2007 Vol. 24, No. 1

Advanced composite materials and aerospace engineering
DU Shanyi
2007, 24(1): 12-12.
Advanced composite materials (ACM) have become the basic materials of the aerospace engineering. In this paper, the requirements and the applications of ACM in the aerospace engineering were presented. Some hot-spot technological fields, such as lattice materials and structures, nano-composite materials and multi-functional materials, were introduced. Their potential applications and developments were prospected. Finally, the problems to be resolved about raw materials, low cost, integration of design and evaluation in ACM were discussed.
Phase structure of a toughened epoxy system
ZHANG Ming, AN Xuefeng, TANG Bangming, YI Xiaosu
2007, 24(1): 13-17.
The SEM was employed to determine the phase structure of the toughened epoxy system, both in-situ and ex-situ system, respectively. The results of the in-situ blending system indicate that the phase reversion occurs when the thermoplastic (TP) content is 16.7%~20.0%. Spherical particle dimension of the phase-separated system was statistically analyzed, showing that the higher the TP component, the smaller the dimension and the narrower the dispersion of the spherical particle sizes. An experimental expression was obtained to establish the relationship between the TP content (φ) and the particle dimension (d). Based on this expression it is estimated that the upper and lower limits of the particle dimension are 1.838μm and 0.925μm, respectively. For the ex-situ toughened resin, a multi-layer structure, i.e. toughened layer -interface layer -bulk layer, is formed. The content of TP keeps a high level in the toughened layer, followed by a dramatically drop in the adjacent plies; hardly any TP resin exists in the bulk layer. Also, the interface is expected of a relatively narrow thickness to achieve preferable toughness.
Temperature and dielectric property of resin during RTM process
SONG Xiugong, WANG Jihui, GAO Guoqiang
2007, 24(1): 18-21.
As a close-mold process, it is difficult to observe the mold filling and chemical reaction procedure in the RTM process. In this study, the reaction information in the mould was obtained using the dielectric analyzer for on-line monitoring. The resin reaction temperature and ionic conductivity under different mold temperatures were investigated. The influence of the fabric volume fraction on the composite permittivity was studied. And the ionic conductivity during the curing process was studied for different fabrics. The results show that the exothermic reaction increases the local temperature in the composite and a complex temperature gradient distribution was formed. In the case of high temperature and low fabric volume fraction, the ionic conductivity changes dramatically, which in turn has a significant influence on the resin curing process. The fabric type also affects the ionic conductivity, with a higher value for random mat reinforced composites than that of woven fabrics.
Effect of fiber distribution uniformity on the mechanical properties of composite laminates
YANG Jinjun, ZHANG Zuoguang, LI Min, SUN Zhijie
2007, 24(1): 22-27.
The effect of fiber distribution on the flexural and impact properties of T300/BMP316 unidirectional composite laminates was studied through the bending test under three-point loading and using a digital impact test machine. The finite-element analysis was performed to investigate the stress distribution of the deformed model structure with nonuniform fiber distribution. An effect coefficient of fiber distribution R was put forward to characterize the mechanic properties of composite materials. The results show that the flexural and impact properties are greatly affected by the fiber distribution type and the loading direction, and the effect coefficient R can be used to justify the properties of the composite laminates with nonuniform fiber distribution.
Self-assembly of the interphase of carbon fiber/epoxy composites
HE Jinmei, HUANG Yudong, ZHOU Haoran, LIU Li
2007, 24(1): 28-33.
A new method based on the molecular self-assembly was proposed for the carbon fiber surface modification. The carbon fiber surface was first metallized by electroless Ag plating and then covered by organic compound self-assembly films. The surface-enhanced Raman scattering spectroscopy (SERS) analysis verifies that two nitrogen-containing or sulphur-containing aromatic heterocyclic compounds were chemisorbed onto the Ag-plated carbon fibers and formed a lie-down phase. XPS further proves the chemisorption of self-assembly films on the carbon fiber surface via the formation of S—Ag or N—Ag bonds. The interfacial bonding strengths of modified carbon fiber/epoxy composites are improved. The relationship between the structures of interfacial regions and properties of the micro-composites is revealed.
Effect of surface modification of Kevlar stitch threads on mechanical interfacial properties of carbon fiber/bismaleimide stitched composites
AI Tao, WANG Rumin, DENG Jie
2007, 24(1): 34-39.
To improve the properties of durability towards combined moisture and temperature attack of stitched composites with Kevlar thread, the surface of Kevlar stitch thread was modified using the metalation and grafting Allyl group. The modified thread was characterized with tensile measurement, SEM and XPS. The results show that the surface of the chemical treated Kevlar stitch thread is rougher than that of the untreated thread. The oxygen content increases by 23% and the tensile strength decreases little under the proper condition. The interfacial properties of the stitched carbon fibre reinforced bismaleimide (BMI) resin composites T300 /QY9512 with Kevlar stitched threads were studied by interlaminar shear strength (ILSS). The result shows that the moisture uptake of carbon fibre/stitched BMI composites with chemical treated Kevlar threads decreases by 52% and the residue ratio of ILSS in the wet state improves by 15%.
Ablation performance of C/C composites with different preforms
YIN Jian, ZHANG Hongbo, XIONG Xiang, HUANG Baiyun
2007, 24(1): 40-44.
The ablation performances of carbon /carbon composites with 3D fine woven pierced felt structure and carbon fiber needled bulk felt structure were respectively tested on an arc heater, and the morphologies of specimens were observed by scanning electron microscopy (SEM).The results show that the ablation process of C/C composites is controlled by chemical erosion and mechanical erosion and mainly by mechanical erosion. The surface roughness would be accelerated because of the existence of Z direction carbon fiber bundles, and the ablation rate of the C/C composite with 3D fine woven pierced structure is higher than that of the unidirectional carbon fiber needled bulk felt structure. In addition, because the unidirectional carbon fibers are perpendicular to the ablation flow, the C/C composite with the unidirectional carbon fiber needled bulk felt structure has good ablation performance.
Kinetic model and mechanisms of oxidation of 2D-C/C composite
GUO Weiming, XIAO Hanning, YASUDA Eiichi
2007, 24(1): 45-52.
The isothermal oxidation of a two-dimensionally reinforced carbon/carbon (2D-C/C) composite was investigated by thermogravimetric analysis, and a kinetic model was proposed. The microstructure of 2D-C/C composite with different mass loss was studied by SEM, and isothermal oxidation mechanisms were discussed. The oxidation exhibits two stages: a linear oxidation stage with mass loss from 0 to 65%, during which the oxidation rate is almost stable; and a non-linear oxidation stage with mass loss between 65% and 100%, in which the oxidation rate decreases. The oxidation Arrhenius curve for 2D-C/C composite consists of two straight lines, the intercept of which is at about 800~850℃. At the linear oxidation stage, the activation energy is 217.2 kJ/mol and 157.0kJ/mol respectively; at the non-linear oxidation stage, the reaction order is 0.55 and 0.65, and the activation energy is 219.3 kJ/mol and 182.0 kJ/mol respectively. By comparing the experimental and theoretical TG curves, the kinetic model can be used to predict the isothermal oxidation of 2D-C/C composite. The oxidation starts from the fiber/matrix interface, and the matrix is oxidized much more rapidly than the carbon fibers, and only the fibers are being attacked in the final stage of oxidation. At 750~800℃, the oxidation is controlled by chemical reaction; at 850~905℃, it is controlled by chemical reaction and gaseous diffusion, but the contribution of gaseous diffusion to oxidation in the non-linear stage is less than that in the linear stage.
Fabrication of particle reinforced copper matrix composites by selective laser sintering
GU Dongdong, SHEN Yifu
2007, 24(1): 53-59.
The sub-micro WC-10%Co particle reinforced Cu matrix composites were prepared using selective laser sintering (SLS). The microstructures of the laser sintered samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and atomic force microscope (AFM). It shows that the WC reinforcing particles are either partially melted and smoothened or completely melted and in situ precipitated, showing continuous and compatible metallurgical interfaces with the matrix. The effects of the processing parameters such as laser power, scan speed, and layer thickness on the microstructures and properties of the laser sintered samples were investigated. It shows that increasing the laser power leads to an improvement in the bonding ability between the reinforcing particles and the matrix. An increase in the scan speed above 0.05m/s results in a homogeneous distribution of the reinforcing particles. Reducing the layer thickness below 0.30mm permits a high densification of the laser sintered part.
Oxidation problem of C-Cu fiber prepared by using boric acid
GAO Song, YAO Guangchun
2007, 24(1): 60-64.
Boric acid was used as a protecting agent on C-Cu fiber surface to solve the oxidizing problem while compounding C-Cu/Al composites. The effects of boric acid on the performance of the composites were analyzed through SEM, XRD and tensile tests. The results show that carbon fibers coated with copper are little only a oxidized when pretreated with 1.0% boric acid solution. These carbon fibers in the composites are finely dispersed and have good cohesion with the matrix. Besides, such an amount of boric acid does no harm to the mechanical properties of the composites.
Damping properties of SiCP/ZL104 composite foams
YU Sirong, LUO Yanru, ZHANG Yingbo, LIU Jiaan
2007, 24(1): 65-69.
The damping properties and damping mechanism were investigated for SiCP/ZL104 composite foams, fabricated by the method of direct melt foaming. The results show that under the conditions of the same pore-diameter, the loss factors of SiCP/ZL104 composite foams are non-linear rising with the increase of porosity at the ambient temperature, and the incremental changes lessen gradually. The damping properties of SiCP/ZL104 composite foams are better than those of foam aluminum, SiCP/ZL104 composites and ZL104 alloy. The loss factors of SiCP/ZL104 composite foams increase with the increase of the content of SiCP and the decrease of granularity of SiCP. Pores and high density dislocations in SiCP/ZL104 composite foams contribute to their damping properties.
Effect of an external electric field on the combustion synthesis process of TiO2-C-Al system
HU Qiaodan, LUO Peng, YAN Youwei
2007, 24(1): 70-74.
Taking 3TiO2+3C+(4+x)Al as a reaction system, a dense TiC-Al2O3-Al composite was directly prepared. The effect of electric-field on the combustion synthesis process of the system was systematically investigated. The results show that the imposition of an external electric field can improve the adiabatic temperature of the reactive system and induce its self-sustaining combustion synthesis process. The electric field also can change the combustion modes of the system. With an increase of the field strength, both the combustion temperature and the self-propagating wave velocity are increased obviously, while the grain size of the in-situ synthesized TiC and Al2O3 particles is decreased significantly. Under the conditions of the Al residual x being 14mol in the system and the electric field strength E being 25V/cm, a dense TiC-Al2O3-Al composite with a relative density of 92.5% can be successfully fabricated, in which TiC and Al2O3 particles have a fine size of 0.2~1.0mm, and distribute uniformly in metal Al.
A method for measuring the in situ constituent modulus in unidirectional fiber-ceramic composites
CHENG Tianle, XIA Yuanming
2007, 24(1): 75-80.
A method which is a combination of meso-theoretical analysis and macro-experimental measurement was first given to calculate the in situ fiber modulus by using the mixture law and the relationships between the stress-strain hysteresis characteristics and the constituent modulus. The method was successfully applied to C/SiC composites. The result from preliminary experiments shows that the method is effective. It also shows that the in situ fiber modulus degrades noteworthily in Cf/SiC composites.
Fractal characteristic of the porous structure of the additive silica xerogels
HE Fei, HE Xiaodong, LI Yao
2007, 24(1): 81-85.
Two-step acid-base catalyzed silica xerogels with different amounts of additives were prepared through sol-gel and ambient pressure drying. The surface fractal dimensions of these silica xerogels were determined based on a nitrogen adsorption-desorption method by means of the Frenkel-Halsey-Hill (FHH) model. The changes of density, pore structure and specific surface area were compared between pure silica xerogels and the impure ones. And the shape of pores was estimated by the theory of de Boer. The results show that the strength of silica xerogels is increased by the additives, and the shrinkage is restrained in the course of drying. The porous structure and the concentration of alkoxide monomers were also changed. The specific surface area of modified silica xerogels is decreased by adding silica xerogels powder and the pore distribution is widened. On the contrary, the specific surface area is increased by adding TiO2 powder and short fibers and the maximal value of 1064.96m2/g is achieved. All the surface fractal dimensions of the samples were between 2.4 to 2.5.
Investigation on tensile and interlaminar shear of plain woven CMC with Z-pin reinforcement
LIU Wei, JIAO Guiqiong, GUAN Guoyang, CHANG Yanjun
2007, 24(1): 86-90.
The tensile and interlaminar shear behaviors of ceramic matrix composite (CMC) with Z-pin reinforcement were investigated. A preform consisting of plain woven fabric and Z-pin through thickness reinforcements was prepared. The process of chemical vapor infiltration (CVI) was used to fabricate the ceramic matrix composite with Z-pins. The tests of uniaxial tensile and unloading-reloading were used to investigate the tensile behavior and the fracture mechanisms of the composite. And a double notch shear (DNS) test was used to investigate the interlaminar shear strength and the fracture mechanism of interlaminar shear. The results show that the tensile stress-strain curve of the plain-woven ceramic matrix composite laminate is nonlinear. Z-pin insertion reduces the tensile strength, and greatly improves the interlaminar shear strength (ILSS) and changes the interlaminar fracture mechanism of the ceramic matrix composite. The debonding of the fabric and the matrix of the interlaminar is changed into double fracture mechanisms of Z-pin shear fracture and the debonding of the fabric and the matrix of the interlaminar.
Preparation and properties of 2D fused-silica fiber reinforced porous Si3N4-SiO2 matrix composites
HAN Guifang, ZHANG Litong, CHENG Laifei, XU Yongdong
2007, 24(1): 91-96.
2D fused-silica fiber reinforced porous Si3N4-SiO2 matrix composites were prepared by combining the slurry method and vacuum infiltration technology. X-ray diffraction technique was used to analyze the crystallization behavior of the fused silica with different binders and of the addition of silicon nitride. The polished section and fracture morphology of the composites with different cycles of infiltration were characterized by SEM. Using crack deflection parameter, the fracture models were discussed. The results show that the concentration of Na+ has great effect on the crystallization of silica, while Si3N4 powder has little influence on it. Increasing the cycles of infiltration, the strength of the composites can not be improved, but the crack deflection parameter decreases, the fracture model converts toughness rupture into brittle rupture, and the fracture morphology turns out to be multistage pull-out rather than whole fiber tow pull-out.
Preparation of mullite sol and mullite sol coated aluminum titanate powder
ZHOU Jianer, LI Huili, WANG Yanxiang, LI Jiake, ZHANG Xiaozhen, HU Xuebing
2007, 24(1): 97-103.
The stable mullite sol with different performances was prepared by the sol-gel method using tetraethyoxysilane(TEOS) and aluminium nitrate as main materials. Aluminium titanate(AT) powders were covered by mullite sol using the dipping film-coating method. The influences of performance and relative amount of mullite sol on the coating effect and improvement of performance of AT powders were researched. The results show that when the concentration of mullite sol is in the range of 0.18~0.30mol/L, viscosity of mullite sol 56~93mPa · s, pH value 3.0, and coating thickness 0.15~0.20μm, the mullite-aluminum titanate powder with better coating and mullite-aluminum titanate composite material with good performance can be obtained. The bending strength of mullite aluminum titanate composite material reaches 38~50MPa, which is 10~15 times that of aluminum titanate material, and the thermal expansion coefficient is 1.89~2.25×10-6/℃(room temperature to 1000℃). The aluminium titanate powders covered with mullite film do not decompose at 1100℃ for 300h.The heated process and the feature of aluminium titanate before or after coating the film, and its compositions were investigated by TG-DSC, XRD, SEM, EPMA, etc. The relationships between performances and structure of the powders and the composite material of mullite-aluminum titanate were studied.
Synthesis and properties of an SiC/Si<em>xO<em>yC<em>z discontinuous reinforced ceramic composite
YUAN Xiaokun, XU Bingshe
2007, 24(1): 104-109.
Using the amorphous Si<em>xO<em>yC<em>z ceramic pyrolyzed from polysiloxane silicon resin YR3370 (GE toshiba silicones) as the matrix, and 0.8μm SiC particle as the discontinuous reinforcement, an SiC/Si<em>xO<em>yC<em>z discontinuous reinforced ceramic composite was prepared. When the biscuit contains 50% of SiC particle and is pyrolyzed in a 99.99% nitrogen flux at 1100~1300℃ for 1h, the ceramic matrix composite has a density of 2.27g/cm3 and a Vickers hardness of 741kg/mm2. The mechanics properties of the composite were discussed through structure modeling and strength calculation. The characteristic of the composite structure is that the discontinuous reinforcement SiC particles are wrapped in the continuous amorphous Si<em>xO<em>yC<em>z ceramic matrix, and there is reasonable thermal expansion compatibility between them, which can improve the brittleness of monolithic ceramic materials.
Preparation and characterization of nano-hydroxyapatite/ chitosan-chondroitin sulfate composite materials
LV Caixia, YAO Zihua
2007, 24(1): 110-115.
Nano-hydroxyapatite/chitosan-chondroitin sulfate composites with different mass ratios were prepared through the co-precipitation method. The properties of these composites were characterized and analyzed by means of XRD, SEM, TGA and Universal Testing Machine. The change of the mineralization surface of the composite, pH and the concentration of system in the simulated body fluid were observed. The results show that the nano-hydroxyapatite/chitosan-chondroitin sulfate composites have small influence on the body microenvironment, a good mineralization effect on the surfaces and an excellent biocompatibility and osteoconduction property. The maximum compressive strength value is 42.3MPa at 50% HA. The n-HA/CS-ChS composite can meet the demand of reparation and substitution of osteo-tissue engineering and will be the load-bearing substitute to treat bone defects.
Application of Monte Carlo-JC method to the reliability assessment of flexural capacity of RC beams strengthened with FRP
HE Zheng, HUANG Yongchun
2007, 24(1): 116-121.
The JC method combined with Monte Carlo simulation procedure (called Monte Carlo-JC method) was applied to conduct a systematic reliability assessment of flexural capacity of FRP reinforced concrete beams designed by the report ACI 440.2R-02 (called ACI guideline). Several programs were made by utilizing the inherent random number generators of Matlab software. The results indicate that the concrete strength f' c, CFRP reinforcement ratio ρf and CFRP mechanical properties are the most significant influencing factors on the mean values and the standard deviations of the strength ratio M/(Mn). The results show that the averaged reliability indexes decrease with increasing the resistance reduction factor and load effect ratio Ln/Dn. The global reliability index for flexural design was found to be 4.40, based on all reliability indexes. The reliability level of ACI guideline is rather conservative. The resistance reduction factor is suggested as a fixed value of 0.90, regardless of the strain level of the tensile steel reinforcement. ACI guideline is the most typical one among all current relevant guidelines. The reliability assessment of this guideline is of general significance.
Fabrication and properties of 1-3 cement based piezoelectric composites
HUANG Shifeng, YE Zhengmao, WANG Shoude, XU Dongyu, CHANG Jun, CHENG Xin
2007, 24(1): 122-126.
1-3 cement based piezoelectric composites were fabricated using cement as matrix by the cut-filling method. The fabrication procedure of the composites was introduced in detail. The effects of width to thickness w/t ratio of the 0.375Pb(Mg1/3Nb2/3)O3-0.375PbTiO3-0.25PbZrO3 piezoelectric ceramic rod on the piezoelectric pro-perties, dielectric properties and acoustic impedance of the composites were studied. The results indicate that the piezoelectric constant d33, the electromechanical coupling coefficients Kp and Kt, dielectric constant εr and dielectric loss tanδ are all dependent on the ratio of width to thickness w/t of piezoelectric ceramic rods. By changing the w/t of piezoelectric ceramic rods, the acoustic impedance of the composites can be tailored to match that of the concrete, which shows that 1-3 cement based piezoelectric composite is suitable to be applied in civil structural health monitoring.
Analytical solution of the nearest surface spacing between neighboring binder grains in fresh cement paste
CHEN Huisu, SUN Wei, ZHOU Yanchang, STROEVEN Piet, SLUYS Lambertus Johannes
2007, 24(1): 127-134.
Based on the nearest surface function formula given by Torquato, an analytical solution of the nearest surface spacing between neighboring binder particles was derived. Computer simulation technology was employed to generate one model paste. By comparison of probability density curve, subinterval probability curve and cumulative probability curves of the nearest surface spacing between neighboring aggregate grains, it was found that the theoretical results are consistent with the simulation very well. Furthermore, for model binder which follows Rosin-Rammler function, these analytical formula were used to study the influence of fineness of cement and water to binder ratio (w/b ratio) on the distribution of the nearest surface spacing between neighboring binder particles. The simulation data show that the fineness of cement exerts more significant influence on the mean value of the nearest surface spacing between neighboring particles than w/b ratio. These analytical solutions provide the criterion to set the proper ratio between powder materials with different particle size distribution and diameter range so as to reach higher packing density. They also provide the criterion to set the size of the model at different scale levels in multi-scale modeling approaches. In addition, these analytical formulas are valuable to quantify the action of micro-aggregate effect of fly ash, and to learn about the interacting degree between neighboring aggregate grains as well as the interference between neighboring interfacial transition zones.
CVI treatment of short carbon fibers and their dispersion in CFRC
WANG Chuang, LI Kezhi, LI Hejun, XU Guozhong
2007, 24(1): 135-140.
The carbon fibers were treated by chemical vapor infiltration (CVI) technology and they were pre-dispersed with the aid of ultrasonic vibration. Both a new dispersant hydroxyethyl cellulose (HEC) and silicon fume were adopted to disperse the carbon fibers in the cement matrix. The fracture surface of CFRC was observed by using SEM to show the dispersion of carbon fibers. The variation coefficient of the mass of separate carbon fibers was applied to evaluate the dispersion of carbon fibers in CFRC. The results show that prior to the adding of dispersants, both CVI surface treatment and pre-dispersion of carbon fibers were helpful for improving the dispersion of carbon fibers. Different mass fractions of HEC and silicon fume in the cement improve the dispersion apparently, which increases with the increasing amount of HEC. The variation coefficient is a minimum when the contents of HEC and silicon fume are 0.6% and 10% in the mixture respectively, at which the dispersion of the carbon fibers is most ideal.
Measurement of complex electromagnetic parameters of composite materials by free-space method
ZHANG Wei, SU Donglin
2007, 24(1): 141-145.
The free-space method is a suitable analysis method for measuring electromagnetic parameters of composite materials, due to its easy changeable incident angle and polarization of electromagnetic waves. This method was used to measure complex electromagnetic parameters of polymers and composites. In order to solve the multi-valued problem caused by the calculation process, several effective ways were proposed for the theoretical analysis. The complex permittivity and permeability of four samples of polymer composite materials were measured in the X-band(8.2~12.4GHz) by using the free-space method. The experimental data are validated with the help of the waveguide technique. The results indicate that the complex electromagnetic parameters of composite materials can be measured exactly by the free-space method.
Experimental investigation on the energy absorption characteristic of braided composite circular tubes subjected to quasi-static axial compression
ZHANG Ping, GUI Liangjin, FAN Zijie
2007, 24(1): 146-150.
Quasi-static axial compression tests were performed to study the failure mechanisms and energy absorption characteristic of the 2D triaxially braided composite circular tubes. The effect of the braid parameters on the energy absorption characteristic was investigated. Four primary failure modes observed in the tests are frond fracture, local buckling, fragmental failure and catastrophic failure. As the braid layers increase or the braid angle decreases, the circular tubes have higher specific energy absorption (Es) in the same fiber volume fraction. The 2D triaxially braided composite circular tubes with high Es are very effective energy absorbers.
Analysis on contact damage problem of composite plates
HU Weiping, ZHANG Xing, MENG Qingchun
2007, 24(1): 151-157.
A continuity damage mechanics method, combined with analysis on the contact problem of non-damaged composite plates, was introduced into the analysis on the contact damage problem of the composite plates under static contact loading. The contact problem of non-damaged composite plates was solved by the inverse method. Considering that the interlaminar material is easy to be damaged in engineering application and to obtain a simple mechanics model firstly, just count the damage of interlaminar glue layer during the analysis on contact problems. The damage development of the glue layer was supposed to be isotropic. The parameters of glue damage development were obtained by the fitting curves of fatigue experiments. The approaches of additional loading and the iteration were applied to the analysis of interlaminar damage and delamination problems of the composite plates under static contact loading. The damage distribution and stress distribution of the glue layers were obtained. The result shows that the above method has good behavior of convergence, and is convenient for application.
Evaluation of elastic properties of 3D 4-directional braided composites
YAN Shi, WU Linzhi, SUN Yuguo, DU Shanyi
2007, 24(1): 158-166.
A relatively reasonable three-cell model for 3D 4-directional braided composites is proposed based on the geometrical characteristic of the yarns. The variation of bending characteristics for the yarns in a three-cell was considered in the present model. The fill factor was proposed to distinguish the different cross-sectional variations of the yarns in the three cells. The model to predict stiffness was then established based on the stiffness volume average method. The elasticity constants of the material were obtained. The effects of the processing parameters and the dimension of the structure on the effective elastic properties of the composite were also studied by the meso-mechanical method. The numerical examples of the structure with different dimensions calculated by the model show that the theoretical predictions compare well with experimental results.
Composite wing optimization design based on distributed computing
CHENG Wenyuan, CHANG Yan, CUI Degang, XIE Xianghui
2007, 24(1): 167-171.
The high accuracy commercial FEA (finite element analysis) software was integrated with GA (genetic algorithm) to solve the composite wing optimization design for aeroelastic request. An optimization algorithm for composite wings was proposed that integrates the distributed computing with GA to enhance the efficiency. Taking the aileron and control surface reversal problem of a high-aspect-ratio composite wing as an example, the result shows that the algorithm can solve the complicated structure optimization problem in engineering.
Evolvement of matrix micro-crack damage of stiffened composite plates excited by simple harmonic dynamic load
WANG Man, CHEN Haoran, BAI Ruixiang, CHENG Feifei
2007, 24(1): 172-178.
The matrix damage evolution behavior and the effect of matrix micro-cracks on the dynamic characteristics of composite stiffened delaminated plates are studied. A stiffness reduction model considering matrix micro-cracks criteria is established. The model can be used to investigate the matrix damage evolution behavior under harmonic excitation effectively as the influence of the number of cycles has been taken into account. On the basis of Mindlin deformation assumption and the modal damping model, a dynamic numerical analysis for investigating the characteristics of damage evolution, stiffness reduction, natural frequency reduction and dynamic response of the delaminated stiffened composite plates has been carried out by the finite element method.
SH wave in piezoelectric composite layered structure
DAI Haitao, CHENG Wei
2007, 24(1): 179-184.
Considering piezoelectric coupling, the characteristic of frequency dispersion was investigated and the transient SH wave was obtained by means of the reverberation matrix-two dimensional spectrum method in the piezoelectric composite layered structure. The numerical results show that the cutoff frequency and phase velocity are raised as the piezoelectric effect, and the energy of SH wave generated by the surface disturbance partially propagates into the depth direction and the other propagates along the surface in the form of surface wave within two-plate-depth. The reverberation matrix-two dimensional spectrum method presents an effective numerical approach for the investigation of the transient wave in multilayer structures.