2007 Vol. 24, No. 5
2007, 24(5): 1-5.
Abstract:
TiB2P/Al composites with different volume fractions were fabricated by squeeze casting, the ambient mechanical properties of the composites were studied by means of scanning electron microscopy (SEM), hardness measurement, tensile testing, etc, and the effects of volume fraction and heat treatment on the mechanical properties of the composites were systematically studied. The results show that the Brinell hardness, bending strength and elastic modulus of the TiB2P/Al composites increase with the increasing of the volume fraction of TiB2. The hardness and bending strength of T6-45vol% TiB2P/Al composite increase by 23% and 40% compared with the compo-site in the anneal state, but the effect of heat treatment on the elastic modulus is not obvious.
TiB2P/Al composites with different volume fractions were fabricated by squeeze casting, the ambient mechanical properties of the composites were studied by means of scanning electron microscopy (SEM), hardness measurement, tensile testing, etc, and the effects of volume fraction and heat treatment on the mechanical properties of the composites were systematically studied. The results show that the Brinell hardness, bending strength and elastic modulus of the TiB2P/Al composites increase with the increasing of the volume fraction of TiB2. The hardness and bending strength of T6-45vol% TiB2P/Al composite increase by 23% and 40% compared with the compo-site in the anneal state, but the effect of heat treatment on the elastic modulus is not obvious.
2007, 24(5): 6-12.
Abstract:
The penetration tests of two kinds of functionally graded plates (FGM) were performed by using a high speed air-gun system. The plates consist of layered structures with two stack sequences prepared by the vacuum hot-pressure diffusion processing. Each layer is made from aluminum matrix composites reinforced by different volume fraction SiC particles (MMCs) by the vacuum hot-pressure sintering method. The numerical simulations of penetration process were carried out by LS-DYNA code. The numerical simulations were also performed to explore the optimal distribution of certain average SiCP fraction. The test results show that the anti-penetration ability of the functionally graded plate is much better than that of the pure aluminum plate. The difference of anti-penetration ability between the two tested functionally graded plates is not apparent. The numerical simulation results are in good agreement with experimental results. From the simulation results, the layered plates have superior anti-penetration ability to the that of homogeneity plate of MMCs. And the anti-penetration of layered plates with the same thickness and the same areal density can be approximately regarded as not sensitive to the particle distribution.
The penetration tests of two kinds of functionally graded plates (FGM) were performed by using a high speed air-gun system. The plates consist of layered structures with two stack sequences prepared by the vacuum hot-pressure diffusion processing. Each layer is made from aluminum matrix composites reinforced by different volume fraction SiC particles (MMCs) by the vacuum hot-pressure sintering method. The numerical simulations of penetration process were carried out by LS-DYNA code. The numerical simulations were also performed to explore the optimal distribution of certain average SiCP fraction. The test results show that the anti-penetration ability of the functionally graded plate is much better than that of the pure aluminum plate. The difference of anti-penetration ability between the two tested functionally graded plates is not apparent. The numerical simulation results are in good agreement with experimental results. From the simulation results, the layered plates have superior anti-penetration ability to the that of homogeneity plate of MMCs. And the anti-penetration of layered plates with the same thickness and the same areal density can be approximately regarded as not sensitive to the particle distribution.
2007, 24(5): 13-18.
Abstract:
Effects of the mass fraction of nano-SiO2 on the mechanical properties of the epoxy composite paint film on the steel plate, such as the hardness, the T-bending performance and the strain were investigated in detail. The corrosion resistant properties of the paint films were measured by the salt spray test and EIS (Electrochemical Impedance Spectroscopy). The results indicate that the performances of the composite paint film with 2.0wt% nano-SiO2 are obviously improved in comparison with the paint film without nano-SiO2. The hardness of the composite paint film increases from H to 2H, the T-bending improves from 4T to 2T, and the anti-salt spray time improves from 720h to 1030h before showing blisters. The resistance of the composite paint film with 2.0% nano-SiO2 is two orders higher than that of the paint film without nano-SiO2 by EIS. Moreover, the nano-SiO2 particles disperse uniformly in the paint film characterized by SEM images.
Effects of the mass fraction of nano-SiO2 on the mechanical properties of the epoxy composite paint film on the steel plate, such as the hardness, the T-bending performance and the strain were investigated in detail. The corrosion resistant properties of the paint films were measured by the salt spray test and EIS (Electrochemical Impedance Spectroscopy). The results indicate that the performances of the composite paint film with 2.0wt% nano-SiO2 are obviously improved in comparison with the paint film without nano-SiO2. The hardness of the composite paint film increases from H to 2H, the T-bending improves from 4T to 2T, and the anti-salt spray time improves from 720h to 1030h before showing blisters. The resistance of the composite paint film with 2.0% nano-SiO2 is two orders higher than that of the paint film without nano-SiO2 by EIS. Moreover, the nano-SiO2 particles disperse uniformly in the paint film characterized by SEM images.
2007, 24(5): 19-22.
Abstract:
The superabsorbent composite of kaolinite/poly (acrylic acid-co-acrylamide) was prepared by UV photopolymerization using N, N-methylene-bis-acrylamide and Iragure 184 as crosslinker and photoinitiator respectively. The effects of the amount of kaolinite on water absorbency, water absorbing rate and water retention were studied. The structure and morphology of the composite were investigated through FTIR, XRD and SEM. The results show that the composite at 15% mass fraction of kaolinite exhibits excellent performance in the water absorbency of 1095 g/g, the salt water absorbency of 94.7g/g, quick absorbing rate and the better retention ability.
The superabsorbent composite of kaolinite/poly (acrylic acid-co-acrylamide) was prepared by UV photopolymerization using N, N-methylene-bis-acrylamide and Iragure 184 as crosslinker and photoinitiator respectively. The effects of the amount of kaolinite on water absorbency, water absorbing rate and water retention were studied. The structure and morphology of the composite were investigated through FTIR, XRD and SEM. The results show that the composite at 15% mass fraction of kaolinite exhibits excellent performance in the water absorbency of 1095 g/g, the salt water absorbency of 94.7g/g, quick absorbing rate and the better retention ability.
2007, 24(5): 23-27.
Abstract:
Oligmers with different end caps (non-side, one-side and both-side capped with NA respectively) and of different molecular weights are used to toughen LP-15 resin. Discussed the toughening mechanism and the influence of end-cap and molecular weight on resins Tg and impact strength. The results showed that all systems revealed one peak in their tan δ-T curves which indicted that these tougheners had good compatibility with LP-15. In the meanwhile, all toughened LP-15 resins maintained the high Tg value of LP-15. Comparing the oligmers with NA end cap with those without NA end cap, the latter exhibited more effectiveness in improving the impact strength of LP-15 resin. To those without NA end cap, the longer the molecular chain, the higher the system toughness.
Oligmers with different end caps (non-side, one-side and both-side capped with NA respectively) and of different molecular weights are used to toughen LP-15 resin. Discussed the toughening mechanism and the influence of end-cap and molecular weight on resins Tg and impact strength. The results showed that all systems revealed one peak in their tan δ-T curves which indicted that these tougheners had good compatibility with LP-15. In the meanwhile, all toughened LP-15 resins maintained the high Tg value of LP-15. Comparing the oligmers with NA end cap with those without NA end cap, the latter exhibited more effectiveness in improving the impact strength of LP-15 resin. To those without NA end cap, the longer the molecular chain, the higher the system toughness.
2007, 24(5): 28-32.
Abstract:
Multiwalled carbon nanotubes/poly (p-phenylene benzobisoxazole) (MWNTs/PBO) composites was prepared by solution blending in MSA solvent. The microstructures of MWNTs/PBO composites were characterized with SEM. The electrical, mechanical and thermal resistance properties of the composites before and after heat treatment were studied. The results show that MWNTs are dispersed uniformly in PBO matrix, and form a network microstructure that can be improved by heat treatment. Compared to MWNTs/PBO composites before heat treatment, the electrical and mechanical properties of the composites after heat treatment are enhanced. The experiments also indicate that the electronic resistivity of 10wt% MWNTs composite after heat treatment reduces approximately nine orders of magnitude over pure PBO polymer, but the tensile strength and modulus increase by 95% and 53%, respectively. MWNTs can obviously improve the thermal resistance of the composites.
Multiwalled carbon nanotubes/poly (p-phenylene benzobisoxazole) (MWNTs/PBO) composites was prepared by solution blending in MSA solvent. The microstructures of MWNTs/PBO composites were characterized with SEM. The electrical, mechanical and thermal resistance properties of the composites before and after heat treatment were studied. The results show that MWNTs are dispersed uniformly in PBO matrix, and form a network microstructure that can be improved by heat treatment. Compared to MWNTs/PBO composites before heat treatment, the electrical and mechanical properties of the composites after heat treatment are enhanced. The experiments also indicate that the electronic resistivity of 10wt% MWNTs composite after heat treatment reduces approximately nine orders of magnitude over pure PBO polymer, but the tensile strength and modulus increase by 95% and 53%, respectively. MWNTs can obviously improve the thermal resistance of the composites.
2007, 24(5): 33-37.
Abstract:
On the basis of the treatment of Kevlar fiber with phosphorous acid (PA)solution, the effects of structure and property of resin matrix on the Kevlar composite were studied. Meanwhile, the mechanical property and thermal mechanical property of Kevlar fiber/epoxy composite were analyzed. The results show that there exist polar functional groups on the fiber surface after being treated with phosphorous solution, which can provide good compatibility between Kevlar fiber and glyceride epoxy resins. For the Kevlar fiber/optimized resin matrix composites, the percentage translation of fiber strength of Naval Ordnance Laboratory (NOL) Rings attains to 95%, while the interlaminar shear strength (ILSS) and the interfacial shear strength (IFSS) are 79MPa and 76MPa, respectively. Moreover, the interfacial properties of the composites are excellent.
On the basis of the treatment of Kevlar fiber with phosphorous acid (PA)solution, the effects of structure and property of resin matrix on the Kevlar composite were studied. Meanwhile, the mechanical property and thermal mechanical property of Kevlar fiber/epoxy composite were analyzed. The results show that there exist polar functional groups on the fiber surface after being treated with phosphorous solution, which can provide good compatibility between Kevlar fiber and glyceride epoxy resins. For the Kevlar fiber/optimized resin matrix composites, the percentage translation of fiber strength of Naval Ordnance Laboratory (NOL) Rings attains to 95%, while the interlaminar shear strength (ILSS) and the interfacial shear strength (IFSS) are 79MPa and 76MPa, respectively. Moreover, the interfacial properties of the composites are excellent.
2007, 24(5): 38-43.
Abstract:
Amine-terminated dendrimer PAMAM was used as an agent in the epoxy resin system, and the influence of the ratio and curing temperature on the properties of cured compounds of PAMAM and epoxy resin was studied by tensile test, impact test, DSC and TGA. The results show that the optimum curing temperature is 140℃, and the influence of the ratio of PAMAM to epoxy resin is different as the curing temperature changes: the optimum ratio is 0.47 (mass ratio of PAMAM to epoxy resin) cured at 80℃, where the optimum mechanical property, the highest glass translation temperature and crosslink density can be obtained. The optimum ratio shifts to a lower ratio as the curing temperature increases: the optimum ratio is 0.28 cured at 140℃, where the optimum mechanical property, the highest glass translation temperature and crosslink density can be obtained. However, the density of the cured compounds and the volume shrinkage reach the maximum when the ratio is 0.47, and the thermal stability is the best when the ratio is 0.28. The cure degree was determined by titration, the result showing that the cure degree of the lower ratio system rapidly soars and approaches the cure degree of the stoichiometric point system as the curing temperature increases.
Amine-terminated dendrimer PAMAM was used as an agent in the epoxy resin system, and the influence of the ratio and curing temperature on the properties of cured compounds of PAMAM and epoxy resin was studied by tensile test, impact test, DSC and TGA. The results show that the optimum curing temperature is 140℃, and the influence of the ratio of PAMAM to epoxy resin is different as the curing temperature changes: the optimum ratio is 0.47 (mass ratio of PAMAM to epoxy resin) cured at 80℃, where the optimum mechanical property, the highest glass translation temperature and crosslink density can be obtained. The optimum ratio shifts to a lower ratio as the curing temperature increases: the optimum ratio is 0.28 cured at 140℃, where the optimum mechanical property, the highest glass translation temperature and crosslink density can be obtained. However, the density of the cured compounds and the volume shrinkage reach the maximum when the ratio is 0.47, and the thermal stability is the best when the ratio is 0.28. The cure degree was determined by titration, the result showing that the cure degree of the lower ratio system rapidly soars and approaches the cure degree of the stoichiometric point system as the curing temperature increases.
2007, 24(5): 44-49.
Abstract:
The thermal conductivity of graphite, carbon fiber modified thermoplastic polyimide was measured, and the effects of the filler content on the mechanical properties and thermal conductivity were investigated. The beha-viors of the thermal conduction of TPI composites were simulated by the Nielsen model and finite element method (FEM), and the shape of the filler was also considered. The results indicate that thermal conductivity of the material is improved obviously by increasing the filler content. The difference between the calculated data by Nielsen model and experimental data is unacceptable. The behaviors of the thermal conduction of TPI composites at the steady state could be simulated properly by FEM. Based on an analysis of the thermal flux in unit of composites, it is found that the influence of the filler thermal conductivity on the composites thermal behavior is not obvious, and the thermal conductivity of the composite with the rectangle filler is much higher than that with rotundity filler.
The thermal conductivity of graphite, carbon fiber modified thermoplastic polyimide was measured, and the effects of the filler content on the mechanical properties and thermal conductivity were investigated. The beha-viors of the thermal conduction of TPI composites were simulated by the Nielsen model and finite element method (FEM), and the shape of the filler was also considered. The results indicate that thermal conductivity of the material is improved obviously by increasing the filler content. The difference between the calculated data by Nielsen model and experimental data is unacceptable. The behaviors of the thermal conduction of TPI composites at the steady state could be simulated properly by FEM. Based on an analysis of the thermal flux in unit of composites, it is found that the influence of the filler thermal conductivity on the composites thermal behavior is not obvious, and the thermal conductivity of the composite with the rectangle filler is much higher than that with rotundity filler.
2007, 24(5): 50-54.
Abstract:
A highly fire-resistant phenolic foam core sandwich reinforced with fiberglass through the thickness Z-direction was prepared, and the effects of distribution density, height, arrangement manner of load-bearing pillars, fineness of stitches and number of stitched layers on its mechanical properties were investigated. The results indicate that the mechanical properties of the Z-direction reinforced foam core sandwich are much better than those of the unstitched foam core sandwich. The arrangement manner of load-bearing pillars has little effect on its mechanical properties under the condition of uniform distribution density of load-bearing pillars. The height, distribution density of load-bearing pillars, fineness of stitches and number of stitched layers have great effects on the mechanical properties of the Z-direction reinforced foam core sandwich.
A highly fire-resistant phenolic foam core sandwich reinforced with fiberglass through the thickness Z-direction was prepared, and the effects of distribution density, height, arrangement manner of load-bearing pillars, fineness of stitches and number of stitched layers on its mechanical properties were investigated. The results indicate that the mechanical properties of the Z-direction reinforced foam core sandwich are much better than those of the unstitched foam core sandwich. The arrangement manner of load-bearing pillars has little effect on its mechanical properties under the condition of uniform distribution density of load-bearing pillars. The height, distribution density of load-bearing pillars, fineness of stitches and number of stitched layers have great effects on the mechanical properties of the Z-direction reinforced foam core sandwich.
Effects of different factors on the void defect in epoxy composite laminates in hot pressing process
2007, 24(5): 55-60.
Abstract:
Glass/epoxy fiber composite laminates were prepared by the vacuum bag and the hot pressing process. The content, shape and distribution of voids were investigated. The several factors which affect the voids formation were studied, including the temperature condition, applied pressure, environmental moisture and the laminate lay-up type. The Kardos void formation model was used to analyze the experimental results. It indicates that the main factors affecting the voids formation change with different processing methods, and the distributions of voids in unidirectional composite laminates have significant coherence; the Kardos void formation model can be used to estimate the voids formation.
Glass/epoxy fiber composite laminates were prepared by the vacuum bag and the hot pressing process. The content, shape and distribution of voids were investigated. The several factors which affect the voids formation were studied, including the temperature condition, applied pressure, environmental moisture and the laminate lay-up type. The Kardos void formation model was used to analyze the experimental results. It indicates that the main factors affecting the voids formation change with different processing methods, and the distributions of voids in unidirectional composite laminates have significant coherence; the Kardos void formation model can be used to estimate the voids formation.
2007, 24(5): 61-65.
Abstract:
A novel composite of carbon fiber (CF) reinforced hydroxyapatite (HA)/ploylactide (PLA) degradable biomaterial was developed by solvent blending. The mechanical properties and degradation properties in vitro of the composite were researched. The CF/HA/PLA composites have excellent mechanical properties. As the hydroxyapatite mass fraction increases, there are respectively peak values with flexural strength and flexural modulus, including maximums of flexural strength of 430MPa and flexural modulus of 26GPa. After degradating in vitro for 3 months, the flexural strength and flexural modulus fall 30% and 36% respectively. The SEM photos indicate that the degradation begins from the interfaces of the composite, after degradating, there are gaps at the interfaces, and the water uptake increases to 5%, but the mass loss is only 1.6%. The pH values of the PBS drop less than 0.1, which can do some favors to the recoveries of the fracture. The results show that the mechanical properties of the composite can meet the requirements of internal fracture fixation.
A novel composite of carbon fiber (CF) reinforced hydroxyapatite (HA)/ploylactide (PLA) degradable biomaterial was developed by solvent blending. The mechanical properties and degradation properties in vitro of the composite were researched. The CF/HA/PLA composites have excellent mechanical properties. As the hydroxyapatite mass fraction increases, there are respectively peak values with flexural strength and flexural modulus, including maximums of flexural strength of 430MPa and flexural modulus of 26GPa. After degradating in vitro for 3 months, the flexural strength and flexural modulus fall 30% and 36% respectively. The SEM photos indicate that the degradation begins from the interfaces of the composite, after degradating, there are gaps at the interfaces, and the water uptake increases to 5%, but the mass loss is only 1.6%. The pH values of the PBS drop less than 0.1, which can do some favors to the recoveries of the fracture. The results show that the mechanical properties of the composite can meet the requirements of internal fracture fixation.
2007, 24(5): 66-71.
Abstract:
The seven layer laminated structures which are alternatively laminated by fiber reinforced composite layers and viscoelastic damping layers were prepared for providing experimental evidence for new type damping structural theory analysis and its application of vibration and noise control, and the influence of different strain amplitudes and boundary conditions on the temperature and frequency characteristics of the structural internal friction were investigated with a dynamic mechanical analyzer (DMA Q800)for the first time. The experimental results show that the structural internal friction decreases with the increasing of structural strain amplitudes under different boundary conditions at 25℃, and the temperature corresponding to the structural internal frictions peak moves towards the low-temperature with increasing the strain amplitudes. The internal frictions are maximum and second-maximum values under the single cantilever model and the double cantilever model, respectively, and the internal friction is the lowest under the 3-point bending model with the same structural strain amplitudes.
The seven layer laminated structures which are alternatively laminated by fiber reinforced composite layers and viscoelastic damping layers were prepared for providing experimental evidence for new type damping structural theory analysis and its application of vibration and noise control, and the influence of different strain amplitudes and boundary conditions on the temperature and frequency characteristics of the structural internal friction were investigated with a dynamic mechanical analyzer (DMA Q800)for the first time. The experimental results show that the structural internal friction decreases with the increasing of structural strain amplitudes under different boundary conditions at 25℃, and the temperature corresponding to the structural internal frictions peak moves towards the low-temperature with increasing the strain amplitudes. The internal frictions are maximum and second-maximum values under the single cantilever model and the double cantilever model, respectively, and the internal friction is the lowest under the 3-point bending model with the same structural strain amplitudes.
2007, 24(5): 72-76.
Abstract:
In order to prepare carbide silicon radar-wave absorbing fibers, the continuous carbide silicon (SiC(Fe)) fibers containing Fe were prepared for the first time from a precursor polyferrocarbosilane (PFCS), which was synthesized from polydimethylsilane and ferrocene, followed by melt-spinning, curing in air, and continuous pyrolysis at 1320℃ in N2 atmosphere. The structural materials prepared with this fibers and resin show good radar-wave absorbing properties. XPS depth analysis shows that a carbon-enriched layer of about 100nm is formed on the surface of the fiber and the atomic concentration of element Fe increases a little from edge to inner. The free carbon arranges gradually in order with increasing the temperature by Raman spectra analysis. The effect of the free carbon on the properties of the continuous SiC(Fe) fibers was studied. The results show that the free carbon is of benefit to decreasing the specific resistance but increasing the complex permittivity (ε' and ε″) and relative complex permittivity (εr) of the fibers.
In order to prepare carbide silicon radar-wave absorbing fibers, the continuous carbide silicon (SiC(Fe)) fibers containing Fe were prepared for the first time from a precursor polyferrocarbosilane (PFCS), which was synthesized from polydimethylsilane and ferrocene, followed by melt-spinning, curing in air, and continuous pyrolysis at 1320℃ in N2 atmosphere. The structural materials prepared with this fibers and resin show good radar-wave absorbing properties. XPS depth analysis shows that a carbon-enriched layer of about 100nm is formed on the surface of the fiber and the atomic concentration of element Fe increases a little from edge to inner. The free carbon arranges gradually in order with increasing the temperature by Raman spectra analysis. The effect of the free carbon on the properties of the continuous SiC(Fe) fibers was studied. The results show that the free carbon is of benefit to decreasing the specific resistance but increasing the complex permittivity (ε' and ε″) and relative complex permittivity (εr) of the fibers.
2007, 24(5): 77-83.
Abstract:
SiC whiskers arrays were prepared by thermal evaporation of Si onto two carbon templates: graphite plate and PAN-carbon fiber at 1600℃ in different levels of vacuum. The XRD analyses and FESEM observations reveal that the products are 3C-SiC whisker arrays: whisker forests standing on the graphite plate and tube brush shaped whisker arrays around the carbon fibers, respectively. The dimensions of the whiskers grown on the two templates are about 100nm in diameter and 50μm in length. Due to the quantum confinement effect of nano-materials, a photoluminescence peak locating around 468nm is observed under 380nm excitation at room temperature. The multi-place selected area electron diffraction (SAED) demonstrates that the SiC whiskers are single crystals, growing in [111] direction. Based on the fact that the silicon melt and carbon templates were separated throughout the whole process, the vapor-solid reaction growth mechanism of the SiC whiskers is discussed.
SiC whiskers arrays were prepared by thermal evaporation of Si onto two carbon templates: graphite plate and PAN-carbon fiber at 1600℃ in different levels of vacuum. The XRD analyses and FESEM observations reveal that the products are 3C-SiC whisker arrays: whisker forests standing on the graphite plate and tube brush shaped whisker arrays around the carbon fibers, respectively. The dimensions of the whiskers grown on the two templates are about 100nm in diameter and 50μm in length. Due to the quantum confinement effect of nano-materials, a photoluminescence peak locating around 468nm is observed under 380nm excitation at room temperature. The multi-place selected area electron diffraction (SAED) demonstrates that the SiC whiskers are single crystals, growing in [111] direction. Based on the fact that the silicon melt and carbon templates were separated throughout the whole process, the vapor-solid reaction growth mechanism of the SiC whiskers is discussed.
2007, 24(5): 84-89.
Abstract:
The calcium phosphate porous ceramic scaffolds with high porosity for the bone tissue engineering were fabricated by the foam impregnation technology, and the composite scaffolds composed of ceramic and gelatin were gained by coating the porous ceramic samples with gelatin solution. It was found that gelatin coatings were formed on the pore walls of porous scaffold samples successfully without destroying their porous characteristic, but these coatings improved the compressive strength and compressive modulus of the samples. The scaffolds, coated with gelatin, were characterized by their nonlinear fractural behavior under compressive loading. Especially, the compressive strength value and the compressive modulus value of porous samples coated with 5% gelatin solution were improved from ~1.04MPa and ~0.105GPa to 5.17MPa and 0.325GPa respectively with the high porosity (82.8%) maintained. The results indicate that the gelatin coatings on the surface of pores reinforce the porous ceramic scaffolds effectively.
The calcium phosphate porous ceramic scaffolds with high porosity for the bone tissue engineering were fabricated by the foam impregnation technology, and the composite scaffolds composed of ceramic and gelatin were gained by coating the porous ceramic samples with gelatin solution. It was found that gelatin coatings were formed on the pore walls of porous scaffold samples successfully without destroying their porous characteristic, but these coatings improved the compressive strength and compressive modulus of the samples. The scaffolds, coated with gelatin, were characterized by their nonlinear fractural behavior under compressive loading. Especially, the compressive strength value and the compressive modulus value of porous samples coated with 5% gelatin solution were improved from ~1.04MPa and ~0.105GPa to 5.17MPa and 0.325GPa respectively with the high porosity (82.8%) maintained. The results indicate that the gelatin coatings on the surface of pores reinforce the porous ceramic scaffolds effectively.
2007, 24(5): 90-96.
Abstract:
The tests for dynamic compressive mechanical properties of two kinds of densifications 2D-C/SiC were performed by using the SHPB system. The materials are made by controlling the parameters of CVI technics. The key issue to apply high strain rates to the 2D-C/SiC is to design the geometrical size of the shaper in the SHPB system. The experimental results of both the dynamic and static loading are successful. They show that the dynamic compressive stress-strain curve is distinctly non-linear. The mechanical properties of the two densifications 2D-C/SiC are both strengthened under high strain rates, which are the higher failure strength, the lower failure strain and the larger shearing damage angle. The higher densification leads to the higher failure strength, lower failure strain and larger shearing damage angle. The dispersive dynamic experimental data are described by Weibull modules, which are 8.36 and 5.27 respectively for high and low densifications. From the SEM, a smooth ruptured surface is found for the high densification. More cracked fibers are observed under high strain rates.
The tests for dynamic compressive mechanical properties of two kinds of densifications 2D-C/SiC were performed by using the SHPB system. The materials are made by controlling the parameters of CVI technics. The key issue to apply high strain rates to the 2D-C/SiC is to design the geometrical size of the shaper in the SHPB system. The experimental results of both the dynamic and static loading are successful. They show that the dynamic compressive stress-strain curve is distinctly non-linear. The mechanical properties of the two densifications 2D-C/SiC are both strengthened under high strain rates, which are the higher failure strength, the lower failure strain and the larger shearing damage angle. The higher densification leads to the higher failure strength, lower failure strain and larger shearing damage angle. The dispersive dynamic experimental data are described by Weibull modules, which are 8.36 and 5.27 respectively for high and low densifications. From the SEM, a smooth ruptured surface is found for the high densification. More cracked fibers are observed under high strain rates.
2007, 24(5): 97-102.
Abstract:
By melting Fe-Si flux on a graphite template at 1500℃, 1600℃, 1650℃ and 1750℃ for 3 hours in Ar atmosphere, SiC grains, SiC grain and whisker complex, SiC whiskers and SiC aerial films were obtained, respectively, over the solidified flux. The XRD proves that all of them are 3C-SiC. The TEM and SAED further confirm that the SiC whiskers belong to single crystalline 3C-SiC, and the growth direction is [111]. Based on these results, the growth mechanisms for the SiC with different morphologies are proposed. At the low temperature (≤1500℃), Fe enhanced the carbon solubility in the melt, and Si reacted with saturated C by the liquid-solid (LS) mode to produce SiC grains. In the higher temperature range (1500~1750℃), the SiC whiskers were grown by the vapor-liquid- solid (VLS) mode and Fe acted as the catalyst. At the temperature of 1750℃, the SiC aerial film was formed due to also the VLS mode but in a less ordered way.
By melting Fe-Si flux on a graphite template at 1500℃, 1600℃, 1650℃ and 1750℃ for 3 hours in Ar atmosphere, SiC grains, SiC grain and whisker complex, SiC whiskers and SiC aerial films were obtained, respectively, over the solidified flux. The XRD proves that all of them are 3C-SiC. The TEM and SAED further confirm that the SiC whiskers belong to single crystalline 3C-SiC, and the growth direction is [111]. Based on these results, the growth mechanisms for the SiC with different morphologies are proposed. At the low temperature (≤1500℃), Fe enhanced the carbon solubility in the melt, and Si reacted with saturated C by the liquid-solid (LS) mode to produce SiC grains. In the higher temperature range (1500~1750℃), the SiC whiskers were grown by the vapor-liquid- solid (VLS) mode and Fe acted as the catalyst. At the temperature of 1750℃, the SiC aerial film was formed due to also the VLS mode but in a less ordered way.
2007, 24(5): 103-108.
Abstract:
The B-C coating was prepared by CVD from BCl3-C3H6-H2 precursor mixtures on the carbon fiber. The effect of the depositing temperature on the coatings character was analyzed. The microstructure of the deposit was analyzed by SEM. The element content and the type of the chemical structure of the deposited coating were studied by X-ray photoelectron spectroscopy. The inducements of the microstructure, component and various types of the chemical structure were discussed with the consideration of the chemical reaction processes. SEM results show that with the depositing temperature rising from 900℃ to 1100℃, the growth rate increases and the cross section microstructure turns from amorphous into laminated structure. XPS results show that with the increasing of temperature, the content of boron increases. The boron accommodates five different chemical structures in the BCx coatings. The content of boron within these different chemical structures is also influenced by the depositing temperature.
The B-C coating was prepared by CVD from BCl3-C3H6-H2 precursor mixtures on the carbon fiber. The effect of the depositing temperature on the coatings character was analyzed. The microstructure of the deposit was analyzed by SEM. The element content and the type of the chemical structure of the deposited coating were studied by X-ray photoelectron spectroscopy. The inducements of the microstructure, component and various types of the chemical structure were discussed with the consideration of the chemical reaction processes. SEM results show that with the depositing temperature rising from 900℃ to 1100℃, the growth rate increases and the cross section microstructure turns from amorphous into laminated structure. XPS results show that with the increasing of temperature, the content of boron increases. The boron accommodates five different chemical structures in the BCx coatings. The content of boron within these different chemical structures is also influenced by the depositing temperature.
2007, 24(5): 109-112.
Abstract:
Cr-Al-Si coating was prepared on the surface of SiC coated C/C composites by the plasma spraying method. The phase composition and microstructure of Cr-Al-Si coating were studied by XRD and SEM. The isothermal oxidation test at 1500℃ was carried out in air. The XRD results show that the outer Cr-Al-Si alloy coating consists of Al3.21Si0.47, Cr3Si and Al2O3. The thickness of the coating was about 120μm, and no penetrable crack was observed in the cross-sectional SEM morphologies of the coating. The oxidation resistance of the single porous β-SiC coating is poor, which can only protect C/C composites from oxidation for 10 h with a mass loss of 10%. After adding the Cr-Al-Si alloy outer coating, the double-layer Cr-Al-Si and SiC show a better oxidation protective ability and 5.3% mass loss of the coated sample after oxidation for 61h.
Cr-Al-Si coating was prepared on the surface of SiC coated C/C composites by the plasma spraying method. The phase composition and microstructure of Cr-Al-Si coating were studied by XRD and SEM. The isothermal oxidation test at 1500℃ was carried out in air. The XRD results show that the outer Cr-Al-Si alloy coating consists of Al3.21Si0.47, Cr3Si and Al2O3. The thickness of the coating was about 120μm, and no penetrable crack was observed in the cross-sectional SEM morphologies of the coating. The oxidation resistance of the single porous β-SiC coating is poor, which can only protect C/C composites from oxidation for 10 h with a mass loss of 10%. After adding the Cr-Al-Si alloy outer coating, the double-layer Cr-Al-Si and SiC show a better oxidation protective ability and 5.3% mass loss of the coated sample after oxidation for 61h.
2007, 24(5): 113-118.
Abstract:
An SiC-Glass multi-layer coating was fabricated on the carbon/carbon (C/C) composites by using the pack cementation technique and the precoating-sintering process. The as-prepared multi-layer was characterized by XRD and SEM analyses. The oxidation kinetics of the coated C/C samples was also investigated at different temperatures. The results indicate that the multi-coating is composed of two layers. The inner layer consist of β-SiC phase and a small quantity of silicon phase. The outer layer is a borosilicate glass layer modified by MoSi2 particles. Additionally, the multi-coating has good interface bonding between the two layers. The experimental data of the oxidation tests show that the SiC-Glass coating exhibits an excellent oxidation resistance in air in the temperature range from 1300℃ to 1600℃, and the oxidation activation energy of the coated C/C is 118.1 kJ/mol. After oxidation at 1600℃ in air for 65 hours, the mass loss of the SiC-Glass coated sample is only 1.02%.
An SiC-Glass multi-layer coating was fabricated on the carbon/carbon (C/C) composites by using the pack cementation technique and the precoating-sintering process. The as-prepared multi-layer was characterized by XRD and SEM analyses. The oxidation kinetics of the coated C/C samples was also investigated at different temperatures. The results indicate that the multi-coating is composed of two layers. The inner layer consist of β-SiC phase and a small quantity of silicon phase. The outer layer is a borosilicate glass layer modified by MoSi2 particles. Additionally, the multi-coating has good interface bonding between the two layers. The experimental data of the oxidation tests show that the SiC-Glass coating exhibits an excellent oxidation resistance in air in the temperature range from 1300℃ to 1600℃, and the oxidation activation energy of the coated C/C is 118.1 kJ/mol. After oxidation at 1600℃ in air for 65 hours, the mass loss of the SiC-Glass coated sample is only 1.02%.
2007, 24(5): 119-124.
Abstract:
A new carbon fiber precursor was prepared from liquefied wood in phenol, which was used to synthesize the spinning solution by melt-spinning. The effect factors of spinning solution on the properties of carbon fiber precursors were studied. The results show that the tensile strength/modulus and the elongation at break of carbon fiber precursors increase obviously with increasing the phenol/wood ratio in the wood liquefaction. Moreover, the tensile strength increases nearly 9 times when the phenol/wood ratio increases from 3 to 4. The mechanical properties of carbon fiber precursors drop with increasing the synthetics content. The peak decreasing amplitude of the tensile strength and modulus of precursors occurs at adding 6% synthetics content, but the elongation at break reaches the maximum at 4% synthetics content. The tensile strength and modulus have no obvious increase with increasing the synthesis temperature, while the elongation at break decreases and shows obvious decreasing amplitude from 110℃ to 115℃. The mechanical properties of precursors are improved with increasing the temperature rise time and then drop, and carbon fiber precursors show optimum mechanical properties at the temperature rise time of 40min.
A new carbon fiber precursor was prepared from liquefied wood in phenol, which was used to synthesize the spinning solution by melt-spinning. The effect factors of spinning solution on the properties of carbon fiber precursors were studied. The results show that the tensile strength/modulus and the elongation at break of carbon fiber precursors increase obviously with increasing the phenol/wood ratio in the wood liquefaction. Moreover, the tensile strength increases nearly 9 times when the phenol/wood ratio increases from 3 to 4. The mechanical properties of carbon fiber precursors drop with increasing the synthetics content. The peak decreasing amplitude of the tensile strength and modulus of precursors occurs at adding 6% synthetics content, but the elongation at break reaches the maximum at 4% synthetics content. The tensile strength and modulus have no obvious increase with increasing the synthesis temperature, while the elongation at break decreases and shows obvious decreasing amplitude from 110℃ to 115℃. The mechanical properties of precursors are improved with increasing the temperature rise time and then drop, and carbon fiber precursors show optimum mechanical properties at the temperature rise time of 40min.
2007, 24(5): 125-129.
Abstract:
A multiple scale viscoelastic model for the 3D woven composites was suggested. Firstly, the repeated unit cells, representing periodic distributions of fibers in a yarn and periodic weave architecture in composite, were constructed. They are named micro scale cell and meso scale cell respectively. Elastic constants of the yarn were obtained by analysis of the micro scale cell model, and then they were used in the meso scale cell model for calculating those of 3D woven composites. The periodic boundary conditions were applied to the two scales cell models; therefore both displacements and stresses on the two cells boundaries satisfy continuum conditions. Then two viscoelastic models for the resin and fiber yarn respectively were suggested. The viscidity parameters of the resin model were determined by creep experiment for the pure resin material, and then they were adopted in the micro scale cell to rectify the viscoelastic model of the yarn. Finally, the two viscoelastic models were adopted in the meso scale cell to simulate the creep test of 3D woven composites numerically. The predictions of both elastic constants and creep curves agree well with experimental data.
A multiple scale viscoelastic model for the 3D woven composites was suggested. Firstly, the repeated unit cells, representing periodic distributions of fibers in a yarn and periodic weave architecture in composite, were constructed. They are named micro scale cell and meso scale cell respectively. Elastic constants of the yarn were obtained by analysis of the micro scale cell model, and then they were used in the meso scale cell model for calculating those of 3D woven composites. The periodic boundary conditions were applied to the two scales cell models; therefore both displacements and stresses on the two cells boundaries satisfy continuum conditions. Then two viscoelastic models for the resin and fiber yarn respectively were suggested. The viscidity parameters of the resin model were determined by creep experiment for the pure resin material, and then they were adopted in the micro scale cell to rectify the viscoelastic model of the yarn. Finally, the two viscoelastic models were adopted in the meso scale cell to simulate the creep test of 3D woven composites numerically. The predictions of both elastic constants and creep curves agree well with experimental data.
2007, 24(5): 130-135.
Abstract:
The numerical simulation was adopted as a novel method to analyze the process and the effect of electrochemical modification of the 3D carbon fiber fabrics. A mathematical model of electrochemical modification of 3D carbon fiber fabrics was constructed on the principle of the macroscopic model. The mathematical model was used to simulate the process of fabric modification. The solution describes the treatment conditions of every part in the fabrics clearly and predicts the effect of the whole fabrics visually. The results indicate that the non-uniform modification existed in the fabrics, and the reason for this is the non-uniform distribution of the electrolyte in the fabrics. An intermittent electrochemical treatment method is raised to improve the effect of electrochemical modification of the whole 3D carbon fiber fabrics.
The numerical simulation was adopted as a novel method to analyze the process and the effect of electrochemical modification of the 3D carbon fiber fabrics. A mathematical model of electrochemical modification of 3D carbon fiber fabrics was constructed on the principle of the macroscopic model. The mathematical model was used to simulate the process of fabric modification. The solution describes the treatment conditions of every part in the fabrics clearly and predicts the effect of the whole fabrics visually. The results indicate that the non-uniform modification existed in the fabrics, and the reason for this is the non-uniform distribution of the electrolyte in the fabrics. An intermittent electrochemical treatment method is raised to improve the effect of electrochemical modification of the whole 3D carbon fiber fabrics.
2007, 24(5): 136-141.
Abstract:
There are complex microstructures of functionally graded materials, and their internal structures are more complex than those of homogeneous materials. Therefore, the analytic solution of the functionally graded structure is difficult to obtain. A new microelement method for the analysis of functionally graded structures was suggested to establish the quantitative relation between the macro-character and microstructures of functionally graded materials, and the mechanism, that different combination and variation of materials have different macro-characters, can be found. The dynamic analyses of functionally graded structures with gap, impurities and component mutation are performed by the microelement method, and the three-dimensional values of natural frequency and the three-dimensional distributions of the mode shape are given in this paper, and there are great influences of the gaps, impurities and component mutation on the macro dynamic characters of the functionally graded structures.
There are complex microstructures of functionally graded materials, and their internal structures are more complex than those of homogeneous materials. Therefore, the analytic solution of the functionally graded structure is difficult to obtain. A new microelement method for the analysis of functionally graded structures was suggested to establish the quantitative relation between the macro-character and microstructures of functionally graded materials, and the mechanism, that different combination and variation of materials have different macro-characters, can be found. The dynamic analyses of functionally graded structures with gap, impurities and component mutation are performed by the microelement method, and the three-dimensional values of natural frequency and the three-dimensional distributions of the mode shape are given in this paper, and there are great influences of the gaps, impurities and component mutation on the macro dynamic characters of the functionally graded structures.
2007, 24(5): 142-148.
Abstract:
An experimental program which includes lots of unidirectional laminas is conducted using T300/BMP-316 material for researching the static and fatigue behavior of the unidirectional ply to set up the expressions of the residual strength degradation and the residual stiffness degradation of a unidirectional ply in the longitudinal, transverse and in-plane shear directions. The factor of nonlinear shear stress-strain behavior is acquired. The expression of shear stiffness in the 1-2 planes during fatigue loading is given. Dye-enhanced X-radiography was used to nondestructively check the specimens. The damage mechanisms are also analyzed. The results obtained from the experiments show that considering the nonlinear shear stress-strain behavior of a unidirectional ply is important in the analysis of stresses for composite laminates.
An experimental program which includes lots of unidirectional laminas is conducted using T300/BMP-316 material for researching the static and fatigue behavior of the unidirectional ply to set up the expressions of the residual strength degradation and the residual stiffness degradation of a unidirectional ply in the longitudinal, transverse and in-plane shear directions. The factor of nonlinear shear stress-strain behavior is acquired. The expression of shear stiffness in the 1-2 planes during fatigue loading is given. Dye-enhanced X-radiography was used to nondestructively check the specimens. The damage mechanisms are also analyzed. The results obtained from the experiments show that considering the nonlinear shear stress-strain behavior of a unidirectional ply is important in the analysis of stresses for composite laminates.
2007, 24(5): 149-153.
Abstract:
The reliability-based optimization (RBO) of composite structures subject to buckling constraint was investigated. Considering the uncertainties of material properties and applied loads, the buckling reliability of the structure was evaluated through the combination of Response Surface Method (RSM) and Finite Element Method (FEM). The RBO of composite structures subject to buckling constraint was conducted in terms of the ply number and orientation angles, using the commercial code iSIGHT combined with the reliability analysis program. The numerical examples of the composite laminate and the cylinder validate the present RBO method, which is useful for the optimization of composite structures subject to buckling constraint in engineering.
The reliability-based optimization (RBO) of composite structures subject to buckling constraint was investigated. Considering the uncertainties of material properties and applied loads, the buckling reliability of the structure was evaluated through the combination of Response Surface Method (RSM) and Finite Element Method (FEM). The RBO of composite structures subject to buckling constraint was conducted in terms of the ply number and orientation angles, using the commercial code iSIGHT combined with the reliability analysis program. The numerical examples of the composite laminate and the cylinder validate the present RBO method, which is useful for the optimization of composite structures subject to buckling constraint in engineering.
