Table of Content

20 April 2018, Volume 0 Issue 4

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BASIC STUDY

DESIGH OF FIBER PLACEMENT PATH AND BUCKLING ANALYSIS OF VARIABLE-STIFFNESS COMPOSITE LAMINATES

WU Chen-jin, ZU Lei, LI Shu-xin, WANG Zhun

2018, 0(4):  5-10. 

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Compared with the straight fiber placement composite laminates, variable-stiffness laminates can achieve the designability of composite materials. And, the optimization of placement pathsof variable-stiffness laminates can increase the buckling load of the laminates. Firstly, expanding the composite laminate fiber placement paths of which orientation angle is linearly changed with the coordinate axis, and then four kinds of nonlinear changed placement paths had been proposed. And these five kinds of placement paths were regarded as the reference paths of the composite laminates to build layers by shifted method. Secondly, the variable-stiffness composite laminates were divided into five types according to the five different placement paths,and those laminates were modeled and analysedby ANSYS software without regard for overlap and gap caused by shifted method. Finally, under the uniaxial and biaxial compression load, the buckling loadsof the variable-stiffness composite laminates were calculated and compared with the fixed fibrous orientation angle laminated plates. The results show that the buckling load of variable-stiffness composite laminates had been considerably increased by the design optimizationof fiber placement paths of laminated plates.

EXPERIMENTAL STUDY ON BOND PERFORMANCE OF NSM CFRP BARS WITH CONCRETE UNDER CHLORIDE SOLUTION WET-DRY CYCLING ENVIRONMENT

GONG Jia-zong, YANG Shu-tong, LIU Yang

2018, 0(4):  11-14. 

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In the island construction, the seawater dry-wet cycling under tidal action is one of the main factors affecting performance of NSM (near-surface-mounted) FRP (fiber-reinforced polymer) strengthened concrete structures. Thus, the present study is aimed at the durability of NSM CFRP bars reinforced concrete with two types of bonding materials, i.e., high performance fiber-reinforced cementitious materials (HPFRC) and epoxy resin, by pull-out test of CFRP bars from concrete blocks under the simulated seawater dry-wet cycling condition. The failure modes and load carrying capacity are then analyzed. The results show that the strengthening performance of the specimens with epoxy decreases slightly. But the strengthening performance of specimens with HPFRC increases steadily in the wet-dry cycles of 90 days, and the load carrying capacity can be improved to 70.30% of that for specimens with epoxy resin. Therefore, HPFRC can be used as bonding materials in NSM FRP reinforced marine concrete structures under tidal environment.

STUDY ON EXTERNAL PRESSURE PROPERTIES OF CARBON FIBER REINFORCED POLYMER WINDING PRODUCTS

YANG Ling-feng, CAI Hao-peng, CHEN En, TIAN Wen-hua

2018, 0(4):  15-20. 

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The effects of the properties of the resin matrix modulus, winding angle and layer on the compressive properties of the carbon fiber composite winding products were studied. The results show that adjusting the content of PMDA in the MNA blending PMDA curing epoxy resin can effectively change the modulus of the cured resin. The resin modulus increases with the increase of the content of PMDA. When the content of PMDA was 5% of MNA, the modulus increased from 3.71 GPa to 4.18 GPa, which increased by 13%. When the content of PMDA was 10% of MNA, the modulus reached the maximum value of 4.61 GPa and increased by 24%. With the increase of matrix modulus, the compressive strength, shear strength and ring stiffness of unidirectional CFRP were increased at first and then decreased. When the matrix modulus was 4.18 GPa, the compressive strength and shear strength of CFRP reached the maximum value, which were 655 MPa and 71.6 MPa, and increased by 16% and 12%, respectively. At this point, the ring stiffness of the winding pipe reaches the maximum value of 277 kN/m² and increases by 87%. At the same time, increasing the winding angle and thickness can improve the anti-buckling stability of the winding pipe.

STUDY ON DAMAGE MECHANISM OF PLAIN WEAVE COMPOSITE UNDER HIGH VELOCITY IMPACT

YANG Guang-meng, ZHAO Mei-ying, WAN Xiao-peng

2018, 0(4):  21-26. 

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According to the fracture morphology of the plain weave carbon laminate, an analytical energy model was developed based on energy conservation law. The model considered that the kinetic energy of the projectile was absorbed by the laminate through shear failure, tensile fracture, compression deformation, delamination and moving in the crushed area during penetration. The influence of strain rate of the composite was taken into account. The depth of shear plugging was obtained by ballistic limit velocity in experiment and theory. Meanwhile, the crack length and the damage area of delamination were measured in impact experiment. The experiment for carbon weave composite laminate was conducted under flat and hemispheric projectile to obtain the ballistic limit velocity. Based on the validated model, further studies show that most energy is absorbed by tensile fracture of back surface under medium velocity, while compression deformation becomes the main absorbing mechanism under high velocity. The influence of delamination in energy absorption should be considered due to the large damage area. Meanwhile, more energy is absorbed by flat projectile than hemispherical projectile.

COMPRESSIVE PROPERTIES STUDIES ON ANGLE CUTTING AND SINGLE JOINT COMPOSITE STRINGER END OF AIRCRAFT CENTER WING

ZHANG Ming-xing

2018, 0(4):  27-31. 

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Angle cutting and single joint stringer end samples of center wing were made and subjected to compression test. Load-strain curves under axial compression load were obtained. The results show that non-linear deformation appeared and under the increasing load, bolts connecting rib flange, skin and stringer were sheared and failed on connection. The largest strain appears on the the first row fastners on the rib flange and skin.

ON-EQUIPMENT ULTRASONIC TESTING TECHNOLOGY OF BONDING QUALITY OF CFRP SKIN-CFRP

GAO Xiao-jin, ZHOU Jin-shuai, JIANG Bai-hong

2018, 0(4):  32-38. 

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According to the characteristics of the bonded structure of CFRP skin-CFRP, short pulse ultrasonic reflecting on-equipment testing method was used to test bonding quality, the influence of bonding film and debonding in structure on ultrasonic reflecting signal were analyzed, and self made short pulse delay block ultrasonic probe was used to test debonding in samples. Simulation results show that, short pulse ultrasonic reflecting signal can test Ⅰ interface debonding Ⅱ interface debonding when d/λ≤0.5. Experiment results show that, the width of pulse produced by self made 5 MHz probe is not larger than 1.5 cycle, which can meet the requirement of short pulse. The self made probe can test Ⅰ interface debonding, and Ⅱ interface debonding when thickness of bonding film is less than 0.5 mm,which can meet on-equipment testing requirement of actual product.

APPLICATION RESEARCH

OPTIMIZATION OF VARI PROCESS PARAMETERS FOR FRP YACHT

CAI Ying-qiang, CHEN Qing-lin, ZHAO Yun-bao, ZHU Zhao-yi

2018, 0(4):  39-44. 

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Taking a FRP Yacht as the object, the three-dimensional entity model and finite element model were established to simulate the resin flow front in porous medium with Darcy's law. Aim to shorten the filling time and reduce production cost, the optimal flow scheme and the injection port spacing were gained. The accuracy of the simulation results were verified by filling test. This work is of guiding significance for the practical production of FRP yacht.

EXPERIMENTAL INVESTIGATION INTO THE DYNAMIC IMPACTRESPONSES OF ALUMINUM HONEYCOMB PANEL FILLED WITH EPP FOAM

LIU Qiang, HE Zhao-heng, CHEN Hang

2018, 0(4):  45-50. 

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The paper investigated the dynamic impactresponses and failure process of aluminum honeycomb panel filled with EPP foam (Expanded polypropylene) experimentally.It was found that the initial peak stress and average stress of EPP foam filled aluminum honeycomb increased by 32.86%~68.57% and 15.00%~72.50% respectively, compared to the bare honeycomb under the same impact velocity. But the specific energy absorption (SEA) reduced by 33.54%~66.56%. For the filled panels with the same foam density, the initial peak stress,average stress and specific energy absorption increased with th increase in impact velocity. The SEA values under the impact velocity of 2.6 m/s and 3.2 m/s increased by 68.10%~152.45% compared to the impact velocity of 2 m/s. By comparing with the characteristics in the static compression test, the initial peak stress in the dynamic impact test increased by 1.72%~12.04%, whereas the average stress decreased by 6.51%~18.84%, and the SEA valuses decreased by 31.50%~65.50%. The study showed that EPP foam filling was effective to improve the impact performance of the bare aluminum honeycomb.

STUDY ON THE LIQUID FORMING PROCESS OF DRY-FIBER PREFORM

WANG Lin-xiang, HUAN Da-jun, XIAO Jun, WANG Jun-sheng

2018, 0(4):  51-55. 

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In order to solve the problem of preparation and setting of preform in RTM process, the dry fiber-liquid forming process was first studied domestically in this article. The main content was the influence mechanism of process parameters and the mechanical properties of liquid-forming process. Method of single factor was used to determine the influence of binder content, injection temperature and filling time on liquid forming. Then, the combination of optimum process was determined by orthogonal method. Finally, the inter-laminar shear and bending properties were compared with molding process. The experimental results show the flow filling of resin will be affected by the process parameter. The influence of injection temperature is the greatest, and the filling time has little effect. The correct combination of process can reduce defects such as pores to ensure the internal quality of composite. The mechanical tests show that the mechanical properties of the dry fiber-liquid forming process were equal to molding process, and the bending strength is slightly reduced.

EFFECT OF LASER TREATMENT ON PROPERTIES OF CFRP/ALUMINUM ADHESIVE

WU Yao, KONG Hai-juan, DING Xiao-ma, Qiao Meng-meng

2018, 0(4):  56-61. 

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Carbon fiber reinforced polymers (CFRP) have been receiving much interest in motivation and aviation fields due to their outstanding properties including lightweight and high strength. However, bonding strength of CFRP between composites and other materials needs to be enhanced because of the strong surface inertia and weak bonding strength. CFRP was treated by lasers with different pulse widths. The modified surface and cementation section of CFRP were characterized by SEM, contact angle test and surface roughness analysis. The results show that the amount of residual resin on CFRP surface decreased with increasing of pulse width, while the surface energy and surface roughness increased. The efficiency of the laser treatment method has been compared with mechanical grinding method through bonding strength and fiber cross section analysis. The bonding strength of CFRP and aluminum for laser treatment method improved 1.95 times and 1.02 times for mechanical grinding method in compassion with the untreated samples. At last, the bonding mechanism and failure mechanism of this dissimilar joint were investigated.

CONSTRUCTION OF AIRWORTHINESS MAINTENANCE KNOWLEDGE BASE FOR COMPOSITE COMPONENT BASED ON CBR

HE Qiang, YANG Xiao-qiang, XU Yi

2018, 0(4):  62-67. 

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To solve the problems encountered in airworthiness maintenance of composite component which strongly dependent on experience and the knowledge reuse, the knowledge base of composite component airworthiness maintenance was created. Firstly, the system framework was constructed based on case-based reasoning. The feature composition of airworthiness maintenance case was analyzed and the case representation model was created. The semantic retrieval index and attribute retrieval index were defined and the corresponding similarity evaluation method was designed. Finally, the knowledge application was realized by customizing the digital maintenance template. The experimental results show that the airworthiness maintenance knowledge of composite structure can be reused effectively by this knowledge base, and the quality and reliability of maintenance could also be improved.

HEAT TRANSFER ANALYSIS OF THE DE-ICING SYSTEM FOR WIND TURBINE BLADES BASED ON GAS THERMAL

YANG Bo, NING Li-wei, WEI Ke-xiang, ZHOU Zhou

2018, 0(4):  68-73. 

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Based on the gas thermal method, heat transfer calculation of the de-icing system for wind turbine blades is analyzed in this paper. First, the formation mechanism of blade icing is introduced. At same time, the principle of gas thermal de-icing system is presented. Second, the convective heat transfer and thermal conductivity are calculated. Then, the heat transfer in the heat transfer process and the minimum heat output of air heaters under optimal de-icing temperature are obtained. Finally, the time required for de-icing effect was obtained by a simulation example.

COMPARATIVE ANALYSIS ON SEVERAL KINDS OF EPOXY RESIN COMPOSITES FOR LARGE-SCALE WIND TURBINE BLADES

DENG Shuang-hui, FENG Yun-long, LIU Zuo-zhen

2018, 0(4):  74-79. 

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In this paper, three kinds of vacuum infusion epoxy resin systems, i.e., MERICAN 3311A/B, another domestic product and an imported product, for wind turbine blades were comparatively analyzed. The wettability of these epoxy resin systems for glass fibers were investigated, and the mechanical properties of their composites prepared by vacuum infusion molding process, were also studied. The results show that MERICAN 3311A/B had low viscosity and good wettability to glass fiber, which was satisfactory for vacuum infusion with glass fibers. Accordingly, through testing the mechanical properties of resin fiberglass plates, three kinds of epoxy resin systems all had good mechanical behavior, and the strength and modulus of MERICAN 3311A/B even exceeded the imported product and the other domestic product. Therefore, according to the comprehensive study of the behaviors, MERICAN 3311A/B can fufill the needs of large-scale wind turbine blades, which can be used to manufacture wind turbine blade.

THE OPTIMAL ANALYSIS OF THE CULVERT PIPE CULVERT OF FRPM UNDER THE MAXIMUM LAYER BOTTOM STRESS CONDITION

WANG Qing-zhou, LIANG Xiao, WEI Lian-yu, WANG Yang

2018, 0(4):  80-85. 

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The application of the glass fiber reinforced plastics mortar pipe in highway culvert becomes more and more extensive. However, due to the lack of micro-mechanical analysis of the pipeline, the application of the pipe in highway culvert engineering lacks some corresponding standards and basis. In this paper, the numerical simulation software ABAQUS was used to establish the model of surface-pipe-soil. Then, the deformation of the pipe and the stress of the bottom layer of the pavement under different conditions were analyzed. Through optimizing the thickness of the pipe wall, the optimal diameter ratio range of the pipe is obtained under the stress of the bottom layer at the critical splitting strength in different condition. Under the safety of the pavement and pipe structure, it provides some reliable analysis basis for minimizing the cost of project.

FROM-FINDING METHOD AND CONSTRUCTION SIMULATION OF HOSTING INDUCED SELF-FORMING GFRP ELASTIC GRIDSHELL

ZOU Le, XIANG Sheng, CHENG Bin

2018, 0(4):  86-91. 

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Hoisting induced self-forming GFRP elastic gridshells are made of long-continuous standardized glass fiber reinforced polymer (GFRP) circular tubes with properties of high elastic strain and low modulus. The space surfaces of the gridshells, which mainly behave as the bending deformations of the tubular members, are automatically formed because of the gravity effects during hoisting. By employing finite element method and programming tools, this paper presents a form-finding algorithm for a certain type of elastic gridshell that has the single symmetry plane, followed by the numerical simulation of hosting construction process. The proposed form-finding algorithm is proved to have good calculation accuracy and efficiency to meet the design and construction requirements. The constructed GFRP gridshell structures are found to behave reliable load bearing capacities.

PRELIMINARY STUDY ON LOW DENSITY SMC

ZHOU Zhen-fang, WANG Li-he, GE Ping, PENG Zhou-gang

2018, 0(4):  92-97. 

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Aiming at achieving low density SMC, raw material selection, formulation design, process control of SMC were studied by molding process. Firstly, the density, the radiance and flexural strength properties of SMC product were investigated by using different hollow glass spheres (HGS). It was found that VS5500 and H40 were appropriate packing for low density SMC. Since the design density and real density of the two products are similar, the mechanical property has small losses. Secondly, the glass fiber content and resin type on mechanical property were also investigated. The survey results indicated that the density of SMC product should be larger than 1.2 g/cm³. Otherwise, the breakage rate of hollow glass spheres will be increased. At the same time, EK100 is a good choice because of effective control of the resin paste viscosity. In addition, the product mechanical properties were enhanced from 148 MPa to 172 MPa by increasing glass fiber from 25% to 30%. If the glass fiber continue to increase, flexural strength would reduce to 140 MPa. The appearance and mechanical properties by using three different types of resin were also studied. It was found that the appearance of product is the best by using P18-03 resin, and flexural strength is 172 MPa, which can satisfy the requirement of automotive mechanical. Lastly, the relationship between parts density and treatment on hollow glass spheres was estimated. The results showed that drying glass spheres can effectively reduce the water content in the resin paste, ensuring SMC compound with an appropriate window for molding.

THE DESIGN AND RESEARCH OF THE EIGHT-WAY FIBER REINFORCEMENT

TIAN Hui-fang, YU Jiang-jiang, CHEN-Pei

2018, 0(4):  98-101. 

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Based on the analysis of the structural features and working principle of the laying equipment, combined with the problems and shortcomings of the existing laying equipment in China, this article designs a composite processing device that combines placement and cutting by PTC Creo Parametric. The device not only enables basic 8 tow placement but also adds a cutting mechanism, it allows the laying and cutting to work in harmony and realizes the computer-defined three-dimensional solid forming. This paper adopts a stacking method to design the cutting module and the module of clamping and re-feeding. It uses press shoes to design a compaction module which can realize individual control of multiple tows and is suitable for laying complex workpieces. It adopts the ultrasonic cutting method to trim and cut the boundary of the carbon fiber ply after laying. This paper also simulates the model established by ADAMS and verifies the stability of the device movement. The various components in the device are modularly designed and have certain expansibility.

EFFECTS OF PHENOLIC HOLLOW MICROSPHERES ON THE PROPERTIES OF POLYMER COMPOSITES

SHEN Xiao-qin

2018, 0(4):  102-105. 

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In this paper, the effects of different contents of the phenolic hollow microspheres on the mechanical properties, thermal insulation and microstructure of the hybrid composites were investigated. Quartz fiber, phenolic fiber and phenolic hollow microspheres were used as reinforcing materials by physical mixing for the production of hybrid composites. Experimental results show that the porosity of composites is increased by the incorporation of phenolic hollow microspheres, and the air bubbles in the pores provids better heat insulation performance. With the increase of the mass fraction of phenolic hollow microspheres, the density and mechanical properties of the composites were all reduced. The addition of phenolic hollow microspheres can obviously improve the thermal insulation property. Through the SEM photographs of fracture surfaces, it was found that when the phenolic hollow microsphere content was 6%, the phenolic hollow microspheres dispersed uniformly. The composites′ thermal insulation increased clearly and their specific tensile strength and compression strength reached maximum, realizing the best effects.