COMPOSITES SCIENCE AND ENGINEERING

MODEL ANALYSIS FOR STABBING PERFORMANCE OF BIAXIAL WARP-KNITTED FABRIC MEMBRANES

ZHANG Yang, CHEN Jian-wen, WU Shan-xiang, XIA Yu-fan

2021, 0(5): 5-11. DOI: 10.19936/j.cnki.2096-8000.20210528.001

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Stabbing damage is one of the main failure types for warp-knitted fabric membranes during their serving life. And the stabbing mechanical properties of fabric membranes are extremely important for the safety of membrane structures. The stabbing performances of biaxial warp-knitted fabric membranes (PVDF 8028) were studied through numerical method. The numerical model of stabbing considering the micro structure of yarns and matrix is established by ABAQUS software. By introducing the square cone punch and sheet punch, the morphological characteristics of PVDF 8028 under different punches were analyzed on mesoscale, and the effects of different stabbing angles were systematically investigated. The FEM models were validated from the good agreement between the FEM results and the theoretical results. The results show that, for the square cone punch, the stabbing strength of the membrane material decreases as the horizontal stabbing angle of the square cone punch increases, and the stabbing strength reduction reaches 39.39% when the horizontal stabbing angle grows from 0° to 90°. In terms of the sheet punch, with the increase of the stabbing angle, the stabbing strength shows a tendency that it increases at first and then decreases, and the peak stabbing force-stabbing angle curve shows an inverted "V" shaped characteristic as the stabbing angle increases. The conclusions obtained could provide useful references for damage assessment and safety analysis of membrane structures.

RESEARCH ON THE EFFECT OF COMPOSITE PLY ANGLE ON NONLINEAR AEROELASTICITY OF HIGH-ASPECT-RATIO WING

WANG Jun-li, LI Qing-qing, LU Zheng-wu, LEI Shuai, LI Tuo-lei, SHEN Nan

2021, 0(5): 12-20. DOI: 10.19936/j.cnki.2096-8000.20210528.002

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In order to reduce weight and increase the lift-to-drag ratio, modern aircraft structures generally adopt high-aspect-ratio layout, and the proportion of lightweight composite materials in the aircraft structure is also increasing. In order to study the effect of composite layering angle on the nonlinear aeroelasticity and longitudinal aerodynamic characteristics of high-aspect-ratio wing, the structural deformation of the wing is selected as the optimization goal, and the structural strength is used as the constraint. The screening method was used to optimize the lay angle of the skin of the composite high-aspect-ratio wing. After optimization, the stiffness of the wing is significantly enhanced. Then, based on the loosely coupled two-way fluid-structure coupling numerical simulation method, the nonlinear aeroelasticity and flow field of the high-aspect-ratio wing before and after optimization are numerically simulated, and the effect of the composite layering angle on the nonlinear aerodynamics of the high-aspect-ratio wing is analyzed. The influence of elastic deformation and longitudinal aerodynamic characteristics is analyzed.

ASSESSMENT OF MULTIPLE DELAMINATIONS IN FIBER REINFORCED COMPOSITES

HUANG Mei, PAN Jing-wen, JIANG Jian, ZHANG Zhi-fang

2021, 0(5): 21-30. DOI: 10.19936/j.cnki.2096-8000.20210528.003

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In this paper, based on the engineering background of fiber reinforced composite (FRP) laminates that may undergo overlapping delamination damage at multiple interfaces after impact, a series of modal frequency changes before and after the occurrence of the multiple delaminations are used to predict the damage in FRP laminates. Firstly, the finite element model of FRP laminates with delaminations were constructed and validated using experimental results in literature. The multiple delaminations was simulated as a shape of ellipse. Then the finite element model is used to generate the corresponding frequency changes in different scenarios of multiple delaminations, which was feed into two inverse detection algorithms, the genetic algorithm (SAGA) and support vector machine (SVM), for predicting the interface, location and size of the multiple delaminations. Numerical validations show that both inverse algorithms SAGA and SVM can successfully identify the multiple damage in FRP laminates through the frequency changes due to the multiple damage.

EFFECTS OF THERMOPLASTIC RESIN CONTENT ON LONGITUDINAL COMPRESSIVE PERFORMANCE OF CARBON FIBER REINFORCED EPOXY COMPOSITES

ZHANG Dai-jun, CHEN Jun, BAO Jian-wen, ZHONG Xiang-yu, GONG Ming, CHEN Xiang-bao

2021, 0(5): 31-36. DOI: 10.19936/j.cnki.2096-8000.20210528.004

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An epoxy-matrix composite, reinforced by CCF800H, a domestic high strength intermediate modulus carbon fiber, was prepared. A thermoplastic resin was used as the toughening agent of the resin. Effects of the content of toughening agent were investigated on the resin elastic modulus by regulating its content in the epoxy resin. Furtherly, effects of the content of toughening agent were studied on the longitudinal compressive performance of the composite. The results show that the resin modulus decreases with the increase of the thermoplastic resin content, and the Poisson's ratio of the composite increases correspondingly. The compressive strength of the carbon fiber composite decreases with the increase of the thermoplastic resin content. The thermoplastic resin content shows little influence on the compressive modulus of the composite.

CURING MECHANISM OF PHENOLIC RESIN MODIFIED BY PHENYLPHENOL BASED ON VARIABLE TEMPERATURE FTIR SPECTRA

ZHANG Ying, HU Hong-lin, WANG Zai-duo, LIU Liang, YU Rui-lian

2021, 0(5): 37-42. DOI: 10.19936/j.cnki.2096-8000.20210528.005

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To solve the problem that the curing mechanism of phenylphenol modified phenolic resin remained unclear, the characteristic structure hydroxymethyl, different substituent methylene, and ether bond were investigated by variable temperature FT-IR. The gas products released with the increase of curing temperature were characterized by Thermogravimetry-Mass Spectrometry. The curing mechanism from 90 ℃ to 230 ℃ was concluded finally. The results showed that the main reaction was the formation of the p-p methylene group in the range of 90 ℃~120 ℃. It is difficult to form the o-p methylene bridge at this stage. In the range of 120 ℃~170 ℃, the main reaction is the formation of the p-p methylene group. From 170 ℃ to 200 ℃, the main reactions are the breaking of the ether bond, the formation of the carbonyl group, and the formation of the propyl bridge. Above 200 ℃, the main reactions could be polycondensation reaction among phenolic hydroxyl groups, and the formation reaction of carbonyl groups. The ether bond breaks completely above 230 ℃. This work provides a new method to study the curing mechanism of phenolic resin. It is a benefit for the rational design of the curing process of phenolic resin.

LIGHTWEIGHT DESIGN OF SOLID ROCKET MOTOR CASING WITH LARGE ASPECT RATIO

FENG Bin-bin, YUAN Jin, HU Xu-hui, ZHANG Xiong-jun, LU Jin-hu

2021, 0(5): 43-48. DOI: 10.19936/j.cnki.2096-8000.20210528.006

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Aiming at the problems of strengthening the head of carbon fiber composite shell with large aspect ratio and lightweight of the shell, based on the grid theory, the ply design of the combustion chamber shell of the ϕ180 mm solid motor is completed. Then the thickness of the spiral winding layer is reduced, and the head is reinforced by carbon cloth and carbon fiber braided prepreg head cap. According to the cubic spline formula, the calculation is carried out through the finite element ABAQUS simulation software, the stress state and burst pressure of the shell are analyzed and calculated. Through the shell trial production and hydraulic burst test, the influence of carbon cloth reinforcement and carbon fiber braided prepreg head cap on the head reinforcement is studied and analyzed. The results show that the reinforcement effect of carbon cloth is not obvious, but the strength of carbon fiber prepreg head cap woven according to a certain longitudinal ring ratio is far greater than that of carbon cloth, and the reinforcement strength is basically consistent with the spiral winding strength. The weight of the head cap with carbon fiber braided prepreg is 14.1% lower than that of the basic sample forming method.

ON REPAIR OF METAL STRUCTURES WITH COMPOSITE PATCHES CURED BY CARBON NANOTUBE FILM RESISTANCE HEATING

ZHANG Ning, YAN Gang

2021, 0(5): 49-54. DOI: 10.19936/j.cnki.2096-8000.20210528.007

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In recent years, composite material bonding repair technology has been widely used in damaged metallic structures, but the traditional patch curing process has problems like high cost, high energy consumption and long molding time. In response to this problem, this paper proposes to integrate the carbon nanotube film (CNTF) as a heating element with the composite prepreg patch, and achieve the purpose of repairing the damaged structure through electric heating and curing. Experimental studies have been conducted by using CNTF electric heating and traditional oven heating methods to cure the composite patches to repair cracked aluminum alloy plates. The energy consumption and curing time required under different methods have been compared, and tests have been conducted to evaluate the mechanical performance of the repaired structures. The results have demonstrated that the CNTF electric heating and curing technology is an energy-saving and energy-efficient method, which can significantly reduce energy consumption and material forming time. Meanwhile, the bearing capacity of the test specimens repaired by CNTF electric heating is similar to that of the test specimens repaired by oven heating, providing a new way for bonding repair of metallic structures with low energy consumption and low cost.

RESEARCH ON PIN CONNECTION OF CARBON FIBER COMPOSITE PIPE FITTINGS AND METAL FITTINGS

LIU Gui-yu, MA Yan, CHU Ming-yue, YANG Yu-qiu

2021, 0(5): 55-60. DOI: 10.19936/j.cnki.2096-8000.20210528.008

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Carbon fiber composite material energy absorbing box is an important candidate of metal in automobile, and the connection problem with metal parts in automobile assembly is an important direction for studying energy absorption. In order to study the feasibility of the energy absorption box assembly, the pin connection method in mechanical connection is used to first study the energy absorption effect of the opening on the pipe fittings in this paper. The energy absorption performance difference between the composite pipe fittings and the metal fittings is analyzed through the positive and off-axial quasi-static compression experiments and damage observation. During the process, the feasibility of the connection method was studied. It is found that the bottom opening has no significant influence on the energy absorption of the pipe fittings. The hanging pin connection method designed in this paper is not stable and effective energy absorption is not feasible, and the non-dangling pin connection method is feasible, non-dangling pin connection research can be used for further research.

IN VITRO EXPERIMENTAL STUDY ON THE MECHANICAL PROPERTIES OF VASCULAR STENTS PREPARED BY 3D PRINTING NANOCELLULOSE/POLY (LACTIC ACID) NANOCOMPOSITES

JIA Li-han, LI Yan

2021, 0(5): 61-67. DOI: 10.19936/j.cnki.2096-8000.20210528.009

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The atherosclerosis is one of the most life-threatening diseases to modern people and percutaneous coronary intervention is an effective method for solving this disease. Currently, bare metal stent (BMS) has been widely used in the clinical practice. But two severe problems may be caused by BMS, i.e. stent thrombosis (ST) and in-stent restenosis (ISR). Bioabsorbable vascular stent (BVS) is one new general vascular stent that may solve the problems caused by BMS because of its good biocompatibility and biodegradability. In this study, the bioabsorbable vascular stents of different stent thickness, stent diameter and infill pattern made by poly(lactic acid) and cellulose nanocomposites were prepared respectively by a fused deposition modeling 3D printer. The in vitro experimental test for mechanical properties of the vascular stents were performed. Planar compression method for radial support property test and three-point bending method for flexibility of the stents were performed respectively. The test results indicate that in comparison to stents made by neat poly(lactic acid), the radial support property of modified composites stents with larger radius is increased by 47.6% and the flexibility is improved by 20.2% at most. The results of range analyses indicate that the stent thickness has the most significant impact on the in vitro mechanical properties and the infill pattern has less influence on the stent mechanical properties.

DESIGN AND DEVELOPMENT OF AUTOMATIC ROLLER COATING EQUIPMENT FOR WIND TURBINE BLADES

LI Guo-liang, YAN Chen, CHEN Xiao-liang, CUI Jun-wei

2021, 0(5): 68-72. DOI: 10.19936/j.cnki.2096-8000.20210528.010

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With the development of large wind turbine blades, more requirements are put forward for blade post-treatment process. At present, the roller coating process of wind power blade post-treatment completely adopts manual operation, which also increases the labor cost of blade manufacturing under the condition of unstable roller coating quality. In this case, the application of automatic equipment in wind power post-processing becomes extremely urgent. This paper mainly discusses a new type of automatic roller coating equipment for wind power blades, which mainly includes AGV intelligent navigation equipment, truss manipulator, automatic paint matching and conveying system, electronic control system integration and other parts. The application of automatic roller coating equipment can effectively improve the working efficiency of wind power blade post-treatment, ensure the quality of blade roller coating, reduce the labor cost of blade manufacturing, and improve the intellectualization degree of blade industry.

DESIGN OF SPECIAL-SHAPED STRUCTURES FRONT COVER OF LAUNCH CANISTER WITH BREAKTHROUGH

AN Qing-sheng, SUN Li-dong, YAN Jin-zhen, WU Qiu-sheng

2021, 0(5): 73-79. DOI: 10.19936/j.cnki.2096-8000.20210528.011

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Aiming at the problem that the front cover of a certain type of launch canister with high comprehensive performance requirements, and the projectile body axis does not coincide with the geometric center line of the launch canister, through demand analysis, structural design, material selection and determination of forming process, then to simulation analysis, sample test verification, a kind of front cover with decentered breaking point was finally determined, in which epoxy resin foaming material was used for main body bearing structure. The success of relevant test examinations and subsequent ejection launch tests indicate that the special-shaped structures front cover of launch canister with breakthrough has good comprehensive technical performance, and meets the design requirements well.

CURING KINETICS AND ISOTHERMAL TRANSFORMATION (TTT) DIAGRAM OF Z616 PHENOLIC RESIN

ZHAO Zhi-ying, TIAN Mou-feng, SONG Jin-mei, XU Ya-feng

2021, 0(5): 80-85. DOI: 10.19936/j.cnki.2096-8000.20210528.012

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Z616 phenolic resin is an ablative resin system, which aimed to be used for hot melt prepreg curing at high temperature. In this paper, utilizing Kissinger equation and Crane equation, the cure kinetics of the phenolic resin system was studied by DSC. The parameters of resin curing reaction were obtained by origin fitting analysis, which gave 77.235 kJ/g for the activation energy, 1.92×10⁸ for the constant factor and 0.9088 as the reaction order. Furthermore, DSC tests were performed on resins with different holding times at a constant temperature to obtain the glass transition temperature and curing degree. DiBenedetto empirical equation is used to establish the relationship model between glass transition temperature and curing degree. Moreover, the gelation process of Z616 phenolic resin was investigated by Haake Mars RS6000 Rotational Rheometer, and the relationship between gel-time and temperature was obtained. The degree of curing at the time of gelation is 0.08, and the glass transition temperature is 89.1 ℃. Finally, the equivalent curing degree, glass temperature transition and gelation were plotted versus time, and the temperature-time-transition (TTT) diagram was formed for the Z616 phenolic resin system. From this TTT diagram, the state of the resin system could be known at any temperature for any time. The forming parameters of Z616 phenolic resin-based composites under the hot-pressing process can be reasonably set.

RESEARCH ON TOUGHENING METHODS OF RTM COMPOSITIES

GUO Cong-cong, WANG Yi-min, SHAN Rui-jun, MENG Meng, LI Zhi-tao, MAO Hui-wen

2021, 0(5): 86-91. DOI: 10.19936/j.cnki.2096-8000.20210528.013

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In-situ and Ex-situ are the main toughening methods to improve the toughness of composites, which are also widely used in RTM composite. This paper concentrates on In-situ and Ex-situ toughening design for EH301 resin, comparing the advantages and disadvantages of two toughening methods used in RTM composite by analyzing manufacturability, thermal properties, CAI and other mechanical properties. Meanwhile, the improval effect of tackified process on the mechanical properties of Ex-situ toughened composite was studied with the SEM morphology of PA veil. The results show that the Ex-situ method has better processibility and remarkable toughening effect which is more suitable for toughening RTM composite. Simultaneously, the negative effect of compression strength and interlaminar shear strength caused by Ex-situ toughening can be improved by increasing the time and temperature of tackified process.

THE REPAIR AND AIR PERMEABILITY CONTROL OF THE FACE-CORE DEBONING HONEYCOMB SANDWICH STRUCTURE

LI Ying-ge, ZHOU Zhan-wei, WEI Shi-hou, ZHOU Mi

2021, 0(5): 92-97. DOI: 10.19936/j.cnki.2096-8000.20210528.014

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This paper introduces the methods of glue injection repair, scarf repair and patch strengthening for the face-core debonding of honeycomb sandwich structure, and analyzes the influence of different repair methods on bonding quality, strength, weight and air permeability of sandwich structure. The results show that all of the repair method can meet the demand of strength and quality. Scarf repair method will not affect the structure breathability and has lower weight increment. After exhausting the air within the sample, it takes 2 seconds to recover. Meanwhile, the lateral positioning glue injection repair method has less influence on the air permeability of the structure higher than 4.5 mm but adds more weight. After exhausting the air within the sample, it takes 4 seconds to recover. The vertical glue injection repair method has the most significant effect on breathability and the most weight increasing due to the adhesive filling of 1/3 honeycomb grid within repair area. After exhausting the air within the sample, it takes 9 seconds to recover. The conclusion obtained in this paper can provide some reference for the repair of the honeycomb sandwich structures.

EXPERIMENTAL STUDY ON STATIC COMPRESSION AND FATIGUE PROPERTIES OF SCARF REPAIRED COMPOSITE LAMINATES

SU Yu-ru, GUAN Zhi-dong, WANG Xin, ZHANG Shu-ming, LI Zeng-shan

2021, 0(5): 98-103. DOI: 10.19936/j.cnki.2096-8000.20210528.015

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Scarf repair is a widely used permanent repair method for composite structures. In this paper, the static compression and compression-compression fatigue properties of scarf repaired composite laminates were studied experimentally. The specimens were repaired by wet layup scarf repair and prepreg scarf repair method, and cured by hot bonder. The scarf ratio was 1∶30, and there were three damage sizes. The peak and valley values of fatigue test were 70% and 7% of the limit load, with a total of one million times. In the process of fatigue test, nondestructive C-scan was used to detect the damage and its extension of the specimens. The strain data, failure load and failure mode of static test and post-fatigue static test were recorded. The results show that there is no damage and its extension happened during the process of fatigue test for the both two repair methods, and the stiffness of the specimens do not decrease after fatigue. The repair method, whether be fatigued or not and the damage size have no influence on the buckling load and the failure load of the specimens. The failure load of the end crush specimen is higher than that of the middle fracture specimen. The failure load of the two repair methods can reach more than 200% of the limit load, indicating that the repair result is ideal.

RESEARCH ON THE EFFECT OF THE FIT CLEARANCES ON THE SKIN/CORE BOND OF THE HONEYCOMB SANDWICH STRUCTURE

LIU Zhi-jie, ZHANG Yan-fang, LIU An-li, LENG Wei-hong, HE Kai

2021, 0(5): 104-109. DOI: 10.19936/j.cnki.2096-8000.20210528.016

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To study the effect of the fit clearances on the skin/core bond, a series of composite sandwich samples with different artificial fit clearances were designed and fabricated, their quality of the skin/core bond was checked by ultrasonic C scan and mechanical performances were measured and analyzed by testing machine. The results of clearance checking were recorded and shot to get a further understanding about the effect of the fit clearance. It is found that the skin/core debond occurred when the fit clearance was thicker than the thickness of the adhesive. A good skin/core bond could be obtained when the foaming adhesive was used to fill the fit clearance as the compensatory adhesive. The reliability of the test to check the clearance depended on the vacuum degree in the bag greatly. The profile of the honeycomb core was milled into steps, which was more beneficial to the skin/core bond than the oblique plane machined.

RESEARCH PROGRESS IN GRAPHENE/EPOXY RESIN NANOCOMPOSITES

LI Li-li, LI Qing, XIAO Wen-gang, CHAI Peng-jun

2021, 0(5): 110-119. DOI: 10.19936/j.cnki.2096-8000.20210528.017

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Epoxy resin is a commonly used thermosetting resin matrix, which plays an important role in the national economy. In recent years, the introduction of graphene with excellent comprehensive properties into epoxy resins and preparation of graphene/epoxy resin nanocomposites have become an important research topic. This paper reviews the research progress of graphene/epoxy resin nanocomposites in recent five years. First, the common preparation methods of graphene/epoxy resin nanocomposites are introduced. Secondly, the mechanical properties, heat resistance, thermal conductivity, electrical conductivity, dielectric properties, flame retardant properties, and anti-corrosion properties of graphene/epoxy resin nanocomposites are focused on. Then, the application status of graphene/epoxy resin nanocomposites is briefly described. Finally, the current problems in this field is pointed out and the development trend is predicted.

PROCESSING TECHNOLOGY AND APPLICATION OF GRAPHENE AND ITS DERIVATIVES IN CARBON FIBER REINFORCED COMPOSITE MATERIALS

WANG Shu-xia, YU Hang, SHANG Yun-long, GUO Jian-jun

2021, 0(5): 120-128. DOI: 10.19936/j.cnki.2096-8000.20210528.018

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Due to the unique two-dimensional lamellar all-carbon aromatic structure, high aspect ratio, good flexibility, and excellent mechanical strength, graphene and its derivatives (GRM) can significantly improve the interfacial wettability of carbon fiber reinforced composite materials (CFRP) and interface adhesion, and give composite materials a variety of functions. In recent years, it haa received extensive attention and carried out recent research. This article starts with the origin of GRM and carbon fiber, focuses on the processing technology of GRM in CFRP, and reviews the current domestic and foreign research status of GRM added to the polymer matrix and GRM in the surface modification of carbon fiber. The application prospects and difficulties of GFRP-GRM in different fields are discussed, and finally the application potential and research trend of CFRP-GRM are prospected.

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