Table of Content

28 June 2018, Volume 0 Issue 6

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BASIC STUDY

CLUSTER ANALYSIS OF AE SIGNALS DURING DAMAGE PROCESS AND COMPRESSIVEDEFORMATION OF COMPOSITE MATERIALS

ZHAO Wen-zheng, LI Min, ZHANG Yan-nan, ZHOU Wei

2018, 0(6):  5-10. 

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The damage evolution of glassfiber composites was studied by using the acoustic emission (AE) and digital image correlation (DIC) method to monitor the compressive test of glass fiber reinforced composites in real time.The characteristic parameters such as peak amplitude, peak frequency, centroid frequency and RA value of AE signals were selected and analyzed by principal component analysis (PCA) and k-means algorithm. The resultsshow that the AE signals of composite compressive damage process can be divided into three clusters. The ranges of characteristic frequency are 0~60 kHz, 100 kHz~150 kHz and 200 kHz~450 kHz, respectively. And three clusters correspond to the three kinds of damage modes such as matrix creaking, fiber/matrix debonding and fiber breakage. The surface displacement field information reflect the deformation and damage characteristics of the composite specimen. The technology combining AE with DIC is effective for monitoring damage evolution of the composite, which can provide the reference for the health monitoring of composite structure.

INFLUENCE OF TOOL-PART INTERACTION ON CURE-INDUCED STRAIN IN COMPOSITE

JIANG Cheng-biao, ZHAN Li-hua, YANG Xiao-bo, LIU Gui-ming

2018, 0(6):  11-15. 

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During the curing process of composite in autoclave, the deformation during demoulding of the workpiece is still an important factor affecting the quality of forming. By using thermocouple and fiber bragg grating sensor, the temperature and strain profile of the composite in autoclave process were monitored in situ, the strain development caused by tool-part interaction were studied, and the influence of resin cure on tool-part interaction were discussed. The results show that, in the initial stage of cure process, the strain is mostly caused by part compaction, resin flow, and gel. Then the tool-part interaction increases along with the resin′s degree of cure grows. The interface of tool and part is translated to sticking condition. As the temperature drops, the detach caused by tool-part interaction leads to stress release in the part, and the stress release would weaken tool-part interaction.

BUCKLING PROPERTIES OF COMPOSITE LAMINATES WITHDIFFERENT DELAMINATION DEFECTS

ZHAO Chen-xi, ZHU He-ming, ZHANG Wen-xing

2018, 0(6):  16-21. 

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Laminates containing delamination were stratified buckling under compression test to study failure modes. In this paper, the buckling failure of both center and edge delamination were tested. Combined with the defected layer position, symmetrical and unsymmetrical delaminated laminate of the two types were compared. On the other hand, the damage behavior of interlayer delamination defects with the cohesive element, and a better agreement with the experimental value of the results were obtained. Further study was done to investigate the effects of delamination size and sample size.

MODE-Ⅰ INTERLAMINAR FRACTURE TOUGHNESS OF CARBON FIBERLAMINATES BY NON-WOVEN INTERLEAF VEILS

WENG Tian-hu, ZU Lei, CAO Dong-feng, PENG Hao-yang

2018, 0(6):  22-27. 

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Compared with the traditional method to improve interlaminar fracture toughness of laminates, non-woven veils interlayer toughening technology is more convenient, more flexible and has the advantage of low cost. In this paper, three non-woven veils, PPS, PEI and PI, were added to the carbon fiber laminates and compared with the non-toughened specimens. The results show that the addition of PPS non-woven veils has the most significant effect on the interlaminar fracture toughness energy release rate of mode-Ⅰ. The fiber bridging effect was observed under mode-Ⅰ loading at the crack tip of the specimens. Microstructure information of laminates was obtained by SEM, and it is proved that the short fiber non-woven veils interlayer forms a three-dimensional interlaced fiber network in the matrix. The debonding and pulling out of the fiber play an important role to hinder the delamination crack. Thus, the interlaminar fracture toughness is improved.

LONG-TERM DEFORMATION BEHAVIOR OF REINFORCED CONCRETE BEAMS STRENGTHENEDWITH CFRP PLATE EXPERIMENTAL RESEARCH AND NUMERICAL SIMULATION

JIANG Shi-yong, CAI Tao, YAO Wei-lai, GONG Hong-wei

2018, 0(6):  28-33. 

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In order to study the long-term deformation performance of RC beams strengthened with CFRP plates in practical engineering and to provide a basis for the judgment of whether the strengthened beam meets the normal service limit state of the structure during the long-term use, and to solve the problems that the long-term test operation is difficult and the time span is too long, the long-term deformation test of reinforced concrete beams strengthened with CFRP sheets is carried out under continuous load. A nonlinear finite element model for calculating long-term deformation of reinforced concrete beams strengthened with CFRP sheets is established. The results of numerical calculation are in good agreement with the experimental results. The long-term deformation of reinforced beams with different thickness of CFRP plates is numerically calculated by using this model. The results show that CFRP plate has little effect on the long-term deformation of reinforced beams, and the total deformation decreases mainly from the restriction of CFRP plates to the instantaneous deformation.

AXIAL SHORTENING ANALYSIS OF CARBON FILAMENT-WOUND PRESSURE CYLINDER WITHTITANIUM ALLOY LINER AFTER HYDROSTATIC TEST

WANG Huan, YU Shan, WANG Te

2018, 0(6):  34-38. 

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Aiming at the axial shortening phenomenon of the carbon filament-wound pressure cylinder with titanium alloy liner after hydrostatic test, the finite element software ANSYS was used to carry out the simulation calculation. Through the analysis of the displacement and strain calculation results of the cylinder body and dome, it is clarified that the fundamental reason for the axial shortening of the cylinder after hydrostatic test is outwardly residual deformation of the dome, and it will be conducive for the cylinder to optimize structural design and improve dimensional stability.

FINITE ELEMENT ANALYSIS OF POST-BUCKLED DELAMINATION OF COMPOSITE LAMINATEWITH PRELIMINARY DEBOND SUBJECTED TO STATIC AND FATIGUE LOADS

DU Hong-yu, XI Xiao-bo, MENG Li-hua, DONG Xiao-li

2018, 0(6):  39-43. 

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A three-dimensional (3D) model of composite laminate was developed, and Virtual Crack Closure Technology (VCCT) was employed to simulate the interaction of laminate debond interface. In order to approach the realistic situation, the initial geometrical imperfection was introduced before analysis. A laminate, embedded with a circle preliminary delamination, was selected as a researh object to predict the post-buckled delimination growth along predefined debond interface. Based on the simulation result from non-lineary postbuckling analysis, low-cycle fatigue simulations were then performed with Paris law as criteria, and the prediction of fatigue delamination onset and propagation was accomplished. According to the FE analysis results, it was deduced that the onset and growth of fatigue delamination were affected by the out-of-plane displacement of thicker component for preliminary debond laminate. Furthermore, compared with axis displacement applied for crack propagation, it was also shown that the axial displacement for the fatigue analysis was much bigger.

APPLICATION RESEARCH

STUDY ON THE PERFORMANCE OF THE MID-TEMPERATURE CURED ADHESIVE FILM USEDFOR BONDING REPAIRING OF CIRRUS SR20 COMPOSITES

XU Yi, HE Qiang

2018, 0(6):  44-47. 

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The differences between the curing process, mechanical properties and temperature of J-12 medium-temperature adhesive film were compared with those of AF-163-2M which was suggested to use in bonding repair of Cirrus SR20 composites. It was found that those two adhesive films have good curing rate between 120 ℃ and 130 ℃, and both of them could maintain good mechanical properties at 150 ℃ and meet the maintenance needs of Cirrus SR20 composites. The single lap shear tensile strength of cured J-12 adhesive film and AF-163-2M film were 30.1 MPa and 27.4 MPa at room temperature, respectively. The shear strength of cured J-12 film is better than that of cured AF-163-2M film. To sum up, the comprehensive performances of J-12 adhesive film are similar to those of AF-163-2M adhesive film, which could be used as an alternative product used in the Cirrus SR20 composites bonding repairing.

RESEARCH ON LARGE DIAMETER HOLE DRILLING METHODOF THE CARBON FIBER REINFORCED PLASTICS

WANG Gong-dong, LI Ying-chi, PENG Tian, LI Nan

2018, 0(6):  48-53. 

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The Carbon Fiber Reinforced Plastics (CFRP) are often processed large-diameter holes in the aerospace industry. In the processing of large-diameter holes, the drilling without pilot hole will cause fiber tear, delamination in hole wall and other serious defects. This paper focuses on the processing principle and axial force of helical milling and prefabricated holes, and estimates the critical thrust force of drilling. In this paper, three methods of helical milling, pre-drilling with a pilot hole and without pilot hole drilling are used to establish the comparative experiment. And thrust force and quality of processing for these three methods are analyzed. The results show that the thrust force of drilling is mainly provided by the chisel edge of the twist drill bit, and thrust force is the main result of delamination. When the thrust force is less than the critical thrust force, the delamination is significantly reduced. The thrust force is reduced by 47% to 61% due to the elimination of the influence of chisel edge.The delamination factor at the exit level is 83% lower than drilling without pilot hole. Therefore, the method of pre-drilling with a pilot hole is outstanding when manufacturing large-diameter holes.

NUMERICAL SIMULATION OF BLAST-RESISTANCE OFAFRP-STRENGTHENED REINFORCED CONCRETE BEAMS

KONG Xiang-qing, QI Xue-jian, GANG Jian-ming, ZHANG Wen-jiao

2018, 0(6):  54-61. 

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Three-dimensional finite element models of reinforced concrete (RC) beams non-strengthened and strengthened with aramid fiber reinforced composite (AFRP) under blast loading were established using nonlinear finite element ANSYS/LS-DYNA software in this paper. The damage distributions and maximum mid-span displacements of non-strengthened and AFRP strengthened RC beams were compared. The numerical results indicates that AFRP can not only change the damage model of the RC beam, but also significantly reduce the deformation of the RC beams. And the maximum mid-span displacement of AFRP-strengthened beam is reduced by about 50.7%. In addition, the effects of the strengthened modes, the strengthened sizes, the AFRP layers and the FRP types of the blast-resistance of reinforced concrete beams were analyzed.

PREPARATION OF Øs50 MILIMETER BASALT FIBER (BF) REINFORCED MODIFIEDPOLYURETHANE COMPOSITES CORE ROD IN COMPOSITE INSULATOR

YANG Hong-jun, WU Zhao-feng, ZOU Yi, YANG Xiao-li

2018, 0(6):  62-65. 

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Basalt fiber (BF) reinforced modified polyurethane composites were prepared using basalt fiber as the reinforcing agent and polyurethane resin as the matrix through pultrusion process. The influences of the content of the fibre and the pulltursion speed on the electrical properties and permeation properties of the basalt fiber (BF) reinforced modified polyurethane composites were systematically studied. And their feasibility was investigated when being used as Ø50 milimeter tonnage composite insulator core in the super/ultra-high line. Under the condition of 300 mm/min of pultrusion speed, 79.7% of fiber content and KH570 as the coupling agent, the PUA/BF showed the most excellent comprehensive performances with good productivity and consistency, which all passed the magenta test. The SEM results show that the PUA had a good adhesion and wetting on the basalt fiber (BF). The electrical property test indicated that the leakage current of composites after being boiled for 100 h were less than 30 μA, which satisfied the insulation requirements of composite insulator core in the super/ultra-high line.

EXPERIMENTAL STUDY ON DYNAMIC MECHANICAL PROPERTIESOF TYPICAL NAVAL SHIP COMPOSITE MATERIALS

YANG Guo-wei, MEI Zhi-yuan, LI Hua-dong, ZHOU Jun

2018, 0(6):  66-72. 

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A typical composite system used in naval ship was selected as the object of study, which include glass fiber (SW220(S2)) and carbon fiber (T700) as the reinforcing fiber, vinyl resin (430LV, 3201) and epoxy resin (350) as the matrix. Through the dynamic mechanical thermal analysis (DMA) test of Fiber Reinforced Polymer (FRP) with different fiber and matrix combination, the damping characteristics of the above materials system were obtained in different temperature and frequency, and the effect of fiber types, ply angle and resin matrix types were analyzed. The results show that the resin matrix is the main factor affecting the damping characteristics. In the three kinds of resin matrix, the tanδ_max(430LV)≈0.88, tanδ_max(3201)≈0.8, and tanδ_{max (350)}≈0.7. At 0 ℃~30 ℃, the loss factor of the resin matrix is about 0.05, and the loss factor of FRP is reduced to about 0.035 because of adding fiber, and the storage modulus is increased by 7 times~8 times. At 0 ℃~30℃, comparing with the composite whose fiber orientation is 0°/90°, the loss factor of composite with ±45° fiber orientation is increased by 0.02~0.03 and the storage modulus is decreased by 6 GPa~8 GPa. At 0 ℃~30 ℃, the loss factor of GFRP is 0.02 higher than that of the CFRP, but the storage modulus is 1/3. When the experimental frequency is increased from 1 Hz to 1000 Hz, the loss factor of FRP is decreased by 45%~70%, but the storage modulus is increased by less than 10%.

STUDY ON THE PREFORMING TECHNOLOGY OF ADVANCEDPULTRUSION FOR HAT STIFFENER

CHEN Yi-chuan, QI Jun-wei, XIAO Jun, WANG Yu

2018, 0(6):  73-77. 

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For hat stiffener′s advanced pultrusion, the preformed deformation process was analyzed. Then, design and manufacturing preformed molds, analysis and formulation of preforming process were carried out to avoid folding and splitting of prepreg inpreforming process which with continuous bending deformation. Experimental verification shows that the stiffener has excellent surface quality. No wrinkles and other defects in the R area, which can meet the requirements of the product, and lay the foundation for the advanced pultrusion manufacturing hat stiffener.

STUDY ON SILICON RUBBER ASSISTED PRESSURIZATION EXTRUSION MOLDINGPROCESS OF RESIN MATRIX COMPOSITE

CHENG Jian-nan, XU Fu-quan, WANG Zhi-gang

2018, 0(6):  78-82. 

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The auxiliary materials are widely used in the forming process of composite materials in order to improve the quality of product and optimize the process. The silicon rubber, which is an auxiliary pressurizing material, is widely used in both curing oven and autoclave moulding process. Silicone rubber has the advantages of high plasticity and heat resistance. During the curing process, it can exert pressure on the product and ensure the surface and internal quality of the product. In this paper, the thermal expansion compression and auxiliary pressure transfer process of silicon rubber are compared, the theoretical analysis for the thermal expansion compression process gap of silicon rubber was carried out, and the realization process of silicon rubber assisted pressurization system is systematically expounded. Then, the relationship between the temperature, the volume of silicon rubber, the clearance of mould and the curing pressure is put forward. This relationship is verified through the design of the tooling and the manufacture of typical resin matrix composite products.

LAYER DESIGN FOR PEV BATTERY BOX OF CARBON FIBER COMPOSITE

DUAN Duan-xiang, ZHAO Xiao-yu

2018, 0(6):  83-88. 

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In order to solve layer design problems of lightweight carbon fiber composite battery box, a battery box of PEV is taken as the research object by using carbon fiber composite material T300/5224. Under the conditions of vertical bumpy, sudden braking and sharp turning, OptiStruct was used to optimize the plies distribution through free size optimization, size optimization and shuffle optimization. The symmetrical arrangement was used to reduce the influences of coupling stiffness, and the manufactured thickness of each ply was 0.125 mm. The best plies order is found to the [±45/0/±45/0/90/0/90/0/±45/0/90/0/90/0/±45/90/±45/90/±45/90/±45/90]_s. Under the premise of meeting the performance demands, component strength check is performed so that the stiffness of battery box is improved and its weight is greatly reduced. Compared with the same steel battery box, the weight is reduced by 65.89%, the advantages of high specific strength and large specific modulus of the carbon fiber composite material are fully exerted, and the effect of lightweight is obvious.

RESEARCH AND DESIGN OF MULTI-STATION FIBER WINDING MACHINE

XU Dong-liang, WANG Cheng, XU Zheng, ZHU Jiong-tao

2018, 0(6):  89-93. 

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Through the study of the present fiber winding machine and the analysis of its working principle and structural characteristics, many problems such as discontinuity and low efficiency in the fiber production process are found in the current operating system. Then the fiber winding machine is improved with a better work-flow. The molding structure of the multi-station fiber winding machine is designed, and its 3D model which is introduced into Workbench to perform a simulation analysis is constructed with Solidworks. This paper optimizes the original fiber winding machine with technical measures including Gantry layout structure, loading-and-unloading mechanism of mandrels with manipulators, power-split output device of the head-stock and an alternative working mode with two mandrels. Therefore, the integrity of the structure is guaranteed. The labor cost can be saved and the automation level of the fiber winding machine is improved, allowing the winding car to realize continuous winding production at the maximum level with the help of the manipulator and consequently significantly enhanced productivity. At the same time, the response surface optimization of the beam is adopted to reduce the weight of the beam and save the cost. On this basis,the beam of fiber winding machine is statistically analyzed to determine whether the design is reasonable.

CURING KINETICS OF EPOXY RESIN FOR WIND-POWER BLADES USING ISOTHERMAL DSC

XIE Zhan-jun, YANG Xi, WANG Ji-hui

2018, 0(6):  94-98. 

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In order to study the curing reaction process of epoxy resin for wind-power blades, isothermal DSC was used to measure heat flow curve of resin system at 60 ℃, 70 ℃, 80 ℃, and three kinds of basic models fitted by Matlab function of n-order dynamics model, the autocatalytic model and Kamal model are analyzed. It turns out that the resin system conforms to the Kamal model. By comparing calculation results with the experimental data, it is found that the calculation results are always higher than the experimental data. Therefore, the effect of diffusion effect must be considered. When we compare the two diffusion control Kamal models, we found that Chern fitting results are better than another. Finally, the curing kinetics equation was obtained by using the correctional Kamal model.

STUDY ON THE EFFECT OF MECHANICAL PERFORMANCE FOR STITCHEDCOMPOSITES BY DIFFERENT MEANS OF STITCHING

YANG Long-ying

2018, 0(6):  99-103. 

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The sticthing technique as the monolithic molding can observably improve the shear property and resisting concussion damage of sticthed composites. There are different ways of stitching. The popular means of stitching are locking-type stitching, chained stitching and Truffing. Different stitching way has different effects on shear property, compressed property, tensile property and bending property of stitched composites. In this article, the effects on tensile property, compressed property and bending property of stitched composites by three different stitching ways were studied and compared.