COMPOSITES SCIENCE AND ENGINEERING

Impact damage identification for honeycomb sandwich panel using printing sensing layer and electrical sparse tomography

ZHOU Deng, YAN Gang, GUO Shu-xiang, SHU Jia-jun

2022, 0(9): 5-10. DOI: 10.19936/j.cnki.2096-8000.20211128.031

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Honeycomb sandwiched structures are widely used in aerospace field, but during service it is inevitable for them to encounter damage, especially impact damage that can significantly reduce their strength. Combined with modern electronic printing technology, this study directly fabricates intelligent sensing layers on the surface of honeycomb sandwiched structure with conductive graphene-doped carbon ink and silver ink through screen printing, and identifies low-velocity impact damage with electrical tomography. Drop-weight device is used to impact the structure with low velocity, and the boundary voltage change of the sensing layer before and after impact is gathered by the electrical test system through injecting a tiny current into it. By analyzing the voltage data, sparse regularization algorithm, SpaRSA, is employed to reconstruct the image of conductivity change of the sensing layer to visualize damage information. Experimental results have demonstrated that, the proposed method can effectively identify the number, locations and approximate sizes of impact damage. And compared with traditional Tikhonov regularization-based algorithm, the sparse tomography algorithm can achieve better identification accuracy for damage sizes, providing a novel way of online impact damage identification for honeycomb sandwiched structures.

Dynamic performance of composite beam embedded by a double-layer damping film

MA Guo-rui, LIANG Sen, YANG Gong-xian

2022, 0(9): 11-22. DOI: 10.19936/j.cnki.2096-8000.20220928.002

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In order to study the dynamic performance of a co-cured double-layer damping film sandwiched composite beam under fixed-support boundary conditions, based on the first-order shear deformation theory (FSDT), the variational principle and the Hamilton principle, a free vibration theoretical model of a co-cured double-layer damping film embedded composite beam was established in this paper. The Galerkin weighted residual value method is used to solve the free vibration theoretical solution under fixed-support boundary conditions. An experimental platform is constructed to obtain experimental data and modal shapes. The validity of the theoretical model is verified by comparing the theoretical calculation results with the modal experiment and ANSYS finite element analysis results. The influence of the distribution and structural geometric parameters of the composite material layer and the damping layer on the dynamic performance of the co-cured double-layer damping film embedded composite beam is further explored, which provides a theoretical basis for the optimal design of the double-layer damping film composite beam structure.

Analytical model and characteristics of circular breathing crack stiffness of composite rotor

YANG Mo, XUAN Hao, XIONG Wei, LIU De-zheng, QIN Tao, LU Yi

2022, 0(9): 23-27. DOI: 10.19936/j.cnki.2096-8000.20220928.003

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The carbon fiber reinforced plastic transmission shaft is a new type of high-performance transmission component, but the composite transmission rotor is easy to cause circular crack in the manufacturing process or when it is collided. In this paper, the stiffness analytical model of the circular breathing crack of composite transmission rotor is established based on the Layer-wise theory of composite structures, which considers the influence of orientation angle and stacking sequence at the crack, and is verified by finite element model. Then the stiffness of composite cracked rotor with the same size and different laminate schemes are compared. The results show that the analytical model proposed in this paper has good accuracy, and the ratio of 0° ply at the circular breathing has a great influence on the bending stiffness of the shaft tube. What′s more, the stacking sequence of the 0° ply has little effect on the bending stiffness, which can be ignored.

Effect of braiding angle on tensile properties of carbon fiber circular tube based on FEM

LI De-bao, ZHU Rui-xiang, ZU Lei, CHEN Shi-jun, ZHANG Qian, ZHANG Gui-ming, WU Qiao-guo

2022, 0(9): 28-34. DOI: 10.19936/j.cnki.2096-8000.20220928.004

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In this paper, a finite element model was established based on meso-mechanics to predict the tensile modulus of braided RVE. Firstly, a two-dimensional triaxial braided structure model was established by parametric modeling, and the effect of braided angle on the thickness and fiber content of braided circular tube was studied by comparing with the actual sample. The results show that with the same modeling method, as the braiding angle increases, the fiber volume content increases first to a certain level and then remains steady at the level. When the monolayer thickness becomes thinner, and the fiber extrusion and accumulation is reduced. Then, the stress, strain and modulus of representative volume element were predicted by finite element simulation. The predicted results are in good agreement with the experimental results. Finally, TORAY T700 carbon fiber and epoxy resin were used to braided 2D triaxial tube. According to GB/5349 standard, the axial tensile test of 2D triaxial braided tube was carried out in order to study the effects of different braided angles on the axial tensile properties of 2D triaxial braided tube and those of braided angles on the modulus. The results suggest that the smaller the braiding angle, the higher the modulus and the better the axial tensile property.

Optimization design and initial tensile damage characteristics of FRP/Steel T-shaped connection structure

CHEN Guo-tao, MEI Zhi-yuan, LI Hua-dong

2022, 0(9): 35-40. DOI: 10.19936/j.cnki.2096-8000.20220928.005

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In order to optimize the design of FRP/steel T-shaped embedded connection structure, this paper proposes two new design schemes of T-joint embedded dovetail groove connection structure for the first time based on the research in references [1] and [2]: the embedded type and the extended type. In this paper, two types of asymmetric joints were designed and manufactured, and the load-bearing characteristics under tensile and bending load were studied. The initial damage characteristics, crack propagation law and failure mechanism of them were analyzed. Then, in order to further explore their initial damage characteristics under tensile bending load, the simulation calculation and analysis are carried out based on the large finite element calculation software Abaqus. The calculation results are in good agreement with the test results. On this basis, the two joints are simulated and their initial damage characteristics were analyzed. The results show that although the extended scheme has higher connection stiffness, the embedded scheme has higher initial failure strength and better water-tightness.

Macro-mechanical analysis of flexural strength of glass/carbon fiber hybrid composites in the hydrothermal environment

ZHAO Xun-peng, SUN Shuang-shuang, WANG Yang

2022, 0(9): 41-47. DOI: 10.19936/j.cnki.2096-8000.20220928.006

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In this paper, the stiffness and strength properties of the composite lamina are expressed as a function of hydrothermal parameters. Based on the classic laminate theory and macro-mechanics methods, a calculation program for the flexural strength of glass/carbon fiber hybrid composites (G/CFHC) under hydrothermal environments is compiled with MATLAB. The influence of the hydrothermal environment on the flexural strength of glass/carbon fiber interlayer hybrid composites and glass/carbon fiber sandwich hybrid composites is studied. The change law of bending strength of G/CFHC laminates with different hybrid methods under hydrothermal environment is analyzed. The results show that after G/CFHC laminates absorb moisture in the temperature range of 20 ℃~100 ℃ in a hydrothermal environment, their flexural strength gradually decreases with the increase of temperature. The G/CFHC laminates with adjacent layers of ±45° are affected by the interlaminar shear stress in a hydrothermal environment, and their bending strength is slightly lower. In the temperature range of 20 ℃~110 ℃ in the hydrothermal environment, with (0°/90°)_m as the incremental unit, the flexural strength of G/CFHC laminates increases with the increase of m.

Electrical conductivity of cement reinforced with recycled CFRP

WU Zhen-hua, LIU Yao, ZHANG Zhi-fang

2022, 0(9): 48-53. DOI: 10.19936/j.cnki.2096-8000.20220928.007

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As high-performance materials, Carbon Fiber-Reinforced Polymer (CFRP) has been widely used in many fields. However, due to the large amount of FRP scraps generated during the production of CFRP, this may bring serious environmental problems, and also cause a waste of resources. In this paper, the CFRP scraps generated during production was treated and added into cement, and the effect of recycled CFRP waste on the mechanical properties and electrical conductivity of cement was studied. The results show that proper amount of recycled CFRP can enhance the compressive and flexural properties of cement. When the amount of recycled CFRP in cement is not high, the reduction in electric resistance of cement is not remarkable. When the amount of recycled CFRP in cement reaches 4%, the electric resistance of cement-based materials decreases sharply. When the amount of recycled CFRP in cement continues to increase, a conductive path mechanism is formed in cement by the carbon fiber in recycled CFRP, and the electric resistance has been reduced to a minimum value and does not change significantly with the age. The study also shows that the electric resistance of cement increases with the increase of the age for cement specimens, and it increases first and then decreases with the decrease of water content in the drying process. Current research can not only help to solve the problem caused by the CFRP waste, but also to greatly relieve the environmental pressure brought by CFRP waste.

Vibration characteristics of carbon fiber/epoxy laminates with delamination damage in hygrothermal environment

JIA Bao-hui, WANG Hao, LU Xiang, SHAN Jin-yang, ZHAO Yao-bin

2022, 0(9): 54-61. DOI: 10.19936/j.cnki.2096-8000.20220928.008

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The vibration characteristics of T700-100/7202K-38 carbon fiber/epoxy composite laminates under free boundary condition are studied in hygrothermal environment through modal experiments and finite element simulations. Hygrothermal vibration experiments were carried out on laminates without delamination, different delamination positions and different delamination angle damage. Based on the principle of hygrothermal equivalence, a finite element model of the laminate was established through ABAQUS, and the simulation results were compared with experimental values to verify the accuracy of the model. Experimental and simulation results show that: The hygrothermal effect has little effect on the natural mode shape of the laminate, but it has the greatest impact on the first-order natural frequency of the laminate. The delamination damage of the laminate will also change its vibration characteristics, when the delamination moves from the surface of the laminate to the middle surface of the laminate, the natural frequency of the laminate is affected more by the hygrothermal effect. When the delamination angle is 90°, the natural frequency value of the laminate drops the most.

Effect of perforated hole and groove size on mechanical properties of core material

JI Xiang, QIN Zhi-wen, FENG Wei, SONG Xiao-fei, FU Shou-jun, WANG Guo-fu

2022, 0(9): 62-68. DOI: 10.19936/j.cnki.2096-8000.20220928.009

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Sandwich structures are widely used in wind turbine blades. Improving the mechanical properties of core material is beneficial to the strength, stiffness and stability of sandwich structures. In order to study the effect of the dimensions of perforated hole and groove on the mechanical properties of the core after resin infusion, a three-dimensional solid finite element model of the core was established, and the model was validated by the experimental results. The results show that increasing the hole diameter and decreasing the groove spacing are the most effective ways to improve core modulus, and increasing the groove width and depth has little contribution to the core modulus. In consideration of minimal cost of core after resin infusion, increasing of the hole diameter is the optimal method to improve the compressive and tensile modulus, and decreasing the groove spacing on both sides is the optimal method to improve the shear modulus.

Application research of AE technology in the test of GFRP adhesive bolted hybrid joints

LI Si-da, WANG Jin-xiao, CHENG Bin

2022, 0(9): 69-75. DOI: 10.19936/j.cnki.2096-8000.20220928.010

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In order to study the applicability of acoustic emission technology in the test of GFRP adhesive bolted hybrid joints, the static failure tests of single lap plate joints under tensile and shear conditions were carried out, and the characteristic parameters of acoustic emission were analyzed. The results show that the acoustic emission characteristics can well reflect the failure law of GFRP adhesive bolted hybrid joints. The failure process of joints can be divided into four stages: Steady development of adhesive layer damage, rapid development of adhesive layer damage, steady development of FRP damage and rapid development of FRP damage, and the acoustic emission results are consistent with the change law of load displacement curves. However, it is difficult to locate the internal failure area of GFRP plates. The results provide a reference for the application of acoustic emission technology in similar structural tests.

Research on heat transfer analysis and test of wind turbine composite blade for antiicing and deicing

LI Wei, WANG Shun-yan, WEN Fei, LIU Xiao-chun, WANG Zhao-li

2022, 0(9): 76-82. DOI: 10.19936/j.cnki.2096-8000.20220928.011

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Mastering the heat transfer characteristics of composite blade shell is important to realize the aerothermal anti-icing and deicing of the wind turbine blade. The three heat transfer models of the blade shell are constructed by choosing three local positions, including the spar cap,leading edge and trailing edge, based on the analysis of the heat transfer theory of the aerothermal method for composite blades, and then different load temperatures are imposed on these models to verify heat transfer simulation, respectively. The simulation analysis shows that the heat transfer characteristics of each model are consistent under different load temperatures. The heat transfer process of the leading edge model and trailing edge model is slower and the temperature drop gradient is maximum because of the different sandwich materials and thickness, while the spar cap model is faster and reaches the equilibrium state after 2 h. The field heat transfer test of 2 MW blade was carried and the temperature change trend at the monitoring point of the leading edge is close to the analysis of the corresponding heat transfer model, and the heat transfer simulation and test results show that the Δ10 ℃ temperature rise on the blade surface after heating for 1.5 h can satisfy the engineering application requirements of composite blade anti-icing and deicing.

Rheological properties of chopped carbon fiber reinforced nylon 66

HUANG Zhen-yuan, LI Bing-hua, CHENG Bin, Chen Yi

2022, 0(9): 83-89. DOI: 10.19936/j.cnki.2096-8000.20220928.012

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The rheological properties of polymers are an important factor affecting the properties of composite materials, this paper studies the rheological properties of the SCF/PA66 blend system. Chopped carbon fiber reinforced nylon 66 (SCF/PA66) composites with different fiber contents were prepared by melt blending, and the effects of fiber content and frequency on the rheological properties of the SCF/PA66 blend system were studied by capillary rheometer, scanning electron microscope and rotary rheometer. The results show that SCF/PA66 is a non-Newtonian fluid. After addition of SCF, the non-Newtonian coefficient decreases and the consistency coefficient increase. When SCF is 10wt%, the apparent viscosity of the melt is the smallest, and when SCF is 20wt% and 40wt%, the apparent viscosity of the melt is the largest. After adding more SCF, the storage modulus and loss modulus of the blend system are greatly improved. When the SCF is 20wt%, the loss factor of the composite system is less than 1, and the elastic response of the material is always dominant.

Experimental and simulation analysis of different processes on curing deformation of stiffened composite panel

CHENG Wen-li, JIANG Ting, WAN Xi-wei, LIU Xiao-dong, YE Hong-jun, GUAN Zhi-dong

2022, 0(9): 90-96. DOI: 10.19936/j.cnki.2096-8000.20220928.013

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Experiments were performed in order to study the influence of different processes on curing deformation of T-shaped and U-shaped stiffened composite panels, and the deformation prediction was carried out by the finite element simulation. The comparison between experimental and simulation results verifies the accuracy of the analytical model. Furthermore, influences of both the bottom plate of T-shaped stiffener on deformation and the structure of the T-shaped and U-shaped, stiffener, were investigated by the analytical model. The results show that compared with the co-curing process, the dry stiffen wet skin process has a tendency to warp the structure longitudinally to the side of the skin while the wet stiffen dry skin process has the opposite effect. The transverse warping deformation and the torsional deformation are hardly influenced by the different processes. The incorporation of the bottom plate of T-shaped stiffener increases the longitudinal warping deformation and restrains the transverse warping deformation. At the same time, torsional deformation occurs due to the asymmetry caused by that plate. The design of the bottom plate is not conducive to the suppression of curing deformation. The U-shaped panel has an asymmetry structure and increased rigidity, which generates no torsional deformation and reduced longitudinal warping deformation. However, the effect of springback is increased, and the transverse warping deformation becomes larger.

Study on dynamic tensile properties of short-cut carbon fiber reinforced concrete

LIU Yu-juan, WANG Li-juan

2022, 0(9): 97-101. DOI: 10.19936/j.cnki.2096-8000.20220928.014

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Due to the non-uniform tension and compression strength of concrete, carbon fiber can be added to concrete to improve its static tensile behavior and increase the tension-compression ratio. In view of the destructive consequences of impacts and explosions, the effects of the stress rates and carbon fiber contents on the dynamic tension behavior of concrete were investigated in this paper. And from the mesoscopic level, the difference between the dynamic and static properties of its tensile strength is discussed. The dynamic splitting tests of concrete with the fiber contents of 0‰, 1‰, 2‰, and 3‰ were carried out by using a split Hopkinson pressure bar (SHPB) device with a diameter of 74 mm. We found that with the increase of fiber content, the static tensile strength of concrete increases obviously, but the increased amplitude tends to decrease. The dynamic tensile strength and dynamic increase factor (DIF) both increase with the increase of stress rate, but the growth rate slows down, showing an obvious rate effect. There are significant differences in the influence of carbon fiber on the dynamic and static strength of concrete. In the design of concrete mixing proportion, the content of carbon fiber should be appropriately selected to meet the requirements of dynamic and static mechanical properties.

Experimental research and simulation analysis on anti-bird strike of the nacelle inlet lip of a civil airliner

FENG Rong-xin, XING Yun, NI Yang, YANG Xian-feng, JI Sheng-cheng, DENG Zhi

2022, 0(9): 102-108. DOI: 10.19936/j.cnki.2096-8000.20220928.015

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In order to study the bird strike resistance performance of the nacelle inlet structure of a civil airliner, this paper carried out a bird strike test study on the nacelle inlet of the composite laminate structure. The experimental research results show that the nacelle inlet structure has tearing at the riveting point between the lip and the lap strip, the fasteners at the connection between the lip and the front wall are pulled off, depression and deformation occurred at the connection of front wall and the inner and outer wall plate, and the outer wall plate of the inlet appeared cracks and other damages. In addition, PAM-CRASH software is used to perform bird impact finite element simulation verification on the nacelle inlet structure. The numerical simulation results show: Bird impact mode, impact process, lip structure damage morphology, and the strain on the front wall and inner and outer wall panels is basically consistent with the test results, indicating that the established bird strike numerical simulation model can better simulate the deformation and failure behavior of the nacelle inlet lip. The bird strike test and numerical simulation analysis show that the front wall of the nacelle inlet was not penetrated despite the lip′s serious damage, which verified the bird strike resistance of the structure. The results of this study can provide references for the structural design of the nacelle inlet.

Research progress on SiC_f/SiC composite and environmental barrier coating system and preparation technology for aeroengine

WANG Han-yi, LU Jia-zheng, HE Qiang

2022, 0(9): 109-123. DOI: 10.19936/j.cnki.2096-8000.20220928.016

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Light and high temperature resistant silicon carbide fiber toughened silicon carbide matrix composites and the environmental barrier coatings (SiC_f/SiC CMCs+EBCs) system show great potential in the rising turbine inlet temperature of aeroengines. With over 20 years of research and development, CMC/EBC components have been successfully used in the high temperature end of aeroengines, and new research is emerging one after another. The key preparation technology of SiC_f/SiC CMCs+EBCs system includes fiber preparation, preform preparation, interphase preparation, matrix densification and coating. Fiber quality, preform structure and interface layer properties determine the mechanical properties of CMC, while matrix and EBC affect the oxidation resistance and environmental stability of the system. There is still room for further improvement of CMC/EBC preparation technology in the development of new precursors, new processes, new coating materials, optimization of weaving structure, utilization of raw materials and process stability.

Review of SiO₂ aerogel fiber composites and its application of building thermal insulation

YU Zhen-zhou

2022, 0(9): 124-132. DOI: 10.19936/j.cnki.2096-8000.20220928.017

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The preparation methods of aerogel fiber composites and its application in pipe and wall insulation area are mainly reviewed. The preparation methods are divided into two categories. One is that aerogel particles are added into the fiber. They can be added in the spinning solution or masterbatch, and they can also be added between the procedure of net forming and reinforcement, or in the process of post finishing. The other is that fibers were added in the sol-gel stage. The added fibers can be divided into short fibers, long fibers, fiber membrane fragments, and fiber preforms according to its pattern. They can be divided into inorganic fibers and organic fibers according to its types. When it was used in the insulation fields such as pipe and walls, the thickness of SiO₂ aerogel felt/board is smaller than half that of traditional insulation materials, and the energy saving rate is higher. The combination with aerogels and traditional insulation materials can effectively reduce the cost.

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