COMPOSITES SCIENCE AND ENGINEERING

STRENGTH ANALYSIS OF NACA COMPOSITE AIR INLET WITH FOAM SANDWICH STRUCTURE

HU Fan, ZU Lei, HU Song, CHEN Dan

2018, 0(5): 5-11.

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Because of its high strength-weight ratio and modulus-weight ratio, excellent thermal insulation performance,the foam sandwich composite has been widely used in aerospace industry. On airplane, it′s applied to some structures which are thin in thickness and bear small loads. Due to its particularity in material, the stress conditions of NACA carbon fiber reinforced composite air inlet with foam sandwich structure is rather complex under combined loads. As a result, there are few studies on the strength analysis of this kind of NACA air inlet so far. In this paper, the NACA composite air inlet with foam sandwich structure was selected as the study subject, and its finite element modeling was built. By analyzing and comparing the equivalent stress contours of the air inlet′s shell in different cases, along with checking the strength in stress concentration areas of the sandwich structure′s each layer, failures of foam core and composite skins were examined, and regularities about influences of loads on the air inlet were figured out. The results indicate that the stress concentrated areas of the composite layer are near the bolt holes, and for the foam layer they are near the joint regions between valve plates and shell of the air inlet. And, based on the results of finite element calculation, the foam would be destroyed under some extreme working-conditions. So foam with better properties should be adopted or stress concentrated areas of the foam layer should be reinforced.

NONLINEAR FINITE ELEMENT ANALYSIS OF THE STRUCTURAL BEHAVIOR OFBFRP REINFORCED SELF-COMPACTING CONCRETE BRIDGE SLAB WITH CONSIDERATION OFCOMPRESSIVE MEMBRANE ACTION

ZHOU Ling-zhu, ZHENG Yu, Susan. E. TAYLOR, LUO Yuan-bin

2018, 0(5): 12-18.

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In this paper, the nonlinear finite element method is adopted to investigate the behavior of self-compacting concrete bridge deck slabs reinforced with basalt fibre reinforced polymer (BFRP) rebar in a real bridge named as Thompson′s bridge in Northern Ireland. By comparing the results from the test and the finite element analysis, it is found that the proposed numerical model shows good agreement with the results from the field test. Based on the accurate validation with the test results, the loading-carrying capacity of self-compacting bridge decks reinforced with BFRP bars is predicted and a series of parametric study is conducted to evaluate the influence of some structural variables on loading carrying capacity of bridge deck slabs in Thompson′s Bridge. The numerical results indicate that the ultimate bearing capacity of the concrete deck slabs in Thompson Bridgeis about 1000 kN, which is about 6 times of European pressure load of 150 kN. However, the ultimate bearing capacity of bridge deck is highly underestimated by existing bridge deck design guidelines due to the ignorance of the existence of the compression membrane action. The results from parametric study show that the reinforcement ratio and the type of reinforcement have no significant effect on the ultimate bearing capacity of the bridge deck due to the influence of compressive membrane action. On the contrary, the concrete strength and the span to depth ratio have strong effect on the loading-carrying capacity of concrete bridge deck reinforced with BFRP bars.

SIMULATION AND EXPERIMENT ON THE FAILURE MECHANISMOF ADHESIVE BONDING REPAIR IN COMPOSITE

YUAN Jun-jun, LI Cheng, TIE Ying, ZHAO Shu-han

2018, 0(5): 19-24.

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In order to investigate the fatigue behavior of the adhesive bonding repair in composite, the model of adhesive bonding structure with different patch dimension has been constructed based on the three-dimensional progressive damage theory. The ultimate static strength and residual strength of the bonding structure are predicted using damage subroutine, and the comparative analysis of fatigue test and static tensile test were performed. Five circle patches of different dimension are selected for evaluating the repair performance. Meanwhile, the damage degradation mechanism of the patch repair structure under different stress levels with different cyclic loadings is studied by microcosmic measurement. The results reveal that the ultimate static strength of the adhesive bonding structure with the 3.5r patch is better than others. And the residual strength of the adhesive bonding structure with the 2.5r patch is maximal. Under low fatigue cyclic loading, the dominant damage is normally matrix cracking, while fiber breaking is the main damage pattern at the high fatigue cyclic loading for composite materials.

STUDY ON MECHANISM AND PREDICTIONOFRIVETED JOINTS OF FIBER METAL LAMINATES

YING Shao-jun, LI Jian-wei, PING Xue-cheng , CHENG Li-peng

2018, 0(5): 25-32.

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Fiber metal laminates (FMLs) rivetdamage is a coupling damage behavior caused by a complex structure composed of connecting pieces, the connectedparts and the rivets.In order to predict rivet damage behavior of FMLs, Johnson-Cook failure criterionis used to predict Aluminum damage, three-dimensional Hashin damage criterion is used to evaluate the damage of fiber layers, and the cohesive model is applied to delamination prediction. And experimental comparative analysis was performed to verify the rationality of the coupling damagemodel. Effects of laminate layers, riveting pretension, aluminum alloy fraction and geometric coefficients on FMLs damage and stiffness of plate riveting were studied by this damage prediction model, and it provides the feasible advice for the design of FMLs rivet. The results show that laminates with more layers are much easier to debond at the bi-material interface, and the interlaminar delamination at free endsdirectly reduces the rivet strength. Rivet strength increases with increasing aluminum fraction, but it will decrease when the aluminum contentis greater than 50%. Pretensioncan delay the damage initiation at fiber and matrix, and enhance the stiffness of the rivet joint, which consequently endow it with the ability to withstand greater external load. The riveting ultimate strength increases with increasing weight-diameter ratio W/D, and end distance-diameter ratio E/D of fiber metal laminate riveting strength have different effects until W/D=3 and E/D=3. Further increase of W/D and E/D will not improve the rivet strength.

STUDY OF MECHANICAL PROPERTIES OF ACIDIFICATION GRAPHENEMODIFIED EPOXY RESIN AND ITS CARBON FIBER COMPOSITE

YU Qian-qian, CHEN Gang, ZHENG Zhi-cai, CHONG Lin

2018, 0(5): 33-40.

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In this paper, for the application of graphene on toughening of composite, the acidification of graphene was conducted. Then, acidification graphene/epoxy resin (EP) casting was prepared by ultrasonic dispersion. Subsequently, acidification graphene/ carbon fiber (CF)/epoxy resin (EP) composites were prepared by compression molding. The surface structure and morphology of acidication graphene were characterized by IR and TEM. Mechanical properties of graphene modified EP and CF-EP were evaluated by mechanical test methods such as stretching, bending and impact. And scanning electron microscopy (SEM) was used to observe the morphology of the tensile section of the composites. The results show that the polar groups such as hydroxyl and carboxyl groups were successfully introduced into the surface of the graphene after acidizing treatment. Acidified graphene can effectively strengthen and toughen EP and CF/EP. When the content of acidified graphene was 0.2wt%, EP tensile strength and impact strength increased by 23.2% and 109.8%, respectively. The tensile strength and the flexural strength of CF/EP composites increased were by 6.0% and 10.6%, respectively. When the addition amount was 0.5wt%, the ILSS of CF/EP composites were increased by 7.4%. The microstructure analysis showed that acidified graphene can enhance CF/EP, which is mainly achieved by strengthening and toughening the EP, which simultaneously improve the interfacial properties between CF and EP.

RESEARCH OF LATERAL BENDING STRENGTH OFSANDWICH COMPOSITE MATERIALS T-JOINT

XIAO Xue-rui, QIU Wei-qiang, MA Wu-wei, KANG Feng-hui

2018, 0(5): 41-47.

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The numerical model of sandwich composite materials T-Joint is built by ANSYS. And, the damage formation, extension, failing process and optimization design of the T-Joint under bend displacement are investigated by numerical simulation. The Cantilever bending performance was tested to verify the simulation results. The test results show that the initial damage displacement is 30～32 mm, and the relative load is 7.5 kN~7.6 kN . The bearing capacity of T-Joint is increased and stiffness is reduced. The failure strength is increased by 41%~55% compared with initial damage strength. The results of experiment is consistent with the numerical simulation, indicating that the clapboard is the weak position of the structure. The initial damage is extrusion damage of composite material and appears to the connections between clapboard and enhancing area. With the increasing of bend displacement, the damage area is increased, leading to the failure of the whole T-Joint. By finite element optimization analysis, the improvement of the down-skin and core thickness of clapboard could lead to reduce the maximum stress and failure factor of down-skin of clapboard, and narrow failure factor difference of two clapboard skins, and give full play to the performance of overall structure.

THE ANALYSIS OF RESPONSE OF BURIED FRPM PIPES IN SHEAR SEISMIC WAVES

LI Yan, ZHU Si-rong

2018, 0(5): 48-52.

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By the finite element method, this paper analyzes the response of glass fiber reinforced plastic mortar pipes under the earthquake loads in addition to standard static load. Considering the anisotropy of composite materials and the interactions between pipes and soil, the finite element model of buried FRPM pipe is established. First, the static loads are applied with a series of incremental load steps. Then, the seismic loading condition is simulated by specifying quasistatic displacements at the peripheral boundaries of the soil envelope to produce a shear-rackingdistortion equivalent to the maximum free-field seismic shear strain from the earthquake. Based on the above model, the response of different materials under earthquakes are compared and analyzed. Then, the influence of the following factors such as the diameter, the ring stiffness, and the depth of the FRPM pipe is studied. The result shows that the FRPM pipe has great potential for earthquake resistance with the designable characteristic and the ring stiffness, and the buried depth are important influence factors on seismic response.

EXPERIMENTAL STUDY ON FLEXURAL BEHAVIOR OFSANDWICH BEAMS WITH TRANSVERSE RIBS

ZHANG Fu-bin, LIU Wei-qing, WANG Hui, QI Yu-jun

2018, 0(5): 53-57.

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This paper explores the flexural performance of sandwich beams with transverse ribs in four point bending tests. The effects of the thickness and space of the ribs on the failure modes, stiffness, ultimate bending strength and ductility properties of the sandwich beams were obtained. Test results indicates that the transverse ribs can change the failure mode of the sandwich beams. The beam without transverse ribs failed in core shear failure, while beams with transverse ribs failed in a more ductility failure mode. The transverse ribs can significantly increase the ductility properties of the sandwich beam with a maximum of 229%. The smaller the rib space, the better ductility performance.

EFFECT OF FIBER MODULUS ON NATURAL FREQUENCY OFCOMPOSITE AUTOMOBILE DRIVE SHAFT

GAO Hong-ping, SUN Ze-yu, TAO Lei, XIONG Feng

2018, 0(5): 58-63.

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In this paper, Ansys Workbench finite element software and pulse excitation technology were used to study the influence of different fibers on the natural frequency of the composite automotive drive shaft from the perspective of the combination of finite element method and experiments. Fiberglass, basalt fiber, T700 carbon fiber and T800 carbon fiber were used to wound composite shaft. The mechanical properties of composites were characterized according to GB/T 1548—2008. The natural frequency of the drive shaft of different fiber composites were characterized by finite element simulation and pulsed vibration mode test. The results show that the method of testing the natural frequency of the drive shaft by pulse excitation mode is more intuitive and the natural frequency of the drive shaft can be obtained accurately. The results of finite element simulation and pulse excitation show a certain deviation. But, the simulation results can be adjusted more accurately to make the simulation results more accurate. It is one of the effective ways to improve the natural frequency of composite shaft by increasing the modulus of composites.

STUDY ON STRUCTURE DESIGN AND FILAMENT WINDING TECHNOLOGY OFCARBON FIBER REINFORCED MORTAR COMPOSITE BARREL

XIONG Chao, LI Bo, YIN Jun-hui, DENG Hui-yong

2018, 0(5): 64-68.

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Carbon fiber reinforced composite can be widely used as a kind of structure material for weapon lightweight design, because it has high specific strength and stiffness, weight-light, excellent designability, good corrosion and fatigue resistance property. In this paper, the mechanical properties of traditional mortar barrel was analyzed, and it shows that the barrel weight cannot be reduced and with a bad designability by using metal. To meet the weight-light need, a double-deck structure of mortar composite barrel was designed which was composed of metal lining and carbon fiber reinforced composite outer layer. The winding lathe and technology of carbon fiber reinforced composite mortar barrel was introduced. The experimental curves of strain-loading vs. winding tension, fiber stacking sequence and carbon fiber types were obtained. Based on the experimental data, the effects of winding tension, fiber layer laying sequence and carbon fiber grade on composite barrel static pressure bearing capacity were analyzed. It can be concluded that the metal lining can be thinner and the barrel can be more lightweight by using the carbon fiber as outer strengthened layer, and stacking sequence had little effect on the static load of the barrel. Besides, strain-loading can be improved by increasing the winding tension properly. All of these can provide a reference for the structure design of composite barrel and other composite cylinder.

APPLICATION OF ORTHOGONAL PROJECTION IN AUTOMATIC LAYING TRAJECTORY PLANNING

CHANG Liang, WANG Xian-feng, LIU Yong-jiao, MA Cheng

2018, 0(5): 69-74.

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In order to meet the requirement of fiber orientation during laying, an algorithm for path generation based on orthogonal projection of gridded surface is proposed in this paper. First, the property of orthogonal projection of the points upon parametric curves to the free-form surface-the closest point from the test point on the parametric surface, is applied to propose the orthogonal projection algorithm of points. On this basis, the problem encountered in the process of determining the projective curve, like invalid projection, is solved. And the designed space curve is projected onto the gridded surface to get the reference path of the laying wire. Then, all the paths are obtained by equidistantly shifting the contour curve along the slicing interface. The algorithm in the paper is implemented by adopting the programming based on VC++. The experimental results show that the algorithm is correctly and validly, and the algorithm of laying wire path generation based on the orthogonal projection of gridding surface can meet the requirement of laying process.

STUDY ON PROPERTY COMPARE OF NON-STYRENE AND STYRENE VINYL ESTER RESIN

LIU Shi-qiang, MAO Ling-feng, ZHANG Wen-xuan, HUANG Zhi-chao

2018, 0(5): 75-78.

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Two kind of vinyl ester resin (VER) properties were tested under the same experimental conditions, including volatile organic compounds (VOC), mechanical properties, thermal properties, air dry and process performance. All the properties were compared. MFE 700-01 was non-styrene VER, while MFE 711 was styrene VER. The results show that VOC of MFE700-01 was lower, which can satisfy environment requirement, and the mechanical properties was same as the latter. Styrene VER can be replaced by non-styrene VER in most occasions.

THE MECHANICAL PROPERTIES AND THERMAL-INSULATING PERFERMANCE OF SiO₂AEROGEL COMPOSITES REINFORCED WITH ALUMINOSILICATE FIBER

JIANG Song-min, DUAN Xiao-hua, WANG Xiao-huan, LI Shu-lin

2018, 0(5): 79-83.

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SiO₂ aerogels have outstanding performance in quality of heat insulation and preservation for its nano-porous microstructure. However, the poor mechanical properties of SiO₂ aerogels restrict its application in many industrial fields. In this paper, aluminosilicate fiber is used as reinforcement to strength the skeleton of SiO₂ aerogels, and a kind of aluminosilicate fiber/SiO₂ aerogels composites was prepared by sol-gel method and atmospheric pressure drying. The microstructure and properties of the composites are characterized by SEM, universal testing machines, thermal conductivity meter and BET. The results indicate that the adding of aluminosilicate fiber provide a new energy expenditure mechanism for the composites under applied force, and the mechanical property of the composites are increased efficiently. The surface area and average pore diameters of the composites are 383.5 m²/g and 8.4 nm, respectively, and the porosity is 87%, belonging to typical mesopore material. At the same time, the thermal conductivity of composites is as low as 0.02 W/(m·K)~0.04 W/(m·K), indicating their good thermal-insulating performance.

THE PROCESSING OF ULTRA-THIN HIGH MODULUS FABRICAND APPLIED ON SATELLITE REFLECTOR

DONG Xiao-yang, ZHAN Guang-liang, XU Yun-yan, ZHAI Dong-kun

2018, 0(5): 84-89.

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In order to satisfy the need of high precision and lighting of the antennal reflector, the theory of the machinery fiber spreading method was analyzed. The ultra-thin high modulus fabric was waved by multi-spreading tow, for which the width of spreading fiber was 4 mm, and the fabric area density was 106 g/m². Then, the carbon fibers tensile tests were conducted. The results show that the tensile strength of spreading fiber was decreased by 1.26% and the modulus was decreased by 1.29%. The single layer fabric sample was manufactured, and the morphology of the ultra-thin fabric was superior to the traditional fabric. In this paper, the ultra-thin high modulus fabric composite was simulated through finite element combining with the structure of antennal reflector. The simulation results show that the base frequency of the reflector was 138.53 Hz, and the weight of skin was less 16.1% compared to the traditional fabric. In addition, the reflector structure which is consistent with the ultra-thin high modulus skin and the honeycomb was tested under the sinusoidal vibration condition. The test results show that the reflector could satisfy the designing requirement.

OPTIMIZATION DESIGN OF AIRCRAFT COMPOSITE CARGODOOR BASED ON STIFFNESS CONSTRAINTS

LI Chao, YAN Ya-bin, YANG Hua-lun

2018, 0(5): 90-95.

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Doors will bear great pressure load when civilian aircraft during the flight. With the increasingly stringent requirements of lightweight design, composite doors gradually become a trend. And, doors in the design must meet the stiffness requirement in addition to meet the strength requirement. In order to study the weight loss potential of composite materials applied on the door, and improve the constraint of stiffness, including maximum deformation, waviness, gaps and steps, and the constraint of strength and layout proportion, an optimization design method of multiple stiffness constraints for aircraft composite door is proposed. Taking the front cargo door of airplane for example, according to the constraint of stiffness, strength and layout proportion, by optimizing the skin, beam and frame by using NASTRAN, the purpose of the lightweight design is realized. The result shows that the weight of the front cargo door is reduced by 24.30% after using composite material and structure optimization. This research could provide some useful advices for the application of composite material in aircraft cargo door.

STUDY OF NONDESTRUATIVE TESTING AND MICROSTATE OF STITCHEDCOMPOSITES WITH DIFFERENT STITCH METHODS

YANG Long-ying, HUANG Dang-ming

2018, 0(5): 96-101.

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The stitching technique as the monolithic molding and low-cost manufacture technique have been widely applied in areaspace. The stitch threads used in stitching process have effects on the nondestructure testing results and the microstate of the stitched composites. The stitch threads have different state inside of the stitched composites with different stitching methods, which have different effects on the nondestructure testing results and the microstate of the stitched composites. In this work, three different stitching ways were studied, which were tufting, chained stitching and locking-type stitching. The impacts of ultrasonic A-scan destructive testing and ultrasonic C-scan destructive testing results and the microstate inside of the stitched composites with the three stitching methods were studied by experiments.

RESEARCH STATUS QUO OF INTERFACIAL BONDING PROPERTIES OFMASONRY STRUCTURES REINFORCED BY FRP BARS

WANG Zuo-hu, LIU Du, YANG Wen-xiong

2018, 0(5): 102-108.

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Near-surface mounted (NSM) reinforcement is the common methods for reinforced masonry structure by FRP tendons. The debonding failure of FRP tendons as the primary failure mode, and the research on the bonding performance and debonding mechanism between FRP bars and masonry become the key to this reinforcement technology. In this paper, the progress of pull test, interface shear test, bending test and numerical simulation of domestic and foreign scholars are reviewed. The interfacial bonding properties of NSM-FRP reinforced masonry structures are studied. The results reveal that the deformation capacity, energy dissipation and ductility of masonry are significantly increased after strengthened by NSM-FRP bars. Increasing the embedding depth of FRP bars can effectively improve the debonding load. Finally, the relevant formulas of the various bonding parameters are checked by using the collected experimental data, and some suggestions are put forward for the future research.

THE DEVELOPMENT AND TENDENCY OF 3D BRAIDING TECHNOLOGY AND MACHINERY

LI Zheng-ning, CHEN Ge, Frank Ko

2018, 0(5): 109-115.

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This paper introduces the details on the development and nowadays status of 3D braiding technologies and 3D braiders. The differences and connection of 2D and 3D braiding technologies are discussed to define their micro-structures and usage. Also, the comparison on different 3D braiding processes characteristics of track and column braiding, rotary braiding and hexagonal braiding was made in order to give the definition on the design and analysis of braiding machines, such as motion patterns, yarn system numbers, fiber volume fraction, braiding angles and etc. For each braiding process, they are applicable for varied shapes and materials 3D preforms according to their characteristics. Finally, for the availability of different 3D braiders, this paper summarized the popular and important research problems on 3D technology and the foreseeable application areas in daily life and industries, which can give the inferences to the researchers.

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