COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL INVESTIGATION ON THE MECHANICAL PROPERTIES OF THE CFRPFILAMENT WINDING HYBRID TUBES UNDER AXIAL CRUSHING

CUI Zheng-liang, LIU Qiang, LAI Li-ping

2020, 0(2): 5-9.

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The main components of hydrogen storage vessel for vehicle include aluminum alloy and CFRP. This paper aims to study the failure modes of filament winding CFRP/aluminum tubes and the influence of the winding angle on the crashworthiness characteristics through the quasi-static axial compression tests. The characteristics has been compared between the single aluminum tube and hybrid tubes. It is found that the outer fiber shows the progressive brittle fracture mode and the inner aluminum failure is mainly the diamond mode. When the winding angle ranges from 30° to 60°, the PCF of all the specimens decreases while increasing the winding angle and the hybrid tubes with the winding angle of 45° have the highest EA, SEA and CFE. The energy absorption of the hybrid tubes mainly comes from the aluminum, the deformation of the CFRP and the interaction between them. This study indicates that the interaction between the CFRP and aluminum could improve the crashworthiness of single aluminum tube effectively.

DAMAGE ANALYSIS OF FIBER COMPOSITE LAMINATES UNDERFOUR POINT BENDING LOAD

ZHAO Yu-qing, JIANG Feng, HUANG Zheng-ming

2020, 0(2): 10-18.

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In this paper, the load-displacement response and fracture strength of _8s T300/7901 carbon fiber/epoxy composite laminate under four-point bending were investigated both experimentally and theoretically. The intra and inter layer damages of the laminate under four-point bending load were analyzed using commercial software Abaqus/CAE incorporated with micromechanical Bridging Model. The analysis scheme is implemented into a user-subroutine VUMAT, which requires input of only the constituent fiber and matrix material data. The constitutive relationship of a unidirectional lamina layer is defined using Bridging Model, and 3D Hashin′s criterion is applied to detect a fiber tensile/compressive or matrix tensile/compressive induced failure of the layer. Once a constituent failure occurs, the Camando′s method is used to degrade its elastic modulus. A thin pure matrix layer is inserted in between two adjacent lamina layers, and an interlayer de-cohesive failure is assumed when the matrix layer′s damage is attained. The simulation results are compared with our experimental data. The results show that the simulated load-displacement curve and ultimate strength agree well with the measured results. The proposed model is capable of predicting the intra- and inter-layer damages of a laminated composite.

A COMPARATIVE STUDY OF SIMULATION AND MODAL TEST FORA SMALL ICING WIND TURINE BLADE

LI Fei-yu, CUI Hong-mei, CHEN Hong-xing, SU Hong-jie

2020, 0(2): 19-24.

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After the wind turbine blades are covered with ice, the normal operation of wind turbine generator system is affected, the wind turbine will be overloaded and the blades will be broken, which will cause safety accidents and waste of resources. Therefore, it is very important to detect the icing condition of wind turbine blades by the modal parameters. In this paper, the modal parameters of wind turbine blade under different icing thickness were measured by modal testing system and calculated by the finite element software ANSYS, and the first four vibration modes and natural frequencies of the blades are obtained. The results show that the results of simulation modal and experimental modal are close, the vibration characteristics are consistent, and the error of fundamental frequency is within 3%. The first-order natural frequency vibration mode of the blade after icing is flap-wise. Starting from the two-order natural frequency vibration mode of the blade, the coupled mode of flap-wise and edge-wise directions appears. The first four-order vibration modes of the blade remain unchanged as the increasing of ice thickness, the main vibration mode is flap-wise, and the amplitude at the tip of the blade decreases gradually. When the ice thickness is 30 mm, the fundamental frequency of the blade decreases by 28.7% compared with that without icing. These results have certain guidance on design of blade icing state detection system based on vibration detection technology.

EFFECT OF EMAA/CNT FILMS ON THE MODE Ⅱ INTERLAMINAR FRACTURE TOUGHNESSAND SELF-HEALING EFFICIENCY OF COMPOSITE MATERIALS

GAO Ya, LIU Ling

2020, 0(2): 25-31.

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Laminated structure is a major structure of fiber reinforced plastics, and delamination caused by weak interlaminar properties will cause a final failure to the laminates. In this paper, poly (ethylene-co-methacrylic acid) (EMAA) and carbon nanotube (CNT) are used to prepare two kinds of EMAA/CNT composite films, i.e., solid and porous membranes. Then, these two films were respectively introduced into the middle interface of glass fiber/epoxy laminates, and how the films affected the mode Ⅱ interlaminar fracture toughness (G_ⅡC) and its self-healing were studied. The results show that porous EMAA/CNT film has better toughening and self-healing properties. Compared with the glass fiber/epoxy blank laminate, porous EMAA/CNT film improves the G_ⅡC by 19.6%, which can be recovered to 92.5% after thermally self-healing. However, solid EMAA/CNT film would decrease the G_ⅡC by 27.5%, although the self-healing efficiency is 81.8%. Microscopic characterization shows that uniform distribution of the porous EMAA/CNT and epoxy at interlaminar interface plays a positive role in toughening and self-healing.

PERFORMANCE RESEARCH AND STRUCTURAL OPTIMIZATION OF FIBER REINFORCEDPLASTIC CONNECTOR CONNECTORS BASED ON ANSYS

WANG Tao, HUANG Ling-li, LIU Yu-jian, HOU Rui-gang

2020, 0(2): 32-38.

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The connection mode and performance of fiber-reinforced plastic connector connectors are studied and structural optimization are studied by the method of finite element analysis, and the analysis results are verified by the experimental method. The results show that mechanical connections are not suitable for joint connection structures of fiber-reinforced plastics that are mainly subject to stretch stress because of the concentration of stress at the bolts, and the plying connection methods of the double-tie board docking have smaller equivalent stresses, overall deformation and contact surface stress, and are not prone to peeling damage. It is shown that the docking of the double-connecting plate should be used as a joint connection method, which is consistent with the measured results, verifying the applicability of ANSYS finite element analysis in the performance study of fiber-reinforced connector connections. Finally, the joint structure is optimized based on the tie-up length, and the results show that the docking method of the double hooking plate with a connection length of 70 mm is optimized.

FINITE ELEMENT ANALYSIS AND EXPERIMENTAL STUDY ON STATIC STRENGTH OFCOMPOSITE WING OF A GENERAL AIRCRAFT

LIU Jia, XIONG Jun, ZHAO Xin-xin, LV Wan-tao

2020, 0(2): 39-43.

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As one key structure of the general aircraft, the wing unit has a significant impact on the flight safety performance of the whole aircraft. In order to evaluate the static structural strength of the all-composite wing of a general aircraft, the finite element model of the whole structure of the wing unit is established by using shell elements in MSC. Patran software. The finite element analysis of the wing unit under the critical load is carried out, and the stress and strain results of the wing unit are given. The test parts and equipment of the wing unit were designed and manufactured, and the test verification was performed. The experimental results are basically in good agreement with the theoretical calculation values, which shows that the finite element model and analysis method of the wing unit are correct and feasible, and provides a basis for the optimization and improvement of the structure in the future.

PREPARATION AND VAPOCHROMIC OF COLORFUL GLASS FIBER

XU Pei-jun, CHENG Jing-qi, ZHANG Ning, FENG Xin

2020, 0(2): 44-47.

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Glass fiber is widely used in various fields of life due to its great flame retardancy, electrical insulation properties, high temperature resistance, and corrosion resistance. With the rise of smart materials, various new materials with responsive characteristics such as light, heat and electromagnetic have come out. Functional glass fiber has become an important direction for the future development of intelligent composite materials. The preparation of color responsive glass fiber will make the color of glass fiber more diversified and expand the application of glass fiber in the intelligent composite materials field. We deposit graphene oxide (GO) solution on the surface of glass fiber by solution vacuum filtration to prepare glass fiber which has the color similar to one-dimensional photonic crystalstructural color coating. The GO layer deposited on the surface of the glass fiber will make the incident light to produce interference phenomenon to form colorful appearance. And the colorful glass fiber has a "water vapor-color" cyclic discoloration function.

DESIGN OF HIGH-THROUGHPUT PREPARATION TECHNOLOGY PLATFORMFOR CONTINUOUS FIBER REINFORCED COMPOSITES

LI Xue-qin, GUO Shuang-xi, Li Bin-tai

2020, 0(2): 48-53.

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High-throughput preparation technology platform on a macro scale for continuous fiber reinforced composites was designed. Realization program of a typical process with this platform was also planned. The design feature of the high-throughput preparation technology platform was the combination of vacuum assisted hot pressing process and advanced prepreg pultrusion process. Composite samples in large quantities can be formed with different process parameters by adjusting pressure and temperature of the platform. The period of preparing composites with different process parameters using the platform is much shorter than using traditional autoclave molding. Heating step by step in the platform makes the temperature gradient along the thickness slightly less than the traditional continuous heating mode. Heating method has little influence on the curing degree evolution of the composite material.

VIBRATION ANALYSIS OF THE EMBEDDED CO-CURING DAMPINGCOMPOSITE RING-OPENING STIFFENED CYLINDRICAL SHELLS

WANG Guang-he, LIANG Sen, ZHOU Yun-fa, ZHENG Chang-sheng

2020, 0(2): 54-61.

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Based on the first-order shear deformation shell theory, the dynamic characteristics of the embedded co-curing damping composite ring-opening stiffened cylindrical shells are studied, and the stiffening ribbings are treated as discrete elements. The Rayleigh-Ritz energy method and Navier method are used to derive the strain energy and kinetic energy expression of the embedded co-curing damping composite ring-opening stiffened cylindrical shells, and the control equation of free vibration is established. The simulation results obtained by ANSYS modeling are used to verify the correctness of the formulas in this paper. Theoretically, the effects of different rib heights and damping sandwich layer thickness on the performance of the cylindrical shell are further discussed in this paper. The research conclusions have certain references for the design and application of lightweight, high stiffness and large damping composite structural members.

AIR COUPLED LAMB WAVE DETECTION TECHNOLOGY FOR HONEYCOMB COMPOSITES

CHANG Jun-jie, LI Yuan-yuan

2020, 0(2): 62-68.

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Paper honeycomb structure should avoid liquid immersion. Aiming at solving the problem that liquid coupling agent can′t be used to detect this kind of material, based on the use of air-coupled penetrating C-scan imaging to detect honeycomb structure material, a method of using air-coupled Lamb wave to detect the debonding defect between skin and honeycomb structure was proposed. A simulation model was established to detect debonding defects in honeycomb structures and visualize the ultrasonic propagation process. The interaction between Lamb wave A0 mode and workpiece structure was studied, and the influence of debonding size on acoustic propagation was analyzed. The results show that the application of air-coupled ultrasonic guided wave technology can better achieve the detection of debonding defects, and can be applied to actual in-service detection.

STUDY ON IMPACT RESISTANCE OF RUBBER ARAMID FIBER COMPOSITES

WANG Ling, LIANG Sen, YAN Sheng-yu, CHEN Xin-le

2020, 0(2): 69-75.

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A new structure of rubber aramid fiber composite is presented. The LS-DYNA dynamics software was used to establish a model to simulate the impact resistance properties of rubber aramid fiber composites under low-speed impact loads. In order to measure the impact resistance parameters of this structure, the impact test instrument was used to perform low-speed impact tests. By comparing the simulation results with experimental results, the validity of the simulation method was verified. Based on the verification model, the influence of the geometric parameters of the structure on the impact resistance was further studied. The conclusion shows that the rubber aramid fiber composite has excellent impact resistance. It lays the foundation for the wide application of rubber aramid fiber composite materials in high-tech fields such as helmets and body armor.

FINITE ELEMENT SIMULATION AND EXPERIMENT VERIFICATION OFBENDING PERFORMANCE INVESTIGATION ON ADHESIVELY REPAIREDFOAM CORE SANDWICH FIBERGLASS COMPOSITE

LIU Guo-chun, PANG Jie, YANG Wen-feng, SUN Ting

2020, 0(2): 76-80.

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For the lack of study on adhesively repaired foam core sandwich composite, a three-dimensional finite element analysis model and corresponding bending experiments verification were developed for the adhesively repaired foam core sandwich composite. The setting of adhesive in finite element model is simplified by test results. The failure load of foam and panel is taken as the initial and ultimate failure load of the repaired structure. The simulated failure load is 18.92% higher than the average test load and 7.14% higher than the maximum test failure load. The strain trend characterization of the model was established by linear loading step, the maximum deviation is 11.2% in the compression laminate and 24.3% in the tension laminate. The conclusion shows that the finite element model of adhesively repaired foam core sandwich composite is feasible and available.

FATIGUE DAMAGE PROPAGATION AND LIFE OF THE MULTI-STEPSBONDING STRUCTURE OF AIRCRAFT COMPOSITES

CAO Shuang-hui, GAO Nong-yue, LIU Bin

2020, 0(2): 81-84.

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Composites have been widely used as the main load-bearing structures′ material in aircraft, and among various structures, stepped topology has been chosen to become the main form of fuselage repairing and connection due to the easy implementation. Although a quantity of literature has given the fatigue performance of single-lap of metal, composite and two hybrids, the fatigue durability of the special multi-lap for high-efficiency load-transferring structure is seldom studied. Besides, the fatigue failure mechanism is still not illustrated adequately. In this research, the experiments on composite stepped-lap adhesively bonded structure, which is made under the process of mold making, prepreg clipping and laying firstly, autoclave solidification secondly, step surface brushing adhesive thirdly and finallycutting into specimens, were conducted. The cyclic tensile load of stress ratio 0.1 was selected in the experiment, and the visible cracks and propagation of fatigue testing process were detected through the experiments. All the specimens have been completely fractured at the end of the experiment in order to obtain the total life span. According to the linear curve fitted by S-N discrete based on the testing data, the fatigue life decreases linearly as the stress level increases. After visible cracks being found, the composite bonded structure only has 10% residual cracks expansion life until being completely fractured, which implies that the component must be repaired or replaced once visible cracks appear. For the cracking mechanism, composites matrix shear-mode damage dominates the fatigue initiation damage, while cohesive failure, adhesive failure, matrix crack, and delamination composed the fracture modes after stepped-surface fracture appearing.

EXPERIMENTAL STUDY ON EFFECT OF CURING PRESSURE ON FIBER DISTRIBUTIONOF THICK L-SHAPED CFRP UNIDIRECTIONAL LAMINATES

ZHANG Kun-qiao, ZHANG Jiang-tao, ZHANG Mei, ZHAI Peng-cheng

2020, 0(2): 85-90.

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The thick L-shaped unidirectional carbon fibre reinforced polymer composite laminates (CFRP) were manufactured by the autoclave process. Based on the analysis of macroscopic and microscopic structure morphology, the effects of autoclave pressure on the laminate thickness and fiber distribution were estimated. The results show that the out-of-plane wrinkling and nonuniform thickness distribution arise in the thick L-shaped CFRP unidirectional laminates manufactured by the autoclave process. The resin-rich regions are present between the prepregs. By increasing the autoclave pressure, the thickness of resin-rich regions between prepregs and the wrinkles in the thick L-shaped CFRP unidirectional laminates can be reduced. The thickness compaction, the fiber content difference between different sections and fiber content gradient in the region closing to the bleeder increase with the increasing the autoclave pressure, the thickness of corner section becomes smaller than that of the flat section, and fiber content near mold surface becomes higher if a high autoclave pressure is applied. Close to the mold side, the resin tends to aggregate into the flat/corner transition region.

STUDY ON COMPOSITE OMIGA STRINGER STIFFENED CURVED PANEL BY AUTOMATICPHASED ARRAY ULTRASONIC INSPECTION TECHNIQUE

ZHANG Ji-min, XIAO Peng, LIU Kui, LIU Fei-fei

2020, 0(2): 91-96.

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Compared with other non-destructive testing technologies, ultrasonic testing is still the most widely used and mature technology for aeronautical composite component testing. In recent years, with the gradual development of domestic phased array ultrasonic testing technology, this technology has gradually moved from the laboratory research stage to the production inspection application stage. The Automatic phased array ultrasonic inspection technique based on the pulsed echo mode was utilized to study the automatic inspection of composite omiga stringer stiffened curved panel. For the curved panel and omiga stringer R structure respectively, different probes, frequencies and focus modes were used to carry out automatic inspection and profile, C scan imaging and defect evaluation. The results prove that the automatic inspection and profile of curved panel can be realized by utilizing ultrasonic profiling measurement method, and the minimum size to Φ3 mm defect can be detected. The omiga stringer R structure can be inspected automatically by customizing the special R structure water shoe.

APPLICATION EVALUATION RESEARCH ON T800/607 CRYOGENIC COMPOSITE MATERIAL

ZHANG Jian-bao, SHANG Cheng-yuan, ZHOU Yu, LIU Yong-jiao

2020, 0(2): 97-100.

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Based on the research situation of the composite cryotank processing technology home and abroad, the properties of T800/607 cryogenic composite were studied through automated fiber placement processing property, mechanical properties and permeability. After that, the application feasibility of T800/607 composite on cryotank without lining was tested and evaluated through cylinder structure member developed and performance tested.

PREPARATION AND STUDY ON PROPERTIES OF THERMALCONDUCTIVE POLYURETHANE POURING SEALANT

ZHANG Bo-wen, MEI Qi-lin, HUANG Yan-kai, XIE Chao

2020, 0(2): 101-105.

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In this paper, polyurethane pouring sealant was prepared by one-step method using polytetrahydrofuran glycol (PTMG), diphenylmethane diisocyanate (MDI) and spherical alumina. The effects of coupling agent dosage, alumina particle size and filling amount on the properties of polyurethane pouring sealant were studied. The filling amount of Al₂O₃ was determined to be the key factor affecting the thermal conductivity of the pouring sealant by orthogonal experimental design. The thermal conductivity of polyurethane pouring sealant was effectively improved by adding coupling agent. When the same content of Al₂O₃ is added, the thermal conductivity of the pouring sealant filled with 2 μm Al₂O₃ is better. At the same particle size, the thermal conductivity of the pouring sealant increases gradually with the addition of Al₂O₃. The volume resistivity of the pouring sealant decreases with the increase of Al₂O₃ filling, but its insulation performance can still meet the requirements of electronic equipment encapsulation.

EFFECT OF FILLER ON MECHANICAL PROPERTIES AND GLASS TRANSITIONTEMPERATURE OF PULTRUSION EPOXY RESIN CASTINGS

WANG Zhi-wei, ZHANG Chun-ying, TIAN Chao-kai, LIU Chuan-rui

2020, 0(2): 106-110.

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In order to study the effect of filler particle size and filler type on the mechanical properties and glass transition temperature of pultruded epoxy resin castings, different size, same type of Al(OH)₃ filler and the same particle size, different kinds of filler are added into the epoxy resin in the present study. The results show that the tensile and compressive strength of the pultruded epoxy resin castings with the Al(OH)₃ filler particle size of 5 μm is the highest when the same filling amount, different particle size and the same kind of filler are added. When the same filling amount, the same particle size, and different kinds of fillers are added, the tensile and compressive strength of the pultruded epoxy resin casting body which contains the heavy calcium carbonate is the highest, and the bending strength is not much different. The glass transition temperature of the pultrusion epoxy resin is increased after the addition of the filler, and the glass transition temperature is higher when the Al(OH)₃ filler with a particle size of 1 μm or the calcined kaolin is added.

SIMULATION AND EXPERIMENT ON THE EFFECT OFPATCH SHAPE ON ADHESIVE REPAIR OF COMPOSITE

HOU Bing-qiang

2020, 0(2): 111-116.

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In order to investigate the performance of the adhesive bonding repair in composite,static tensile test is carried out on the bonding structure numerically and experimentally. The tensile load-displacement behaviors of T9001 composite adhesive bonding structure is studied under room temperature. Based on the three-dimensional progressive damage theory, the model of adhesive bonding structure with different patch shape has been constructed, and the final failure strength is predicted using APDL language. Moreover, experiment has been performed on each adhesive bonding structure with different patch shape. The results indicate a good agreement with numerical predictions. And, it is found that the repair effect of the adhesive bonding structure with the square patch is better than others. The final damage pattern and damage range of the patch repair structure are also tested by X-ray machine, which is consistent with the simulation results.

PREPARATION OF MODIFIED 2-ETHYLIMIDAZOLE LATENTCURING AGENT FOR EPOXY RESIN

SHEN Zhong-tao, ZHANG Qiao-xin

2020, 0(2): 117-121.

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In order to prepare imidazole latent curing agents, two modified 2-ethylimidazole derivatives were synthesized by the reaction of 2-ethylimidazole (2EI) with N-(4-hydroxyphenyl) maleimide (HPM) and trichlorocyanide, respectively. Their molecular structures were characterized by IR and NMR. The results showed that N-(4-hydroxyphenyl) maleimide (HPM) and cyanuric chloride reacted with 2-ethylimidazole respectively and completely, and the corresponding target products were obtained. The modified imidazole curing agent was mixed with epoxy resin to study the curing properties and latency of the resin system. The results show that compared with EP/2EI system, the exothermic zone of the modified curing system moves to the high temperature region, and the modified curing system has a longer storage period at room temperature. Maleimide group and triazine ring with strong electron absorption effect reduce the nucleophilicity of imidazole ring and inhibit the curing activity of curing agent at room temperature. In addition, the modified curing agent can overcome the energy barrier of curing reaction and restore the rapid curing ability under the heating condition.

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