SBCC, the ultimate compressive stress of SBCCB increases by 26% averagely.
A new type of square thin-walled steel tube/bamboo plywood composite hollow column with horizontal binding bars (SBCCB) was proposed to solve the issue that the square thin-walled steel tube/bamboo plywood composite hollow column (SBCC) was liable to glue failure under compressive load. Nine SBCCB were used to perform the axial compression tests firstly. The failure modes of SBCCB loaded were investigated, the influences of the cross-sectional size, slenderness ratio and sectional combination mode of SBCCB on the glue failure load and ultimate bearing load of it were analyzed, and the ultimate compressive stress of SBCCB was compared with existing data of SBCC. Then, the calculating formula for the axial compression bearing-capacity of SBCCB was derived through the nonlinear regression analysis. The results indicate that the axial compressive failure damage of SBCCB is primarily the glue failure of bamboo plywood between horizontal binding bars of the end of column and the middle of column the glue failure as well as material broken damage of bamboo plywood. The ultimate bearing capacity is not only related to the cross-sectional size and slenderness ratio, but also affected by the sectional combination mode. By setting horizontal binding bars, the glue failure binding can be suppressed effectively, the ultimate failure mode changes, and the ultimate carrying capacity improves significantly. Compared with the ultimate compressive stress of SBCC, the ultimate compressive stress of SBCCB increases by 26% averagely.
2016, 33(10): 2336-2343.
doi: 10.13801/j.cnki.fhclxb.20160201.001
Abstract:
In order to ascertain the applications of bistable composite laminated structures in complicated environment, the viscoelastic behaviors of bistable composite laminated structures were investigated. The fiber was reduced to elastic material and the viscoelastic behaviors of matrix material were taken into consideration firstly. Then, based on the material properties of fiber and matrix, the viscoelastic material properties of the bistable composite laminated structure were obtained by theoretical analyses. A viscoelastic model of the bistable composite laminated structure was developed on the foundation of classical lamination theory, the principle of minimum potential energy and Maxwell viscoelasticity model, and the changing relationships between the second stable principal curvature, twist curvature and loading time, temperature were obtained by theoretical analyses. At the same time, the corresponding finite element model was developed using finite element software ABAQUS and its subroutine UMAT, and the influences of loading time and temperature on the second stable properties of laminated structures were investigated. Both of the theoretical and simulation results show that the second stable principal curvature of laminated structures increases with the loading time extension and temperature increasing. The twist curvature decreases with the loading time extension and increases with the temperature increasing in general case, but when the loading time is relatively long and the temperature is relatively high, may appear the circumstance of twist curvature decreases with the temperature increasing. The comparison of theoretical results and finite element simulation results show that both of them fit well, and it is feasible to investigate the viscoelastic behaviors of the bistable composite laminated structures by finite element simulation.
In order to ascertain the applications of bistable composite laminated structures in complicated environment, the viscoelastic behaviors of bistable composite laminated structures were investigated. The fiber was reduced to elastic material and the viscoelastic behaviors of matrix material were taken into consideration firstly. Then, based on the material properties of fiber and matrix, the viscoelastic material properties of the bistable composite laminated structure were obtained by theoretical analyses. A viscoelastic model of the bistable composite laminated structure was developed on the foundation of classical lamination theory, the principle of minimum potential energy and Maxwell viscoelasticity model, and the changing relationships between the second stable principal curvature, twist curvature and loading time, temperature were obtained by theoretical analyses. At the same time, the corresponding finite element model was developed using finite element software ABAQUS and its subroutine UMAT, and the influences of loading time and temperature on the second stable properties of laminated structures were investigated. Both of the theoretical and simulation results show that the second stable principal curvature of laminated structures increases with the loading time extension and temperature increasing. The twist curvature decreases with the loading time extension and increases with the temperature increasing in general case, but when the loading time is relatively long and the temperature is relatively high, may appear the circumstance of twist curvature decreases with the temperature increasing. The comparison of theoretical results and finite element simulation results show that both of them fit well, and it is feasible to investigate the viscoelastic behaviors of the bistable composite laminated structures by finite element simulation.
2016, 33(10): 2344-2354.
doi: 10.13801/j.cnki.fhclxb.20160523.002
Abstract:
In order to predict the damage initiation and destruction process of composite box accurately, the progressive damage finite element analysis technique of integral multi-spar composite box which took material failure into consideration was investigated. Based on ABAQUS software, the progressive damage analysis model of box was established firstly by using the material mechanical property parameters obtained by standard tests, and three dimensional Hashin failure criteria and square stress failure criteria were adopted as the failure criteria of composite ply and adhesive interface, respectively. Then, the solution for post-buckling loading capability of the integral multi-spar composite box was accomplished by the model, and the analysis model was validated by failure test. The results show that the finite element analysis results for loading capability and stress of structure coincide well with test values, and the failure mode predicted is also consistent with the test results. The errors of buckling load and loading capability are within 5%. The conclusions obtained show that the analysis model which takes failure of ply and debonding of interface into consideration can simulate the damage process of integral multi-spar box effectively.
In order to predict the damage initiation and destruction process of composite box accurately, the progressive damage finite element analysis technique of integral multi-spar composite box which took material failure into consideration was investigated. Based on ABAQUS software, the progressive damage analysis model of box was established firstly by using the material mechanical property parameters obtained by standard tests, and three dimensional Hashin failure criteria and square stress failure criteria were adopted as the failure criteria of composite ply and adhesive interface, respectively. Then, the solution for post-buckling loading capability of the integral multi-spar composite box was accomplished by the model, and the analysis model was validated by failure test. The results show that the finite element analysis results for loading capability and stress of structure coincide well with test values, and the failure mode predicted is also consistent with the test results. The errors of buckling load and loading capability are within 5%. The conclusions obtained show that the analysis model which takes failure of ply and debonding of interface into consideration can simulate the damage process of integral multi-spar box effectively.
2016, 33(10): 2355-2362.
doi: 10.13801/j.cnki.fhclxb.20160621.001
Abstract:
In order to promote the wide application of lightweight soil in geotechnical engineering, modified polypropylene fiber was added to improve its mechanical properties, the influencing factors of strength-deformation characteristics, compressive failure mode and unconfined compressive strength of fiber expanded polystyrene (EPS) particles lightweight soil were analyzed and discussed by unconfined compressive strength test, and the mechanics mechanism of fiber EPS particle lightweight soil was analyzed from micro level by SEM. The results show that when the EPS particle, fiber and cement contents are different, the stress-strain curves of fiber EPS particle lightweight soil are different. EPS and cement contents are the main factors which influence strength, and fiber content is the second. The strength decreases sharply with the increase of EPS content, and increases sharply with the increase of cement content. The EPS particle lightweight soil without adding fiber becomes loose and broken easily, and loses strength suddenly. The addition of fiber can enhance the peak strength, residual strength, integrity and toughness of lightweight soil, and improve its brittle failure mode. However, when the EPS content is higher (more than 3% for the mass of dry soil), the adhesion between fiber and cemented soil is limited, and the improvement performance for mechanical properties of EPS particle lightweight soil is weaker. EPS particle is hollow honeycomb structure, fiber is covered with the needle-like hydration of cement on the surfaces and forms space network structure. The conclusions obtained show that fiber improves the mechanical properties of lightweight soil.
In order to promote the wide application of lightweight soil in geotechnical engineering, modified polypropylene fiber was added to improve its mechanical properties, the influencing factors of strength-deformation characteristics, compressive failure mode and unconfined compressive strength of fiber expanded polystyrene (EPS) particles lightweight soil were analyzed and discussed by unconfined compressive strength test, and the mechanics mechanism of fiber EPS particle lightweight soil was analyzed from micro level by SEM. The results show that when the EPS particle, fiber and cement contents are different, the stress-strain curves of fiber EPS particle lightweight soil are different. EPS and cement contents are the main factors which influence strength, and fiber content is the second. The strength decreases sharply with the increase of EPS content, and increases sharply with the increase of cement content. The EPS particle lightweight soil without adding fiber becomes loose and broken easily, and loses strength suddenly. The addition of fiber can enhance the peak strength, residual strength, integrity and toughness of lightweight soil, and improve its brittle failure mode. However, when the EPS content is higher (more than 3% for the mass of dry soil), the adhesion between fiber and cemented soil is limited, and the improvement performance for mechanical properties of EPS particle lightweight soil is weaker. EPS particle is hollow honeycomb structure, fiber is covered with the needle-like hydration of cement on the surfaces and forms space network structure. The conclusions obtained show that fiber improves the mechanical properties of lightweight soil.
2016, 33(10): 2363-2370.
doi: 10.13801/j.cnki.fhclxb.20151211.002
Abstract:
In order to investigate the influence of moisture resistance agents chlorinated paraffin and glycerol on the moisture resistance, microstructure and chemical structure of wheat straw/vegetable protein adhesive composites, composites added with two moisture resistance agents were prepared by hot pressing molding method. The mechanical properties, water and moisture absorption rate variation of wheat straw/vegetable protein adhesive composites were measured respectively, and the functional group variations were analyzed by FTIR. The wettability was analyzed by testing contact angles, and the bending cross-section microstructure of the composites was observed by the stereo microscope.The results show that the maximum bending strength and bending elastic modulus of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin increase by 67% and 129% respectively compared with those of wheat straw/vegetable protein adhesive composites without additive. The maximum impact strength of wheat straw/vegetable protein adhesive composites adding glycerol increases by 44% compared with that of wheat straw/vegetable protein adhesive composites without additive. The 2 h thickness swelling rate of water absorption of the wheat straw/vegetable protein adhesive composites adding chlorinated paraffin and glycerol are generally smaller than that of composites without additive. With the moisture absorption time increasing, the moisture absorption rate of three composites increases, and the smallest rate of balanced moisture absorption of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin is 4.3%. The bending cross-section microstructure of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin is better than that of other composites, the inner surface is integrated tightly and the surface of the fiber is less exposed and the moisture resistance is the best.
In order to investigate the influence of moisture resistance agents chlorinated paraffin and glycerol on the moisture resistance, microstructure and chemical structure of wheat straw/vegetable protein adhesive composites, composites added with two moisture resistance agents were prepared by hot pressing molding method. The mechanical properties, water and moisture absorption rate variation of wheat straw/vegetable protein adhesive composites were measured respectively, and the functional group variations were analyzed by FTIR. The wettability was analyzed by testing contact angles, and the bending cross-section microstructure of the composites was observed by the stereo microscope.The results show that the maximum bending strength and bending elastic modulus of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin increase by 67% and 129% respectively compared with those of wheat straw/vegetable protein adhesive composites without additive. The maximum impact strength of wheat straw/vegetable protein adhesive composites adding glycerol increases by 44% compared with that of wheat straw/vegetable protein adhesive composites without additive. The 2 h thickness swelling rate of water absorption of the wheat straw/vegetable protein adhesive composites adding chlorinated paraffin and glycerol are generally smaller than that of composites without additive. With the moisture absorption time increasing, the moisture absorption rate of three composites increases, and the smallest rate of balanced moisture absorption of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin is 4.3%. The bending cross-section microstructure of wheat straw/vegetable protein adhesive composites adding chlorinated paraffin is better than that of other composites, the inner surface is integrated tightly and the surface of the fiber is less exposed and the moisture resistance is the best.
2016, 33(10): 2371-2379.
doi: 10.13801/j.cnki.fhclxb.20151209.004
Abstract:
Carboxymethyl-chitosan (OCMC) with high water solubilities was obtained by carboxymethylation of chitosan. It has good stability and antibacterial property. Comparing the solubility of OCMC dissolving in difference solvents, it is found that the best solvent condition of OCMC is 2wt% acetic acid aqueous. The Ag-OCMC composite particles were obtained by complex of OCMC and Ag nanoparticles (AgNPs). The composition, microstructure and thermal properties of Ag-OCMC composite particles were characterized by UV-Vis, FTIR, XPS, TEM, SEM and TG-DTA. Antimicrobial activities of Ag-OCMC composite particles were performed by using typical bacteria of E.coli and S.aureus. The results show that AgNPs are face-centered cubic crystallites with the average diameter size in 40-50 nm. The decomposition temperatures of chitosan and OCMC are raised by the introduction of AgNPs. The antibacterial activity of Ag-OCMC composite particles is significantly higher than single chitosan based antibacterials.
Carboxymethyl-chitosan (OCMC) with high water solubilities was obtained by carboxymethylation of chitosan. It has good stability and antibacterial property. Comparing the solubility of OCMC dissolving in difference solvents, it is found that the best solvent condition of OCMC is 2wt% acetic acid aqueous. The Ag-OCMC composite particles were obtained by complex of OCMC and Ag nanoparticles (AgNPs). The composition, microstructure and thermal properties of Ag-OCMC composite particles were characterized by UV-Vis, FTIR, XPS, TEM, SEM and TG-DTA. Antimicrobial activities of Ag-OCMC composite particles were performed by using typical bacteria of E.coli and S.aureus. The results show that AgNPs are face-centered cubic crystallites with the average diameter size in 40-50 nm. The decomposition temperatures of chitosan and OCMC are raised by the introduction of AgNPs. The antibacterial activity of Ag-OCMC composite particles is significantly higher than single chitosan based antibacterials.
2016, 33(10): 2380-2389.
doi: 10.13801/j.cnki.fhclxb.20151221.001
Abstract:
According to the theory of surface energy, the surface free energy parameters of styrene- butadiene-styrene (SBS), crumb rubber (CR) and composite crumb rubber (CCR) of three kinds of polymer modified asphalt before and after salt freezing cycle and limestone, basalt, granite were measured by contact angle measurement method. Adhesion work and spalling work of asphalt-aggregate system were calculated before and after salt freezing cycle, so as to determine the influence of salt freezing cycle on the adhesion and spalling properties of asphalt-aggregate system. The results show that the specific surface free energy variation of adhesion process and spalling process of asphalt and aggregate system are all negative before and after salt freezing cycle, explaining the process of adhesion and spalling of asphalt and aggregate are all spontaneous. With the increase of salt freezing cycles and salt concentration, the adhesion work of asphalt-aggregate system gradually decreases, and the spalling work gradually increases, adhesion and resistance to water damage ability are weakened gradually. When the asphalt type is the same, the adhesive work of asphalt and limestone is the largest, and the spalling work is the smallest, the adhesive work of the asphalt and granite is the smallest, and the spalling work is the largest. When the aggregate type is the same, the adhesive work of CCR modified asphalt and limestone is the largest, and the spalling work is the smallest, the adhesive work of the SBS modified asphalt and granite is the smallest, and the spalling work is the largest.
According to the theory of surface energy, the surface free energy parameters of styrene- butadiene-styrene (SBS), crumb rubber (CR) and composite crumb rubber (CCR) of three kinds of polymer modified asphalt before and after salt freezing cycle and limestone, basalt, granite were measured by contact angle measurement method. Adhesion work and spalling work of asphalt-aggregate system were calculated before and after salt freezing cycle, so as to determine the influence of salt freezing cycle on the adhesion and spalling properties of asphalt-aggregate system. The results show that the specific surface free energy variation of adhesion process and spalling process of asphalt and aggregate system are all negative before and after salt freezing cycle, explaining the process of adhesion and spalling of asphalt and aggregate are all spontaneous. With the increase of salt freezing cycles and salt concentration, the adhesion work of asphalt-aggregate system gradually decreases, and the spalling work gradually increases, adhesion and resistance to water damage ability are weakened gradually. When the asphalt type is the same, the adhesive work of asphalt and limestone is the largest, and the spalling work is the smallest, the adhesive work of the asphalt and granite is the smallest, and the spalling work is the largest. When the aggregate type is the same, the adhesive work of CCR modified asphalt and limestone is the largest, and the spalling work is the smallest, the adhesive work of the SBS modified asphalt and granite is the smallest, and the spalling work is the largest.
2016, 33(10): 2390-2396.
doi: 10.13801/j.cnki.fhclxb.20151209.002
Abstract:
A lithium-sulfur battery interlayer flexible material composed of precursor carbon material was prepared by multi-step temperature carbonization process with lotus-leaf as the raw material, ball-milling blending and vacuum filtrating precursor carbon material, Ketjen Black (KB) as well as polytetrafluo-roethylene(PTFE) at the mass ratio of 2:2:3. The porous structure of PTFE/KB-C composites can not only provide a large number of three-phase reaction sites for further reduction of higher-order sulfide Li2Sn (4≤n≤8), but also suppress the shuttle effect of soluble polysulphide by good multilayer porous chemical adsorption effect of PTFE/KB-C composites. The lithium-sulfur battery capacity property test characterization of interlayer with pure sulfur as the anode material shows that initial discharge specific capacity is as high as 1 350 mAh·g-1 at 1.0 C rate (current density is 1 675 mA·g-1) and remains 960 mAh·g-1 after 100 charge-discharge cycles without nitric acid lithium additives. Coulomb efficiency above 95% is achieved, demonstrating high performance of cycle stability.
A lithium-sulfur battery interlayer flexible material composed of precursor carbon material was prepared by multi-step temperature carbonization process with lotus-leaf as the raw material, ball-milling blending and vacuum filtrating precursor carbon material, Ketjen Black (KB) as well as polytetrafluo-roethylene(PTFE) at the mass ratio of 2:2:3. The porous structure of PTFE/KB-C composites can not only provide a large number of three-phase reaction sites for further reduction of higher-order sulfide Li2Sn (4≤n≤8), but also suppress the shuttle effect of soluble polysulphide by good multilayer porous chemical adsorption effect of PTFE/KB-C composites. The lithium-sulfur battery capacity property test characterization of interlayer with pure sulfur as the anode material shows that initial discharge specific capacity is as high as 1 350 mAh·g-1 at 1.0 C rate (current density is 1 675 mA·g-1) and remains 960 mAh·g-1 after 100 charge-discharge cycles without nitric acid lithium additives. Coulomb efficiency above 95% is achieved, demonstrating high performance of cycle stability.
2016, 33(10): 2397-2403.
doi: 10.13801/j.cnki.fhclxb.20160302.003
Abstract:
To consider the influence of initial ovality on the tension stiffness of helical wound structure, a analytical model was presented based on the elliptical cylinder and helix. A new geometrical relationship was established between them. The axial strain, curvature variation of helix on elliptical cylinder and contact pressure between cylinder and helical layer were considered in the model. A 3D finite element model using ABAQUS was developed to validate the reasonability of the theoretical model. In the theoretical model, initial ovality was parametric analyzed to obtain the effect of initial ovality on the tension stiffness in helical layer. With the increase of initial ovality of pipe, the tension stiffness of helical layer decreases, but the decline is small.
To consider the influence of initial ovality on the tension stiffness of helical wound structure, a analytical model was presented based on the elliptical cylinder and helix. A new geometrical relationship was established between them. The axial strain, curvature variation of helix on elliptical cylinder and contact pressure between cylinder and helical layer were considered in the model. A 3D finite element model using ABAQUS was developed to validate the reasonability of the theoretical model. In the theoretical model, initial ovality was parametric analyzed to obtain the effect of initial ovality on the tension stiffness in helical layer. With the increase of initial ovality of pipe, the tension stiffness of helical layer decreases, but the decline is small.
