2010 Vol. 27, No. 2
2010, 27(2): 1-8.
Abstract:
To solve the conflict about the effects of particle size on magnetost rictive properties of polymer-bonded Terfenol-D composites studied by different scholars, Terfenol-D/unsaturated polyester resin composites were prepared with 20 % volume fraction Terfenol-D powders in six particle-size ranges (30～53μm, 53～150μm, 150～300μm, 300～450μm, 450～500μm and 30～500μm). The static and dynamic magnetostrictive properties, magnetomechanical coupling coefficient, Young modulus and compressive strength were tested. The results indicate that the composite with particles of 53～150μm distribution presents the largest static and dynamic magnetostrictive properties among all the five monodispersed distribution samples. The sample with particle size in 30～500μm shows even larger response than that with 53～150μm particle size distribution. It indicates that the particle size plays a double-edged sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to prepare polymer-bonded Terfenol-D composites results from the competition between the positive effects and negative effects of increasing the particle size.
To solve the conflict about the effects of particle size on magnetost rictive properties of polymer-bonded Terfenol-D composites studied by different scholars, Terfenol-D/unsaturated polyester resin composites were prepared with 20 % volume fraction Terfenol-D powders in six particle-size ranges (30～53μm, 53～150μm, 150～300μm, 300～450μm, 450～500μm and 30～500μm). The static and dynamic magnetostrictive properties, magnetomechanical coupling coefficient, Young modulus and compressive strength were tested. The results indicate that the composite with particles of 53～150μm distribution presents the largest static and dynamic magnetostrictive properties among all the five monodispersed distribution samples. The sample with particle size in 30～500μm shows even larger response than that with 53～150μm particle size distribution. It indicates that the particle size plays a double-edged sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to prepare polymer-bonded Terfenol-D composites results from the competition between the positive effects and negative effects of increasing the particle size.
2010, 27(2): 9-15.
Abstract:
To provide a theoretical basis for developing heat-resisting material and cryogenic temperature material, the tensile properties of nylon short fiber reinforced foam rubber composites (SFRFRC) with the identical spongy rate but different short fiber volume fractions and the identical short fiber volume fraction but differently spongy rates were tested at 213～398 K. The results show that the compressive properties of SFRFRC changed obviously from high-elastic state to glass state at 213 K, and the glass transition temperatures are in the range of 213～233 K.Short fiber volume fraction and spongy rate have a significant effect on the low-temperature-resistant properties of the SFRFRC. It can significantly improve the compressive properties of SFRFRC by adding the short fiber volume fraction and changing appropriately the spongy rate at low temperatures. Under conditions of 160 N and 5 mm, the permanent compression set of SFRFRC with the identical spongy rate but different short fiber volume fractions decreases with the short fiber volume fraction increasing, and the permanent compression set of SFRFRC with 5 % short fiber volume fraction with different spongy rates increases with the spongy rate increasing.
To provide a theoretical basis for developing heat-resisting material and cryogenic temperature material, the tensile properties of nylon short fiber reinforced foam rubber composites (SFRFRC) with the identical spongy rate but different short fiber volume fractions and the identical short fiber volume fraction but differently spongy rates were tested at 213～398 K. The results show that the compressive properties of SFRFRC changed obviously from high-elastic state to glass state at 213 K, and the glass transition temperatures are in the range of 213～233 K.Short fiber volume fraction and spongy rate have a significant effect on the low-temperature-resistant properties of the SFRFRC. It can significantly improve the compressive properties of SFRFRC by adding the short fiber volume fraction and changing appropriately the spongy rate at low temperatures. Under conditions of 160 N and 5 mm, the permanent compression set of SFRFRC with the identical spongy rate but different short fiber volume fractions decreases with the short fiber volume fraction increasing, and the permanent compression set of SFRFRC with 5 % short fiber volume fraction with different spongy rates increases with the spongy rate increasing.
2010, 27(2): 16-23.
Abstract:
Starch-g-MAH-St(SMS), prepared by the solid state reaction method, is the graft copolymer of corn starch, maleic anhydride (MAH) and styrene (St ). SMS/styrene-butadiene rubber (SBR) composite was prepared by mechanical blending. The mechanical properties, hot air aging properties, dynamic mechanical properties and micro morphology were investigated. The results show that the mechanical properties of SMS/SBR composite are superior to those of starch/SBR composite and vulcanized SBR. When the charging amounts of St and MAH are both 10 % of the weight of starch and the content of SMS is 20 g per 100 g SBR, SMS/SBR composite has the best mechanical properties. The tensile strength of composite is 10 MPa after hot air aging at 100℃for 48 h. The glass transition temperature ( Tg) of SMS/SBR composite is lower than that of vulcanized SBR. The micro morphology analysis shows that the size of starch particle is decreased, the dispersibility of starch is increased and the compatibility between starch and SBR is improved after modification.
Starch-g-MAH-St(SMS), prepared by the solid state reaction method, is the graft copolymer of corn starch, maleic anhydride (MAH) and styrene (St ). SMS/styrene-butadiene rubber (SBR) composite was prepared by mechanical blending. The mechanical properties, hot air aging properties, dynamic mechanical properties and micro morphology were investigated. The results show that the mechanical properties of SMS/SBR composite are superior to those of starch/SBR composite and vulcanized SBR. When the charging amounts of St and MAH are both 10 % of the weight of starch and the content of SMS is 20 g per 100 g SBR, SMS/SBR composite has the best mechanical properties. The tensile strength of composite is 10 MPa after hot air aging at 100℃for 48 h. The glass transition temperature ( Tg) of SMS/SBR composite is lower than that of vulcanized SBR. The micro morphology analysis shows that the size of starch particle is decreased, the dispersibility of starch is increased and the compatibility between starch and SBR is improved after modification.
2010, 27(2): 24-30.
Abstract:
The effect of void content on the moisture absorption and interlaminar shear strength (ILSS) of [(±45) 4/(0,90) /(±45)2]S and [(±45) /(0, 90)2/(±45) ]S carbon fiber reinforced epoxy composite laminates used in a aircraf twas studied. The carbon fiber/epoxy laminates with different void volume fractions were prepared by applying different curing pressures. The microstructure characteristics of voids were studied using optical image analysis.The results show that the voids mainly locate between the plies and grow with the increasing void content. The rate of water uptake and the maximum level of moisture absorption in the two carbon/epoxy composite laminates increase with the increasing void content. The ILSS of aged and unaged laminates decrease with the increasing void content.The ILSS of unaged and aged [(±45) 4/(0,90) /(±45)2]S laminates with the void volume fractions 0.6 %～6.3 % and 0.4 %～7.0 % decrease 6 % and 9 %, respectively. The ILSS of unaged and aged [(±45) /(0, 90)2/(±45) ]S laminates with the void volume fractions 0.4 %～6.9 % and 0.2 %～8.9 % decrease 14 % and 7 %, respectively.
The effect of void content on the moisture absorption and interlaminar shear strength (ILSS) of [(±45) 4/(0,90) /(±45)2]S and [(±45) /(0, 90)2/(±45) ]S carbon fiber reinforced epoxy composite laminates used in a aircraf twas studied. The carbon fiber/epoxy laminates with different void volume fractions were prepared by applying different curing pressures. The microstructure characteristics of voids were studied using optical image analysis.The results show that the voids mainly locate between the plies and grow with the increasing void content. The rate of water uptake and the maximum level of moisture absorption in the two carbon/epoxy composite laminates increase with the increasing void content. The ILSS of aged and unaged laminates decrease with the increasing void content.The ILSS of unaged and aged [(±45) 4/(0,90) /(±45)2]S laminates with the void volume fractions 0.6 %～6.3 % and 0.4 %～7.0 % decrease 6 % and 9 %, respectively. The ILSS of unaged and aged [(±45) /(0, 90)2/(±45) ]S laminates with the void volume fractions 0.4 %～6.9 % and 0.2 %～8.9 % decrease 14 % and 7 %, respectively.
2010, 27(2): 31-37.
Abstract:
Ultrafine nano-hydroxyapatite(nHA) /silk fibroin(SF)/poly( ε-caprolactone)(PCL) composite fibers were prepared via electrospinning. Scanning electron microscopy(SEM), attenuated total reflectance-Fourier transform infrared spect roscopy ( ATR-FTIR) and X-ray diffraction(XRD) were used to characterize the electrospun ultrafine nHA/SF/PCL composite fibers. The mechanical properties of fibers were also tested. The results show that the diameter of the fibers decreases and the crystallinity of PCL in the fibers becomes poor with increasing nHA content in the fibers. Compared with SF/PCL fibers, the mechanical properties of ultrafine nHA/SF/PCL composite fibers are still well when the nHA mass ratio is 30 % in the fibers. In vitro mouse fibroblast (L929) cell culture indicates that the ultrafine nHA/ SF/PCL composite fibers are non-toxicity.
Ultrafine nano-hydroxyapatite(nHA) /silk fibroin(SF)/poly( ε-caprolactone)(PCL) composite fibers were prepared via electrospinning. Scanning electron microscopy(SEM), attenuated total reflectance-Fourier transform infrared spect roscopy ( ATR-FTIR) and X-ray diffraction(XRD) were used to characterize the electrospun ultrafine nHA/SF/PCL composite fibers. The mechanical properties of fibers were also tested. The results show that the diameter of the fibers decreases and the crystallinity of PCL in the fibers becomes poor with increasing nHA content in the fibers. Compared with SF/PCL fibers, the mechanical properties of ultrafine nHA/SF/PCL composite fibers are still well when the nHA mass ratio is 30 % in the fibers. In vitro mouse fibroblast (L929) cell culture indicates that the ultrafine nHA/ SF/PCL composite fibers are non-toxicity.
2010, 27(2): 38-42.
Abstract:
1. 5 wt% carbon fiber(Cf) reinforced polymethyl methacrylate-polymethyl acrylate ( PMMA-PMA)matrix composites were prepared by the suspension polymerization process with initiation reaction using methyl methacrylate (MMA) and methyl acrylate (MA) as raw materials, and potassium persulfate(KPS) as initiator.The effects on flexural strength and bioactivity of the prepared composites fatigue behavior were particularly investigated. The flexural strength, microstructures and phase composition of the composites were characterized by the universal testing machine, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses, respectively. The results show that the composites flexural strength displays no clear change and there are no cracks on the stress surface of the composites within 0～5000 cycles. The deposition of the hydroxyapatite particles increases with extending soaping time of Cf/PMMA-PMA composites dipping in simulated body fluid (SBF) solution, which shows that the prepared composites have good bioactivity. In addition, there is almost no influence on the mechanical performance of the composites when they are soaped in SBF solution.
1. 5 wt% carbon fiber(Cf) reinforced polymethyl methacrylate-polymethyl acrylate ( PMMA-PMA)matrix composites were prepared by the suspension polymerization process with initiation reaction using methyl methacrylate (MMA) and methyl acrylate (MA) as raw materials, and potassium persulfate(KPS) as initiator.The effects on flexural strength and bioactivity of the prepared composites fatigue behavior were particularly investigated. The flexural strength, microstructures and phase composition of the composites were characterized by the universal testing machine, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses, respectively. The results show that the composites flexural strength displays no clear change and there are no cracks on the stress surface of the composites within 0～5000 cycles. The deposition of the hydroxyapatite particles increases with extending soaping time of Cf/PMMA-PMA composites dipping in simulated body fluid (SBF) solution, which shows that the prepared composites have good bioactivity. In addition, there is almost no influence on the mechanical performance of the composites when they are soaped in SBF solution.
2010, 27(2): 43-49.
Abstract:
To prepare the poly( ε-caprolactone) (PCL) porous scaffolds whose structure and property could meet the needs of bone tissue engineering, a series of PCL porous scaffolds were prepared by means of the immersion precipitation method using acetic acid and acetone as the blend solvent, distilled water as the quenching bath and chitosan (CS) as the additives. The effects of solvent, PCL concentration and the amount of CS on the structure and property were studied. The results show that the addition of CS is beneficial for forming three-dimensionally porous scaffolds. With the CS amount increasing, the porosity decreases slightly while the ompressive strength improves. The porosity decreases obviously with the increasing of PCL mass fraction. When the content of acetone is 50 wt% ～60 wt% and the content of PCL is below 10 wt% , three-dimensionally porous PCL scaffolds with satisfying porosity and mechanical property could form by adjusting the amount of CS.
To prepare the poly( ε-caprolactone) (PCL) porous scaffolds whose structure and property could meet the needs of bone tissue engineering, a series of PCL porous scaffolds were prepared by means of the immersion precipitation method using acetic acid and acetone as the blend solvent, distilled water as the quenching bath and chitosan (CS) as the additives. The effects of solvent, PCL concentration and the amount of CS on the structure and property were studied. The results show that the addition of CS is beneficial for forming three-dimensionally porous scaffolds. With the CS amount increasing, the porosity decreases slightly while the ompressive strength improves. The porosity decreases obviously with the increasing of PCL mass fraction. When the content of acetone is 50 wt% ～60 wt% and the content of PCL is below 10 wt% , three-dimensionally porous PCL scaffolds with satisfying porosity and mechanical property could form by adjusting the amount of CS.
2010, 27(2): 50-57.
Abstract:
3D needled C/SiC brake materials were prepared by a combination of chemical vapor infiltration (CVI)and reactive melt infilt ration (RMI). The tribological properties of the as-manufactured C/SiC composites were systematically studied by MM-1000 tribological tester. The microst ructure characteristics of the f riction surface and wear debris were observed by optical microscope and SEM, respectively. The results indicate that at the same braking speed the dry friction coefficient falls down with the increase of braking pressure; and at the same braking pressure the dry friction coefficient firstly increases and then decreases with the increase of braking speed. The dry friction coefficient falls down obviously as the initial braking temperature rising. The wet friction coefficient fades down a little (about 8 % of the dry f riction coefficient) and recovers quickly. The static f riction coefficient is about 0.56～0.61. The wear rate arises with the increase of braking speed at the same braking pressure. When the braking speed is more than 20 m/s, the wear rate increases obviously with the increase of braking pressure.
3D needled C/SiC brake materials were prepared by a combination of chemical vapor infiltration (CVI)and reactive melt infilt ration (RMI). The tribological properties of the as-manufactured C/SiC composites were systematically studied by MM-1000 tribological tester. The microst ructure characteristics of the f riction surface and wear debris were observed by optical microscope and SEM, respectively. The results indicate that at the same braking speed the dry friction coefficient falls down with the increase of braking pressure; and at the same braking pressure the dry friction coefficient firstly increases and then decreases with the increase of braking speed. The dry friction coefficient falls down obviously as the initial braking temperature rising. The wet friction coefficient fades down a little (about 8 % of the dry f riction coefficient) and recovers quickly. The static f riction coefficient is about 0.56～0.61. The wear rate arises with the increase of braking speed at the same braking pressure. When the braking speed is more than 20 m/s, the wear rate increases obviously with the increase of braking pressure.
2010, 27(2): 58-61.
Abstract:
Y2Si2O7 whisker-toughened MoSi2 oxidation resistant coatings were deposited on SiC-C/C composites surface by a hydrothermal electrophoretic deposition process. The phase compositions and microstructures of coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy(SEM). The influences of Y2Si2O7 whisker on the microstructure and oxidation resistance of coatings were particularly investigated. The results show that Y2Si2O7 whisker has a strong influence on the microstructure and oxidation resistant performance of the coated composites. Compared with MoSi2/ SiC coating, Y2Si2O7-MoSi2/SiC coating exhibits dense, uniform and homogeneous morphologies without any microcracks. Y2Si2O7 whisker can effectively prevent coatings from cracking as a result of improving oxidation resistant performance of the coated composites. The as-prepared multi-layer coating can protect C/C composites from oxidation for 100 h at 1773 K with a mass loss of 0.73 %. The corresponding mass loss rate is 1.48×10-5 g·cm-2·h-1.
Y2Si2O7 whisker-toughened MoSi2 oxidation resistant coatings were deposited on SiC-C/C composites surface by a hydrothermal electrophoretic deposition process. The phase compositions and microstructures of coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy(SEM). The influences of Y2Si2O7 whisker on the microstructure and oxidation resistance of coatings were particularly investigated. The results show that Y2Si2O7 whisker has a strong influence on the microstructure and oxidation resistant performance of the coated composites. Compared with MoSi2/ SiC coating, Y2Si2O7-MoSi2/SiC coating exhibits dense, uniform and homogeneous morphologies without any microcracks. Y2Si2O7 whisker can effectively prevent coatings from cracking as a result of improving oxidation resistant performance of the coated composites. The as-prepared multi-layer coating can protect C/C composites from oxidation for 100 h at 1773 K with a mass loss of 0.73 %. The corresponding mass loss rate is 1.48×10-5 g·cm-2·h-1.
2010, 27(2): 62-65.
Abstract:
A study on the preparation and performance of vapor grown carbon fibers(VGCFs) reinforced cement-matrix composites was carried out. VGCFs were prepared from de-oiled asphalt (DOA) by chemical vapor deposition(CVD) and then the cement-matrix composites were prepared with the VGCFs. The results show that the compressive strength and electrical conductivity of VGCFs reinforced cement-matrix composites with lower fiber content can be enhanced. The resistivity of cement-matrix composites decreases and compressive strength increases with weight fraction of VGCFs increasing from 0 to 0.6 % in the paste. A fiber content of 0.4 % by mass of cement is recommended, yielding a resistivity of 1.49×103 Ω·cm. This value is lower by two orders of magnitude the value 5 of 3.25×105 Ω·cm for the same paste without VGCFs. And the compressive st rength increases by 28.8 % as the VGCFs content increases from 0 to 0.4 % by mass of cement .
A study on the preparation and performance of vapor grown carbon fibers(VGCFs) reinforced cement-matrix composites was carried out. VGCFs were prepared from de-oiled asphalt (DOA) by chemical vapor deposition(CVD) and then the cement-matrix composites were prepared with the VGCFs. The results show that the compressive strength and electrical conductivity of VGCFs reinforced cement-matrix composites with lower fiber content can be enhanced. The resistivity of cement-matrix composites decreases and compressive strength increases with weight fraction of VGCFs increasing from 0 to 0.6 % in the paste. A fiber content of 0.4 % by mass of cement is recommended, yielding a resistivity of 1.49×103 Ω·cm. This value is lower by two orders of magnitude the value 5 of 3.25×105 Ω·cm for the same paste without VGCFs. And the compressive st rength increases by 28.8 % as the VGCFs content increases from 0 to 0.4 % by mass of cement .
2010, 27(2): 66-71.
Abstract:
In order to study the mechanical properties of concrete beam with high performance composite rebar (CFRP rebar) during the whole course, a geometrically nonlinear combined shell element analytical model of the beam with CFRP rebar was presented. The Von Karman theory was introduced and the Piola-Kirchhoff st ress matrix and geometrical stiffness matrix were deduced in the local coordinative system. The prest ressed CFRP rebar and the GFRP rebar were respectively modeled by the combined shell element and the layered shell element and then the cont ribution stiffness matrix of the prest ressed CFRP element to the combined shell element was completed.Based on Heterosis selecting integral technology, the shearing lock and the zero energy pattern were both avoided. The nonlinear analytical procedure was compiled, with which the computational results were obtained. The calculations including displacement variation regularity and strain variation regularity of CFRP rebar are in good agreement with those in the experiment results, which show the efficiency of the studied nonlinear element and the correctness of the finished nonlinear procedure. CFRP rebars are still in elastic status when the beam reaches the ultimate loads because of high strength property. The stiffness degraded regularity of the beam was studied by using the strain redistribution coefficient of CFRP rebar , and the result showes that in the final stage of adding loads, the stiffness degradation is decreased when the GFRP rebar substitutes the common steel.
In order to study the mechanical properties of concrete beam with high performance composite rebar (CFRP rebar) during the whole course, a geometrically nonlinear combined shell element analytical model of the beam with CFRP rebar was presented. The Von Karman theory was introduced and the Piola-Kirchhoff st ress matrix and geometrical stiffness matrix were deduced in the local coordinative system. The prest ressed CFRP rebar and the GFRP rebar were respectively modeled by the combined shell element and the layered shell element and then the cont ribution stiffness matrix of the prest ressed CFRP element to the combined shell element was completed.Based on Heterosis selecting integral technology, the shearing lock and the zero energy pattern were both avoided. The nonlinear analytical procedure was compiled, with which the computational results were obtained. The calculations including displacement variation regularity and strain variation regularity of CFRP rebar are in good agreement with those in the experiment results, which show the efficiency of the studied nonlinear element and the correctness of the finished nonlinear procedure. CFRP rebars are still in elastic status when the beam reaches the ultimate loads because of high strength property. The stiffness degraded regularity of the beam was studied by using the strain redistribution coefficient of CFRP rebar , and the result showes that in the final stage of adding loads, the stiffness degradation is decreased when the GFRP rebar substitutes the common steel.
2010, 27(2): 72-76.
Abstract:
TiB2/Ti composites were fabricated by powder metallurgy. The isothermal oxidation behavior of TiB2/Ti composites sintered at different temperatures (800 , 900 , 1000 and 1100℃) at 600 , 700 , 800 and 900℃ in air were investigated. The reaction product s in the oxidation layer were examined by XRD. The surface morphology and cross2sectional microst ructure of the oxidation layer were analyzed by SEM. The results show that an oxidation layer mainly consist s of rutile-TiB2, Fe2O3, Al2O3and B2O3. No other Ti oxides are observed within the oxidation layer. Oxidation kinetics curves of TiB2/Ti composites at 800℃ in air show that the oxidation speed is rapid at the beginning of oxidation, but with the increase of oxidation time the oxidation speed becomes slow due to the formation of an oxidation film. With the increase of volume fraction of TiB2 reinforcements and sintering temperature, the oxidation resistance of TiB2/Ti composites can be increased. It is attributed to the formation of the thin and dense oxidation film.
TiB2/Ti composites were fabricated by powder metallurgy. The isothermal oxidation behavior of TiB2/Ti composites sintered at different temperatures (800 , 900 , 1000 and 1100℃) at 600 , 700 , 800 and 900℃ in air were investigated. The reaction product s in the oxidation layer were examined by XRD. The surface morphology and cross2sectional microst ructure of the oxidation layer were analyzed by SEM. The results show that an oxidation layer mainly consist s of rutile-TiB2, Fe2O3, Al2O3and B2O3. No other Ti oxides are observed within the oxidation layer. Oxidation kinetics curves of TiB2/Ti composites at 800℃ in air show that the oxidation speed is rapid at the beginning of oxidation, but with the increase of oxidation time the oxidation speed becomes slow due to the formation of an oxidation film. With the increase of volume fraction of TiB2 reinforcements and sintering temperature, the oxidation resistance of TiB2/Ti composites can be increased. It is attributed to the formation of the thin and dense oxidation film.
2010, 27(2): 77-83.
Abstract:
The quasi-static indentation tests of the closed-cell aluminum foam under the spherical-end cylindrical indenters were performed. The effects of indenter size, relative density and boundary condition on the indentation hardness, energy absorbing capability and energy absorbing efficiency of aluminum foam were investigated. The results show that the power function can be used to describe the indentation response curves of Al foam under the spherical-end cylindrical indenters and the index of power function linearly increases with the increasing of indenter size. Cross-sectional views of the indented specimens show that the deformation is confined to the region under the indenter with very little transverse spread, and the indentation deformation of aluminum foam is non-uniform. The indentation hardness linearly decreases with the increasing of indenter sizes, but it linearly increases with the increasing of relative density. The energy absorbing efficiency of aluminum foam is not related to the indenter size and relative density. In a certain indentation depth range, the difference between rigid foundation and simply supported conditions on the indentation response of Al foam can be ignored. Finally, the relations between the indentation hardness, energy absorption capacity, the indenter size and relative density are established by fitting the experimental data.
The quasi-static indentation tests of the closed-cell aluminum foam under the spherical-end cylindrical indenters were performed. The effects of indenter size, relative density and boundary condition on the indentation hardness, energy absorbing capability and energy absorbing efficiency of aluminum foam were investigated. The results show that the power function can be used to describe the indentation response curves of Al foam under the spherical-end cylindrical indenters and the index of power function linearly increases with the increasing of indenter size. Cross-sectional views of the indented specimens show that the deformation is confined to the region under the indenter with very little transverse spread, and the indentation deformation of aluminum foam is non-uniform. The indentation hardness linearly decreases with the increasing of indenter sizes, but it linearly increases with the increasing of relative density. The energy absorbing efficiency of aluminum foam is not related to the indenter size and relative density. In a certain indentation depth range, the difference between rigid foundation and simply supported conditions on the indentation response of Al foam can be ignored. Finally, the relations between the indentation hardness, energy absorption capacity, the indenter size and relative density are established by fitting the experimental data.
2010, 27(2): 84-89.
Abstract:
A micro-structure model for the double scale porous media was set up. An mathematical expression of sink function was derived. The governing equation for local unsaturated flow was obtained. The finite element control volume method was employed to simulate the unsaturated flow. Finally, the results from numerical simulations and experiments were compared, which agreed well.
A micro-structure model for the double scale porous media was set up. An mathematical expression of sink function was derived. The governing equation for local unsaturated flow was obtained. The finite element control volume method was employed to simulate the unsaturated flow. Finally, the results from numerical simulations and experiments were compared, which agreed well.
2010, 27(2): 90-94.
Abstract:
By analyzing the non-isothermal RTM process, it is well known that the curing process is the key moment during composite molding. Using control volume and difference scheme methods, the numerical simulation of curing procedure was gotten. In this paper, the internal heat generation caused by the exothermic cure reaction was treated as the nodal lumped load with the help of the control volume technique. The numerical example of a thick plank was compared with experiment data publicly published and good agreement was obtained. The results show that the present procedure is right. The analysis about the influence of the curing process on the material performance on the basis of the procedure is correct.
By analyzing the non-isothermal RTM process, it is well known that the curing process is the key moment during composite molding. Using control volume and difference scheme methods, the numerical simulation of curing procedure was gotten. In this paper, the internal heat generation caused by the exothermic cure reaction was treated as the nodal lumped load with the help of the control volume technique. The numerical example of a thick plank was compared with experiment data publicly published and good agreement was obtained. The results show that the present procedure is right. The analysis about the influence of the curing process on the material performance on the basis of the procedure is correct.
2010, 27(2): 95-100.
Abstract:
In order to deal with the issue of interface fracture including rubber material, a modified virtual crack closure technique was proposed, in which both material and geometric nonlinearities were considered through the method of step-by-step linearization. Firstly, the energy release rate was calculated on the crack tip of rubber specimens with double cracks. It can be seen through the comparison with existing papers that the modified virtual crack closure technique provided is of validity and efficiency. Then, an SLB model with a rubber sandwich was studied, the calculation of modeⅠand Ⅱcomponent of energy release rate indicates that the introduction of a rubber sandwich raises the total energy release rate and greatly increases the proportion of mode Ⅱcomponent. In the fractural analysis of joint-structures with multi-material system, energy release rates under different positions of delaminations were calculated, and the effect of dimension of outer fiber-reinforced composite upon the value of total energy release rate was considered. Finally, a fracture criterion for joint-structures with multi-material system was established.
In order to deal with the issue of interface fracture including rubber material, a modified virtual crack closure technique was proposed, in which both material and geometric nonlinearities were considered through the method of step-by-step linearization. Firstly, the energy release rate was calculated on the crack tip of rubber specimens with double cracks. It can be seen through the comparison with existing papers that the modified virtual crack closure technique provided is of validity and efficiency. Then, an SLB model with a rubber sandwich was studied, the calculation of modeⅠand Ⅱcomponent of energy release rate indicates that the introduction of a rubber sandwich raises the total energy release rate and greatly increases the proportion of mode Ⅱcomponent. In the fractural analysis of joint-structures with multi-material system, energy release rates under different positions of delaminations were calculated, and the effect of dimension of outer fiber-reinforced composite upon the value of total energy release rate was considered. Finally, a fracture criterion for joint-structures with multi-material system was established.
2010, 27(2): 101-107.
Abstract:
A piezoelectric sensors array and active Lamb wave based structural damage imaging method was researched which was helpful to overcome the problems of damage monitoring with multi-mode and mode convention of Lamb wave propagation on plate-like structures, especially on those of composite materials. The principle of time reversal focusing of multi-damage scattering signals was analyzed. Based on this principle, a signal synthesis imaging method based on Shannon complex wavelet and time reversal focusing was proposed. In this method, calculation of time-of-arrival of Lamb wave response signals was an important issue to signal synthesis. A Shannon complex wavelet based time-of-arrival of Lamb wave response signals calculating method was proposed. The signal synthesis imaging method was validated on a carbon fiber composite plate. The result shows that this method could estimate the positions of multi-damages in the same monitoring area efficiently. Compared with the monitoring area of 30 cm ×30 cm, the damage localization errors are no more than 2 cm. It can promote the practical applications of SHM technology.
A piezoelectric sensors array and active Lamb wave based structural damage imaging method was researched which was helpful to overcome the problems of damage monitoring with multi-mode and mode convention of Lamb wave propagation on plate-like structures, especially on those of composite materials. The principle of time reversal focusing of multi-damage scattering signals was analyzed. Based on this principle, a signal synthesis imaging method based on Shannon complex wavelet and time reversal focusing was proposed. In this method, calculation of time-of-arrival of Lamb wave response signals was an important issue to signal synthesis. A Shannon complex wavelet based time-of-arrival of Lamb wave response signals calculating method was proposed. The signal synthesis imaging method was validated on a carbon fiber composite plate. The result shows that this method could estimate the positions of multi-damages in the same monitoring area efficiently. Compared with the monitoring area of 30 cm ×30 cm, the damage localization errors are no more than 2 cm. It can promote the practical applications of SHM technology.
2010, 27(2): 108-112.
Abstract:
The homogenization method has been proved to be a validated and precise method which can be used to predict the effective properties of periodical unit cell composite materials. However due to the complication of the control equation of homogenization method, the homogenization method can not be conveniently realized in commonly used finite element software. The paper describes the boundary force method based on the homogenization method. The homogenization equations were converted to a general three dimension stress problem using Gauss theory in the boundary force method. The surface distributed force of heterogenous material interface is given and the homogenization method control equation is solved by applying the surface boundary force. The effective properties of unidirectional composite material and three dimension four direction braided composite material were calculated by the boundary force method, and the results show that the predictions compare well with theoretical and experimental results.
The homogenization method has been proved to be a validated and precise method which can be used to predict the effective properties of periodical unit cell composite materials. However due to the complication of the control equation of homogenization method, the homogenization method can not be conveniently realized in commonly used finite element software. The paper describes the boundary force method based on the homogenization method. The homogenization equations were converted to a general three dimension stress problem using Gauss theory in the boundary force method. The surface distributed force of heterogenous material interface is given and the homogenization method control equation is solved by applying the surface boundary force. The effective properties of unidirectional composite material and three dimension four direction braided composite material were calculated by the boundary force method, and the results show that the predictions compare well with theoretical and experimental results.
2010, 27(2): 113-116.
Abstract:
By means of the introduction of the classic laminate theory with considering hygrothermal effect into the finite element method, the mechanical properties of composite in hygrothermal environment were accurately forecasted and the damage evolution was tracked through careful consideration of equivalent lamina parameters reduction and unloading after initial damage and estimation of final damage. The tensile and compressive strengths of three different lay-up composite laminates in hygrothermal environment were studied. There is good agreementbetween experiment and simulation results.
By means of the introduction of the classic laminate theory with considering hygrothermal effect into the finite element method, the mechanical properties of composite in hygrothermal environment were accurately forecasted and the damage evolution was tracked through careful consideration of equivalent lamina parameters reduction and unloading after initial damage and estimation of final damage. The tensile and compressive strengths of three different lay-up composite laminates in hygrothermal environment were studied. There is good agreementbetween experiment and simulation results.
2010, 27(2): 117-122.
Abstract:
Damage tolerance analysis and design are usually needed for modern helicopter rotor blades, while the influence of damage on the vibration performance of rotor blade structures is an important aspect. Vibration performance analysis was carried out here by the finite element method for a selected segment of helicopter composite blades with a perforation damage. Comparison of the result was performed with that of the blade segment without damage. The effect of the size and location of the perforation on vibration performance was obtained. The results show that the vibration modes of the rotating blade segment are the same with those of the still segment, while all the vibration frequencies have increased. The damage on the blade segment is more serious when the perforation size is greater. But the perforation damage does not change the modes of the blade segment, and the vibration frequency variations are small. The frequency variation depends on the perforation location. The perforations located in the blade segment root or front edge of the blade section have greater effect on the vibration frequencies of the blade segment.
Damage tolerance analysis and design are usually needed for modern helicopter rotor blades, while the influence of damage on the vibration performance of rotor blade structures is an important aspect. Vibration performance analysis was carried out here by the finite element method for a selected segment of helicopter composite blades with a perforation damage. Comparison of the result was performed with that of the blade segment without damage. The effect of the size and location of the perforation on vibration performance was obtained. The results show that the vibration modes of the rotating blade segment are the same with those of the still segment, while all the vibration frequencies have increased. The damage on the blade segment is more serious when the perforation size is greater. But the perforation damage does not change the modes of the blade segment, and the vibration frequency variations are small. The frequency variation depends on the perforation location. The perforations located in the blade segment root or front edge of the blade section have greater effect on the vibration frequencies of the blade segment.
2010, 27(2): 123-126.
Abstract:
Delamination in laminated composites with uncertain parameters was studied. Based on the interval mathematics, with uncertain parameters being modelled as interval numbers, an interval analysis method was proposed about delamination in laminated composites with uncertain parameters. The interval analysis was compared with the probability method with respect to the mathematical proof and numerical examples, which verifies the reliability. For a fixed pre-crack length or layer number, the upper and lower critical loads of DCB with uncertain parameters were obtained. It would provide reference for engineering design.
Delamination in laminated composites with uncertain parameters was studied. Based on the interval mathematics, with uncertain parameters being modelled as interval numbers, an interval analysis method was proposed about delamination in laminated composites with uncertain parameters. The interval analysis was compared with the probability method with respect to the mathematical proof and numerical examples, which verifies the reliability. For a fixed pre-crack length or layer number, the upper and lower critical loads of DCB with uncertain parameters were obtained. It would provide reference for engineering design.
2010, 27(2): 127-132.
Abstract:
Robust optimization design of aeroelastic st ructures was investigated by using the genetic-gradient hybrid algorithm. The method was applied to an optimization design process of a robust aeroelastic structure with the high-aspect-ratio composite wing, which demonst rates the applicability and the efficiency of the method. The difference was revealed by comparing a robust structural optimal design with a traditional optimal design. The research indicates that a structure resulting from an optimization, in which the robustness constrains are taken into accoun , is more anti-jamming than a structure resulting from a traditional way, when the design variables are uncertain. However, the mass increment is paid for satisfying the robustness requirement. The higher robustness the structure needs, the greater the mass increment is.
Robust optimization design of aeroelastic st ructures was investigated by using the genetic-gradient hybrid algorithm. The method was applied to an optimization design process of a robust aeroelastic structure with the high-aspect-ratio composite wing, which demonst rates the applicability and the efficiency of the method. The difference was revealed by comparing a robust structural optimal design with a traditional optimal design. The research indicates that a structure resulting from an optimization, in which the robustness constrains are taken into accoun , is more anti-jamming than a structure resulting from a traditional way, when the design variables are uncertain. However, the mass increment is paid for satisfying the robustness requirement. The higher robustness the structure needs, the greater the mass increment is.
In-plane compressive mechanics behavior and failure mechanism for SW200/ LWR-2 glass-woven composite
2010, 27(2): 133-139.
Abstract:
In order to investigate the in-plane compressive mechanics behavior of the SW200/LWR-2 glass-woven composite and establish the constitutive model, the in-plane compressive tests for this material were performed with the strain rates of 0. 001 s -1, 0. 1 s-1, 500 s-1 and a temperature range from - 55 ℃ to 100 ℃. The dynamic compressive tests were carried out using the SHPB technique, a constant loading strain rate was achieved with a waveform shaper, and it is also verified that the stresses on the two sides of the specimen are in balance. Experimental results show that the mechanical properties of the SW200/LWR-2 glass-woven composite are sensitive to the strain rate and temperature; its strength increases with increasing strain rate, and decreasing temperature. Macro- and microscopical observation reveals that the samples under quasi-static loading presents hearing failure mode , and the fibre bundles of the samples are extensively debonded and pulled out. The samples under dynamic loading present shearing and delamination modes with lots of rags, and at the same time the debonding of the fibre bundles is restrained. Finally, based on the damage mechanics theory, a compressive constitutive model including the strain rate and temperature effects for the SW200/LWR-2 composite is established, and the modeling results have good agreement with the experimental results.
In order to investigate the in-plane compressive mechanics behavior of the SW200/LWR-2 glass-woven composite and establish the constitutive model, the in-plane compressive tests for this material were performed with the strain rates of 0. 001 s -1, 0. 1 s-1, 500 s-1 and a temperature range from - 55 ℃ to 100 ℃. The dynamic compressive tests were carried out using the SHPB technique, a constant loading strain rate was achieved with a waveform shaper, and it is also verified that the stresses on the two sides of the specimen are in balance. Experimental results show that the mechanical properties of the SW200/LWR-2 glass-woven composite are sensitive to the strain rate and temperature; its strength increases with increasing strain rate, and decreasing temperature. Macro- and microscopical observation reveals that the samples under quasi-static loading presents hearing failure mode , and the fibre bundles of the samples are extensively debonded and pulled out. The samples under dynamic loading present shearing and delamination modes with lots of rags, and at the same time the debonding of the fibre bundles is restrained. Finally, based on the damage mechanics theory, a compressive constitutive model including the strain rate and temperature effects for the SW200/LWR-2 composite is established, and the modeling results have good agreement with the experimental results.
2010, 27(2): 140-147.
Abstract:
The theory of two-leveled randomly-enlarging critical core was put forward to predict the tensile strength of unidirectional bundle-reinforced composites. According to the manufacture technologies of FRP, a model was established to calculate the fiber spacing and the quantity of fibers in a bundle. The fibers in composites were treated through 2 levels: fiber bundle, and array of fiber bundles. The father core and son core were put forward so as to precisely describe the structure of a critical core. Beyerleinps formula was adopted to calculate the average stress concent ration factor of the bundle, which is caused by the sequential failure of bundles. Sivasambups formula was applied to calculating the stress concentration factor of the fiber inside bundle, which is caused by the sequential failure of fibers. Based on the propagation mode of fiberps failure, according to the statistics theory, considering the enlarging ineffective length inside the bundle, the formulas calculating the failure possibility of composites were deduced. A computer program was compiled. Through this program, the tensile strengths of plastics reinforced respectively by unidirectional woven rovings of S glass, E glass, and Basalt fiber were predicted. Meanwhile, along with the mechanical performance of the matrix under tension and shearing, the tensile strengths of these FRPs were gained through experiments. Then , the predicted result s were compared with the experiment results. Research result shows that the predicted results, which meet the experiments, can be gained by directly inputting the material and geomet ry parameters of experiment specimens.
The theory of two-leveled randomly-enlarging critical core was put forward to predict the tensile strength of unidirectional bundle-reinforced composites. According to the manufacture technologies of FRP, a model was established to calculate the fiber spacing and the quantity of fibers in a bundle. The fibers in composites were treated through 2 levels: fiber bundle, and array of fiber bundles. The father core and son core were put forward so as to precisely describe the structure of a critical core. Beyerleinps formula was adopted to calculate the average stress concent ration factor of the bundle, which is caused by the sequential failure of bundles. Sivasambups formula was applied to calculating the stress concentration factor of the fiber inside bundle, which is caused by the sequential failure of fibers. Based on the propagation mode of fiberps failure, according to the statistics theory, considering the enlarging ineffective length inside the bundle, the formulas calculating the failure possibility of composites were deduced. A computer program was compiled. Through this program, the tensile strengths of plastics reinforced respectively by unidirectional woven rovings of S glass, E glass, and Basalt fiber were predicted. Meanwhile, along with the mechanical performance of the matrix under tension and shearing, the tensile strengths of these FRPs were gained through experiments. Then , the predicted result s were compared with the experiment results. Research result shows that the predicted results, which meet the experiments, can be gained by directly inputting the material and geomet ry parameters of experiment specimens.
2010, 27(2): 148-153.
Abstract:
On the basis of microscopic observations, a reasonable 3D unit cell model of 3-dimensional (3D) five- directional braided composites was established. The yarn packing factor and the cross-section deformation due to the later compression, which were neglected in the existing model, were both considered in the model. Based on the unit cell model, the elastic modulus of the material was calculated by 3D finite element analysis ( FEA). The numerical results show good agreement with the experiment data. The stress field of the model under tensile load was analyzed, which provides a basis for farther strength prediction.
On the basis of microscopic observations, a reasonable 3D unit cell model of 3-dimensional (3D) five- directional braided composites was established. The yarn packing factor and the cross-section deformation due to the later compression, which were neglected in the existing model, were both considered in the model. Based on the unit cell model, the elastic modulus of the material was calculated by 3D finite element analysis ( FEA). The numerical results show good agreement with the experiment data. The stress field of the model under tensile load was analyzed, which provides a basis for farther strength prediction.
2010, 27(2): 154-160.
Abstract:
Tackified fabric is the material which is used in liquid composite molding, and it can improve the shape precision and dimension precision of the composite component. The property of the fabric is changed due to the tackifier. Based on the picture frame experiment, a theoretical model was built. The effects of the bending rigidity and friction coefficient of tackified yarn on the shear behavior were analysed in the article, and the axial force of yarn during the shear process was considered in the model. In addition the variation of width of tackified yarn during the shear loading was observed by the microscope, and the influence of tackifier and fabric architecture was considered. An shear model was derived from the equilibrium equation. The results show that the model can predict the shear performance of the tackified plain fabric well.
Tackified fabric is the material which is used in liquid composite molding, and it can improve the shape precision and dimension precision of the composite component. The property of the fabric is changed due to the tackifier. Based on the picture frame experiment, a theoretical model was built. The effects of the bending rigidity and friction coefficient of tackified yarn on the shear behavior were analysed in the article, and the axial force of yarn during the shear process was considered in the model. In addition the variation of width of tackified yarn during the shear loading was observed by the microscope, and the influence of tackifier and fabric architecture was considered. An shear model was derived from the equilibrium equation. The results show that the model can predict the shear performance of the tackified plain fabric well.
2010, 27(2): 161-168.
Abstract:
The cohesive zone model (CZM) was employed to simulate the delamination and random crack initiation in composite joints. A bilinear cohesive law incorporating mode Ⅰ, Ⅱ and mixed mode was presented, which was validated by the simulation of double cantilever beam (DCB) test. Cohesive elements were inserted into the space between every two solid elements to predict the random crack initiation in the filler at the root of the composite joint. The composite joint was simulated under pull-off load, and the numerical result is in good agreement with experimental one. In addition, a series of simulation was carried out under different conditions, i. e. different strength of matrix and adhesive, different radius and different filler property. The numerical result shows that the strengths of matrix, adhesive and filler have great influence on the loading capability and the failure modes of the composite joint. The performance of the structure increases with increasing the filler radius.
The cohesive zone model (CZM) was employed to simulate the delamination and random crack initiation in composite joints. A bilinear cohesive law incorporating mode Ⅰ, Ⅱ and mixed mode was presented, which was validated by the simulation of double cantilever beam (DCB) test. Cohesive elements were inserted into the space between every two solid elements to predict the random crack initiation in the filler at the root of the composite joint. The composite joint was simulated under pull-off load, and the numerical result is in good agreement with experimental one. In addition, a series of simulation was carried out under different conditions, i. e. different strength of matrix and adhesive, different radius and different filler property. The numerical result shows that the strengths of matrix, adhesive and filler have great influence on the loading capability and the failure modes of the composite joint. The performance of the structure increases with increasing the filler radius.
2010, 27(2): 169-175.
Abstract:
Based on the dispersion equation and the displacement field expression of ultrasonic guided waves, ultrasonic guided wave amplitude spectra have been studied numerically for a unidirectional carbon fiber sheet. The gray images of ultrasonic guided wave amplitude spectra that can straightforwardly characterize the degree of fatigue in composite sheets are obtained. The numerical results show that, with the tension-tension or bending fatigue loading, there is a monotonic relationship between the average gray value of gray images of ultrasonic guided wave amplitude spectra and the change rate of equivalent Young‘s modulus or equivalent shear modulus. It is concluded that the ultrasonic guided wave amplitude spectra may be used to effectively characterize the early stages of fatigue damage in composite sheets.
Based on the dispersion equation and the displacement field expression of ultrasonic guided waves, ultrasonic guided wave amplitude spectra have been studied numerically for a unidirectional carbon fiber sheet. The gray images of ultrasonic guided wave amplitude spectra that can straightforwardly characterize the degree of fatigue in composite sheets are obtained. The numerical results show that, with the tension-tension or bending fatigue loading, there is a monotonic relationship between the average gray value of gray images of ultrasonic guided wave amplitude spectra and the change rate of equivalent Young‘s modulus or equivalent shear modulus. It is concluded that the ultrasonic guided wave amplitude spectra may be used to effectively characterize the early stages of fatigue damage in composite sheets.
2010, 27(2): 176-182.
Abstract:
Considering the effects of geometrical nonlinearity and damping, the vibration differential equation of simply supported rectangular orthotropic laminated plate excited by two-term harmonic forces was established. The non-dimensional Duffing nonlinear forced vibration equation was deduced by using Galerkin method. The amplitude frequency response equation of system steady motion under combination resonance was obtained by the method of multiple scales. Based on Lyapunov stable theory, the critical conditions of steady-state solutionsp stability were got. By some examples, the influence of different parameters on nonlinear combination resonances and bifurcation properties of system was analyzed. The results show that the detuning parameter, thickness of plate, damping and amplitude of excitation have different influences on combination resonance and bifurcation. With the change of parameters, the jump phenomenon, hysteresis phenomenon and unstable solutions will occur. It is also shown that the system presents relatively complicated dynamics behaviors, and there exists multi-valued phenomenon, and the dynamics behaviors will change in some values.
Considering the effects of geometrical nonlinearity and damping, the vibration differential equation of simply supported rectangular orthotropic laminated plate excited by two-term harmonic forces was established. The non-dimensional Duffing nonlinear forced vibration equation was deduced by using Galerkin method. The amplitude frequency response equation of system steady motion under combination resonance was obtained by the method of multiple scales. Based on Lyapunov stable theory, the critical conditions of steady-state solutionsp stability were got. By some examples, the influence of different parameters on nonlinear combination resonances and bifurcation properties of system was analyzed. The results show that the detuning parameter, thickness of plate, damping and amplitude of excitation have different influences on combination resonance and bifurcation. With the change of parameters, the jump phenomenon, hysteresis phenomenon and unstable solutions will occur. It is also shown that the system presents relatively complicated dynamics behaviors, and there exists multi-valued phenomenon, and the dynamics behaviors will change in some values.
