Table of Content

28 August 2016, Volume 0 Issue 8

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BASIC STUDY

NUMERICAL SIMULATION ON FIBER COMPACTION PROCESS OF FIBER WINDING COMPOSITES IN CURING PROCESS

REN Ming-fa, LIU Chang-zhi, CONG Jie, ZHANG Jing

2016, 0(8):  5-12. 

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In the curing process of fiber winding composites, the fiber volume fractions and the thickness of winding layer are affected by the performance of resin flow and winding tension. Based on Squeeze-sponge′ model, a corresponding finite element model is developed to simulate resin flow and fiber compaction process in the curing process. The curing degree, temperature, resin viscosity and permeability of fiber winding composites are taken into account. Winding features including winding tension and winding patterns are considered. According to data in reference, the numerical model was proved to possess relative superior reliability. The effects of the variation of winding tension on the resin pressure, fiber volume fractions during curing process was studied attentively. It is found that when prepreg tape wind with constant interlaminar stress, resin distributes more symmetrically in the radial direction, and fiber volume fraction of layers tend to be more uniform compared with prepreg tape winding with constant tension. Increasing winding tension of layers which are away from the resin export can make fiber volume fraction equal in every layer.

REINFORCING AND TOUGHENING OF QUARTZ FIBER(QF)/SILICON-CONTAINING ARYLACETYLENE (PSA) COMPOSITES WITH NEW SILANE COUPLING AGENT

YANG Hai-hui, HU Yan-hong, DU Lei, GU Yuan-bo

2016, 0(8):  13-21. 

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A novel silane coupling agent AAS, designed and synthesized by our team, which contains terminal alkyne, ether linkage, and imide rings was employed to reinforce and toughen quartz fiber(QF)/ silicon-containing arylacetylene (PSA) composites. The curing process of AAS and PSA was analyzed by FT-IR, DSC and TGA. XPS analysis indicates that chemical bondings are formed between AAS and QF. The interfacial properties of QF/PSA are improved after AAS treatment. The date of ILSS and flexual strength increased by 50.6% and 43.0%, respectively, compared with those of unmodified at room temperature, and the retention ratios of mechanical strengths are 66.0% and 84.2% when heated up to 250 ℃. The impact resistance of the composites treated by coupling agent was also improved. At room temperature, the impact strength of the material is improved by 20.4%.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF RESIDUAL STRESS FOR SCARF REPAIRED COMPOSITES DURING CURING PROCESS

PANG Jie, LIU Guo-chun

2016, 0(8):  22-26. 

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Based on the thermochemical and residual stress theory, a three-dimensional finite element model of composite was developed during the curing process by coupled thermos-mechanical method. The accuracy of the simulation model is verified by comparing with the literature results of C-shape part. Based on the model, modulus and residual stress variation of the scarf repaired AS4/3501 composite laminate were calculated during the curing process. The results indicate that the modulus of resin and composite perpendicular to the fiber is very small before gelation point, residual stress existes in the direction of fiber. After gelation point, modulus increases to constant valve with the curing time quickly, and residual stress develops gradually, then increases quickly during the cooldown phase.

PARAMETRIC ANALYSIS AND OPTIMIZATION OF FREQUENCY PROPERTY OF VARIABLE ANGLE TOW LAMINATES

SUN Shi-ping, DENG Tong-qiang, HU Zheng

2016, 0(8):  27-32. 

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The aim of this paper is to trace the influence of fiber path parameters on frequency property so as to design VAT laminates effectively. Firstly, the parametric finite element model of VAT laminate was established to investigate effect of path parameters on the frequency property, by utilizing the definition of linear variation of fiber angle. Secondly, influences of aspect ratio and thickness of VAT laminate on frequency characteristic were analyzed and discussed based on the periodical distribution of fiber path. Finally, optimization design fiber path of square VAT laminate was conducted under different boundary conditions using sequential response surface method, for maximizing the first order frequency and the difference of first and second order frequency. The results show that the band gap of first and second order frequency of VAT laminates can be effectively improved by the optimization of fiber reference direction angle, which has little influence on the first order frequency. Effect of characteristic length on frequency performance is decreasing with increasing aspect ratio. The thinner VAT laminates, the greater the impact of fiber path on frequency performance. The results provide guidance for frequency performance design of VAT laminates.

MOLECULAR SIMULATION AND EXPERIMENTAL ANALYSIS ON ELASTIC MODULUS OF EPOXY RESIN AT HIGH-LOW TEMPERATURE

LI Hao, ZHANG Qing-jie, GAO Liang, ZHANG Wen-qing

2016, 0(8):  33-37. 

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The relationship between mechanical properties of epoxy resin-amine system and temperature has attracted extensive attention. In this paper, two crosslinking unit cells of DDM/DGEBA and DDS/DGEBA were established by using molecular dynamic (MD) simulation. On the basis of simulation analysis of glass transition temperature (T_g) obtained from density-temperature curves, the elastic modulus from high temperature (420 K) to cryogenic temperature (100 K) of two systems were investigated by using MD simulation and experimental methods. Furthermore, the relationship between modulus and a serious of microstructure, i.e. cohesive energy density (CED) and free volume of epoxy resin-amine system on the change of elastic modulus were investigated. Both MD results and experimental results showed that the elastic modulus of two epoxy resin systems increased as the temperature decreasing, which was attributed to the decrease of CED as well as the increase of free volume fraction as temperature decreasing.

ALKALI SOLUTION FATIGUE UNDER COUPLING ACTION OF BFRP REINFORCED BENDING EXPERIMENTAL STUDY ON THE DAMAGE OF REINFORCED CONCRETE BEAM

WANG Hai-liang, LI Long

2016, 0(8):  38-43. 

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Based on the complex environment and the particular load of the bridge structure, this paper attempts to explore the performance of damaged RC beams strengthened with BFRP sheets in alkali solution environment and fatigue loading. Damaged RC beams strengthened with two layers of BFRP sheets in alkali solution environment where the pH values are 7,9,10 and fatigue loading have been carried out. Test results show that even under the coupling of the alkali solution and the fatigue loading, the BFRP sheets can improve the ultimate bearing capacity and flexural rigidity of damaged RC beams. Under the same fatigue times, in solution environment where the pH value is 9, the deflection of the beams effected by 90 days increased by 23.13% as compared to the beams effected by 60 days. When other parameters are same, the bending strength of beams effected by alkali solution where the pH values are 7 and 10 decreased by 10.06% and 21.15% relative to beams without environment effect. So, with the increase of the concentration of alkali solution and the time of action, the ultimate bearing capacity, flexural rigidity and anti fatigue properties of RC beams decreased significantly. Finally, regarding the deflection changes as fatigue damage index, we fitted deformation modulus of strengthened beams, with the consideration of the pH value and the fatigue times.

3D FINITE ELEMENT METHOD PROGRESSIVE DAMAGE ANALYSIS FOR THE OPEN-HOLE LAMINATES BASED ON ZINOVIEV THEORY

CHANG Lei, LI Shu-xin, DING An-xin, WANG Ji-hui

2016, 0(8):  44-49. 

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An investiagtion was conducted to study tensile failure of composite laminates with an open hole. Both a numerical simulation and experiments were performed during the study. A three-dimensional finite element model for composite laminate with an open hole was built. The progressive damage analysis contains four parts: the constitutive model, calculating the stresses, failure criteria and the stiffness degradation. Many theories have been proposed based on different physical,mechanical or logical considerations. There were great differences by using difference theory. A three-dimensional stiffness degradation model based on the two-dimensional Zinoviev theroy and combined with the improved three-dimensional Hashin criterion was proposed. This paper described composite laminates′ failure process in three aspects: fiber failure, matrix failure and delamination failure, and predicted the ultimate tensile strengths and damage progression of the open-hole composite laminates. Overall, good agreement were found between numerical simulation and experiment. And, it proved the high accuracy of the three-dimensional stiffness reduction model, which could be used to guide the composite laminates′ progressive failure analysis.

A STUDY ON ASSEMBLY PRE-TENSIONING FORCE OF WIND TURBINE BLADE

WU Sheng-jun, FENG Wei, YUAN Fei-qi, HAN Tao

2016, 0(8):  50-52. 

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The root joint of wind turbine blade is the only and critical component to connect blade and hub. Therefore, the bolt pre-tensioning force should be applied when installation to keep blade and hub closely. The value of pre-tensioning force applied influences not only the bolt functions, but also the normal operation of blade. However, simulating the bolt pre-tensioning force with high accuracy is very difficult and complicated in FEA of bolt connection. This paper illuminates the theoretical calculation process and uses FEA method to simulate the bolt pre-tensioning force in ANSYS WORKBENCH. The results provide basis and direction for applying the pre-tensioning force.

APPLICATION RESEARCH

NUMERICAL ANALYSIS OF ANTI-EXPLOSION PERFORMANCES OF RC BEAM WITH INITIAL CRACKS STRENGTHENED WITH CFRP SHEETS

QU Yan-dong, LI Xin, LIU Wan-li, ZHANG Wen-jiao

2016, 0(8):  53-56. 

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Building structures strengthened with CFRP is a kind of new technology. Only limited research has been developed to study anti-explosion performances of simply supported RC beams with initial cracks (pre-cracked RC beam). Based on the large nonlinear dynamics analysis software LS-DYNA, nonlinear finite element analysis of the anti-explosion behavior of pre-cracked RC beams locally strengthened with CFRP in the form of full package were conducted from two aspects of strengthening layers and lengths of CFRP. The results show that, when the pre-cracked RC beam locally was strengthened by CFRP, the overall stiffness of the pre-cracked RC beam is improved, and that the damage and deformation under blasting load is reduced. When four layers of 300 mm wide CFRP sheets in the form of full package were locally bonded to the surface of pre-cracked RC beam, where the initial cracks located, the anti-explosion properties of the pre-cracked RC beam could be effectively improved to some extent. The obtained results are of great significance to the anti-explosion design and reinforcements of RC structures.

STUDY ON THE BOND PERFORMANCE BETWEEN BFRP BARS AND STEAM CURING CONCRETE

WAN Chao-yang, CHEN Guo-xin, CHEN Lei, WANG Kang

2016, 0(8):  57-61. 

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In order to study the bond performance of BFRP bars and concrete, BFRP bars concrete specimens were steamed 8 h and then cured 3 d and 28 d, respectively. After that, the center pull out of specimens was tested. On the basis of specimens′ failure pattern in different age and the change rule of specimens′ bond strength between concrete strength and bond length, 1stOpt software was used to test quadratic nonlinear curved surface fitting relationship between specimens′ bond strength and influencing factors. The results showed that the main failure pattern of specimens were pulled-out of BFRP bars and split tensile failure of concrete. Compared with the bond length, the bond strength of concrete strength was significantly influenced by the strength of concrete at different age. Compared with C25, the bond strength of C40 was increased by 29.1%, and compared with 7.5 d, the bond strength of 17.5 d was decreased by 21.4%. The bond strength formula of 1stOpt software fitting is the theoretical basis for the bond strength of different concrete strength and different bond length.

RESEARCH OF HOT MOLDING PRESS ON LONG GLASS FIBER REINFORCED POLYPROPYLENE COMPOSITE

TANG Rong-hua, YANG Xu-jing, ZHENG Juan

2016, 0(8):  62-67. 

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To improve the basic mechanical properties and the stability of mould pressed products formed by long glass fiber reinforced polypropylene (LGFRP), the hot molding process was subdivided into three parts: preheating process, moulding process and forming operation. And, the three parts contain seven parameters which were studied with the orthogonal test and single factor test method .The effect of the seven parameters on the mechanical properties of mould pressed products prepared from LGFRP composite material was discussed and analyzed, and the better molding process parameters are optimized. The results show that the effect of process parameters on mechanical properties is influenced by processing conditions, and refine of the molding process can improve the basic mechanical properties of mould pressed products, and enhance the stability of moulding process.

EXPERIMENTAL STUDY OF HYBRID DE-ICING SYSTEMS COMBINING THERMOELECTRIC AND HYDROPHOBIC COATINGS

WANG Yan-ming, NI Ai-qing, WANG Ji-hui, HU Hai-xiao

2016, 0(8):  68-72. 

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In this paper, a new compound de-icing system combining thermoelectric advantage with hydrophobic superiority is presented, aiming at solving the problem in the wind turbine blade that the energy consumption of thermoelectric is too huge and the effect of the hydrophobic coatings is not satisfied. In order to verify the feasibility and reliability of the compound de-icing system, the specific experiments using GFRP plates containing thermoelectric and hydrophobic coatings were carried out. The compound de-icing system not only meets the de-icing requirement of the wind turbine blade, but also reduces the energy consumption. Furthermore, the compound de-icing system is expected to reduce the damage caused by ice ridge.

RESEARCH OF FORCE MECHANIC CHARACTERISTICS TESTS AND NUMERICAL SIMULATION OF FRPM PIPE

WEI Lian-yu, ZHANG Guo-pan, ZHANG Ji-yuan, WANG Jin-wei

2016, 0(8):  73-77. 

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Combined with an engineering practice in Chengde, Hebei province, the vehicle static load tests were carried out to test the force conditions of FRPM pipe as buried culvert for guiding actual engineering. Its force conditions are closely related with different filling heights and loads. Therefore, on the basis of stress characters obtained by field measurement, under condition of plain strain, the Pipe-Soil interaction model of field tests is established by ABAQUS for numerical analysis in order to reduce numbers and manpower costs of traditional tests. The results show that the pipe culvert buried under the minimum 0.5 m in soil. And, under different vehicle loads, the maximum deformation of the pipe culvert is 1.3 mm, and the stress of the pipe culvert is good. By comparing the results of static load test and numerical simulation results, the validity of the model was proved.

TENSILE PROPERTIES OF THE INTERLOCK LAYING-IN WEFT KNITTED FABRIC REINFORCED COMPOSITES

MA Xiao-hong, QIN Zhi-gang

2016, 0(8):  78-81. 

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The three interlock laying-in weft knitted fabrics are knitted on a computerized flat knitting machine with glass continuous-filament yarns. The glass fiber knitted fabrics are used as reinforcement, the laminates of knitted fabrics/epoxy resin composites were prepared by manual molding technology. The tensile properties of the composite specimens are tested in universal testing machine. The results show that the tensile stress-strain curves of composites appear approximately linear. The tensile curves in the wale direction have obvious yield phenomenon. The tensile strength and modulus in the course direction are the highest, these in the diagonal direction are the second, the lowest in the wale direction. The strain along the course direction is the smallest. The tensile properties of composites possess obvious orthotropic characteristics. The tensile properties of the composite are related to the stitch and density of fabrics, and fiber volume fraction.

MECHANICAL CALCULATION AND ENGINEERING APPLICATION FOR THE CONDUCTOR WITH THE INFLECTION POINT TEMPERATURE CHARACTERISTIC

BAO Xing-hui, YANG Chang-long, ZHANG Yu-liang, JIN Peng

2016, 0(8):  82-86. 

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The special conductor with inflection point temperature characteristics is made of special core wire with outer stranded aluminum wire. In replace of steel core, the special core wire (such as carbon fiber composite) is made of material whose expansion coefficient is far smaller than steel wire. The special core wire has excellent heating tolerance and lower linear expansion coefficient, the temperature for conductor can be allowed to raise to 160 ℃ or higher. So the transmission capacity increases and the conductor is with low sag characteristics.The stringing mechanical properties of the conductor is different from ACSR. The calculation method of inflection point temperature and tension is derived from the conductor by using Hooke′s law of elastic deformation and catenary equation of conductor. The method has been applyed in multiple transmission lines in Liaoning province and achieved good results.

THE PERFORMANCE INFLUENCE OF THE PROCESS GAP ON THE COMPOSITE CIRCULAR TUBES BY THE INFLATABLE BLADDER MOLDING

WANG Ying-nan, PAN Li-jian, LIU Guo-feng, HU Xiu-feng

2016, 0(8):  87-91. 

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This article introduces the design and produce process of stainless mold for composite tubes made by inflatable bladder by using silicone circular tubes as the bladder for pressure. Meanwhile, different carbon composite circular tube under different designed process gaps were fabricated. The micro appearance of the circular tubes section was observed by metalloscope. The compressive properties of the circular tubes were tested, and the mechanical properties results were compared with the plate by the autoclave, which were molding with the same materials and the curing cycle. The results show that, under such forming process, the quality of this product is best. When the ratio of the process gap and the designed thickness of the circular tubes is 34%, the monolayer thickness is relatively lower and uniform, and there are few defects in the tube wall inner. The compressive strength is 634 MPa which is equivalent to the one made by autoclave molding with a compressive strength of 647 MPa. The forming quality and the compressive strength were reduced with the increase of the process gap. Significantly delamination,porosity and defects were shown when the process gap ratio is 86.7%. Meanwhile, the monolayer thickness became larger and uneven. The compressive strength is 427 MPa, which was reduced by 34% compared with the highest value. Forming properties and compressive strength will show the decreased trend when the process gap was reduced, however, it is not significant.

REVIEW

PROGRESS OF RESEARCH ON THIN-PLY LAMINATED COMPOSITES

HE Ming-chang, HUANG Chun-fang, ZHENG Qing, JU Su

2016, 0(8):  92-98. 

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A brief introduction on thin-thickness prepreg of carbon fiber and thin-ply laminated composites was made in the paper, which focuses on the preparation methods of the thin-thickness prepreg of carbon fiber and the mechanical properties of the thin-ply laminated composites. The difference of mechanical properties of the laminated composites with thin and standard thickness plies were summarized, including static mechanical properties, toughness as well as fatigue properties. Effects of the ply thickness on the mechanical properties of the laminated composite were highlighted. At last, the research trends and prospects of the thin-ply laminated composite were discussed.

THE RECENT DEVELOPMENT OF ADVANCED LIQUID COMPOSITE MOLDING TECHNIQUE AND ITS APPLICATION IN AVIATION

LI Pei-xu, CHEN Ping, SU Jia-zhi, LIU Wei-ping

2016, 0(8):  99-104. 

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The widespread application of composite materials has become an important symbol of advanced aircraft technical level. Moreover, it′s one of the important factors to improve the performance and market competitiveness of aircraft products. With the incerase of the amount of composite applied in aircraft structures, the cost issue became prominent. Thus, the liquid composite molding (LCM) technology has caused more and more research attention. This article reviewed the aviation application of LCM technology at home and abroad, introduced the application characteristics based on the developing cases of typical aircraft composite parts, and analyzed the future development tendency.