COMPOSITES SCIENCE AND ENGINEERING

Stress wave-based damage probability imaging for composite cylindrical shell structures

LIU Xiang, YAN Gang, TANG Jian-fei

2021, 0(9): 5-11. DOI: 10.19936/j.cnki.2096-8000.20210928.001

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This paper studies health monitoring of cylindrical composite shell structures with stress waves technique and fused damage probability imaging algorithm to detect and identify damage. Firstly, a piezoelectric sensor array is mounted on the inner surface of the cylindrical shell structure and a multi-channel array scanning system is used to excite and receive stress wave signals in the structure. Then, the signals are processed by correlation coefficient analysis and box dimension fractal analysis to calculate the damage indices on different sensor paths. Finally, the damage probability imaging algorithm improved by coordinate transformation and image fusion method is used to realize the visual identification of damage in composite cylindrical shell structures. Numerical simulation and experimental results have demonstrated that the stress waves can effectively detect and identify damage in the composite cylindrical shell structure, and the fused damage probability imaging algorithm can improve the identification accuracy of the damage position.

Analysis of temperature field for thermoplastic composites based on hot gas heating in an in-situ consolidation process

SUN Shi-yong, DONG Chen-hua, LIU Guan-san, YANG Rui

2021, 0(9): 12-17. DOI: 10.19936/j.cnki.2096-8000.20210928.002

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During the automated fiber placement and in-situ consolidation process of thermoplastic composites, the temperature history has a great influence on the final quality and performance of composites. Taking the temperature field during the laying process of the carbon fiber reinforced peek as the research object, a two-dimensional transient heat transfer model of the temperature field was established, the boundary conditions were established by dividing the model. The influence of the hot gas temperature, laying speed and the initial temperature of the mold on the temperature field of the layers was analyzed. Through the principle laying experiment, the temperature field measurement system was established, which verified the correctness of the finite element model. The results show that with the increase of the hot gas temperature and the decrease of the laying speed, the peak temperature of each layer gradually increases. When the initial temperature of the mold is room temperature, in order to meet the molding requirements, the hot gas temperature is 650 ℃ and the maximum laying speed is 6 mm/s. The initial temperature of the mold has a great influence on the temperature field of the first layer. In order to improve the bonding and melting effect of the first layer, increase the laying efficiency and reduce the overall temperature gradient, the mold temperature and the laying speed should be appropriately increased, and the hot gas temperature should be reduced.

Optimization and verification of static test load for wind turbine blades

HE Jia-hao, ZHANG Wen-wei, DENG Hang, JIN Jiao-tong, FENG Xue-bin, PENG Chao-yi, XIE Hong-jie

2021, 0(9): 18-21. DOI: 10.19936/j.cnki.2096-8000.20210928.003

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Wind turbine blade static test is an effective way to verify the blade structure strength. For the blade static test, the loading procedure is usually planed based on the undeformed geometry of blade. However, when the blade undergoes a large deformation, especially under the maximum flapwise load case, both the spanwise position and the load direction of the load point will change greatly, resulting in a mismatch between the test load and the given blade design load. So the structure strength of the blade may not fully verified in some areas during the test. This article proposes how to consider the effect of large blade deformation in the blade static test simulation model, and how to extract the load of each cross section after the blade large deformation. Besides, an equivalent beam model to accelerate the iteration process of the test loads is put forward. Finally, the full-scale blade test is carried out to verify the feasibility and the accuracy of the improved loading plan.

Single-objective optimization of CFRP laminated board scarf-repair structure based on response surface method

TIAN Ke-ke, LI Cheng, HU Chun-xing, GUO Jian

2021, 0(9): 22-30. DOI: 10.19936/j.cnki.2096-8000.20210928.004

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To obtain the optimization of scarf repair structure of CFRP laminates. Firstly, a three-dimensional damage accumulation model is established through three-dimensional solid elements, and the validity of the established simulation model is verified through experiments. Moreover, a surrogate model of tensile strength was constructed using Latin hypercube sampling (LHS) method and response surface method (RSM). Finally, the optimized design of scarf repair structure is obtained by combination of the surrogate model and genetic algorithm (GA). The research results show that, the error is less than 10% between the numerical and experimental results, indicating that the established finite element model is valid. The failure model of the scarf repair structure under tensile load is mainly the shear failure of the adhesive layer. The adhesive layer damage starts at the position corresponding to the 0° layer of the laminates and the patch, and then expands around. After the adhesive layer fails, the patch loses its load. Capacity, the mother board continues to bear the load and breaks at the narrowest point. The best adhesive layer thickness, scarf repair angle and rotation angle are 0.1035 mm, 2.5° and 0°, respectively. Compared with the conventional scarf repair structure, the tensile strength is increased by 12.57%. Genetic algorithm is used to optimize the scarf repair structure of CFRP laminates, which is of great significance to improve the mechanical properties of scarf repair structure.

The influence of the residual compressive strength of epoxy composites in wet and hot environments after impact

OUYANG Jun-jie, WANG Fu-sheng, KONG Fan-qi, WANG Bing-qian, CHEN Ya-jun

2021, 0(9): 31-37. DOI: 10.19936/j.cnki.2096-8000.20210928.005

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Composite material with holes treated in wet and hot environments is used to study its change law and mechanism of impact resistance and residual compressive strength with low-speed impact testing, compression mechanics testing and digital image correlation technology (DIC). Firstly, the composite material is treated in wet/heated environment, and the degree of change is evaluated by the moisture absorption rate and weight loss rate. Secondly, a low-speed impact test was performed on the treated laminate simple, and then a compression after impact (CAI) test was performed to evaluate the residual strength. DIC information was collected for the crushing process at same time, and finally the scanning electron microscope (SEM) was used to characterize the microscopic morphology with treatments. The results show that the thermal treatments are more harmful than water-induced treatment. The difference between the strain data collected by DIC technology and strain gauge (SG) is relatively small, and the dispersion of DIC data is lower, which has the feasibility of replacing strain gauge. The microscopic morphology analysis shows that the moisture environment affects the epoxy resin bonding fiber, and the matrix swells when it absorbs water. In a thermal environment, the matrix reacts with the outside oxygen. The matrix in the layer shrinks, but it is still bonded to the fibers.

Tack variation of composite tows for automated fiber placement under multi influence factors

GOU Jian-jie, YANG Yang, CHEN Dai-xin, DENG Xiao-chun, ZHANG Peng

2021, 0(9): 38-45. DOI: 10.19936/j.cnki.2096-8000.20210928.006

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Automated fiber placement is an advanced low-cost and automatic manufacturing process for composite materials. It is usually used to manufacture aircraft fuselage, S-shaped inlet and other composite components with large curvature. During the layup process, the tack of prepreg shows a great influence on the final quality of the products. The tack of prepreg should not be too low to ensure the smooth adhesion between adjacent tows. Meanwhile, the tack of prepreg should also not be too high in order to enable convenient modification in case of failure of layup. The existing evaluation methods of prepreg tack are mainly 90 degree peel test and 180 degree peel test, which mainly aims at wider tapes in automated tape placement. Preliminary experiments show that the experimental data will fluctuate greatly when the standard single tow peel test is utilized, which could not meet the relevant detection requirements. In view of this, this paper establishes the detection criteria of prepreg tack, and multi tow 180 degree peel test is proposed to detect the prepreg tack. Based on the criteria, the influence of layup pressure, layup speed, layup temperature and aging time on the tow tack is investigated through a series of experiments.

Performance of short carbon fiber reinforced nylon composite and it's application in battery pack

LIU Ying, MA Yi-tao, LIU Qiang

2021, 0(9): 46-54. DOI: 10.19936/j.cnki.2096-8000.20210928.007

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It is difficult to predict the mechanical properties of short fiber reinforced composites which are used for battery pack lightweight due to anisotropy. This paper studies the mechanical properties of short carbon fiber reinforced nylon 66 composites (PA66CF) with different fiber contents. Furthermore, the simulation method and application effect of different fiber contents PA66CF applied to battery pack are studied. Firstly, the stress-strain curve of PA66CF were obtained through tensile experiments. Then the PA66 material parameters were corrected, and the tensile sample FE models using the criterion of maximum strain were established to verify the accuracy of the simulation process. Finally, the corrected material model and failure criterion were applied to the mechanical analysis of emergency braking and abrupt-turning on the bumpy road of the battery pack, and the maximum displacement, the maximum stress of the system and the maximum stress of the pack are compared with the metal battery pack. The results showed that compared with the metal pack, the mass of PA66CF packs were reduced by 84%, and the maximum stress of the PA66CF packs were reduced by 30%~50% under the above two conditions. Additionaly, the maximum displacement of battery pack could be affected by the carbon fiber content. The research in this paper provides simulation reference for the application of PA66CF material in battery pack.

Effect of deflection on winding quality of composite shells with large aspect ratio

XI Wang, GE Qing, XIAO Kang, ZHANG Qian, ZU Lei

2021, 0(9): 55-61. DOI: 10.19936/j.cnki.2096-8000.20210928.008

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A composite material with a large aspect ratio is wound around the molded shell, which causes deflection during the molding process. In this paper, the effects of deflection on the winding shape, winding tension and curing residual stress of the shell are studied. Through analytical calculation and numerical simulation, the geometric model and finite element model of the composite shell with large aspect ratio are established. The geodesic winding method was used to explore the effect of deflection on the fiber winding linear type; the positive axis and off-axis strain conversion method was used to explore the effect of deflection on the fiber winding tension; the CHILE constitutive model was used to investigate the effect of deflection on the fiber winding residual stress. Through the simulation analysis of the composite shell with large aspect ratio, it is found that the deflection has little effect on the fiber winding linearity, and the deflection has a certain effect on the fiber winding tension. The tension increases with the increase of the shell deflection displacement value. It has a certain effect on the residual stress of fiber winding and curing, and it is regularly distributed in the circumferential direction of the shell.

Design of crane jib frame based on sandwich structure of carbon fiber reinforced plastic and balsa wood

MA Ze-chao, HU Ye-fa, FENG Zheng-feng, XU Sheng-feng, YAN Dong

2021, 0(9): 62-67. DOI: 10.19936/j.cnki.2096-8000.20210928.009

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In this paper, in response to the lightweight design requirements of the truck crane boom, a jib boom with a sandwich structure of carbon fiber reinforced plastic and balsa wood for a truck crane is designed. Carbon fiber reinforced plastic is an advanced material with excellent mechanical properties such as low density, high specific strength and high specific modulus,which can reduce the quality of parts. The finite element software ABAQUS is used to carry out structural design and simulation analysis on the jib frame of a truck crane with a carbon fiber composite balsa sandwich structure. The research results show that the thickness of the upper and lower panels of the carbon fiber composite material in the balsa sandwich structure jib frame is 10 mm and 8 mm respectively, and the upper and lower panel plies are [0/±45/0₂]₁₀ and [0/±45/ 0₂]₈. Compared with the carbon fiber reinforced plastic jib frame, its strength has a larger safety margin, and its rigidity also meets the needs of use. At this time, the weight of the jib frame of the sandwich structure of carbon fiber composite material and balsa wood is 251.4 kg, and the weight is reduced by 40%, which has a good lightweight effect.

Research on electro-thermal damage characteristics of aircraft composite fuel tank skin after lightning strike

HU Jing, WU Tian-hang, GONG Han-lin, LI Zhi-bao, LI Xiao-er, SI Xiao-liang

2021, 0(9): 68-73. DOI: 10.19936/j.cnki.2096-8000.20210928.010

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With the extensive use of carbon fiber-reinforced polymer (CFRP) in modern aircraft, due to the anisotropy of CFRP's electrical conductivity and heat transfer coefficient, its temperature distribution is different from traditional metal materials after lightning strike. In order to explore the electro-thermal damage characteristics of CFRP fuel tanks for lightning protection, this paper uses COMSOL Multiphysics simulation software to establish a CFRP laminate and flame sprayed aluminum protection CFRP laminate to simulate a fuel tank skin model for simulation research, and develop a typical lightning current combination waveform lightning current the injection test verifies the simulation results. The results show that after the lightning current waveform is injected, for the unprotected CFRP board, the temperature of each layer is distributed along the fiber direction. For the flame sprayed aluminum protection CFRP board, the temperature is approximately circular, and the high temperature damage area and damage depth are both smaller than non-protective CFRP board. The surface temperature is greatly affected by the lightning current D wave, while the damage depth is greatly affected by the B and C^* waves. After the lightning waveform injection is completed, the heat generated by the lightning strike will be conducted downwards along the CFRP layer, the hot spot causes the bottom surface temperature to rise but does not exceed 200 ℃ under the condition of 2.6 mm thickness. The use of flame sprayed aluminum can have a good lightning protection effect on the CFRP fuel tank.

Failure analysis of carbon fibre reinforced composite curved beams under bending load

DENG Zhong, YU Yin, LIU Long-quan, WANG Hai

2021, 0(9): 74-78. DOI: 10.19936/j.cnki.2096-8000.20210928.011

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Based on the continuous stiffness reduction scheme of composite materials and the three-dimensional Hashin failure criterion, the progressive damage analysis model of composite materials is established, and the user material subroutine (UMAT) corresponding to the model is compiled. The program is called by ABAQUS to simulate the four-point bending of carbon fiber reinforced composite curved beams. The simulation results are compared with the experimental results, and the effectiveness of the progressive damage analysis model is verified. The failure behavior of composite curved beams is analyzed. It is found that under bending load, the main failure modes of carbon fiber reinforced composite curved beams are tensile delamination failure and matrix tensile failure in the curved region. After the tensile delamination failure occurred, it expanded rapidly, the composite curved beam quickly lost the bearing capacity and finally failed. The main cause of delamination failure of the composite curved beam is the excessive interlaminar tensile stress.

Study on double-vacuum curing technique for composite skins

ZHANG Yu-jie, YE Qi-fei, LIANG Yan-min, LIU Qi-bao, KE Chang-yi, YE Peng-hua

2021, 0(9): 79-82. DOI: 10.19936/j.cnki.2096-8000.20210928.012

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Composites are widely used in aerospace field. Thick composite skins made from solution prepared prepreg experienced long production period, which have higher porosity that against the spacecrafts. The article takes double-vacuum curing technique for example, and optimizes the preparation process of composite skins. The internal quality was evaluated by nondestructive testing, section microscopic quality, porosity. The result indicates that the porosity of a 4 mm thick composite skin was controlled to 1.65% and the internal quality was promoted by double-vacuum curing technique.

Study on the anti-crash energy absorption characteristic of composite structure in the sub-cargo structure

SHI Meng, WANG Yang, WU Zhi-bin, LIU Fu

2021, 0(9): 83-88. DOI: 10.19936/j.cnki.2096-8000.20210928.013

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In a survivable crash, the sub-cargo structure is the main energy-absorbing component in the process of an aircraft crash. As an important energy-absorbing element during a crash, the composite stanchion has an important impact on the crash resistance of the sub-cargo structure. The vertical crash test of the sub-cargo structure was carried out. Comparing the structural deformation failure modes and energy absorption conditions, the relationship between energy absorption characteristics of the sub-cargo structure at a crash speed of 9.144 m/s and the angle of the stanchion, the thickness of the stanchion and the trigger form are obtained. The results show that when the angle of the stanchion is 90 degrees, the thickness of the stanchion varies in sections and the connection between the stanchion and the frame is weak, and the sub-cargo structure has the best energy-absorbing performance.

No-wash gun technology and application of epoxy resin mixing equipment for large wind turbine blades

YAN Chen, ZHOU Rui-rui, CHENG Chao-ying, BU Li-jing

2021, 0(9): 89-93. DOI: 10.19936/j.cnki.2096-8000.20210928.014

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The epoxy resin infusion used in the production of wind turbine blades is a two-component glue. After the infusion operation, a certain amount of two-component glue will remain in the mixing block and static mixing tube of the resin pouring machine. The remaining two-component glue, after a certain period of time, will solidify and block the mixing block and static mixing tube. In order to avoid clogging of the mixing block and the static mixing tube, a flushing and flushing of the gun is required before and after each use of the equipment. The amount of resin for each blade flushing gun is about 15 kg, which causes a lot of waste. This article introduces the application of epoxy resin mixing equipment no-clean gun technology in the molding process of large wind turbine blades, and compares its advantages with the conventional infusion resin mixing machine gun cleaning technology, which proves the higher application value of this technology. Practice has shown that compared with conventional technology, this technology can achieve the correct and uniform mixing ratio of the resin mixer. The mixing block is free of maintenance for 2 months, and a single blade reduces 15 kg of resin waste, which has high engineering application value.

Study on resin sandblasting progress of composites adhesive surface

LI Ya-yuan, ZHU Jun-jun, XU Wei-wei, LI Bo, LUO Ji

2021, 0(9): 94-98. DOI: 10.19936/j.cnki.2096-8000.20210928.015

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This paper studied the surface appearance and bond strength of composites with different surface roughing treatment and different sandblasting times. The result shows that resin sandblasting can remove surface resin of composites effectively without breaking fiber. As the times of resin sandblasting increases, the roughness effect increases. However, too much time can destroy fiber and reduce tensile lap-shear strength. Two times resin sandblasting is optional. By increasing the sandblasting time of resin sand, the recycle resin sand can attain the effect of first use.

Influence of assembly gap on fatigue performance of composite components under bending load

GE En-de, SHANG Yan-wei, LIU Xue-shu, LI Ru-peng

2021, 0(9): 99-106. DOI: 10.19936/j.cnki.2096-8000.20210928.016

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Geometrical deformation of composite component is usually unavoidable due to the anisotropic properties of carbon fiber reinforced plastics (CFRP) after curing, which introduces gaps at the matching surfaces during assembly. Mechanical performance of the composite structure is consequently affected. To investigate the influence of assembly gap on fatigue performance of composite structures under bending load, experiments are designed and conducted, which involves the usage of electronic universal testing machine and hydraulic fatigue machine as well. It was found that the assembly gap has great influence on failure process of composite structure under bending load condition and decreases their fatigue life as a result. Moreover, when the height of assembly gap falls into certain span, the fatigue life increases with the increasing of gap length. Compared to the length of assembly gap, the height of assembly gap has greater effects on fatigue life of composite structure.

Research progress in carbon nanotubes filled poly(phenylene sulfide) nanostructured composites

DONG Hui-min, WENG Chuan-xin, LIU Cong, CHENG Li-jun, LI Yue-teng, QIAN Huang-hai

2021, 0(9): 107-117. DOI: 10.19936/j.cnki.2096-8000.20210928.017

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Polyphenylene sulfide (PPS) has higher strength, flame retardant, chemical resistance and heat proof, as well as better processing properties. However, its application is mostly constrained by the intrinsic brittleness. To improve the impact toughness, additional fillers, such as CNTs are usually used to enhance the properties. The applications of PPS reinforced by CNTs were concluded in detail and its preparation methods were summarized. The unique properties, concluding the crystallization behavior, the rheological properties, the mechanical, tribological, thermal, electrical along with electromagnetic properties were simply introduced. The effects of the surface modification, loading, dispersion and alignment of CNTs, preparation parameters, interphase and morphology on the properties of CNTs/PPS composites were also discussed. In addition, the insight into the excellent properties of CNTs/PPS nanocomposites was explored. Finally, the application prospect of CNTs/PPS was predicted.

Toughing modification dopment and the application status of phenolic resin

XU Guo-juan, JIA Chen-hui, LIU Jing, TIAN Mou-feng

2021, 0(9): 118-128. DOI: 10.19936/j.cnki.2096-8000.20210928.018

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In this review, the research progress of toughing modification of phenolic resin in China is introduced, including chemical reaction and physical blending. Also, the mechanism and research status of various toughing agent are described. The present situation of the application fields of phenol resin in China is summarized.

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