COMPOSITES SCIENCE AND ENGINEERING

STUDY ON THE PROPERTIES AND MECHANISM OF TOUGHENED EPOXY RESIN SYSTEM WITH DIFFERENT CORE SHELL PARTICLES

WANG Jing,XUE Zhong-min,LI Gang*,YANG Xiao-ping

2018, 0(7): 5-11.

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Core-shell particles are usually consist of a high glass transition temperature "shell" and a rubber "core". The advantage is that the core-shell structure does not change during the process of resin curing. But the uniform dispersion of nanoparticles has always been a difficult problem in the use of epoxy additives. In this paper, we adopt three different kinds of core-shell particles with different composition and sizes to toughen bisphenol F epoxy resin matrix to prepare a series of epoxy resin system with excellent heat resistance. The dispersion of nano-particles by two steps pre-dispersing is studied to obtain a uniform system. The toughening systems have great improvement on resin toughness. The mechanical properties, thermo-properties, rheological properties and microstructure properties has been tested and analyzed. A multi-scale core-shell nanoparticles toughening epoxy system was prepared and its toughening mechanism is illustrated.

DELAMINATION IDENTIFICATION OF COMPOSITE LAMINATED BEAMS BASED ON SUPPORT VECTOR MACHINE

HE Meng-yue,LIANG Zhi-hong,ZHANG Zhi-fang*

2018, 0(7): 12-18.

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Support vector machine (SVM) has not yet been introduced to detect delaminations for fibre reinforced composite materials, and this paper is proposed to assess the delaminations in carbon fiber reinforced polymer (CFRP) beams based on SVM regression, through the changes in modal frequencies due to the damage occurs. Firstly, the finite element model of CFRP beam was established to generate the database of "delamination variables vs. modal frequencies" as well as the test cases for numerical validation. Three different parameter optimization methods, namely, cross validation (CV), genetic algorithm (GA) and particle swarm optimization (PSO), were applied to obtain the suitable parameters for SVM to improve the prediction accuracy. Furthermore, the Polytec laser scanning vibrameter was adopted to conduct the model testing for CFRP beam specimens. The measured frequencies of the specimens were used for validating the SVM regression experimentally, which confirmed that the SVM can be used to detect delamination in CFRP beams.

DAMAGE MONITORING OF CARBON FIBER REINFORCED PLASTIC π ADHESIVE JOINT BASED ON FIBER BRAGG GRATING

JIANG Feng,HU Ye-fa,SONG Chun-sheng

2018, 0(7): 19-25.

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Aiming at the damage monitoring of carbon fiber reinforced plastic π adhesive joint under tensile load, a finite element model of carbon fiber reinforced plastic π adhesive joint is established, and the failure location of the joint is predicted. The mapping relationship between damage evolution and stress distribution is also analyzed. Then, the reflection spectrum of the fiber Bragg grating at the damage location is calculated based on the transfer matrix method, and the effectiveness of the reflection spectrum calculation is verified by the experiment. Finally, the stress distribution is reconstructed by genetic algorithm, and the stress distribution form of the damaged part is obtained, which provides a new method for the damage monitoring of carbon fiber reinforced plastic π adhesive joint in engineering applications.

STRESS AND MODEL ANALYSIS OF THE BLADE OF A ROTATING WIND TURBINE UNDER THE CONDITION OF ICING

CHEN Cai-feng,YANG Jie,CHENG Bin*,LI Xi-yang

2018, 0(7): 26-30.

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Taking rotor blades of rotating ice as the research object, the artificial icing test of blades is carried out. According to the experimental results, a finite element model of wind turbine blades is established, and the stress and modal analysis of blades with different icing thickness are carried out. The analysis results show that the amount of ice change is positively correlated with the stress magnitude of the blades. The different natural frequencies of the blades will be significantly changed by the amount of ice, causing the fatigue damage and deformation of the wind turbine blades, which verifies the results of artificial experiments.

PREPARATION AND STUDY OF PHOTOINITIATED IN SITU POLYMERIZED POLYACRYLATE/GLASS FIBER PREPREG

LIU Chuan-qi,WANG Xiang,*,WANG Jun,

2018, 0(7): 31-35.

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Thermoplastic composite materials with high damage resistance and impact resistance obtained a rapid development, but the problems of impregnation between thermoplastic resin matrix and reinforcing materials hindered the promotion of thermoplastic composite materials. In order to improve the interface performance of thermoplastic composites, polyacrylate resin/glass fiber prepreg was fabricated by in-situ polymerization under the conditon of UV light, with methyl methacrylate, butyl acrylate, glycidyl methacrylate as monomer, with the unidirectional glass fiber as the reinforcing material. Composite materials were prepared by hot pressing. The composite resin content, thermal stability, mechanical properties and microstructure of composite were studied. The experimental results show that the thermal decomposition temperature of polyacrylate resin increases with the increase of GMA content. The resin content is stable in 30%. The glass transition temperature decreased with the increase of GMA content. The tensile strength and the flexural strength showed a trend of increasing at first and then decreasing with the increase of GMA content, and reached a maximum value at the GMA content of 20%, with the values of which were 861.4 MPa and 780.9 MPa, respectively. The observation of the micro morphology of the composite showed that the resin and fiber were compact, and good impregnating effect was achieved.

RESEARCH OF PRESSURE ONLINE MONITORING OF RESIN MATRIX COMPOSITE HAT-STIFFENED COMPONENT DURING CURING PROCESS

DENG Fan,ZHAN Li-hua,*,ZOU Jing

2018, 0(7): 36-41.

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In order to study the pressure distribution of polymer matrix composite during its curing process, this paper builds a pressure online monitoring system with capillary pressure sensor as the core.With this system,the pressure distribution of the key parts of the curing process was obtained. The pressure distribution in each part of the hat-stiffened component curing process was analyzed by the influence of the rubber mandrel adjusting hole ratio. The forming precision and the microscopic quality of hat-stiffened component cured with different adjusting hole ratio were studied. The results show that when the adjusting hole ratio is 0.099, the pressure distribution of the hat-stiffened component during curing is better, and the forming precision and the microscopic quality of the component are higher.

THE COMPARATIVE STUDY OF POROSITY CHARACTERIZATION METHOD OF CARBON FIBER COMPOSITE BY ULTRASOUND

LU Ming-hui,ZHANG Xue-song*,ZHENG Shan-pu,JIANG Shu-ling

2018, 0(7): 42-48.

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In this paper, we studied the method of characterizing the porosity of composites by ultrasonic method, characterized porosity using the non-linear coefficients of frequency-domain parameters, defined the classical and improved nonlinear coefficient expressions, analyzed the characteristics of the two nonlinear coefficients, and discussed the sensitivity of two kinds of nonlinear coefficients to evaluate the porosity. The porosity of carbon fiber composites was generated by changing the curing pressure. The porosity was measured by metallographic analysis, and the comparison between nonlinear coefficients and attenuation to characterize porosity was carried out. The results show that the improved nonlinear coefficient has the best effect, followed by the classical nonlinear coefficient, and the attenuation coefficient has the worst effect. Improved nonlinear coefficients are more suitable for characterizing porosity.

OPTIMIZATION OF PATH COVERAGE OF AUTOMATED FIBER PLACEMENT BASED ON DYNAMIC ADJUSTMENT OF THE POSITION OF TOW CUTTING AND RESTARTING

JIANG Min,WU Bao-lin,*

2018, 0(7): 49-56.

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Composites are increasingly used in aerospace and automotive because of their high strength and stiffness. Among the production technologies, Automated Fiber Placement (AFP) is a high-efficiency one to manufacture high-quality composites, especially for complicated surface structures. During the process of AFP, path planning is an essential technology and the coverage of fiber path has a great impact on the strength of composite parts. When the fiber is laid on the mould, the distance between adjacent laying paths can′t be kept constant due to the complex shape of structures, and it will cause many fiber overlaps and gaps. Although overlaps and gaps can be reduced by applying the tow cutting and restarting operation, the existing methods just select a fixed operation position. This strategy doesn′t take into account the geometric features of structures. To overcome this problem, the paper proposed a novel strategy in which the position of the tow cutting and restarting is dynamically adjusted. Firstly, the fiber overlap and gap in various situations are analyzed. Then, an optimization model is established, in which the total area of the fiber overlaps and gaps is defined as the optimization objective. By optimizing the position of the tow cutting and restarting, the area of fiber overlaps and gaps can be reduced effectively. Finally, a series of simulation experiments are conducted, the optimization leads to a 66.67% and 20.41% reduction in the total area of fiber overlaps and gaps, respectively, in the two situations at most, which is a considerable improvement compared to the existing method. Therefore, the fiber cutting and restarting strategy proposed in this paper can indeed reduce the fiber overlaps and gaps, it can improve the quality of composite parts.

EXPERIMENTAL STUDY ON INTERFACIAL PROPERTIES OF GLASS FIBER REINFORCED EPOXY RESIN MODIFIED BY AMIDO ACID EMULSION

YE Ying,LIU Yuan,LI Min,GUO Bing-bing

2018, 0(7): 57-63.

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The interface between glass fiber and epoxy resin is the key to improve the properties of composites. In this experiment, the amic acid emulsion (SA-1) was synthesized, and the polyvinylpyrrolidone(PVP) was added to the emulsion to Compound SA-2. The surface of glass fiber was modified by the SA-1 and SA-2 amic acid emulsion in order to have a good interfacial adhesion with epoxy resin. The emulsion particle size were characterized by the Nano-particle size analyzer, transmission electron microscopy (TEM) and the sizing components of the functional group was tested by Fourier transform infrared spectroscopy (FT-IR). The effect of sizing treatment on the surface morphology of glass fiber was studied by scanning electron microscope (SEM) and atomic force microscope (AFM), and the tensile properties of single fibers and interface shear properties of composites (IFSS) were measured by monofilament stretch and micro-sticky method, respectively. The results showed that the average particle size of SA-2 emulsion was 99 nm and the distribution range was 21 nm~200 nm, which was better than the SA-1. The film layer of SA-1 emulsion sizing agent was smooth with an average thickness of 0.20 μm, and after the SA-2 sizing, the surface roughness of the glass fiber was increased and the thickness of the film layer was 0.12 μm. The tensile properties of the monofilament decreased from 1.401 GPa to 1.369 GPa, and the IFSS of the composite increased from 20.06 MPa to 26.84 MPa after SA-1 sizing. The IFSS of the composite after sizing treatment of SA-2 was 32.70 MPa, which was increased by 63.01%, while the tensile properties of the monofilament decreased to 1.383 GPa.

FATIGUE PERFORMANCE TEST OF BOND-TYPE ANCHORAGE FOR CFRP TENDON

XIE Gui-hua,TANG Yong-sheng,*,LI Shi-quan,YAO Jia-cheng

2018, 0(7): 64-68.

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In order to study the fatigue performance of adhesive anchorage system for CFRP tendon, epoxy resin mixed with sand was adopted as bond medium to make the bond-type anchorage systems for CFRP tendon, and they are tested under different cyclic loading conditions. Then the static performance of these systems which have experienced fatigue loading was inspected by static load test. The result shows as follows: ①a certain degree of fatigue loading is benefit to improve the synergistic effect and anchorage performance of the system. With the increasing of cycles, the relative position of the two ends of the anchorage system tends to be more stable. When P-1, P-2 and P-3 were loaded to 200,000, 150,000 and 700,000 times, respectively, the relative displacement no longer increased and the system entered into a stable state. ②The fatigue loading improved the bond performance of the anchorage system when the tensile loadwas low, while it was declined when the load was high.

THE REPLACE APPLICATION STUDY OF DOMESTIC 12K T700 GRADE CARBON FIBER IN COMPOSITE CORE CONDUCTOR

SUN Xiao-guang,HE Zhou-wen,LAN Feng-tao,YANG Qing

2018, 0(7): 69-73.

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The carbon fiber accounted for more than 60% in the raw materials cost of carbon fiber composite core. It is an effective way to cost down by replacing the 12K T700 grade carbon fiber with domestic fibers. This pater selected three domestic 12K T700 grade PAN-based carbon fiber to make carbon fiber composite core, for which the main performance can meet the standard requirements. These domestic carbon fibers can replace the imported Toray T700S carbon fiber with only 70%~80% of the price, which is beneficial to the popularization and application of carbon fiber composite core conductor.

INFLUENCES OF MOLD SCHEME ON RESIN PRESSURE AND PROCESSING QUALITY OF CO-CURED I-STIFFENED SKIN

LI Bo,ZHANG Wei-bo,WEN You-yi,MA Kai-wei

2018, 0(7): 74-81.

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In this paper, the influences of mold scheme on resin pressure distribution and processing quality of carbon fiber/bismaleimide resin I-stiffened skin fabricated by autoclave co-cured process were studied. Three kinds of mold schemes for two sides of stiffener were designed, including aluminum mold/aluminum mold, rubber mold/aluminum mold and rubber mold with corner reinforced by prepreg/aluminum mold. And resin pressure distribution inside I-stiffened skin processed with these three mold schemes was investigated by means of self-developed resin pressure online monitoring system. Furthermore, considering dimension and inner defects of I-stiffened skin, the influences of mold scheme on resin flow, fitting state between mold and prepreg stack and compaction process of prepreg stack were studied. The results show that rubber mold significantly improves fitting degree between mold and prepreg stack, thus increasing pressure transferring efficiency of mold and compaction degree of composite. The stiffness of the corner in rubber mold has a significant impact on processing quality of I-stiffened skin. Too low corner stiffness results in larger deformation of mold during processing, which is detrimental to fitting degree between aluminum mold placed at the other side and prepreg stack. It also leads to decrease in dimensional accuracy of I-stiffened skin. Nevertheless, appropriately increasing the corner stiffness of rubber mold can improve uniformity of compaction pressure and processing quality. The mold scheme, which uses rubber mold with reasonable stiffness and metal mold, is suitable for fabricating stiffened skin structure using autoclave co-cured process.

STUDY ON MECHANICAL PROPERTY OF MULTIPLE FRPM PIPES CULVERT

WANG Qing-zhou,WANG Yang*,WEI Lian-yu,LIANG Xiao

2018, 0(7): 82-88.

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Based on the full-scale indoor test about double FRPM pipes culvert and finite element theory, the finite element numerical model of three FRPM pipes culvert is established for numerical simulation. Through the analysis of multiple pipes culvert under different working conditions, the stress state and deformation characteristics of multiple pipes are explored, and the influence of the pipe spacing on the deformation of adjacent pipe is also discussed. Therefore, the most unfavorable pipe and its most unfavorable part about multiple pipes culvert under loading conditions is known. The soil compactness and the pipe spacing have a positive impact on the deformation of multiple pipes culvert, which provide the design basis and practical value for the selection about multiple pipes culvert in practical highway projects.

EFFECT OF PLUNGER ON DAMAGE DIMENSIONS AND RESIDUAL COMPRESSIVE STRENGTH OF LAMINATES SUBJECTED TO LOW-ENERGY IMPACT

LIU Yi-zhong,LI Min,CHEN Lv

2018, 0(7): 89-92.

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In order to investigate the effect of plunger on damage dimensions and residual compressive strength of laminates subjected to low-energy impact, the T700/DS1202 laminates were impacted by tapered and round plunger. Then, the dimensions of the damage were measured by superdepth microscope and compressive test. The results show that the damages caused by tapered plunger go deeper when the energy increase, and the damage area of round plunger is larger. When the depth of the damage ≥0.315 mm, the back on laminates will be cracked, which will result in the decreasing of the residual compressive strength to the 90% or below. Meanwhile, the threshold value of impact energy will be effected by the shape of plunger, and the threshold value of the tapered and round plunger is 5 J·mm^-1 and 6.67 J·mm^-1, respectively.

THE APPLICATION OF SHEET MOLDING PROCESS IN THE PRODUCTION OF THE ANTENNA ENVELOP OF PHASED ARRAY RADAR

WANG Wei,FANG Fang

2018, 0(7): 93-96.

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By comparing three common molding processes for composite materials, it is found that the sheet molding compound process is suitable for the batch production of the antenna envelop of phased array radar. In this paper, the processes of manufacture and testing were briefly introduced. The results of mechanical testing as well as antenna performance verification showed that this envelop fulfilled the requirements of radar. Nowadays, this process has been applied in many radar systems.

IDENTIFY CHARACTERISTIC PARAMETERS OF THE HONEYCOMB SANDWICH PANELS BASE ON THE STRUCTURAL DYNAMIC MODEL UPDATING

WANG De-xin,WANG Ting-ting,JIANG Nian-chao,LI Jia-chun

2018, 0(7): 97-102.

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In order to solve the problem of large difference between the initial finite element analysis and experimental test, the model test data of the honeycomb sandwich panels are used as updated target to identify the cure thickness of laminate panel and the material parameters of honeycomb core based on the structural dynamic model updating. The updated results show that updated FE model has high rationality and could be used for other dynamic problems analysis. Beside, for complicated engineering structures, the simple tests can be adopted to modify the design parameters so as to improve the overall analysis accuracy and have certain engineering practical value.

STUDY ON PROPAGATION LAW OF VIBRATION AND ACOUSTIC SIGNALS OF FRP TANKS

CHEN Jian-fei,XIE Ke-ming*,YANG Yong,LIU Yan-guo

2018, 0(7): 103-107.

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The problem of weak acoustic emission signal for passive detection of large tank is studied. According to the detection of acoustic vibration principle, the incentive raw materials (nylon, stainless steel, plastic) were selected to do active tapping test on the 10 mm wall thickness epoxy resin glass fiber reinforced plastic storage tank. Based on the acquisition of signals using acoustic emission equipment, stainless steel was selected as optimal material, and a spring hammer frock was designed. Acoustic vibration test of FRP tanks in laboratory was carried out by using spring hammer, the results show that the hitting speed is the fastest and the amplitude attenuation is minimum in the horizontal direction. As the direction angle increases, the wave velocity decreases gradually and the amplitude attenuation rate increases gradually. The propagation model and amplitude attenuation law of acoustic and vibration signals are obtained. Overall, the sound vibration signal propagation distance is longer than the passive acoustic emission signal, which lays the foundation for the later research on the inspection of FRP tank defects by acoustic vibration method.

RESEARCH STATUS ANALYSIS OF FRP REINFORCED CONCRETE STRUCTURES

HUANG Hua,HAO Run-qi,HUANG Min

2018, 0(7): 108-116.

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Recent years, a lot of research has been done on the mechanical properties of FRP bars and FRP reinforced concrete structures at home and abroad. Durability of FRP bars, bonding mechanism between FRP bars and concrete, mechanical behavior of FRP reinforced concrete beams and columns, and seismic performance of FRP reinforced concrete columns and frame structures are the main research directions. The existing studies show that the tensile strength of the FRP bars in most of the bending members can be fully utilized as the longitudinal reinforcement, but the structure is prone to brittle failure. The calculation method of the current code is not suitable for the calculation of this kind of components. FRP bars instead of steel bars as the main force tendons will lead to lower compressive strength and poor ductility. Fibrous concrete can significantly improve the ductility of FRP reinforced concrete members, and the seismic behavior of composite reinforced columns with FRP bars and reinforced bars is obviously better than that of FRP reinforced columns. The next step is to establish a reliable durability test and evaluation method for FRP materials and components; to improve the bonding behavior between FRP tendons and concrete, especially modified concrete; to improve the calculation method of bearing capacity of FRP reinforcement members in current codes; to establish seismic design system of FRP reinforcement members.

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