COMPOSITES SCIENCE AND ENGINEERING

STRUCTURAL DESIGN AND STRENGTH ANALYSIS OF DRY FILAMENT WINDING COMPOSITE PRESSURE VESSELS

CHEN Dan, ZU Lei, XU Jia-zhong, LIU Mei-jun

2019, 0(2): 5-12.

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Compared with the traditional shell element modeling and analysis methods for resin based fiber winding composite pressure vessels, this paper proposes a modeling and finite element analysis method for dry filament wound pressure vessels based on the fiber bundle model. The parametric modeling of the dry fiber winding layer was accomplished through Python programming and MATLAB. The finite element software ABAQUS was used to study the mechanical response of the dry fiber wound pressure vessel under working pressure. Using a robot winding station to complete the dry yarn winding experiment of the pressure vessel, the feasibility of design parameters and line type was verified. The calculation results show that the parametric modeling method based on dry yarn bundles can accurately reflect the true path of filament winding. The continuous layering scheme at the same angle makes the mechanical properties of the fiber more fully utilized. Under the working pressure (i. e.,4 MPa), the stress values in each zone of the cylinder are all designed to meet the design requirements, the maximum principal stress of the fiber in the loop layer of the cylinder body is much greater than that of the spiral layer. When the internal pressure reaches 16 MPa, fiber breakage in the circumferential direction causes the failure of pressure vessel.

EXPERIMENTAL INVESTIGATION ON THE COMPOSITE BEAMS STRENGTHENED WITH CFRP SHEETS

LU Yi-hui, YANG Jian, WANG Fei-liang, LIU Qing-feng

2019, 0(2): 13-19.

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This paper presents the works of investigating the structural behaviors of composite beams before and after being strengthened with CFRP strips at the tension soffit. Seven samples were examined by the four-point bending loading tests. Among the seven samples, one was un-strengthened and the remaining six were strengthened by bonding CFRP strips of different numbers, width and length, respectively. All samples were tested beyond their ultimate failure. By recording the load-deflection data for the entire history, the first crack load, the CFRP debonding load or concrete longitudinal failure loads were identified. Meanwhile, the typical failure modes are documented and their respective mechanisms are analyzed. Comparing the strengthened beams with the reference one, the ultimate strength of composite beams strengthened by CFRP strips is significantly increased, and the most effective one is the beam strengthened by the CFRP strip of 60% beam length. In addition, a truss model is proposed to calculate the internal forces in the concrete, steel beam and FRP strips, from which the prediction for the failure load can be performed.

THE INFLUENCES OF COHESIVE ELEMENT COMPRESSIVE STRESS AND ITS THICKNESS ON DELAMINATION PREDICTION OF COMPOSITE

GUO Shuang-xi, LI Xue-qin

2019, 0(2): 20-25.

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To model the delamination initiation and propagation of the composite laminates, the cohesive element is often used. But, unfortunately, the numerical result may depend on element size, and it can′t model the interface failure caused by large compressive stress. Firstly, three models with different thickness of the cohesive element, i.e. the double cantilever beam model, the end-loaded split model and the dynamic impact model, are established to simulate the delamination evolution of the composite. The influences of the cohesive element thickness on the load-displacement curve and interface damage area are studied. Then, the constitutive relation of cohesive element is defined by the subroutine to consider the interface failure caused by compressive stress, and the impact of interface failure caused by compressive stress during impact response of composites is analyzed. The results show that the thickness of cohesive element has a significant influence on the interface damage area. Under conditions of the same loading, the damage area of the interface becomes smaller as the cohesive element thickness becomes larger. With the consideration of the interface layer failure caused by compressive stress, the interface damage area would be larger and the interface modes contains compression failure and shear failure.

STUDY ON STRENGTH AND FAILURE MODE OF ADHESIVELY BONDED SINGLE LAP JOINTS OF COMPOSITE MATERIAL

YANG Ben-ning, ZHENG Yan-ping, LI Cheng, HOU Yu-liang

2019, 0(2): 26-32.

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In order to explore the influence of the parameters on the joint strength of adhesively bonded single lap joints, the corresponding finite element model has been constructed using ANSYS. The modified Tserpes failure criterion has been utilized to predict its joint strength. Moreover, the failure mode of the joint with each parameter was simulated visually. The results show that, the strength of the composite-to-composite adhesive joint is higher than the strength of composite-to-titanium alloy adhesive joints. With the process of lap length, lap width increasing, the strength of joint is enhanced obviously first and then decreases. And, in the static tension, the main failure mode of the composite-to-titanium alloy adhesive joint is the adhesive failure. The main failure mode of the composite-to-composite adhesive joint is mixed failure, which is characterized by the layer peeling and delamination failure of the first layer and the second layer of the composite material immediately adjacent to the adhesive layer, while partial adhesion failure occurs in the adhesive layer.

INFLUENCE OF PROCESS FACTOR FOR CURING TEMPERATURE FIELD ON FIBER-REINFORCED RESIN MATRIX COMPOSITES

HUANG Pin-bo, WEN Song-tao, SU Chong-xi, CHEN Si-yi

2019, 0(2): 33-38.

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This paper mainly focuses on curing temperature field of composite materials with auxiliary material layer and forced convection. Using finite element method, the solutions of temperature-chemical coupling field and fluid-solid heat transfer field are obtained. Especially, the effects of the thickness, density of breath cloth, thickness and wind pressure of laminar air flow on curing temperature, curing degree and curing rate are analyzed numerically.The results show that the density and thickness of auxiliary material layer have little effect on curing field. The laminar thickness and the wind pressure will cause the curing temperature lag and overstep and the curing rate of the resin can be modulated by wind pressure or wind speed in autoclave.

VARTM MOLDING AND IMPACT PROPERTIES OF LAMINATES BASED ON BI-AXIAL WARP-KNITTING FABRICS

WANG Wei, LIU Ling

2019, 0(2): 39-44.

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Multi-axial Warpknitting Fabrics (MWK) have been widely used in energy, transportation, vehicle, sports, equipment and other fields due to its great advantages in term of cost and performance. Based on bi-axial (45/-45) MWKs, two kinds of laminates, [(45/-45)/(0/90)]_2s (Layup-1) and [(60/-30)(-60/30)(0/90)]_s (Layup-2), with various layup angles and thicknesses were prepared by using of vacuum assisted resin transfer molding (VARTM). The molding quality, fiber volume fraction, impact and compressive strength after impact of the obtained laminates were measured and evaluated. The results have shown that laminates with uniform quality and 54.2 vol% can be obtained by reasonably controlling the process. The layup-1 possesses larger capacity of anti-impact and compression. While, the layup-2 has larger ability to resist impact deformation and can absorb more impact energy during the impact process. Also, the layup-2 laminate shows significant stage of damage initiation and accumulation, but it′s compressive strength after impact is relatively lower than that of the layup-1.

CHARACTERIZATION OF LOW ENERGY IMPACT BEHAVIOR OF COMPOSITE LAMINATES BY CLOSE DEGREE METHOD

XU Guo-dong, LI Di-hong, WU Hao-yu, ZHANG Jing-wei

2019, 0(2): 45-50.

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Surface damage is the most direct observation and description of composite after impact.In this paper, the damage degree of composite materials is divided into five grades. Based on the fuzzy closeness evaluation method, the relationship between the damage information and the damage level of the low energy impact surface of composite materials is established. In this paper, the superficial depth microscope is used to observe, record, and analyze the surface damage of composite impact specimens. By combining with the fuzzy assessment method of progress assessment, a numerical relationship between the damage level and the posting progress threshold is established. It is proved that the same damage level can be determined by the characterization method of this paper when the surface damage of different composite materials and different thickness has the same characteristics.

SIMULATION ANALYSIS AND EXPERIMENTAL STUDY ON SURFACE TEMPERATURE OF PHOTOCURABLE SURFACE IN RING WINDING FORMING

LI Shi-tao, TIAN Ming, GAO Xue-feng, TANG Han-yu

2019, 0(2): 51-56.

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For the problem that the surface temperature of material tape is so difficult to control in the process of laser heating and solidifying shell forming that influence the molding quality, we analyzed the related technological parameters that affected the surface temperature of the material tape during the forming process and deduced theoretically for their relationship. By the ANSYS finite element analysis software, we built a thermodynamic transient analysis model to simulate the surface temperature change of the material strip during the shell forming and analyzed the simulation results. We tested the temperature changes and the influence of temperature on the strength of the shell through experiments, and then compared the experimental data with the simulation results to verify the correctness of the simulation model, and get the relationship among the forming temperature of the surface of the material, the forming speed and the laser power, based on which the relationship between the molding temperature and the shell strength was deduced.

MULTI-PARAMETER COLLABORATIVE ON-LINE MONITORING SYSTEM STUDY FOR CURING PROCESS OF COMPOSITE MATERIALS

KANG Xu-hui, ZHAN Li-hua, TAN Wei, WU Xin-tong

2019, 0(2): 57-62.

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The forming quality of composite materials is influenced cooperatively by the environment of autoclave curing process and physical and chemical reaction inside of component. The majority of the existing monitoring methods used to monitor the curing process are offline and discrete. Those methods bring about a heavy workload of subsequent data processing and the difficulty in detecting the interior change in the parts directly, making it hard to realize the online feedback control of the molding quality. Moreover, the amount of physical quantities detected is so small that the interaction among physical quantities cannot be comprehensively studied. In order to achieve the multi-parameter collaborative on-line monitoring of advanced composite materials forming process, in this paper, a kind of combined measurement method based on the classical laminated plate theory, "thermocouple+optical fiber Bragg grating" and "capillary pressure sensor" is introduced and a set of online monitoring PC software system using LabVIEW graphical programming language, data communication and database technology is developed, which have realized the synchronous online data communication and the synergy among temperature, pressure, strain and stress. The curing experiment of shrinkage part of a large aircraft wing box wall have corroborated the feasibility of the real-time monitoring for multi-parameters of the whole process of composite materials forming by the monitoring system and the stability and reliability of the system, which are of practical significance for ascertaining the mechanism of curing defects generated and realizing the online feedback control.

TEMPERATURE FIELD FEA OF WIND TURBINE BLADES BASED ON ELECTRIC HEATING ANTI-ICE TECHNOLOGY

YANG Wen-tao, CAI Ming, YAN Yong-jun, GAO Kang

2019, 0(2): 63-68.

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For wind-turbine and lives nearby, active anti-icing can avoid all kinds of risk caused by passive de-icing. So, based on the principle of electric heating method, a anti-ice thermodynamics computational model is established for MW wind turbine blades. The model is used to calculate the steady-state temperature of composite surface in different heating power density. The results show good agreements between the mathematical model and FEA. Then a blade electric heating system with accurate distribution of heating power density along the lengthwise direction, designed by means of FEA, is equipped in a 2 MW wind turbine. The tests in wind-farm show that, in -15 ℃ environment, the whole heating area of blades can reach 1 ℃ to anti-ice state in 360 s. This system could be applied to anti-icing of wind turbine blades.

STUDY ON PULL SENSITIVITY OF CARBON NANOTUBES EPOXY COMPOSITES

TIAN Chang-jin, GUAN Yan-hua, GE Zhi, GAO Jie

2019, 0(2): 69-74.

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Carbon nanotube is an emerging material with excellent mechanical properties and electrical properties in recent years. The addition of carbon nanotubes to epoxy resins can be made into composites with sensing effect. The bipolar method was used to determine the percolation threshold of carbon nanotube epoxy composites by changing the concentration of carbon nanotubes. The effects of temperature and humidity on the electrical conductivity of the composites were investigated. At the same time, the cyclic loading method was used to study the pulling sensitivity of the composite. It was found that the intervals of percolation threshold of carbon nanotubes epoxy resin matrix composites was ranging from 0.5wt% to 0.8wt%. In this interval, with the increase of the amount of carbon nanotubes, the electrical resistivity of the carbon nanotube epoxy composite decreased significantly. As the temperature increases and decreases, the resistivity of the composite material also shows a corresponding increase and decrease. Moisture in the environment has almost no effect on the resistivity of the composite. The pulling sensitivity of the material appears obviously when the amount of carbon nanotubes is 0.9wt% and the pulling sensitivity fades away when the amount of carbon nanotubes is 1.2wt%. It is proved that the pulling sensitivity of the material is the best when the amount of carbon nanotubes is 1.0wt%.

FINITE ELEMENT ANALYSIS AND FATIGUE LIFE PREDICTION OF HYBRID FIBER CNG2 CYLINDER

XIE Zhi-gang, CHEN Xiao-qin, LU Xu-jin, ZHANG Hong-xing

2019, 0(2): 75-78.

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Promoting gas vehicles is of great significance for haze treatment and use of clean energy. On the base of establishing a carbon/glass hybrid fiber CNG2 gas cylinder finite element model, the stress difference about liner and fiber layer under two conditions, without preloading and preloading, is analyzed. By reading the nominal stress intensity of the dangerous point of the liner cylinder during loading history, the local stress and strain under low cyclic fatigue loading are calculated firstly, and then the fatigue life is calculated by combining Manson-Coffin formula. The calculation results show that blending with carbon fiber can increase the fatigue life of cylinders by 7% in the absence of preloading. Meanwhile, the local stress concentration of the liner is improved. The fatigue life of pre-tightened hybrid fiber cylinders is further increased by 19%.

STUDY ON THE MECHANICAL PROPERTIES OF A NEW TYPE OF LOOPED FABRIC REINFORCED HONEYCOMB SANDWICH PANEL

JI Dong-can, ZHOU Guang-ming, CUI Wei-yun, HUANG You-da

2019, 0(2): 79-82.

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The composite sandwich structure is widely used in today′s aviation industry because of its superior mechanical properties, but the traditional woven two-dimensional composite sandwich plate has poor resistance to delamination and peeling resistance in the thickness direction. As a new type of three-dimensional woven composite material, the looping fabric(U-cor) can effectively improve the mechanical properties of the composite sandwich structure in the thickness direction by pre-woven fabric loops. However, at present, there are few studies on the mechanical properties of the looped fabric reinforced sandwich structure in China. In this paper, the mechanical properties of flat-pulled honeycomb sandwich panels are studied. Firstly, a glass fiber looped fabric reinforced sandwich panel and a traditional glass fiber sandwich panel were fabricated by the vacuum bag forming process, and the flat pull test was completed. The force displacement curve and tensile strength were obtained. The test results show that the looped fabric reinforced honeycomb sandwich panel has a higher flat modulus and flat tensile strength. The main reason is that epoxy resin formed glue columns in the looped fabric panel during curing. The glue columns are involved in the stress of the core material to increase the tensile modulus, and the loops embedded in the glue columns also improves the flat tensile strength. It can be concluded that the loop fabric can effectively improve the flat tension performance of the honeycomb sandwich panel. Finally, the corresponding improvement methods and ideas are proposed for some problems in the research.

STUDY ON THE TENSILE PROPERTY OF SINGLE SIDE PATCH REPAIR OF COMPOSITE LAMINATES

FAN Rong-tao, GUAN Zhi-dong, HUANG Yong-jie, SU Yu-ru

2019, 0(2): 83-90.

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Patch repairis a technologically simple and extensively employed composite structure repair technology. Tensile experiments on the composite laminate for experimental purpose with through-hole damage after single side patch repair is conducted. During the experiments, a research on how the diameter of patch influence the effectiveness of single side patch repair by changing patches′ diameters while keeping their ply stacking sequence and thickness constant is accomplished as well as an analysis of its failure mechanism based on the strain data of laminates at corresponding places collected during the experiment and the load-displacement curve on the basis of the data. The results show that the recovery rate of failure strength of test pieces after single-side patch repair is about 34% to 50%, and bonded repair has a recovery effect on the stiffness of laminates with through-hole damage. The longer the patch diameter, the higher the recovery rate of failure strength. When the patch diameter is relatively short, the adhesive fails before parent laminate. Hence, the repair effect is not obvious under this circumstance. When it increases to a certain extent, the strength of the adhesive is higher than parent laminate. At this time, patch repair can help increase the tensile strength of the damaged specimen. A finite element model is established based on the experiments, which can effectively predict failure modes and tensile strength of the test pieceand analyze its stress distribution. By changing the parameters of the model, a study on the relationship between patch sizes and damage apertures providing best repair effect is conducted. The results show that high repair efficiency can be obtained when the patch diameter is 30 mm~40 mm longer than the damage aperture. This paper provides references for composite laminates patch repair plan design.

MECHANICAL PROPERTIES OF T700 CARBON FIBER/CYANATE ESTER COMPOSITES FABRICATED BY WETTING WINDING

ZHAO Kai, GAO Wei, CHEN Shu-hua

2019, 0(2): 91-95.

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This article was to investigate the mechanical properties of T700 carbon fiber/cyanate ester resin (T700/CE) naval ordnance laboratory (NOL) rings and unidirectional laminate composites which were fabricated by wetting winding process. The relationship of viscosity with temperature of the formula was characterized. Mechanical properties of NOL rings composites including tensile strength, shear strength were measured. The damage morphology of tensile specimen was observed by scanning electron microscopy (SEM). Mechanical properties of unidirectional laminate composites including longitudinal tensile property, flexural property, interlaminar shear strength (ILSS) at room temperature and flexural property at high temperature were measured. The results show that the viscosity of the formula is 800 cps at 25 ℃, which indicates that the formula can be used to wetting winding process directly at room temperature. Meanwhile, the pot life is adequate. The tensile strength of NOL rings is 2220 MPa and the shear strength is 56.8 MPa. The CE matrix has good infiltration to carbon fiber. The high strength property of the carbon fiber can be better expressed. The high temperature mechanical properties of T700/CE unidirectional laminate composites is superior. The retention rate of flexural property at 200 ℃ is 60.4%, and the retention rate is 45.2% at 250 ℃.

STUDY ON THE THICKNESS MEASUREMENT METHOD OF MULTI-LAYER ANNULAR WINDING COMPOSITE MATERIAL BASED ON INDUSTRIAL CT

JIANG Bai-hong, YU Shi-zhang, DONG Jia-ju, ZHANG Kai

2019, 0(2): 96-101.

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Focusing on the multi-slice winding composite laminate′ thickness measurement, a fast thickness measurement method based on industrial CT technology was proposed. Based on the characteristics of the CT image of annular component section, at first the circle center of the annular component was quickly determined by using two strings. Then, the boundary of different materials in industrial CT image was determined by half-height method. Finally, the thickness of composite material along radius direction is calculated according to the gray curve variation. A double-layer annular contrast standard sample was tested, the thickness measurement of the standard sample was realized by using the proposed method of this paper, and the results were compared with the three-coordinate system′s measurement results. The comparisons proved that the proposed method of this paper can realize the rapid measurement of arbitrary layer thickness of multi-layer annular composite components, and the maximum relative error is less than 1% for the measurement of annular contrast standard sample thickness.

PRESENT RESEARCH SITUATION OF ADVANCED TECHNOLOGY IN COMPOSITE WIND BLADE

CHAI Hong-mei, YUAN Ling, LI Ying, HAN Rui

2019, 0(2): 102-107.

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The industry of composite wind blade will enter a new stage of adjustment and transformation. The development of digital automation will become a trend in the wind blade industry. The research status and development trend of advanced manufacturing technology of composite wind turbine blades are introduced in this paper, including intelligent temperature control mold, automatic lamination technology, intelligent grinding system, digital production integration technology, etc., which can provide reference for the automation and further intelligent manufacturing of composite wind turbine blades.

DEVELOPMENT OF SEAWATER RESISTANT OF FRP EPOXY COMPOSITES

CHEN Shang-neng, SHEN Ming-xia, ZENG Shao-hua, LU Feng-ling

2019, 0(2): 108-114.

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Benefiting from good mechanical properties, excellent corrosion resistance and light weight property, glass fiber reinforced polymer composites are recommended for use in marine infrastructures. However, the poor marine environment accelerates the corrosion of composites, which can easily result in the deterioration of material properties. In this paper, the seawater (SW) ageing of epoxy/glass fiber composites(GFRP) was summarized. The changes of water absorption and mechanical properties with immersion time were discussed, and the influence factors and corrosion mechanism of seawater immersion corrosion were analyzed. The results show that temperatures, preparation crafts, water species and fiber volume fraction of GFRP have great influence on the water absorption and mechanical properties of GFRP. Water and chemical substances, such as acids, bases, salts, and microbes contained in seawater, will lead to the physical and chemical degradation of GFRP. In addition, water creates a dual mechanism of positive effect by plasticizing and swelling and negative structural damage caused by corrosion, which leads to the fluctuation of mechanical properties of GFRP in the early stage of aging.

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