Table of Content

28 August 2021, Volume 0 Issue 8

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BASIC STUDY

Analysis of calculation method of critical loads for local buckling of I-section FRP members

ZHAN Yang, LI Ben-ben, CUI Jing, YANG Ya-qiang

2021, 0(8):  5-10.  DOI: 10.19936/j.cnki.2096-8000.20210828.001

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The prediction accuracies of the seven generic closed-form solutions recommended by Kollar, Qiao, Cardoso, Pecce, ASCE, Strongwell and Creative corporations which can be used to predict the local buckling loads of I-section FRP members are evaluated according to test results published in the literature. The results show that the closed-form equations recommended by ASCE and Cardoso are too conservative with corresponding average absolute errors (AAE) of 53% and 49%, approximately. The equation recommended by Strongwell is the most unconservative of all equations with AAE of 60%. The equations recommended by Pecce and Creative are established based on ASCE equations, and the corresponding coefficients are used to improve prediction accuracy. However, the two equations cannot reflect the mechanical mechanism of local buckling failure of FRP members, and the corresponding coefficients have no specific mechanical implication. The AAE values of the two equations from Pecce and Creative are 17% and 15%, respectively. The two solutions provided by Kollar and Qiao are developed based on the discrete element method and the constraint stiffness between flange and web is taken into account. The AAE values of the two equations from Kollar and Qiao are 17% and 18%, respectively. Considering the mechanical implication and prediction accuracy, the closed-form solution developed by Kollar is recommended to be used to predict the local buckling loads of I-section FRP members.

Damage mechanism identification of carbon fiber reinforced polymer based on modal acoustic emission

ZHANG Hong-yuan, JIANG Peng, SONG Jia-yu, LI Wei, ZHANG Zhi-yuan, LI Cai-rui, YAN Xiao-wei

2021, 0(8):  11-17.  DOI: 10.19936/j.cnki.2096-8000.20210828.002

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As a new material with high performance, Carbon Fiber Reinforced Polymer (CFRP) have been widely used in aerospace, new energy vehicles and other fields because of their high specific strength, specific modulus and fatigue resistance. However, it will be affected by fatigue, creep and other factors during its service, resulting in internal damage to the structure, consequently reducing the safety and reliability of the material. Nowadays, the damage detection and evaluation of CFRP has become a research hotspot. At present, acoustic emission detection technology has been widely used in the damage detection of CFRP. With its unique ability of on-line and continuous monitoring, the damage process of materials can be monitored and evaluated in real time. However, due to the complexity of damage mechanism in CFRP, there are still some problems in the correct identification of damage acoustic emission signals. For this reason, an algorithm for identifying and classifying damage signals of CFRP based on modal separation method was proposed in this paper, which could realize the modal characterization of damage acoustic emission signals of composites. First of all, based on the modal analysis results of simulated sound sources of CFRP laminate, different ranges of digital filters were designed to realize the separation of S₀ and A₀ modes in acoustic emission signals. Then, according to the modal characteristics of the single damage type signals of fiber breakage and matrix cracking, the identification and classification algorithm of damage signals was established, and its resolution to the single damage type signals was verified. Finally, the algorithm was used to analyze the in-plane bending damage signals of laminates to verify its effectiveness in the identification of complete structural damage signals of CFRP. The results show that the resolution of this algorithm in fiber breakage and matrix cracking tests is as high as 97.3% and 92% respectively, and the damage process characterization of carbon fiber composite laminates is also realized. It is proved that it can be used to identify the damage mechanism of complete structures of CFRP.

Quasi-static compression test of lattice web reinforced foam sandwich composite beam

LI Chong, FANG Hai, ZHU Lu, QIAN Zhen, LI Xiao-long

2021, 0(8):  18-24.  DOI: 10.19936/j.cnki.2096-8000.20210828.003

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The vacuum introduction molding process is used to prepare a two-way lattice web reinforced foam sandwich composite beam with polyurethane foam as the core material and glass fiber reinforced composite material as the panel and lattice web. The quasi-static compression performance test and comparative analysis of ordinary foam sandwich beam and lattice web reinforced foam sandwich beam are carried out. The results show that compared with ordinary foam sandwich beams, the compression resistance of the lattice web reinforced foam sandwich beam has been significantly improved. Through theoretical deduction, the quasi-static compression expression of the lattice web reinforced foam sandwich composite beam is obtained. And compared with the experiment, the results are consistent.

A study on damage identification of functionally graded euler-bernoulli beam by the method based on modal strain energy and frequency fusion

LIANG Fu-an, HUANG Jun, HUANG Li-xin

2021, 0(8):  25-30.  DOI: 10.19936/j.cnki.2096-8000.20210828.004

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For functionally graded (FG) Euler-Bernoulli (EB) beams, a new damage identification method based on modal strain energy fusing with the natural frequency is proposed in this study. The natural frequency and shape modal parameters of the structure are firstly calculated by finite element method, and then the calculation formula of modal frequency strain energy is constructed on the basis of the elemental modal strain energy fusing with the natural frequency. The change of elemental modal frequency strain energy is calculated before and after the damage of the beam structure, and the elemental index of damage identification is defined. Numerical examples show that the new damage identification method of the FG Euler-Bernoulli beam can effectively identify the damage elements of the beam. It is found from the identified results that the new method has good noise resistance performance.

Study on reaction mechanism of vinyl polysilazane/benzoxazine

XU Ya-feng, SONG Jin-mei

2021, 0(8):  31-38.  DOI: 10.19936/j.cnki.2096-8000.20210828.005

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Vinyl polysilazane (PSN) and purified benzoxazine monomer (BZ) melt blending were used to prepare a PSN/BZ hot melt resin with both ceramicization and higher mechanical properties. The effect of PSN, BZ, and DCP on the reactivity of PSN/BZ were compared and analyzed by a step-by-step multi-factor controlled variable DSC experiment. The curing reaction kinetics of PSN/BZ were studied by non-isothermal DSC, and comprehensive analysis by IR and DSC PSN/BZ functional group evolved to characterize the curing reaction mechanism of PSN/BZ. The results show that the curing reaction mechanism of PSN/BZ is mainly the C=C opening addition polymerization of PSN initiated by DCP, the deamination condensation reaction between N-H bonds, and the ring-opening polymerization of BZ initiated at high temperature. At the same time, the phenolic hydroxyl group in the BZ polymer and the Si-N bond in the PSN can also partially react to form Si-O-Si. The curing reaction of PSN/BZ is approximately a first-order reaction, and the curing reaction order is not an integer, which proves that the curing process is more complicated, its activation energy is low, and the reaction is easy to proceed, but the curing temperature is relatively high.

Analysis on tensile properties of BFRC

HE Jing-jing, SHI Jun-ping, ZHANG Yong, DI Sheng-jie, LU Hao-dan, LIU Xiao-min

2021, 0(8):  39-43.  DOI: 10.19936/j.cnki.2096-8000.20210828.006

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Based on the experimental study, the influence of fiber volume fraction and fiber length on the tensile strength and tensile strain of BFRC are discussed. And the tensile failure mode of BFRC is analyzed. The results show that the fiber volume fraction can significantly improve the tensile strength of BFRC. The tensile strain of BFRC is obviously enhanced by fiber length. The fracture surface roughness coefficient of BFRC decreases in power function with the increase of fiber volume fraction. And the roughness coefficient can be used as the evaluation index of FRC tensile properties.

APPLICATION RESEARCH

The effect of high temperature on the tensile properties and structure of several organic high-performance fibers

LIN Ting-ting, SHAO Hui-qi, JIANG Jin-hua, CHEN Nan-liang, LIU Shi-hai

2021, 0(8):  44-49.  DOI: 10.19936/j.cnki.2096-8000.20210828.007

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Lightweight, high-strength, organic high-performance fibers with a wide temperature range are often used in high-temperature filtration, national defense, military, special protection, aerospace and other fields. In order to explore the heat resistance and structural changes of several organic high-performance fibers, i.e., the polyimide fiber (PI) and polyarylate fiber (PAR)^®, polyarylate fiber (PAR) Yokolar^® and aramid Ⅲ fiber, Vectran scanning electron microscope, thermogravimetric analyzer, and Fourier infrared spectrometer were used to study. The surface morphology, tensile properties, and chemical structure changes of four organic high-performance fibers after being treated at a high temperature of 200 ℃ to 350 ℃ for a certain period of time. The results show that: PI, Vectran^®, Yokolar^® and Aramid Ⅲ fiber have a breaking stress of 3.3 GPa, 4.0 GPa, 3.9 GPa and 5.0 GPa. After a long time treatment at 200 ℃~350 ℃, the PI fiber surface has no obvious defects, the other three types of fiber grooves, particles and other defect structures have increased. The characteristic peaks of the infrared spectrum of PI fiber have not changed significantly, and the corresponding functional groups have not been completely destroyed by high temperature. The other three kinds of fibers' infrared spectra characteristic peaks have different degrees of weakening or disappearance, some chemical bonds are broken; heat resistance PI>Aramid Ⅲ>Vectran^®>Yokolar^®, the temperature corresponding to 5% mass loss is 529 ℃, 506 ℃, 472 ℃ and 445 ℃. Molecular chain breakage and the increase of fracture and surface defects are the key influencing factors for the decline of fiber mechanical properties.

Low velocity impact properties of foam core sandwich composites with looped fabric

CUI Wei-yun, CHEN Guang-si, XIONG Xin-fa, PENG Jin-feng, CAI Deng-an, ZHOU Guang-ming

2021, 0(8):  50-59.  DOI: 10.19936/j.cnki.2096-8000.20210828.008

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According to the ASTM test standard D7136, the impact test of low impact impact on the wound fabric foam sandwich composite (U-cor) was carried out by drop hammer impact test. Four kinds of sandwich density, two kinds of sandwich thickness and three kinds of panel layers were prepared by polyurethane foaming process. The impact tests were carried out under the energy of 5 J, 10 J and 15 J, respectively. The experimental results show that under low energy impact, when the density of sandwich is pretty high, the contact force-time history curve is close to a quadratic curve symmetrical along the vertex. When the impact energy increases to a certain extent, the maximum contact load of loop starting fabric sandwich panel is higher than that of the same type of plain weave fabric sandwich panel. Due to the special forming process of the foam core sandwich composite with loop fabric, the increase of the core thickness will increase the local stiffness near the impact surface when the average density of the sandwich is the same, which will lead to a larger difference in impact response and an increase in impact resistance of sandwich panels with different thickness.

Research on bearing/ablation integrated composite wing of hypersonic speed missile

ZU Lei, LU Jin-hu, ZHANG Qian, ZHANG Gui-ming, WU Qiao-guo, WANG Hua-bi

2021, 0(8):  60-65.  DOI: 10.19936/j.cnki.2096-8000.20210828.009

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In this paper, the composite wing structure of a missile is designed. According to the requirement of ablative resistance performance and stiffness performance, this paper presents the molding technology scheme of the ablative resistance functional layer for the outer layer and the bearing layer for the inner layer, and the co-curing of the functional layer and bearing layer. According to the ablation test, it was found that the ablative performance of boron phenolic resin was better, so the prepreg of boron phenolic resin was used as the functional layer of the wing of missile and the prepreg of epoxy resin as the bearing layer. The experimental results of ablative and mechanical properties were satisfactory. The mechanical properties of the missile wing were numerically simulated by ABAQUS finite element analysis software. The maximum deformation was located at the back and upper part of the missile wing. The simulation results were in good agreement with the test results, and the error rate was 6.47%. Compared with the traditional aluminum alloy missile wing, the composite missile wing can reduce the weight by 42.8%, which has obvious advantages.

Experimental study on axial compression bearing capacity of concrete short column strengthened with different fiber reinforced composites

GUO Xiao-yun, CHEN Jie, TANG Yong-ming

2021, 0(8):  66-72.  DOI: 10.19936/j.cnki.2096-8000.20210828.010

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Axial compression tests were conducted with 70 concrete short columns, including 5 concrete columns with square cross sections, 5 concrete columns with circular cross sections, 30 confining square concrete columns with fiber reinforced composite material and 30 confining circle concrete columns with fiber reinforced composite material. The effectiveness of strengthening between different shaped reinforcing columns with different FRP were analyzed and compared. Design values of compression bearing capacity were calculated according to Chinese "Code for design of strengthening concrete structure" (GB 50367—2013) and American "Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures" (ACI 440.2R-17). By comparing the test results and calculated results, the safety reserve of bearing capacity design value of FRP strengthened column in Chinese and American codes was analyzed. Suggestions for further revision on code for design of FRP strengthening concrete are put forward.

Unconfined compressive properties of fiber modified cement stabilized iron tailings

JIANG Ping, YANG Jian-dong, LI Na, QIAN Jian

2021, 0(8):  73-79.  DOI: 10.19936/j.cnki.2096-8000.20210828.011

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The resource utilization of iron tailings is an effective measure to reduce the risk of tailings inventory and save construction materials. Polypropylene fiber and glass fiber were used to modify cement stabilized iron tailings. The fiber content is 0, 0.25%, 0.5%, 0.75%, 1%, and the curing period is 7 days and 28 days, respectively. Fiber modified cement stabilized iron tailings (FCIT) was characterized by brittleness index, modulus strength ratio and toughness index. The mechanism of fiber was analyzed by SEM. The results show that the optimal content of glass fiber is 0.5%, while that of polypropylene fiber is 1%. Under the optimal dosage, the effect of glass fiber and polypropylene fiber on unconfined compressive properties of cement iron tailings is basically the same. Under the same fiber content, the unconfined compressive strength and toughness index of 7-day curing age are lower than that of 28 days, and the effect of curing age on the brittleness index of CIT is not obvious without fiber. The action mechanism of fiber on cement iron tailings can be divided into drawing, interweaving and agglomeration.

Design and experiment of carbon fiber pre impregnated belt forming equipment based on industrial robot

YAN Dong, HU Ye-fa, ZHANG Jin-guang, MA Ze-chao, FU Kai

2021, 0(8):  80-84.  DOI: 10.19936/j.cnki.2096-8000.20210828.012

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To achieve winding and laying of different parts and meet the requirements of flexible manufacturing, a design scheme of carbon fiber pre impregnated tape forming equipment based on KUKA robot is proposed in this paper. This paper first puts forward the overall scheme of the equipment, then introduces the different structural principles of the equipment and the working process of the equipment. Finally, it shows the real object of the molding equipment and verifies that the equipment can be used in the actual production and processing.

Experimental study on mechanical properties of basalt fiber SiO₂ reinforced concrete

REN Li-li

2021, 0(8):  85-90.  DOI: 10.19936/j.cnki.2096-8000.20210828.013

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The mechanical properties of basalt fiber and nano-SiO₂ reinforced concrete were studied by cube compressive strength, splitting tensile strength, and flexural strength tests with basalt fiber volume fraction and nano-SiO₂ substitution rate as factors. It is found that the basalt fiber can change the failure mode of Nano-SiO₂ concrete. When basalt fiber and nano-SiO₂ are mixed, the cube compressive strength, splitting tensile strength, and flexural strength of concrete matrix are improved. The results show that the cubic compressive strength and flexural strength of basalt fiber nano-SiO₂ concrete are the best when basalt fiber volume content is 0.10% and nano-SiO₂ content is 1.0%. When the volume fraction of basalt fiber is 0.15% and the replacement rate of Nano-SiO₂ is 1.5%, the splitting tensile strength of basalt fiber nano-SiO₂ concrete is the best, which is 22.97% higher than that of plain concrete. Based on the experimental data, the cube compressive strength prediction model of basalt fiber nano-SiO₂ reinforced concrete is established.

Investigation of the microstructure and high temperature anti-oxidation property of SiC-Mo(Si,Al)₂ multi-coating for carbon/carbon composites

HOU Dang-she, LI Ke-zhi

2021, 0(8):  91-94.  DOI: 10.19936/j.cnki.2096-8000.20210828.014

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A SiC-Mo(Si,Al)₂ oxidation protective coating on carbon/carbon composites was prepared by high temperature in-situ reaction. Effects of the content of Al and Si on the microstructure and high temperature anti-oxidation property of the multi-coating were studied by XRD, SEM and isothermal oxidation test, and the failure reason of the coating at high temperature was analyzed. The results showed that the addition of Al enhanced the infiltration capacity of the embedded powder. When the molar ratio of Al/Si was 1∶10, the coating was composed of mainly Mo(Si,Al)₂, MoSi₂, SiC and Si, and it was thick and dense, giving good oxidation protective ability. The holes were formed in the SiO₂ glass layer during oxidation, resulting in the quick consumption of the coating materials and the formation of the penetration cracks in the coating, which was the main reason for the failure of the coating.

Experimental study on failure mechanism of sandwich T-joint by tenon-and-mortise subjected to flexure

ZHANG Kuan, GUO Xiao-ning, ZHANG Xiao-jing

2021, 0(8):  95-99.  DOI: 10.19936/j.cnki.2096-8000.20210828.015

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As a special form of composite material, the composite honeycomb sandwich structure has high specific bending stiffness, specific bending strength and designability, as well as physical properties such as sound absorption, sound insulation and heat insulation, and is used in the aviation field. Composite sandwich structure T-joints, as a common connection form in the aviation and marine fields, have attracted lots of attention from scholars. Tenon and mortise T-shaped structure can effectively improve the structure efficiency and reduce weight. However, the existing work mainly focuses on the theoretical analysis and experimental research of the traditional T-joint, and there is little research on the tenon-and-mortise T-joint. This article presents an experimental study on the bending failure mode and load-bearing capacity of the composite honeycomb sandwich tenon-and-mortise T-joint. Five kinds of T-joint test specimens with different tenon widths and different tenon numbers were tested, and bending moment-displacement curves were drawn. The bending test results show that the failure of the T-joint specimens includes tensile failure of the adhesive surface in the tenon shoulder area, shear failure of the adhesive surface of the upper panel in the tenon area or tensile fracture of upper panel. In the process of loading, the tenon shoulder area is firstly debonded, then the tenon area bears most of the load, and finally the upper panel and the bottom plate in the tenon area are debonded or the panel is broken. Parameter studies show that the increase of the width and number of tenons can significantly increase the bending stiffness of T-joints, and it also makes an important contribution to improve the bending bearing capacity of the T-joint.

Some research and innovation thinking base on wind blade process

ZHAO Li-yan, LIU Yan, WANG Xiang-dong, XU Jun

2021, 0(8):  100-104.  DOI: 10.19936/j.cnki.2096-8000.20210828.016

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The rationality of wind turbine blade manufacturing process system has far-reaching influence on the successful production of new product development, manufacture and models. Based on the aeronautical technology research system and the actual situation of wind turbine blades, the logic structure and organizational characteristics of the process system of large composite component-wind turbine blades are summarized, and the process design logic for wind turbine blade manufacturing is formed. Finally, constructed for manufacturing process research and innovation system, put forward wind-power blades driven design process database, based on the process parameters, manufacturing entity oriented, efficient control and so on, and expounds the concrete contents, for the large composite components-a process of wind-power blades to provide effective support capacity building and innovation.

Research on VARI process simulation and manufacturing technology of composite panel with hat-shaped stringer

CHEN Ji-ping, ZHONG Zhen-chao, LIU Yu-ting, ZHENG Yi-zhu, NING Bo

2021, 0(8):  105-111.  DOI: 10.19936/j.cnki.2096-8000.20210828.017

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The VARI process simulation of panel with hat-shaped stringer is carried out by PAM-RTM software. During the simulation, effect of the distribution position and quantity of injection ports and vent ports in typical areas such as panel skins and stringers, gravity of resin and vent port close sequence were analyzed respectively. The simulation results show that the possibility of defect appearance tends to be the lowest, when flow channel is designed in following way: ① The injection ports are distributed at panel skin edge and the vent ports at top of stringer. ② The vent ports close sequentially from the edge of the panel to the central area. Through the simulation results which were verified by the panel manufacturing with VARI and quality inspection results, the optimal resin flow and tooling design was finally obtained.

REVIEW

Research progress of influencing factors on the interfacial strength between carbon fiber and polyetherketoneketone

ZHANG Feng, JIAO Meng-xiao, LI Bo-lan, ZHANG Xiao-hua

2021, 0(8):  112-119.  DOI: 10.19936/j.cnki.2096-8000.20210828.018

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Polyetherketoneketone (PEKK) is a semi-crystalline thermoplastic with high mechanical performances, high heat resistance, and chemical resistance. Therefore, carbon fiber (CF) reinforced PEKK composite has become a potential advanced thermoplastic composite owing to the superior mechanical properties, and simple processing technique as well. However, the weak interfacial bonding between CF and PEKK, as prepared by using the existing methods, strongly hinder the real applications. In this paper, by summerizing the present research progresses, the key factors affecting the interfacial strength are discussed and concluded by analyzing the effects of interface structure and stress transfer in the composites. Thus far, the infiltration theory, chemical bond theory, and physical adsorption theory have been widely discussed and successfully applied in the interface enhancement. For the CF/PEKK composites, the interface can further be improved by adjusting the proportion of terephthalyl/isophthalyl isomers ratio in the PEKK molecular chain or developing suitable ether-ketone-based sizing agents.

Research progress in heat-resistant modification of phenolic resin

XU Guo-juan, CHEN Jing-ju, PAN Tian-chi, ZHANG Li

2021, 0(8):  120-128.  DOI: 10.19936/j.cnki.2096-8000.20210828.019

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With excellent heat resistance and ablative property, good mechanical properties and outstanding flame retardant properties, phenolic resin is widely used in aerospace, friction materials, fire retardant and other fields. Improving the heat resistance of phenolic resin has always been a hotspot in the industry. This article reviews the heat resistance modification methods of phenolic resin in recent years, including structural modification, nano-doping, volatile capture, and ceramicization. The structural modification method is highlighted. Finally, the problems existing in this field are summarized and their development prospects are prospected.