COMPOSITES SCIENCE AND ENGINEERING

STRENGTH AND PROGRESSIVE FAILURE RESEARCH OF COUNTERSUNK COMPOSITE JOINTS

SONG Guang-shu, ZHENG Yan-ping, ZHAO Jiang-ming

2017, 0(4): 5-10.

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In this paper, based on the theory of three-dimensional progressive failure, Tserpes failure criterion and its further stiffness deterioration criterion are introduced to build the models of double-bolt, single-lap, countersunk composite joints. Experimental verification is carried out to prove the numerical simulation model. It is demonstrated that end distance, width and tightening torque can improve the structural strength in different extent. And, damage propagation process is simulated visually. The results indicate that the joint strength is enhanced obviously during the process of end distance-diameter from 2 to 4, width-diameter ratio from 3 to 5 and tightening torque from 0 to 5.9 N·m. It′s earlier and more serious than bolt-1 in static tension that the damage around bolt-2 will eventually lead to joint failure. The damage in the 90° layer is mainly matrix cracking which occurs the earliest. The weakest damage occurs on 0° layer. As the ±45° layer, the matrix cracking spreads along the -45° of the plate, and then a large number of fiber fracture turns up along the plate width.

STUDY ON THE CURE KINETICS OF T800/EPOXY RESIN PREPREG BASED ON ACTIVATION ENERGY VARIABLE MODEL

YIN Rui, ZHAN Li-hua, LI Shu-jian

2017, 0(4): 11-16.

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To further analyze the curing behavior of a new kind of high temperature curing T800/epoxy resin prepreg, dynamic differential scanning calorimetry (DSC) method was carried out to investigate the cure behavior of T800/prepreg. The characteristic temperatures and cure kinetics parameters of the prepreg were systematically investigated based on phenomenological model, and the cure reaction kinetic model of the epoxy resin was determined to be the autocatalytic model. The relation of activation energy versus degree of cure was obtained by iso-conversional method for the epoxy resin in prepreg. The results show that the reaction activation energy of epoxy resin in the prepreg changed significantly with increasing degree of cure during the whole curing process. Thus, the curing model based on the assumption that the activation energy was a constant during the whole curing process could not describe this curing reaction accurately. Therefore, an activation energy variable autocatalytic kinetic model and particle swarm global optimization algorithm were used to obtain the cure kinetic equation of T800/epoxy resin prepreg. The results show that this model achieves a good correlation with the experiment data, hence providing a theoretical base for further study on thermodynamic properties and enables the quality control during the curing process for the prepreg.

THE OPTIMIZATION DESIGN OF QUADROTOR UAV CARBON FIBER STRUCTURE AND NATURAL VIBRATION ANALYSIS BASED ON FINITE ELEMENT METHOD

LIU feng, GAO Hong-jian, YU Hui, DAI Hai-liang

2017, 0(4): 17-23.

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According to the performance requirements, a full carbon fiber structural consumer-grade quadrotor UAV is designed,which has the features of light weight, high strength, long navigation time and simple configuration. The finite element model of quadrotor UAV structure is established, and the structure stress state of the UAV under the rated load is analyzed. The structure strength is checked based on the maximum stress strength criterion. The stability of the initial UAV structure is analyzed, and the critical buckling load and buckling modes are calculated. Based on the minimum weight requirement, the carbon fiber laminates optimization design of the initial structure is carried out. The natural vibration analysis of the optimized structure is conducted, and the first four natural frequencies and vibration modes are given. Under condition of 2 g load factor, the structure ultimate load is 2.57 times of the maximum service load, and the buckling critical load is 2.09 times of the maximum service load. The design goals and requirements are met. The weight of optimized structure is decreased by 21%, and reduced to 108.6 g. Payload is about three times of the structure weight.

APPLICATION OF ANSYS COMPOSITE PREP/POST IN STRUCTURE DESIGN OF AN UNDERWATER VEHICLE MADE OF COMPOSITE MATERIAL

YANG Zhuo-yi, SONG Lei

2017, 0(4): 24-28.

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The structure strength of an underwater vehicle in the hoisting condition was analyzed using the composite analysis module ANSYS composite Prep/Post. The structure failure modes of the underwater vehicle were compared by the two different failure criteria, i.e., Hill-Tsai strength theory and Tsai-Wu strength theory. Parametric setting was applied in layer number of carbon fiber woven material at the different areas of the underwater vehicle structure. The optimal design scheme was gained from the calculation samples arranged by design of experiment effectively. This method which combines composite structure FEM and design of experiment provides valuable reference for the direct optimization for composite engineering structures.

ANALYSIS OF INTERFACE PLY ANGLE EFFECTS ON STRESS DISTRIBUTION AND FAILURE FORCE OF COMPOSITE JOINT

PENG Hai-jun,QIN Zhi-wen,WANG Ji-hui,YANG Ke

2017, 0(4): 29-34.

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To study the relations between joint failure force and ply angle of Ply Adjacent to Adhesive Layer (PAAL), designed a series of single-lap joints with same tensile modulus and bending modulus adherends but different orientation angles of PAAL, to analysis the effects of PAAL on stress distribution, using Finite Element Method (FEM) to model the adhesively bonded composite single-lap joints with different stacking sequences, stresses of adhesive layer and PAAL were analyzed, and introduced a failure index with Tsai-Wu failure criterion to compare the failure level of PAALs. The result shows the ply orientation of PAAL cause stress variation, with 0°, the stress of adhesive layer is highest, when the stress and failure index of PAAL is lowest; with 90°, the stress of adhesive layer is lowest, when the stress and failure index of PAAL is highest; the stress level of adhesive layer and failure index level of PAAL with 45° are between the results of 0° and 90°. A common rule was achieved by comparing the result and experiments data.

STUDY ON ABLATION HEAT TRANSFER CALCULATION AND INFLUENCING FACTORS OF THERMAL PROTECTION MATERIALS UNDER HYPERSONIC THERMAL ENVIRONMENT

YANG Chi, LIU Na, KONG Wei-xuan, ZHANG Li-song

2017, 0(4): 35-41.

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As the accuracy of the ablation temperature field calculation of thermal protective composite materials was not high, a calculation method was established to analyze the carbon-based and silicon-based thermal protective material under specific thermal environment. Comparing the ablation temperature results with the simplified model and ground test results, the method in this study was proved to be reasonable. Several thermal parameters, thermal conductivity, density, surface emissivity, pyrolysis and carbide, were studied under specific thermal environment to analyze the influence law of the factors on the ablation heat transfer. The results show that the influence of various factors on the ablation heat transfer behavior is different. The thermal conductivity and the emissivity has a major contribution to the influence on internal and external temperature of the thermal protective material, respectively. The influence of the emissivity on the internal temperature is time-dependent. The activation energy has a certain impacts on the internal temperature of the material. Both the activation energy and thermal conductivity has significant impacts on the material pyrolysis carbonization process. The results provide an important theoretical basis to the correction of the ablative heat transfer calculation method.

TWO DIMENSIONAL SIMULATION OF TEMPERATURE FIELD FOR THE I-SHAPED BEAM DURING THE ADVANCED PULTRUSION

CHI Jian-tao, XIAO Jun, QI Jun-wei

2017, 0(4): 42-48.

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The degree of curing and temperature are coupled during the advanced pultrusion (ADP) of carbon fiber reinforced plastics (CFRP). This paper is based on the thermal conduct theory with nonlinear source, using finite volume method to study the history of temperature and degree of curing during the curing of I-shaped beam in the advanced pultrusion. It is found that the temperature field and curing degree field of the I-shaped beam are uniform, and the thickness will not have a great impact on the quality of curing. When the thickness of the beam reaches 11 mm, the highest temperature will be 10.7 ℃ higher than the mold temperature, and the thickness will have a great impact on the curing quality of the beam.

EXPERIMENTAL STUDY ON BONDING PROPERTY OF GFRP-PAULOWNIA IN THE HYGROTHERMAL ENVIRONMENT

ZHAO Peng-fei, FANG Yuan, LIU Wei-qing, XU Dan-yang

2017, 0(4): 49-53.

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The way of artificial accelerated aging to simulate hygrothermal environment was used to investigate the effect of the bonding property of GFRP and paulownia wood in the environment. And, the DCB method was used to test the interfacial properties of the GFRP paulownia sandwich structure. Based on the energy release rates from the test data, the effect of the hygrothermal environment to the interface toughness of the GFRP paulownia sandwich structure was analyzed. Moreover, the tensile property change of paulownia and GFRP in the hygrothermal environment was studied. It was concluded that after 90 days hygrothermal aging, the energy release rate of the paulownia GFRP sandwich composite structures was declined by 32.3%, and the tensile strength of the paulownia cores was decreased by 11.6%. Meanwhile, the tensile modulus of GFRP laminates was reduced by 11.0%.

CONNECTION PROPERTY OF JOINING COMPOSITE SHEETS WITH ROLLING RIVETING, BONDING AND HYBRID JOINTS

HUANG Zhi-chao, FENG Jia, ZHANG Yong-chao

2017, 0(4): 54-59.

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The connection quality of glass fiber reinforced resin matrix composites connected by rolling riveting, bonding and hybrid (rolling riveting/bonding) joints was studied by tensile tests. The effects of different connection methods on connection quality were compared. A series of tensile tests were carried out for test pieces obtained from different joint conditions, such as different bonding time, the presence or absence of washer and number of rivets. The experiment results show that the connection performance had been improved significantly by using hybrid joints of glass fiber reinforced resin matrix composites. Furthermore, the washer is the most important influencing factor on the connection property. The bearing capacity of test pieces with washers had been increased by around 29% than that of the one without washers. In addition, to some extent, the bearing capacity of test pieces could be enhanced a lot by the extended time of bonding. However, the connection property with two rivets at the same direction as tensile test could not be improved.

STUDY ON THE MECHANICS PERFORMANCE OF ES/CEP BLENDING AND ITS COMPOSITE MATERIALS WITH UV CURING

YU Zhou-hui, ZHAO Pei-zhong, HU Fang-you

2017, 0(4): 60-65.

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The blend mixed by silicon epoxies and cycloaliphatic epoxide resin which has different mass ratio is designed. Also, ES/CEP polymer sample (EP), GF reinforced composite (GF/ES-CEP) and repair aluminum alloy specimens with GF/ES-CEP composite as patch are prepared through UV curing technology. We mainly study the impact of the mass fraction of silicon epoxies (ES) on the tensile mechanical properties of samples. The results show that: with ES added into CEP, the tensile strength of EP had gradually decline, while the elongation increased after the first drop, mechanical properties of EP with 15% of ES reached best; GF/ES-CEP composites tensile strength and elongation were falling after the first increase with the increase of the proportion of ES. Moreover, repair aluminum alloy specimens with GF/ES-CEP composite as patch mainly appeared debonding failure between collagen and injury structural interface. It showed that the mechanical property of composites was superior to interface mechanical characteristic. After the water bathing treatment, the mechanical properties of GF/ES-CEP composite repair aluminum alloy samples would decrease significantly, and adding suitable amount of organic silicon resin can improve the wet and heat resistant of repair specimen.

STUDY ON WETTING BEHAVIOR BETWEEN PHENOLIC RESIN SYSTEM AND GLASS FIBER

MAO Ya-sai, PAN Qiao, WANG Wen-jie, YANG Ke-lun

2017, 0(4): 66-69.

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In order to study the wettability of phenolic resin to glass fiber and better guide the actual production, two kinds of phenolic resin and three kinds of glass fiber were investigated in this paper. The best resin and glass fiber was confirmed selected considering the surface tension, viscosity and dynamic contact angle through introducing diluents and dispersants, and combining the target test that determined the wetting rate of resin penetrating into glass fiber, respectively. The results show that the lower the surface tension was, the smaller the viscosity was, the smaller the dynamic contact angle between resin and glass fiber was, and the better the effect of the resin to glass fiber.

ULTRASONIC CHARACTERIZATION AND ANALYSIS OF MACRO DEFECTS IN RTM CARBON FIBER COMPOSITES

LU Ming-hui,WANG Jun-dong,ZHANG Yi-ping,LI Pei-rui

2017, 0(4): 70-74.

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The research object of this paper is RTM carbon fiber composite material. The ultrasonic characteristic scanning system is used to detect a large number of samples. Theoretically, the reflection characteristics of ultrasonic wave will vary with the type of macro defects. In this paper, the reflection characteristics of each defect are analyzed theoretically. Then, different macroscopic natural defects are found out, and the image characteristics of each defect are summarized. Then, the samples were cut into pieces and polished by destructive method, and the morphological characteristics of different defects were observed by microscope. The results show that the ultrasonic characteristic scanning system can detect and distinguish different macroscopic defects, and the morphological features of different types of defects are different by observing the metallographic diagram of defects, which provides a feasible method for the macroscopic defect detection and morphology study of RTM carbon fiber composite.

THE ANALYSIS OF HOMOGENIZING OF BOND LAYER IN THE CARBON FIBER DRIVE SHAFT

WANG Xiao-guang, REN Qing, ZHANG Jin-guang

2017, 0(4): 75-79.

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When the carbon fiber drive shaft is connected by adhesive transfers load, the stress in the end of bonding layer will be greatly enhanced while the middle part will be reduced, which causes the destruction of adhesive joint generates in the end of the bonding layer first, then affects the performance of the coupling. This article explains the adhesive bonding layer stress curve regular from the perspective of strain and puts forward several factors which influence the stress distribution of bonding layer. These factors involve internal and external circumferential deformation of bonding layer and the thickness of bonding layer. Then, we put forward several methods to homogenize the bonding layer stress, which were verified by the finite element analysis method. Firstly, increasing the bonding layer thickness can homogenize the stress while the degree of homogenizing is not obvious, and it will increase the bonding layer defects in engineering. Secondly, the drum-shaped adhesion with variable thickness bonding layer makes the stress homogenization of the bonding layer more obvious. At last, this article indicates several factors that affect the stress homogenizing of the drum-shaped adhesive bonding layer such as the length of variable thickness bonding layer (L) and the maximum thickness of bonding layer (H).

ANALYSIS OF COMPOSITE LAMINATES WITH DAMAGE AND THE PATCHING INVESTIGATION BASED ON THE SOFTWARE OF MSC

WANG Ke-xuan, WANG Ting-ting, WANG De-xin, SONG Jun

2017, 0(4): 80-84.

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Based on the Patran/Nastran software, the finite element models of the three types of composite laminates of intact, damaged and patched were modeled. The strength of the three types of laminated plates was estimated. By analyzing the strength values of laminated plates under different patch angles, a reasonable patch angle parameter is obtained. The strength values of the three kinds of laminated plates were obtained by tensile test. The results were compared with the results of simulation analysis. The results show that the simulation model is in good agreement with the experimental data. The results of simulation model matched with the experimental data, and the simulation model is effective to predict the residual strength of laminated plates with different repair angles.

THE EXPERIMENTAL RESEARCH OF COMPRESSIONAL DAMAGE FOR SINGLE BOLTED JOINTS OF COMPOSITES UNDER SINGLE SHEARING AND DOUBLE SHEARING

LU Zhi-xian, TUO Hong-liang, LIU Bin

2017, 0(4): 85-89.

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The mechanical bolted structures of composites are widely applied in aeronautical structures. In the proceeding of loading, compressional damage dominating the damage mode needs to be concerned. For single bolted joints of composites, single shearing case exists secondary bending, but double shearing only exists pure compressional loading mode. This paper adopted experimental methodology to study damage modes, compressional deformation, yield strength and compressional strength for single shear load and double shear load of single bolted joints of different thickness. It was found that the single bolted plates of composite under single shear load of secondary bending has strong effects on strength and deformation, and the single bolted plates under double shear load enhance yield strength and compressional strength substantially. In the condition of keeping plies percentage constant, by changing plies number,force analysis and damage of single bolted joints of single shearing were investigated. The results show that making composite plates thicker cannot improve yield and compressional strength obviously.

STUDY ON THE ATL TECHNOLOGY FOR PREPREG T700/3234

HE Kai, GONG Zhi-hong, XU Heng-yuan, WEN You-yi

2017, 0(4): 90-93.

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The Automatic Tape Layup (ATL) technique is extensively applied on laying up the unidirectional prepreg for the large-scale composite panels of an aircraft, instead of artificial. In this paper, by studying on how the heating temperature has influence on the prepreg tack and how pressure from the rubber roll and gap between two tapes have influence on the lamination performance when using ATL, the automatic tape layup technology for an unidirectional tape prepreg, T700/3234 is discussed, and the appropriate processing parameters are determined when T700/3234 is used for ATL, such as the heating temperature should be set as 50 ℃, the pressure from the rubber should be 7 Bar and the gap between two tapes should be set as 1 mm. A large-scale wing panel from T700/3234 composite has been successfully manufactured by the ATL parameters for a fighter.

STUDY ON CURING MECHANISM AND PROPERTIES OF FURAN/EPOXY/AMINE BLENDS

CAO Ni, WANG Zhi, DU Rui-kui, LIU Ya-qing

2017, 0(4): 94-98.

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In this paper, a blend of furan/epoxy/amine blends was prepared by solution method. The processability, curing mechanism and mechanical properties of the cured blend were studied with rotational viscometer, differential scanning calorimetry (DSC), fourier transform infrared (FT-IR), scanning electrical machine (SEM) and mechanical test machine. The blends showed excellent processability. The viscosity of blends was low enough to satisfy the special requirements. With increasing the epoxy content in blends, the curing of blends was delaying. It was found that the polymerization reaction of furan and epoxy/amine was occurred at lower temperature (180 ℃) and then the residual epoxy need higher temperature (280 ℃) to cure. The two components had no co-reaction between them. The cured blends showed excellent flexural and impact properties and the properties improved with increasing the content of epoxy in blend. For flexural properties, the highest value of flexural strength was 113 MPa, flexural modulus was 4129 MPa. For impact strength, the highest one was 19.1 kJ/m². All modified system showed improved mechanical properties compared with the each component. The surface of sample after impact test was examined by SEM and possible improved reason was discussed. It was found that the micro-phase separation structure was showed in blends which may be caused by each component cured at different temperatures, and maybe the main reason for excellent impact properties.

REVIEW OF LASER CUTTING CARBON FIBER REINFORCED PLASTIC COMPOSITES

ZHANG Chen, YUAN Gen-fu, CONG Qi-dong

2017, 0(4): 99-103.

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The research progress of laser cutting carbon fiber reinforced plastic composites in China and abroad was reviewed. The features and contents of surface quality of laser cutting carbon fiber reinforced plastic composites and its influence factors, its research progress are described. At last, the comments on the development of the laser cutting carbon fiber reinforced plastic composites were prospected.

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