COMPOSITES SCIENCE AND ENGINEERING

MECHANICAL PROPERTIES AND PHASE SEPARATION OF EPOXY RESIN TOUGHENED BY POLYETHER SULFONE

JIA Wen-pin, ZHOU Jin-li, YU Mu-huo, HAN Ke-qing

2017, 0(3): 5-10.

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Epoxy resin had been widely used in light industry, construction, machinery, aerospace, etc. But after curing, there were some disadvantages such as high crosslink density, excessive internal stress, crisp, poor fatigue resistance and impact resistance. Those shortcomings limite its application in a number of high-tech fields. In this paper, polyether sulfone (PES) was used to toughen epoxy resin. Different proportions of PES/E51 system were prepared by hot melt. Hot stage microscope, SEM and mechanical tests were applied to investigate morphologies and structures of E51 modified by PES, and also to evaluate fracture surface, phase separation, strength and toughness of castings. The results show that PES can dissolve in the E51 by hot melt in the absence of solvent. At PES content of 15wt%, the tensile strength and impact strength of castings increased by 130% and 200%. Phase separation occurred when the castings were cured. PES formed a semi-continuous or continuous phase structure in the E51. When PES was 15wt%, bicontinuous structure appeared in the castings.

FINITE ELEMENT ANALYSIS FOR EFFECTIVE ELECTRO-ELASTIC PROPERTIES OF THREE-DIMENSIONAL BRAIDED PIEZOELECTRIC CERAMIC MATRIX COMPOSITES

MA Xiao, WEI Gao-feng

2017, 0(3): 11-16.

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Based on the microstructure of three-dimensional (3-D) braided perform, the electro-elastic coupling field volume average theory and finite element method, the effective electro-elastic properties of 3-D braided piezoelectric ceramic matrix composites are studied, and a finite element model of 3-D braided piezoelectric ceramic matrix composites in displacement-electric coupling field is established. By applying the displacement load and electric load boundary conditions to the representative volume element of the composites, the effective elastic coefficients, piezoelectric coefficients and dielectric coefficients of 3-D braided piezoelectric ceramic matrix composites with different fiber volume fraction are predicted. Numerical results illustrate that 3-D braided piezoelectric ceramic matrix composites can improve the overall mechanical properties of the piezoelectric ceramic significantly, and the good electrical properties are maintained.

STUDY ON THE POST IMPACT CURVED BEAM STRENGTH AND FAILURE MODE OF CARBON/EPOXY LAMINATES

MA Li-ting, CHEN Xin-wen, WANG Xiang, GUO Guang-ping

2017, 0(3): 17-20.

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In this paper, the curved beam strength and strength-after-impact characteristics of carbon/epoxy laminated curved beams were studied experimentally using four-point bending test and low velocity impact. First, the post impact damage characterizations of the laminated curved beams with different radii were analyzed based on ultrasonic C-scan images. Second, the effect of impact damage on both the failure strength and the maximum interlaminar radial stresses of the laminated curved beams were investigated. Finally, the full field displacement distributions of the laminated curved beams were obtained using Digital Speckle Correlation Method (DSCM). Experimental results play a significant role for strength evaluating of laminated curved beams with and without impact damage.

EXPERIMENTAL STUDY OF FATIGUE PERFORMANCE FOR FRPM PIPE BURIED IN HIGHWAY

SHI Hua-wang, WEI Lian-yu, CHEN Zhao-nan, ZHANG Guo-pan

2017, 0(3): 21-24.

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Buried FRPM pipe culvert is a new kind of highway culvert type. Stress simulation of pipe culvert was carried out with indoor fatigue test, test results show that the strength and stiffness of FRPM pipe culvert was not significantly reduced under 2.5 million times of fatigue load, and layered peeling and brittle fracture phenomena do not appear, which could completely meet the requirement of the highway culvert application. This paper puts forward the fatigue residual stiffness in according with the highway standard, and the prediction formula of fatigue life calculation value is good agreement with the test results. This work provides reliable basis of the analysis for FRPM pipe in highway culvert of durability design.

LONG-TERM LIFE PREDICTION OF COMPOSITE MATERIALS BASED ON ACCELERATED TESTING METHODOLOGY

KANG Jun, CHEN Yong-qiang, CHEN Shang, MU Xing-ke

2017, 0(3): 25-30.

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A long-term fatigue life and failure process analysis methods were proposed based on micro-mechanics of failure (MMF), accelerated testing methodology (ATM) and progressive damage analysis (PDA) combined method. MMF theory was modified by distinguishing matrix tensile and compressive failure. The calculation process of MMF/ATM/PDA analysis method in finite element analysis was established. The implementation procedure in ABAQUS using UMAT was described in detail. The time and temperature dependent MMF/ATM critical parameters of composite materials were determined by measuring the static and fatigue life at different temperatures in the longitudinal and transverse, tension and compression directions of unidirectional CFRP. Long-term life of open-hole composite laminates and the damage process of fiber and matrix were predicted based on MMF/ATM/PDA combined method. The results show that the test results and the prediction results are in good agreement, demonstrating the validity of this method.

STUDY ON INTERFACIAL PROPERTIES OF CF/GF HYBRID COMPOSITES BASED ON FBG SENSOR

ZHU Qi-feng, ZHANG Sheng, WANG Ji-hui, LI Shu-xin (1.College of Science, Wuhan University of Technology, Wuhan 430070, China; 2.School of Materials Science and Technology, Wuhan University of Technology, Wuhan 430070, China)

2017, 0(3): 31-35.

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In this paper, the FBG sensor was used to study the interfacial properties of CF/GF hybrid composites during and after the curing process. In order to investigate the properties of hybrid composites, the strain changes in CF/CF layer and GF/GF layer are also monitored. The results show that when no external force, good linear relationship between strain and temperature existed in GF/FG, GF/CF and CF/CF layers, and the order of thermal expansion coefficient is: GF/GF layer>GF/CF layer>CF/CF layer. FBG sensor for the monitoring of CF/GF hybrid composite heat swelling values for the coefficient of the transition temperature and the matrix resin (79.09 ℃) coincide. CF/GF hybrid composites in 20~120 ℃ heating and cooling process do not show destruction of the interface.

EXPERIMENTAL STUDY OF CFRP-PCPs COMPOSITE REINFORCED CONCRETE ECCENTRIC COMPRESSION COLUMNS

ZHONG Qing-yu, ZHANG Peng, CHEN Hua, KANG Kan

2017, 0(3): 36-43.

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In order to study the mechanical performance of CFRP-PCPs composite reinforced concrete eccentric compression columns, fifteen specimens are designed for eccentric loading tests. Four variable factors such as eccentricity, ratio of composite reinforcement, tension control stress of CFRP bars and general reinforcement ratio are taken into consideration. According to the test, the stress distribution, cracking load, ultimate bearing capacity, load-strain curve and other important data are obtained, and the influence of four variable factors on cracking load and the ultimate capacity of CFRP-PCPs composite reinforced concrete eccentric compression columns is analyzed. The results show that the damage process and failure mode of a CFRP-PCPs composite reinforced concrete eccentric compression column are similar to those occurred in an ordinary reinforced concrete eccentric compression column, where the cracking load and the limited supporting capacity decreased gradually with the increase of eccentricity. The cracking load and the limited supporting capacity of CFRP-PCPs composite reinforced concrete columns can be improved effectively by increasing the stress of tension control, increasing the ratio of CFRP-PCPs composite reinforcement and ordinary steel bars.

PREPARATION AND FLEXURAL ANALYSIS OF BALSA WOOD CORE SANDWICH COMPOSITE BRIDGE DECK REINFORCED BY LATTICE WEBS

ZOU Fang, FANG Hai, QI Yu-jun, LIU Wei-qing

2017, 0(3): 44-48.

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This study proposed a new sandwich composite bridge deck reinforced by lattice webs to replace the used bridge deck because of its high bending stiffness, high strength to weight ratios and corrosion resistance, etc. The surface layers, lattice web and core material are integrally formed in the mould at one time through vacuum infusion process, and lattice web integrates surface layers and core material into a whole organically, which thus greatly improve the performance of the new bridge deck. The flexural analysis of the panel is carried out by using the theory of composite sandwich structure. The results show that the stiffness of the new bridge deck can be satisfied. Both normal stress of the fiber surface and the shear stress of the wood core can meet the strength requirements, and the weight of the bridge panel is greatly reduced by 57%.

EXPERIMENTAL AND NUMERICAL INVESTIGATION INTO THE COMPRESSION CHARACTERISTICS OF ALUMINUM HONEYCOMB PANEL FILLED WITH EPP

LIU Qiang, CHEN Hang

2017, 0(3): 49-52.

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The paper investigates the compression characteristics and failure process of aluminum honeycomb panel filled with EPP foam (Expanded polypropylene) by experiments and numerical simulations. The test results show that the peak load, mean crushing strength and absorbed energy of the filled aluminum honeycomb panel increased by 1.9%~43.33%, 46.59%~179.53% and 46.26%~179.04%, respectively, compared to the bare aluminum honeycomb panel. By comparing to the sum of bare panel and bare EPP foam, the mean crushing strength and absorbed energy of EPP foam filled aluminum honeycomb panel are increased by 2%~23.5% and 3.9%~23.3%. In addition, the numerical results using the Ls-dyna software show the predicted failure mode and load-displacement curves agree well with the exprimental results, indicating that the EPP foam filling could resist the deformation of the honeycomb wall. This study indicates that aluminum honeycomb panel filled with EPP foam structure could effectively improve axial compression properties of bare aluminum honeycomb structure.

MECHANICAL PROPERTIES OF 3D FABRIC COMPOSITES MANUFACTURED BY MICROWAVE CURING

YUAN Tie-jun, ZHOU Lai-shui, ZHENG Wei-feng, AN Lu-ling

2017, 0(3): 53-59.

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Aiming at improving the curing uniformity of microwave curing process of 3D spacer fabric composites, two different methods were proposed, i.e., additional mould for external heat-conducting and microwave absorber for internal heat-conducting. Compression test, shear test and short-beam flexural test were utilized to study the effect of material and thickness of addition mould and the kind and content of microwave absorber on the mechanical properties of spacer fabric composites. The experimental results indicate that the failure modes of compression includes the instability and crushing of core, and the failure modes of shear test are the shear failure of core and interfacial debonding, while the failure mode of short-beam flexure is the buckling after interfacial debonding. Compared with the specimens with no additional mould, the mould of AlN and Al₂O₃ could both improve the mechanical properties of the 3D spacer fabric composites, and the reinforcing effect of AlN mould is more significant. However, increasing the thickness of AlN mould is adverse to the mechanical properties. When the thickness is increased from 0.5mm to 1.5mm, the compression, shear and core shear strength were all decreased. The addition of microwave absorber could improve the mechanical properties. The shear and core shear strength increased with the increasing of graphite′s content, while the compressive strength first increased then decreased. The change of Fe₃O₄′s content didn′t affect the mechanical properties significantly.

DESIGN AND EXPERIMENTAL RESEARCH OF AUTOMATED FIBER PLACEMENT EQUIPMENT

CAO Zhong-liang, HAN Zhen-yu, FU Hong-ya

2017, 0(3): 60-63.

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Automated fiber placement is a very important composite automation forming method. This paper proposed a new general mechanism and control system solutions of fiber placement machine driven by an air cylinder and a pressure roller cutter as actuator to achieve fiber cutting and clamping. A new type of tension control system with linear displacement sensor as the feedback element is constructed. Meanwhile, an open control system based on the main stream of industrial control computer (IPC) and motion controller (UMAC) is designed. Finally, the related placement experiments are carried out. The operation results show that the motion of each axis is in good condition, the control system is stable, the design of each module is reasonable and the expected effect is achieved.

EXPERIMENTAL RESEARCH ON THE FEASIBILITY OF THE DRILLING OF CFRP ROTARY CUTTING TOOL

NIE Xiao-ju, SUN Hui-lai, LIU Xue-mei, ZHAO Fang-fang

2017, 0(3): 64-69.

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CFRP is a typical material which is difficult to machine, especially for drilling holes with large diameter d≥8 mm. In this paper, a new drill cutting of CFRP rotary cutting tool was designed, based on drilling experiment of rotary cutting tool, twist drill and brazed diamond core drill under different spindle speed and feed rate. Then MATLAB is used to fit the empirical formula of three kinds of tools, and the influence of axial force speed and feed speed under different contrast on three kinds of tools is analyzed. The results show that the rotary cutting tool has best effect on drilling CFRP hole.

INFLUENCE OF RADIUS FILLER FILLING AMOUNT ON QUALITY OF T-SHAPED STIFFENERS

ZOU Jing, ZHAN Li-hua, ZHANG Yong-an, ZENG Li-ran

2017, 0(3): 70-75.

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Stiffened structure is widely used in large composite loading-carrying structure. Radius filler must be used as a kind of filling material in triangle gap of these structures. The filling effect of radius filler can significantly affect the quality of cured structure. To optimize filling amount formula of radius filler and improve the quality of loading-carrying structure, different filling volume of radius filler were filled in three kind of radius of concave corner of T-shaped stiffeners. To investigate the filling volume of radius filler on quality of R region of T-shaped stiffeners, the microstructure of R region were characterized by optical digital microscope. The results show that when the volume of radius filler is far less than the theory filling volume, disperse pores will be easily produced in the interface of radius filler and web plate, and delamination will happen in the interface of skin and radius filler. When the volume of radius filler is larger than the theoretical filling volume, delamination and pores will be significantly improved, but the huge volume of radius filler can cause fiber fold and sinking in the skin. According to the experimental results, the correction coefficient of filling amount is 0.9. Finally, the filling formula of radius filler is determined as V= 0.9(R+nh)2(2-π/2)L.

EFFECT OF MATRIX′S PROPERTIES ON THE MECHANICAL PROPERTIES OF ARAMID FIBER Ⅲ COMPOSITES

LI Ming-ming, YAN Wen-cong, WANG Xiao-jie

2017, 0(3): 76-80.

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Three kinds of epoxy resin were designed and the effect of matrix′s properties on the mechanical properties of aramid fiber Ⅲ composites were studied. Acoustic emission characteristic parameters of interlaminar shear failure process of composites with different toughness were compared. The results show that the toughness of the three kinds of resin matrix was R1>R2>R3. The interlaminar shear strength (ILSS) of aramid fiber Ⅲ composites were 49 MPa, 44.8 MPa, and 40.1 MPa. ILSS is increased with the increase of the toughness of the resin matrix. Acoustic emission experiments show that with the increase of the matrix′s toughness, the sharp damage of the composites was delayed, and the number of acoustic emission events was significantly reduced.

STUDY ON THE PROPERTIES OF A BISMALEIMIDE RESIN WITH LOW VISCOSITY AND ITS COMPOSITE

LI Ya-long , HE Si-min, WEN You-yi, LUO Ji

2017, 0(3): 81-85.

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The properties of a bismaleimide resin QY8911-Ⅳ with low viscosity for resin transfer molding (RTM) were reported in this work. Its viscosity characteristic and curing characteristic were studied firstly. The heat resistance, mechanical properties and water absorption of the resin cast cured at different post-curing temperatures were investigated and compared. The results suggest that this resin system show good performance including low viscosity (200 mPa·s at 80 ℃), low curing shrinkage (1%), good heat resistance (a T_g of 260 ℃), good mechanical property (flexural strength is 170 MPa and impact strength is 20 kJ/m²) and low water absorption (0.39%). The appropriate injection process and curing process were selected to prepare the carbon fiber reinforced composites by RTM, and the mechanical properties of the composites were tested. The flexural modulus is 754 MPa and the impact strength is 110.9 kJ/m².

EFFECTS OF DIFFERENT JET FLOW TIME ON THE INTERLAMINAR SHEAR STRENGTH (ILSS) OF GLASS FIBER REINFORCED RESIN COMPOSITES

HU Li-ming, YANG Jiao-ping, DANG Hai-yan, ZHANG Zhi-yong

2017, 0(3): 86-89.

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This paper investigated the effects of different jet flow time on the inter-laminar shear strength (ILSS) of glass fiber cloth reinforced polymer (GFRP) composites. The results indicate that with the increase of the jet flow ablating time, the quantity of carbonized glass fiber cloth laminate increases linearly. The ILSS of remained GFRP composites decrease a bit, which indicates that the carbonized laminates on the surface of composite have little influence on the ILSS of remained deep-layer GERP composites. However, fracture model of glass fiber turn from tough to brittle. The results provide important data to the application of glass fiber cloth reinforced composites in the jet flow conditions.

STUDY ON THE PREPARATION AND CURING PROCESS OF OoA PREPREGS

CHEN Shuai-jin, XU Chen, WU Guo-qing, LI Guo-ming

2017, 0(3): 90-95.

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In this study, Out of Autoclave (OoA) prepregs were prepared by single film impregnation process. Prepreg impregnation levels were measured using three methods. Laminate porosity and mechanical properties were tested to compare the prepregs with various impregnation levels. The preferred impregnation level of 22% was identified to offer the best overall performance for the selected prepreg system. Processing parameters for CFRP manufacturing are crucial in OoA process. Laminates with various processing parameters were evaluated using NDT, porosity, microstructure and mechanical properties. A cure cycle of 2 hours at 120 ℃ was selected as the most suitable key process parameters for the selected prepreg system. Overall thermal and mechanical performance comparison was carried out for the laminates manufactured via OoA and autoclave processes. For the selected OoA prepreg system, the thermal and mechanical performance of the laminates via OoA process are equivalent to those via autoclave process.

ADVANCE OF IMPROVEMENT RESEARCH OF GLASS FIBER REINFORCED POLYAMIDE 66

LI Yue-wen

2017, 0(3): 96-100.

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Advance of improvement research on toughening, flame retardancy, solvent resistance, abrasion resistance, interphase property, compounding and preparation technology of glass fiber (GF) reinforced polyamide 66 (PA66) was expounded. The toughness of PA66/GF composites could be improved via adding toughner, but the compatibility between toughner and PA66 had to be increased. Microencapsulation red phosphorus and P-N type flame retardant had fine inflaming retarding effect for GF/PA66 composites. Surface covering treatment of red phosphorus was necessary, because of bad compatibility between it and PA66 and its amaranth. Solvent resistance of the composites could be enhanced via adding low polarity resin and using anti-hydrolysis GF. Friction and wear resistance of the composites was improved when they were mixed with self lubricating resin and wear resistant filler. The interfacial structure between GF and PA66 could be improved by coupling or infiltration treatment of GF. Its mechanical property was enhanced when suitable other fillers were added into the composites, as a result of synergistic effect between GF and the fillers. After appropriate technological method of composite was selected, and the process parameters were optimized, the retention length of GF increased, resulting of improvement of mechanical property of the composites.

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