COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL INVESTIGATION ON LAMINATE SHELL STRUCTURES BONDED WITH COMPOSITE PATCHES

QIU Qiu-yuan, FAN Hai-rong, LIN Zhen-neng

2015, 0(4): 5-10.

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In actual engineering structures, there are a lot of curved composite structures with large curvature. Due to its special shape and aerodynamic requirements, the patch bonded repair parameters of them can not be simply equated with the planar composite structures. Aiming at the laminate shell structure, for which the size (length×radius×central angle) is 300mm×50mm×PI/3rad and contains a penetration hole of 20mm diameter in the center, two types of composite patch were used to repair it. And then, the mechanism of the laminate shell structures was investigated experimentally. Generally, the hole in the laminate shell structure can reduce a great loss of the failure strength, and the loss rate can reach more than 61%; while the static mechanic properties of the bonded structures are significantly improved. The failure strength and static stiffness of the bonded structures could be the same as the perfect ones. Meanwhile, cuneal patch is beneficial to improve the stress condition of the patch and mother plate in repair structures.

SIMULATING IDEAL WIDTH OF THE TRAILING EDGE ADHESIVE GLUE OF WIND TURBINE BLADES

XUE Cai-hong, Li Cheng-liang, ZHU Xiao-qin

2015, 0(4): 11-15.

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In recent years, with the rapid development of wind power industry, the crack of the trailing edge bonding of blade acts as a major failure mode. Therefore, simulating the ideal width of the trailing edge adhesive glue has significant necessity. The results show that: the best bonding width of the trailing edge adhesive glue is ranging from 100~150mm.

QUASI-EQUAL STRENGTH DESIGN AND FINITE ELEMENT ANALYSIS FOR COMPOSITE MAIN WING BOX OF X UAV

LIU Feng, MA Jia, ZHANG Chun, YU Hui

2015, 0(4): 16-21.

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A research on load segmentation envelope design and layer optimization method is carried out for quasi-equal strength design and optimization of an unmanned aerial vehicle composite main wing box. The load segmentation distribution of the quasi-equal strength front spar of the main wing box is calculated using load envelope method with constant step. The initial layer structure of the front and rear spar is given. The finite element model of the main wing box is built. The strength, stiffness and stability of the main wing box are checked based on the results of finite element analysis. The optimized layer constructions of the front and rear spars and the skin are presented. It is shown that it is very convenient to calculate the segmented load of the front and rear spar using load segmentation method with constant step. The layer optimization design of the segmented main wing box can be done efficiently based on the initial layer construction design using the classical laminate theory and structure mechanical check by finite element method. Under the compression load caused by maximum positive lift, local buckling occurs easily at the wing root of the upper skin and the front spar’s upper strip, especially for the high-aspect-ratio wing box. The weight of the main wing box can be cut down by 5.23% through reducing the layers of the lower chord of the front and rear spar and the lower skin.

MEASUREMENT OF MODE-I STRESS INTENSITY FACTOR IN A DOUBLE-CRACKED COMPOSITE SHEET USING DIGITAL IMAGE CORRELATION METHOD

HAO Wen-feng, YUAN Ya-nan, YAO Xue-feng, MA Yin-ji

2015, 0(4): 22-26.

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Digital image correlation method was used to measure mode-I stress intensity factor in a double-cracked composite sheet. First, the principle of DIC was introduced, and the relationship between the stress intensity factor and the displacement at the crack tip was established based on least square fitting. Then, the non-contact optical measurement system of DIC was built up, and the full field displacements at the crack tip were obtained by tensile experiments using double-cracked composite sheets. Finally, the stress intensity factors were extracted from the full field displacements, and the effects of least square fitting terms, sub size and sub spacing of DIC on the stress intensity factors were analyzed.

FINITE ELEMENT ANALYSIS OF THREE HOLLOW SANDWICH COMPOSITES ON SIDE COMPRESSIVE PROPERTIES

PU Guang-yi, CAO Hai-jian

2015, 0(4): 27-30.

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On the basis of previous studies, a new structural model was built to study compressive properties of three-dimensional hollow sandwich composites (3D composites) by using the finite element software ANSYS Workbench. The distribution of stress & strain on the fibers, resin and the 3D composites was discussed under compressive loads of 2 mm displacement by using the model. The results show that the maximum value of stress occured between the overlap of piles, where the 3D composites were damaged easily. The minimum value of stress occured on the up and down face-sheet, where the 3D composites were damaged difficultly. The main loads were supported by fibers and the minor loads were supported by resin. The main failure mode of the 3D composites are resin fracture when the 3D composites suffered compressive loads.

RESEARCH OF FBG-BASED COMPOSITE DAMAGE MONITORING SUBJECTED TO LOW-VELOCITY IMPACT

GU Guang-wei, WAG Qing-tao, LI Wei

2015, 0(4): 31-34.

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Glass fiber composite will easily occur internal damage when subjected to low-velocity impact, the impact is particular damaging in the case of composites where the fibers are elastic and brittle as well as the matrix. In this paper, 2J′s impact was conducted to different specimens for 1-7 times to study FBG′s survivability and reflect of FBG to the internal strain of laminate. Strains at thickness direction were analyzed and compared with the damage of the laminates. The result showed that the change of the wavelength can accurately reflect the internal strains of the composite specimens. Meanwhile, FBG was still in good condition after multiple impacts, so it can be used in long-term online monitoring of composite parts. This work built some basis for the monitoring of the composite parts using FBG.

EXPERIMENTAL STUDY ON THE SIZE EFFECT OF TENSILE PERFORMANCE OF GFRP BARS WITH DIFFERENT DIAMETERS

WU Jun, CHEN Wen-xue, JIAO Yu-zhao

2015, 0(4): 35-40.

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In order to study the law of size effect on the tensile performance indexes of GFRP bars, the tensile performance experiments of GFRP bars with 5 kinds of different diameters were conducted by the electro-hydraulic servo universal testing machine. The experimental results show that the influence of size effect on ultimate strength and ultimate tensile strain are significant. With the diameter increases, the ultimate strength and ultimate tensile strain increase as well, while the influence on elastic modulus is not obvious. The failure mode of specimens belongs to splitting failure and the stress-strain curves show a linear relationship; The average value of elastic modulus is 48.06GPa. The influence of different slenderness ratio on the ultimate strength of specimens with the same diameter should conduct a further study.

RESEARCH AND ANALYSIS ON THE MECHANICAL PROPERTIES AND OPTIMIZATION FOR COMPOSITE T-JOINT

LI Ling, XU Feng, ZHENG Shao-wen

2015, 0(4): 41-46.

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As common connection form of composite structure, T-joints’ mechanical properties is directly related to the safety of structure. This paper establishes finite element model of composite T-joints considering bond layers. Then the simulation results are compared with experimental images, whose deformation and failure modes fit the experiment well. Research indicates that: T-joint presents “S” bending in the vertical loading;stress concentration appears in the corner of skin and at the end of weld;shear stress is high at both end, while the middle part appears low stress groove area;the bending normal stress and the equivalent stress appear double peak value feature;the most likely damage form is stripping between skin and bond layer, while the failure of core is shear failure and tensile failure due to stress concentration. Rounding in the corner of skin and smooth transition at the end of weld can obviously eliminate stress concentration.

FINITE ELEMENT ASSESSMENT OF CFRP LAMINATE LAYUPS REGARDING PEDESTRIAN HEAD SAFETY

ZHOU Bing-jie, GAO Xiao, ZHU Jia-qiang , LI Wei

2015, 0(4): 47-51.

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In this paper, the FE model of collision between head impactor and CFRP laminate was established in the ABAQUS software according to the GB/T 24500-2009 standard. Nine laminate layups were designed to analyze the effects layup degree types and different layup degrees had on both HIC value and maximum penetration. The HIC value relationships with maximum penetration, impact duration and impact energy absorption were also evaluated. It was shown that HIC value had certain inverse relationships with maximum penetration, impact duration and impact energy absorption; laminate with three-degree type was the best for head protection; forty-five degree contributed the most in decreasing HIC value and maximum penetration.

THE EFFECT OF PLY ANGLE DECLINATION ON TENSILE STRENGTH OF COMPOSITE STEP-LAP REPAIR

LIU Guo-chun, XING Li-wen, YANG Wen-feng, ZHANG Ji-wu

2015, 0(4): 52-56.

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According to ply angle declination of composite repair, a three dimensional finite element analysis model is developed for the composite laminated plates with a step-lap repair, which conforms with the results of experiments. Both single ply declination and total plies declination were calculated for the deviation of laying and benchmark. The result of calculations shows that few effects on tensile strength that the declinate ply is under middle plane. The larger angle declination and the position more close to the top ply, the stress level of whole structure is lager. The most serious case occurs on when the angle declination of top ply. The additional ply affords much more loads, and the general 0° angle may not fit for all the repair cases. The conclusion has great significance in directing the engineering practice of composite repair.

THREE-DIMENSIONAL HYBRID METHOD FOR FELTING PROCESS AND THE IMPACT ON THE MECHANICAL PROPERTIES OF THE GLASS FIBER REINFORCED THERMOPLASTIC COMPOSITE

YANG Xu-jing, LU Xiong, DUAN Shu-yong, ZHEN Juan

2015, 0(4): 57-61.

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To improve the impregnation quality of glass fiber reinforced thermoplastic composite, the three-dimensional hybrid method acts as a new kind of technology for felting process has been developed in this study, which could greatly increase the mechanical properties of the glass fiber reinforced thermoplastic composite. Glass fiber and matrix resin in this technology will be drawn into sarciniform, then the fibers are fully separated and the three-dimensional blended felt can be obtained by the improved opening, mixture, airflow, and lapping machines. The blended felts are made into composite plates by laminate hot-press approach, and mechanics performance testing of the composite plates is conducted. The experimental results show that there is a stronger adaptability to glass fiber reinforced plate impregnating process for three-dimensional blended felt. The three-dimensional blended felt shows a shorter impregnating distance and an increased interface between the matrix resin and the glass fiber, which make the reinforced fiber glass impregnated more thoroughly. The impregnation quality of thermoplastic composite plates made by three-dimensional hybrid method is better than that made by traditional technology. Moreover, the tensile strength, bending strength, and impact strength of the plates made by the new kind of technology has greatly improved under the same weight and glass fiber content.

STUDY ON CHOPPED GLASS FIBERS AND K₂Ti₆O₁₃WHISKERS MODIFIED PHENOLIC FOAM

SONG Han, WU Xiao-qing

2015, 0(4): 62-65.

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In order to study the effect of K₂Ti₆O₁₃whiskers and chopped glass fibers to the properties of phenolic foam (PF), samples of phenolic foam modified with K₂Ti₆O₁₃whiskers, chopped glass fibers and chopped glass fibers/4% K₂Ti₆O₁₃whiskers were prepared. Macrostructure, mechanical property and thermal insulating property of different phenolic foam samples were examined. The results show that with the addition of K₂Ti₆O₁₃whiskers the cell structure was more spherical and regular; the compressive strength, bending strength and thermal insulating property were improved compared with the neat phenolic foam. The compressive strength and bending strength of phenolic foam modified with different content of chopped glass fibers were obviously higher than neat phenolic foam, as the content of chopped glass fibers raised the compressive strength and bending strength of phenolic foam increased. The phenolic foam containing 8wt% chopped glass fibers has a higher compressive strength and bending strength, while compressive strength increased by 126% and bending strength increased by 208% compared with the neat phenolic foam; the thermal insulating property was rarely decreased. It was also found that the compressive strength, bending strength and thermal insulating property of the phenolic foam modified with chopped glass fibers/4% K₂Ti₆O₁₃whiskers were higher than the phenolic foam modified with chopped glass fibers.

STUDY ON PERFORMANCE OF COMPOSITE-METAL MECHANICAL JOINTS

JIA Yun-chao, GUAN Zhi-dong, SONG Xiao-jun

2015, 0(4): 66-70.

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An experiment investigation has been carried out with different kinds of specimens to investigate the failure mode and the damage load. The ultrasonic evaluations were used to show the situation of bearing damage near the hole. A numerical model by ABAQUS was established in order to point out the influence of different bolt types (protruding and countersunk joints), with or without gasket and joint types on composite joints. The study shows that the protruding joints are able to sustain 30% more load than the countersunk ones and the joints with gasket have higher load-carrying capability. The double-bolt joints can double the load-carrying capability as compared to the single-bolt joints.

APPLICATION OF PREPREG IN RTM PROCESS

HE Xian-cheng, LIU Gang, BAO Jian-wen

2015, 0(4): 71-75.

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The carbon fiber reinforced epoxy resin 5284RTM/5228A composite laminates were fabricated via co-cured RTM process. The internal quality of laminates was analyzed using Ultrasonic C-Scan inspection and microscopic analysis, short beam shear strength and bending properties were measured to evaluate the inter-laminar property of laminates, and thermal properties were determined by DMA. The results show that the pretreatment of the prepreg layer has no significant effect on the internal quality, the mechanical property, and the heat resistance of laminates. Besides the application of thermosetting medi-layer did not affect the internal quality and the mechanical property, but caused the reduction of the heat resistance of laminates.

ABLATION AND INSULATION BEHAVIORS OF GLASS CLOTH/PHENOLIC LAMINATES WITH VARIABLE PROCESSING TECHNIQUES

LUO Li-ping, NA Wei

2015, 0(4): 76-79.

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Glass cloth/phenolic laminates are widely used in industrial high-temperature equipments and thermal protection systems of various high speed space vehicles due to their good ablation-resistant and insulation behaviors. However, it exhibits substantial differences when the glass cloth/phenolic products were made from several variable processing techniques/factors, e.g., thickness of the glass fiber fabric, fiber winding technique, curing schedule and adding organic fiber into the glass cloth. In order to compare their ablation-resistant and insulation properties, the glass cloth/phenolic samples chosen in this study were tested using an arc-jet apparatus, the mass-loss and cool-side temperature of the samples gauged in the test were used to estimate their ablation-resistant and insulation behaviors. The test indicates that the tilt winding FRP is better to the others, consistent with the estimation, whose results served as the reference basis for engineering applications.

STUDY ON THE CHANGE OF THE UNIDIRECTIONAL COMPOSITE CURED PLY THICKNESS OF WIND TURBINE BLADES

JIA Zhi-yuan, GUAN Xiao-fang, WANG Zhan-jian, HOU Bo

2015, 0(4): 80-84.

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The cured ply thickness (CPT) of unidirectional composites is a very important parameter for the design of wind turbine blades. If the value of CPT is not accurate, the adhesive thickness of web and spar cap may be in excess of the deviation requirements, then the service life of the blade structure would be greatly reduced. The paper studied the change law of the CPT of two kinds of unidirectional composites. It was found that the CPT is mainly affected by the kind of raw materials, number of layers. And, some typical parameters such as degree of vacuum, temperature has little effect. The study also found that there was a linear relationship between the total thickness and number of layers. It can be described by mathematical model. This study laid a good foundation for the rational design of the blade.

CURRENT RESEARCH AND FUTURE DEVELOPMENT OF SCARF REPAIR FOR COMPOSITE COMPONENT

HE Qiang, YANG Wen-feng, TANG Qing-ru

2015, 0(4): 85-90.

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The rapid increasing in the usage of composite materials in modern aircraft leads to an immediate and active demand on composite structure repair technologies with high efficiency and reliability. Scarf repair of composite material has been proved to be an important and advanced repairing technology. Firstly, the architecture of scarf repair was introduced. Then, the detail surveys on key technologies of scarf repair were summarized. Finally, some challenges and the future directions were presented. The scarf repair provided support for design, manufacturing, operation in aircraft lifecycle. It also improved safety and reduced cost of aircraft.

THE SUMMARIZATION OF RESEARCH AND APPLICATION OF WOOD STRUCTURE STRENGTHENED WITH FRP

SHAO Jin-song, XUE Wei-chen, LIU Wei-qing, WANG Le

2015, 0(4): 91-95.

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Using FRP (Fiber Reinforced Polymer) to reinforce wood structures has the properties of light weight, high strength, easy manipulation and high durability, comparing with the traditional methods. Therefore, the study on FRP reinforcing wood structures has the practical significance. The research methods and conclusion about compression, flection and shear behavior of wood structures reinforced with FRP are described in detailed. Application of technology of FRP reinforcing wood structures in architecture and bridge is introduced. The lack of research is bound effect of FRP on the wood column, the flection property of reinforced wood beam on the basis of the actual stress-strain model and the shear property of the wood beam reinforced with FRP. The further research about the influence of the methods and design parameters on the behavior of strengthened wood members is proposed to formulate standard of FRP reinforcing wood structures.

Industry information contents

2015, 0(4): 96-128.

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