Table of Content

28 September 2016, Volume 0 Issue 9

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BASIC STUDY

EXPERIMENTAL STUDY ON DEFORMATION AND FAILURE OF COMPOSITE MATERIAL BONDING INTERFACE UNDER CYCLIC LOADING

YANG Zhi, LU Bo-yuan, LV Zhi-hui, LI Zhi-yuan

2016, 0(9):  5-11. 

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Researches on damage deformation and evolution behavior of adhesively bonded composite joints in real-time are of great importance for structural safety and its reliability assessment in service. In this paper, we use of Digital Image Correlation (DIC) and Acoustic Emission (AE) as complementary techniques for studying interfacial damage, deformation and failure behavior of adhesive-bonded composite single-lap joints under cyclic tension. On the basis of the average tensile failure load value, cyclic tensile tests were conducted with 70% and 80% of quasi-static failure loading, respectively. According to the damage deformation field, strain field information, and AE signals originated from damage of adhesive-bonded composite single-lap joints at different stages, the relationships between the mechanical failure mechanism of composite single-lap joints and the corresponding real-time deformation and AE signals were analyzed. The results show that the real-time micro-displacement field, AE relative energy, cumulative hits and amplitude spectra obtained from damage and failure of adhesive-bonded composite single-lap joints are connected with the initiation and propagation behavior of microcracks at adhesive interfaces. As the stress levels increase, the number of loading cycles that the joints can sustain before failure decreases.

STRESS-STRAIN RELATIONSHIP MODEL OF PVC-CFRP CONFINED REINFORCED CONCRETE COLUMN SUBJECTED TO AXIAL COMPRESSION

YU Feng, NIU Di-tao

2016, 0(9):  12-16. 

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Experimental study of 10 PVC-FRP confined reinforced concrete column subjected to axial compression were carried out. The experimental results show that the stress-strain curves can be divided into two stages: the first section of the stress-strain relationship curves is parabola, which is similar to that of reinforced concrete column with the same reinforcement ratio; the second section of the stress-strain relationship curves take on the strengthening stage, and the stress, strain and the strengthening slope gradually reduce with the increment of the hoop spacing of FRP strips. Due to the axial reinforcement, the bearing capacity and deformation of core concrete are greatly improved. The reinforcement ratio almost have no effect on the strengthening slope. According to the regression of experimental results, the calculation formula of bearing capacity and ultimate compressive strain are put forward, and then the related stress-strain model is also established.

EXPERIMANTAL STUDY ON COMPRESSION PERFORMANCE OF CONCRETE-ENCASED FRP CONFINED CONCRETE SUB-COLUMNS/CORES COLUMNS WITH WEAK CONFINE

SUN Yun-lou, QI Yu-jun, LIU Wei-qing

2016, 0(9):  17-25. 

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A novel column named concrete-encased FRP confined concrete sub-columns/cores column (CEFC) consisting of steel rebar, concrete and fiber-reinforced polymer (FRP) tube is presented. The sectional form of CEFC consists of the outer common reinforced columns (RC) and 4 inner Concrete-Filled FRP Tubes (CFFT), which located near 4 corners of square CEFC. The compression performance of RC and CEFC were studied and compared through experiment and Finite Element Method (FEM). The result indicates that the typical failure mode of CEFC with weak confine was local crushing and overall damage of CEFC was prevented by CFFT. What′s more, ductility of CEFC was improved. Moreover, second order stiffness and enhancement of strength were observed when CEFC was under eccentric compression.

EFFECT OF HYBRID EFFECT ON THE MECHANICAL PROPERTIES OF HYBRID FIBER REINFORCED CONCRETE

HE Jing-jing, SHI Jun-ping, WANG Xue-zhi, HAN Tie-lin

2016, 0(9):  26-32. 

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The influence of "hybrid effect" caused by the basalt fiber and polypropylene fiber on the mechanical properties of the concrete of matrix is discussed. The results show that the splitting tensile strength and flexural strength of basalt-polypropylene hybrid fiber reinforced concrete (B-P HFRC) is obviously higher than those of basalt fiber reinforced concrete (BFRC) and polypropylene fiber reinforced concrete (PFRC). Meanwhile, the concept of "fiber hybrid effect function" was proposed. The hybrid effect function of basalt-polypropylene hybrid fibers is obtained by the method of MATLAB data fitting. By confounding the "the hybrid effect function of basalt-polypropylene hybrid fibers" extremum the optimum basalt-polypropylene hybrid fibers volume mixing ratio, which improves the mechanical properties of concrete, was obtained.

ESTIMATION OF ELASTIC MODULUS AND ANALYSIS OF STRESS OF UNIDIRECTIONAL FIBER COMPOSITES BASED ON IMPERFECT INTERFACE

DENG Zhi-kang, DENG Jing-lan, WANG Ji-hui, HUANG Zhi-qiang

2016, 0(9):  33-38. 

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The interface defects have a significant effect on the properties of the materials performance. In this paper, the spring model without thickness has been considered to investigate the composite properties with imperfect interface in the elastic theory and energy principle. The relationships between the imperfect parameter, the volume fraction of fiber, and the effective properties, including the effective longitudinal and transverse elastic modulus and Poisson′s ratio were studied. Meanwhile, the results for the imperfect interface were compared by the classical results of perfect interface and a hole at two limit cases, and the test data. The result for finite positive values of interface parameter shows that the interface parameter can be used to estimate the material properties with the interface defects.

EFFECTS OF SPRAY GLUE ON COMPOSITES SHEAR MECHANICAL PROPERTIES OF WIND TURBINE BLADE

PAN Zu-jin, WU Jian-zhong, LIU Jian, SUN Yuan-rong

2016, 0(9):  39-43. 

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Effects of spray glue on composites shear properties of wind turbine blade in vacuum injection process were studied. The process of laying different type of fiber glass cloths on mould fixed by glue was simulated in the laboratory. Fiber glass reinforced polymer (epoxy resin) matrix composites (GFRP) were fabricated by vacuum injection process. The different groups of fiber glass content was tested by the method of calcined.The influence of fiber content on in-plane shear strength was analyzed in theory. Interlaminar shear strength of GFRP laminates was tested by mechanical testing machine. Results show that, the fiber glass content of the GFRP was almost the same as the spray glue was used on the undirectional fiber glass cloths, but for triaxial fiber glass cloths, it decreased by 6.9% in volume. Interlaminar shear strength of composites with unidirectional fiber glass cloths decreased by 61.4 %, and that of the composites with triaxial fabrics decreased by 18.8%. Therefore, spray glue on unidirectional fabric cloths should be prohibited. The triaxial cloths could be fixed by glue in moderation.

THE STUDY OF EFFECTS OF STACKING STRUCTURE ON THE INTERLAMINAR SHEAR STRENGTH OF COMPOSITES

ZHOU Lei, LI Da-sheng, HOU Rui-gang

2016, 0(9):  44-48. 

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An investigation was conducted to study the effects of stacking sequence and unidirectional glass fiber relative volume fraction on the interlaminar shear strengths (ILSS) of laminated composites. The six laminated composites with different stacking sequence follow as: (UF)₅, (UF, CSM, UF, CSM, UF), (CSM, UF, CSM, UF, CSM), (UF, CSM, CSM, CSM, UF), (CSM, UF, UF, CSM, CSM), (CSM)₅, and they were 100%, 60%, 40%, 40%, 40%, 0%, respectively. Experimental results indicated that the unidirectional glass fiber relative volume fraction has a huge effect on ILSS, and the ILSS of (UF)₅ reaches 40.768 MPa and the ILSS of (CSM)₅ only reaches 15.867 MPa. On the contrary, the stacking sequence has little influence on ILSS. Meanwhile, the failure modes were studied with a newly mathematical statistics method-"The Rank-Sum Test", which found that even the ILSS present a larger scatter because of different failure modes in the same type stacking sequence, the sample values can still be analyzed as a entirety.

THE INFLUENCE OF NANO-SiO₂ AND PP-g-MAH ON THE PROPERTIES OF GLASS FIBER REINFORCED PP COMPOSITES

YANG Jian-jun, HE Ya-dong, ZHANG Zhi-cheng, XIN Chun-ling

2016, 0(9):  49-54. 

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The interfacial bonding strength between fiber and resin is the key factor that determines the performance of composite materials. In this paper, we will study the influence of glass fiber surface coated with nano-SiO₂ that was treated by silane coupling agent KH550 and PP-g-MAH addition in PP on the interfacial bonding strength and mechanical properties of glass fiber reinforced polypropylene composites. The results show that KH550 surface treatment can reduce the surface energy of nano-SiO₂, which makes the nano-SiO₂ be advantageous to disperse on fiber surface. Fiber surface coated with nano-SiO₂ and addition of PP-g-MAH in PP is helpful to enhance the interfacial bonding strength between the fiber and resin. Meanwhile, shear strength of composite increased by 116.06%, tensile strength increased by 109.14%, and bending strength increased by 99.85%.

THE COMPARISON OF NUMERICAL SIMULATION METHOD OF CNG-2 CYLINDERS

LIU Pei-qi, CHAI Sen, CHEN Zu-zhi, GU Chun-lin

2016, 0(9):  55-60. 

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For the dispute between two usually used models (i.e. axisymmetric model and three-dimensional shell element model) in numerical simulation of CNG-2 cylinders,the results between two models was compared in detailed, and the effect caused by filament winding angle was discussed. The conclusion is that: for CNG-2 cylinders,when winding angle of the fiber layer was close to 90°, the stress distributions of two models are basically the same;the theoretical defects of shell element was the primary reason for the radial stress in fiber layer closed to zero when three-dimensional shell element model was used;when winding angle is equal to 90°, three-dimensional shell element model could be replaced by axisymmetric model when the stress analysis of CNG-2 cylinders stress was made, which can reduce computational workload;when the filament winding angle is not equal to 90°, the error between two models changed with winding angle, but is less than 5% when the angle ranged from 90° to 70°, and axisymmetric model can also be used within the engineering permissible range. Those conclusions can provide beneficial guidance for hoop-wrapped composite cylinders numerical analysis.

APPLICATION RESEARCH

EFFECT OF NONWOVEN TPU/CNF TO GLASS FIBER/EXPOXY COMPOSITES ON SOLID PARTICLE EROSION RESISTANCE

LV Guang-chao, LIU Chun-tai, DONG Meng-yao, ZHANG Na

2016, 0(9):  61-65. 

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The excellent wear resistance of nonwoven thermoplastic polyurethane (NTPU)was chosen as shielding structure. Vacuum assistant spray method was used to fabricate the NTPU/carbon nonfiber (NTPU/CNF) composites,the GF reinforced epoxy (EP) composites toughened by CNF/NTPU was fabricated via resin transfer molding (RTM) process, meanwhile the mechanical properties and solid particle erosion resistance of composites were measured and compared to EP fiber reinforced plastics (FRP). The results show that, compared to FRP, one layer of 0.1 mm NTPU made the tensile strength of the NTPU/CNF/GF/EP composites decrease about 10%, and the solid particle erosion resistance increase by 8 times. Meanwhile, ~500 μm of eroded particles exhibited a maximum erosion rate after 30 seconds of erosion at distance of 76 mm from the spout and impingement angle of 90°.

EXPERIMENTAL STUDY ON BOND BEHAVIOR OF GFRP REBARS AND RECYCLED CONCRETE

ZHANG Wei-dong, WANG Zhen-bo, WANG Cheng-wu

2016, 0(9):  66-69. 

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Based on the pull-out tests of 12 groups specimens which were designed according to CSA standard, the influence of four factors (the diameter of GFRP rebars, the incorporation rate of recycled concrete coarse aggregate, cubic compressive strength and splitting strength) on bond behavior of GFRP rebars and recycled concrete were systematically studied. The test results show that the source of coarse aggregate has little influence on bond failure pattern, and most of the patterns are pull-out failure, but the average bond strength decreases with the incorporation rate of recycled concrete coarse aggregate increasing; the cubic compressive strength and splitting strength have similar influence on the average bond strength which decreases with the strength of recycled concrete decreasing; and due to the adverse effect of shear lag, the average bond strength decreases when the diameter of GFRP rebars is increasing.

STUDY ON BENDING STIFFNESS OF HOLLOW INTEGRATED SANDWICH COMPOSITES

LIU Chang, ZHOU Guang-ming, WANG Di-hui, ZHU Ji-wei

2016, 0(9):  70-74. 

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Based on the structure characteristics of the hollow integrated sandwich composites and the analysis of warp and weft bending deformation, two kinds of sandwich beam models were established and the analytical expressions of warp and weft bending stiffness were derived, respectively. By comparing the theoretical solution, the results of FEM and experimental results, the accuracy and rationality of the models were verified. On this basis, influence of yarn density on bending stiffness was discussed by using this paper′s theoretical method. The results show that the warp and weft bending stiffness of the hollow integrated sandwich composites increase linearly with the increase of the yarn density. The influence factors of the warp bending stiffness from large to small is as follows: warp, pile and weft. The influence factors of the weft bending stiffness from large to small is as follows: weft, warp and pile. The influence of pile on warp stiffness is greater than that on the weft bending.

EXPERIMENTAL STUDY OF PRE-DAMAGE ECCENTRIC COMPRESSION SHORT COLUMN BY BFRP MIXED REINFORCEMENT

LIU Hua-xin, HAN Ding-jie, YANG Long, WANG Hui-ling

2016, 0(9):  75-80. 

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Based on the eccentric compressive experiment of five pre-damage reinforced concrete (RC) short columns and one contrast specimen with different reinforcement methods, the failure process and ultimate strength of the specimens were described. The stress-strain relationship of steel bars, basalt fiber plastic bar, concrete, basalt fiber plastic sheets and load-deflection of columns was compared and analyzed under the different ways of BFRP reinforcement. The result shows that mixed reinforcement techniques is more effective than merely use near surface mounted (NSM) method due to the mixed effects. The bearing capacity calculation and the simplified design method were proposed for reference on the basis of the test results and the basic assumption.

SAFETY EVALUATION OF GLASS FIBER REINFORCED PLASTIC PIPE CULVERT UNDER OVERLOAD OF VEHICLE

WEI Lian-yu, CHEN Zhao-nan, ZHENG Yan-jun, ZHANG Ji-yan

2016, 0(9):  81-85. 

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For the evaluation of underground glass steel sand inclusion pipe culvert safety, ensure the safety of road traffic and transportation, according to the theoretical analysis as the foundation, field test method using, comprehensive analysis of ground vehicle load and the vertical soil pressure spread to highway of buried steel fiber glass sand inclusion tube of force and pipe culvert by force deformation characteristics, and then regression prediction calculation of values of the mechanical parameters of 1200 kN load model, verifying tube culvert operational safety. Results show that: theoretical calculation and field test are compared and verified the vehicle loads with a diameter of 1.5 and 38 mm thick glass reinforced plastic mortar pipe of safety and reliability, glass steel clip Sand pipe design to provide scientific theory basis.

MODIFICATION ON HYDROLYTIC STABILITY OF POLYURETHANE BY INTRODUCTION OF POLYPROPYLENE GLYCOL

TANG Ling, WEN Liang, WANG Jun

2016, 0(9):  86-90. 

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The polyurethane elastomer is widely used in building materials, transportation products, machinery and medical applications and many other fields, due to its excellent overall performance. In this paper, the effects of HDI content and PPG content on mechanical properties of the polyurethane elastomers and hydrolytic stability were investigated. Infrared spectroscopy showed that, with the reduction and PPG, HDI content of hydrogen bond formation region, absorption peak intensity increased, indicating that the increase of hydrogen bonds in the polyurethane. Polyurethane elastomers hydrolytic stability test results showed that the increase on the content of PPG contributes to better hydrolytic stability and the decrease of HDI.

MOLD DESIGN OF CARBON FIBER COMPOSITE PROPELLER BLADE USED FOR COMPRESSION MOLDING

LIU Hai-xin, XU Jia, ZHU Kun, LI Jia-sheng

2016, 0(9):  91-95. 

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Composite propeller has obvious advantages compared to traditional metal propeller such as resistant corrosion, high specific strength and excellent acoustic damping performance. There are immeasurable application prospects in the aerospace and ship vessel. The design of mold plays a capital and irreplaceable role in variety of factors about composite propeller molding. The physical design exists many challenges for the high production efficiency and precision. The super invar was selected as the material of mold cavity according to the forming factors of carbon fiber composite, such as the expansion coefficient. Three criterions of the propeller blade hub were determined based on the requirement of assembling. Then, the cavity of mold was designed that was pushed out integrally and separated into several parts during the demolding. Finally, the mold of the blade was assembled and the composite propeller blade was fabricated, which prove the correction and feasibility of this design. The difficulties of forming and demolding about the composite are solved.

FEA′S APPLICATION ON SMC EXTERIOR PARTS OF HEAVY TRUCK

WANG Yong-hong

2016, 0(9):  96-101. 

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According to actual case, this paper mainly elaborate finite element analysis function to assist products structure designing in developing for heavy truck′s exterior parts. It explains how to realize decreased truck body′s weight, validate product′s strength and stiffness, analyze part′s intrinsic frequency and improve part′s structure designing to reduce quality defect. Also, SMC material′s physical properties and application at medium and heavy duty truck were introduced.

EFFECT OF ACCELERATED THERMO-OXIDATIVE AGING ON THERMAL PHYSICS PROPERTIES OF GLASS FIBER/PHENOL COMPOSITES

YANG Yang, WANG Xuan, ZHANG Ni, WANG Ying

2016, 0(9):  102-104. 

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Accelerated thermo-oxidative aging on glass fiber/phenol composite materials was performed at 130 ℃, and the thermal physical properties were tested, 30 days, 60 days, 90 days, and 120 days before aging test, respectively. IR spectroscopy and SEM were organized before aging and after aging for 120 days. The results show that the linear thermal expansion coefficients and specific heat capacity decrease, and then increase, and decrease again. Thermal conductivity has no change during the whole aging time. Physical aging exists all the time, and chemistry aging arises after 120 days.