COMPOSITES SCIENCE AND ENGINEERING

DAMAGE CHARACTERISTICS OF CARBON FIBER COMPOSITESBASED ON ACOUSTIC EMISSION TECHNOLOGY

MENG Chao, ZHANG Xi, HE Zhi-xiang, PENG Wei-dong

2019, 0(10): 5-9.

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Acoustic emission (AE) signal acquisition of carbon fiber composites in tensile fracture test is completed by using the self-designed AE detection system. Wavelet analysis, spectrum analysis and characteristic parameter analysis are used to analyze the two sets of AE signals obtained in the test. The relationship between the failure characteristic frequency and the damage mode of carbon fibre composites is established, and the main variation rule of acoustic emission signals in the damage process of carbon fibre composites is found.

EFFECT OF MULTI-INTERVAL HEATING ON THE FORMING QUALITYOF ADVANCED PULTRUSION PARTS

WANG Yu, QI Jun-wei, WANG Yue-quan, XIAO Jun

2019, 0(10): 10-18.

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Advanced pultrusion molding technology takes prepreg as raw material, realizes the mechanical property designability of the parts through the combination of different layers, and has unique advantages in controlling the production cost and flexibility. This subject selects X850 prepreg for research, analyzes the difference between its typical hot pressing tank forming process and advanced pultrusion process. The function of each interval in the forming process is analyzed for the characteristics of hot-pressure curing in advanced pultrusion molding. The curing kinetics of resin in X850 prepreg is measured through differential scanning calorimetry. The selection principle of temperature system in each interval is determined. In order to prevent the formation and growth of pores, the pressure system of each interval is reasonably selected. A curing process experimental scheme is designed by means of orthogonal experiment, and the influence trend of multi-interval temperature system and pressure system on the forming quality of parts is studied. The specimen is prepared by the equipment designed by the laboratory, and the scheme No. 6(with pretreatment temperature at 160 ℃ for 30 min, curing temperature at 180 ℃ for 20 min and curing pressure at 0.8 MPa)is selected as the final pultrusion process in the orthogonal test scheme, for which the bending strength, interlaminar shear strength and porosity are characterized.

STUDY ON BENDING PERFORMANCE AND MECHANISM OFFIBER REINFORCED CEMENTITIOUS COMPOSITES

GONG Hong-wei, JIANG Shi-yong, CHEN Jin, TAO Shuai

2019, 0(10): 19-25.

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To study the bending properties of fiber reinforced cementitious composite, five groups of specimens with different PVA fiber content were studied by four-point bending test. The experimental results show that the fiber content has a significant effect on the bending properties of specimens. Appropriate amount of fiber can significantly improve the brittleness of specimens, and crack is small and dense. When the fiber volume V_f≤2.0%, the initial cracking bending strength, peak bending strength, equivalent bending strength and toughness index increase with the increase of fiber content. For specimens with V_f=2.5%, the flowability is poor and some fiber agglomerates. As a result, the bending strength of specimens with V_f=2.5% is lower than specimens with V_f=2.0%. Combined with the load-deflection curve, the mechanism of fiber in the composite was qualitatively analyzed by scanning electron microscope, and the factors affecting the fiber bridging effect were studied.

FINITE ELEMENT ANALYSIS OF THE INFLUENCE OF INTERPHASE PROPERTIES ONTHE MECHANICAL PROPERTIES OF GRAPHENE NANOCOMPOSITE

HUANG Jun, WU Yu, HUANG Li-xin

2019, 0(10): 26-32.

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The phenomenon that interphase of graphene nanocomposites has non-uniform distribution of material properties in the thickness direction has been confirmed by many studies. However, in those studies, interphase with changing properties is either equivalent to a homogeneous layer or segmental assigned in thickness direction. None of those methods can achieve good calculation accuracy and efficiency. In order to deal with this problem, a two-node isoparametric gradient finite element that can simulate interphase with any kinds of material distribution is proposed in this paper. An embedded represented volume element (RVE) model of graphene nanocomposite is established by finite element method to study the mechanical properties of graphene nanocomposite, under the assumption that the monolayer graphene was uniformly distributed in the matrix without agglomeration. To simplify the calculation, graphene and matrix are considered as isotropic materials, and simulated by plate element and solid element, respectively. The interphase layer is simulated by the presented two-node isoparametric gradient finite element. The effect of graphene fraction V^g_fr, the thickness t_in of interphase layer and the debondded condition between graphene and matrix on the overall mechanical properties of nanocomposites are discussed. The results show that, in case of V^g_fr=3.0%, the increase of t_in from 0.17 nm to 1.02 nm will lead to a deviation of 17.4% with the prediction result of Young′s modulus E_cx of the composite material.In the discussion of the debonding condition between graphene and matrix, it was found that E_cx decreased significantly when the edge of graphene was debondded, and the modulus decreased by about 10% when the debonding edge area was 1/6 of the total area.

DAMAGE PREDICTION AND MODELLING COMPARISON OF CARBON FIBER-REINFORCEDCOMPOSITE OPEN-HOLE LAMINATES UNDER COMPRESSION

TANG Jing, CHEN Xiao, YANG Ke

2019, 0(10): 33-39.

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The finite element models of shell elements, shell-cohesive mixed elements and shell-solid mixed elements were developed in software Abaqus to model two open-hole composite laminates (OHC), i.e. flat OHC and cylindrical OHC. The universal Abaqus built-in software and proprietary user-subroutine were respectively adopted to analyze compressive damage. The buckling, intralaminar failure and delamination of both OHCs under compression were predicted by Hashin failure criteria, modified Tsai-Wu failure criteria and Quads failure criteria, then compared with experimental results. The results show that the predicted strength of cylindrical OHC is less than 7% error for proposed five models; the damage initiation around hole and loss of loading-carrying capacity can be captured by all models. The shell model solely relying on Abaqus software with built-in Hashin failure criteria can provide an effective strength assessment of cylindrical OHC, while user-subroutines with modified Tsai-Wu failure criteria can offer a more reliable alternative for flat OHC.

RESEARCH ON THE EFFECT OF INTERFACIAL BOND-SLIP PROPERTY ON FLEXURALPERFORMANCE OF CONCRETE BEAMS STRENGTHENED WITH NSM-FRP STRIPS

ZHANG Zhi-mei, HUANG Qing-bin, ZHAO Lei

2019, 0(10): 40-45.

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The concrete beam strengthened with near-surface mounted FRP strips(NSM-FRP strips) is simulated by finite element method using ABAQUS software, and the simulation method of reinforced beam considering the interface failure of FRP-concrete is proposed. In order to study the effect of interface bonding-slip performance on the bending behavior of the concrete beam strengthened with NSM-FRP strips, the spring2 nonlinear elements is used to simulate the bond-slip relationship of FRP-concrete interface. The flexural behavior of RC beams under different interface bonding relationships was recorded and compared. The results show that the bond slip of the FRP-concrete interface has a great influence on the bending resistance of the beam strengthened with NSM FRP and must be considered. The nonlinear spring connection between the interfaces can do a better job in simulating the bond-slip failure of the interface. When studying the performance of the reinforced beam under serviceability limit state, it is more convenient and accurate to use the linear spring connection to simulate the NSM FRP strengthened beam.

COMPARATIVE STUDY ON LOW VELOCITY IMPACT DAMAGE OF GLASS FIBERREINFORCED POLYPROPYLENE AND EPOXY COMPOSITES

LUO Chuan-long, NI Ai-qing, WANG Ji-hui, CHEN Hong-da

2019, 0(10): 46-50.

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In this study, continuous E-glass fiber reinforced composites have been manufactured with two types of resin, polypropylene (thermoplastic) and epoxy (thermoset), and they have been subjected to the low velocity impact and compression test after impact and effect of resin type on the impact damage response of composite laminates were investigated. Impact energies were chosen as 30 J, 40 J, 50 J and 60 J, and the residual compressive strength was obtained by compression after impact test. The results show that the damage area, dent depth, post-impact compression failure mechanism and residual compressive strength values of glass fiber reinforced polypropylene and epoxy composite laminates are different due to the different interlaminar fracture toughness and toughness of the resin matrix. The type of matrix material has a crucial effect on the low velocity impact damage of composites.

STUDY ON DISPERSION CHARACTERISTICS OF ELASTIC GUIDED WAVESIN AN INFINITE FUNCTIONALLY GRADED PLATE

LIAO Zhi-qi, LUO Yi

2019, 0(10): 51-57.

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In order to investigate the dispersion characteristics of elastic guided waves in an infinite functionally graded plate, this article built the theoretical analysis model for elastic guided waves of a functionally graded plate, and established the geometric equation under Cartesian coordinate system. In this paper, the Legendre orthogonal polynomial is introduced as trial functions of displacement. According to the Hamilton principle, Raleigh-Ritz Method (RRM) is applied to obtain the dispersion equation of elastic guided waves in a functionally graded plate. It is found that Raleigh-Ritz method has a great convergence and accuracy in solving guided wave propagation problems when using high-order node numbers for calculation. Raleigh-Ritz Method is not limited to homogenous plates. Phase velocity and group velocity dispersion curves of an infinite functionally graded plate composed of anisotropic materials are given, and the influences of different volume fraction indexes N and incident angle θ on dispersive behavior for guided wave propagation are analyzed.

COMPOSITE MATERIAL REPAIR COMPRESSION ANALYSIS MODEL AND DICHOTOMYANALYSIS OF ULTIMATE LOAD IN HYGROTHERMAL ENVIRONMENT

SU Ri-xin, YU Yin

2019, 0(10): 58-64.

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The analytical model has the advantages of fast calculation speed and intuitive response to the influence of various parameters on mechanical properties. A compression analysis model for composite material repair in hygrothermal environment was established. The influence of hygrothermal on the mechanical properties of the composite and the wet thermal stress generated by hygrothermal were considered in the model. After the repair structure is under pressure, the model assumes that the structure′s failure mode is classified into three types: the compression failure of the motherboard, the compression failure of the patch and the shear failure of the adhesive. Any failure mode occurs first, and the corresponding load is the ultimate load. In hygrothermal environment, if the failure mode of the repair structure is the compression failure of the motherboard or patch, the model directly obtains its corresponding ultimate load first. Using the dichotomy method, the corresponding ultimate load in the shear failure mode of the adhesive in hygrothermal environment is obtained. The compression test of the composite repairing structure in different hygrothermal environments was carried out, and the analytical solution was obtained by the method of this paper. The test results were in good agreement with the analytical solution. The method of this paper can provide reference for the design of the composite glue repairing structure in hygrothermal environment.

ENERGY ABSORPTION OF DOUBLE-CELL CFRP SQUARE TUBES UNDER AXIAL COMPRESSION

LIU Qiang, HE Zhao-heng, MA Yi-tao, FU Jie

2019, 0(10): 65-69.

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This paper aims to study the energy absorption characteristics of CFRP double-cell tubes under axial compression. A preparation process of integrated carbon fiber multi-cell square tubes is proposed. The influence of energy absorption characteristics of multi-cell tubes with equal mass and wall thickness is explored. Finally, the energy absorption mechanism of multi-cell tube failure is analyzed by observing the failure modes of the tubes. The experimental results show that the energy absorption of CFRP single-cell tubes is higher than that of double-cell tubes. Compared with single-cell tubes, the specific energy absorption of equal-mass and equal-wall-thickness double-cell tubes decreased by 49.05% and 3.34%, respectively, which was due to the phenomenon of central crack and incomplete energy absorption in some region. Setting trigger is an effective way to reduce peak force and increase specific energy absorption. After setting trigger, peak force decreases by 26.21%~41.74%, and specific energy absorption increases by 2.52%~11.31%. Therefore, for the CFRP multi-cell square tubes, the double-cell tubes can not effectively enhance the energy absorption characteristics, and the destruction of the single-cell tubes are more stable than that of the double-cell tubes.

DESIGN AND RESEARCH OF CARBON FIBER COMPOSITE HELICOPTER DRIVE SHAFT

CAI Guang-sheng, ZHANG Jin-guang, MAO Ge

2019, 0(10): 70-74.

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Carbon fiber composite has the characteristics of high specific strength, high specific modulus, light weight and good vibration reduction performance. According to the requirements of strength and critical speed of a helicopter drive shaft, a carbon fiber composite helicopter drive shaft was designed. The cohesive finite element simulation of the weak links of the carbon fiber drive shaft was carried out by ABAQUS, and the simulation results show that the design of the adhesive layer is reasonable. In addition, the natural frequencies of the carbon fiber reinforced composite helicopter drive shaft are simulated and analyzed. The experimental results are in agreement with the theoretical analysis, and the error between the experimental results and the simulation results is small. It shows that the critical speed of the carbon fiber reinforced composite drive shaft designed can meet the requirements of the helicopter drive shaft.

EXPERIMENTAL STUDY ON SHEAR BEHAVIOUR OF REINFORCEDCONCRETE DAMAGED BEAMS REINFORCED BY AFRP

XING Li-li, KONG Xiang-qing, HAN Fei, HE Wen-chang

2019, 0(10): 75-81.

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The experimental study on the shear behaviour of seven concrete damaged beams reinforced by aramid fiber reinforced composite (AFRP), the influence of different levels of damage, FRP strips spacing and different types of FRP on shear capacity were investigated. The characteristic loads, failure modes, beams of load-deflection curves, stirrups and FRP of load-strain curves were analyzed, and compared with reinforced concrete beam without FRP sheets during experimental study. The test result indicated that AFRP reinforcement technology can effectively improve the shear capacity of reinforced concrete beams. Different degrees of damage have a great influence on the reinforced concrete damaged beams strengthened by AFRP, and increasing level of damage can reduce the reinforcement effect. When the level damage reaches the ultimate load of the concrete beam without FRP 70% and above, the improvement effect of the shear capacity of FRP reinforced concrete beam is not obvious, which even can′t reach the ultimate shear capacity of the reinforced concrete beam without FRP sheets. And it is found that the smaller the spacing of the FRP strips, the better the reinforcement effect. In addition, it is found that the shear capacity of reinforced concrete beams with AFRP is slightly higher compared with the test result of the reinforced concrete beam with BFRP. According to the test results, the shear capacity formula of reinforced concrete damaged beams strengthened with FRP is obtained, and it showed good agreement with the experimental results.

EFFECT OF SHORT CARBON FIBER ON MECHANICAL ANDTRIBOLOGICAL PROPERTIES FOR NITRILE RUBBER

WANG Guang-fei, XU Jia-wang, ZHOU Wei, HE Qiang

2019, 0(10): 82-89.

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In order to study the effect of short carbon fiber on the mechanical and tribological properties of nitrile rubber, different mass fractions of short carbon fiber (CF) were added to nitrile rubber (NBR) by mechanical blending to carry out tensile and tear tests. Combined with the three-dimensional morphology and scanning electron microscopy, the friction properties of 0 and 15 parts of short CF vulcanizate under different loading force and speed were analyzed. The results show that short CF can enhance the matrix strength of nitrile rubber and increase its hardness. However, when the addition is excessive, the degree of bonding of the short CF to the rubber matrix is decreased, and the fiber is easily pulled out during stretching, tearing and rubbing. Adding 15 parts of short CF to the nitrile rubber reduces the friction coefficient and the amount of wear. The CF/NBR friction coefficient is less affected by the rotating speed. When the rotating speed is higher, the frictional interface of the vulcanized rubber will generate a large amount of thermal energy, which will cause melting phenomenon, resulting in less grinding debris. During the friction process, the short CF and the rubber matrix jointly carry the force, so that the CF/NBR composite has good wear resistance.

INFLUENCE OF HYGROSCOPICITY AND PEEL PLY SURFACETREATMENT TOWARDS ADHESION OF COMPOSITES

WANG Ying-nan, PAN Li-jian, LIU Jun-tian, LIU Yu-ting

2019, 0(10): 90-95.

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Composite laminates with different surface properties made of T300/Cycom 970 prepreg and four plies, which include R60, R60s, P60001 and EA9895, were fabricated by autoclave. The pretreatment condition was (80±2)RH%, (70±1) ℃ for 0, 10 d, 20 d, 40 d, respectively. The Henkel Aerospace PL7000 adhesive film was used to bond the strippable laminates for testing. The effects of hygroscopicity and strippable treatment on the bonding properties of composites were investigated by the analysis of single lap shear strength, peel strength and bond failure forms. Influence of hygroscopicity and different types of peel ply on composite bonding interface was studied by SEM and XPS. Results show that with the increase of hygroscopic time, the hygroscopic rate of polyamide peel plies is about 80%, while polyester is about 60%. As the hygroscopic increases, the mechanical properties of the composite material decrease by 40%~50%. When the hygroscopic time is 40 d, the properties of the four peel plies are very close. The controlled samples always have adhesion failure, while the failure mode of the peel ply treated samples is also adhesion failure in the early stage of moisture absorption, then gradually turns to the cohesive failure of the material. After the hygroscopic treatment, the surface of the composite materials forms more cavities and defects than the non-hygroscopic, and there are residual polymer residues on the surface. The surface nitrogen content of polyamide-based peel ply composites is about 25% higher than before, which may affect the chemical properties of the bonding surface.

DISCUSSION ON THE BOM MODULARIZATION MANAGEMENTBASED ON WIND TURBINE BLADE

LIU Yan, SONG Jie, ZHAO Li-yan, GAO Guo-qiang

2019, 0(10): 96-101.

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BOM is the most basic data for enterprise management in the wind power blade industry, and is applied to multiple aspects. However, with the increasing fierce competition in the new energy industry, the traditional BOM management method cannot meet the needs of customized and fast delivery. This paper analyzed the problems of the traditional BOM management method in the wind turbine blade manufacturing process, and discussed the method of BOM configuration and BOM modularization. In this paper, the BOM modularization creation principles and the method to improve the BOM data accuracy was discussed. In conclusion, the BOM configuration method can reduce data redundancy and improve BOM management efficiency.

DESIGN AND MANUFACTURE FOR THE DEMOULDING MECHANISM OFLOCAL PUNCH DIE IN THE COMPOSITE FORMING MOULD

SHEN Ge-feng

2019, 0(10): 102-105.

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The defects such as rich glue, poor adhesive, bubble, delamination and other defects are easy to occur in the single-mode and rubber-bag moulding for composite products with small radius of curvature. A simple demoulding mechanism is designed to solve the problem of loading and unloading after the rubber-bag moulding of local punch die, which has deep embedding depth and less striping Angle. The problem of positioning and clamping of local punch die in manufacture and repair is solved by using special fixture positioning and machining on the numerical control machine tool. Therefore, the demoulding mechanism can solve all kinds of problems in the forming process of rubber-bag moulding for the composite material products with local small radius of curvature.

EFFECT OF HOMOGENINZING ON THE INTERFACE ANDPROPERTIES OF EP/GF COMPOSITES

LI Ya-feng, GUO Miao-cai, HONG Xu-hui

2019, 0(10): 106-111.

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The epoxy resin with its curing agent of dicyandiamide+polyurea was homogenized with self-made solvent to get a uniform resin system. The micro-debonding method was used to study the formation of microspheres and interfacial shear strength before and after homogenization. The result showed that the uniformity of the resin on the micro scale was distinctly improved after homogenization. Before homogenization, the interfacial shear strength was increased with the diameter of the resin microspheres, and the average strength was relatively low. However, after homogenization, there was no obvious correlation between the diameter of microspheres and the interfacial shear strength. In the meantime, the average strength increased by 39%. It was found that the stability of the composite improved correspondingly.

WIND EROSION BLADE COATING CORROSION RESISTANCE

GUI Yong-qiang, NI Ai-qing, WANG Ji-hui

2019, 0(10): 112-117.

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The model of raindrop impact blade coating leading edge is established. The dynamics software is used to study the stress state of rainwater impact coating process. The viewpoint is proved by experiments, and then the optimal combination of coating materials is proposed. Finally, the buffering effect of water film on the surface of raindrops on raindrop impact during rain erosion is studied. The results show that the impact of raindrops will cause tensile fatigue damage of the coating. In the optimized combination of coatings, the paint with lower modulus is placed on the surface layer to reduce the tensile stress on the coating. The water film can significantly reduce the stress of the coating when it is impacted.

STUDY ON DRIVE SHAFT OF CARBON FIBER COMPOSITESFOR UNDERWATER EQUIPMENT

JI Li-chao, ZONG Fang-yong, LIU Wei-wei, XIAO Wen-gang

2019, 0(10): 118-122.

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In this paper, the drive shaft of carbon fiber composites for underwater equipment was designed from raw material selection and composite laminated structure. The design and calculation process of the transmission shaft was introduced emphatically. According to the design index, the layer design of the transmission shaft was firstly carried out. Then the torsional buckling, torsional load and critical revolutions of the drive shaft were analyzed by combining theory and finite element methods. Furthermore, the simulated sample was made on the basis of the designed laminated scheme and the torsion test of the sample was carried out. The results show that the designed laminated scheme can meet the requirements of the design index of the drive shaft.

TECHNICAL ANALYSIS AND CURRENT SITUATION RESEARCHON MANUFACTURING COMPOSITE FUSELAGE FRAME

WANG Lin, HAN Xiao-yong, TIAN Cha, SU Jia-zhi

2019, 0(10): 123-128.

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In this paper, the function and structural characters of composite fuselage frame were introduced. Composite fuseluge frames are the primary structures of airplane. They have features of particular structure, large number and high quality uniformity requirement. These features enhanced the difficulty of manufacture. On this basis, key process difficulties during manufacture were analyzed, including fiber wrinkle control, fiber gap and angular deviation control, thickness and curing quality control of corner area, cured-induced deformation control and automated manufacturing technology. Then the process researches and applications of this part in domestic and foreign were introduced. It also pointed out the trend for manufacturing composite fuselage frame automatically with the development of composite.

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