2008 Vol. 25, No. 1
2008, 25(1): 1-10.
Abstract:
The development of aviation industry, especially the large commercial aircraft industry, has boosted the
progress of composite materials technology. Applications of advanced composite materials have created new standard and market access threshold for next generation commercial aircraft. There has been a series of plans to develop and apply composite material technology in aircraft industry in the western contries. In China, research in this field is lagging behind. With the background of large aircraft development plan taken as national key project, the suggestions were put forward on accelerated development of composite technology from stratagem, organizational, technical and industrial aspects.
The development of aviation industry, especially the large commercial aircraft industry, has boosted the
progress of composite materials technology. Applications of advanced composite materials have created new standard and market access threshold for next generation commercial aircraft. There has been a series of plans to develop and apply composite material technology in aircraft industry in the western contries. In China, research in this field is lagging behind. With the background of large aircraft development plan taken as national key project, the suggestions were put forward on accelerated development of composite technology from stratagem, organizational, technical and industrial aspects.
2008, 25(1): 11-16.
Abstract:
For polymer bonded Terfenol-D composites, the difference between cure temperature and application
temperature and the difference in thermal expansion coefficient between the magnetost rictive particle and polymer matrix result in thermal stress in particles, which will influence the magnetost rictive properties of the smart composites. In this paper, the value of the thermal stress and the factors which influence it are analyzed theoretically, which indicates that the thermal stress increases with the increase of the temperature difference and the decrease of the particle volume fraction. Then at various cure temperatures and a constant orientation field, 20% and 50% volume fraction epoxy-bonded Terfenol-D composites were fabricated and tested at room temperature. The experimental results indicate that both the dynamic and static magnetostrictive properties of the composites increase with the increasing cure temperature because of the increase of the thermal stress. But they do not decrease with the increase of the particle volume fraction although the thermal stress decreases, because the positive effect of the increase of the function phase offsets or even exceeds the negative effect.
For polymer bonded Terfenol-D composites, the difference between cure temperature and application
temperature and the difference in thermal expansion coefficient between the magnetost rictive particle and polymer matrix result in thermal stress in particles, which will influence the magnetost rictive properties of the smart composites. In this paper, the value of the thermal stress and the factors which influence it are analyzed theoretically, which indicates that the thermal stress increases with the increase of the temperature difference and the decrease of the particle volume fraction. Then at various cure temperatures and a constant orientation field, 20% and 50% volume fraction epoxy-bonded Terfenol-D composites were fabricated and tested at room temperature. The experimental results indicate that both the dynamic and static magnetostrictive properties of the composites increase with the increasing cure temperature because of the increase of the thermal stress. But they do not decrease with the increase of the particle volume fraction although the thermal stress decreases, because the positive effect of the increase of the function phase offsets or even exceeds the negative effect.
2008, 25(1): 17-22.
Abstract:
Using paraffin as the phase change material, and polyvinyl alcohol ( PVA) as the matrix, the energy storage fibers with a phase change material mass f raction 30 % were prepared by the wet spinning process. Structure
and phase change properties were characterized by scanning electron microscope, wide angle X-rays diffraction and differential scanning calorimetry. The results show that the paraffin as the islands is dispersed in the acetalized PVA fiber matrix, and the crystalline region account s for 34 % of the whole fibers. When the fibers are heat-drawn in 2～4 times , the heat efficiency varies f rom 81. 9 % to 71. 2 %, and af ter 25 times washing, the remaining heat efficiency is remarkable. The linear density, strength and initial modulus of the paraffin/ PVA fibers are 0. 62～0. 32 tex , 28.1～66. 2 N/ tex , 373～794 N/tex, respectively. The softening point in water is 108℃, which is suitable for textile use.
Using paraffin as the phase change material, and polyvinyl alcohol ( PVA) as the matrix, the energy storage fibers with a phase change material mass f raction 30 % were prepared by the wet spinning process. Structure
and phase change properties were characterized by scanning electron microscope, wide angle X-rays diffraction and differential scanning calorimetry. The results show that the paraffin as the islands is dispersed in the acetalized PVA fiber matrix, and the crystalline region account s for 34 % of the whole fibers. When the fibers are heat-drawn in 2～4 times , the heat efficiency varies f rom 81. 9 % to 71. 2 %, and af ter 25 times washing, the remaining heat efficiency is remarkable. The linear density, strength and initial modulus of the paraffin/ PVA fibers are 0. 62～0. 32 tex , 28.1～66. 2 N/ tex , 373～794 N/tex, respectively. The softening point in water is 108℃, which is suitable for textile use.
2008, 25(1): 23-27.
Abstract:
The missile cabin is unable to be fabricated by normal RTM (Resin transfer molding) in one step for it slarge size and complicated internal structure. The bladder assisted RTM was used to fabricate the missile cabin in
this paper. This process does not need a metal mandrel, the whole mold is light and the component consolidation is apparent by the inflated bladder pressure. The results show that the fiber volume fraction of the specimen formed by bladder assisted RTM reaches 61 %, and the tensile strength and the flexural strength are improved by 25 % and 26 % respectively compared to that by normal RTM. The missile cabin ultimate axial compression load and ultimate flexural load reach 130 % and 132 % of the target ultimate load.
The missile cabin is unable to be fabricated by normal RTM (Resin transfer molding) in one step for it slarge size and complicated internal structure. The bladder assisted RTM was used to fabricate the missile cabin in
this paper. This process does not need a metal mandrel, the whole mold is light and the component consolidation is apparent by the inflated bladder pressure. The results show that the fiber volume fraction of the specimen formed by bladder assisted RTM reaches 61 %, and the tensile strength and the flexural strength are improved by 25 % and 26 % respectively compared to that by normal RTM. The missile cabin ultimate axial compression load and ultimate flexural load reach 130 % and 132 % of the target ultimate load.
2008, 25(1): 28-34.
Abstract:
Cu/n-TiO2/PBO composite fibers were prepared with nano-TiO2 deposited on PBO fibers by dipping,
and then Cu deposited on nano-TiO2 thin films by electroless plating. The main effective factors on the nano-TiO2 and Cu depositing rates were studied. The results show that the concentration ratio ofnano-TiO2 and coupling reagent works as the key effective factor on the nano-TiO2 depositing rate. Thenano-TiO2 is well deposited on PBO fibers when the concent ration ratio is 1:1. 2. The main effective factors on the Cu depositing rate are bath composition, reaction time and reaction temperature. Cu is well deposited on then-TiO2/PBO composite fibers under the condition of CuSO4·5H2O 12 g ·L-1,KNaC4H4 O6 8 g·L-1,HCHO 6 mL ·L-1, NaOH 10 g·L-1, reaction temperature 50℃ and reaction time 20 min.
Cu/n-TiO2/PBO composite fibers were prepared with nano-TiO2 deposited on PBO fibers by dipping,
and then Cu deposited on nano-TiO2 thin films by electroless plating. The main effective factors on the nano-TiO2 and Cu depositing rates were studied. The results show that the concentration ratio ofnano-TiO2 and coupling reagent works as the key effective factor on the nano-TiO2 depositing rate. Thenano-TiO2 is well deposited on PBO fibers when the concent ration ratio is 1:1. 2. The main effective factors on the Cu depositing rate are bath composition, reaction time and reaction temperature. Cu is well deposited on then-TiO2/PBO composite fibers under the condition of CuSO4·5H2O 12 g ·L-1,KNaC4H4 O6 8 g·L-1,HCHO 6 mL ·L-1, NaOH 10 g·L-1, reaction temperature 50℃ and reaction time 20 min.
2008, 25(1): 35-39.
Abstract:
Expanded graphite/poly (ethylene terephthalate) ( EG/PET) conductive composites were prepared by
the melt2blending method. The effect s of the preparation method on the microst ructures and conductivity properties of the composites were studied by scanning elect ron microscopy (SEM) and conductivity measurement. The results show that the graphite nanosheet s are effectively dispersed in the PET matrix with the assistance of the shear effect on EG and the interaction between EG and PET, which promotes the formation of the conductive network and makes the percolation threshold value of EG/ PET composites only 3. 14 %. The strong mutual effects between the epoxy group and the functional groups on EG surface cause the epoxy resin to exert more exfoliation effect on EG,which leads to the percolation value to descend to 1. 80 %. Using the classic statistic percolation theory, the conductivity behavior of the composites was investigated. The nonuniversal critical exponent ( t) should be at tributed to the anisotropy of conductivity, the existence of the tunneling conduction above the percolation threshold and the particular structure.
Expanded graphite/poly (ethylene terephthalate) ( EG/PET) conductive composites were prepared by
the melt2blending method. The effect s of the preparation method on the microst ructures and conductivity properties of the composites were studied by scanning elect ron microscopy (SEM) and conductivity measurement. The results show that the graphite nanosheet s are effectively dispersed in the PET matrix with the assistance of the shear effect on EG and the interaction between EG and PET, which promotes the formation of the conductive network and makes the percolation threshold value of EG/ PET composites only 3. 14 %. The strong mutual effects between the epoxy group and the functional groups on EG surface cause the epoxy resin to exert more exfoliation effect on EG,which leads to the percolation value to descend to 1. 80 %. Using the classic statistic percolation theory, the conductivity behavior of the composites was investigated. The nonuniversal critical exponent ( t) should be at tributed to the anisotropy of conductivity, the existence of the tunneling conduction above the percolation threshold and the particular structure.
2008, 25(1): 40-45.
Abstract:
Using polypropylene ( PP) and ramie cloth as raw materials, and maleated polypropylene (MAPP) as
the compatibilizer, the composites were compressed at 175℃ under 5, 10, 15 and 20 MPa , respectively. The
effects of the mass fractions of both MAPP and ramie cloth and pressures on the mechanical properties of the composites were investigated. The maximum tensile strength of 46. 72 MPa and flexural strength of 68. 43 MPa of the composites are obtained when 3 % and 5 % MAPP are used, which are increased from those of the composites without MAPP by 50.95 % and 61. 81 % , respectively. Both the tensile and flexural moduli increase because of the application of MAPP, while the elongations at break will decrease. When more ramie cloths are used, the modulus always increases; the composites containing 10 % or 20 % ramie cloth have greater strength when formed under lower pressures (5, 10 MPa), but no regulations can be found for the effects of pressures on the strength when the mass fractions of ramie cloth are more than 20 %.
Using polypropylene ( PP) and ramie cloth as raw materials, and maleated polypropylene (MAPP) as
the compatibilizer, the composites were compressed at 175℃ under 5, 10, 15 and 20 MPa , respectively. The
effects of the mass fractions of both MAPP and ramie cloth and pressures on the mechanical properties of the composites were investigated. The maximum tensile strength of 46. 72 MPa and flexural strength of 68. 43 MPa of the composites are obtained when 3 % and 5 % MAPP are used, which are increased from those of the composites without MAPP by 50.95 % and 61. 81 % , respectively. Both the tensile and flexural moduli increase because of the application of MAPP, while the elongations at break will decrease. When more ramie cloths are used, the modulus always increases; the composites containing 10 % or 20 % ramie cloth have greater strength when formed under lower pressures (5, 10 MPa), but no regulations can be found for the effects of pressures on the strength when the mass fractions of ramie cloth are more than 20 %.
2008, 25(1): 46-51.
Abstract:
In order to carry out a numerical simulation of the unstable temperature field and curing degree in the
pult rusion process of GFRP, a mathematical model was established for the variation of temperature dist ribution and curing degree on the basis of curing kinetic and unstable thermal conduction theories. The kinetics parameters based on the models are determined by using differential scanning calorimetry (DSC). A numerical model was established for the temperature and curing degree by combining the two-dimensional finite element with finite differential and the coupled question was solved by using Euler-Cauch step- by- step iterative method. The effect s of processing parameters including pulling speed, die wall temperature and initial temperature on the profile of curing degree and temperature in the die are discussed with the pult rusion simulation program compiled with FEPG. The result of the numerical simulation corresponds well to the FBG sensor test result, which provides useful information for the pultrusion design.
In order to carry out a numerical simulation of the unstable temperature field and curing degree in the
pult rusion process of GFRP, a mathematical model was established for the variation of temperature dist ribution and curing degree on the basis of curing kinetic and unstable thermal conduction theories. The kinetics parameters based on the models are determined by using differential scanning calorimetry (DSC). A numerical model was established for the temperature and curing degree by combining the two-dimensional finite element with finite differential and the coupled question was solved by using Euler-Cauch step- by- step iterative method. The effect s of processing parameters including pulling speed, die wall temperature and initial temperature on the profile of curing degree and temperature in the die are discussed with the pult rusion simulation program compiled with FEPG. The result of the numerical simulation corresponds well to the FBG sensor test result, which provides useful information for the pultrusion design.
2008, 25(1): 52-58.
Abstract:
The sodium polystyrene sulfonate (PSS) /polyaniline (PANI) composite films were prepared from
aniline (AN) monomers by in-situ polymerization , self2acid2doping and layer-by-layer self-assembly through the electrostatic force. In order to completely know the factors to control the nanostructure, the progress of polymerization of the PSS/PANI films was monitored by the UV-Vis spectra , and the influences of reaction conditions , such as subst rates , amount s of oxidant , and dipping time on the st ructure of PSS /PANI composite films were also stud2 ied. The (PSS/PANI) ncomposite films with different nanost ructures were then prepared at different aniline concen2 t rations. Atomic force microscope (AFM) , field emission scanning elect ron microscope (FESEM) and ellipsomet rywere employed to characterize the (PSS/ PANI)n composite films. By optimizing the deposition conditions, the thickness of the PSS/ PANI bilayer was controlled within 40～100 nm and the electrical conductivity of the PSS/PANI bilayer was 2. 675 mS ·cm-1. The uniform (PSS/PANI)8 composite films were also prepared under the optimumconditions. The result s of the thermal gravimetry analysis (TGA) showed that the thermal stability of (PSS/PANI) ncomposite films was stronger than that of general PSS/PANI composite films.
The sodium polystyrene sulfonate (PSS) /polyaniline (PANI) composite films were prepared from
aniline (AN) monomers by in-situ polymerization , self2acid2doping and layer-by-layer self-assembly through the electrostatic force. In order to completely know the factors to control the nanostructure, the progress of polymerization of the PSS/PANI films was monitored by the UV-Vis spectra , and the influences of reaction conditions , such as subst rates , amount s of oxidant , and dipping time on the st ructure of PSS /PANI composite films were also stud2 ied. The (PSS/PANI) ncomposite films with different nanost ructures were then prepared at different aniline concen2 t rations. Atomic force microscope (AFM) , field emission scanning elect ron microscope (FESEM) and ellipsomet rywere employed to characterize the (PSS/ PANI)n composite films. By optimizing the deposition conditions, the thickness of the PSS/ PANI bilayer was controlled within 40～100 nm and the electrical conductivity of the PSS/PANI bilayer was 2. 675 mS ·cm-1. The uniform (PSS/PANI)8 composite films were also prepared under the optimumconditions. The result s of the thermal gravimetry analysis (TGA) showed that the thermal stability of (PSS/PANI) ncomposite films was stronger than that of general PSS/PANI composite films.
2008, 25(1): 59-63.
Abstract:
To enhance the interfacial adhesion between the carbon fibers and the epoxy resin matrix, the phenolic
resin surface treatment agent is used. The influences of different concent rations of the phenolic resin treatment agent on the interfacial adhesion of the carbon fiber reinforced epoxy resin composites were investigated by interlaminar shear strength (ILSS), atomic force microscopy (AFM), X-ray photoelectron spect roscopy (XPS) and scanning electron microscopy (SEM). The results of XPS and AFM analysis indicate that the interface of carbon fiber is grafted by the phenolic resin surface treatment agent. The surface of carbon fiber becomes more and more smooth if the concent ration of the phenolic resin surface treatment agent increases. The results of SEM and ILSS indicate that with the increasing of the concentration of the phenolic resin agent the interfacial adhesion is improved greatly.
To enhance the interfacial adhesion between the carbon fibers and the epoxy resin matrix, the phenolic
resin surface treatment agent is used. The influences of different concent rations of the phenolic resin treatment agent on the interfacial adhesion of the carbon fiber reinforced epoxy resin composites were investigated by interlaminar shear strength (ILSS), atomic force microscopy (AFM), X-ray photoelectron spect roscopy (XPS) and scanning electron microscopy (SEM). The results of XPS and AFM analysis indicate that the interface of carbon fiber is grafted by the phenolic resin surface treatment agent. The surface of carbon fiber becomes more and more smooth if the concent ration of the phenolic resin surface treatment agent increases. The results of SEM and ILSS indicate that with the increasing of the concentration of the phenolic resin agent the interfacial adhesion is improved greatly.
2008, 25(1): 64-68.
Abstract:
The porous n-HA/PA-6 composite was developed by the injection molding technique, and it s performances were investigated by SEM, XRD, and IR. The results indicate that the obtained porous composite has inter-connected and uniformly dist ributed pores , and the diameters of pores range from about 100 μm to 700 μm with the average diameters between 300 μm and 500 μm. Many micropores can be observed on the wall of macropores. The total porosity of the porous composite could be controlled by adjusting the processing parameters, and can reach as high as 88. 6%. The interconnected porosity decreases with the decrease of total porosity. Additionally, the porous composite has good compressive strength (1. 1～15. 6 MPa) and compressive modulus (0. 4～4 GPa), which increases with the growth of the mass fractions of n-HA in the composite. The structures and properties of HA and PA-6 in the n-HA/PA-6 composite can not be affected by the foamer and the process of pores formation. This porous composite is a promising material for tissue engineering scaffold materials and non-load bearing bone implants.
The porous n-HA/PA-6 composite was developed by the injection molding technique, and it s performances were investigated by SEM, XRD, and IR. The results indicate that the obtained porous composite has inter-connected and uniformly dist ributed pores , and the diameters of pores range from about 100 μm to 700 μm with the average diameters between 300 μm and 500 μm. Many micropores can be observed on the wall of macropores. The total porosity of the porous composite could be controlled by adjusting the processing parameters, and can reach as high as 88. 6%. The interconnected porosity decreases with the decrease of total porosity. Additionally, the porous composite has good compressive strength (1. 1～15. 6 MPa) and compressive modulus (0. 4～4 GPa), which increases with the growth of the mass fractions of n-HA in the composite. The structures and properties of HA and PA-6 in the n-HA/PA-6 composite can not be affected by the foamer and the process of pores formation. This porous composite is a promising material for tissue engineering scaffold materials and non-load bearing bone implants.
2008, 25(1): 69-74.
Abstract:
The pectin/poly (vinyl alcohol) composite (CoPP) hydrogel was prepared by low f requency oscillation
and freezing-thawing. The structure of CoPP hydrogel was characterized by FTIR, DSC, XRD and SEM, the swelling properties were observed, and the diffusion of water and the swelling dynamics were also discussed. The experimental results show that CoPP hydrogel is porous, and has two kinds of crystal regions. The diffusion characteristic index which water molecule immerses into CoPP hydrogel was near 0. 5, which indicates the diffusion is in Fick model. The swelling velocity constant of CoPP, the swelling ratio of mass (197. 38 %～252. 49 %) and swelling ratio of volume (241. 47 %～308. 93 %) of CoPP at the swelling equilibration were superior to those of poly (vinylalcohol) (PVA) hydrogel. Therefore, the swelling properties of CoPP composite hydrogel are faster and larger, which makes it possible to implant the artificial nucleus pulposus prosthesis in smaller size with the minimally invasive surgery.
The pectin/poly (vinyl alcohol) composite (CoPP) hydrogel was prepared by low f requency oscillation
and freezing-thawing. The structure of CoPP hydrogel was characterized by FTIR, DSC, XRD and SEM, the swelling properties were observed, and the diffusion of water and the swelling dynamics were also discussed. The experimental results show that CoPP hydrogel is porous, and has two kinds of crystal regions. The diffusion characteristic index which water molecule immerses into CoPP hydrogel was near 0. 5, which indicates the diffusion is in Fick model. The swelling velocity constant of CoPP, the swelling ratio of mass (197. 38 %～252. 49 %) and swelling ratio of volume (241. 47 %～308. 93 %) of CoPP at the swelling equilibration were superior to those of poly (vinylalcohol) (PVA) hydrogel. Therefore, the swelling properties of CoPP composite hydrogel are faster and larger, which makes it possible to implant the artificial nucleus pulposus prosthesis in smaller size with the minimally invasive surgery.
2008, 25(1): 75-79.
Abstract:
Carbon fiber and glass fiber (CG fibers) reinforced rubber composite was prepared by using mill mixing
in solid state, and it screeping curve and stress relaxing curve were measured using Gleeble 3500 thermal simulator,and the viscoelasticity was also studied. The results indicate that , when the volume fraction of CG mixture fibers was less than 15 %, the rubber creep resistance and stress relaxing resistance were improved; when the volume fraction of CG mixed fibers was more than 15 %, the rubber creep resistance and stress relaxing resistance began to decrease. The relationship of creep and stress relaxation of rubber composites is reciprocal in value.
Carbon fiber and glass fiber (CG fibers) reinforced rubber composite was prepared by using mill mixing
in solid state, and it screeping curve and stress relaxing curve were measured using Gleeble 3500 thermal simulator,and the viscoelasticity was also studied. The results indicate that , when the volume fraction of CG mixture fibers was less than 15 %, the rubber creep resistance and stress relaxing resistance were improved; when the volume fraction of CG mixed fibers was more than 15 %, the rubber creep resistance and stress relaxing resistance began to decrease. The relationship of creep and stress relaxation of rubber composites is reciprocal in value.
2008, 25(1): 80-83.
Abstract:
Made f rom the quickly renewable and high performance bamboo as raw material, engineering materials
of bamboo have three productions, glued bamboo sheets, laminated bamboo slices and graded bamboo filament com2posites. In the whole period of growth, collecting, processing, making, using and discarding, the materials used less energy, and caused no pollution. Compared with other engineering materials, the bamboos are badly uniform and regular. So, many ways can be used to improve the uniformity and regularity, such as grading, regular processing , soaking resin, orienting, laminating and pressing, controlling quality, and inspecting. Engineering bamboo materials have high mechanical properties, and can be used in wind turbine blades and boats.
Made f rom the quickly renewable and high performance bamboo as raw material, engineering materials
of bamboo have three productions, glued bamboo sheets, laminated bamboo slices and graded bamboo filament com2posites. In the whole period of growth, collecting, processing, making, using and discarding, the materials used less energy, and caused no pollution. Compared with other engineering materials, the bamboos are badly uniform and regular. So, many ways can be used to improve the uniformity and regularity, such as grading, regular processing , soaking resin, orienting, laminating and pressing, controlling quality, and inspecting. Engineering bamboo materials have high mechanical properties, and can be used in wind turbine blades and boats.
2008, 25(1): 84-87.
Abstract:
Bamboos are one of the best biomass materials, which have good properties, quick growth, richness in
natural resources, and low price. Bamboos are made up from the vascular and thin wall cells, and the vascular is composed mainly of bamboo fiber based on the grading bamboo and processing filaments, and the filament s have good behavior in mechanic, impacting and fatigue. The bundles of filaments can be made to prepreg by soaking in resin and compressing. The composite can be made by layup and pressure. With the high performances, the composites can be used in wind turbine blades and boats.
Bamboos are one of the best biomass materials, which have good properties, quick growth, richness in
natural resources, and low price. Bamboos are made up from the vascular and thin wall cells, and the vascular is composed mainly of bamboo fiber based on the grading bamboo and processing filaments, and the filament s have good behavior in mechanic, impacting and fatigue. The bundles of filaments can be made to prepreg by soaking in resin and compressing. The composite can be made by layup and pressure. With the high performances, the composites can be used in wind turbine blades and boats.
2008, 25(1): 88-93.
Abstract:
The microst ructures at the interfaces of the aluminum matrix composite reinforced by Al2O3 particles
were characterized by means of high resolution t ransmission elect ron microscopy (HRTEM). It was revealed that Al(200) and Al (111) planes of the Al matrix should first grow along the surfaces of the Al2O3 particles, such orien2tation relationship as Al (200) ∥ Al2O3(101 2) and Al [ 011 ] ∥ Al2O3 [ 0221 ], and partial-coherent interface exist in one of the interfaces between the Al matrix and the Al2O3 particles, a coherent relationship with Al(111) ∥ Al2O3 (1120) appears in another interface, but no resultant production is found along those interfaces. Frank partial edge dislocation with 1/ 3 [111 ] Burgers vector, which is responsible for forming of remarkable lat tice deformation field with the scale about 20～30 atomic planes, is observed within the Al mat rix near the interface, however, no dislocations and other defect s are found within the area of the Al2O3 particles near the interfaces. At the same time, the mechanism for forming the interface features is analyzed from the viewpoint of crystallography.
The microst ructures at the interfaces of the aluminum matrix composite reinforced by Al2O3 particles
were characterized by means of high resolution t ransmission elect ron microscopy (HRTEM). It was revealed that Al(200) and Al (111) planes of the Al matrix should first grow along the surfaces of the Al2O3 particles, such orien2tation relationship as Al (200) ∥ Al2O3(101 2) and Al [ 011 ] ∥ Al2O3 [ 0221 ], and partial-coherent interface exist in one of the interfaces between the Al matrix and the Al2O3 particles, a coherent relationship with Al(111) ∥ Al2O3 (1120) appears in another interface, but no resultant production is found along those interfaces. Frank partial edge dislocation with 1/ 3 [111 ] Burgers vector, which is responsible for forming of remarkable lat tice deformation field with the scale about 20～30 atomic planes, is observed within the Al mat rix near the interface, however, no dislocations and other defect s are found within the area of the Al2O3 particles near the interfaces. At the same time, the mechanism for forming the interface features is analyzed from the viewpoint of crystallography.
2008, 25(1): 94-99.
Abstract:
To improve the reinforcing effect, a CNTs embedding microst ructure model for CNTs/Al2O3 composites was suggested. SWNTs/ Al2O3, MWNTs/Al2O3 and aligned MWNTs/Al2O3 with this kind of microstructure were synthesized by heterocoagulation. Based on the microst ructure and properties analysis, it has been found that the type, morphology and dispersibility of CNTs influence greatly the forming of CNTs embedding microst ructure model. The thin and straight SWNTs are advantageous to the forming of CNTs embedding microstructure model.
To improve the reinforcing effect, a CNTs embedding microst ructure model for CNTs/Al2O3 composites was suggested. SWNTs/ Al2O3, MWNTs/Al2O3 and aligned MWNTs/Al2O3 with this kind of microstructure were synthesized by heterocoagulation. Based on the microst ructure and properties analysis, it has been found that the type, morphology and dispersibility of CNTs influence greatly the forming of CNTs embedding microst ructure model. The thin and straight SWNTs are advantageous to the forming of CNTs embedding microstructure model.
2008, 25(1): 100-104.
Abstract:
The nano 2NiO / hollow glass sphere composite particles were successfully prepared by homogeneous
precipitation. Scanning elect ron microscope ( SEM), X-ray diffractometer(XRD) and energy dispersion X-ray
(EDS) results indicate that a uniform NiO coating is found on the surface of the hollow glass spheres. The coating is composed of threadlike NiO crystal with face-center-cubic (fcc) crystalline structure. The diameter of NiO crystal in composite particles is about 14 nm. FTIR results show that the composite particles have bet ter infrared absorption characteristic in both far and near-infrared areas than hollow glass spheres.
The nano 2NiO / hollow glass sphere composite particles were successfully prepared by homogeneous
precipitation. Scanning elect ron microscope ( SEM), X-ray diffractometer(XRD) and energy dispersion X-ray
(EDS) results indicate that a uniform NiO coating is found on the surface of the hollow glass spheres. The coating is composed of threadlike NiO crystal with face-center-cubic (fcc) crystalline structure. The diameter of NiO crystal in composite particles is about 14 nm. FTIR results show that the composite particles have bet ter infrared absorption characteristic in both far and near-infrared areas than hollow glass spheres.
2008, 25(1): 105-111.
Abstract:
In this paper, TG/DSC and high temperature XRD were engaged in studying phase transformation behavior of quartz fibers, high resolution SEM was engaged in studying surface micromorphology of heat t reated quartz fibers at different temperatures, and the tensile strength of these quartz fibers was measured by a tensile strength tester. The results indicate that thermal damage of quartz fibers under 1000℃ has two stages: (1) with heat treatment under 600℃, the tensile strength decreases slowly with increasing temperature because diameters of quartz fibers decrease and the original cracks, strip and round bulges on the surface are exposed after surface finishing agent volatilized; (2) with heat treatment at 600～1000℃, thermal stress caused those bulges to flake off and formed some new rifts and cracks. The higher heat treatment temperature is, the more rifts and cracks occur. This is one of the important factors that decreases tensile strength markedly. The results on quartz fiber by TG/DSC and XRD show that though no obvious crystallization occurs, the crystal structure ordering increases after heat treatment under 1000℃ and a little α-cristobalite occurs on the surface causing new bulge defects. This is also another one of the important factors resulting in thermal damage of quartz fibers.
In this paper, TG/DSC and high temperature XRD were engaged in studying phase transformation behavior of quartz fibers, high resolution SEM was engaged in studying surface micromorphology of heat t reated quartz fibers at different temperatures, and the tensile strength of these quartz fibers was measured by a tensile strength tester. The results indicate that thermal damage of quartz fibers under 1000℃ has two stages: (1) with heat treatment under 600℃, the tensile strength decreases slowly with increasing temperature because diameters of quartz fibers decrease and the original cracks, strip and round bulges on the surface are exposed after surface finishing agent volatilized; (2) with heat treatment at 600～1000℃, thermal stress caused those bulges to flake off and formed some new rifts and cracks. The higher heat treatment temperature is, the more rifts and cracks occur. This is one of the important factors that decreases tensile strength markedly. The results on quartz fiber by TG/DSC and XRD show that though no obvious crystallization occurs, the crystal structure ordering increases after heat treatment under 1000℃ and a little α-cristobalite occurs on the surface causing new bulge defects. This is also another one of the important factors resulting in thermal damage of quartz fibers.
2008, 25(1): 112-118.
Abstract:
A cement based piezoelect ric composite sensor was fabricated using the 123 cement based piezoelect ric
composite as a sensing element . The f requency response , linearity and sensing properties of the sensor were investi2 gated. The result s indicate that the output voltage amplitude of the sensor increase with increasing f requency of load under 5 Hz. When the f requency of load is larger than about 5 Hz , the output voltage amplitude of the sensor is nearly independent of f requency. There exist s an obviously linear relationship between the output voltage amplitude and input load amplitude of the sensor . The 12 3 cement based piezoelect ric composite sensor embedded into the concrete st ructure exhibit s excellent sensing properties. The output voltages of the sensor are correspondent to the complex load , random load and pulse load very well . The phase difference between the output voltage and input load is near zero. The experimental output voltage value of the sensor is in good agreement with the theoretical value.Such sensor has a good potential to be used in civil engineering st ructural health monitoring.
A cement based piezoelect ric composite sensor was fabricated using the 123 cement based piezoelect ric
composite as a sensing element . The f requency response , linearity and sensing properties of the sensor were investi2 gated. The result s indicate that the output voltage amplitude of the sensor increase with increasing f requency of load under 5 Hz. When the f requency of load is larger than about 5 Hz , the output voltage amplitude of the sensor is nearly independent of f requency. There exist s an obviously linear relationship between the output voltage amplitude and input load amplitude of the sensor . The 12 3 cement based piezoelect ric composite sensor embedded into the concrete st ructure exhibit s excellent sensing properties. The output voltages of the sensor are correspondent to the complex load , random load and pulse load very well . The phase difference between the output voltage and input load is near zero. The experimental output voltage value of the sensor is in good agreement with the theoretical value.Such sensor has a good potential to be used in civil engineering st ructural health monitoring.
2008, 25(1): 119-126.
Abstract:
This paper presents the test results of the experimental study on 30 different rib geometries of the glass
fiber reinforced composite(GFRP) ribbed rebars. 90 standard pull-out specimens were used to study the bond behavior of GFRP ribbed rebars to concrete. The test variables were the rebar diameter, the rib spacing and the rib height. For each rebar, the bond strength and the slip at the loaded end were obtained, and the corresponding bond-slip relationship curves were analyzed. Using the optimum criterion, design recommendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics. The test results show that the bond behavior between GFRP ribbed rebars and concrete varies obviously with the rib geometries: the optimal rib spacing of GFRP ribbed rebars is 1 times the rebar diameter, the optimal rib height is 6 % of the rebar diameter, and the optimal ratio of rib height to rib spacing is 0.06.
This paper presents the test results of the experimental study on 30 different rib geometries of the glass
fiber reinforced composite(GFRP) ribbed rebars. 90 standard pull-out specimens were used to study the bond behavior of GFRP ribbed rebars to concrete. The test variables were the rebar diameter, the rib spacing and the rib height. For each rebar, the bond strength and the slip at the loaded end were obtained, and the corresponding bond-slip relationship curves were analyzed. Using the optimum criterion, design recommendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics. The test results show that the bond behavior between GFRP ribbed rebars and concrete varies obviously with the rib geometries: the optimal rib spacing of GFRP ribbed rebars is 1 times the rebar diameter, the optimal rib height is 6 % of the rebar diameter, and the optimal ratio of rib height to rib spacing is 0.06.
2008, 25(1): 127-132.
Abstract:
The stitching joint 3D braided composites with various stitching direction , lap length and stitching densi2
ty were experimentally studied to reveal the effect of stitching parameters on the tensile property. The tensile prop2erty of the stitching joint 3D braided composites was compared with that of 3D integral braided composites. The re2 sult s indicate that the tensile st rength and modulus of the stitching joint 3D braided composites are lower than those of 3D integral braided composites. The tensile st rength reduces about 25 %～50 % , and the initial modulus decreases 35 %～55 %. The tensile st rength and modulus are influenced by the lap length greatly. The tensile property of the composites shows the character , which the tensile property increases earlier , and then falls with the lap length increasing. When the ratio of lap length to width of the sample is about 2. 5 , the tensile property of the stitching joint 3D braided composites is bet ter , only a decrease of 25 %. The tensile property of the middle stitching density is bet ter comparatively. However the tensile property has no notable change with the stitching direction.
The stitching joint 3D braided composites with various stitching direction , lap length and stitching densi2
ty were experimentally studied to reveal the effect of stitching parameters on the tensile property. The tensile prop2erty of the stitching joint 3D braided composites was compared with that of 3D integral braided composites. The re2 sult s indicate that the tensile st rength and modulus of the stitching joint 3D braided composites are lower than those of 3D integral braided composites. The tensile st rength reduces about 25 %～50 % , and the initial modulus decreases 35 %～55 %. The tensile st rength and modulus are influenced by the lap length greatly. The tensile property of the composites shows the character , which the tensile property increases earlier , and then falls with the lap length increasing. When the ratio of lap length to width of the sample is about 2. 5 , the tensile property of the stitching joint 3D braided composites is bet ter , only a decrease of 25 %. The tensile property of the middle stitching density is bet ter comparatively. However the tensile property has no notable change with the stitching direction.
2008, 25(1): 133-139.
Abstract:
The compressive experiment s were performed for the three dimensional and five directional carbon fiber/
phenolic braided composites with different braiding angles and fiber volume f ractions in the longitudinal ( braiding)direction and t ransverse direction at different temperatures. The principal compressive properties of the composites were obtained. The influences of braiding parameters and temperature on the compressive properties were also ana2 lyzed. The macro and micro pictures of the f racture surface of specimens were observed in order to understand the deformation and the failure mechanism of the composites. The result s show that the compressive st ress2st rain curves of 3D & 5D carbon fiber/ phenolic braided composites exhibit the nonlinear characteristics and the effect s of tempera2 ture are apparent . The braiding angle and the fiber volume f raction still were the most important parameters to affect the compressive properties of the composites. The longitudinal compressive failure of the composites is very different f rom the t ransverse compressive failure.
The compressive experiment s were performed for the three dimensional and five directional carbon fiber/
phenolic braided composites with different braiding angles and fiber volume f ractions in the longitudinal ( braiding)direction and t ransverse direction at different temperatures. The principal compressive properties of the composites were obtained. The influences of braiding parameters and temperature on the compressive properties were also ana2 lyzed. The macro and micro pictures of the f racture surface of specimens were observed in order to understand the deformation and the failure mechanism of the composites. The result s show that the compressive st ress2st rain curves of 3D & 5D carbon fiber/ phenolic braided composites exhibit the nonlinear characteristics and the effect s of tempera2 ture are apparent . The braiding angle and the fiber volume f raction still were the most important parameters to affect the compressive properties of the composites. The longitudinal compressive failure of the composites is very different f rom the t ransverse compressive failure.
2008, 25(1): 140-146.
Abstract:
The compressive failure tests were carried out on the composite laminates af ter low velocity impact dam-
age to study compressive failure mechanisms of laminates af ter low velocity impact damage. The effects of impact energy on the f ront surface dent depth , back surface resin crack length , damage area and residual compressive st rength were studied. Based on the experiment , a reduced stiffness inclusion model was developed to predict the residual compressive st rength of composite laminates af ter low velocity impact . In this model , the damage was considered as a soft elliptical zone of the material . A hybrid st ress finite element with an arbit rary elliptical inclusion for anisot ropic plates was programmed to compute the stress distribution. The point st ress criterion was used to determine whether the post-impact laminates are compressed to failure or not . Good agreement between predicted residual compressive st rength and experimental result s is obtained.
The compressive failure tests were carried out on the composite laminates af ter low velocity impact dam-
age to study compressive failure mechanisms of laminates af ter low velocity impact damage. The effects of impact energy on the f ront surface dent depth , back surface resin crack length , damage area and residual compressive st rength were studied. Based on the experiment , a reduced stiffness inclusion model was developed to predict the residual compressive st rength of composite laminates af ter low velocity impact . In this model , the damage was considered as a soft elliptical zone of the material . A hybrid st ress finite element with an arbit rary elliptical inclusion for anisot ropic plates was programmed to compute the stress distribution. The point st ress criterion was used to determine whether the post-impact laminates are compressed to failure or not . Good agreement between predicted residual compressive st rength and experimental result s is obtained.
2008, 25(1): 147-152.
Abstract:
With a single“easy flow”direction and larger surface area density , two2dimensional (2D) cellular mate2
rials exhibit at t ractive thermal capability besides the high specific rigidity and specific st rength. The research of it sheat dissipation characteristic through forced convection has significant importance. A numerical method is used to solve the flow field and conjugate heat t ransfer between fluid and solid in two2dimension cellular materials. The sen2sitivity of porosity and microst ructure size to the heat dissipation capability was explored and the design parameters are optimized. The effect of microst ructure type on heat dissipation efficiency was investigated by analyzing and comparing five typical kinds of 2D cellular materials. A new optimization design concept is presented , in which the design parameters range ( the acceptable range of the design parameters which can satisfy the requirement ) is maximized under given heat dissipation capability const raint s. The result s obtained by this design concept are more suitable for the multifunctional design of the materials based on other requirement s. The analysis indicates that 2D cellular materials with regular hexagonal cells provide the highest level of heat dissipation efficiency and are more suitable for the ult ralight multifunctional design.
With a single“easy flow”direction and larger surface area density , two2dimensional (2D) cellular mate2
rials exhibit at t ractive thermal capability besides the high specific rigidity and specific st rength. The research of it sheat dissipation characteristic through forced convection has significant importance. A numerical method is used to solve the flow field and conjugate heat t ransfer between fluid and solid in two2dimension cellular materials. The sen2sitivity of porosity and microst ructure size to the heat dissipation capability was explored and the design parameters are optimized. The effect of microst ructure type on heat dissipation efficiency was investigated by analyzing and comparing five typical kinds of 2D cellular materials. A new optimization design concept is presented , in which the design parameters range ( the acceptable range of the design parameters which can satisfy the requirement ) is maximized under given heat dissipation capability const raint s. The result s obtained by this design concept are more suitable for the multifunctional design of the materials based on other requirement s. The analysis indicates that 2D cellular materials with regular hexagonal cells provide the highest level of heat dissipation efficiency and are more suitable for the ult ralight multifunctional design.
2008, 25(1): 153-160.
Abstract:
Based on the single particle representative volume element of particle reinforced composites , the mono-
tonic tensile st ress-strain curve and uniaxial ratcheting behavior of SiC P/ 6061Al alloy composites were numerically simulated by using finite element code ABAQUS and considering different particulate shapes , and the effect of parti2cle shape on the ratcheting of the composite was discussed. The shapes of the particles are sphere , cube , short prisms and short cylinder . The result s show that for the particles with prescribed shapes , the reinforcing degree of the spherical particle to the matrix is the weakest , and it s composite produces the largest ratcheting st rain in the cyclic st ressing. For the short prismatic particle , it s reinforcing degree depends on the number of it s edges , i . e. ,the reinforcing degree of the pentagonal prism particle is the highest , and then the reinforcing degree of the short prismatic particle decreases with the increase of the edge number , and finally becomes close to that of the short cy2lindrical particle. Moreover , based on the numerical result s , the mesoscopic plastic deformation and it s evolution features of the composites were also discussed , which is very useful in studying the damage and failure mechanism of particle reinforced metal mat rix composites.
Based on the single particle representative volume element of particle reinforced composites , the mono-
tonic tensile st ress-strain curve and uniaxial ratcheting behavior of SiC P/ 6061Al alloy composites were numerically simulated by using finite element code ABAQUS and considering different particulate shapes , and the effect of parti2cle shape on the ratcheting of the composite was discussed. The shapes of the particles are sphere , cube , short prisms and short cylinder . The result s show that for the particles with prescribed shapes , the reinforcing degree of the spherical particle to the matrix is the weakest , and it s composite produces the largest ratcheting st rain in the cyclic st ressing. For the short prismatic particle , it s reinforcing degree depends on the number of it s edges , i . e. ,the reinforcing degree of the pentagonal prism particle is the highest , and then the reinforcing degree of the short prismatic particle decreases with the increase of the edge number , and finally becomes close to that of the short cy2lindrical particle. Moreover , based on the numerical result s , the mesoscopic plastic deformation and it s evolution features of the composites were also discussed , which is very useful in studying the damage and failure mechanism of particle reinforced metal mat rix composites.
2008, 25(1): 161-167.
Abstract:
The composite sine-wave beam is a typically function-integrated st ructure for energy absorption application. The crushing peak stress and the progressive mean st ress associated to the specific energy absorption ratio are critical for the function. Both of them are cont rolled significantly by the trigger system embedded in the beam. In this study , three t rigger systems were designed and manufactured including an end bore weakened , chamfer weakened and gradient weakened beam , respectively. The crush experiment s and the macro- and micro st ructural studies showed that the different t riggers greatly affected the peak stress , the mean st ress and the crush mechanism. The end chamfer weakened trigger exhibited the relatively best energy absorption behavior characterized by the peak st ress , mean st ress and the specific energy absorption ratio.
The composite sine-wave beam is a typically function-integrated st ructure for energy absorption application. The crushing peak stress and the progressive mean st ress associated to the specific energy absorption ratio are critical for the function. Both of them are cont rolled significantly by the trigger system embedded in the beam. In this study , three t rigger systems were designed and manufactured including an end bore weakened , chamfer weakened and gradient weakened beam , respectively. The crush experiment s and the macro- and micro st ructural studies showed that the different t riggers greatly affected the peak stress , the mean st ress and the crush mechanism. The end chamfer weakened trigger exhibited the relatively best energy absorption behavior characterized by the peak st ress , mean st ress and the specific energy absorption ratio.
2008, 25(1): 168-172.
Abstract:
The composite with interleaved acrylonit rile butadiene rubber (NBR) layer was fabricated by the co2
curing process. The temperature spect rum of loss factor for the composite were tested using dynamic mechanical analysis (DMA) equipment . The damping properties and damping mechanism of the composite were investigated at different temperatures. The result indicates that the loss factor of the composite is small and almost invariant with temperature when the temperature is within an elastomeric state and glassy state of the damping layer . The loss factor increases to the peak value and then decreases rapidly when the temperature is within a viscous state of the damping layer . The max loss factor of composites with interleaved damping layer is 19. 2 % and is about 13 times of the composite without interleaved damping layer . The damping properties of the cocured composite decrease with the decrease of the loss factor of the damping layer during the cocurig process , and the loss factor by DMA is less than that by prediction in the viscous state of the damping layer remarkably. The damping properties of the cocured composite increase owing to the damping of the interface , and the loss factor by DMA is higher than that by prediction when the damping layer is in the glassy state.
The composite with interleaved acrylonit rile butadiene rubber (NBR) layer was fabricated by the co2
curing process. The temperature spect rum of loss factor for the composite were tested using dynamic mechanical analysis (DMA) equipment . The damping properties and damping mechanism of the composite were investigated at different temperatures. The result indicates that the loss factor of the composite is small and almost invariant with temperature when the temperature is within an elastomeric state and glassy state of the damping layer . The loss factor increases to the peak value and then decreases rapidly when the temperature is within a viscous state of the damping layer . The max loss factor of composites with interleaved damping layer is 19. 2 % and is about 13 times of the composite without interleaved damping layer . The damping properties of the cocured composite decrease with the decrease of the loss factor of the damping layer during the cocurig process , and the loss factor by DMA is less than that by prediction in the viscous state of the damping layer remarkably. The damping properties of the cocured composite increase owing to the damping of the interface , and the loss factor by DMA is higher than that by prediction when the damping layer is in the glassy state.
2008, 25(1): 173-179.
Abstract:
The equations of virtual work based on the theory of time increment were deduced to analyze stress-
strain states under fatigue loading conditions. A progressive damage method of predicting the fatigue life of mecha2nically fastened joint s in fibre- reinforced plastics was established , which is integrated fatigue material property degradation models. The three-dimensional Hashin-type fatigue failure criteria were int roduced into the method to detect damage for diverse damage modes. The criteria of the structure catast rophe and the sudden material property degradation rules including the correlation among four basic damage mechanisms were also established. The fatigue life , failure initiation , propagation and catast rophic failure of composite bolted joint s under tension2tension fatigue loading conditions are predicted by using the fatigue progressive damage method established in the paper . Excellent agreement is found between data obtained f rom this study and the experiment .
The equations of virtual work based on the theory of time increment were deduced to analyze stress-
strain states under fatigue loading conditions. A progressive damage method of predicting the fatigue life of mecha2nically fastened joint s in fibre- reinforced plastics was established , which is integrated fatigue material property degradation models. The three-dimensional Hashin-type fatigue failure criteria were int roduced into the method to detect damage for diverse damage modes. The criteria of the structure catast rophe and the sudden material property degradation rules including the correlation among four basic damage mechanisms were also established. The fatigue life , failure initiation , propagation and catast rophic failure of composite bolted joint s under tension2tension fatigue loading conditions are predicted by using the fatigue progressive damage method established in the paper . Excellent agreement is found between data obtained f rom this study and the experiment .
2008, 25(1): 180-191.
Abstract:
Plate end debonding failure loads of RC beams st rengthened in flexure by bonding an FRP or steel plate
to the tension face were investigated in detail . Based on studies of the cont rolling parameters , the available test data and comparisons of these test data with existing debonding strength models , a simple , rationally- based predictive model for plate end debonding failure loads was presented. In this model , pure flexural debonding for a plate end located in a pure bending region and pure shear debonding for a plate end located in a high- shear zero (or low) -moment region are first dealt with. The general case of a plate end under the combined action of shear and bending is treated as the interaction of these two ext reme conditions. The proposed model is shown to be accurate through comparisons with available test results. The model relates the debonding failure load to the shear capacity of the beam and a number of well2defined parameters , and can be easily incorporated in future design codes and guidelines , and may be used in practical applications.
Plate end debonding failure loads of RC beams st rengthened in flexure by bonding an FRP or steel plate
to the tension face were investigated in detail . Based on studies of the cont rolling parameters , the available test data and comparisons of these test data with existing debonding strength models , a simple , rationally- based predictive model for plate end debonding failure loads was presented. In this model , pure flexural debonding for a plate end located in a pure bending region and pure shear debonding for a plate end located in a high- shear zero (or low) -moment region are first dealt with. The general case of a plate end under the combined action of shear and bending is treated as the interaction of these two ext reme conditions. The proposed model is shown to be accurate through comparisons with available test results. The model relates the debonding failure load to the shear capacity of the beam and a number of well2defined parameters , and can be easily incorporated in future design codes and guidelines , and may be used in practical applications.
2008, 25(1): 192-195.
Abstract:
An adaptive weighted sum algorithm proposed for multiple objective problems is presented to optimize
the topology of the microst ructure with periodic two2phase materials. The microst ructure of porous composite with a certain volume f raction of solid materials and st ructural symmet ry is studied. By means of the homogenization method and method of moving approximating (MMA) , the equivalent elastic module of cell is calculated and maxi2 mized , based on the finite element method. The relative density of each element of the cell is defined as the design variable based on the finite element method , with SIMP density2stiffness scheme which has the effect of penalizing to element s with intermediate density. During the process of iteration , the weighing coefficient is adaptively adjusted according to the variety of the objective function. Several microst ructure topologies are obtained by the adaptive weighting algorithm with different combinations of equivalent elastic module and weighing coefficient s. Numerical result s verify the validity of the proposed adaptive weighted sum algorithm in the multiple objective topology design of microst ructures.
An adaptive weighted sum algorithm proposed for multiple objective problems is presented to optimize
the topology of the microst ructure with periodic two2phase materials. The microst ructure of porous composite with a certain volume f raction of solid materials and st ructural symmet ry is studied. By means of the homogenization method and method of moving approximating (MMA) , the equivalent elastic module of cell is calculated and maxi2 mized , based on the finite element method. The relative density of each element of the cell is defined as the design variable based on the finite element method , with SIMP density2stiffness scheme which has the effect of penalizing to element s with intermediate density. During the process of iteration , the weighing coefficient is adaptively adjusted according to the variety of the objective function. Several microst ructure topologies are obtained by the adaptive weighting algorithm with different combinations of equivalent elastic module and weighing coefficient s. Numerical result s verify the validity of the proposed adaptive weighted sum algorithm in the multiple objective topology design of microst ructures.
2008, 25(1): 196-199.
Abstract:
The aeroelastic analysis was performed on the high-aspect- ratio composite wings with unbalance lami-
nates in up side and downside skins. Considering the effect of the variation of the unbalance laminates of skins on the aeroelastic performance , aeroelastic models were built for the high - aspect - ratio composite wings with different swept angles and unbalance laminates in the skins. The variations of the deformation and the lif t performance in the case of heavy loads with the unbalance level of the skin laminates were analyzed for the wings , as well as the variation tendency of the vibration characteristics and the divergence/ flut ter speed. The result s show that the unbalance level of the skin laminates has great effect s on the divergence speed and static aeroelastic characteristics of the wings , but lit tle effect s on the natural f requencies and flut ter speed.
The aeroelastic analysis was performed on the high-aspect- ratio composite wings with unbalance lami-
nates in up side and downside skins. Considering the effect of the variation of the unbalance laminates of skins on the aeroelastic performance , aeroelastic models were built for the high - aspect - ratio composite wings with different swept angles and unbalance laminates in the skins. The variations of the deformation and the lif t performance in the case of heavy loads with the unbalance level of the skin laminates were analyzed for the wings , as well as the variation tendency of the vibration characteristics and the divergence/ flut ter speed. The result s show that the unbalance level of the skin laminates has great effect s on the divergence speed and static aeroelastic characteristics of the wings , but lit tle effect s on the natural f requencies and flut ter speed.
2008, 25(1): 200-204.
Abstract:
The divergence experimental prediction and model design techniques were studied for composite forward
-swept wings , and the Southwell method , a subcritical divergence experimental technique with testing of st ructural st rain , was used to predict the divergence dynamic pressure. Two high-aspect-ratio composite forward-swept wings were tested using the subcritical method. In order to predict and validate the result s of the subcritical experiment , the divergence dynamic pressures were calculated prior to the subcritical wind- tunnel experiment , and the critical divergence wind2tunnel experiment s were performed especially af ter the subcritical wind- tunnel experiment . Both the calculation results and testing result s indicate that bet ter result s could be at tained by using the Southwell method. The subcritical method could be used in high2 pressure divergence tests and flight tests. The divergence speed decreases with increase of the forward-swept angle.
The divergence experimental prediction and model design techniques were studied for composite forward
-swept wings , and the Southwell method , a subcritical divergence experimental technique with testing of st ructural st rain , was used to predict the divergence dynamic pressure. Two high-aspect-ratio composite forward-swept wings were tested using the subcritical method. In order to predict and validate the result s of the subcritical experiment , the divergence dynamic pressures were calculated prior to the subcritical wind- tunnel experiment , and the critical divergence wind2tunnel experiment s were performed especially af ter the subcritical wind- tunnel experiment . Both the calculation results and testing result s indicate that bet ter result s could be at tained by using the Southwell method. The subcritical method could be used in high2 pressure divergence tests and flight tests. The divergence speed decreases with increase of the forward-swept angle.
