COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL STUDY ON BOND-SLIP BEHAVIOR BETWEENNSM FRP BARS AND CONCRETE

ZHANG Hai-xia, HE Lu-yuan

2016, 0(3): 5-12.

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Under the pullout specimens strengthened with near-surface mounted (NSM) FRP bars, the bearing capacity process and the failure mode of the specimens are analyzed, and the influence of the parameters about the diameter of FRP bars, bonded length and the type of FRP on bond-slip behavior are studied. The results show that four types of failure modes including debonding failure at the interface between FRP bars and adhesive interface, debonding failure at the interface between concrete and adhesive epoxy, rupture of FRP bars and split of adhesive epoxy are obtained. The bond stress of the specimen with NSM BFRP increases with the bonded length, on the contrary, for the specimen with NSM GFRP bars. Due to the decrease of Poisson ratio of the FRP bars and the shear lag effect, the bond stress of the specimen decreases with increasing the diameter of FRP bars. At the same time, the model of the bond-slip constitutive relationship for the specimen strengthened with NSM-FRP bars is established and the mathematic representation of the characteristic points in the model is proposed based on the analysis and fitting of test results. The comparison between the fitting curve and experimental curve illustrates that the bond-slip constitutive relationship can accurately simulate the bond-slip behavior of concrete strengthened with NSM FRP bars.

EXPERIMENTAL RESEARCH ON FLEXURAL PERFORMANCE OF SANDWICHBEAMS WITH DIFFERENT CORE DENSITIES

ZHANG Fu-bin, LIU Wei-qing, QI Yu-jun, ZHOU Ding

2016, 0(3): 13-17.

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This paper presents the experimental research on the flexural performance of sandwich beams with high different foam core densities. First, five foam cores with different densities are explored (48~413 kg/m³) using three point bending tests. Test results show that, when the foam core density is less than 199 kg/m³, the ultimate bending strength of the sandwich beams increase with the core density increase, but when the core density is greater than or equal to 199 kg/m³, the ultimate bending strength of sandwich beams tends to a fixed value. The failure mode of the composite beams changed from core indentation failure to face compressive failure as the core densities increase. Second, high-order theory based on variational principle was used to analyze the deflection and the strain distribution of the sandwich beams. Finally, analysis of the ultimate bending strength of the sandwich beams was conducted.

STUDY ON THE MA-BENZOXAZINE/PHENOLIC-CYANATE RESIN BLENDS

GU Wu, YANG Po, MENG Fan-sheng, ZHU Rong-qi

2016, 0(3): 18-22.

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MA-NCE resin blends based on aldehyde-containing benzoxazine/methylene dianilinebis-benzoxazine resin (MA) and cyanate ester (NCE) were prepared. The gelation time and curing behavior of the blends and thermal mechanical property of the cured products were characterized. Then diisocyanate (MDI) was added into the blend as a polymerization retarder and the influence of MDI was discussed. The results show that, with the increase of cyanate ester content in the blends, Tg increased and modulus decreased; the addition of diisocyanate can effectively prolong the gelation time and improve the processing performance of the blend. Finally, a new high Tg resin used for hot melt prepreg is developed.

THE OPTIMUM DESIGN OF COMPOSITE LATTICE STRUCTURE

XU Wei, ZHAO Qi-lin

2016, 0(3): 23-26.

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The lattice structure is a good structure which can exert the mechanical property of composite. The topology and dimension optimization methods were studied, and the space manipulator was optimized by finite element analysis software. The topology optimization method was used to make conceptual design and get the approximate shape of the truss. The dimension optimization method was used to make sure the specific sizes of every bar. The optimization result is a lattice structure whose cross section has sixteen edge. Comparing with the filament-wound composite pipe, the composite lattice structure has lighter weight. There is some reference value for the composite lattice structure optimum design.

ANALYSIS OF PLACEMENT MANUFACTURABILITY OF FIXED-ANGLE TRAJECTORYFOR COMPOSITE CONICAL SHELL

HUANG Wei, WANG Xian-feng, XIAO Jun

2016, 0(3): 27-30.

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In order to study the placement manufacturability of fixed-angle automated fiber placement trajectory for composite conical shell, this paper proposes a new evaluation criterion for placement manufacturability based on the compressive strain of prepreg strands. As the compressive strain depends considerably on geodesic curvature of trajectory, the formula for geodesic curvature of conical logarithmic spiral is derived by proving the equivalence of conical logarithmic spiral and fixed-angle trajectory. The formula shows that compressive strain of prepreg strands on fixed-angle trajectory decreases with the diameter of the conic section, and increases with the laying angle and the cone angle. The proposal is validated by practical placement experiment using X850 prepreg.

LOW-VELOCITY IMPACT DAMAGE MECHANISM OF CARBON/EPOXY COMPOSITE LAMINATES

WU Pan, YAN Jian-hua, YU Jian-yong, GU Hai-lin

2016, 0(3): 31-37.

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In this paper, the low-velocity impact response of unidirectional and woven carbon/epoxy laminates was compared by analyzing the mechanism of impact damage. All samples are circular specimen, the stacking sequence of unidirectional laminate are _2s and _2s. The results show that the spread of impact energy is associated with the stacking sequence of composite laminate, the direction and space structure of fiber in each layer can also influence the spread of impact energy. Impact energy spread quickly in straight fiber. Compared with the woven laminate, the unidirectional laminate has lower degree of damage in the center of impact area, but it has a wider range of damage. Fiber bending will lower the speed of impact energy along the fiber axial. In the woven laminate, weaving point makes the impact energy concentrated in the central area of impact, resulting in more fiber fracture. On the other hand, the more arrangement direction of fiber in each layer, the more evenly impact energy within each layer spread. And it is helpful to reduce the impact damage of the composite material.

THE MECHANICAL BEHAVIOR OF UNIDIRECTIONAL COMPOSITELAMINA WITH UNIFORM WAVINESS

OUYANG Jia-si, NI Ai-qing, ZHU Jun, WU Wei-qing

2016, 0(3): 38-43.

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In this paper, the fiber waviness frequently appeared during the manufacturing process of composite wind turbines is investigated. A micro-mechanical finite element model is established to predict the elastic properties of unidirectional lamina with uniform waviness. Parametric modeling method is employed to build up this type of sinusoidal RVE (representative volume element) via ANSYS. Homogenization method and periodic boundary conditions are taken into account in this analysis. The effective stiffness of composites is calculated by stress/strain relation under different loading conditions. Furthermore, the local stress distribution along the fiber direction is acquired by numerical simulation under the axial compression load. Results show that the degree of waviness has great influence on the stiffness of composites. Especially, the longitudinal modulus decreased seriously, and the normal and interlaminar stress change obviously along the waviness direction.

COMPARISON OF WALL-THICKNESS DESIGN METHODS OF HOOP WRAPPEDCYLINDERS WITH STEEL LINER

LIU Pei-qi, CHEN Zu-zhi, ZHOU Tian-song, GU Chun-lin

2016, 0(3): 44-48.

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Because the wall-thickness design formulas of liner are not explicitly specified in related design and manufacturing standards of hoop wrapped cylinders, which makes certain difference among some parameters, such as wall thickness of liner and autofrettage pressure, about the same specification in the market. Therefor, some inconveniences are brought to the regulatory work. Design method of steel liner was comprehensively summarized firstly; then the finite element analysis models are established according to design results; at last, wall thicknesses differences caused by different standard systems and changes of fiber stress ratio and autofrettage pressure caused by differences of wall thickness are compared and analyzed. The results showed that wall thickness designed by GB 5099 is larger compared with the other two kinds of standard systems, and the difference is about 4.35%~6.0%, leading to the difference of fiber stress ratio ranges from 3.5% to 30.8%. At the same time, the reasonable range of autofrettage pressure is also different.

RESEARCH AND NUMERICAL SIMULATION OF THE IN-SITU CURINGOF SYMMETRIC FRP LARGE CONES

CHEN Hai-yan, ZHANG Xi, XU Jia-zhong, WANG Yan

2016, 0(3): 49-54.

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The forming of FRP large cones with internal curing process is studied with FEM (finite element method). The internal curing process simulation program is written based on ANSYS, and the temperature and degree of curing change is numerically simulated. The result shows that the simulation result corresponds to internal curing change law, approximating the experiment data, which proves the accuracy of the simulation. During the curing process of the FRP large cones, the heat passes from the inner layer of the composite to its outer layer and the peak temperature in the curing process becomes higher from the inner layer to outer layer. In the range of curable thickness, curing time becomes shorter gradually from the inner layer to outer layer. When the symmetrical FRP large cones get thicker, the time reaching to peak gets later, the peak becomes higher and the curing time becomes later. FRP large cones of 600~660 MW steam turbine generator completes solidified part for the thickest 7 cm in the internal hear-curing process according to the simulation result. More than 7 cm parts of FRP large cones can′t receive heat, because the FRP large cones is too thick and inner layer cured parts influence on composite performance of heat conduction. Within the prescribed time of internal heat-curing process, FRP large cones large diameter and small diameter can′t synchronously complete task of curing. Parts of no internal heating curing can realize full curing after curing process.

THE STUDY OF COMPOSITES VOIDS CONTENT ULTRASONICMULTI-PARAMETER EVALUATION METHOD

LU Ming-hui, LI Pei-rui, WANG Xu

2016, 0(3): 55-59.

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Due to the advantages of high strength and good fatigue strength, composites are widely used in aerospace field. However, voids are easily produced in the preparation process, and it significantly decreased the materials′ final mechanical properties. This paper proposes a composite pore content ultrasonic parameter evaluation method, which works through the measurement of ultrasonic relative nonlinear coefficient, and comparative study sound velocity and acoustic attenuation measurement, set up internal relation of composite pore defects and various parameters and evaluation method. The experimental results show that the relative nonlinear coefficient, velocity of sound and acoustic attenuation coefficient can evaluate composite pore content. Among them, the sound velocity can quickly reflect the density of composite materials. The sound attenuation coefficient within the scope of a certain size can be used as more accurate evaluation. For the samples that the change of sound velocity and acoustic attenuation coefficient is not obvious, using ultrasonic nonlinear coefficient of relative evaluation is more suitable. The study of evaluation for composite pore content provides the reference.

THE INFLUENCE OF SURFACE TREATMENT PROCESS ON ILSS AND INTERFACEMORPHOLOGY OF CARBON FIBER/RESIN COMPOSITES

CHEN Qiu-fei, DAI Hui-ping, GUO Peng-zong, LIAN Feng

2016, 0(3): 60-64.

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Surface treatment process is one of the most important conditions for preparing high-performance carbon fibers. This article studies the influence of the interlaminar shear strength and cross section and level morphology of carbon fiber/resin composites under different surface treatment process of PAN-based carbon fiber. We tested the tensile strength of carbon fibers and the interlaminar shear strength of its composites. We also analyze and evaluate the influence of different surface production processes on ILSS of carbon fiber/resin composites by SEM. The results show that, the electric conductivity of 12 ms/cm is a better choice in surface treatment technology, interlaminar shear strength is 81.2 MPa of composite materials and the ratio of tensile strength is 1.02% between un-surface treatment and surface treatment carbon fiber. The changes between interlaminar shear strength and electricity of high-performance dry jet wet spinning carbon fibers are conformed to the "layer enter type materialized double model". The better choice of electrolyte is NaOH, the better choice of concentration is 2%, and the better choice of electricity is 10 C/g when preparing high-interlaminar shear strength carbon fiber and composite materials. The level morphology between SYT49 carbon fiber composite materials and T700G are the same under the surface treatment process.

PREPARATION OF MICRO & NANO SIZED CELLULOSE AND ITS MODIFICATIONON THE PROPERTIES OF UP RESIN

YU Wang-wang, WANG Cui-na, LEI Wen, BAO Yu-heng

2016, 0(3): 65-69.

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Aiming at improving the properties of UP resin casting, ramie fiber was used as raw material, and micro & nano sized cellulose reinforced UP resin composite was prepared by treating ramie fiber with NaOH solution first and then followed by hydrolysis with the action of mixed acid. The mechanical and thermal properties of micro & nano cellulose reinforced UP resin composite and pure UP resin casting were comparatively investigated. The results show that, when 3wt% micro & nano cellulose is added, the tesnsile strength,tensile modulus and impact strength of the casting is increased by 55.42%, 9% and 62.42%, respectively. And, the breaking state of the casting turns from original brittle rupture into ductile one, the initial decomposition temperature of the casting increases from 363.10℃ to 369.41℃. These indicate that the micro & nano cellulsoe can not only improve the mechanical and thermal properties, but also change the breaking properties from brittle rupture to ductile one.

SHELF LIFE PROPERTY OF POLYMETHACRYLIMIDE (PMI) FOAM CORE

LI Ke-di, FANG Yong, HU Ai-jun, XU Shi-yu

2016, 0(3): 70-74.

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In order to realize the best performance of PMI foam under rational storage condition, this paper investigated the moisture absorption performance, the mechanical and thermal creep properties after moisture absorption of PMI foam. It is found that, PMI foam has the fastest absorption rate in the first 15 days after being exposed to humidity air. Moisture absorption saturates after around 120 days. The compression strength after moisture absorption is consistent with the dried one in the room temperature. However, the high temperature compressive creep performance declines significantly. The impact of compressive creep performance after drying was also discussed.

MOULD DESIGN OF THE COMPOSITE LAUNCH BOX

LIU Hai-xin, TANG Ze-hui, LIU Gui, CHEN Yu-lin

2016, 0(3): 75-78.

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This paper uses the unique mould design to slove the demoulding problem of the launch box. According to the technical features of composite launch box′s large size and high precision,combined with the process characteristics of integral SCRIMP forming and demoulding, through the finite element analysis, the steel mould with arch door ribs and web ribs was designed and optimized. Using the CAD/CAE technology to design the launch box mould and taking variable fillet to solve the problem of demoulding, the prototype of the launch box was successfully manufactured and it had met the requirements of product design.Through those works, a feasible technological plan of the mould design technology for compsite products with large long axis structure was explored.

INFLUENCE AND CONTROL OF PARAMETERS ON THE COMPOSITE FIBERVOLUME FRACTION BY VARI PROCESS

CHEN Ji-ping, GAO Long-fei, SU Jia-zhi, HAN Xiao-yong

2016, 0(3): 79-82.

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The composite laminates were manufactured by VARI technology with different preform and infusion parameters, and the effect of the technology parameters to the fiber volume fraction are investigated. The results show that the fiber volume fraction of the composite laminate can be improved through the way of increasing resin over infusion and over vent time, decreasing the resin viscosity or increasing the preform pressure. With the above methods, the fiber can be re-configurated for longer time so that the fiber can be compacted more deeply. The fiber volume fraction can reach to 57.1% for the compacted laminate by VARI manufactuing process.

LOW-CYCLE FATIGUE OF COMPOSITES BASED ON VCCT

XU Xiao-chen, QIAN Xuan

2016, 0(3): 83-85.

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A composite low-cycle fatigue analysis model, which can forecast delamination fatigue life of laminates, is created based on VCCT. Low-cycle fatigue of delamination growth is analyzed by ABAQUS with the method of direct cyclic approach, by first defining the interface through delamination, and the fracture energy release rates at the crack tips in the interface. Elements are calculated based on VCCT technique, and the onset and delamination growth are characterized using the Paris law.

STUDY ON WETTING BEHAVIOR BETWEEN VINYLESTER RESIN SYSTEM AND GLASS FIBER

TANG Ze-hui, WANG Lin, DONG Qing-hai, CHEN YU-lin

2016, 0(3): 86-88.

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To obtain the nice wetting behavior between vinyl ester resin and glass fiber, two kinds of vinyl ester systems and three kinds of glass fiber were investigated. The suitable resin and additive ingredient ratio was confirmed based upon changing the surface tension through introducing additive, and combining the target test that determined the wetting rate of resin penetrating into glass fiber, respectively. The checked resin system was applied to composite plates by using RTM technology to ensure the consistency between the research and workmanship. So, the best corporation that what kinds of resin system and fiberglass is determined. It revealed that the wetting behavior of resin will be improved by decreasing surface tension of resin system.

RECENT PROGRESS IN WARP KNITTED FABRIC PREFORMS

YAN Tao-hai, JIANG Jin-hua, CHEN Dong-sheng

2016, 0(3): 89-94.

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Warp knitted fabric for composites has attracted great academic interest because of its perfect three-dimensional structure, quasi isotropic and many other excellent properties. Warp knitted spacer fabric preforms system is the basis of the high-strength composite materials. Compared with the ordinary fabric preforms, non-crimp fabric composite materials have excellent mechanical properties, which can use carbon fiber and glass fiber to manufacture non-crimp fabric without damaging the strength, providing broader application for composite materials. This paper outlines the warp knitted fabric preparation method, structure and properties, and the prospect of warp knitted reinforced fabric preforms.

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