COMPOSITES SCIENCE AND ENGINEERING

EXPERIMENTAL AND NUMERICAL ANALYSIS OF BIAXIALLY TEARING PROPERTIES OF WARP-KNITTED FABRIC MEMBRANES

GUAN Xiao-yu, CHEN Jian-wen, XIA Yu-fan, ZHANG Yang

2020, 0(7): 5-12.

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In practical engineering, biaxial tearing damage of fabric membranes is the main cause of membrane structures′ failure. And the tearing mechanical properties of fabric membranes are extremely important for the safety of membrane structures. In this paper, the biaxially tearing mechanical behaviors of warp-knitted fabric composite membranes are studied by experimental and numerical methods. A numerical model of biaxially tearing considering the micro-structure of yarns and matrix is established by ABAQUS software. And the tearing-failure process of the membranes under multi-stress ratio was analyzed. The tear strength and failure mode characteristics of the membranes were obtained, and the effect of stress ratio on tearing mechanical properties of membranes was discussed. The results show that the variation of stress state significantly affects the tearing failure mode, stress distributions, and tearing strength of the membranes. In the critical stress state, the greater the difference between the warp and weft stresses, the more obvious the stress concentration at the crack tip.

PROGRESSIVE FAILURE ANALYSIS OF TENSILE STRENGTH OF GLASS FIBER REINFORCED COMPOSITE LAMINATES WITH WRINKLE DEFECTS

QIAN Ruo-li, MU Xiao-guang, WANG Xuan, LI Quan-zhou

2020, 0(7): 13-19.

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In order to study the effect of wrinkle defects on the tensile properties of glass fiber reinforced resin matrix composite laminates, Abaqus finite element software was combined with USDFLD subroutine to establish a progressive damage analytical model for wrinkle-containing glass fiber reinforced composite laminate. The strength degradation and progressive failure process of wrinkle-containing laminates under tensile load were studied by numerical simulation analysis. The influence of wrinkle aspect ratio on the tensile properties of laminates was analyzed. The results show that the strength prediction value and the initial position of the damage are in good agreement with the experimental results in the literature, verifying simulation analysis model. The tensile failure load and strength decrease significantly with the increase of the wrinkle aspect ratio. Under the application of tensile load, there is stress concentration in the wrinkle deformation layer adjacent to the resin-rich area. The damage of the laminate is gradually extended from the resin-rich area to the wrinkle deformation area, and finally completely fails in the wrinkle deformation area. Affected by wrinkles, the laminates undergo bending deformation during the stretching process. In the linear elastic stage, the deformation increases with the increase of the wrinkle aspect ratio under the same load condition.

MONITORING OF DELAMINATION GROWTH FOR COMPOSITE STRUCTURE BY USING LAMB WAVES

WANG Zi-yao, YAN Gang

2020, 0(7): 20-26.

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Delamination damage can severely weaken the strength and stability of composite structures, so it is very important to monitor and identify it to ensure the structural safety. This paper proposes an approach to continuously monitor delamination growth in composite structures by using Lamb waves and time-frequency analysis. First, the propagation characteristic of Lamb waves in composite laminate containing delamination damage is studied, and the relationship between time of flights (TOFs) and the length of delamination is established to provide theoretical basis for delamination growth monitoring. Then the wavelet transform is applied to analyze the Lamb waves signal acquired by piezoelectric sensor in time and frequency domain to measure the TOFs between two sensors to determine the length of delamination. Numerical simulation and experimental results have demonstrated that the TOFs of Lamb waves between two sensors increase with the increase of the delamination length which is basically linear. And, through the TOFs extracted by wavelet transform, the delamination growth can be monitored, verifying the effectiveness of the proposed approach.

STUDY ON INTERLAMINATION DAMAGE DETECTION OF COMPOSITE MATERIALS BY USING PZT-METAL STRUCTURE

WANG Xu, ZHENG Yan-ping, XIA Xiao-song, ZHANG Chao-yu

2020, 0(7): 27-32.

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Electro-mechanical impedance (EMI) method has been widely used in nondestructive testing of composite materials, but its accuracy in damage detection is still unsatisfactory. In this paper, based on the electro-mechanical impedance method, the damage of composite laminates is studied in the low frequency range by using the PZT-metal structure with the aid of the finite element software ANSYS. At the same time, the impedance curve of the PZT is plotted with the single-PZT structure as the comparison, and the root mean square deviation (RMSD) value is used as the standard of damage identification. It is proved that the PZT-metal structure has higher detection accuracy in low frequency and short distance from damage.

EQUIVALENT STIFFNESS CALCULATION OF TYPICAL PLATE ELEMENT OF COMPOSITE CAP STIFFENED LAMINATES

QIU Jia-bo, LI Hua-dong

2020, 0(7): 33-39.

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Based on typical laminates theory and equivalent stiffness principle, this paper deduced the theoretical solutions of equivalent in-plane stiffness and bending stiffness of typical plate element of composite cap stiffened laminates. By concrete example, the theoretical solutions and Abaqus FEM solutions are compared, the results shows that both solutions are in good agreement and the theoretical calculation method is accurate and reliable. The research results of this paper can be applied on stiffness calculations of composite cap stiffened laminates and composite ship with single-plate frame hull structure.

SIMULATION ANALYSIS OF INFLUENCE PARAMETERS OF COMPOSITE PATCH BONDED REPAIR STEEL PLATE

XU Ming-yang, YIN Chen-bo, LI Xiang-dong, CHEN Xi

2020, 0(7): 40-44.

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During bonding repair of steel structures, different bonding schemes have a significant effect on the repair results. In order to make a better bonding repair plan, a finite element model was established in ABAQUS, focusing on the comprehensive influence of patch size and glue layer parameters on stress intensity factor (SIF) and glue layer stress. The results show that the stress intensity factor at the crack tip can be reduced and the stress at the end of the adhesive layer can be increased by increasing the thickness of the patch and the shear rigidity of the adhesive layer. It is better to increase the thickness of patch than to increase the shear stiffness of adhesive layer. The thickness of patch is about 1.5 mm, and the shear rigidity of adhesive layer is about 5 GPa. Patch repair with equal width has better reinforcement effect on steel plate, and it is not recommended to carry out bonding repair on thicker structure.

PREPARATION AND CHARACTERIZATION OF SILICA AEROGEL COMPOSITE REINFORCED BY OXYGEN PLASMA MODIFIED GLASS FIBER

TIAN Jia-qi, TAN Hui-jun, Sameera Shafi, ZHAO Ya-ping

2020, 0(7): 45-52.

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In order to prepare the hydrophobic silica aerogel composite with excellent performance, we used oxygen plasma treated glass fiber as the reinforcing phase, combined with sol-gel method and supercritical CO₂ drying process to prepare silica aerogel composite and characterized the structure, surface group, hydrophobicity, thermal and mechanical properties of the composites. On the one hand, the results showed that oxygen plasma treatment enhanced thermal insulation and mechanical performance of the composites by improving the bonding ability of glass fiber and silica aerogel. On the other hand, the results showed that the hydrophobic silica aerogel composite reinforced by oxygen plasma treated glass fiber had low density (0.228 g/cm³), low thermal conductivity (0.0214 W/m·K), high porosity (80.0%) , high specific surface area (741.66 m²·g^-1), high hydrophobic angle (129.2°) and high compressive strength (σ_20%=152.88 kPa) when the ratio of MTMS to TEOS is 0.4∶1. These excellent performances indicated that silica aerogel composites reinforced by oxygen plasma treated glass fiber have broad applications prospects in the field of thermal insulation.

STRUCTURE SCHEME OF OFFSET ELLIPSOIDAL SHELL ADVANCED COMPOSITE REAR PRESSURE BULKHEAD

XU Fei-fan, ZHOU Shi-gang, CAI Qi-yang

2020, 0(7): 53-57.

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In this paper, the offset ellipsoid equation is studied, and the rear pressure bulkhead of different sizes and shapes can be obtained by changing the relevant parameters. A method for determining the shape of the rear pressure bulkhead is obtained. The shape of the rear pressure bulkhead is determined by the size requirements of a certain type of aircraft. The strain analysis under the internal pressure and the stability analysis under the external pressure are carried out by the finite element method. The stability of parts of the rear pressure bulkhead determines the basic scheme of reinforcement. This article also analyzes the stability of the rear pressure bulkhead after grid reinforcement, considering the influence of different reinforcement forms, and finally obtains a better grid reinforcement structure scheme.

RESEARCH ON AXIAL COMPRESSION ULTIMATE STRENGTH OF FRP-CONFINED RECTANGULAR CONCRETE COLUMN BASED ON BAYESIAN THEORY

CHEN Jing, LI Xiang-yu

2020, 0(7): 58-67.

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Based on Bayesian theory, the model parameter identification method can not only consider the influence of model error, but also obtain the most probable value of the parameters in the model, and quantitatively describe the uncertainty of each parameter. In order to obtain a more reasonable axial compression ultimate strength model of FRP-confined square and rectangular concrete columns, the existing experimental data are extensively compiled, and the existing ultimate strength model is evaluated. Four typical stress-strain curve shapes and three typical types of ultimate strength model are summarized. Based on the identification of the existing average strain rate calculation formulas, the parameter identification framework of the ultimate strength model based on Bayesian theory is established. The most probable value and covariance matrix of the model parameters are obtained by MATLAB programming. Based on the most probable values, a new model was proposed, which is consistent with the FRP-constrained circular concrete axial compression ultimate strength model. Compared with some existing ultimate strength models, the newly proposed model is more accurate in intensity prediction, and the model form is more scientific and reasonable.

LAYUP OPTIMIZATION METHOD OF COMPOSITE WING BASED ON DEEP LEARNING

BAI Guo-dong, TONG Xiao-yan, YAO Lei-jiang

2020, 0(7): 68-73.

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Composite wings have been widely used in engineering, the optimization of the ply is essential to improve the carrying capacity of the structure. In this paper, a neural network is trained by samples, and then the neural network mode is used to quickly predict the design result. A genetic algorithm evolution operation is used according to the prediction result to search for the optimal solution of the composite laminate design problem and accelerate the design efficiency of the laminate. Applying deep learning technology to quickly solve the optimal layup order of laminates, and comparing with the optimization results obtained by traditional optimization algorithms, it proves a convenience and effectiveness of deep learning technology in the optimization of laminates. The trained neural network can quickly predict the layering sequence optimization index and provide guidance for the optimization process, which has certain guiding significance for further development of the potential and engineering design of the laminate.

EFFECTS OF UV AGING ON FATIGUE PROPERTIES OF GLASS FIBER REINFORCED EPOXY RESIN COMPOSITES

FU Chen-yang, NI Ai-qing, WANG Ji-hui, SUN Liang-liang

2020, 0(7): 74-80.

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In this paper, the effects of UV aging on fatigue properties of glass fiber reinforced epoxy resin composite materials were studied. The microstructure, chemical structure and dynamic mechanical behavior of the composite materials were analyzed by SEM, FTIR and DMA. The results show that UV irradiation causes photodegradation of epoxy resin, breaks the chemical bond or intermolecular force in the chain segment, weakens the bond between resin and fiber, and disbonds part of the interface. After 28 days of UV aging, the static tensile strength of the composites decreased by 18%. The tension-tension fatigue tests show that the effect of UV aging on low cycle fatigue of composites is greater than that of high cycle fatigue. The degradation rate and extent of the stiffness of the composite materials after UV aging are higher than those of unaged samples, indicating that it is the UV aging that caused the decrease of the fatigue properties of the composite materials.

LAYING MODE AND FORMING PARAMETERS ON PEELING PERFORMANCE OF LAMINATE ROLLER

ZHU Xiu-di, SUN Chao-ming, HOU Xin, HE Jing

2020, 0(7): 81-84.

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The hot pressed laminate of glass fiber cloth/toughened phenolic resin was taken as the research object,the surface-surface bonding properties of the laminate were characterized by drum peeling strength, and the microstructure of the failure form of the adhesive surface was observed by electron microscope. Combined with the above tests, the effects of laying mode, testing direction, warp and weft density, forming parameters on the peeling strength of eight three flying satin laminate rollers are studied and the laws are found out. The results show that when the stripping surface is weft yarn surface,the drum peeling strength for which peeling surface long floating fiber are vertical and parallel to the loading direction is better than warp surface. The interlaminar adhesive property of 0° is the best, and the laying direction of non-stripping surface has no effect on the drum peeling strength. And the increase of theodolite density is helpful to improve the drum peeling strength. In a certain range of heating rate, reducing the heating rate is helpful to improve the peeling strength of the drum. And the time of pressure has no effect on the peeling of the interlaminar drum.

IMPACT LOCALIZATION OF GLASS FIBER REINFORCED POLYETHYLENE THERMOPLASTIC COMPOSITE

WANG Han, NI Ai-qing, WANG Ji-hui, CHEN Hong-da

2020, 0(7): 85-92.

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As far as the application of glass fiber reinforced polyethylene thermoplastic composite (CGF/PE) is concerned, an online impact localization method was presented here based on optic fiber sensing and correlation coefficient method. First, the total experimental impact area of the glass fiber reinforced polyethylene thermoplastic composite laminate was divided into nine parts with equal areas. The impact response signals were collected by fiber Bragg grating (FBG) and de-noised by wavelet threshold method. Then, the time domain characteristic signals were collected at the maximum variances of the central wavelengths and the correlation coefficients of the time domain signals were calculated for impact localization. The result shows that 100% prediction accuracy is achieved for the composite laminate with initial divisions by online impact localization method proposed. Thereafter,the experimental area was subdivided in order to examine the prediction precision of the method. And the results show that the accuracy of 100% is achieved for 70 mm and 23.3 mm scales and 87.5% for 11.6 mm. Finally, the accuracy of the impact point location under three kinds of energies is explored. The results show that the accuracy rate on the 70 mm and 23.3 mm scales is 100%, and the scale on the 11.6 mm scale is 87.5%. High prediction accuracy with good precision is achieved by this method and its application in industry is truly promising.

A HIGH-EFFICIENCY HALOGEN-FREE FLAME RETARDANT EPOXY RESIN FOR LIQUID MOLDING

NAN Xun, JIANG Wen-ge, ZHOU Yu, SHANG Cheng-yuan

2020, 0(7): 93-97.

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The core of the flame retardant was a novel reactive phosphorus-silicone and the low viscosity liquid flame retardant improve the processing property of the system, synergistically intensifying the property of the flame retardant. Synthetically considering the influence of different components on the flame retardancy, thermal and mechnical properties of the resin system, a high-efficiency flame retardant epoxy resin with molding interval time for 1 hour at 60 ℃ is prepared, for which the tensile strength, flexural strength and impact toughness are 72.4 MPa, 105 MPa and 8.43 kJ·m^-2. The results reveal that V-0 level is reached during the UL-94 vertical combustion, the oxygen index (LOI) can be promoted up to 30.0 and the resin exhibits self-extinguish away from the fire. Composite materials of the resin immediately exhibit excellent mechanical properties, for which the tensile, flexural and shear strength are 459 MPa, 612 MPa and 52.4 MPa. The flame retardant and mechanical properties of the resin are comparable to the commercial halogen-free flame retardant prepregs.

STUDY AND SOLUTION OF INFUSION CRAZING IN VACUUM PERFUSION OF LARGE WIND TURBINE BLADES

WU Shuang, HE Gui-bin, NIU Peng-peng

2020, 0(7): 98-102.

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With the development of offshore and onshore wind power with low wind speed, the length and root diameter of the wind turbine blade increase rapidly, resulting in the problem of large blade root infusion crazing grain. The results show that the problem of blade root infusion crazing mainly occurs in the resin infusion curing process. In this paper, by studying and adjusting the internal stress of resin infusion and curing at the root of blades, the internal stress release during the post-curing process of blades is slowed down, and the problem of blade root crazing is effectively solved.

EFFECT OF METAL MESH COMPOSITE FILM ON CURING DEFORMATION OF ZT7H/5429 COMPOSITE PLATE

ZHANG Chen-qian, LI Shao-liang, ZHAI Quan-sheng, YE Hong-jun

2020, 0(7): 103-109.

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In this paper, the physical parameters of 5429 resin and ZT7H/5429 composite after curing, such as modulus of elasticity, density, Poisson′s ratio, coefficient of heat conduction and so on, are determined by different test methods. Based on the relationship between the degree of cure of 5429 resin and chemical shrinkage strain, the expressions of density, modulus of elasticity and degree of cure of 5429 viscosity and viscoelasticity are derived. Based on this, a three-dimensional finite element analysis model of the whole curing process of ZT7H/5429 composite with metal mesh composite film is established, which includes heat conduction model, curing dynamic model and residual stress model. The model is used to calculate the distribution of temperature field and degree of solidification during the curing process of ZT7H/5429. The results of calculation are compared with the experimental results, and the reliability of the three-dimensional finite element analysis model is verified. On this basis, the influence of J-403C on the solidification deformation of ZT7H/5429 composite plate was analyzed. The results show that increasing the thickness of the layer and adjusting the sequence of the layer can effectively reduce the influence of the metal mesh composite film on the curing deformation of ZT7H/5429 composite plate. The error between the experimental data and the calculated results is not more than 5%, which proves the validity of the model again.

PROCESS SIMULATION AND VERIFICATION OF CARBON SPAR CAP BY VARTM PROCESS

CHEN Xing-yu, WANG Zun, BU Ji-ling, CHEN Huang

2020, 0(7): 110-113.

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Carbon wind turbine blade is one of the important directions of wind turbine blade, this paper aims to carry out the process simulation analysis of carbon spar cap by using PAM-RTM. The permeability test of biaxial glass fabric was conducted in order to provide three-directional permeability parameters. The process simulation analysis and the verification test of 5 meter carbon spar cap have been accomplished. After the contrasting and comparison, the deviation of total infusion time between the simulation result and verification result is about +18%. Meanwhile, the maximum value of flow front deviation between the simulation result and verification result is +18%. Also, no defect was found after observation by cutting.

CALCULATION AND EXPERIMENT OF TENSIONED MEMBRANE STRUCTURE RADOME

XU Xiao-chen, DAI Su-ya, GU Ye-qing

2020, 0(7): 114-116.

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Structure calculation and experiment have been performed on tensioned membrane structure radome based on curved surface with negative gauss. Form-finding analysis, geometry nonlinear calculation and experiment were carried out on a physical model. After all of the work, we found the membrane stress error is 8.4% between the calculation and the experiment, and the membrane displacement error is 5.1% between the calculation and the experiment. Error band is reasonable, so we are sure that the method of calculation is accurate.

RESEARCH PROGRESS ON DURABILITY OF BOND INTERFACE OF FRP SHEET REINFORCED STRUCTURES

WANG Zuo-hu, SHEN Shu-yang, YANG Ju, SHAO Ming-zhe

2020, 0(7): 117-122.

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Fiber reinforced polymer (FRP) is favored by civil engineers because of its advantages of light weight, high strength and good fatigue resistance. The strengthening effect of FRP sheet depends on the bonding performance between FRP and reinforced structure interface. For outdoor concrete structure and masonry structure, the long-term bonding performance of interface under environmental erosion should be guaranteed. Scholars at home and abroad have done a lot of experimental research on the durability of bond interface between FRP reinforced concrete structure and masonry structure under the accelerated aging test conditions of freeze-thaw cycle, dry wet cycle and acid-base medium, etc., and put forward many degradation models of bond performance. This paper summarizes the research status of bond interface durability of FRP reinforced concrete structure and masonry structure at home and abroad, and puts forward suggestions for future research work at the end of the paper.

RESEARCH PROGRESS IN CREEP PROPERTY OF THE GLASS FIBER REINFORCED PLASTIC PIPES

YANG Jie-biao, ZHANG Li-chen, WANG Zhe

2020, 0(7): 123-128.

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The creep will occur during the long-term use process time of glass fiber reinforced plastics, which may lead to the failure of the products. Creep property research has become an important part of the design, manufacture and application of glass fiber reinforced plastics. This paper briefly introduces the research progress of the creep property of glass fiber reinforced plastics. This paper mainly summarizes and analyzes the research progress of the mathematical models and tests related to the creep property at home and abroad of glass fiber reinforced thermosetting plastic pipes, which is a representative product of glass fiber reinforced plastics, and the current domestic and foreign standards related to the creep property of the pipes are summarized. In addition, the creep property research of glass fiber reinforced plastics in China is prospected.

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