Table of Content

28 February 2018, Volume 0 Issue 2

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BASIC STUDY

STUDY ON LIMIT AXIAL-LOAD RATIO OF PVC-FRP CONFINED REINFORCED CONCRETE COLUMN

YU Feng, NIU Di-tao

2018, 0(2):  5-7. 

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The mechanical behavior is analyzed according to the stress-strain relationship of PVC-FRP confined reinforced concrete column. Based on the equilibrium condition of large and small eccentric limit compression, the basic assumptions for limit axial-load ratio of PVC-FRP confined reinforced concrete column are proposed, and then a calculating method of limit axial-load ratio is derived. It is shown that the limit axial-load ratio of PVC-FRP confined reinforced concrete column decreases with the increasing hoop spacing of CFRP strips. The limit axial-load ratio of PVC-FRP confined reinforced concrete column is greatly improved compared with that of reinforced concrete column.

RESEARCH ON NON-GEODESIC WINDING LINEAR DESIGN AND STRENGTH ANALYSIS OF COMPOSITE SPHERICAL GAS CYLINDER

LIU Meng, ZU Lei, LI Shu-xin, WANG Yang

2018, 0(2):  8-14. 

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Carbon fiber winding spherical gas cylinders have been widely used in aerospace and civilian industry for its high specific strength and stiffness, and fatigue resistance. Based on the differential geometry, the trajectory equation of the doffing point satisfying the basic principle of spherical gas cylinder winding was derived. The fiber trajectories for non-geodesic over wound spherical gas cylinders and related stable winding condition were given. Then, the winding trajectories were simulated. Considering the variable curvature of spherical shells, the winding angle and thickness of winding layer were designed by Finite Element Analysis. By this method, the stress distribution of the aluminum liner and the winding layer were analyzed at the operating pressure. The bursting pressure of the spherical gas cylinders was also predicted. The results show that the optimal winding parameters simultaneously satisfy the basic requirements of the winding technology and improve the mechanical performance of the spherical gas cylinders effectively. The results of this paper are of important significance to design and manufacture the composite spherical pressure vessels.

EXPERIMENTAL STUDY ON SHEAR BEHAVIOR OF BFRP REINFORCED RAC BEAMS

HAN Ding-jie, LIU Zhong-xian, LIU Hua-xin, ZHANG Zhi-jin

2018, 0(2):  15-20. 

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The shear performances are presented for recycled aggregate concrete (RAC) beams reinforced with basalt fiber-reinforced polymer (BFRP) bars. Four beams reinforced with BFRP bars with and without stirrups were constructed and tested. The failure modes, load-deflection, load-strain behavior of longitudinal reinforcement and stirrups, and shear capacity were discussed respectively. And, a comparative analysis was carried out with four steel bars reinforced RAC beams with the same size. It was observed that all the BFRP bars reinforced concrete beams failed in shear, but the steel bars reinforced RAC beams is changed from shear failure to flexural failure after being configured the stirrups. Stirrups on the improvement of BFRP bars reinforced beam shear capacity is more significant. The deformability of BFRP bars reinforced concrete beams with stirrups is better than that of beams without stirrups, and the shear resistance ance effect of the stirrups is related to the position and inclination of the shear cracks in the beam.

CROSS SECTION STRUCTURE DESIGN AND STRENGTH ANALYSIS OF GLASS FIBER REINFORCED FLEXIBLE PIPE IN DEEP SEA

PAN Jun, ZHANG Dong-sheng, LI Peng, CONG Ri-feng

2018, 0(2):  21-27. 

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Traditional steel pipes applied to as submarine pipelines and risers in the deep oil exploitation have defects of poor corrosion resistance, large weight and weak flexibility. The thermoplastic glass fiber reinforced flexible pipes with features of high corrosion resistance, light weight and high strength and good flexibility are becoming the trend of marine pipelines development. Aiming at designing cross section structure of reinforcement layer of glass fiber reinforced flexible pipes, which are utilized to oil well in 500 m deep sea, according to DNVGL-RP-F119 specification and ABS relevant regulation, combination models of ±30°~±75°winding angle and 20~40 winding layers are set by experience, in response to the problem of winding angle and winding layers in reinforcement layer. ABAQUS finite element analysis software is employed to make strength analysis under three load cases in which the inner pressure is 30 MPa, tensile load is 60 t, external pressure is 5 MPa. Optimal winding angle ±60° is obtained which is satisfied with above three kinds of load cases. Moreover, after strength check of 90 MPa burst pressure and combined load case of tensile load and external pressure , it reveals that the reinforcement structure in which the optimal winding angle is ±60°and minimum winding layers are 36 can meet the requirement of technical indicators.

NUMERICAL SIMULATION OF CARRYING CAPACITY OF COMPOSITE REINFORCED PANELS WITH DEFECT

ZHOU Zheng-gen, CAO Dong-feng, HU Hai-xiao, ZHONG Yu-cheng

2018, 0(2):  28-35. 

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Carbon fiber composite Skin/Stringer is a typical component of aircraft structure. However, the manufacturing process of laminated composite structure can lead to the existence of defects in the bonds. The pre-existing defects have a great effect on the ultimate bearing capacity and failure behavior of Skin/Stringer. Therefore, it is important to assess structural integrity. In this paper, the specimens were subjected to three-point bending. To evaluate the debonding mechanisms between the skin and the stringer, different sizes and locations of defects were taken into consideration. First, a three-dimensional finite element model based on Abaqus/Standard was established, and the bilinear cohesive zone model (CZM) was used to simulate the interface failure between the skin and the stringer; Then, the validity of the model were verified through the experimental data of the literatures. Finally based on the finite element model, the influence of the sizes and locations of the defects on the failure modes and the load-carrying capacity of the structure were investigated. The result indicats that the calculated results show good agreement with those of experiments. The load capacity of the structure is found to decrease with increasing defect size, and Skin-Stringer is very sensitive to defects at the middle of the interface; The failure modes of the Skin/Stringer changes because of the pre-existing defects. But the initial crack always occurs in the matrix near the interface area.

RESEARCH OF REPAIRING PERFORMANCE AND FAILURE MECHANISM OF GLASS FIBER-ALUMINUM LAMINATES

CUI Hai-chao, WANG Hai-peng

2018, 0(2):  36-40. 

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The tensile test was carried out before and after the repairing of the glass fiber-aluminum laminates with presetting hole defects. The influence of the load on the tensile displacement during the stretching process was discussed, and the influence of the reinforcing sheet on the tensile strength of the material was analyzed. The results show that all the glass fiber-aluminum laminates have experienced the yield stage, the repaired laminates exhibit a more obvious yield phenomenon, and the load fluctuates greatly before the damage. The ultimate strength of the repair rate was 17.7%, 13.2%, 20.6%, respectively, for the aminates, containing 6 mm,10 mm,12 mm hole defects. Due to the repairing plates, the laminates showed double fan damage in the fracture position after the tensile fracture. The damage form of the repairing plates was shear failure of the film, which occurred on the surface of the aluminum alloy.

FIBER TENSION ON THE ANALYSIS OF COMPOSITE WINDING TRACK

TIAN Jian-de, LIU Bao-quan, MA Mei-qin, ZHANG Jian

2018, 0(2):  41-46. 

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In order to realize the high-quality formation of filament-wound composite pipes, the fiber tension plays a key role and the degree of the tension fluctuation directly affects the performance of composite pipes molding. In order to reduce the differences between the tension levels in the winding process, the impacts of the fiber tension should be taken into account when the winding trajectory is projected and the method of adding the preset tension load to the end of the manipulator ought to be proposed. Also, establishing a wound model of sixfreedomdegrees’robotic arms and using the kinematic equations to find solutions. Meanwhile, needing to design a winding track by means of establishing a MATLAB and ADAMS cosimulation platform and the winding track affected by the tension issimulated. At the same time, it’s also necessary to perform the winding experiment about the composite pipe fiber with or without tension load at the end of the mechanical arms. Finally, the simulation results suggest that the winding trajectory under the tension load can effectively restrain the fluctuation of the tension in the winding process.

APPLICATION RESEARCH

RESEARCH ON THE INFLUENCING FACTORS AND LAWS ABOUT BENDING STIFFNESS OF GRILLE REINFORCED SANDWICH PANEL

WANG Ya-nan, MEI Zhi-yuan, LI Hua-dong, CHENGuo-tao

2018, 0(2):  47-51. 

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Based on finite element simulation and experiment, influencing factors and laws about bending stiffness of grille reinforced sandwich panels were studied. Firstly, the influence of grille structure on the flexural properties of sandwich panels was simulated and analyzed. It was found that the grille structure can significantly improve the bending stiffness of sandwich panels. Then, the influence of several important parameters, such as the skin fiber angle and the density of the grille, about the bending stiffness of the grille reinforced sandwich panels were simulated and analyzed. Finally, the accuracy of the simulation was verified by experiments. The analysis results show that the sandwich panel had the best bending stiffness when sandwich panel skin fiberswas laid at ±45 degrees. And, if the total volume of the grillewas certain, that is, a certain amount of grille, the thickness of the single grille can be reduced to increase the density of the grille in a certain range, and the bending stiffness of the sandwich panel will be greatly improved.

THE EXPERIMENT OF BENDING PERFORMANCE AND THEORETICAL METHOD RESEARCH OF CFRP-PCPS REINFORCEMENT CONCRETE BEAM

DENG Yu, GAN De-li, ZHANG Peng, YANG Xi-tao

2018, 0(2):  52-57. 

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The article, through static test of the 7 concrete beam specimens, compares the bearing capacity, deflection, crack of the reinforcement concrete beam, common prestressed CFRP reinforcement concrete beam, CFRP-PCPs reinforcement concrete beam and CFRP-PCPs reinforcement concrete beam of different prestresse level of CFRP reinforcement. The research results show that the normal use stage of CFRP-PCPs reinforcement concrete beam′s deflection and crack satisfy the use requirement of structure safety. And, CFRP-PCPs reinforcement concrete beam can effectively overcome the disadvantage of large deflection and crack width of common prestressed CFRP reinforcement concrete beam. Further, CFRP-PCPs reinforcement can effectively delay the crack propagation of traditional prestressed CFRP reinforced concrete beam, increase the overall stiffness and strength of component, improve ductility and make full use advantages of CFRP materials. Based on the related experimental results, this paper puts forward the design and calculation method of flexural bearing capacity,crack width and deflection of CFRP-PCPs reinforced concrete beam. The results show that the calculated value can agree well with the test results.

EFFECTS OF HEATING RATE ON THE THERMAL STRESS OF COMPOSITE PATCHES DURING CURING PROCESS

LI Shi-lin, CHEN Shu-xian, TIAN Qiu-shi, LIANG Zhen-yu

2018, 0(2):  58-65. 

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The heat-blanket thermal curing process of thermosetting resin matrix composite patch was simulated using the finite element method. The distribution and variation characteristics of temperature and thermal stress of the composite patch for different heating rates were analyzed, and the effects of heating rates on the residual thermal stress in the patch at different time points were studied. The results show that the thermal stress is mainly concentrated on the central region of the patch top surface and in its contact area with the mother plate during the heating stage, and the thermal stress in the internal area is higher than that at the patch top surface during the isothermal and cooling stage. The results also show that the faster the heating rate is, the faster the curing is. But, the greater the peak thermal stress is during the heating phase. And the value and distribution of thermal stress of the patch are independent of the heating rate during the isothermal and cooling stage. The results also indicate that the maximum value of the thermal stress appears at the end of the heating stage for the lower heating rate, while the maximum thermal stress appears near the end of the heating stage for higher heating rates. The research results provide the good numerical basis for selection of the heating rate to reduce the internal thermal stress and to control the delamination of the patch in the heating stage.

THE MECHANICAL PROPERTIES OF 3D BRAID COMPOSITE ADHESIVE JOINTS

YANG Guan-xia, YANG Tao, DU Yu

2018, 0(2):  66-69. 

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In order to compare the efficiency of 3D braid composite repair of different type joints, the mechanical properties of step lap joint and nested joint subjected to tensile and bending load were examined experimentally by keeping the same joint length for all samples. Load-displacement curves were obtained for each type of joint by the test. Then, the strength of samples and the repair efficiency were acquired by comparing the strength of joints with intact specimens. Meanwhile, the tensile and bending damage evolution and profiles of specimens were analyzed and summarized. The test results show that the step lap joint has better mechanical properties. The repair efficiency of step lap joint under tensile load was 37.75%, and under bending load, the repair efficiency was 66.25%. The repair efficiency of nested joint under tensile load can reach 18.97%, and under bending load, the repair efficiency can reach 21.44%.

SPRING-BACK STUDY FOR COMPOSITES SPAR

HUANG Gang-hua, JIA Li-jie, XU Peng

2018, 0(2):  70-73. 

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Composite materials have been widely used in aerospace field for its high strength to weight ratio, high modulus, desirable fatigue resistance properties and other fine qualities. But, it is influenced by a variety of factors, such as material properties, ply orientations, curing system, mould material and so on. As a matter of fact, the shape of the composites after curing is not certain, spring-back may be caused, and even lead to scrapping of the cured part and mould due to deformation over tolerance. This article, through spring-back experiments on different parts of wing spar, simulates the spring-back of the demonstrator by finite element method. Then, we linearly amend it by comparing with the actual measured result, and acquire the amendatory formula, finally calculate the amendatory value, use it in the research and manufacturing of 3 m spar, and validate the amendatory formula.

STUDY ON CURING KINETICS OF EPOXY RESIN FOR FILAMENT WINDING

LIU Wei-wei, YANG Ke-lun, LI Tong, XIAO Wen-gang

2018, 0(2):  74-77. 

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The curing kinetics of an epoxy resin system for filament wound were investigated by non-isothermal DSC method. Based on the test data at different heating rates,the curing process parameters were determined. A n-order kinetic model was established and the activation energies obtained by the Kissinger equation and the Ozawa equation were compared. The results show that the gelation temperature of the resin system is 89.44 ℃, the curing temperature is 114.5 ℃, and the post-treatment temperature is 155.04 ℃. The curing process is in accordance with the n-order kinetic model.

THE INFLUENCE OF RAW MINERAL MATERIALS FOR SiO₂-Al₂O₃-MgO SYSTEM GLASS

HUANG Song-lin, ZU Qun, HUANG San-xi, ZHANG Yan

2018, 0(2):  78-82. 

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Silica sand, aluminium oxide and magnesium oxide have always been selected as main raw materials for the production of S high-strength fiber glass in the SiO₂-Al₂O₃-MgO system. The high purity of these chemicals helps to improve the stability of product composition and performance, which bring highly energy-consuming, require higher temperature and have difficulties in glass melt clarification and homogenizing meanwhile. To improve the melting process performance of SiO₂-Al₂O₃-MgO system S-glass, the influence of kaolin and talc in S-glass melting is studied in this paper. The characteristic temperature of glass is analyzed by DSC, the phase transformation in the batch melting process is characterized by XRD. The batch melting experiment has been carried out in a muffle furnace, and the strength test of the new born glass fiber was carried out. Studies have shown that use of the batch of kaolin and talc can significantly lower the melting temperature about 50 ℃, reduce energy consumption and improve the system of S-glass melting process performance. Also it is found that minerals of Fe²⁺ content in raw materials is larger, which increase the temperature gradient in glass melt and is not conducive to glass clarification. So, in order to improve the glass clarification and avoid the glass fiber performance affected, measures should be taken to reduce the content of Fe²⁺ in S-glass batch melting.

DESIGN OF SINGLE-SIDE DOUBLE-LINE STITCHING DEVICE FOR COMPOSITES

TIAN Hui-fang, LIU Li-jun, CHEN Pei

2018, 0(2):  83-86. 

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Through the analysis of the suture technology and the characteristics of the suture, the problems and shortcomings of the existing double-sided suture and the single-side suture techniques are found. Then, by combining with the advantages of the existing OSS single-side suture and the traditional double-sided hook suture, this paper presents a single-side double-line suture technology. And, based on this technology, the detailed structure has been designed, and the 3D model has been built by SolidWorks. This suture technology can form a smooth and stable line similar to the improved hook line. Finally, Adams has been used to verify the feasibility of the design.

STRUCTURE DESIGN OF COMPOSITE PV BRACKET AND THE APPLICATION STUDY OF ENGINEERING

KE Rui, ZHU Xiao-dong, DONG Zhong-qiang, WU Xiong

2018, 0(2):  87-93. 

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In order to develop a stable, durable and lightweight PV bracket, based on a PV bracket pilot project, this paper designs a polymer matrix composite PV bracket. Based on the wind load, snow load, self-weight load and earthquake load, the strength of the key component and the nodes have been checked according to calculation. At the same time, the feasibility of the application of the composite PV bracket was verified by the wind tunnel test of PV bracket and the 4000 h multi-factor aging properties of composite materials.

REVIEW

A LITERATURE REVIEW OF FIRE BEHAVIOUR OF RC BEAMS STRENGTHENED WITH EBR-CFRP STRIPS

YIN Zhong-hao, XU Jie, HAN Qing-hua

2018, 0(2):  94-100. 

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CFRP have been used for a long time as a new kind of reinforcing material. Externally Bonded Reinforced (EBR) is one of the most commonly technologies used in CFRP reinforcement works. But CFRP is sensitive to temperature. When the temperature exceeds the glass transition temperature(T_g)of CFRP, the matrix used to cure the fibers will soften, which leads to the rapid degradation of the mechanical properties of CFRP. This has seriously affected the development of this technology in the field of civil engineering. For solving the problem, many research was done. This paper presents a review of studies on the high temperature properties of CFRP, CFRP-concrete contact surface and fire resistance of EBR-CFRP strengthened beams. In general, when the temperature reaches about 300 ℃, the matrix in CFRP will melt. The tensile strength of CFRP strips will degrade to 50% of their original strength. However, the CFRP-concrete interface is also sensitive to fire. Without fire prevention, the CFRP strips are easy to spin-off. One of the most effective measures is setting fire insulation at the surface of beams. However, there is no integrated theory of fire-resistance design for CFRP strengthened beams up to now. Recommendations for further research are given at the end of the paper.

PRESENT SITUATION AND PROSPECT OF RESEARCH ON THE JOIN TECHNOLOGY OF COMPOSITE MATERIALS

GAO Jia-jia, CHU Long-sheng

2018, 0(2):  101-108. 

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The current research status of the joint techniques of composite materials is reviewed, which includes the mechanical joint, adhesive joint and hybrid joint. The advantages and disadvantages, applicable fields, and the prospect of these joints are explained in this study. The results show the traditional mechanical joint has strong ability to resist the inter-laminar shear and stripping, which is suitable for heavy load. The adhesive joint is a kind of efficient and low-cost joint techniques with light weight and high efficiency, so it suits for complicated thin-walled parts. And the hybrid joint has the advantages of the mechanical joint and the adhesive joint, namely, the reliable quality and resistance to the harsh environment, so it can join the heterogeneous parts. Finally, the join techniques of composite materials in the direction of structural integration in the future are discussed.