2008 Vol. 25, No. 3
2008, 25(3): 1-7.
Abstract:
Poly (phthalazinone ether sulfone ketone) (PPESK) is a novel high performance thermoplastic material with out standing high temperature resistance and excellent mechanical properties，and therefore it is a very ideal candidate matrix for advanced composites. However，it s high melting viscosity of PPESK makes it difficult to melt-ingly process. In this paper，two well-known high performance thermoplastics，polyetherimide (PEI) and poly-ethersulfone (PES) were introduced to PPESK in order to reduce the melting viscosity of PPESK and improve the properties of composites. The effect of addition of PEI and PES on the resultant composites was studied. A series of unidirectional composites were made with PPESK and its PEI and PES blends as matrix and continuous carbon fiber (T700) as reinforcement. The solution prepregging method and hot-press molding method were used in preparation of the composites. The viscosities of polymer blends solutions were tested. The effects of the polymer blends matrix on the mechanical properties and fracture mode were studied by three points bending，interlaminar shearing，porosity and SEM test. The results show that the mechanical properties increase and the porosity decreases after blending PEI or PES in matrix. Addition of PEI and PES to PPESK results in an obvious transition of fracture mode.
Poly (phthalazinone ether sulfone ketone) (PPESK) is a novel high performance thermoplastic material with out standing high temperature resistance and excellent mechanical properties，and therefore it is a very ideal candidate matrix for advanced composites. However，it s high melting viscosity of PPESK makes it difficult to melt-ingly process. In this paper，two well-known high performance thermoplastics，polyetherimide (PEI) and poly-ethersulfone (PES) were introduced to PPESK in order to reduce the melting viscosity of PPESK and improve the properties of composites. The effect of addition of PEI and PES on the resultant composites was studied. A series of unidirectional composites were made with PPESK and its PEI and PES blends as matrix and continuous carbon fiber (T700) as reinforcement. The solution prepregging method and hot-press molding method were used in preparation of the composites. The viscosities of polymer blends solutions were tested. The effects of the polymer blends matrix on the mechanical properties and fracture mode were studied by three points bending，interlaminar shearing，porosity and SEM test. The results show that the mechanical properties increase and the porosity decreases after blending PEI or PES in matrix. Addition of PEI and PES to PPESK results in an obvious transition of fracture mode.
2008, 25(3): 8-11.
Abstract:
The in-situ polymerization method was employed to prepare nano-TiO2/polylactide (PLA) composites with different contents of TiO2. Scanning electron microscope (SEM) was used to study the dispersion of surfaced-modified nano-TiO2 in the composites and the results show that nano-TiO2 dispersed in the PLA evenly when the content of TiO2 is low ( less than 3wt%). The differential scanning calorimeter (DSC)，thermogravimetry analysis (TGA) and Erichsen test were used to study the thermal and mechanical properties of the composites. The results show that both the thermal and mechanical properties are markedly improved when the content of TiO2 is 3wt%. It smaximum temperature of heat decomposition T max and the glass transition temperature T g increase by 25.3℃and 4.9℃，respectively，and simultaneously，its tensile strength，elongation at break and Young‘s modulus increase by 83.6%、6.73% and 129.4%.
The in-situ polymerization method was employed to prepare nano-TiO2/polylactide (PLA) composites with different contents of TiO2. Scanning electron microscope (SEM) was used to study the dispersion of surfaced-modified nano-TiO2 in the composites and the results show that nano-TiO2 dispersed in the PLA evenly when the content of TiO2 is low ( less than 3wt%). The differential scanning calorimeter (DSC)，thermogravimetry analysis (TGA) and Erichsen test were used to study the thermal and mechanical properties of the composites. The results show that both the thermal and mechanical properties are markedly improved when the content of TiO2 is 3wt%. It smaximum temperature of heat decomposition T max and the glass transition temperature T g increase by 25.3℃and 4.9℃，respectively，and simultaneously，its tensile strength，elongation at break and Young‘s modulus increase by 83.6%、6.73% and 129.4%.
2008, 25(3): 12-19.
Abstract:
The collagen was crosslinked by glutaraldehyde (GTA). The influences of the GTA content，collagen concent ration and glycerol content on the swelling ratio of the modified collagen were investigated. Using the modified collagen as the matrix and sisal fiber as the reinforcement，the sisal fiber/collagen composite was prepared. The morphologies of the composites were characterized by using scanning elect ron microscopy (SEM). The influences of the sisal fiber treatment，fiber content and fiber length on the mechanical properties of the composites were discussed. It is found that the alkali treatment improves the surface structure of the sisal fiber and increases the mechanical properties of the composite. The mechanical properties were improved dramatically when the sisal fiber mass fraction is 15 % and the fiber length is 7～8 mm. The composites can be used as packaging materials.
The collagen was crosslinked by glutaraldehyde (GTA). The influences of the GTA content，collagen concent ration and glycerol content on the swelling ratio of the modified collagen were investigated. Using the modified collagen as the matrix and sisal fiber as the reinforcement，the sisal fiber/collagen composite was prepared. The morphologies of the composites were characterized by using scanning elect ron microscopy (SEM). The influences of the sisal fiber treatment，fiber content and fiber length on the mechanical properties of the composites were discussed. It is found that the alkali treatment improves the surface structure of the sisal fiber and increases the mechanical properties of the composite. The mechanical properties were improved dramatically when the sisal fiber mass fraction is 15 % and the fiber length is 7～8 mm. The composites can be used as packaging materials.
Experimental study on low-velocity impact performance of carbon fiber reinforced composite laminates
2008, 25(3): 20-24.
Abstract:
The drop-weight impact tests and compression after impact tests were conducted on three kinds of carbon fiber reinforced composite laminates (T300/NY9200Z，T300/QY8911 and T700S/5228). The low-velocity impact performances (damage resistance and damage tolerance) of these carbon fiber reinforced composites were analyzed through d-e curves，S-d curves，and ε-d curves. The detailed damage state around the transformation point was obtained by means of the thermal deply technique and the damage mechanism was discussed. The test results in-dicate that there are homologous knee points in these curves and these points are also the transformation points at which the damage mechanisms change significantly. The dominant damage is delamination and matrix cracking be-fore the point，and it becomes fiber breakage after the point .
The drop-weight impact tests and compression after impact tests were conducted on three kinds of carbon fiber reinforced composite laminates (T300/NY9200Z，T300/QY8911 and T700S/5228). The low-velocity impact performances (damage resistance and damage tolerance) of these carbon fiber reinforced composites were analyzed through d-e curves，S-d curves，and ε-d curves. The detailed damage state around the transformation point was obtained by means of the thermal deply technique and the damage mechanism was discussed. The test results in-dicate that there are homologous knee points in these curves and these points are also the transformation points at which the damage mechanisms change significantly. The dominant damage is delamination and matrix cracking be-fore the point，and it becomes fiber breakage after the point .
2008, 25(3): 25-30.
Abstract:
Nylon 12-coated aluminum composite powders with different aluminum contents were prepared. The morphology and the thermal properties of the composite powder were characterized by SEM，EDX，DSC and TG. Specimens were fabricated by selective laser sintering (SLS)，then the effects of the aluminum content on dimensional accuracy and mechanical properties of the sintered part were studied. The results show that there is strong interfacial adhesion between nylon and aluminum powder，the nylon is melted during the sintering process and aluminum powders are dispersed uniformly in the nylon matrix. As the aluminum content increases，the flexural strength and modulus of the sintered part increase remarkably，but the impact strength decreases gradually. With 50 wt% aluminum content，the flexural strength and modulus of the sintered part are improved by 62. 1% and 122. 3%，respectively，compared to the sintered part of nylon powder. The increasing of aluminum content would effectively restrain the shrinkage of the nylon matrix，and enhance the dimensional accuracy of the sintered part .
Nylon 12-coated aluminum composite powders with different aluminum contents were prepared. The morphology and the thermal properties of the composite powder were characterized by SEM，EDX，DSC and TG. Specimens were fabricated by selective laser sintering (SLS)，then the effects of the aluminum content on dimensional accuracy and mechanical properties of the sintered part were studied. The results show that there is strong interfacial adhesion between nylon and aluminum powder，the nylon is melted during the sintering process and aluminum powders are dispersed uniformly in the nylon matrix. As the aluminum content increases，the flexural strength and modulus of the sintered part increase remarkably，but the impact strength decreases gradually. With 50 wt% aluminum content，the flexural strength and modulus of the sintered part are improved by 62. 1% and 122. 3%，respectively，compared to the sintered part of nylon powder. The increasing of aluminum content would effectively restrain the shrinkage of the nylon matrix，and enhance the dimensional accuracy of the sintered part .
2008, 25(3): 31-38.
Abstract:
MoS2 reinforced aromatic and partially alipahatic polyetherimide (PEI) films were prepared in different solvents via the two-step method，end capped by acetic anhydride and trifluoroacetic anhydride (TFAA). The thermal imidization degrees were measured by FT-IR spectrum，the thermal transitions were characterized by SDT Q600，the tribological performances were measured by M2200 tribo-tester，and the effects of molecular flexibility，end cap，proportion of MoS2 were investigated. The effects of load and proportion of MoS2 on μ (average value of μ during the stable friction period) were also investigated. Based on the SEM morphologies of the worn surface，the wear mechanism was determined. The result indicates that the Tg of partially aliphatic PEI greatly decreases without obvious degeneration of PEIs‘thermal stability. μ-t curve of PEI shows it s tendency：firstly fluctuates for a short period followed by a friction stable period，and lastly increases scalariformly until lubricating failure. Flexible molecular structure，end cap of TFAA and suitable proportion of MoS2 at tribute to the better performances of the films. The 70 wt% MoS2/PEI-2 film has the values ofμas low as 0. 027，and μ of PEI composite films varies with load and proportion of MoS2.
MoS2 reinforced aromatic and partially alipahatic polyetherimide (PEI) films were prepared in different solvents via the two-step method，end capped by acetic anhydride and trifluoroacetic anhydride (TFAA). The thermal imidization degrees were measured by FT-IR spectrum，the thermal transitions were characterized by SDT Q600，the tribological performances were measured by M2200 tribo-tester，and the effects of molecular flexibility，end cap，proportion of MoS2 were investigated. The effects of load and proportion of MoS2 on μ (average value of μ during the stable friction period) were also investigated. Based on the SEM morphologies of the worn surface，the wear mechanism was determined. The result indicates that the Tg of partially aliphatic PEI greatly decreases without obvious degeneration of PEIs‘thermal stability. μ-t curve of PEI shows it s tendency：firstly fluctuates for a short period followed by a friction stable period，and lastly increases scalariformly until lubricating failure. Flexible molecular structure，end cap of TFAA and suitable proportion of MoS2 at tribute to the better performances of the films. The 70 wt% MoS2/PEI-2 film has the values ofμas low as 0. 027，and μ of PEI composite films varies with load and proportion of MoS2.
2008, 25(3): 39-44.
Abstract:
The feasibility of measuring the electrical resistance by using the four electrode method based on the embedded loop electrode was verified in order to explore the piezoresistivity of cement-based materials with acetylene carbon black. The variation regularity of electrical resistivity of cement-based materials with acetylene carbon black was studied under single compressive loading. The reproducibility of piezoresistivity of these cement-based materials within the elastic regime was also investigated. The influence of measurement current and eccentric loading on the piezoresistivity of cement-based materials with acetylene carbon black was discussed. The research results show that the errors of electrical resistance measured by using the four elect rode method based on the embedded loop elect rode are lower than 10 %，which indicates that the four electrode method based on the embedded loop electrode is feasible for measuring electrical resistance. The fractional change in electrical resistivity of cement-based materials with 15 vol% acetylene carbon black goes up to 55 % and 35 % under single compressive loading and within the elastic regime，respectively. And the piezoresistivity is almost free from the influence of measurement current and eccentric loading. These findings suggest that the acetylene carbon black is an effective component for manufacturing piezoresistive cement-based materials with high sensitivity.
The feasibility of measuring the electrical resistance by using the four electrode method based on the embedded loop electrode was verified in order to explore the piezoresistivity of cement-based materials with acetylene carbon black. The variation regularity of electrical resistivity of cement-based materials with acetylene carbon black was studied under single compressive loading. The reproducibility of piezoresistivity of these cement-based materials within the elastic regime was also investigated. The influence of measurement current and eccentric loading on the piezoresistivity of cement-based materials with acetylene carbon black was discussed. The research results show that the errors of electrical resistance measured by using the four elect rode method based on the embedded loop elect rode are lower than 10 %，which indicates that the four electrode method based on the embedded loop electrode is feasible for measuring electrical resistance. The fractional change in electrical resistivity of cement-based materials with 15 vol% acetylene carbon black goes up to 55 % and 35 % under single compressive loading and within the elastic regime，respectively. And the piezoresistivity is almost free from the influence of measurement current and eccentric loading. These findings suggest that the acetylene carbon black is an effective component for manufacturing piezoresistive cement-based materials with high sensitivity.
2008, 25(3): 45-50.
Abstract:
The microstructure of an epoxy-bonded Terfenol-D 1-3 type composite with 53 % particle volume fraction was analyzed. To evaluate static and dynamic properties of the composite and monolithic Tefernol-D,such parameters as static and dynamic magnetostriction,dynamic relative permeability,the dependence of electrical impedance on frequency,two Young's moduli ( E33Hand E33B),magnetomechanical coupling coefficient,and characteristic frequency,were tested. The experimental results indicate that both magnetostrictive properties and Young's moduli of the composite are less than those of those of monolithic Terfenol -D,but its characteristic frequency is much higher than that of the later,which suggestes that the composite can provide superior high frequency performance compared with monolithic Terfenol-D.
The microstructure of an epoxy-bonded Terfenol-D 1-3 type composite with 53 % particle volume fraction was analyzed. To evaluate static and dynamic properties of the composite and monolithic Tefernol-D,such parameters as static and dynamic magnetostriction,dynamic relative permeability,the dependence of electrical impedance on frequency,two Young's moduli ( E33Hand E33B),magnetomechanical coupling coefficient,and characteristic frequency,were tested. The experimental results indicate that both magnetostrictive properties and Young's moduli of the composite are less than those of those of monolithic Terfenol -D,but its characteristic frequency is much higher than that of the later,which suggestes that the composite can provide superior high frequency performance compared with monolithic Terfenol-D.
2008, 25(3): 51-56.
Abstract:
0-3 PMN/epoxy composites were prepared by the casting method. The effects of piezoelectric ceramic lead magnesium niobate-lead zirconate-lead titanate (PMN) on curing of epoxy resin were studied by DSC analysis.The researches on dielectric properties show that the dielectric constant and dielectric loss increase nonlinearly with PMN content increasing. The dielectric constant decreases sharply with frequency increasing when the frequency is lower than 105 Hz,which is at tributed to the interfacial polarization in the composite. At high frequency,the dielectric constant changes slightly,which means that the PMN/EP composites have a good high frequency stability. In the testing frequency range,the dielectric loss decreases slightly with the frequency increasing,but the extent is very narrow. DMA analyses indicate that the storage modulus,loss modulus,the peak of the damping loss factor curve and the damping temperature range of composites are all affected by the content of PMN. When the PMN content was 87. 24 wt%,a new peak in the damping loss factor curve at about 90℃ was observed,and the temperature of the new peak did not shift with the testing frequency change. The dielectric loss of composite may contribute to ap-pearance of the new damping loss factor peak.
0-3 PMN/epoxy composites were prepared by the casting method. The effects of piezoelectric ceramic lead magnesium niobate-lead zirconate-lead titanate (PMN) on curing of epoxy resin were studied by DSC analysis.The researches on dielectric properties show that the dielectric constant and dielectric loss increase nonlinearly with PMN content increasing. The dielectric constant decreases sharply with frequency increasing when the frequency is lower than 105 Hz,which is at tributed to the interfacial polarization in the composite. At high frequency,the dielectric constant changes slightly,which means that the PMN/EP composites have a good high frequency stability. In the testing frequency range,the dielectric loss decreases slightly with the frequency increasing,but the extent is very narrow. DMA analyses indicate that the storage modulus,loss modulus,the peak of the damping loss factor curve and the damping temperature range of composites are all affected by the content of PMN. When the PMN content was 87. 24 wt%,a new peak in the damping loss factor curve at about 90℃ was observed,and the temperature of the new peak did not shift with the testing frequency change. The dielectric loss of composite may contribute to ap-pearance of the new damping loss factor peak.
2008, 25(3): 57-62.
Abstract:
In order to solve the security problems of the lithium-ion batteries,a nano-SiO2/poly(vinylidene fluoride-co-hexafluoro-propylene) (PVDF-HFP) gel polymer electrolyte with high ionic conductivity was prepared,using nano-SiO2 as an additive,LiClO4 as the salt,and propylene carbonate (PC) and dimethyl carbonate (DMC) as the plasticizer. The structure and microstructure were characterized using XRD,the ionic conductivity was determined by AC impedance method,the electrochemical stability was measured by linear scan voltammetry experiment,and the charge-discharge of the polymer lithium batteries based on this composite gel polymer electrolyte was investigated. The results indicate that the highest conductivity of the gel polymer electrolyte is 7. 56 ×10-3 S/ cm at 20℃,and the electrochemical character of the gel polymer electrolyte is stable under 4. 6 V,and the polymer lithium batteries have excellent electrochemical performances. The SiO2/LiClO4/PVDF-HFP composite gel polymer electrolyte shows the potential application in lithium ion batteries.
In order to solve the security problems of the lithium-ion batteries,a nano-SiO2/poly(vinylidene fluoride-co-hexafluoro-propylene) (PVDF-HFP) gel polymer electrolyte with high ionic conductivity was prepared,using nano-SiO2 as an additive,LiClO4 as the salt,and propylene carbonate (PC) and dimethyl carbonate (DMC) as the plasticizer. The structure and microstructure were characterized using XRD,the ionic conductivity was determined by AC impedance method,the electrochemical stability was measured by linear scan voltammetry experiment,and the charge-discharge of the polymer lithium batteries based on this composite gel polymer electrolyte was investigated. The results indicate that the highest conductivity of the gel polymer electrolyte is 7. 56 ×10-3 S/ cm at 20℃,and the electrochemical character of the gel polymer electrolyte is stable under 4. 6 V,and the polymer lithium batteries have excellent electrochemical performances. The SiO2/LiClO4/PVDF-HFP composite gel polymer electrolyte shows the potential application in lithium ion batteries.
2008, 25(3): 63-67.
Abstract:
The surface modification of nano-hydroxyapatite with stearic acid was studied. The nano-hydroxyapatite/polycarbonate composite biomaterial was prepared. The samples were characterized by TEM , FTIR , XRD and SEM techniques. The results show that the stearic acid bound on the surface of nano-hydroxyapatite particles by forming an organic coating layer . The interface compatibility of polycarbonate and hydroxyapatite was improved through their interface integration by the hydrogen bond. The mechanical properties of the composite are found to match well with those of a natural bone.
The surface modification of nano-hydroxyapatite with stearic acid was studied. The nano-hydroxyapatite/polycarbonate composite biomaterial was prepared. The samples were characterized by TEM , FTIR , XRD and SEM techniques. The results show that the stearic acid bound on the surface of nano-hydroxyapatite particles by forming an organic coating layer . The interface compatibility of polycarbonate and hydroxyapatite was improved through their interface integration by the hydrogen bond. The mechanical properties of the composite are found to match well with those of a natural bone.
2008, 25(3): 68-72.
Abstract:
The in vitro bioactivity of nano-hydroxyapatite/polycarbonate (n-HA/PC) composite was studied in SBF (simulated body fluid) . The sample surface was characterized by FTIR , XRD and SEM. The results show that n-HA/ PC composite is chemically active in SBF , and the Ca and P ions of carbonated-apatite (CHA) deposit on the surface during soaking in SBF. The Ca-P precipitate on the surface of n-HA/PC composite was CHA. The layer of deposited CHA increases with time , and the morphology of CHA crystal gradually forms. By MTT and SEM analyses , the results show that n-HA/PC composite is not cell toxic and has a good biocompatibility to MG-63 cells.Therefore , this kind of composite could be one of the best potential bioactive materials for the load bearing bone substitute.
The in vitro bioactivity of nano-hydroxyapatite/polycarbonate (n-HA/PC) composite was studied in SBF (simulated body fluid) . The sample surface was characterized by FTIR , XRD and SEM. The results show that n-HA/ PC composite is chemically active in SBF , and the Ca and P ions of carbonated-apatite (CHA) deposit on the surface during soaking in SBF. The Ca-P precipitate on the surface of n-HA/PC composite was CHA. The layer of deposited CHA increases with time , and the morphology of CHA crystal gradually forms. By MTT and SEM analyses , the results show that n-HA/PC composite is not cell toxic and has a good biocompatibility to MG-63 cells.Therefore , this kind of composite could be one of the best potential bioactive materials for the load bearing bone substitute.
2008, 25(3): 73-77.
Abstract:
The macroporous calcium phosphate cement (CPC) scaffold was fabricated by dissolving the rod-shaped
monosodium glutamate crystals. Gelatin,PLA,PCL,PLGA and PHBV solutions were infiltrated into the pores of a CPC scaffold to improve its mechanical strength. The results indicate that the contact angle of water on the polymers varies from each other in the sequence of PHBV > PCL > PLA > PL GA > Gelatin , and the compressive strength of the composite scaffolds increases with the increase of the hydrophilicity of the polymers. The CPC scaffold is markedly reinforced by the polymers infiltration except for PHBV,and the strength of Gelatin/CPC scaffold reaches 2. 25 MPa,which is 25 times that of CPC scaffold. The reinforced CPC scaffolds are promising for being used in the bone tissue engineering.
The macroporous calcium phosphate cement (CPC) scaffold was fabricated by dissolving the rod-shaped
monosodium glutamate crystals. Gelatin,PLA,PCL,PLGA and PHBV solutions were infiltrated into the pores of a CPC scaffold to improve its mechanical strength. The results indicate that the contact angle of water on the polymers varies from each other in the sequence of PHBV > PCL > PLA > PL GA > Gelatin , and the compressive strength of the composite scaffolds increases with the increase of the hydrophilicity of the polymers. The CPC scaffold is markedly reinforced by the polymers infiltration except for PHBV,and the strength of Gelatin/CPC scaffold reaches 2. 25 MPa,which is 25 times that of CPC scaffold. The reinforced CPC scaffolds are promising for being used in the bone tissue engineering.
2008, 25(3): 78-83.
Abstract:
Based on Biot principle and Darcy's law , a two dimensional flow/compaction model and the finite element program was developed. The laminate deformation and pressure dist ribution can be predicted in the L-shaped laminates. Through comparison between the numerical and experimental data for thickness reduction of AS4 carbon fiber/epoxy 350126 laminate , the reliability of the numerical model and finite element program was validated. The laminate thickness variation was analyzed for 90° lay-up S-2 glass fiber/epoxy 648 laminates with the convex tool . It is found that the shear modulus has a significant effect on the laminate deformation at the corner and in the transition area between the flat and the corner sections. The length of flat part has a more obvious effect on the corner part deformation while relatively small influence on the flat section. The 90°lay-up S-2 glass fiber/epoxy 648 L-shaped laminates were fabricated with the autoclave process. The experimental data show that the cured laminate thickness is uneven with thicker corner and the flat part length affects the corner part thickness variation , which is consistent with the numerical results.
Based on Biot principle and Darcy's law , a two dimensional flow/compaction model and the finite element program was developed. The laminate deformation and pressure dist ribution can be predicted in the L-shaped laminates. Through comparison between the numerical and experimental data for thickness reduction of AS4 carbon fiber/epoxy 350126 laminate , the reliability of the numerical model and finite element program was validated. The laminate thickness variation was analyzed for 90° lay-up S-2 glass fiber/epoxy 648 laminates with the convex tool . It is found that the shear modulus has a significant effect on the laminate deformation at the corner and in the transition area between the flat and the corner sections. The length of flat part has a more obvious effect on the corner part deformation while relatively small influence on the flat section. The 90°lay-up S-2 glass fiber/epoxy 648 L-shaped laminates were fabricated with the autoclave process. The experimental data show that the cured laminate thickness is uneven with thicker corner and the flat part length affects the corner part thickness variation , which is consistent with the numerical results.
2008, 25(3): 84-92.
Abstract:
In order to develop an epoxy matrix resin film used in the low-cost technique of RFI , a new resin film was synthesized with epoxy of E51 , high temperature latent curing agent BF3-400 and ethylene glycol , through optimizing the ingredient s by the orthogonal design method and controlling the primary reaction degree. The results of the research on its chemorheology show that the least viscosity of this resin film reaches 360 mPa· s , the time of low viscosity below 1000 mPa· s is up to 32 min , and the gel time is 48 min at 130℃ work temperature. The resin film is not sticky and has good flexibility at 25℃ room temperature. Through DSC scanning with different temperature rising rates , the activation energy Eα of the original resin system and that of the resin film were analyzed. It is found that the Eα of the resin film is greater than that of the other one , and increases with the rising of cure degree. Based on the double Arrhenius theory , the prediction function of viscosity and the prediction function of gel time which are both proved to have good applicability by tests were established. According to the viscosity requirement of RFI process , a function for the infusion coefficient is set up , and the optimal theoretical infusion temperature 128. 4 ℃is found.
In order to develop an epoxy matrix resin film used in the low-cost technique of RFI , a new resin film was synthesized with epoxy of E51 , high temperature latent curing agent BF3-400 and ethylene glycol , through optimizing the ingredient s by the orthogonal design method and controlling the primary reaction degree. The results of the research on its chemorheology show that the least viscosity of this resin film reaches 360 mPa· s , the time of low viscosity below 1000 mPa· s is up to 32 min , and the gel time is 48 min at 130℃ work temperature. The resin film is not sticky and has good flexibility at 25℃ room temperature. Through DSC scanning with different temperature rising rates , the activation energy Eα of the original resin system and that of the resin film were analyzed. It is found that the Eα of the resin film is greater than that of the other one , and increases with the rising of cure degree. Based on the double Arrhenius theory , the prediction function of viscosity and the prediction function of gel time which are both proved to have good applicability by tests were established. According to the viscosity requirement of RFI process , a function for the infusion coefficient is set up , and the optimal theoretical infusion temperature 128. 4 ℃is found.
2008, 25(3): 93-97.
Abstract:
The permeability of stitched preform was measured by the radial technology. The influences of the sewing needle and stitching parameters on the permeability were studied. The experimental results show that the permeability increases with increasing the stitching density and diameter of sewing needle except when the stitching density is lower than 0. 66 pts/m using 100 type sewing needle. The types of the sewing needle and thread affect the permeability simultaneously. The sewing needle plays a promoting role , while the thread plays a limiting role. With a thread mass fraction of 0. 18 % , the permeability is increased greatly by 58. 6 % with respect to the same unstitched fabric. Transverse permeabilities of stitched and unstitched fabrics were measured by one-dimensional flow experiments. The influences of the fiber stacking sequence and stitching density on the transverse permeability were studied. The experimental results show that the transverse permeability strongly increases with increasing the stitching density.
The permeability of stitched preform was measured by the radial technology. The influences of the sewing needle and stitching parameters on the permeability were studied. The experimental results show that the permeability increases with increasing the stitching density and diameter of sewing needle except when the stitching density is lower than 0. 66 pts/m using 100 type sewing needle. The types of the sewing needle and thread affect the permeability simultaneously. The sewing needle plays a promoting role , while the thread plays a limiting role. With a thread mass fraction of 0. 18 % , the permeability is increased greatly by 58. 6 % with respect to the same unstitched fabric. Transverse permeabilities of stitched and unstitched fabrics were measured by one-dimensional flow experiments. The influences of the fiber stacking sequence and stitching density on the transverse permeability were studied. The experimental results show that the transverse permeability strongly increases with increasing the stitching density.
2008, 25(3): 98-104.
Abstract:
The electrospinning was used to produce multi-walled nanotubes (MWNTs) and polyurethane (PU) compound nanofibers. The morphology and microstructure of the compound nanofibers were analyzed by scanning electron microscope (SEM) and transmission electron microscopy (TEM). The crystallization and glass transition temperature (Tg) of the membranes were examined by XRD and DSC analysis. The relationship between the tensile properties of the membranes and the mass fraction of the MWNTs was revealed by tensile testing. The results show that the MWNTs with a suitable content can be efficiently dispersed in PU solutions and compound ultrafine fibers can be obtained. With the increasing of the content of the MWNTs in PU solutions , the diameters of the compound nanofibers become smaller,while the Tg becomes higher . Furthermore , the tensile strength and elongation at break of the studied membranes increase with the increase of MWNTs content in the hybrid nanofibers.
The electrospinning was used to produce multi-walled nanotubes (MWNTs) and polyurethane (PU) compound nanofibers. The morphology and microstructure of the compound nanofibers were analyzed by scanning electron microscope (SEM) and transmission electron microscopy (TEM). The crystallization and glass transition temperature (Tg) of the membranes were examined by XRD and DSC analysis. The relationship between the tensile properties of the membranes and the mass fraction of the MWNTs was revealed by tensile testing. The results show that the MWNTs with a suitable content can be efficiently dispersed in PU solutions and compound ultrafine fibers can be obtained. With the increasing of the content of the MWNTs in PU solutions , the diameters of the compound nanofibers become smaller,while the Tg becomes higher . Furthermore , the tensile strength and elongation at break of the studied membranes increase with the increase of MWNTs content in the hybrid nanofibers.
2008, 25(3): 105-109.
Abstract:
The applicability of Weibull distribution model and Gauss distribution model was confirmed by hypothesis testing in the bundle strength statistics of basal fibers. The bundle st rength dist ributions in different lengths of basalt fiber BF-CSH-01 , BF-CMD-02 and BF-CAH-01 were analyzed with both the models. When the fiber and sample length change , the bundle strength transformation trends are the same in the two models. Among the three kinds of basalt fibers , the fiber BF-CSH-01 has the highest bundle strength and the fiber BF-CMD-02 has the smallest variation coefficient . For the same basalt fiber , when the sample length increases , the bundle strengths and the variation coefficient s of the strength decrease. A comparison between the Weibull model and Gauss model shows that the former has the higher bundle strength and a bigger variation coefficient .
The applicability of Weibull distribution model and Gauss distribution model was confirmed by hypothesis testing in the bundle strength statistics of basal fibers. The bundle st rength dist ributions in different lengths of basalt fiber BF-CSH-01 , BF-CMD-02 and BF-CAH-01 were analyzed with both the models. When the fiber and sample length change , the bundle strength transformation trends are the same in the two models. Among the three kinds of basalt fibers , the fiber BF-CSH-01 has the highest bundle strength and the fiber BF-CMD-02 has the smallest variation coefficient . For the same basalt fiber , when the sample length increases , the bundle strengths and the variation coefficient s of the strength decrease. A comparison between the Weibull model and Gauss model shows that the former has the higher bundle strength and a bigger variation coefficient .
2008, 25(3): 110-114.
Abstract:
The ultrasonic reflection coefficient |R0| is up to 21 % at the resin pocket of carbon fiber woven composites. However，|R0| is dependent on the wavelength and resin-thickness between neighboring interlaminar stacks at interlaminar interface. The 3D microstucture of woven composites was well visualized by using ultrasonic B-scan and T-scan imaging techniques，based on the sonic information resulting from reflections at the resin pocket，fiber bundle and interlaminar interface. The experimental results show that the orientation，shape，distribution and size of the resin pockets，woven fiber bundles and their topologies as well as lay-up of woven laminate can be seen well by employing the ultrasonic imaging technique with high-resolution. It provides an effective instrument for characterization of bulk microstructures and evaluation of micro-defects in woven composites.
The ultrasonic reflection coefficient |R0| is up to 21 % at the resin pocket of carbon fiber woven composites. However，|R0| is dependent on the wavelength and resin-thickness between neighboring interlaminar stacks at interlaminar interface. The 3D microstucture of woven composites was well visualized by using ultrasonic B-scan and T-scan imaging techniques，based on the sonic information resulting from reflections at the resin pocket，fiber bundle and interlaminar interface. The experimental results show that the orientation，shape，distribution and size of the resin pockets，woven fiber bundles and their topologies as well as lay-up of woven laminate can be seen well by employing the ultrasonic imaging technique with high-resolution. It provides an effective instrument for characterization of bulk microstructures and evaluation of micro-defects in woven composites.
2008, 25(3): 115-120.
Abstract:
The finite element method was applied to analyze the factors influencing the shear modulus test results with the current press-shear test method in order to verify this test method's applicability to sandwich construction with a high shear modulus. The results show that the bending deflection of the loading plate's loading end decreases the accuracy of the test results , especially to those with the high shear modulus. The test errors will exceed 6 % when the sandwich construction's modulus is over 100 MPa. Based on the study of the current test system parameters , an improved press-shear method was put forward : reducing the bending deflection of the loading plate's loading end by improving the loading method. This new test method covers the determination of the shear modulus of sandwich construction whose shear modulus is lower than 500 MPa , with a test error less than 3 %. The improved test method also reduces the sensitivity of test results to fixture dimension parameters variations , and improves the test reliability.
The finite element method was applied to analyze the factors influencing the shear modulus test results with the current press-shear test method in order to verify this test method's applicability to sandwich construction with a high shear modulus. The results show that the bending deflection of the loading plate's loading end decreases the accuracy of the test results , especially to those with the high shear modulus. The test errors will exceed 6 % when the sandwich construction's modulus is over 100 MPa. Based on the study of the current test system parameters , an improved press-shear method was put forward : reducing the bending deflection of the loading plate's loading end by improving the loading method. This new test method covers the determination of the shear modulus of sandwich construction whose shear modulus is lower than 500 MPa , with a test error less than 3 %. The improved test method also reduces the sensitivity of test results to fixture dimension parameters variations , and improves the test reliability.
2008, 25(3): 121-126.
Abstract:
A new-style fabric radar absorbing material (RAM) composed of copper coating and absorbing coating was prepared on two fabrics. In order to analyze the effects of electroless copper coating on the microwave properties of the composite RAM,the copper coatings of various components,fabric with different conformations and multi-layer structures were adopted. The results show that for the structure of the absorbing coating as the first layer and the copper coating as the second layer after electroless copper plating at room temperature,after air oxidation for 8 days,compared with initial copper-plating composite,the reflectivity of non-woven RAM with copper-plating decreases from - 11 dB to - 13. 2 dB. For the structure of the copper coating as the first layer and the absorbing coating as the second layer,the whole thickness of the non-woven composite RAM after copper-plating at 40℃reduces by 1. 4 mm approximately,compared with that after copper plating at room temperature in the state of an adjacent reflectivity peak value. The results indicate that copper coating can be used to improve the microwave property of RAM.
A new-style fabric radar absorbing material (RAM) composed of copper coating and absorbing coating was prepared on two fabrics. In order to analyze the effects of electroless copper coating on the microwave properties of the composite RAM,the copper coatings of various components,fabric with different conformations and multi-layer structures were adopted. The results show that for the structure of the absorbing coating as the first layer and the copper coating as the second layer after electroless copper plating at room temperature,after air oxidation for 8 days,compared with initial copper-plating composite,the reflectivity of non-woven RAM with copper-plating decreases from - 11 dB to - 13. 2 dB. For the structure of the copper coating as the first layer and the absorbing coating as the second layer,the whole thickness of the non-woven composite RAM after copper-plating at 40℃reduces by 1. 4 mm approximately,compared with that after copper plating at room temperature in the state of an adjacent reflectivity peak value. The results indicate that copper coating can be used to improve the microwave property of RAM.
2008, 25(3): 127-131.
Abstract:
The experiments were performed on tensile,compressive and flexible properties of high volume fraction SiCP/Al composites. The result indicates that the composites have no obvious linear yield process. Loading and unloading experiments were carried out . It is found that the macroscopic properties of this SiCP/Al composite are similar to plasticity of metal materials under external load. It has a quantity of residual strain on unloading,and the reloading course is approximately the same as the last unloading course. The residual strain caused by tension is greater than that by compression. The material has a stable tangent modulus with the best potential of residual plastic formation under three-point bending. From the analysis on SEM fractography , it shows that the local and gradual microyields of nonhomogeneous distribution of the matrix are the main reasons that get the behavior of high volume fraction SiCP/Al composites similar to that of plastic materials in macroscope. The residual stress in the process and microdefects in the matrix make the residual strain by tension greater than that by compression.
The experiments were performed on tensile,compressive and flexible properties of high volume fraction SiCP/Al composites. The result indicates that the composites have no obvious linear yield process. Loading and unloading experiments were carried out . It is found that the macroscopic properties of this SiCP/Al composite are similar to plasticity of metal materials under external load. It has a quantity of residual strain on unloading,and the reloading course is approximately the same as the last unloading course. The residual strain caused by tension is greater than that by compression. The material has a stable tangent modulus with the best potential of residual plastic formation under three-point bending. From the analysis on SEM fractography , it shows that the local and gradual microyields of nonhomogeneous distribution of the matrix are the main reasons that get the behavior of high volume fraction SiCP/Al composites similar to that of plastic materials in macroscope. The residual stress in the process and microdefects in the matrix make the residual strain by tension greater than that by compression.
2008, 25(3): 132-137.
Abstract:
The ZnAl2O4 coating was fabricated on the surface of the aluminum borate whiskers by a sol-gel method,and the 6061Al matrix composite reinforced with ZnAl2O4-coated aluminum borate whiskers was fabricated by squeeze casting. The effects of the ZnAl2O4 coating on interface wet tability,tensile properties at room temperature and interfacial thermal stability after thermal exposure of the composite were investigated. The experimental results show that the nano- ZnAl2O4 coating can remarkably improve the interface wet tability of the composite,and thus improve the tensile properties at room temperature of the composite. The uniform ZnAl2O4 coating can effectively hinder the interfacial reaction and make the composite keep good thermal stability. At the same time,the effect of the coating on the tensile fracture behavior of the composite in as-cast and after thermal exposure was investigated. The fracture of whiskers is in the majority during the tensile deformation of the aluminum matrix composite reinforced with uncoated aluminum borate whiskers,however,the pull-out of whiskers is in the majority during the tensile deformation of the aluminum matrix composite reinforced with ZnAl2O4-coated aluminum borate whiskers.
The ZnAl2O4 coating was fabricated on the surface of the aluminum borate whiskers by a sol-gel method,and the 6061Al matrix composite reinforced with ZnAl2O4-coated aluminum borate whiskers was fabricated by squeeze casting. The effects of the ZnAl2O4 coating on interface wet tability,tensile properties at room temperature and interfacial thermal stability after thermal exposure of the composite were investigated. The experimental results show that the nano- ZnAl2O4 coating can remarkably improve the interface wet tability of the composite,and thus improve the tensile properties at room temperature of the composite. The uniform ZnAl2O4 coating can effectively hinder the interfacial reaction and make the composite keep good thermal stability. At the same time,the effect of the coating on the tensile fracture behavior of the composite in as-cast and after thermal exposure was investigated. The fracture of whiskers is in the majority during the tensile deformation of the aluminum matrix composite reinforced with uncoated aluminum borate whiskers,however,the pull-out of whiskers is in the majority during the tensile deformation of the aluminum matrix composite reinforced with ZnAl2O4-coated aluminum borate whiskers.
2008, 25(3): 138-143.
Abstract:
The hollow TiO2/SiO2 composite nanofibres were successfully synthesized via an electrospinning technique. The samples were studied by TGA-DTA , FTIR , XRD , SEM , TEM and EDS. The results indicate that the outer-wall of the as-prepared TiO2/SiO2 nanofibres is amorphous SiO2 and the inner-wall is composed of TiO2 nanoparticles of 50 nm in diameter . The composite hollow nanofibres are 2μm in the mean diameter and greater than 100μm in length. Their formation mechanisms were also discussed. During the calcination of composite fibres , the TiO2 nanoparticles are diffused from the core toward the inner surface , new bonds are formed between TiO2 nano-particles and SiO2 shell , and composite hollow nanofibres are finally obtained.
The hollow TiO2/SiO2 composite nanofibres were successfully synthesized via an electrospinning technique. The samples were studied by TGA-DTA , FTIR , XRD , SEM , TEM and EDS. The results indicate that the outer-wall of the as-prepared TiO2/SiO2 nanofibres is amorphous SiO2 and the inner-wall is composed of TiO2 nanoparticles of 50 nm in diameter . The composite hollow nanofibres are 2μm in the mean diameter and greater than 100μm in length. Their formation mechanisms were also discussed. During the calcination of composite fibres , the TiO2 nanoparticles are diffused from the core toward the inner surface , new bonds are formed between TiO2 nano-particles and SiO2 shell , and composite hollow nanofibres are finally obtained.
2008, 25(3): 144-148.
Abstract:
The CoFe2O4/SiO2 nanocomposite was prepared by the sol-gel method. The structure , crystalline size and magnetic properties of samples were investigated by XRD , TEM , VSM and Mssbauer effect . The results show that the grain size of CoFe2O4 increases with the increasing of heating temperature , and the growth of CoFe2O4 grain is restricted effectively with the existence of amorphous SiO2. VSM result s show that the saturation magnetization and coercivity of the samples increase with the increasing of the grain size. With the rise in treatment temperature , the samples transform from the superparamagnetic and magnetic order mixed state to an entire magnetic order state ,which is confirmed by the Mssbauer effect .
The CoFe2O4/SiO2 nanocomposite was prepared by the sol-gel method. The structure , crystalline size and magnetic properties of samples were investigated by XRD , TEM , VSM and Mssbauer effect . The results show that the grain size of CoFe2O4 increases with the increasing of heating temperature , and the growth of CoFe2O4 grain is restricted effectively with the existence of amorphous SiO2. VSM result s show that the saturation magnetization and coercivity of the samples increase with the increasing of the grain size. With the rise in treatment temperature , the samples transform from the superparamagnetic and magnetic order mixed state to an entire magnetic order state ,which is confirmed by the Mssbauer effect .
2008, 25(3): 149-153.
Abstract:
A method of predicting the damage resistance of composite laminates subjected to quasi-static indentation was proposed. Damage variables were introduced to represent the matrix crack , delamination and fiber breakage , respectively , and stiffness degradation criteria were proposed for different damage modes. A progressive damage analysis was conducted for composite laminates under quasi-static transverse compressive loading by using a strain- based Hashin and Yeh failure criterion as well as the finite element method. The damage resistance was predicted. The numerical analysis was implemented with a commercial finite element code , ABAQUS/standard , via its user subroutine UMAT. The numerical results indicate that the onset and propagation of the delamination induce a discontinuity in the slope of the force-displacement curve , and the fiber breakages are induced once the contact force reaches its maximum. The numerical results agree well with the test data for the delamination onset load and the maximum contact force.
A method of predicting the damage resistance of composite laminates subjected to quasi-static indentation was proposed. Damage variables were introduced to represent the matrix crack , delamination and fiber breakage , respectively , and stiffness degradation criteria were proposed for different damage modes. A progressive damage analysis was conducted for composite laminates under quasi-static transverse compressive loading by using a strain- based Hashin and Yeh failure criterion as well as the finite element method. The damage resistance was predicted. The numerical analysis was implemented with a commercial finite element code , ABAQUS/standard , via its user subroutine UMAT. The numerical results indicate that the onset and propagation of the delamination induce a discontinuity in the slope of the force-displacement curve , and the fiber breakages are induced once the contact force reaches its maximum. The numerical results agree well with the test data for the delamination onset load and the maximum contact force.
2008, 25(3): 154-159.
Abstract:
A micromechanical model was proposed to estimate the overall nonlinear viscoelastic behavior for the particulate polymer composites. The method was based on the generalized secant method and Laplace transform technique. Schapery's thermodynamics constitutive law was used to simulate the experimental data of high-density polythene (HDPE) matrix and the material functions were identified. The stress and strain relation at a constant strain rate for HDPE-matrix composite filled with glass beads was analyzed. The predicted results agree well with the experimental ones. The results show that the GB/HDPE composites present obvious nonlinear behavior . The model can well predict the nonlinear viscoelastic properties for polymer composites.
A micromechanical model was proposed to estimate the overall nonlinear viscoelastic behavior for the particulate polymer composites. The method was based on the generalized secant method and Laplace transform technique. Schapery's thermodynamics constitutive law was used to simulate the experimental data of high-density polythene (HDPE) matrix and the material functions were identified. The stress and strain relation at a constant strain rate for HDPE-matrix composite filled with glass beads was analyzed. The predicted results agree well with the experimental ones. The results show that the GB/HDPE composites present obvious nonlinear behavior . The model can well predict the nonlinear viscoelastic properties for polymer composites.
2008, 25(3): 160-167.
Abstract:
To investigate the effect of glue's adhesive on the mechanical properties of CFRP and its reinforced concrete structure mechanical behavior , the CFRP sheets and concrete beams were prefabricated , and the mechanical properties of them were investigated by the axial tension and four-point bending beams tests. The experiment compare of carbon cloth's tension strength with and without glue indicates that the epoxy resin can not only make the fiber adhesive united but also increase the tensile strength. The strain gauges were adhered on the surface of CFRP of a four-point bending concrete beam. With the electrometric method , the damage process curves of the materials were obtained. Through the mechanics analysis model and the least square method , the axis force and shear stress distributions of CFRP were analyzed , respectively. With the debonding of interface between FRP and concrete beam , the maximum value of tension stress of FRP reduces , thus a strain rebound phenomenon appears.
To investigate the effect of glue's adhesive on the mechanical properties of CFRP and its reinforced concrete structure mechanical behavior , the CFRP sheets and concrete beams were prefabricated , and the mechanical properties of them were investigated by the axial tension and four-point bending beams tests. The experiment compare of carbon cloth's tension strength with and without glue indicates that the epoxy resin can not only make the fiber adhesive united but also increase the tensile strength. The strain gauges were adhered on the surface of CFRP of a four-point bending concrete beam. With the electrometric method , the damage process curves of the materials were obtained. Through the mechanics analysis model and the least square method , the axis force and shear stress distributions of CFRP were analyzed , respectively. With the debonding of interface between FRP and concrete beam , the maximum value of tension stress of FRP reduces , thus a strain rebound phenomenon appears.
2008, 25(3): 168-173.
Abstract:
The elastic properties of composite materials with a doubly periodic array of coated fibers under antiplane shear were studied. An analytical solution for the problem was presented by applying the Eshelby's equivalent inclusion method and Laurent 's series expansion technique as well as combining the theory of the doubly quasi-periodic Riemann boundary value problem. The expressions for the stress field and effective modulus were obtained. The comparisons with the finite element method (FEM) show the efficiency and accuracy of the present method. The influence of the coating parameters on the stress concent ration and the effective modulus of the composites was discussed. A very high stress concent ration may occur in the coating , and the stiffer and thinner the coating is , the higher the stress concent ration. A very soft or very hard coating can shield the contribution of the fiber stiffness to the effective modulus of composites.
The elastic properties of composite materials with a doubly periodic array of coated fibers under antiplane shear were studied. An analytical solution for the problem was presented by applying the Eshelby's equivalent inclusion method and Laurent 's series expansion technique as well as combining the theory of the doubly quasi-periodic Riemann boundary value problem. The expressions for the stress field and effective modulus were obtained. The comparisons with the finite element method (FEM) show the efficiency and accuracy of the present method. The influence of the coating parameters on the stress concent ration and the effective modulus of the composites was discussed. A very high stress concent ration may occur in the coating , and the stiffer and thinner the coating is , the higher the stress concent ration. A very soft or very hard coating can shield the contribution of the fiber stiffness to the effective modulus of composites.
2008, 25(3): 174-181.
Abstract:
The shape derivatives of the functional for domain integral and boundary integral were derived in details by employing the material distribution function of the level set . A theoretical model of the stiff continuum structure for the composite laminated structure was established. By the combination of the shape derivative and the augmented Lagrangian multipliers , a novel sensitivity analysis for the mean compliance with the composite laminated structure was presented. The evolution of the structural design boundary was cont rolled by the artificial velocity which makes the objective function descent . The level set surface of a higher-dimensional function can be moved up and down without changing its topology structure , and the optimization boundaries embedded on level set function can automatically modify the topology structure by the boundaries merging and breaking. The extensively studied 2D examples of the clamped beam were employed to demonst rate the validity of the present methodologies.
The shape derivatives of the functional for domain integral and boundary integral were derived in details by employing the material distribution function of the level set . A theoretical model of the stiff continuum structure for the composite laminated structure was established. By the combination of the shape derivative and the augmented Lagrangian multipliers , a novel sensitivity analysis for the mean compliance with the composite laminated structure was presented. The evolution of the structural design boundary was cont rolled by the artificial velocity which makes the objective function descent . The level set surface of a higher-dimensional function can be moved up and down without changing its topology structure , and the optimization boundaries embedded on level set function can automatically modify the topology structure by the boundaries merging and breaking. The extensively studied 2D examples of the clamped beam were employed to demonst rate the validity of the present methodologies.
2008, 25(3): 182-189.
Abstract:
The woven carbon fiber reinforced C-SiC binary matrix (C/C-SiC) composite manufactured by chemical
vapor infiltration (CVI) method was investigated. Based on the material tomography of scanning electron microscopy (SEM) , distributions of porosities and micro-cracks were identified and included in the finite element model of C/C-SiC composites. The homogenization method was used for the evaluation of effective modulus of woven C/C-SiC composites. The results of the numerical computing and experimental tests were compared for two cases of C/C-SiC composites with different layer thickness. It is shown that the proposed finite element models of C/C-SiC can characterize physically the real situation of the involved porosities and micro-cracks related to the CVI process. The numerical results of effective modulus agree reasonably with the experimental ones.
The woven carbon fiber reinforced C-SiC binary matrix (C/C-SiC) composite manufactured by chemical
vapor infiltration (CVI) method was investigated. Based on the material tomography of scanning electron microscopy (SEM) , distributions of porosities and micro-cracks were identified and included in the finite element model of C/C-SiC composites. The homogenization method was used for the evaluation of effective modulus of woven C/C-SiC composites. The results of the numerical computing and experimental tests were compared for two cases of C/C-SiC composites with different layer thickness. It is shown that the proposed finite element models of C/C-SiC can characterize physically the real situation of the involved porosities and micro-cracks related to the CVI process. The numerical results of effective modulus agree reasonably with the experimental ones.
2008, 25(3): 190-196.
Abstract:
High precision sandwich reflector panels of compact antenna test range are made of aluminum face sheet and honeycomb core treated by a special process. The constitutive parameters of this kind of sandwich panel are difficult to obtain by the traditional analytical methods and mechanical property tests. A mixed numerical-experimental model method was proposed to estimate the panel's equivalent elastic material parameters. In this method , the forward analysis was predicted using the finite element method and the inverse analysis was an algorithm combined genetic algorithm and gradient method. By using the proposed optimization algorithm and seamless integration between forward and inverse analyses , the mixed numerical-experimental model method was more efficient . A comparison between the results of numerical simulation and the experiment shows that material parameters from inverse identification describe the constitutive relations of this kind of sandwich panel faithfully. The numerical simulation model based on the parameters is reliable.
High precision sandwich reflector panels of compact antenna test range are made of aluminum face sheet and honeycomb core treated by a special process. The constitutive parameters of this kind of sandwich panel are difficult to obtain by the traditional analytical methods and mechanical property tests. A mixed numerical-experimental model method was proposed to estimate the panel's equivalent elastic material parameters. In this method , the forward analysis was predicted using the finite element method and the inverse analysis was an algorithm combined genetic algorithm and gradient method. By using the proposed optimization algorithm and seamless integration between forward and inverse analyses , the mixed numerical-experimental model method was more efficient . A comparison between the results of numerical simulation and the experiment shows that material parameters from inverse identification describe the constitutive relations of this kind of sandwich panel faithfully. The numerical simulation model based on the parameters is reliable.
2008, 25(3): 197-201.
Abstract:
Metallic honeycomb material has one easy flow direction and superior surface area to volume ratio , so that it exhibits at tractive heat capacity except for the high specific rigidity and specific strength. It is of great significance for multifunctional design to study its heat transfer efficiency subjected to forced convection. The heat transfer in the honeycomb material with a number of micro cells subjected to air convection is difficult to solve by using the method of computational fluid dynamics (CFD) directly , which is the obstacle to design optimization. Thus , it is very valuable in theory and application to develop a fast numerical algorithm. In this paper , the fast numerical algorithm for evaluating the thermal performance of metallic honeycomb materials was presented. It's an about 3～4 order of magnitudes improvement in computational velocity of this method compared with the finite volume method. The validity and applicability of the method were proved by two examples.
Metallic honeycomb material has one easy flow direction and superior surface area to volume ratio , so that it exhibits at tractive heat capacity except for the high specific rigidity and specific strength. It is of great significance for multifunctional design to study its heat transfer efficiency subjected to forced convection. The heat transfer in the honeycomb material with a number of micro cells subjected to air convection is difficult to solve by using the method of computational fluid dynamics (CFD) directly , which is the obstacle to design optimization. Thus , it is very valuable in theory and application to develop a fast numerical algorithm. In this paper , the fast numerical algorithm for evaluating the thermal performance of metallic honeycomb materials was presented. It's an about 3～4 order of magnitudes improvement in computational velocity of this method compared with the finite volume method. The validity and applicability of the method were proved by two examples.
2008, 25(3): 202-209.
Abstract:
Based on the multifunctional demand for the effective heat transfer performance at specified pumping power and structural stiffness , a multi-functional optimization design was studied for sandwich panels filled with orthotropic honeycomb cores , such as rectangular cell . Orthot ropic cellular correlation coefficients were derived. Due to the shortage of the traditional product-type multifunctional index , two level programming models which served as the basis of the engineering optimization index for the heat dissipation-mechanical load performance were constructed in order to obtain a Pareto set of multi-object optimization design. In contrast with optimization of the single specific index , the presented method is efficient and offers a wide design choice for engineers , especially for the orthotropic cellular materials due to multi sensitive parameters. Finally , the optimum honeycomb morphology parameters were obtained and discussed under different scale effects.
Based on the multifunctional demand for the effective heat transfer performance at specified pumping power and structural stiffness , a multi-functional optimization design was studied for sandwich panels filled with orthotropic honeycomb cores , such as rectangular cell . Orthot ropic cellular correlation coefficients were derived. Due to the shortage of the traditional product-type multifunctional index , two level programming models which served as the basis of the engineering optimization index for the heat dissipation-mechanical load performance were constructed in order to obtain a Pareto set of multi-object optimization design. In contrast with optimization of the single specific index , the presented method is efficient and offers a wide design choice for engineers , especially for the orthotropic cellular materials due to multi sensitive parameters. Finally , the optimum honeycomb morphology parameters were obtained and discussed under different scale effects.
