2020 Vol. 37, No. 10
2020, 37(10): 2572-2581.
doi: 10.13801/j.cnki.fhclxb.20200423.001
Abstract:
Hydroxyapatite (HAP) nanofibers with ultra-high aspect ratio were prepared by a solvothermal method. HAP nanofibers reinforced composite hydrogel combined with gelatin modified by methacrylic anhydride(GelMA) was prepared by UV crosslinking. The composite hydrogel was characterized by SEM, XRD, mechanical test, swelling test, degradation test and cell culture, etc. The results of the cross-sectional morphology show that the HAP fiber/GelMA composite hydrogel has 3D porous structure with porous structure. Mechanical experiments show that HAP nanofibers can effectively enhance the elastic modulus of the composite hydrogel. With the increase of HAP nanofibers addition, the mechanical performance enhancement effect of the HAP/GelMA composite hydrogel is more obvious. The swelling experiments show that the swelling rate does not change significantly when the mass fraction of HAP fiber is 5.2wt%-14.2wt%, while the swelling rate decreases when the mass fraction is 18.2wt%. The degradation experiments show that the addition of HAP nanofibers can effectively maintain the structure of hydrogel and make it more stable and controllable. The cell co-culture experiments show that the HAP nanofibers/GelMA composite hydrogel can provide a great 3D growth environment for encapsulated cells, showing excellent biocompatibility. The HAP nanofibers/GelMA composite hydrogel prepared in the experiment has a good application prospect in the field of tissue engineering.
Hydroxyapatite (HAP) nanofibers with ultra-high aspect ratio were prepared by a solvothermal method. HAP nanofibers reinforced composite hydrogel combined with gelatin modified by methacrylic anhydride(GelMA) was prepared by UV crosslinking. The composite hydrogel was characterized by SEM, XRD, mechanical test, swelling test, degradation test and cell culture, etc. The results of the cross-sectional morphology show that the HAP fiber/GelMA composite hydrogel has 3D porous structure with porous structure. Mechanical experiments show that HAP nanofibers can effectively enhance the elastic modulus of the composite hydrogel. With the increase of HAP nanofibers addition, the mechanical performance enhancement effect of the HAP/GelMA composite hydrogel is more obvious. The swelling experiments show that the swelling rate does not change significantly when the mass fraction of HAP fiber is 5.2wt%-14.2wt%, while the swelling rate decreases when the mass fraction is 18.2wt%. The degradation experiments show that the addition of HAP nanofibers can effectively maintain the structure of hydrogel and make it more stable and controllable. The cell co-culture experiments show that the HAP nanofibers/GelMA composite hydrogel can provide a great 3D growth environment for encapsulated cells, showing excellent biocompatibility. The HAP nanofibers/GelMA composite hydrogel prepared in the experiment has a good application prospect in the field of tissue engineering.
2020, 37(10): 2582-2589.
doi: 10.13801/j.cnki.fhclxb.20200313.001
Abstract:
The carbon nanotubes(CNTs)/oleic acid (OA) composite was prepared by filling OA into CNTs, then the nanofluid was prepared by the CNTs/oleic acid composite as additive. The conductivity and wettability of the nanofluid were investigated, and the effects of the content, acidification time, test temperature and electric field on the above properties were also studied. The results show that the composite is successfully formed with a filling rate of about 20%. During the preparing process, the end face of the CNTs is chemically modified, and the best acidification time is about 8 h. Compared with the acidified CNTs, the CNTs/OA composite has better surface activity and dispersion in the base solution, which can better improve the conductivity and wettability of the nanofluid, and the optimal content of the composite is about 0.1%. Under the condition of electrowetting, the wettability of the nanofluid with the higher content of the composite can be improved more obviously with the increase of voltage. This may be because the conductivity and capacitance of the CNTs are improved after the filling of OA, and the nanofluid prepared by the composite also has better conductivity and capacitance.
The carbon nanotubes(CNTs)/oleic acid (OA) composite was prepared by filling OA into CNTs, then the nanofluid was prepared by the CNTs/oleic acid composite as additive. The conductivity and wettability of the nanofluid were investigated, and the effects of the content, acidification time, test temperature and electric field on the above properties were also studied. The results show that the composite is successfully formed with a filling rate of about 20%. During the preparing process, the end face of the CNTs is chemically modified, and the best acidification time is about 8 h. Compared with the acidified CNTs, the CNTs/OA composite has better surface activity and dispersion in the base solution, which can better improve the conductivity and wettability of the nanofluid, and the optimal content of the composite is about 0.1%. Under the condition of electrowetting, the wettability of the nanofluid with the higher content of the composite can be improved more obviously with the increase of voltage. This may be because the conductivity and capacitance of the CNTs are improved after the filling of OA, and the nanofluid prepared by the composite also has better conductivity and capacitance.
2020, 37(10): 2590-2601.
doi: 10.13801/j.cnki.fhclxb.20200203.002
Abstract:
Based on the axial compression test of 5 ultra-high performance concrete (UHPC) columns confined by high-strength stirrups and 4 UHPC columns confined by normal-strength stirrups, the bearing capacity, failure mode, steel strain and stress-strain curve for the confined UHPC columns were studied, and the influences of volume stirrup ratio, strength, spacing and configuration of stirrup on the axial compression behavior of confined UHPC were analyzed by combining ductility and toughness index. The results show that all the specimens have ductility damages, and the damage degree of UHPC columns confined by high-strength stirrups is lighter. The confined UHPC columns with high volume stirrup ratio, closely spaced, high-strength and complex ties configuration have good confinement efficiency, bearing capacity and deformation performance, which also leads to an ideal axial compression behavior. The effect of volume stirrup ratio on the axial compression behavior of specimens is greater than that of stirrup strength. Among the three factors affecting the volume stirrup ratio, such as spacing, configuration and diameter of stirrup, the stirrup spacing contributes most to the improvement of confinement performance, followed by the configuration and diameter of stirrup. The UHPC confined by high-strength stirrups presents better axial compression performance and residual bearing capacity than the normal-stirrups. The micro-bending of the longitudinal bars accelerates the cover spalling, while the high-strength stirrups with close space effectively delays the buckling of longitudinal bars, and significantly improves the overall performance of the confined UHPC. The micro-bending of longitudinal bars weakens the confine effect of the high-strength stirrups on the core UHPC, and the combination of high-strength longitudinal bars and stirrups is suggested. Based on the test data, the formulas to determine the bearing capacity of UHPC columns confined by stirrups are drawn.
Based on the axial compression test of 5 ultra-high performance concrete (UHPC) columns confined by high-strength stirrups and 4 UHPC columns confined by normal-strength stirrups, the bearing capacity, failure mode, steel strain and stress-strain curve for the confined UHPC columns were studied, and the influences of volume stirrup ratio, strength, spacing and configuration of stirrup on the axial compression behavior of confined UHPC were analyzed by combining ductility and toughness index. The results show that all the specimens have ductility damages, and the damage degree of UHPC columns confined by high-strength stirrups is lighter. The confined UHPC columns with high volume stirrup ratio, closely spaced, high-strength and complex ties configuration have good confinement efficiency, bearing capacity and deformation performance, which also leads to an ideal axial compression behavior. The effect of volume stirrup ratio on the axial compression behavior of specimens is greater than that of stirrup strength. Among the three factors affecting the volume stirrup ratio, such as spacing, configuration and diameter of stirrup, the stirrup spacing contributes most to the improvement of confinement performance, followed by the configuration and diameter of stirrup. The UHPC confined by high-strength stirrups presents better axial compression performance and residual bearing capacity than the normal-stirrups. The micro-bending of the longitudinal bars accelerates the cover spalling, while the high-strength stirrups with close space effectively delays the buckling of longitudinal bars, and significantly improves the overall performance of the confined UHPC. The micro-bending of longitudinal bars weakens the confine effect of the high-strength stirrups on the core UHPC, and the combination of high-strength longitudinal bars and stirrups is suggested. Based on the test data, the formulas to determine the bearing capacity of UHPC columns confined by stirrups are drawn.
2020, 37(10): 2602-2609.
doi: 10.13801/j.cnki.fhclxb.20200316.002
Abstract:
The physical index of recycled coarse aggregate is far lower than that of natural coarse aggregate due to the existence of residual mortar, which leads to the poor mechanical properties and durability of recycled aggregate concrete (RAC). Furthermore, the ingress of water and aggressive ion is the main cause of the degradation of concrete properties. The durabilities of concrete with various replacement ratios by mass of recycled concrete aggregate(0%, 30%, 50%), which has been impregnated by 8wt% silane, were studied through a series of tests, including the compressive strength, capillary water absorption and chloride penetration depth. Finally, the microstructure of the recycled concrete was analyzed by SEM. The experimental results show that the water absorption rate of the recycled coarse aggregate treated by silane impregnationis decreases significantly, and the compressive strength of the recycled concrete prepared by silane decreases slightly. Moreover, the capillary water absorption of the modified recycled concrete is obviously reduced while the chloride penetration resistance is significantly increased. The chloride diffusion coefficient of the treated recycled concrete with the aggregate replacement ratio by mass of 50% is reduced by 37.5%. This research indicates that the recycled coarse aggregate impregnated by silane is an effective way to improve the durability of the recycled aggregate concrete.
The physical index of recycled coarse aggregate is far lower than that of natural coarse aggregate due to the existence of residual mortar, which leads to the poor mechanical properties and durability of recycled aggregate concrete (RAC). Furthermore, the ingress of water and aggressive ion is the main cause of the degradation of concrete properties. The durabilities of concrete with various replacement ratios by mass of recycled concrete aggregate(0%, 30%, 50%), which has been impregnated by 8wt% silane, were studied through a series of tests, including the compressive strength, capillary water absorption and chloride penetration depth. Finally, the microstructure of the recycled concrete was analyzed by SEM. The experimental results show that the water absorption rate of the recycled coarse aggregate treated by silane impregnationis decreases significantly, and the compressive strength of the recycled concrete prepared by silane decreases slightly. Moreover, the capillary water absorption of the modified recycled concrete is obviously reduced while the chloride penetration resistance is significantly increased. The chloride diffusion coefficient of the treated recycled concrete with the aggregate replacement ratio by mass of 50% is reduced by 37.5%. This research indicates that the recycled coarse aggregate impregnated by silane is an effective way to improve the durability of the recycled aggregate concrete.
2020, 37(10): 2610-2618.
doi: 10.13801/j.cnki.fhclxb.20200225.001
Abstract:
The four-electrode method was used to measure the fraction change in resistance (ρFCR) during the crack propagation of the concrete beam subjected to bending. The effect of carbon black(CB), steel fiber (SF) and carbon fiber (CF) content and their combination on the crack self sensing gauge factor (K) of the concrete beam was compared and analyzed. Based on the fractal theory, the effect of different conductive materials on the noise level of the normalized fractional change in resistance - crack opening displacement curve (ρ’FCR-w’COD) was studied. The results show that the linear fitting analysis fit well with the fraction change in resistance-crack opening displacement curve (ρFCR-wCOD) and K can be characterized as the slope of the fitted line. In addition, K decreases with the increasing of the SF content. The specimens with the addition of SF and nano CB reveal the best crack self sensing ability among all the specimens. K can be improved while the tortuosity of the ρ’FCR-w’COD curve is reduced by the addition of nano CB. Specifically, the K values exhibit an increasing tendency till the CB increases to a certain content and then K decreases for even higher content of CB. However, the fractal dimensions (D) of the specimens and CB content show an inverse tendency. Furthermore, the optimum dosage of nano CB is 1.0-1.5 kg/m3. There exists a negative effect on the K value with the addition of CF, however, the standard deviation of D of the ρ'FCR-w'COD curves is reduced for the specimens with CF.
The four-electrode method was used to measure the fraction change in resistance (ρFCR) during the crack propagation of the concrete beam subjected to bending. The effect of carbon black(CB), steel fiber (SF) and carbon fiber (CF) content and their combination on the crack self sensing gauge factor (K) of the concrete beam was compared and analyzed. Based on the fractal theory, the effect of different conductive materials on the noise level of the normalized fractional change in resistance - crack opening displacement curve (ρ’FCR-w’COD) was studied. The results show that the linear fitting analysis fit well with the fraction change in resistance-crack opening displacement curve (ρFCR-wCOD) and K can be characterized as the slope of the fitted line. In addition, K decreases with the increasing of the SF content. The specimens with the addition of SF and nano CB reveal the best crack self sensing ability among all the specimens. K can be improved while the tortuosity of the ρ’FCR-w’COD curve is reduced by the addition of nano CB. Specifically, the K values exhibit an increasing tendency till the CB increases to a certain content and then K decreases for even higher content of CB. However, the fractal dimensions (D) of the specimens and CB content show an inverse tendency. Furthermore, the optimum dosage of nano CB is 1.0-1.5 kg/m3. There exists a negative effect on the K value with the addition of CF, however, the standard deviation of D of the ρ'FCR-w'COD curves is reduced for the specimens with CF.
2020, 37(10): 2619-2635.
doi: 10.13801/j.cnki.fhclxb.20200319.001
Abstract:
The mechanical performance of adhesives has significant effects on the interfacial bond behavior of the carbon fiber reinforced polymer (CFRP)-reinforced steel structures. Based on the developed ratio of adhesives, the effects of different nano-SiO2 on the basic mechanical properties and microstructure of the adhesives after curing at room temperature were analyzed. A total of 31 CFRP plate-steel double lap joint specimens were fabricated, and the experimental researches on bearing capacity, effective bonding length, force transmission mode, and bond-slip constitutive after curing at room temperature were carried out. The influence of the amount of nano-SiO2 on the interfacial bonding properties of CFRP-steel lap joints was obtained and compared with commonly used adhesives. The results show that with the increase of nano-SiO2, the stress-strain relationship of the adhesive changes from linear to nonlinear, the strain energy, elongation at break and shear strength are increased by 292.10%, 202.88% and 133.12%, respectively. Microstructural analysis shows that the addition of nano-SiO2 significantly increases the section roughness forms dense plastic cavities, resulting in more microcracks, and greatly improves the toughness of the adhesive. When the amount of nano-SiO2 is from 0 to 1wt%, the failure mode changes from interface failure to CFRP plate delamination. The incorporation of nano-SiO2 can increase the ultimate bearing capacity of the lap test piece (increase by 256.96%) and the effective bond length of the interface (up to 3 times), and improve the strain and interfacial shear stress peak of CFRP surface. The bond-slip curves could be simplified into a bilinear model (triangle-shape) for CFRP-steel joints with 0 and 0.5wt% of the nano-SiO2, the bond-slip curve could be simplified into a trilinear model (trapezoidal-shape) of CFRP-steel joints with 1wt% of nano-SiO2, and the bonding interface toughness is greatly improved. The bearing capacity of CFRP-steel interface is affected by the tensile strength and elongation at break of the adhesive. The CFRP-steel lap joint based on nonlinear high-strength adhesive (i.e. adhesive with higher strain energy) has excellent interface performance.
The mechanical performance of adhesives has significant effects on the interfacial bond behavior of the carbon fiber reinforced polymer (CFRP)-reinforced steel structures. Based on the developed ratio of adhesives, the effects of different nano-SiO2 on the basic mechanical properties and microstructure of the adhesives after curing at room temperature were analyzed. A total of 31 CFRP plate-steel double lap joint specimens were fabricated, and the experimental researches on bearing capacity, effective bonding length, force transmission mode, and bond-slip constitutive after curing at room temperature were carried out. The influence of the amount of nano-SiO2 on the interfacial bonding properties of CFRP-steel lap joints was obtained and compared with commonly used adhesives. The results show that with the increase of nano-SiO2, the stress-strain relationship of the adhesive changes from linear to nonlinear, the strain energy, elongation at break and shear strength are increased by 292.10%, 202.88% and 133.12%, respectively. Microstructural analysis shows that the addition of nano-SiO2 significantly increases the section roughness forms dense plastic cavities, resulting in more microcracks, and greatly improves the toughness of the adhesive. When the amount of nano-SiO2 is from 0 to 1wt%, the failure mode changes from interface failure to CFRP plate delamination. The incorporation of nano-SiO2 can increase the ultimate bearing capacity of the lap test piece (increase by 256.96%) and the effective bond length of the interface (up to 3 times), and improve the strain and interfacial shear stress peak of CFRP surface. The bond-slip curves could be simplified into a bilinear model (triangle-shape) for CFRP-steel joints with 0 and 0.5wt% of the nano-SiO2, the bond-slip curve could be simplified into a trilinear model (trapezoidal-shape) of CFRP-steel joints with 1wt% of nano-SiO2, and the bonding interface toughness is greatly improved. The bearing capacity of CFRP-steel interface is affected by the tensile strength and elongation at break of the adhesive. The CFRP-steel lap joint based on nonlinear high-strength adhesive (i.e. adhesive with higher strain energy) has excellent interface performance.
2020, 37(10): 2636-2644.
doi: 10.13801/j.cnki.fhclxb.20200225.003
Abstract:
The Ce/MOF-5 materials with different properties were synthesized by means of hydrothermal synthesis method by mixing Ce with the reaction precursors required for the synthesis of metal organic framework materials (MOFs). The synthetic materials were characterized by SEM, XRD and BET, etc. The results show that the Ce/MOF-5 synthesized by different methods shows significant differences in morphology and fluorine adsorption performance. The effect of the initial concentration, pH value and adsorption time on the adsorption effect of F− was also determined. The experiments show that the adsorption of F− by Ce/MOF-5 material synthesized by the "one-pot method" obtains an adsorption balance of 109.6 mg·g−1 at pH=7, with a adsorption time of about 60 min. It conforms to the quasi-second order kinetic model and Freundlich isothermal adsorption model.
The Ce/MOF-5 materials with different properties were synthesized by means of hydrothermal synthesis method by mixing Ce with the reaction precursors required for the synthesis of metal organic framework materials (MOFs). The synthetic materials were characterized by SEM, XRD and BET, etc. The results show that the Ce/MOF-5 synthesized by different methods shows significant differences in morphology and fluorine adsorption performance. The effect of the initial concentration, pH value and adsorption time on the adsorption effect of F− was also determined. The experiments show that the adsorption of F− by Ce/MOF-5 material synthesized by the "one-pot method" obtains an adsorption balance of 109.6 mg·g−1 at pH=7, with a adsorption time of about 60 min. It conforms to the quasi-second order kinetic model and Freundlich isothermal adsorption model.
2020, 37(10): 2645-2655.
doi: 10.13801/j.cnki.fhclxb.20200212.001
Abstract:
The size effect on the seismic behavior of the reinforced concrete (RC) columns strengthened by carbon fiber reinforced polymer (CFRP) which subjected to low-cyclic loading was investigated. Three groups of geometrically similar RC columns with cross-sectional height ranging from 150 mm to 450 mm and a shear-span ratio of 3 were designed and tested. The influences of the number of CFRP layers, the size of the cross-section and the axial compression ratio on the seismic performance of the RC columns were also examined. It is indicated that: with the same structural size and axial compression ratio, the seismic behavior including the bearing capacity, the capacity of dissipated energy, the ductility capacity and the horizontal displacement of the CFRP strengthened RC columns are improved to different extents compared with the unreinforced columns, and the results indicate the existence of size effect; as the structural size of the tested columns increases, the dimensionless nominal bearing capacity of the CFRP strengthened RC columns is weaken and there is obvious size effect; as the structural size of the tested RC columns increases, the safety reserve coefficients decrease pronouncedly.
The size effect on the seismic behavior of the reinforced concrete (RC) columns strengthened by carbon fiber reinforced polymer (CFRP) which subjected to low-cyclic loading was investigated. Three groups of geometrically similar RC columns with cross-sectional height ranging from 150 mm to 450 mm and a shear-span ratio of 3 were designed and tested. The influences of the number of CFRP layers, the size of the cross-section and the axial compression ratio on the seismic performance of the RC columns were also examined. It is indicated that: with the same structural size and axial compression ratio, the seismic behavior including the bearing capacity, the capacity of dissipated energy, the ductility capacity and the horizontal displacement of the CFRP strengthened RC columns are improved to different extents compared with the unreinforced columns, and the results indicate the existence of size effect; as the structural size of the tested columns increases, the dimensionless nominal bearing capacity of the CFRP strengthened RC columns is weaken and there is obvious size effect; as the structural size of the tested RC columns increases, the safety reserve coefficients decrease pronouncedly.
2020, 37(10): 2367-2375.
doi: 10.13801/j.cnki.fhclxb.20200622.003
Abstract:
Thermally-induced shape memory plastic composite (SMPC) is an intelligent material which can respond to the external temperature stimulation. Compared with the traditional thermally-induced SMPC, the high thermal conductivity graphene(GR)-carbon fiber(CF) hybrid reinforced thermally-induced SMPC has a series of excellent properties, such as excellent shape memory performance, high specific strength and strong thermal conductivity. In recent years, people have paid much attention to it and carried out relevant research. Starting from the historical origin and applications of shape memory material, this paper focuses on the research frontier of GR-CF hybrid reinforced SMPC, and reviewes the domestic and foreign research status of the composite material in four aspects: infiltration law, molding process, shape memory performance enhancement rule and bending failure rule. Combined with the existing research situation, the future research direction of the thermally-induced SMPC is pointed out.
Thermally-induced shape memory plastic composite (SMPC) is an intelligent material which can respond to the external temperature stimulation. Compared with the traditional thermally-induced SMPC, the high thermal conductivity graphene(GR)-carbon fiber(CF) hybrid reinforced thermally-induced SMPC has a series of excellent properties, such as excellent shape memory performance, high specific strength and strong thermal conductivity. In recent years, people have paid much attention to it and carried out relevant research. Starting from the historical origin and applications of shape memory material, this paper focuses on the research frontier of GR-CF hybrid reinforced SMPC, and reviewes the domestic and foreign research status of the composite material in four aspects: infiltration law, molding process, shape memory performance enhancement rule and bending failure rule. Combined with the existing research situation, the future research direction of the thermally-induced SMPC is pointed out.
2020, 37(10): 2376-2385.
doi: 10.13801/j.cnki.fhclxb.20200701.001
Abstract:
WC binderless tungsten carbide (BTC) without metal binder which has high hardness, good wear resistance and corrosion resistance, is widely used in the field of tools, wear resistant parts, etc. and has become a research focus in the field of cemented carbide in recent years. However, due to the absence of the addition of metal binder, the grain growth is easy to occur in the sintering process, the densification is difficult to increase, the requirements of sintering method and process are higher and the toughness clearly inferior to the BTC without metal binder. Therefore, some researchers inhibit grain growth and promote its densification by adding nonmetallic binder and adjusting sintering process, so as to effectively improve the performance of BTC materials without metal binder. In this paper, the application of metal oxides, metal carbides, carbon materials and composite reinforcement to enhance the performance of BTC with metal binder are reviewed.
WC binderless tungsten carbide (BTC) without metal binder which has high hardness, good wear resistance and corrosion resistance, is widely used in the field of tools, wear resistant parts, etc. and has become a research focus in the field of cemented carbide in recent years. However, due to the absence of the addition of metal binder, the grain growth is easy to occur in the sintering process, the densification is difficult to increase, the requirements of sintering method and process are higher and the toughness clearly inferior to the BTC without metal binder. Therefore, some researchers inhibit grain growth and promote its densification by adding nonmetallic binder and adjusting sintering process, so as to effectively improve the performance of BTC materials without metal binder. In this paper, the application of metal oxides, metal carbides, carbon materials and composite reinforcement to enhance the performance of BTC with metal binder are reviewed.
2020, 37(10): 2386-2393.
doi: 10.13801/j.cnki.fhclxb.20190902.003
Abstract:
The flame retardant modification of nylon 66 (PA66) was carried out by melt blending method using aluminium diethyl phosphate (ADP) and halloysite nanotubes (HNTs) as flame retardant system. The effects of the ratio of ADP to HNTs on the flame retardant properties, mechanical properties and thermal stability of ADP-HNTs/PA66 composites were studied. The combustion carbon layer was observed by SEM. The flame retardant mechanism was studied by TG-IR and FTIR. The results show that the flame retardancy of the ADP-HNTs/PA66 composites increases first and then decreases with the increase of the proportion of HNTs. When the flame retardant system is 11wt%ADP-1wt%HNTs, the UL94 flame retardant grade of the ADP-HNTs/PA66 composite is V-0 grade, the limiting oxygen index (LOI) is 35.6%, and it has synergistic flame retardant effect. The tensile strength and elongation at break increase with the increase of the proportion of HNTs in the ADP-HNTs flame retardant system, while the impact strength decreases gradually. TG analysis shows that HNTs can promote charring and slow down the degradation. SEM shows that ADP-HNTs flame retardant system can form a continuous dense carbon layer. TG-IR and FTIR analysis show that ADP has both gas phase and condensed phase flame retardancy, and the introduction of HNTs can interact with ADP in the condensed phase to promote cross-linking and charring.
The flame retardant modification of nylon 66 (PA66) was carried out by melt blending method using aluminium diethyl phosphate (ADP) and halloysite nanotubes (HNTs) as flame retardant system. The effects of the ratio of ADP to HNTs on the flame retardant properties, mechanical properties and thermal stability of ADP-HNTs/PA66 composites were studied. The combustion carbon layer was observed by SEM. The flame retardant mechanism was studied by TG-IR and FTIR. The results show that the flame retardancy of the ADP-HNTs/PA66 composites increases first and then decreases with the increase of the proportion of HNTs. When the flame retardant system is 11wt%ADP-1wt%HNTs, the UL94 flame retardant grade of the ADP-HNTs/PA66 composite is V-0 grade, the limiting oxygen index (LOI) is 35.6%, and it has synergistic flame retardant effect. The tensile strength and elongation at break increase with the increase of the proportion of HNTs in the ADP-HNTs flame retardant system, while the impact strength decreases gradually. TG analysis shows that HNTs can promote charring and slow down the degradation. SEM shows that ADP-HNTs flame retardant system can form a continuous dense carbon layer. TG-IR and FTIR analysis show that ADP has both gas phase and condensed phase flame retardancy, and the introduction of HNTs can interact with ADP in the condensed phase to promote cross-linking and charring.
2020, 37(10): 2394-2400.
doi: 10.13801/j.cnki.fhclxb.20200215.001
Abstract:
The chemical reaction characterization and rheological property of KH-370 polyimide resin were characterized by DSC, TG, FTIR and rheometer. The QWB200/KH-370 composite was prepared by hot pressing technology with QWB200 quartz fiber as reinforcement.The effects of different process parameters (pressing temperature, pressure, curing temperature) on the mechanical properties of QWB200/KH-370 composites were studied. On this basis, the molding process system of the composites was determined.The mechanical strength of the composite at 400℃ and the dielectric properties at broad frequency were also investigated. According to the results, the best process parameters for the preparation of QWB200/KH-370 composites are: pressing temperature of 290-310℃, pressure range of 3.0-4.0 MPa, curing temperature of 380℃. The prepared QWB200/KH-370 composites exhibit excellent mechanical properties at room temperature, and the retention rates of mechanical strength at 400℃ is above 58%, showing good heat resistance. The QWB200/KH-370 composites show stable dielectric constant and dielectric loss at broad frequency from 1 GHz to 18 GHz.
The chemical reaction characterization and rheological property of KH-370 polyimide resin were characterized by DSC, TG, FTIR and rheometer. The QWB200/KH-370 composite was prepared by hot pressing technology with QWB200 quartz fiber as reinforcement.The effects of different process parameters (pressing temperature, pressure, curing temperature) on the mechanical properties of QWB200/KH-370 composites were studied. On this basis, the molding process system of the composites was determined.The mechanical strength of the composite at 400℃ and the dielectric properties at broad frequency were also investigated. According to the results, the best process parameters for the preparation of QWB200/KH-370 composites are: pressing temperature of 290-310℃, pressure range of 3.0-4.0 MPa, curing temperature of 380℃. The prepared QWB200/KH-370 composites exhibit excellent mechanical properties at room temperature, and the retention rates of mechanical strength at 400℃ is above 58%, showing good heat resistance. The QWB200/KH-370 composites show stable dielectric constant and dielectric loss at broad frequency from 1 GHz to 18 GHz.
2020, 37(10): 2401-2408.
doi: 10.13801/j.cnki.fhclxb.20200106.001
Abstract:
A vacuum-assisted compression molding and free curing method suitable for the preparation of epoxy resin-based solid buoyancy materials was proposed by learning from the ceramic material molding process, which realized the separation of molding and solidification during the preparation of solid buoyancy materials and provided a new method for the preparation of high performance solid buoyancy materials. The epoxy resin (E-4221) was used as the matrix, and the hollow glass microsphere (HGMS) was used as the filling material. The HGMS/E-4221 solid buoyancy material with high HGMS volume fraction was prepared by compression molding and free curing method. The effects of volume fraction of HGMS and molding pressure on the density, compressive strength and water absorption of HGMS/E-4221 solid buoyancy materials were studied. The results show that the vacuum-assisted compression molding and free curing method is suitable for the preparation of HGMS/E-4221 solid buoyancy materials with HGMS volume fraction of 65%-67%. The obtained HGMS/E-4221 solid buoyancy material has a den-sity of 0.621-0.655 g/cm3 and a suitable depth of 8 000-10 000 m.
A vacuum-assisted compression molding and free curing method suitable for the preparation of epoxy resin-based solid buoyancy materials was proposed by learning from the ceramic material molding process, which realized the separation of molding and solidification during the preparation of solid buoyancy materials and provided a new method for the preparation of high performance solid buoyancy materials. The epoxy resin (E-4221) was used as the matrix, and the hollow glass microsphere (HGMS) was used as the filling material. The HGMS/E-4221 solid buoyancy material with high HGMS volume fraction was prepared by compression molding and free curing method. The effects of volume fraction of HGMS and molding pressure on the density, compressive strength and water absorption of HGMS/E-4221 solid buoyancy materials were studied. The results show that the vacuum-assisted compression molding and free curing method is suitable for the preparation of HGMS/E-4221 solid buoyancy materials with HGMS volume fraction of 65%-67%. The obtained HGMS/E-4221 solid buoyancy material has a den-sity of 0.621-0.655 g/cm3 and a suitable depth of 8 000-10 000 m.
2020, 37(10): 2409-2417.
doi: 10.13801/j.cnki.fhclxb.20200110.001
Abstract:
Three kinds of multilayer multiaxial interlock 3D woven composites (M3DAWC) were designed and prepared. Digital image correlation system (DIC) and SEM were employed to study the tensile properties of these composites. The results show that the fabric structure has significant effects on the mechanical behavior of M3DAWC. In 0° loading direction, with the increase of the bias yarn volume fraction, the failure mode changes from the neat damage to bias yarn withdrawal. The failure mode exhibits similar trends with that of 0° when the specimens were stretched along 90°, which are pull-out and slippage of the bias yarns. Meanwhile, the volume fraction of the bias yarn also has a significant influence on the tensile strength and modulus of the M3DAWC. In 0° loading direction, the tensile strength and modulus gradually decrease with the increase of bias yarn volume fraction. However, the tensile strength and modulus show an opposite pattern in 90° loading direction.
Three kinds of multilayer multiaxial interlock 3D woven composites (M3DAWC) were designed and prepared. Digital image correlation system (DIC) and SEM were employed to study the tensile properties of these composites. The results show that the fabric structure has significant effects on the mechanical behavior of M3DAWC. In 0° loading direction, with the increase of the bias yarn volume fraction, the failure mode changes from the neat damage to bias yarn withdrawal. The failure mode exhibits similar trends with that of 0° when the specimens were stretched along 90°, which are pull-out and slippage of the bias yarns. Meanwhile, the volume fraction of the bias yarn also has a significant influence on the tensile strength and modulus of the M3DAWC. In 0° loading direction, the tensile strength and modulus gradually decrease with the increase of bias yarn volume fraction. However, the tensile strength and modulus show an opposite pattern in 90° loading direction.
2020, 37(10): 2418-2427.
doi: 10.13801/j.cnki.fhclxb.20200215.002
Abstract:
The synergistic effects of the metal surface treatments and interleaves on the interlaminar mechanical properties of the carbon fiber reinforced plastics (CFRP) composite-thermoformed steel super-hybrid laminates were investigated. Double cantilever beam tests (DCB) show that the Mode-I interlaminar fracture toughness of the laminates can be greatly improved by combining metal surface treatment and inserting interleaf. Among them, the interlaminar Mode-I fracture toughness of the specimens with sandblasting/adhesive film interleaves (GB36#/AF) and sandblasting/epoxy resin interleaves (GB36#/EP) increase by 343% and 129% compared with that of the degreased specimens respectively. In addition, based on the cohesive zone model, the delamination of the CFRP-thermoformed steel super-hybrid laminates was analyzed by finite element method. Finally, to uncover the toughing mechanism, confocal laser scanning microscopy (LSM), contact angle goniometer (CAG) and scanning electron microscopy (SEM) were employed to characterize the surface morphology of the thermoformed steel and the fracture surface of the tested laminates.
The synergistic effects of the metal surface treatments and interleaves on the interlaminar mechanical properties of the carbon fiber reinforced plastics (CFRP) composite-thermoformed steel super-hybrid laminates were investigated. Double cantilever beam tests (DCB) show that the Mode-I interlaminar fracture toughness of the laminates can be greatly improved by combining metal surface treatment and inserting interleaf. Among them, the interlaminar Mode-I fracture toughness of the specimens with sandblasting/adhesive film interleaves (GB36#/AF) and sandblasting/epoxy resin interleaves (GB36#/EP) increase by 343% and 129% compared with that of the degreased specimens respectively. In addition, based on the cohesive zone model, the delamination of the CFRP-thermoformed steel super-hybrid laminates was analyzed by finite element method. Finally, to uncover the toughing mechanism, confocal laser scanning microscopy (LSM), contact angle goniometer (CAG) and scanning electron microscopy (SEM) were employed to characterize the surface morphology of the thermoformed steel and the fracture surface of the tested laminates.
2020, 37(10): 2428-2438.
doi: 10.13801/j.cnki.fhclxb.20200219.003
Abstract:
In view of the insufficiency of durability of ordinary reinforced concrete structures in severe corrosive marine environments in South China Sea Islands, the basalt fiber reinforced polymer (BFRP) bar was proposed to reinforce coral reef and sea sand concrete. Axial compression test on 15 columns was conducted. The failure mode, load-displacement relationship and load-axial strain relationship were documented during the loading process. Test results indicate that, the failure of coral reef sand concrete initiates from the low strength coral reef aggregate, and finally experiences total failure at both aggregate and interface. The development law of column failure is characterized as three stages. The load capacity of BFRP coral reef and sea sand column is equivalent to that of steel bar.
In view of the insufficiency of durability of ordinary reinforced concrete structures in severe corrosive marine environments in South China Sea Islands, the basalt fiber reinforced polymer (BFRP) bar was proposed to reinforce coral reef and sea sand concrete. Axial compression test on 15 columns was conducted. The failure mode, load-displacement relationship and load-axial strain relationship were documented during the loading process. Test results indicate that, the failure of coral reef sand concrete initiates from the low strength coral reef aggregate, and finally experiences total failure at both aggregate and interface. The development law of column failure is characterized as three stages. The load capacity of BFRP coral reef and sea sand column is equivalent to that of steel bar.
2020, 37(10): 2452-2462.
doi: 10.13801/j.cnki.fhclxb.20200102.002
Abstract:
This paper deals with the delamination behaviors and damage evolution modes of woven composites under quasi-static/cyclic loading. Mode II delamination propagation tests were conducted on twill woven CF3052/3238A carbon fiber/epoxy resin composites subjected to quasi-static/cyclic loading. Experimental results demonstrate that due to the latitudinal fiber bundles, a periodical retardation occurs during interlaminar delamination propagation accompanying with intralaminar debonding between latitudinal fiber bundles. Although the crack growth rate for mode II delamination of the twill woven CF3052/3238A carbon fiber/epoxy resin composites follows the Paris model, the variation law in fatigue driven force under load-control mode differs from that under displacement-control mode. That is, fatigue driven force changes parabolic monotonously under load-control mode, but wavily under displacement-control mode. Fatigue driven model is apt to characterize the damage evolution of the twill woven CF3052/3238A carbon fiber/epoxy resin composites under load-control and displacement-control modes. Good correlation is achieved between the proposed model and experimental results.
This paper deals with the delamination behaviors and damage evolution modes of woven composites under quasi-static/cyclic loading. Mode II delamination propagation tests were conducted on twill woven CF3052/3238A carbon fiber/epoxy resin composites subjected to quasi-static/cyclic loading. Experimental results demonstrate that due to the latitudinal fiber bundles, a periodical retardation occurs during interlaminar delamination propagation accompanying with intralaminar debonding between latitudinal fiber bundles. Although the crack growth rate for mode II delamination of the twill woven CF3052/3238A carbon fiber/epoxy resin composites follows the Paris model, the variation law in fatigue driven force under load-control mode differs from that under displacement-control mode. That is, fatigue driven force changes parabolic monotonously under load-control mode, but wavily under displacement-control mode. Fatigue driven model is apt to characterize the damage evolution of the twill woven CF3052/3238A carbon fiber/epoxy resin composites under load-control and displacement-control modes. Good correlation is achieved between the proposed model and experimental results.
2020, 37(10): 2463-2472.
doi: 10.13801/j.cnki.fhclxb.20191221.001
Abstract:
The failure mechanism of the composite fuselage curved panel under circumferential bending load was studied by four-point bending test and finite element analysis (FEA). A set of strengthening and connecting fixture was designed to avoid undesirable failure. A finite element model was also established, in which cohesive element was used to simulate the interface between the hat stringer and skin. Quads criterion and Hashin criterion were used as failure criteria of the interface and the laminate respectively. The results obtained by experiment and FEA are in good agreement. It can be concluded the crack initiates from the R-zone of the bonding area between the hat stringer and skin, due to local buckling of the skin at the bottom of the hat stringer. Then it extends and causes debonding of the hat stringers. With the extension of skin buckling and stringer debonding, the skin shows global instability and loses its bearing capacity, which eventually leads to the failure of the frame due to excessive load. According to the initial damage mode, the full around bonding process between the hat stringer and skin is adopted to improve the circumferential stability of the curved composite panel. The bending test result shows that the bending loads of the initial buckling and overall failure increase 21.9%and 16.8%, respectively.
The failure mechanism of the composite fuselage curved panel under circumferential bending load was studied by four-point bending test and finite element analysis (FEA). A set of strengthening and connecting fixture was designed to avoid undesirable failure. A finite element model was also established, in which cohesive element was used to simulate the interface between the hat stringer and skin. Quads criterion and Hashin criterion were used as failure criteria of the interface and the laminate respectively. The results obtained by experiment and FEA are in good agreement. It can be concluded the crack initiates from the R-zone of the bonding area between the hat stringer and skin, due to local buckling of the skin at the bottom of the hat stringer. Then it extends and causes debonding of the hat stringers. With the extension of skin buckling and stringer debonding, the skin shows global instability and loses its bearing capacity, which eventually leads to the failure of the frame due to excessive load. According to the initial damage mode, the full around bonding process between the hat stringer and skin is adopted to improve the circumferential stability of the curved composite panel. The bending test result shows that the bending loads of the initial buckling and overall failure increase 21.9%and 16.8%, respectively.
2020, 37(10): 2473-2481.
doi: 10.13801/j.cnki.fhclxb.20191224.002
Abstract:
In order to investigate the damage development regularity of composites subjected to fatigue loading, a normalized derivative damage model based on the residual strength was proposed. In this model, it is assumed that the cumulative damage and stress level have a linear relationship, based on which, the damage curves of untested stress levels can be derived from that of tested stress levels with positive stress ratios. Fatigue tests of 8mm-diameter carbon fiber reinforced polymer (CFRP) composite tendons for different stress situations were conducted, and the experimental data of glass fiber reinforced polymer (GFRP) composite laminates from references were adopted to validate the reliability of the proposed damage model. The experimental results show that the damage model can well reflect the three-stage development law of CFRP composite tendons, and the derived damage curves show a good agreement with the damage curves obtained by fitting the experimental data. Besides, this paper investigates the influence of stress level on the damage evolution of composites. As the stress level increases, the boundaries between adjacent stages of damage curves become unobvious.
In order to investigate the damage development regularity of composites subjected to fatigue loading, a normalized derivative damage model based on the residual strength was proposed. In this model, it is assumed that the cumulative damage and stress level have a linear relationship, based on which, the damage curves of untested stress levels can be derived from that of tested stress levels with positive stress ratios. Fatigue tests of 8mm-diameter carbon fiber reinforced polymer (CFRP) composite tendons for different stress situations were conducted, and the experimental data of glass fiber reinforced polymer (GFRP) composite laminates from references were adopted to validate the reliability of the proposed damage model. The experimental results show that the damage model can well reflect the three-stage development law of CFRP composite tendons, and the derived damage curves show a good agreement with the damage curves obtained by fitting the experimental data. Besides, this paper investigates the influence of stress level on the damage evolution of composites. As the stress level increases, the boundaries between adjacent stages of damage curves become unobvious.
2020, 37(10): 2482-2488.
doi: 10.13801/j.cnki.fhclxb.20200111.004
Abstract:
Air bubbles and gaps in epoxy matrix composites seriously influence its thermal conductivity. Research on the effect of bubbles and gaps on the thermal conductivity of composites benefits to improve the accuracy of thermal conductive model and provides guidance for optimization of thermal conductivity. A numerical model of hexagonal boron nitride (h-BN)/epoxy composites with air bubbles and gaps was established by finite element method. The effects of bubble size and number, gap size and number on the thermal conductivity of h-BN/epoxy composites were systematically analyzed. This model was validated by other thermally conductive models and experimental data. The results show that with the increase of bubble size and number, the thermal conductivity of h-BN/epoxy composites decreases gradually, and a turning point occurs in the thermal conductivity curve changing with bubble size. Bubbles with diameter greater than the thickness of unit cell have a great impact on the thermal conductivity of h-BN/epoxy composites. With the increase of gap diameter and thickness, the thermal conductivity of h-BN/epoxy composites decreases slowly first, and then fast. Finally, the thermal conductivity of h-BN/epoxy composites decreases linearly. With the increase of the gap number, the thermal conductivity of h-BN/epoxy composites decreases gradually. The air gaps at the interface of h-BN and epoxy have a greater influence than those in the epoxy matrix.
Air bubbles and gaps in epoxy matrix composites seriously influence its thermal conductivity. Research on the effect of bubbles and gaps on the thermal conductivity of composites benefits to improve the accuracy of thermal conductive model and provides guidance for optimization of thermal conductivity. A numerical model of hexagonal boron nitride (h-BN)/epoxy composites with air bubbles and gaps was established by finite element method. The effects of bubble size and number, gap size and number on the thermal conductivity of h-BN/epoxy composites were systematically analyzed. This model was validated by other thermally conductive models and experimental data. The results show that with the increase of bubble size and number, the thermal conductivity of h-BN/epoxy composites decreases gradually, and a turning point occurs in the thermal conductivity curve changing with bubble size. Bubbles with diameter greater than the thickness of unit cell have a great impact on the thermal conductivity of h-BN/epoxy composites. With the increase of gap diameter and thickness, the thermal conductivity of h-BN/epoxy composites decreases slowly first, and then fast. Finally, the thermal conductivity of h-BN/epoxy composites decreases linearly. With the increase of the gap number, the thermal conductivity of h-BN/epoxy composites decreases gradually. The air gaps at the interface of h-BN and epoxy have a greater influence than those in the epoxy matrix.
2020, 37(10): 2439-2451.
doi: 10.13801/j.cnki.fhclxb.20200121.002
Abstract:
An uniaxial compression test was conducted for T-stiffened composite curved panels which were automatic fiber placement (AFP) manufactured or hand-laid. A 3D optical measurement method which was based on the digital image correlation (DIC) was used to monitor the local buckling and post-buckling, and the results were compared with that of strain gauges and displacement transducers. The results show that the displacement field can be accurately captured by DIC, and the buckling mode observed using DIC is consistent with that the values of the strain gauges reflect. Different from the conventional method of strain gauges, the whole progress of the buckling mode transition of the skin caused by the secondary instability is accurately captured by DIC. The buckling modes at different times (i.e. different load levels) are clearly and intuitively observed using DIC equipment, so the buckling load of the structure is easy to determine and the error is less than 5% compared with the load indicating the strain-load curves separation. A numerical simulation analysis based on finite element software ABAQUS was carried out. The computation results were compared with the test results, revealing that there is a good consistency among the computational results, results from DIC and results of conventional method.
An uniaxial compression test was conducted for T-stiffened composite curved panels which were automatic fiber placement (AFP) manufactured or hand-laid. A 3D optical measurement method which was based on the digital image correlation (DIC) was used to monitor the local buckling and post-buckling, and the results were compared with that of strain gauges and displacement transducers. The results show that the displacement field can be accurately captured by DIC, and the buckling mode observed using DIC is consistent with that the values of the strain gauges reflect. Different from the conventional method of strain gauges, the whole progress of the buckling mode transition of the skin caused by the secondary instability is accurately captured by DIC. The buckling modes at different times (i.e. different load levels) are clearly and intuitively observed using DIC equipment, so the buckling load of the structure is easy to determine and the error is less than 5% compared with the load indicating the strain-load curves separation. A numerical simulation analysis based on finite element software ABAQUS was carried out. The computation results were compared with the test results, revealing that there is a good consistency among the computational results, results from DIC and results of conventional method.
2020, 37(10): 2489-2500.
doi: 10.13801/j.cnki.fhclxb.20200203.001
Abstract:
WC-graphene oxide(GO)/Ni composite coating was fabricated by vacuum cladding technique. The microstructural change and phase composition of the coating at different temperatures were observed and analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer. The results show that the WC-GO/Ni composite coating with dense microstructure and good metallurgical fusion with the matrix was successfully fabricated on the ZG45 substrate. There are four sub-layers from the coating surface to substrate, they are composite layer with about 1.5 mm thickness, transition layer with about 360 μm thickness, diffusion fusion layer with about 50 μm thickness and diffusion affected layer with 100 μm thickness. The main phases of WC-GO/Ni composite coating are Cr7C3, FeNi3, WC, Cr23C6, Ni3Si, C, Fe7W6, γ-Ni solid solution. FeNi3 and Fe7W6 are dispersed in the metallurgical fusion zone, and the main phase of the diffusion affected zone is pearlite. The phase size of the composite zone is smaller than that of the interface zone. The changing of metal particles at composite area precedes that at the interface area. The clusters (Cr7C3/Cr23C6) formed on the incompletely melted metal particles surface and grew into needle shape. The needle carbides are embedded in the Ni-based solid solution among the coating.
WC-graphene oxide(GO)/Ni composite coating was fabricated by vacuum cladding technique. The microstructural change and phase composition of the coating at different temperatures were observed and analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer. The results show that the WC-GO/Ni composite coating with dense microstructure and good metallurgical fusion with the matrix was successfully fabricated on the ZG45 substrate. There are four sub-layers from the coating surface to substrate, they are composite layer with about 1.5 mm thickness, transition layer with about 360 μm thickness, diffusion fusion layer with about 50 μm thickness and diffusion affected layer with 100 μm thickness. The main phases of WC-GO/Ni composite coating are Cr7C3, FeNi3, WC, Cr23C6, Ni3Si, C, Fe7W6, γ-Ni solid solution. FeNi3 and Fe7W6 are dispersed in the metallurgical fusion zone, and the main phase of the diffusion affected zone is pearlite. The phase size of the composite zone is smaller than that of the interface zone. The changing of metal particles at composite area precedes that at the interface area. The clusters (Cr7C3/Cr23C6) formed on the incompletely melted metal particles surface and grew into needle shape. The needle carbides are embedded in the Ni-based solid solution among the coating.
2020, 37(10): 2501-2511.
doi: 10.13801/j.cnki.fhclxb.20200111.003
Abstract:
Through comparing and analyzing the materials loss characteristics under pure corrosion, pure wear and corrosion-wear conditons, the corrosion-wear behavior and synergy mechanism between corrosion and wear of Ti3AlC2-Al2O3/TiAl3 composite in molten aluminum were investigated. The results show that the loss of corrosion-wear of Ti3AlC2-Al2O3/TiAl3 composite is two orders of magnitude lower than that of H13 steel. With the increase of load and speed, the wear of Ti3AlC2-Al2O3/TiAl3 composite changes from abrasive wear to adhesive wear. The synergy ratio of corrosion-wear is less than 47.5% in the experiments. Under the condition of low load or low velocity, the Ti3AlC2-Al2O3/TiAl3 composite even exhibits negative synergy. This is partly due to no intermetallic compound formed in the interface, but just a little Ti dissolved into the molten aluminum when the Ti3AlC2-Al2O3/TiAl3 composite corroded in Al melt. On the other hand, the interpenetrating structure of TiAl3 matrix and Al2O3 reinforcement improves the wear resistance of Ti3AlC2-Al2O3/TiAl3 composite in molten aluminum.
Through comparing and analyzing the materials loss characteristics under pure corrosion, pure wear and corrosion-wear conditons, the corrosion-wear behavior and synergy mechanism between corrosion and wear of Ti3AlC2-Al2O3/TiAl3 composite in molten aluminum were investigated. The results show that the loss of corrosion-wear of Ti3AlC2-Al2O3/TiAl3 composite is two orders of magnitude lower than that of H13 steel. With the increase of load and speed, the wear of Ti3AlC2-Al2O3/TiAl3 composite changes from abrasive wear to adhesive wear. The synergy ratio of corrosion-wear is less than 47.5% in the experiments. Under the condition of low load or low velocity, the Ti3AlC2-Al2O3/TiAl3 composite even exhibits negative synergy. This is partly due to no intermetallic compound formed in the interface, but just a little Ti dissolved into the molten aluminum when the Ti3AlC2-Al2O3/TiAl3 composite corroded in Al melt. On the other hand, the interpenetrating structure of TiAl3 matrix and Al2O3 reinforcement improves the wear resistance of Ti3AlC2-Al2O3/TiAl3 composite in molten aluminum.
2020, 37(10): 2512-2517.
doi: 10.13801/j.cnki.fhclxb.20200221.001
Abstract:
The new way of the ball milling-spray-stirring process was used to fabricate nano-Al2O3 particle (Al2O3p)/Al(7075) composites and the spray-stirring device was designed which can inject continuously a spot of nano-Al2O3p into the Al melt. The effect of nano-Al2O3p reinforcement on the microstructure of Al(7075) matrix alloy was observed, and the wear characteristics of Al(7075) matrix and nano-Al2O3p/Al(7075) composites were tested. The wear characteristics of the nano-Al2O3p/Al(7075) composites and Al(7075) matrix were measured at various loads(15 N, 25 N and 35 N). The results show the nano-Al2O3p/Al(7075) composites appears as fine grain, and the distribution of the reinforcement in the matrix is uniform, and well bonded with the matrix. As the load increasing, the wear lose of the nano-Al2O3p/Al(7075) composites is slower than the Al(7075) matrix. When the load is 35 N, the nano-Al2O3p/Al(7075) composites exhibite smaller wear width and wear debris. The improvement of the wear resistance of the nano-Al2O3p/Al(7075) composites occurs mainly by supporting of the Al2O3p and strengthening of the fine-grain.
The new way of the ball milling-spray-stirring process was used to fabricate nano-Al2O3 particle (Al2O3p)/Al(7075) composites and the spray-stirring device was designed which can inject continuously a spot of nano-Al2O3p into the Al melt. The effect of nano-Al2O3p reinforcement on the microstructure of Al(7075) matrix alloy was observed, and the wear characteristics of Al(7075) matrix and nano-Al2O3p/Al(7075) composites were tested. The wear characteristics of the nano-Al2O3p/Al(7075) composites and Al(7075) matrix were measured at various loads(15 N, 25 N and 35 N). The results show the nano-Al2O3p/Al(7075) composites appears as fine grain, and the distribution of the reinforcement in the matrix is uniform, and well bonded with the matrix. As the load increasing, the wear lose of the nano-Al2O3p/Al(7075) composites is slower than the Al(7075) matrix. When the load is 35 N, the nano-Al2O3p/Al(7075) composites exhibite smaller wear width and wear debris. The improvement of the wear resistance of the nano-Al2O3p/Al(7075) composites occurs mainly by supporting of the Al2O3p and strengthening of the fine-grain.
2020, 37(10): 2518-2525.
doi: 10.13801/j.cnki.fhclxb.20200226.001
Abstract:
In order to investigate the effect of hole diameter in honeycomb preform on the W diffusion uniformity, the WC/Fe composites with different diameters were fabricated by vacuum expendable pattern casting (V-EPC) process. Based on the W mass fraction distribution analysis, it is found that the W distributes uniformity when the hole diameter is too large or too smallthe, while wear resistance of WC/Fe composites with the proper hole diameter of preform is the best, and the differences of the W mass fraction and hardness between initial hole wall and initial hole center are reduced. The simulation results by diffusion dynamics show that the uniformity of W diffusion is both influenced by diffusion distance and diffusion time. The W diffusion is limited when the hole diameter is samll and the diffusion distance is short although the diffusion time decreases, resluted from the fast internal matrix solidification. The W diffusion is also limited when the hole diameter is large, although the internal matrix solidifies slow and the diffusion time increases, but the diffusion distance increases. So the proper hole diameter has positive influence on the W diffusion uniformity with reasonable diffusion distance and diffusion time. On the contrary, the W diffusion uniformity is undesirable, and the W mass fraction and the hardness at the initial hole center are lower, resulting in the reduction of wear resistance within a certain range.
In order to investigate the effect of hole diameter in honeycomb preform on the W diffusion uniformity, the WC/Fe composites with different diameters were fabricated by vacuum expendable pattern casting (V-EPC) process. Based on the W mass fraction distribution analysis, it is found that the W distributes uniformity when the hole diameter is too large or too smallthe, while wear resistance of WC/Fe composites with the proper hole diameter of preform is the best, and the differences of the W mass fraction and hardness between initial hole wall and initial hole center are reduced. The simulation results by diffusion dynamics show that the uniformity of W diffusion is both influenced by diffusion distance and diffusion time. The W diffusion is limited when the hole diameter is samll and the diffusion distance is short although the diffusion time decreases, resluted from the fast internal matrix solidification. The W diffusion is also limited when the hole diameter is large, although the internal matrix solidifies slow and the diffusion time increases, but the diffusion distance increases. So the proper hole diameter has positive influence on the W diffusion uniformity with reasonable diffusion distance and diffusion time. On the contrary, the W diffusion uniformity is undesirable, and the W mass fraction and the hardness at the initial hole center are lower, resulting in the reduction of wear resistance within a certain range.
2020, 37(10): 2526-2533.
doi: 10.13801/j.cnki.fhclxb.20200217.001
Abstract:
TiB2/Cu composites with multi-particle (2 μm+10 μm+50 μm) were prepared by powder metallurgy. The arc erosion resistance of multi-particle TiB2/Cu composites was tested in a JF04C contact material testing system. The arc erosion resistance and morphology of TiB2/Cu composites were studied when the mass ratios of TiB2 particles (2 μm+10 μm+50 μm) were 1∶1∶1, 1∶1∶3, 1∶3∶1 and 3∶1∶1, respectively. The results show that when the (2 μm+10 μm+50 μm) TiB2 particle mass ratio is 1∶1∶1, the TiB2/Cu composite has the highest relative density and conductivity of 99.1% and 87.1%IACS, respectively. When the (2 m+10 m+50 m) TiB2 particle mass ratio are 1∶1∶1 and 1∶3∶1, the structure uniformity of the TiB2/Cu composites is better, the material loss is the same after arc erosion, and the material loss of the TiB2/Cu composite is lower than the composites with other ratios. When the ratio is 1∶3∶1, the TiB2/Cu composite has the lowest average arc energy, and the arc duration and arc energy are the most stable. It can be concluded that the introduction of appropriate multi-particle TiB2 particles into Cu matrix can improve the density and electrical conductivity of the TiB2/Cu composites. In the process of arc erosion, TiB2 particles with different sizes cooperate with each other, which is helpful to enhance the arc erosion resistance and service stability of the TiB2/Cu composites.
TiB2/Cu composites with multi-particle (2 μm+10 μm+50 μm) were prepared by powder metallurgy. The arc erosion resistance of multi-particle TiB2/Cu composites was tested in a JF04C contact material testing system. The arc erosion resistance and morphology of TiB2/Cu composites were studied when the mass ratios of TiB2 particles (2 μm+10 μm+50 μm) were 1∶1∶1, 1∶1∶3, 1∶3∶1 and 3∶1∶1, respectively. The results show that when the (2 μm+10 μm+50 μm) TiB2 particle mass ratio is 1∶1∶1, the TiB2/Cu composite has the highest relative density and conductivity of 99.1% and 87.1%IACS, respectively. When the (2 m+10 m+50 m) TiB2 particle mass ratio are 1∶1∶1 and 1∶3∶1, the structure uniformity of the TiB2/Cu composites is better, the material loss is the same after arc erosion, and the material loss of the TiB2/Cu composite is lower than the composites with other ratios. When the ratio is 1∶3∶1, the TiB2/Cu composite has the lowest average arc energy, and the arc duration and arc energy are the most stable. It can be concluded that the introduction of appropriate multi-particle TiB2 particles into Cu matrix can improve the density and electrical conductivity of the TiB2/Cu composites. In the process of arc erosion, TiB2 particles with different sizes cooperate with each other, which is helpful to enhance the arc erosion resistance and service stability of the TiB2/Cu composites.
2020, 37(10): 2552-2560.
doi: 10.13801/j.cnki.fhclxb.20200617.003
Abstract:
In order to fabricate the TiCN-based cermet with better comprehensive mechanical properties, the effects of the sintering temperature on hte microstructure and mechanical properties of TiCN-HfN cermet were investigated. And a model of a coexisted microstructure of particle dispersion and core-rim structure was built for this cermet. Meanwhile, the densification, hardened, toughened and strengthened mechanisms were disclosed. The results show that the TiCN-HfN cermet fabricated at 1 500℃ has this coexisted microstructure and better comprehensive mechanical properties. The dispersed particle is HfN, the core consists of TiCN, and the rim is mainly composed of (Ti,Hf,Mo)CN solid solution. The relative density, hardness, flexural strength and fracture toughness of this cermet are 99.7%, 20.6 GPa, 1 682.5 MPa, 8.5 MPa·m1/2, respectively. This cermet completes densification by particles and metal liquid that filled in the sintering necks in the cermet. This cermet is hardened by its densification and particle pinning effect, and is toughened by particle dispersion and particle pinning effect, and is strengthened by the formed skeleton structure and particle pinning effect.
In order to fabricate the TiCN-based cermet with better comprehensive mechanical properties, the effects of the sintering temperature on hte microstructure and mechanical properties of TiCN-HfN cermet were investigated. And a model of a coexisted microstructure of particle dispersion and core-rim structure was built for this cermet. Meanwhile, the densification, hardened, toughened and strengthened mechanisms were disclosed. The results show that the TiCN-HfN cermet fabricated at 1 500℃ has this coexisted microstructure and better comprehensive mechanical properties. The dispersed particle is HfN, the core consists of TiCN, and the rim is mainly composed of (Ti,Hf,Mo)CN solid solution. The relative density, hardness, flexural strength and fracture toughness of this cermet are 99.7%, 20.6 GPa, 1 682.5 MPa, 8.5 MPa·m1/2, respectively. This cermet completes densification by particles and metal liquid that filled in the sintering necks in the cermet. This cermet is hardened by its densification and particle pinning effect, and is toughened by particle dispersion and particle pinning effect, and is strengthened by the formed skeleton structure and particle pinning effect.
2020, 37(10): 2534-2542.
doi: 10.13801/j.cnki.fhclxb.20200224.003
Abstract:
ANSYS was used to simulate the thermal conduction process of TiB2/Cu composites with different TiB2 particle sizes. The TiB2/Cu composites with different TiB2 particle sizes were prepared by powder metallurgy. LINSEIS LFA1600 laser thermal conductivity instrument was used to determine the thermal conductivity of the TiB2/Cu composites ranging from room temperature to 280℃, and the measured values were compared with the simulation results. The simulation results are in good agreement with the measured values. In the range of 50-200℃, the thermal conductivities of the TiB2/Cu composites fluctuate in the range of 6%-9%. When the temperature is above 200℃, both the simulated results and the measured values increase with the increase of temperature, and they match well with each other. This is because the large difference of their thermal expansion coefficients in the interface between TiB2 and Cu below 200℃ is not considered in the simulation process. When the temperature is above 200℃, the simulation results have good accordance with the measured values. At 200℃, due to the influence of two-phase thermal expansion coefficients, the equivalent stress at the internal interface of the composite is larger than the yield strength of the Cu matrix, thus causing plastic deformation, which leads to a significant change in the thermal conductivity. In addition, the thermal conductivity increases and then decreases with the increase of particle size, and reaches its maximum value at 10 μm. This is because when the particle diameter is less than the critical average diameter, the increased particle diameter reduces the number of interfaces, thus reducing the interfacial thermal resistance. When the particle diameter is larger than the critical mean diameter, the mean free path l greatly increases and the thermal conductivity reduces.
ANSYS was used to simulate the thermal conduction process of TiB2/Cu composites with different TiB2 particle sizes. The TiB2/Cu composites with different TiB2 particle sizes were prepared by powder metallurgy. LINSEIS LFA1600 laser thermal conductivity instrument was used to determine the thermal conductivity of the TiB2/Cu composites ranging from room temperature to 280℃, and the measured values were compared with the simulation results. The simulation results are in good agreement with the measured values. In the range of 50-200℃, the thermal conductivities of the TiB2/Cu composites fluctuate in the range of 6%-9%. When the temperature is above 200℃, both the simulated results and the measured values increase with the increase of temperature, and they match well with each other. This is because the large difference of their thermal expansion coefficients in the interface between TiB2 and Cu below 200℃ is not considered in the simulation process. When the temperature is above 200℃, the simulation results have good accordance with the measured values. At 200℃, due to the influence of two-phase thermal expansion coefficients, the equivalent stress at the internal interface of the composite is larger than the yield strength of the Cu matrix, thus causing plastic deformation, which leads to a significant change in the thermal conductivity. In addition, the thermal conductivity increases and then decreases with the increase of particle size, and reaches its maximum value at 10 μm. This is because when the particle diameter is less than the critical average diameter, the increased particle diameter reduces the number of interfaces, thus reducing the interfacial thermal resistance. When the particle diameter is larger than the critical mean diameter, the mean free path l greatly increases and the thermal conductivity reduces.
2020, 37(10): 2543-2551.
doi: 10.13801/j.cnki.fhclxb.20200311.001
Abstract:
For effectively killing the bacillus coli in the water and adsorbing endotoxin released on the death at the same time, the new bi-functional material of Ag nanoclusters enclosed into X-zeolite (Ag@NaX) was prepared by in-situ synthesis method for the first time. The results of HR-TEM and STEM show that most of the Ag clusters are uniformly located at the zeolite cages, whose average size is 1.03 nm. This bi-functional material was used for killing the bacillus coli in water and showed an excellent performance. The amount of 2.5 mg/100 mL material (1.07wt% mass fraction of Ag loading) could totally remove the bacillus coli at 20 min. The endotoxin released on the death is also adsorbed by the zeolite efficiently, leading to the amount of endotoxin keeping at 8×10−9g/100 mL, whose amount is lower than the safety standards of endotoxin for drinking water in relevant regulations. The composite material has excellent bi-function of sterilization and adsorption at the same time under the join effects of Ag clusters and zeolite endow. The material has a excellent stability due to the Ag clusters is effectively prevented from losing by the zeolite skeleton, which leads to the performance of this material keeping well after several numbers of using.
For effectively killing the bacillus coli in the water and adsorbing endotoxin released on the death at the same time, the new bi-functional material of Ag nanoclusters enclosed into X-zeolite (Ag@NaX) was prepared by in-situ synthesis method for the first time. The results of HR-TEM and STEM show that most of the Ag clusters are uniformly located at the zeolite cages, whose average size is 1.03 nm. This bi-functional material was used for killing the bacillus coli in water and showed an excellent performance. The amount of 2.5 mg/100 mL material (1.07wt% mass fraction of Ag loading) could totally remove the bacillus coli at 20 min. The endotoxin released on the death is also adsorbed by the zeolite efficiently, leading to the amount of endotoxin keeping at 8×10−9g/100 mL, whose amount is lower than the safety standards of endotoxin for drinking water in relevant regulations. The composite material has excellent bi-function of sterilization and adsorption at the same time under the join effects of Ag clusters and zeolite endow. The material has a excellent stability due to the Ag clusters is effectively prevented from losing by the zeolite skeleton, which leads to the performance of this material keeping well after several numbers of using.
2020, 37(10): 2561-2571.
doi: 10.13801/j.cnki.fhclxb.20200121.001
Abstract:
The improvement of body armor can significantly enhance the individual fighting ability, and bio-mimic can provide new idea for the design of high-performance body armor. The shell of armadillo is made of hexagonal scales closely joined together, with a layered structure, which has high flexibility and protective capacity. The geometric assembly mode of armadillo shell was adopted, and the hard layer and soft layer were simulated with the SiC ceramic and ultrahigh molecular weight polyethylene(UHMWPE) hot-compressed plate, respectively. The thickness ratio of two layers was chosen as 1∶1 for the design and fabrication of bionic composite scales. and the bionic scales were closely arranged together to form a new type flexible ballistic plate. In order to examine the actual ballistic performance and characterize the damage modes of the ballistic plate, ballistic testing was conducted to investigate the ballistic limit. Meanwhile, the finite element model was built to analyze the penetration resistance of the ballistic plate against 7.62 mm handgun bullets. The results indicate that the new ballistic plate not only meets the requirements in terms of ballistic performance, but also has good flexibility, which can provide a reference for the design and optimization of new types of ballistic plate in the future.
The improvement of body armor can significantly enhance the individual fighting ability, and bio-mimic can provide new idea for the design of high-performance body armor. The shell of armadillo is made of hexagonal scales closely joined together, with a layered structure, which has high flexibility and protective capacity. The geometric assembly mode of armadillo shell was adopted, and the hard layer and soft layer were simulated with the SiC ceramic and ultrahigh molecular weight polyethylene(UHMWPE) hot-compressed plate, respectively. The thickness ratio of two layers was chosen as 1∶1 for the design and fabrication of bionic composite scales. and the bionic scales were closely arranged together to form a new type flexible ballistic plate. In order to examine the actual ballistic performance and characterize the damage modes of the ballistic plate, ballistic testing was conducted to investigate the ballistic limit. Meanwhile, the finite element model was built to analyze the penetration resistance of the ballistic plate against 7.62 mm handgun bullets. The results indicate that the new ballistic plate not only meets the requirements in terms of ballistic performance, but also has good flexibility, which can provide a reference for the design and optimization of new types of ballistic plate in the future.
