COMPOSITES SCIENCE AND ENGINEERING

Measurement and calculation of interlaminar shear strength of heterogeneous multilayer plates

ZHOU Jun, WANG Yang, HUANG Ming, ZHAI Menglei, CHEN Wenguang, ZHANG Na, LIU Chuntai

2023, 0(11): 5-11. DOI: 10.19936/j.cnki.2096-8000.20231128.001

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For the existed testing methods of composite interlaminar shear strength(ILSS), the formula used to calculate ILSS only contains the geometric parameters of the sample without considering the changes in modulus and neutral plane, so they are only applicable to isotropic or transversely isotropic composite plates. For the heterogeneous multilayer plates, these methods will bring different degrees of error results. In view of this, a new calculation method for neutral plane position and interlaminar shear stress of three-layer heterogeneous composite plates was firstly constructed in this paper, and then the general formula for calculating neutral plane and interlaminar shear stress of n-layer composite plates was derived. Combined with the short beam shear method, the measurement and calculation method of ILSS of heterogeneous multi-layer composite plates was proposed. The analysis show that the maximum relative interlaminar shear stress of the heterogeneous composite plate will change with the change of the modulus of each layer, and the neutral plane is no longer located in the geometric center of the sample. Short beam shear tests were carried out for two types of heterogeneous composite plates composed of GFRPP/glue/GFRPP and GFRPP/glue/steel respectively. The results indicate that the proposed method can accurately measure and calculate the ILSS of heterogeneous composite plates,while the results obtained by the existed methods gradually deviate from the true value with the increase of the anisotropy degree of composite plates.

Research on the moisture andthermal vibration characteristics of the lap length on repair laminates

CUI Kaixin, LU Xiang, ZHAO Yaobin

2023, 0(11): 12-20. DOI: 10.19936/j.cnki.2096-8000.20231128.002

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It is particularly important to determine the lap length of the mesh according to the damage size of the composite laminate, and the appropriate lap length can effectively improve the strength of the laminate and extend the service life. Through numerical simulation and experimental verification, the effect of the lap length of the mesh on the vibration characteristics of the repair laminate under the effect of hygrothermal was studied. Based on the first-order shear deformation theory (FSDT) and Hamilton’s principle, the constitutive equation and the free vibration control equation of laminates under hygrothermal effect are derived. The double-sided stepped repair laminate model was established by ABAQUS software, and the vibration characteristics of the patch repair laminate and the complete board using p of 8 mm, 10 mm, 12.7 mm, 14 mm, 16 mm and 18 mm respectively were analyzed under the coupling action of different temperatures, moisture contents and hygrothermal. The results show that when the temperature T is 300~320.15 K and the lap length (p) is 12.7 mm, the thermal stability and stiffness recovery effect of the laminate are better; when the moisture content C is 0%~0.158% and the p-value is 14 mm, the wet stability and stiffness recovery effect of the laminate are better. Under the coupling of hygrothermal, the natural frequency changes greatly by using a patch with a small lap length, and the use of a patch with an excessive lap length will expand the repair area and reduce the remaining stiffness of the laminate. The closer the p-value is to the repair configuration of 12.7~14 mm, the smaller the influence of hygrothermal effect on the natural frequency, and the better the moist heat stability and repair effect of the laminate.

Study on three impact damage of composite materials based on prefabricated layered damage method

XU Liang, HU Hongming, ZHOU Song, SONG Wanwan

2023, 0(11): 21-27. DOI: 10.19936/j.cnki.2096-8000.20231128.003

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In ABAQUS/Explicit, a three-dimensional simulation model of three impacts of composite laminates is established. The state variables of the previous impact damage are prefabricated into the next impact model by means of prefabricated layered damage method, and the three-dimensional Hashin criterion and stiffness degradation scheme are programmed into the VUMAT subroutine. The intra-layer damage, inter-layer damage and contact force of laminates during three impact process were analyzed. The results show that the simulation results are in good agreement with the impact test results, and the established model can better react to the damage evolution process under the three impacts of the composite laminate. Compared with the subsequent impact, the maximum contact force of the first impact is the smallest, the shape of the delamination damage is mainly formed by the first damage, and the subsequent impact only increases the damage area of the delamination damage.

Numerical simulation of residual tensile strength of FMLs with low-velocity impact damage

ZHANG Shaofeng, WEI Jinhui, TANG Xinchun, XU Jiajing, LIU Xinyu, YAO Lu

2023, 0(11): 28-36. DOI: 10.19936/j.cnki.2096-8000.20231128.004

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Fiber metal laminates (FMLs) combine the excellent properties of composite materials and metal materials, which is gradually used as a lightweight structure for automobiles and airplanes. However, some damage must appear inside FMLs after low-velocity impact, especially the complex damage modes in the composite material, which can cause inestimable loss for the residual tensile strength of FMLs. Therefore, it is of great engineering significance to explore the residual tensile strength of FMLs with various impact damage. In this paper, the numerical models of FMLs under low-velocity impact and quasi-static tensile are firstly established, and their accuracy and reliability are verified by the low-velocity impact/tensile tests. Then, in virtue of finite element restart technology, an integrated numerical model combined with impact, separation and tension of FMLs is established, and the residual tensile strength of FMLs under different impact loadings is numerically simulated, and the residual strength rules after impact loadings can be further summarized. Finally, the residual tensile strength of FMLs is studied based on the quantitative model after impact, and compared with the results between the integrated numerical model and the quantitative mode. The accuracy of the quantitative analysis method is verified, which can save the calculation cost and improve the research efficiency.

Study on interfacial compatibility between AC531 resin and adhesive film

ZHAI Quansheng, MIAO Chunhui, CUI Haichao, ZHANG Chenqian, ZHAO Yanwen, YE Hongjun

2023, 0(11): 37-43. DOI: 10.19936/j.cnki.2096-8000.20231128.005

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In this paper, J-116B adhesive and J-375 adhesive were used to prepare adhesive samples by co-curing molding method, and the adhesive samples were subjected to wet heat accelerated aging. The tensile and shear properties of the samples before and after aging were tested, and the reasons for the difference in properties and the mechanism of interface failure were analyzed. The results show that the interfacial compatibility between AC531 resin and J-375 adhesive is better than that between AC531 resin and J-116B adhesive. This is because the AC531 resin and the J-375 adhesive have a higher degree of overlap in the curing reaction process window, and the apparent activation energies of the two are closer.

Research on hygrothermal ageing models of carbon fiber composites

WANG Weili, WEI Cheng, TIAN Jing

2023, 0(11): 44-48. DOI: 10.19936/j.cnki.2096-8000.20231128.006

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Hygrothermal ageing test of carbon fiber composites were carried out with three temperature conditions of 40 ℃, 60 ℃ and 80 ℃ in 90%RH, and dynamic and mechanical properties of the composites were tested. Based on the results of SEM, mechanical characteristics,IR and DSC, two kinds of hygrothermal ageing models were selected, then formulas of two hygrothermal ageing models were proposed in 90%RH after parameters were calculated. The results show that the dynamic model should be chosen in the conditions with different temperatures, while the residual strength model should be chosen in the conditions with extended time variable.

Research on composite material forming mould compensation and component adaptive adjustment method

BAO Yidong, ZHANG Heng, ZHANG Huijie, HUAN Lei, YANG Zhiyong, ZUO Xiaobiao, AN Luling

2023, 0(11): 49-57. DOI: 10.19936/j.cnki.2096-8000.20231128.007

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The finite element model of composite component should be re-modeled for mould compensation after curing deformation which is with low efficiency, heavy workload and lack of validation. A method of mould surface compensation for composite material molding and component adaptive adjustment was proposed to aim at the problem that the finite element model of compsite component needs to be adjusted after mould surface compensation of composite forming mould. The virtual material model was used to realize the fully fitting of the component mesh and the compensated mould mesh. The typical component was used to verify the correctness of the method, and the experimental results of this method were discussed based on an example of a complex barrel-shaped panel. The results show that: ①The curing deformation of T-stiffened panels and complex barrel-shaped panels can be significantly reduced by mould surface compensation; ②The method proposed in this paper was used to test the curing deformation of T-stiffened panels and the maximum relative error between the measured test deviation and the numerical simulation deviation was 17.20% which meets the engineering acceptance standard; ③The method of composite material forming mould compensation and component adaptive adjustment can avoid the reconstruction operation of component finite element model after mould compensation, improve the compensation efficiency, and improve the accuracy of the results.

Axial compression properties of basalt fiber reinforced polymer-polyvinyl chloride composite reinforced fiber recycled concrete short columns

ZHANG Zhenlei

2023, 0(11): 58-69. DOI: 10.19936/j.cnki.2096-8000.20231128.008

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In order to study the axial compression performance of fiber-recycled concrete short columns under different restraint conditions, 45 recycled concrete short columns were studied in static axial compression tests. The influence of the polyvinyl chloride (PVC) pipe, the number of basalt fiber reinforced polymer (BFRP) sheet layers, and the composite reinforcement of BFRP sheet-PVC pipe on its uniaxial axial compression performance were discussed. The results show that: the bearing capacity, ultimate strain, and ductility of specimens are all improved as the number of BFRP layers is raised. BFRP-PVC reinforcement specimens, when coupled with the benefits of various materials, not only enhance concrete’s compressive strength but also solve the problem of brittle failure to a certain extent, and has broad application prospects. In addition, the ultimate stress model and ultimate strain model formulas are established, and the calculated values are in good agreement with the test values, providing a certain theoretical basis for future engineering applications.

Optimal layup analysis and anti-fatigue verification of bicycle rim with inter-ply hybrid carbon/glass fiber reinforced composites

ZHOU Yongjun, QIU Yuhong, LI Hongzhou

2023, 0(11): 70-77. DOI: 10.19936/j.cnki.2096-8000.20231128.009

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Bicycle rim with moderate cost, high safety performance, anti-fatigue and other characteristics can be designed through numerically optimal analysis of bicycle rim with inter-ply carbon/glass hybrid fiber reinforced polymer composites. To simulate the behavior of the composite bicycle rim in service by finite element analysis, it can provide relatively reliable scheme for experiments and minimize the waste of the raw material in experiments, and reduce the cost of design and preparation of the composite rim. In this paper, a bicycle rim model was constructed by adjusting the order of carbon fiber prepreg and glass fiber prepreg, the proportion and order of each ply orientation, and the mechanical properties of the rim in service were calculated by the software ABAQUS. The optimal layup scheme was obtained by comparing each scheme of the simulated composite rim in service. The results of accelerated fatigue test (50 000 times) demonstrate that selecting the optimal lay up scheme of rim sidewall and rim bead to make the composite bicycle rim can significantly improve its anti-fatigue capability.

Lamination optimization research on the rear spar of a composite horizontal tail

LIU Jia, WU Jiang, ZHANG Fuen, WU Daoming

2023, 0(11): 78-83. DOI: 10.19936/j.cnki.2096-8000.20231128.010

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In order to effectively reduce the weight of the horizontal tail, reasonably arrange the lay-up method and improve the utilization efficiency of the composite material, the finite element model of the horizontal tail was established with the help of professional analysis software Patran & Nastran, and the static strength of the horizontal tail was calibrated. Then the test piece and test fixture of the main bearing structure of the horizontal tail are designed and manufactured, and the test verification is completed. The test results show that the stress distribution of the two methods is basically the same, which shows that the finite element model is reasonable. When the horizontal tail is bearing the maximum inertia overload, the maximum stress value of the rear spar of the main load-bearing member is far less than the allowable value of the composite material. Taking the thickness of the layer as the design variable and the material stress limit as the constraint, the layout style of the rear spar is optimized. The results show that the weight of the optimized structure is reduced by 15.75%, and the strength performance meets the requirements.

Analysis and study on multiple factors affecting compaction of 3D four-directional C/C composite preform

REN Hongqing, DONG Jiuzhi, MEI Baolong, CHEN Yunjun, JIANG Xiuming

2023, 0(11): 84-89. DOI: 10.19936/j.cnki.2096-8000.20231128.011

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In order to improve the fiber volume fraction of the preform, based on the 3D four-direction C/C preform compaction process, the orthogonal experiment was designed to analyze the influence of the compaction times per cycle, pressure duration and content of additives on the fiber volume fraction. Results show that the content of additives has the greatest impact on the final fiber volume fraction, followed by the compaction times per cycle and the impact of pressure duration is the smallest. The fiber volume fraction first increases and then decreases with the increase of content of additives, with the increase of pressure duration and compaction times per cycle. The BBD response surface optimization experiment was designed to establish the corresponding fiber volume fraction mathematical model and verify the reliability of the model, and the process parameters were optimized and verified by experiments. The results show that each cycle is compacted three times, pressure duration is 7 s, two bundles of fibers with additives are the optimal parameters. The final fiber volume fraction of the preform woven under the optimal parameters is only 0.24% different from the predicted value, which is at least 4.54% higher than that of the original process parameters. Finally, it can be seen from the microscopic observation that the preform woven under the optimal parameters is more dense.

Stiffness analysis of embedded bushing with stud bolt connection in wind turbine blades

GAO Xiang, YU Guang’an, LIU Zhiqiang, XI Zhenzhao, LIU Fangfang, SONG Xiaofei, QIN Zhiwen

2023, 0(11): 90-95. DOI: 10.19936/j.cnki.2096-8000.20231128.012

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Embedded bushing with stud bolt connection is a major method for root connection and segment joint of large wind turbine blades. Accurate computation of clamped member stiffness is a key issue to ensure the safety design of static and fatigue loads of wind turbine blades. Based on the embedded bushing with stud bolt connection used in a real sectional blade, assuming frustum distribution of the stress field of the hollow cone clamped embedded bushing members, the analytical expression of axial member stiffness could be derived. The finite element method was implemented to determine the suitable conical half-angle. The effects of the bolt diameter, the thickness of the bushing, and the grip length on the axial member stiffness were further studied. By comparing the analytic and numerical solutions, the accuracy of the theoretical expression of axial member stiffness was verified. Member stiffness increases with the diameter of the bolt and the thickness of the embedded bushing but reduces gradually with grip length. The results indicated that the preferable conical half-angle for embedded bushing with stud bolt connection is between 15° and 18°.

Automatic fiber placement of large-size gradual section spar

XUE Ke, HE Daliang, XUE Kai, MA Zhanyu, TANG Shanshan, ZHANG Liang, FANG Xiaobin

2023, 0(11): 96-101. DOI: 10.19936/j.cnki.2096-8000.20231128.013

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Spar is the main load-bearing component of the aircraft. In order to ensure its forming quality and production efficiency, it is necessary to adopt an automated forming method to manufacture the spar component. In this paper, the application and research status of the spar forming methods are introduced. According to the structural characteristics of large-size gradual section spar (>10 m long), the automatic fiber placement technology of composite spar is studied. Then, with the gantry-type automated fiber placement machine of M.TORRES as the laying platform, the key points of automatic fiber placement in spar are put forward. Furthermore, the trajectory planning method of the layup at different angles is determined. Combined with the trajectory planning, the optimization scheme of fiber placement for spar is proposed. Finally, the feasibility and correctness of the trajectory planning algorithm and the optimization scheme are verified by the manufacturing of the full-size composite spar using the automatic fiber placement, which provides a reference for the application of the automatic fiber placement technology in the forming of the large-size composite spar in China.

Prediction model of FRP-concrete bond strength based on GMDH

YI Xiaoyuan, ZHANG Ailing

2023, 0(11): 102-107. DOI: 10.19936/j.cnki.2096-8000.20231128.014

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In recent years, fiber-reinforced polymer (FRP) has been widely used in concrete reinforcement. However, the prediction accuracy of the existing FRP-concrete interface bond strength prediction models is low, which cannot provide an effective reference for the practical applications of FRP composites. Therefore, a large database consisting of 855 sets of test data was established in this study, and a bond strength model with high prediction accuracy was proposed by using group method of data handling (GMDH). In order to verify whether the GMDH model can provide a more valuable reference for the calculation of the bond strength of the FRP-concrete interface, the GMDH model was compared with seven existing literature models, and coefficient of determination (R²), coefficient of variation (COV) and relative square root error (RRSE) were used to evaluate the prediction results of these models. The results showed that, compared with the existing literature models, the R², COV and RRSE values of the proposed GMDH model were improved by at least 11.9%, 30.9% and 35.3%, respectively. Therefore, the GMDH model can provide a more effective reference for the practical applications of FRP composites.

Comparison of process-induced distortion prediction methods of carbon fiber composites

LUO Ling, ZHANG Tao, TIAN Zhili, LIU Leibo, XIA Yanan, LI Zhuoda, WEI Hongfeng

2023, 0(11): 108-115. DOI: 10.19936/j.cnki.2096-8000.20231128.015

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Process-induced distortion (PID) of the carbon fiber composite parts cause assembly difficulties and residual stresses. Hence, it is very necessary to establish an accurate prediction method for PID. In this study, we compared the two most widely used PID simulation methods: The semi-empirical model and the CHILE model, and validated them through the autoclave process experiment. Experimental results suggest that the two models can accurately predict the PID behavior of composite plates with the errors less than 10%. Based on the CHILE model, the influence of material parameters on PID was studied. The results suggest that the transverse coefficient of thermal expansion had a significant influence on the PID, then, the transvers coefficient of curing shrinkage also had an important influence on the PID.

A review of the development of LCM forming technology for carbon fiber complex components

LI Xianyang, LIU Bin, YU Yalin, ZHOU Helezi, ZHOU Huamin

2023, 0(11): 116-121. DOI: 10.19936/j.cnki.2096-8000.20231128.016

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Liquid composite molding (LCM) is one of the main molding processes for fiber reinforced resin matrix composites. With the development of the aerospace industry, high-end equipment has put forward more requirements on the performance and complexity of composite components, and it is necessary to innovate the current LCM molding process. Therefore, the new composite material molding process has become a research hotspot. According to the process categories, this paper summarizes the principle, process characteristics and industrial applications of LCM, automated fiber placement LCM, three-dimensional textile preform LCM and co-curing LCM. Finally, the future development direction of LCM process is suggested.

Research progress in 3D printing of fiber-reinforced thermoplastic composites

REN Jiajun, SUN Ying, JU Bowen, YU Xiao

2023, 0(11): 122-128. DOI: 10.19936/j.cnki.2096-8000.20231128.017

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3D printing (3DP), also known as additive manufacturing (AM), is an emerging technology for constructing three-dimensional objects through successive layered slicing and layered deposition of materials. In recent years, research on 3D printing technology has grown exponentially around the world. 3D printing technology has a wide range of applications in aerospace, rail transportation, electronics and biomedicine. With the application of fiber as reinforcement in 3D printing of thermoplastic polymer, the comprehensive mechanical properties of composite materials are greatly improved. Based on a brief introduction of the development history of 3D printing of fiber reinforced composites, this paper reviews the performance optimization methods, existing problems and future development trends of 3D printing of fiber reinforced composites.

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