COMPOSITES SCIENCE AND ENGINEERING

MECHANICAL BEHAVIOR OF ADHESIVELY BONDED CFRP LAMINATES BASED ON COHESIVE ZONE MODEL

ZHU Zhao-yi, LI Xiao-wen, LI Yan, XIONG Yun-feng

2019, 0(8): 5-10.

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Since light weight is desirable for the development of ships, carbon fiber reinforced composite materials and bonding technology have received widespread attention from the shipbuilding industry. The CFRP laminate bonding structure combining carbon fiber reinforced plastic and bonding technology is a typical form, and its mechanical behavior is vital to the safety of ship structure. Based on the mechanical experiments and finite element simulation, the geometrical model, theoretical model and finite element model of the CFRP laminate bonding structure were built, and its ultimate bearing capacity and damage behavior were investigated. The results show that the numerical simulation results using the cohesive zone model are in good agreement with the mechanical tests, which can effectively distinguish the linear segment from the nonlinear one. The bonding region is the weak link of the CFRP laminate single-lap structure. The failure behavior of CFRP laminated adhesive plate is complicated, and there are various failure modes such as cohesive failure, adhesion failure and adherence failure in the bonding area. This work is useful for the study of the mechanical properties of complex FRP bonded structures.

DRY SPOT PREDICTION SIMULATION AND DEFECT ANALYSIS OF RESIN-IMPREGNATED FIBER PROCESS FOR HIGH VOLTAGE INSULATED PULL ROD

ZHANG Zhuo, YANG Wei, YAN Bing-yue, CHU Wei

2019, 0(8): 11-16.

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Based on Volume of Fluid method, two-phase flow model of resin and air was established to describe vacuum assisted resin-impregnated fiber process for high voltage insulated pull rod. In the model, two kinds of two-phase flow sub-models were integrated, which separately describe the two-phase flow in the gaps between mould inner surfaces and fibre preform and the two-phase flow in mixed fibre preform. The geometric model of insulated pull pod was also established and then mesh generation was accomplished. By Finite Volume Method and using Fluent software, the two-phase flow model of resin and air was solved. In the whole mould area, the two-phase flow and dry spots formation were simulated. The correctness of simulation research was verified by experiments and the causes of dry spots were analyzed. Furthermore, thoughts and methods to eliminate dry spot defects were presented. Feasibility and effectiveness of some methods were verified by simulations and experiments.

A THEORETICAL STUDY OF THE MECHANICAL INTERLOCKING ON THE BONDED COMPOSITE REPAIR

ZHANG Hua-zhong, YANG Wen-feng, LI Shao-long

2019, 0(8): 17-22.

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Bonded repair has been the primary maintenance way for composite aircraft structure. Mechanical interlocking, electrostatic adsorption and chemical bonding were employed to reveal the surface bonding mechanism and maintenance effect. However, it′s difficult to separate the three adhesion theories to study single-factor for the repair result. In this paper, fluorocarbon additive (CF) with low surface energy was used to form a CF film on the surface of laser-treated (LA-CF) and polish-treated (PO-CF) composite laminate. LSCM contact angle, XPS and lap shear test was applied to investigate morphologies and roughness (Sa), surface free energy, chemical property and adhesion strength, respectively. The results showed that PO-CF and LA-CF specimen did not change their morphologies and roughness. Howerver, the surface energy decreased to around 10 mJ/m² and the contact angle increased to around 115°. Deconvolution bands of the XPS C1s displayed the same peak location and intensity. Lap shear test revealed that the shear bonding strength of LA-CF was 8.1 MPa higher than that of the PO-CF specimen. It demonstrated that mechanical interlocking played a bigger role than electrostatic adsorption and chemical bonding in this mechanism research of interface combination.

ULTRASONIC PHASED ARRAY INSPECTION METHOD FOR THE CORNER OF CARBON FIBER COMPOSITE SQUARE ROD

SHI Hong-yuan, ZHANG Yi-wei, SHAO Hong-liang

2019, 0(8): 23-28.

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Aiming at the problem of detecting the defects of the corner of the carbon fiber composite square bar, the difficulty of detecting the corner of the composite bar is analyzed. The sound field distribution of the common linear array transducer probe was simulated and analyzed. The CIVA software was used to optimize the simulation process of the carbon fiber square rod. The comparative test block with natural defects was tested and verified. The ultrasonic phase control was proposed. Based on the detection scheme of the array detection method, the test results show that the method of line sweep and fan sweep using the line array transducer can effectively solve the defect detection problem of the corner of carbon fiber composite rods.

FINITE ELEMENT ANALYSIS OF RADIAL COMPRESSIVE BEHAVIOR OF ACCC CONSIDERING CONTACT FRICTION AND ANISOTROPIC PROPERTIES

ZHU Yuan-yuan, ZHANG Xiao-min, LONG Peng, JIANG Yu

2019, 0(8): 29-34.

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In order to study the compression failure and contact friction behavior of carbon fiber composite core conductors (Orthotropic material) during the pressure connection construction, and to ensure the safe and stable operation of overhead conductors with carbon fiber composite mandrel in the power grid, ANSYS software is used in a ratio of 1∶1 established the three-dimensional finite element model of 7.5 mm carbon fiber composite core rod and strain clamp. Tsai-Wu failure criterion is used to determine the failure behavior of composite mandrel,considering the contact and friction behavior between composite mandrel, outer aluminium conductor and strain clamp connector. The nonlinear static finite element analysis of the splicing process of composite mandrel was carried out. The results show that the core is easy to be pulled out of the metal cavities if the single-mode pressure is less than 24 MPa, and the core is easy to be crushed if the pressure is greater than 28 MPa. However, the composite core is easy to stress concentration on the side of the metal fitting near the wedge clamp, resulting in pressure loss. The side pressure should be relatively small, preferably in the range of 21 MPa~23 MPa.

STRENGTH TEST AND NUMERICAL SIMULATION OF CFRP SQUARE TUBE SINGLE-NAIL CONNECTION STRUCTURE

ZHU Xiu-jie, XIONG Chao, YIN De-jun, YIN Jun-hui

2019, 0(8): 35-41.

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The compression test of four kinds of carbon fiber laminated square tube single-nail connection structures with different bolt diameters was carried out, and the compressive ultimate failure load and load-displacement curve of the joint structure were obtained. The energy evolution-based composite square tube bolt connection structure was established respectively. The progressive damage analysis model simulates the failure process and failure mode of the composite square pipe joint structure under compressive load. The stress distribution and damage propagation of the CFRP laminated square tube under different bolt diameters are analyzed. Based on the verified finite element model, the influence of the change of the ply angle on the ultimate compressive load of the CFRP square tube is analyzed.

EXPERIMENTAL INVESTIGATION ON BONDING PROPERTY OF EPOXY ADHESIVE MODIFIED BY GRAPHENE AND MULTI-WALL CARBON NANOTUBES

HUANG Hai-xin, RAO Qiong, PENG Xiong-qi

2019, 0(8): 42-46.

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To improve the bonding property and thermal property of epoxy adhesive, graphene and multi-wall carbon nanotubes (MWCNTs) were separately and proportionally (1∶1) added into the adhesive. Single-lap shear specimens of carbon fiber reinforced composite laminates were prepared for testing the shear strength of the unmodified adhesive and the modified adhesive. The fracture mechanism of modified adhesive layer was investigated using Scanning Electron Microscope (SEM). The effects of nano-materials on the thermal property of modified epoxy adhesive were studied using Thermo-gravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC). The results show that adding graphene and MWCNTs can improve the interfacial adhesion force of epoxy adhesive and the shear strength of single-lap joints. In addition, the modification has a synergistic effect, when 0.5wt% graphene and MWCNTs were added for hybrid modification, the shear strength of the single-lap joints is the strongest, increasing by 34.52%. At the optimum content, the decomposition temperature of the modified epoxy adhesive is also the highest, and thus the thermal stability is the best. However, the reinforcement of nano-materials at higher content tends to decrease due to their agglomeration. The DSC results show that the modification of graphene and MWCNTs does not affect the glass transition temperature of the epoxy adhesive.

LIGHTWEIGHT DESIGN OF CARBON FIBER REINFORCED PLASTIC SUSPENSION CONTROL ARM

LIU Yue, JIANG Rong-chao, LIU Da-wei, CHEN Huan-ming

2019, 0(8): 47-52.

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Considering the lightweight and high-strength properties of carbon fiber reinforced plastic (CFRP), the lightweight design method of suspension control arm using carbon fiber reinforced plastic instead of steel was studied. The CFRP control arm was designed based on the principle of equal stiffness, and the structural properties of the two types of control arm were analyzed. On this basis, the orthogonal array design was used to optimize the stacking sequence of CFRP control arm. The results show that the carbon fiber composite control arm achieved a mass reduction of 48.32% compared with the original steel control arm under the premise of meeting the requirements of the stiffness. The strength performance of CFRP control arm was greatly improved. Moreover, the proposed method is proved to be effective for lightweight design of suspension control arm.

EFFECT OF PMI FOAM ON LOW-VELOCITY IMPACT RESISTANCE OF CARBON FIBER COMPOSITES

WANG Shi-jie, SUN Ze-yu, TAO Lei, YANG Qing

2019, 0(8): 53-58.

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In this paper, the effect of PMI foam on the low-velocity impact resistance of carbon fiber composites was studied by drop weight impact test. Experiments were carried out on carbon fiber composite laminates with a thickness of 5 mm and PMI foam (3 mm thick) sandwich carbon fiber composites (2.5 mm each for upper and lower skins) with low-velocity impact energy of 5 J, 10 J, 20 J, 40 J, respectively. The experimental results show that the energy absorption effect of foam sandwich carbon fiber composites is better than that of carbon fiber composite laminates. Along with the increase of impact energy, the impact energy absorption effect between the foam sandwich composite material and the carbon fiber composite laminate is getting smaller and smaller, but the impact damage of the sandwich panel is better than that of the laminate. As the impact energy increases, the ratio of the absorbed impact energy of the carbon fiber composite laminate increases gradually and the foam sandwich carbon fiber composite decreases gradually. However, under the impact energy of 40 J and below, the absorption energy ratio of the carbon fiber composite laminate is lower than that of the foam sandwich carbon fiber composite.

STUDY ON THE PROPERTIES OF METAL-COMPOSITE BOND STRUCTURE

XIONG Yong-jian, ZHENG Yan-ping, XIA Xiao-song, YANG Ben-ning

2019, 0(8): 59-65.

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Based on three-dimensional progressive damage theory, the failure modes of the new metal-lap composite structure (consisting of aluminum alloy substrate and double CFRP composites reinforced structure) in the riveting, bonding and mixed connection form under the static load are investigated, respectively. Moreover, the influences of jointing parameters of this structure on the failure load are discussed. The results show that: The failure mode of rivet joint is shear failure of rivet. It is the failure of adhesive layer for the failure form of bonding. The hybrid joint was initially adhesive layer failure, and then overall failure due to shear failure of rivets. The failure load of the structure decreases first and then increases with the increase of the thickness of the up-adhesive, and increases first and then decreases with the increase of the thickness of the down-adhesive. As the bond width increases the failure load of the bond structure increases. When the bonding length increases, the failure load of the bond structure gradually increases first and then tends to be stable.

CONNECTION PERFORMANCE TEST ON RIB-STIFFENED FLANGE OF COMPOSITE FOAM CORE SANDWICH TUBE

LI Feng, ZHAO Zhi-bo, TAO Jie

2019, 0(8): 66-71.

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In order to realize the effective connection between composite foam core sandwich tubes or between composite foam core sandwich tubes and other structures, a connection form of rib-stiffened flange is put forward, and integral molding composite foam core sandwich tube and rib-stiffened flange were produced by vacuum assisted resin introduction technique. Eccentric compression tests and cantilever lateral load tests were carried out on two-group specimens of composite foam core sandwich tube rib-stiffened flanges respectively. The loading process and failure mode were observed and the load-displacement curve was obtained. The results showed that when composite foam core sandwich tube rib-stiffened flange was under eccentric load, the failure mode of fiber compression fracture occurred in the transition position between stiffening ribs and sandwich tube body, and this position was the weak point of the specimen under eccentric compression. Under the effect of transverse load, the rib-stiffened flange was firstly subjected to fiber peeling failure of stiffening rib skin, then subjected to the fiber tensile failure at the connecting part of the composite flange and tube body. Finally, the flange of composite material appeared the failure of integral fold deformation. The failure process of flange has obvious characteristic of progressive failure.

OPTICAL BEHAVIOR AND SIMULATION OF LASER IRRADIATED CARBON FIBER COMPOSITES

ZHU Wen-kai, HUAN Da-jun, XIAO Jun, WANG Wu-qiang

2019, 0(8): 72-77.

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In this study, the carbon fiber reinforced polyetheretherketone composite (CF/PEEK) was used as a test sample to study the optical behavior of laser irradiated carbon fiber composites. The reflectance of the sample as a function of wavelength and angle of incidence was measured by an integrating sphere experiment. A laser beam reflection experiment was carried out to observe the behavior of the macroscopic reflection pattern as a function of the incident angle of the light and the angle of the sample. The microscopic behavior between the laser and the sample was analyzed, and the reflection process was simulated by optical design software. The integrating sphere experiment shows that the reflectance of the sample becomes larger as the wavelength increases, and becomes smaller as the incident angle increases. Macroscopic reflection experiment shows that the incident angle of light and the off-angle of the sample have a great influence on the reflection pattern. The reflection behavior is mainly dominated by the specular reflection of the surface fibers, and the simulation results are basically consistent with the experimental results. Based on the Fresnel equation, the effective refractive index of the sample fitted according to the least squares method is n=2.26.

RESIDUAL COMPRESSIVE STRENGTH AND ULTRASONIC TESTING AFTER MIXING FIBER RPC AT ELEVATED TEMPERATURE

HE Yi-xuan, DU Hong-xiu

2019, 0(8): 78-81.

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In order to study high temperature damage of reactive powder concrete (RPC), in the present experiment, the volume of polypropylene fiber and basalt fiber was controlled to be 0.2% and 0.1%, respectively. Then, the residual compressive strength, mass loss rate, ultrasonic velocity and its relationship with the fire temperature of steel fiber reactive powder concrete with different volume of 0,1%,1.5 % and 2% after high temperature were analyzed. The results show that the residual compressive strength and ultrasonic velocity of RPC specimens decrease continuously with the increase of fire temperature. The incorporation of steel fiber can increase the residual compressive strength and ultrasonic velocity value of the mixed fiber RPC specimen after high temperature. The compressive strength and ultrasonic velocity of the blended fiber RPC specimens increase with the increase of the steel fiber volume.

VIBRATION FREQUENCY ANALYSIS AND EXPERIMENTAL STUDY OF WET DESULFURIZATION FRP FLUE IN COAL-FIRED POWER PLANT

SHEN Zhi-yong, MA Xiu-yuan

2019, 0(8): 82-86.

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The FRP flue duct is gradually applied and popularized in the coal-fired power plant wet desulfurization system. However, there is no vibration calculation specification for FRP flue duct design, and the vibration calculation specification of the steel structure is not applicable to the FRP flue duct. Therefore, it is necessary to analyze the vibration of FRP flue duct, obtain the law between FRP flue duct structure and vibration, and propose the relationship between the center distance of the flue duct reinforcement rib and vibration. In this paper, the bending of the flue duct composite panel is regarded as the large deflection of the thin plate. The vibration equation of FRP flue duct wall is obtained by Mindlin theory, and the relationship between the center distance and frequency of flue duct reinforcement rib is derived. On the other hand, the vibration mode experiment was performed on the laminate. The results show that the steel flue duct technical specifications and Mindlin theoretical calculation results are 5.51% and 2.47% compared with the experimental results. The error of Mindlin′s theoretical calculation results is smaller, which significantly improves the design accuracy of FRP flue duct.

PRESSURE TRANSFER FOR COMPOSITE AUTOCLAVE PROCESS WITH TWO-SIDE RIGID MOLD AND THE INFLUENCING FACTORS ON ITS PROCESS QUALITY

LU Xin, LI Qian-qian, WANG Shao-kai, LI Yan-xia

2019, 0(8): 87-93.

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This paper focuses on the autoclave process by using two-side rigid steel mold. The influence of mold tolerance on the process quality of composite laminate was investigated. The effects of mold tolerance and prepreg thickness difference on stress distribution and resin flow inside prepreg were revealed by finite element analysis. Furthermore, a self-designed resin pressure online monitoring system was used to verify the stress distribution caused by two-side rigid mold. The results show that the process quality is closely related to mold tolerance when the two-side rigid mold is used. Void and delamination are easy to be caused at the negative tolerance area. The lamina and interlaminar thicknesses at positive tolerance area are smaller than those at negative tolerance area. Both resin pressure measurement and finite element analysis indicate that mold tolerance and prepreg thickness difference may cause uneven stress distribution, which are also the main reasons for manufacturing defects. Thicker prepreg and full impreg-nation of the gap between mold and prepreg are beneficial to improve stress distribution. These results may contribute to the manufacturing and quality control of advanced composite with high surface precision.

VIBRATION ANALYSIS OF CARBON FIBER COMPOSITE MOTOR FRAME

YANG Hai-ru, LI Xiong, CHEN Guo-zhi

2019, 0(8): 94-97.

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In this paper, a carbon fiber reinforced polymer (CFRP) motor frame is designed, which is similar to the metal motor frame. The Abaqus finite element analysis software is used for the modal analysis of the motor base. The natural frequencies and harmonic responses of the CFRP motor frame are obtained and compared with those of the metal motor frame. The results show that the natural frequencies of the CFRP motor frame are much higher than those of the metal motor. By comparing the natural frequencies of the metal frame, it is proved that CFRP motor base has advantages of low vibration.

LIGHTWEIGHT AND OPTIMIZED DESIGN OF CARBON FIBER COMPOSITE FRONT BUMPER BEAM

ZHANG Xin, ZHAO Xiao-yu, LAN Xiang, CHEN Ling-li

2019, 0(8): 98-103.

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In order to realize the lightweight design of the car and improve its passive safety, the front bumper beam of a car is taken as the research object. According to the regulations, the low-speed collision model of steel and carbon fiber T300/5208 was established respectively. The collision simulation was carried out and the energy absorption of the two materials was analyzed. In the HyperStudy software, the optimal Latin hypercube sampling method is used to obtain the sample points and data, and then the HyperKriging method is used to construct the approximate model. Then the genetic algorithm is used to optimize the calculation. Finally, the optimal solution is obtained and experimental verification is carried out. The optimization results show that the energy absorption of the carbon fiber material bumper beam increases by 6.4% at low speed collision, the energy absorption is about 3.7 times that of the original steel, the weight loss reaches 71.4%, and the error between the optimized result and the actual solution result is less than 1%. The energy absorption characteristics and the lightweight effect are significantly improved.

DESIGN AND VERIFICATION OF VARI PROCESS FOR ASYMMETRIC COMPLEX FOAM SANDWICH COMPOSITES

LIU Ya-nan, LIU Chen-xiao, LI Yong-hang, YUAN Chong-xin

2019, 0(8): 104-108.

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Aiming to solve the manufacture problems of civil aircraft aft fairing structure using vacuum assisted resin infusion (VARI) process, PAM-RTM simulation was adopted to assist the designing and optimization of resin flow during the resin infusion process for asymmetric foam sandwich composite structures. Firstly, the simulation process of resin flow was established based on PAM-RTM software, and four different resin injection schemes were proposed and conducted. Through comparison and analysis of the four different simulation schemes, the resin flow rules during injection process for the complex foam sandwich composite material with opening area have been obtained. Then, the optimum injection scheme was selected and verified by experiment. Finally, the quality of the fabricated foam sandwich composite was tested, and the non-destructive testing results demonstrated the good quality without defects, as well as good uniformity in thickness. The research results might be useful for the application of complex foam sandwich composites manufactured by liquid forming technology in civil aircraft structures.

APPLICATION RESEARCH OF PFMEA IN AEROSPACE COMPOSITE STRUCTURAL PARTS FORMING

ZHENG Guo-dong, WANG Yang, ZHAO Ming, ZHANG Jing

2019, 0(8): 109-114.

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Aiming at the problem of quality risk identification of high-precision products, especially aerospace composite structural parts, the failure mode identification method is proposed by analyzing the production process and combining the molding process and production factors of composite structural parts. The effectiveness of the severity (S) and detectability (D) evaluation criteria is improved by increasing the evaluation dimension, the frequency (O) is accurately defined by the similar process method. Combined with the production process of CZ-5 fairing, the application of PFMEA in the forming of large-scale aerospace composite structural parts is expounded, which provides a reference for small batches of multi-variety products to avoid quality risks.

APPLICATION STATUS AND DEVELOPMENT TREND OF ACOUSTIC EMISSION IN RESEARCH ON DAMAGE MECHANISM OF COMPOSITE MATERIALS

NI Ying-ge, YANG Yu, LV Yi, ZHANG Wei

2019, 0(8): 115-126.

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Acoustic emission has the characteristics of real-time and continuous monitoring, and has achieved good performance in the research on composite damage mechanism. In this paper, the analysis methods and application status of acoustic emission technology in composite damage mechanism research are summarized. The advantages and disadvantages of parameter analysis method, waveform analysis method and pattern recognition are pointed out. Key technologies to be solved and future development trend are put forward in the investigation on composite damage mechanism, in order to lay the foundation for the improvement of acoustic emission in composite damage mechanism research.

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