COMPOSITES SCIENCE AND ENGINEERING

RESEARCH ON THE INITIAL FAILURE LOAD OF COMPOSITEFIBER REINFORCED PLASTIC BOX GIRDER

DING Guo-ping, ZHU Yong, DAI Zi-lun, TAN Jian

2017, 0(11): 5-11.

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A theoretical calculation method for the initial failure load of CFRP box girder is established by combining the classical laminated plate theory and the folding plate theory. The initial failure load of the box girder of 【0₄/±45/0₄】, 【0₂/±45/0₂/±45/0₂】 and 【±45/0₂/±45/0₂/±45】 is calculated by this method. At the same time, the three-point bending experiment is carried out on the CFRP box girder by using DNS100 electronic universal testing machine. The theoretical calculation value of the initial failure load of the composite box girder is compared with the experimental value. The theoretical calculation error is less than 4%. The results show that the theoretical calculation method of the initial failure load of the composite box girder is correct and the higher the 0° ply ratio, the initial failure load of composite box girder is higher.

NUMERICAL SIMULATION ON PROGRESSIVE COLLAPSE PROCESS OF COMPOSITESTIFFENED PANEL WITH INITIAL DEBONDING DEFECT

ZOU Hua-min, CUI Xiang-bin, REN Ming-fa, CHANG Xin

2017, 0(11): 12-18.

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A numerical analysis model was established to study the progressive collapse behavior of composite stiffened panel with initial debonding defect. Three typical intralaminar damage modes including fiber failure, matrix failure and fiber-matrix shear failure were considered in the model. The user-defined material subroutine VUMAT was used to distinguish the in-plane failure types and to degrade the corresponding material properties. The Virtual Crack Closure Technique was applied to calculate the strain energy release rate of the interlaminar crack front and the onset of debond propagation was determined using the B-K mixed-mode criterion. The buckling and post-buckling processes up to collapse of the panel under compressive load were quasi-static solved by the explicit dynamic method. The reasonability and validity of the model were verified by the good agreement between the numerical analysis result and the literature′s experimental and numerical results, and the damage evolution processes and the progressive collapse behavior of the debonded panel were investigated in detail.

EFFECT OF POLYAMIDE AND ETHYLENE DIGLYCIDYL ETHER ON MECHANICALPROPERTIES AND DAMPING PROPERTIES OF EPOXY RESIN SYSTEM

LI Feng-kai, DENG An-zhong, RONG Xiang, CHEN Ke

2017, 0(11): 19-24.

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In order to design an epoxy resin system with certain mechanical strength, good construction performance and high damping internal friction, the effect of content of low molecular weight agent polyamide on the cross-linking degree, mechanical properties and damping property of epoxy resin was studied. Then, by adding ethylene diglycidyl ether, the effects of ethylene diglycidyl ether on the viscosity, mechanical properties and damping properties of epoxy resin were discussed, and the effect of cross-linking degree on the properties of resin was analyzed. The results show that the cross-linking degree decreases, the compression strength and tensile strength decrease, and the elongation at break increases and the T_g transfers to low temperature with the increase of the content of polyamide or active diluent. When the ratio of polyamide to epoxy resin is 1∶1, damping loss factor is the highest.With the increase of the content of active diluent, the loss factor of epoxy system increased firstly and then decreased, and the damping performance was the best when the content was 20%.

STRESS ANALYSIS OF COMPOSITE PRE-TIGHTENED TEETH CONNECTIONJOINT UNDER MULTIAXIAL LOADING CONDITION

YAN Xiao-qiang, LIU Ya-wen, ZHAO Qi-lin, LI Fei

2017, 0(11): 25-31.

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To explore the composite space truss bridge key node pre-tightened teeth joint stress distribution under the multiaxial loading state, multiscale finite element model of the composite space truss bridge was established. The multi-scale model can not only obtain the overall structural performance of the truss bridge and the stress distribution of the local joint, but also can effectively reflect the interaction between the two. Through this model, the stress distribution of the joint in the multi-directional loading state is studied. The results show that when the joint force is applied, the normal stress of the tooth surface attenuation is within 5 MPa with respect to when the assembly is completed, and the multi-directional force joint attenuation is mitigatory relative to the one-way force connector. After the attenuation, the normal stress of the multi-direction joint is slightly higher than that of the uniaxial joint. The ratio of each tooth load distribution of the multi-directional force joint is basically the same with that of the unidirectional force joint, and distribution is high on both sides and low in the middle. The transverse shear stress of the composite of the joint is higher than that of the uniaxial force joint, but the transverse shear stress is much smaller than the transverse shear strength of the material. The joint is in the safe state. The results can provide a reference for the design of composite pre-tightened teeth joint.

STUDY ON MOLECULAR STRUCTURE OF POLYMETHACRYLIMIDE FOAM

LI Xiao-chuan, LI Ke-di, MENG Jia-li , HU Ai-jun

2017, 0(11): 32-36.

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In this paper, the molecular structure of polymethacrylimide (PMI) was studied. Based on the Fourier transform infrared (FR-IR) analysis in situ heating, it was found that the Casecell IH PMI foam prepolymer began the reaction of -COOH and -CN groups turning hexahydric imide ring in the condition of 160 ℃/2 h. The -NH stretching vibration peak type and area were no longer changed, and -C=N stretching vibration peak appeared after treatment at 200 ℃/2 h. The results of ¹³C NMR showed that the adjacent -COOH groups were not included in Casecell IH PMI prepolymer. PMI foam prepolymer only underwent ring formation of the imidization reaction and trapezoidal reaction at high temperature. The molecular weight and distribution of Casecell IH were measured by laser light scattering (LLS) and gel permeation chromatography (GPC). The results showed that the weight average molecular weight appeared double peaks, indicating that the molecular weight of Casecell IH perpolymer was larger and the distribution wide, consistent with the characteristics of free radical copolymerization.

EXPERIMENTAL AND NUMERICAL STUDY ON THERMAL INSULATIONPERFORMANCE OF LIGHT EPOXY COMPOSITES

YANG Xiao-xiang, ZHU Qing-shuai, BAO Rui, YAN Shi-lin

2017, 0(11): 37-42.

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The thermal insulation performance of hollow glass bead/epoxy composites were studied by experiment and numerical simulation method. The representative volume element was established by ANSYS/APDL parametric finite elements analysis technology, and then the effects of model size, volume fraction, particle size and ratio of thermal conductivity of matrix and particle (λ_m/λ_p, λ_m remain a constant) on the thermal conductivity of composites were investigated. The numerical results show that model size has little influence on the thermal conductivity of composites when it is larger than 500 μm. The thermal conductivity of composites decreases with the increase of volume fraction of particle and λ_m/λ_p. What is more, the thermal conductivity of composites is barely affected by the particle average size. By comparison, the calculated values are in good agreement with theoretical and measured values, which proves the reliability of the calculation method. In addition, the incorporation of hollow glass bead effectively reduces the density of the resin. Lightweight insulated hollow glass bead/epoxy composites have the potential to become an energy-saving and environmentally friendly material with a wide range of applications.

THE STRUCTURE DESIGN AND APPLICATION OF COMPOSITE ANTI-COLLISION FENDER

YAN Gai, FANG Ming-xia

2017, 0(11): 43-49.

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This paper sets composite anti-collision fender as the research object. By using Finite Element Method, the dynamics of ship-bridge collisions with different bow shapes were studied, which provides a theoretical basis for the structure design of anti-collision fender. By comparing impact test with numerical simulation results from ANSYS/LS-DYNA software, it improves the finite element model of the collision fenders. Then, three structural types of composite anti-collision fenders are designed, which are D-type and L-type. And the date of collision force, energy dissipation and indentation were from the simulation of the collision among 1000 DWT wedge bow ship, 3000 DWT bulbous bow-shaped boats and three structural type fenders by ANSYS/LS-DYNA. Both structure types of collision fenders′ adaptability of different shapes are comparatively analyzed. The results showed that the D-type fender protected the wedge bow boat better, but it cannot protect bow-shaped boat. The L-type fenders dissipated energy well for the two kinds of ship, which plays a role in protecting bridges and ships. Therefore, in practical engineering, many factors should be taken into consideration in order to choose the most reasonable anti-collision fender structure. So far, the L-type collision fender has been applied in the Hong Kong-Zhuhai-Macao Bridge protection works. It effectively prevents the risk caused by ship-bridge collision, and provides an important model to promote the application of composite anti-collision fender.

AGING AND CORROSION PROPERTY OF GFRP WITHROLLING RIVETING AND BONDING JOINTS

HUANG Zhi-chao, HE Jun-hua, FENG Jia

2017, 0(11): 50-55.

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In this paper, the aging and corrosion tests of the glass fiber reinforced polymer (GFRP) with hybrid joints (rolling riveting/bonding) were carried out. The effects of temperature and corrosion medium on the mechanical properties of the joint were analyzed by static tensile test. The experiment results show that the peak load of the adhesive layer decreases with the increase of holding time at the same temperature, and the peak load of the adhesive layer decreases with the increase of temperature at the same holding time. Furthermore, in 5% NaCl solution, corrosion resistance has little influence on the tensile properties of the connector when the corrosion time is prolonged. But when corrosion was carried out in 5% NaOH solution and 5% HNO₃ solution, the tensile properties of the joints are greatly affected, and the peak load of the samples are decreased obviously. The failure of the sample is mainly divided into two gradations of the adhesive failure and rivet failure.

RESEARCH OF THE THERMAL DEGRADATION OF T700 CARBON FIBER RESIN MATRIX COMPOSITES

JIN Xin, SUI Gang, YANG Xiao-ping

2017, 0(11): 56-61.

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In this paper, the research of the pyrolysis process of T700 carbon fiber reinforced epoxy resin composites was carried out. The results show that carbon fiber has increased the activation energy required for epoxy resin degradation. The reaction temperature, time and atmosphere factors had affects on the degradation effect of epoxy resin matrix and tensile properties of recycling carbon fiber. There was no residue on the surface of carbon fiber after 30 min pyrolysis at 500 ℃ in air condition, but the retention rate of tensile strength was only about 77.6%. Through the first heat treatment in nitrogen atmosphere at high temperature for a short time, and the second treatment that was pyrolysis at 450 ℃ for 30 min in air, the residual carbon on the surface of carbon fiber were removed. The tensile strength of recycling carbon fiber retention rate reached 90.4% and the interlaminar shear strength of unidirectional composites retention rate can reach 75.8%.

THE STUDY OF PEEL STRENGTH OF PMI FOAM SANDWICH STRUCTURE COMPOSITES

MAO Min-liang, PENG Kun, ZHENG Fan-fan, FANG Yong

2017, 0(11): 62-65.

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The effect of density, cell size, molding method and surface roughening treatment (foam, panel) on the peel strength of PMI foam sandwich structure composites were systematically investigated. The results showed that foam density, cell size, molding method and surface roughening treatment can efficiently improve the peel strength. And, the most significant is the foam density and cell size, which improve 157% and 95%, respectively. This study provides excellent technical guidance for the improvement of peel strength for PMI foam sandwich structure composites.

BASED ON LABORATORY TEST ABOUT FINITE ELEMENT ANALYSISOF HIGHWAY FRPM PIPE CULVERT

CHEN Zhao-nan, WEI Lian-yu, ZHANG Ji-yuan, PEI Ya-nan

2017, 0(11): 66-71.

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In order to study the mechanical properties of FRPM pipes, based on laboratory model test results and engineering practice, the finite element analysis model is established by means of ABAQUS, and the test results of two kinds of working conditions in laboratory test are compared with numerical simulation. The results show that the lateral confinement ring is very close to the simulation results and the measured value to the strain, verifying the correctness of the numerical simulation. No sand pipe and indoor results exhibit the same stress variation test model of unconfined buried FRPM pipe confined deformation. When it reaches a diameter of 5% vertical pipe culvert, ultimate bearing capacity of the corresponding upper pipe top filling height of 50 cm, and 70 cm were 66 t and 71 t, respectively providing and an important theoretical basis for the popularization and application of highway FRPM pipe culvert.

EXPERIMENTAL STUDY ON TENSILE PROPERTIES OF GFRP BARS WITHDIFFERENT BASE MATERIALS IN ALKALINE ENVIRONMENT

HU Shao-feng, LI Ming, ZHANG Yan-da, XIAO Hai-yuan

2017, 0(11): 72-76.

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Glass Fiber Reinforced Polymer (GFRP) bars is a new type of building materials which has been used as an alternative steel bar. It has been used in concrete structure. In this paper, by studying in the alkaline environment of simulated concrete, the corrosion mechanism, failure modes and tensile strength, elastic modulus and other tensile properties of GFRP bars of different matrix materials during 90 days immersion period were investigated. The results show that the two forms of damage typical matrix material GFRP bars is substantially the same, and brittle strands are shaped blasting. The tensile strength of the GFRP bars with a base material for the Unsaturated polyester resin is reduced, elastic modulus have a slight growth in the early and reduced later. When the final soaking period reaches 90 d, the attenuation of tensile strength and elastic modulus is lower than the minimum requirement of the standard. The tensile strength of the GFRP bars with a base material for the vinyl ester resin is reduced. But the decay-rate is lower than the base material of the unsaturated polyester resin GFRP bars. And the elastic modulus changes are not obvious. When the final soaking period reaches 90 days, the tensile strength and elastic modulus fulfill the minimum requirements of the standard.

THE RESEARCH OF WATER SOLUBLE CORE USED IN VARI MOLDING PROCESS

LUO Hao, TAO Hong-bo, LU Xian-xiao, GUO Wan-tao

2017, 0(11): 77-79.

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In this paper, a low-cost, easy-to-form water-soluble core mold was prepared and its shrinkage, compression property, water solubility and air tightness were studied. The results show that the soluble core mold prepared by quartz sand has good dimensional stability before and after molding, the compressive strength was higher than 3 MPa at room temperature to 120 ℃ and it could be quickly collapsed into the sand condition within 1 min at room temperature. The airtightness of the mold which should satisty vacuum assisted resin infusion (VARI) molding process was achieved after surface sealing treatment. The VARI process validation test was carried out on the surface of the hollow metal frame filled with water-soluble core mold. It shows that the water-soluble core mold prepared in this paper can be used as a VARI process mold which has little effect on the apparent quality of the product. The mold release is simple and convenient, and the core mold has a good application prospects.

THE OPTIMIZATION OF COMPOSITE LAMINATES FORSONAR DOME BY GENETIC ALGORITHM

WU Jia-nan, NI Ai-qing, YANG Bin, WANG Ji-hui

2017, 0(11): 80-85.

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In this paper, based on the Classical Laminate Theory of composite mechanics, an optimization platform of composite laminate design by Matlab and Ansys were developed for sonar dome. The optimization platform is verified by considering a laminate under uniaxialloading, with the optimization results compared with experiments.The results show that the strength of the laminates improves as the optimization progresses, and the optimum design gives greatly improved strength, and good agreement is achieved between the numerical and experimental results. Thereafter, the laminate of the sonar domeare is optimized according to the actual underwater load conditions. The stress and strain fields of the optimized laminate are obtained by ANSYS. It is shown that the strength and stiffness of the sonar dome has been significantly improved, and the optimization of the sonar dome laminate is fulfilled successfully.

ANALYSIS ON SHEAR FATIGUE AND CREEP PERFORMANCE OFADHESIVE IN WIND TURBINE BLADE

WU Li-ping, JIN Xiao-chen, LIU Wei-sheng

2017, 0(11): 86-88.

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Importance of adhesive in blade was described briefly in this paper. Epoxy adhesive is commonly applied in rotor blade. The glass transition temperature, shear fatigue and creep performance of abroad and domestic kind were tested according to design requirement. The result was that import kind fracture area is typical toughness, while the domestic kind is combination toughness and brittleness according to SEM. It is very urgent for domestic kind adhesive to improve the toughness of adhesive and compatibility.

EXPLORATION OF TENSILE PERFORMANCE OF CARBON FIBERREINFORCED ALUMINUM LAMINATES

YUAN Bin, HUANG Ya-xin, LIN Yuan, XU Ruo-hang

2017, 0(11): 89-94.

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The tensile performance of carbon fiber reinforced aluminum laminates (CARALL) of two different fiber orientations with hole and without hole were studied experimentally and theoretically. Tensile properties of CARALL were obtained. Meanwhile, the theory of metal volume fraction and the point stress criterion to predict the strength of unbroken laminated plates and that were punched a hole have been proved.

PROGRESS ON RESEARCH ON COMPOSITE-METAL ADHESIVE JOINTS

WANG Shu-xin, SHANG Xin-long, JU Su, JIANG Da-zhi

2017, 0(11): 95-100.

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Adhesive bonding is one of the most appropriate method to connect two adherends in construction of composite structure. And adhesive bonded joints are used extensively in automotive and aerospace structures. Limited by the technology, composite materials can not fully replace metal, and the bonding between composite and metal becomes a critical problem. This paper analyses the characteristics of adhesive joints, including second bending, dissimilarity on stiffness and coefficient of thermal expansion between adherends and load transfer in joints. And then the methods are summarized on how to improve the mechanical strength of adhesive joints, including increasing the overlap length and width, choosing proper adhesive, surface treatment, designing of spew and adherends shape. At last, a brief prospect on the development trend of adhesive joints is proposed.

AUTOMATED FIBER PLACEMENT AND ITS APPLICATION IN AIRCRAFT COMPOSITE PARTS

YAN Chao, CHEN Ping

2017, 0(11): 101-105.

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Automated fiber placement, as an advanced automated manufacturing technology, is applied more and more widely because of its more placement flexibility and lower scrap, and broaden the application of composites enormously. This paper introduces the materials, processing software of automated fiber placement, the application of composite parts in aviation, and then gives the development trend of this technology.

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