Table of Content

28 October 2018, Volume 0 Issue 10

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BASIC STUDY

EXPERIMENTAL STUDY ON ANCHORAGE PRESTRESSED TENSION OF CFRP CABLE SUSPENDOME

ZHANG Xiang-yu, LIU Rong-gui, XIE Fu-zhe, XIE Gui-hua

2018, 0(10):  5-11. 

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Based on the formula of bearing capacity of cohesion force model, the CFRP cable bondage anchorage was optimized. The test of anchorage performance of the test piece was carried out. It was applied to the CFRP cable string dome structure, and the anchorage performance was verified and analyzed. The stress distribution of interfacial stress during the loading of radial cables. The results show that there are five stages in the interface stress distribution in the anchorage zone, and the free end stress is the largest in all stages. Before reaching the critical stage, the stress of the central cable is less than the stress at the loading end. After the critical stage, the stress in the middle is greater than the stress at the loading end. The stress at the free end of the cable is always higher than that of other parts in each stage.

THE TRAJECTORY PLANNING ALGORITHM OF FIBER PLACEMENT FOR SMALL AIRCRAFT TAIL PARTS

ZHANG Yi-zhuo, HAN Miao-ling, ZHAO Yao-xu, CAO Zhong-liang

2018, 0(10):  12-19. 

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For the complex conical shell parts, the traditional trajectory planning algorithm named isometric offset algorithm is difficult to make the trajectory angle unchangeable. Also, the isometric offset algorithm makes a serious impact on the laying area in the actual laying process. In order to overcome this problem, this paper puts forward the complete same-angles algorithm for the 0° and ±45° trajectory planning and the variable-angles algorithm for the 90° trajectory planning. The complete same-angles algorithm not only makes the trajectory angle of the points on the every trajectory constant, but also causes the deviation between the actual placement angle and the designed fiber ply angle. The variable-angles algorithm can ensure that the trajectory has no gaps and no overlapping in the laying progress and every filament has no resend and clipping process except at the beginning or ending of laying progress. And then, the center line of every filament will be generated by the use of the isometric offset algorithm. After the boundary treatment and the calculation of filament number, the special points like the drop points and the resend points will be obtained. What′s more, the terminal path will be obtained by connecting every paths by using SLERP. Besides, the software is developed based on the V5 Automation technology of CATIA and Visual Studio 2015. At last, the algorithm has been successfully used to plan the trajectory of the small aircraft tail by using the software, which proves that the algorithm is reasonable and feasible.

TENSILE DEFORMATION AND DAMAGE ACOUSTIC EMISSION MONITORING OF CARBON/ARAMID HYBRID WOVEN COMPOSITES

YIN Han-fei, ZHANG Peng-fei, DING Zhen-jun, ZHOU Wei

2018, 0(10):  20-25. 

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Carbon/aramid hybrid fiber woven fabrics were used to prepare composite laminates by different layering methods. In order to study the damage evolution of carbon/aramid hybrid woven composites during tensile process, tensile loading tests of the composites were monitored by using acoustic emission (AE) and digital image correlation (DIC) complementary techniques. According to AE signals and the surface displacement fields of the composites during the tensile loading, AE response characterizations and variation of surface deformation fields of carbon/aramid hybrid woven composites were analyzed. The results show that the amplitude attenuation in the carbon fiber direction is lower than that in the aramid fiber of the composites. In the case of type-A specimens, when the specimens are loaded in carbon fiber and aramid fiber direction, the highest tensile strength and toughness can be obtained, respectively. The tensile strength of type-B composite specimens is higher than that of type-A in the direction of aramid fiber, while the toughness is better than that of type-A in the direction of carbon fiber. The deformation and damage characteristics of composite laminates are clearly reflected by surface deformation fields. AE and DIC complementary technologies provide an effective method for nondestructive testing, damage assessment and health monitoring of the composites.

STUDY ON THE LAMB PROPAGATION CHARACTERISTICS IN THE DELAMINATION DAMAGE AREA OF CFRP-STEEL BONDING INTERFACE

HE Chao-chao, LIU Zhi-ping, SHEN Yong, CHEN Shan

2018, 0(10):  26-32. 

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For the bonding interface delamination damage of CFRP-steel plate, the propagation and reflection process of Lamb wave in the delamination area is studied by displacement cloud of simulation. The influence of the delamination length on the damage echo is analyzed, and then the test is designed to verify the simulation conclusion. The displacement curve of the upper and lower interface nodes of delamination is extracted by simulation, and the cause of the Lamb wave′s high order harmonic is analyzed. The influence of the depth position, length of delamination and excitation amplitude on the nonlinear characteristics is studied. The research results shows that Lamb wave is more sensitive to the exit end of delamination, and in the region of thin side of delamination area the standing wave is generated. The reflection coefficient and the nonlinear coefficient of the wave all show the trend of vibration with the increase of the delamination length. When the delamination locates near the surface or the symmetrical center of the plate thick, the nonlinear characteristics are not obvious. The research work of this paper provides an important reference for the detection and application of Lamb wave aiming at the delamination damage of CFRP-steel bonding interface.

EXPERIMENTAL STUDY ON COMPRESSIVE BEHAVIOR OF A NOVEL GFRP-COLD FORMED STEEL COMPOSITE SANDWICH STRUCTURE

ZHANG Fu-bin, XU Jing, LIU Wei-qing, FANG Hai

2018, 0(10):  33-38. 

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The GFRP-Cold Formed Steel composite sandwich structure (GCS structure) is composed of glass fiber reinforced polymer (GFRP) skins, light-weight PU foam core and cold formed steel (profiled steel sheet). The profiled steel sheet was embedded into the PU foam core to improve its Z-direction compression stiffness and strength. Compression tests were carried out to explore the compressive behavior of the GCS structures. By comparing to the conventional sandwich structures, the effects of the different parameters on the stiffness, ultimate compressive strength, failure modes and the energy absorption capacity of the novel sandwich structures were obtained. Test results indicated that the initial compressive stiffness and compressive strength were increased by 216.3% and 115.8%, compared to the conventional sandwich structures, respectively. But the energy absorption rate showed a decrease of 20.8%. The GCS structure shows the highest strength and stiffness-to-weight ratio. The stainless steel core rivet has little influence on the compressive performance of the GCS structure.

THE THERMAL STRESS OF THICK-SECTIONED RESIN MATRIX COMPOSITES PATCHES AT DIFFERENT REPAIRING PARAMETERS

CHEN Shu-xian, TIAN Qiu-shi, BAO Zheng-tao, GU Wei

2018, 0(10):  39-46. 

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The finite element method is used to simulate the varying process of temperature, curing degree and thermal stress in the co-curing process of thick-sectioned resin matrix composite patch with mother board, and the correctness of the numerical methodology is verified by comparison with the experimental results. The effects of scarf slope, fiber orientation and fiber layup order on distributions of temperature and thermal stress field in patch at different stages during curing process are studied. The results show that the slope of scarf has a great influence on the thermal stress in the patch during the heating and isothermal stages, and has little effect on the thermal stress of the patch at the end of cooling. Increasing the scarf slope can reduce the thermal stress of the patch during the heating and isothermal stages, and can also avoid large thermal stress concentration. During the whole curing process, the residual thermal stress in the patches is the smallest with 0° fiber orientation while the value is the largest with 90° fiber orientation, and there is a strong stress concentration at the center of the top of the patches corresponding to the latter one. In order to reduce the residual thermal stress, the orientation of the fibers should be parallel to the contact surface of the patch with the motherboard, i.e. perpendicular to the direction constrained by the motherboard. Symmetric ply patches have less thermal stress throughout the curing process, while thermal stresses are greater in the patches with sequential spacer plies and anti-symmetric plies. Symmetry ply design principles should be used for resin matrix composites patch plies.

DISPERSION CURVES OF LAMB WAVE IN ORTHOTROPIC PLATE

CAI Ying-long, TIE ying, CHEN Jiang-yi

2018, 0(10):  47-50. 

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The dispersion curves of Lamb wave in orthotropic plate is solved in this paper. By virtue of wave equation of guided wave in orthotropic plate, the analytical expressions of displacement components in plate is obtained based on the solution of eigenvalue problems. Taking traction free conditions on the top and bottom surface of plate into account, the dispersion equation of Lamb in orthotropic plate is derived. Based on this dispersion equation, the range of wave numbers in different phase velocities is analyzed. Taking the dispersion equation of symmetry mode as an example, the reasonable search interval for the root of the dispersion equation is determined, and the bisection method is used to calculate the dispersion equation. Two kinds of plate, isotropic and orthotropic, are taken as numerical examples. And their dispersion curves are plotted, which are significantly different from those in isotropic plate.

EFFECT OF SURFACE TOPOGRAPHY ON THE ADHESIVE SHEAR STRENGTH FOR GFRP AND ALUMINUM ALLOY BONDING

GUO Feng, SUN Shi-yong, YANG Rui, LI Pan

2018, 0(10):  51-55. 

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The bonding interface is the weakest place in the bonding of glass fiber reinforced plastic (GFRP)and metal plate. In order to study the effect of metal surface topography on the bonding strength of GFRP and metal plate, different aluminum alloy surface topography was obtained by grinding with different types of sand paper. After grinding, the aluminum alloy was used to prepare single lap joint of GFRP and aluminum alloy by co-curing process. The shear test was carried out to study the relationship between roughness parameters R_c (mean height of profile elements), R_sm (mean width of the profile elements), R_lo (developed length) and shear strength. On this basis, the change trend of shear strength with the ratio of R_sm to R_c is studied. The results show that too rough surface is not conducive to the bonding of GFRP and aluminum alloy. When the ratio of R_sm to R_c is in a reasonable range, the adhesive can fully fill the surface profile of aluminum alloy and R_lo is the main influencing factor of bonding strength.

OPTIMIZATION DESIGN AND ANALYSIS OF COMPOSITE AIRFRAME OF A CERTAIN TETHERED HOVERING UNMANNED AERIAL VEHICLE

FENG Kun-cheng, GAO Jiu-zhou

2018, 0(10):  56-61. 

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Tethered hovering unmanned aerial vehicle is a long time hovering platform which is secured by a cable serving as power supply and wideband data link. The purpose of tethered power supply method is to resolve the short time endurance problem of tradition UAV. Hovering platform is now applied in surveillance for military, public security, fire control etc. For increasing the hovering height of the UAV, the weight of structures has to be declined in the preliminary design program. Consequently, composite materials are always used in the airframe structure. Composite material has been widely used in UAV structures because of the various excellent performances, such as strength and stiffness ratio, as well as the performances in the process of manufacturing. Meanwhile, composite laminate has excellent designable property in the process of manufacturing. So, it is widely used among all the types of composite materials. In this paper, the airframe structure of a certain tethered hovering unmanned aerial vehicle is selected as the research objective, and the finite element model of a composite airframe is created. Then the mass of the structure is chosen as the objective function, the failure index are chosen as constraints, and the composite airframe structure is optimized by using the engineer software, where the results should meet the demand of strength and stiffness during the optimization. The final optimization results show that the ratio and thickness of plies of the composite material has been redesigned. Compared with the previous designing scheme, the weight of airframe is obviously reduced after the free-sizing optimization, which could achieve the objective of optimization.

SENSING ABILITY OF GRAPHENE AND CARBON NANOTUBES MODIFIED EPOXY RESIN

TIAN Chang-jin, LU Qing, XU Xi-xi, SUN Ren-juan

2018, 0(10):  62-69. 

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This study analyzed the sensing ability of carbon nanotubes and grapheme modified epoxy resin. The mass fraction of carbon nanotubes (CNTs) was fixed at 0.3%. The resistivity and sensitivity of the composites with different graphene content were obtained by changing the content of C and M graphene. The results show that the threshold range of C-graphene composites is 11%~15%. When the content of C-graphene is 11%, the sample has the best pressure-sensitivity and the least noise. When the dosage is 15%, the best tensile property is obtained. And, when the stress is 1.25 MPa, the maximum rate of resistance change is 0.89%. The threshold range for M-grade graphene nanotubes composites is 3%~6%. When the content of M graphene is 3%, the maximum rate of resistance change of pressure-sensitive specimen is 3.21%, but the phenomenon of hysteresis is serious. When the content of M-graphene is 5%, the tensile sensitivity is the best and the noise is the least. Under the same dispersion process, M-grade graphene is superior to C grade graphene.

OPTIMIZATION OF THE LAMINATED COMPOSITE PLATE BASED ON DIFFERENTIAL EVOLUTION ALGORITHM

MA Sen, ZHAO Qi-lin

2018, 0(10):  70-75. 

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The minimum weight design of the laminated composite plate with the number of plies and ply orientations considered as design variables is performed. Analyses of the characteristics of the optimization problem are carried out. Focusing on the characteristics of the optimization problem, an improved evolutionary algorithm is proposed. In the improved evolutionary algorithm, the search interval shrinks with the evolutionary process, and individuals in the population gather around the global optimal point gradually. Test examples show that the proposed algorithm has excellent global search ability.

APPLICATION RESEARCH

PERFORMANCE COMPARISON OF TYPICAL WARP KNITTED MESHES FOR COMPOSITE REINFORCEMENT

SHAO Hui-qi, LI Jian-na, SHAO Guang-wei, CHEN Nan-liang

2018, 0(10):  76-81. 

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The warp knitted fabrics have been widely used as structural reinforcement of rigid, semi-rigid and flexible composite materials. In order to meet the performance requirements of different engineering applications, four typical warp knitted meshes of rectangular, square, circular and diamond were designed and developed. Their thickness, weight density, porosity, bursting, uniaxial and biaxial tensile properties were tested and compared in this research. The results show that the thickness of the diamond warp knitted mesh is the smallest and its porosity is the highest (77.9%). The square warp knitted mesh is tested to be softest with the smallest bending stiffness. The bursting strength of these four mesh fabrics does not differ significantly. The biaxial tensile behavior of warp knitted meshes tends to be more isotropic, in which the anisotropy level of diamond warp knitted mesh is the lowest (λ=0.046), while the rectangular one is the most anisotropic (λ=0.303).

RESEARCH ABOUT THE EFFECT OF ICING STIFFNESS AND MASS ON THE MODE OF LARGE WIND TURBINE BLADE

LI Zheng-nong, ZHU Sheng-bing, PAN Yue-yue

2018, 0(10):  82-89. 

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In order to prevent from catastrophic destruction when the iced blade is disturbed by the flow, the dynamic characteristics of the blade with or without icing are analyzed by using ANSYS to model a 46.5 m blade. In specific, first two-order flap-wise and lag-wise modes and first-order torsional mode are calculated, which are under five kinds of working conditions of the blade including ice-free, uniform or non-uniform icing conditions influenced only by ice mass or by mass and its stiffness together. And then they are comparatively modal analyzed to understand how ice mass and stiffness affect dynamic characteristics of the blade through MAC. The results show that ice can significantly increase the mass of blade resulting in reduced natural frequencies of blade, with the first-order flap-wise frequency decreasing by a maximum of 47.79 percent. At the same time, it can also increase the stiffness of blade resulting in the increase of the nature frequencies of blade, with the first-order torsional frequency increasing by a maximum of 39.51 percent. Flap-wise and lag-wise modal shapes of blade are less influenced by ice, but torsional modal shape of blade in 30 m~46.5 m is greatly affected among which it is the first torsional modal shape of blade under uniform icing condition that is influenced more obviously.

ACCELERATED AGING PERFORMANCE AND LIFE PREDICTION OF CARBON-GLASS FIBER REINFORCED COMPOSITE FOR YACHT

LI Meng, LI Zhi-zheng, BIN Yuan-hong

2018, 0(10):  90-95. 

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In this paper, the composite materials of carbon fiber and glass fiber reinforced 2597PT unsaturated resin were fabricated. In combination with the actual use of yacht under the marine environment, the salt fog purple diplomatic aging test is carried out by artificial accelerated aging method, and its performance evolution rules under this aging environment are studied. The residual strength model is established and the residual strength of composite materials is predicted. The results show that with the increase of the aging period of the salt fog and purple, the chromatic aberration of the material becomes larger and the surface is yellow. The mechanical properties of the composite gradually decrease, and the decrease is more obvious in the early age of aging. Based on the residual strength theory of Gunyaev, the residual tensile strength formula of the composite is S=S₀+14.13(1-e^-0.61t)-9.16ln(1+2.49t), and the correlation coefficient R²=0.997. According to the requirements of CCS "Materials and Welding Code", we can predicte that the material can be used for about 30 years under the above conditions.

THERMO-MECHANICAL PROPERTY EVOLUTION OF A UNIDIRECTIONAL PULTRUDED CARBON FIBER REINFORCED POLYURETHANE PLATES SUBJECTED TO IMMERSION

ZHANG Lei, HONG Bin, LI Jing, HUANG Sheng-de

2018, 0(10):  96-101. 

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In the present paper, the effects of immersion in distilled water, strong alkaline solution and artificial seawater at 20 ℃, 40 ℃ and 60 ℃ on the thermo-mechanical properties of a unidirectional pultruded carbon fiber reinforced polyurethane plates were studied. As found, after one year of immersion, the in-plane shear strength and the glass transition temperatures of the plates decreased by less than 15%, while the tensile strength was only reduced by 5%. Meanwhile, the plates were insensitive to the immersion media and temperatures. FTIR (Fourier Transform Infrared Spectroscopy) analysis indicated that postcuring of the resin matrix occurred, and the degradation of the thermo-mechanical properties was mainly attributed to the plasticization of the resin. Finally, the durability performances of the polyurethane matrix plates was compared to the epoxy resin based carbon fiber plates.

STUDIES ON PROPERTY OF PHENOLIC RESINS FOR RTM PROCESS AND PROCESSING TECHNOLOGY FOR COMPOSITE WITH ABLATION RESISTANCE

SUN Chao-ming, LU Dong-bin, SUN-Yi

2018, 0(10):  102-107. 

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According to the RTM phenolic resin system, rheological behavior, curing properties, ablation properties and others properties were studied, which provides the process parameter basis for preparation of composites. The influence of temperature and fiber volume on the properties of composites was studied by the process experiments, and the molding parameters were determined. The results show that the phenolic resin system has lower viscosity and a long low-viscosity keeping time at 70 ℃~80 ℃, which satisfied RTM requirement. The curing temperature step is 90 ℃, 120 ℃, 160 ℃, and the suitable volume content of the fiber is 50%~55%, which is the key technology of phenolic RTM process for the fabrication of ablation resistant composite with large and complex structures.

INTRODUCTION TO THE RELEVANT STANDARDS AND REGULATIONS ON CLASSIFICATION AND TECHNICAL REQUIREMENTS INTERPRETATION OF FIBER REINFORCED PLASTIC PRESSURE VESSEL

LI Guo-shu

2018, 0(10):  108-111. 

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Fiber reinforced plastic pressure vessel is widely used in China. New national regulations and national standards have been published recently. This paper explains how to classify pressure vessels according to the new national standards and regulations, and explains the technical content associated with fiber reinforced plastics pressure vessels. This paper provides the design method of fiber reinforced plastic pressure vessel. The quality inspection and acceptance methods of fiber reinforced plastic pressure vessel are presented, which put forward the definition and criterion of appearance quality in detail, provide the mechanics performance test and water pressure test method, and put forward the method of acoustic emission testing. In accordance with the relevant provisions of the national regulations, specific requirements for pressure vessel test of pressure vessels are put forward in this standard. As a non-destructive testing technology, acoustic emission is widely used in international standards. The acoustic emission detection technology is introduced into the detection of glass fiber reinforced plastics pressure vessel manufacturing industry, and the test procedures and methods are summarized through field experiments.

STUDY ON MECHANICAL PROPERTIES OF CARBON FIBER COMPOSITES BEFORE AND AFTER ELECTROPHORETIC DRYING PROCESS

ZHANG Ran-ran, WANG Yu-xin, XIONG Jian-min, NIU Li-yuan

2018, 0(10):  112-116. 

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Electrophoretic drying process is an important part of the car body coating, so the carbon fiber composites as body parts need to consider the mechanical properties affected by electrophoretic drying process. In this paper, the mechanical properties of carbon fiber composites, cured at 120 ℃, before and after electrophoretic drying process were compared, and the failure modes and mechanism of splines were analyzed. The results show that the tensile strength of carbon fiber composites increased after electrophoretic drying, which is promoted by 13.44% and 21.12% in fiber direction and vertical fiber direction, respectively. In terms of compression performance, the strength in fiber direction was improved (21.2%), while the strength and modulus vertical fiber direction were significantly reduced (12.45%, 11.61%). In terms of shear performance, both longitudinal-transverse shear and interlaminar shear performance were reduced. Meanwhile, it was also found that the fibers showed de-bonding phenomenon, and the interfacial bonding strength between the resin matrix and the fiber was reduced after electrophoresis drying. In summary, it can be seen that in the design phase of carbon fiber composites, the vertical fiber direction property and interlaminar shear property need to be enhanced, so that the performance of the car body parts prepared by the carbon fiber composites system can reach the corresponding requirements after the electrophoresis drying process.