COMPOSITES SCIENCE AND ENGINEERING

Research on compression damage of CFR plain woven material after impact based on progressive homogenization multi-scale method

ZHANG Chen-xi, LOU Yuan-feng, TIE Ying, CONG Shi-fan, LI Yao-lei

2021, 0(10): 5-12. DOI: 10.19936/j.cnki.2096-8000.20211028.001

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A progressive homogenization multi-scale analysis method is developed to predict the response and damage of CFR plain woven laminates under low velocity impact and compression after impact (CAI) in this paper. First, a microscopic unit cell model of the carbon fiber bundle is established, the equivalent stiffness and strength of the fiber bundles are calculated. Then, a mesoscopic unit cell model is established, and the mechanical properties at 0° and 90° are calculated. Additionally, the mesoscopic model is transformed into an equivalent subcell model usinga progressive homogenization method, which is then expand into a macro-scale integrated three-dimensional finite element model with low-velocity impact and compression. The three-dimensional Hashin failure criterion and the continuous damage mechanics model are used to simulate the damage initiation and evolution of CFR plain woven material laminates, and the cohesive zone model is used to evaluate the interlayer damage. The results show that the numerical analysis results of CFR plain weave material after low-velocity impact and compression are in good agreement with the experimental results, which verifies the reliability and accuracy of the progressive homogenization multi-scale analysis method. With the increase of impact energy, the remaining compressive strength of the laminate decreases nonlinearly. For the fiber damage and matrix damage under low-velocity impact load, as the impact energy increases, the damage also increases. However, the CAI behavior is the opposite. The area of compression damage decreases with the increase of impact energy.

Experimental study on dynamic mechanical properties of carbon fiber reinforced concrete

WU Wei, FENG Hu

2021, 0(10): 13-18. DOI: 10.19936/j.cnki.2096-8000.20211028.002

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In order to explore the safety of carbon fiber reinforced concrete under dynamic load, the longitudinal wave velocity of carbon fiber reinforced concrete specimens with different content was measured by non-metallic ultrasonic detector, and scanning electron microscopy was used to observe the bonding method between carbon fiber and concrete. The 74 mm diameter variable cross-section separated Hopkinson pressure bar test device was used to perform impact compression tests on four concrete specimens with different carbon fiber content at different strain rates, and analyze their stress-strain curves, peak stress, ultimate strain and DIF (dynamic intensity enhancement factor) change law. The results show that as the content of carbon fiber increases, the longitudinal wave speed of the specimen increases, and the carbon fiber can form a spatial network structure inside the concrete specimen to enhance the integrity of the specimen. With the same carbon fiber content, the peak stress, ultimate strain and DIF of the specimen increase with the increase of the strain rate, and the specimen has an obvious strain rate effect. Under the same strain rate, as the content of carbon fiber increases, the peak stress of the specimen first increases and then tends to a fixed value, and the two show a good quadratic function relationship. The DIF increases, the ultimate strain decreases, and the two show a linear relationship. The strength and integrity of the concrete specimens with carbon fiber are significantly improved.

Study on pull-out failure behavior of composite honeycomb sandwich fasteners

WANG Ru, WANG Man, BAI Rui-xiang

2021, 0(10): 19-25. DOI: 10.19936/j.cnki.2096-8000.20211028.003

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The failure study of honeycomb sandwich structure still mainly depends on pull-out test currently. In this paper, the fracture form and carrying capacity of the composite honeycomb sandwich fastener connection under pull-out load are studied by experiment first, and the corresponding failure mechanism is revealed. But there is a need to quickly get the structure bearing capacity and failure form during designing and optimizing, in order to establish the finite element model. The stiffness theory of composite material panel and equivalent model of honeycomb sandwich is introduced. In this paper, the fracture mode and ultimate load of the structure are predicted numerically, and the results are compared with the test, which proves the validity of the numerical calculation method. Test and numerical calculation results indicate that the failure area of the composite honeycomb sandwich structure is mainly concentrated in the connection area. In order to improve the bearing capacity of the structure, the honeycomb in the connection area of the composite honeycomb sandwich structure is tried to be hollowed out and then sealed. Numerical calculations of the hollowed out honeycomb sealing structure are carried out. The performance of the local sealing composite honeycomb sandwich is better than that of the hollowed out honeycomb sealing structure, and the bearing capacity is significantly improved.

Research on low-velocity impact damage of composite materials based on nonlinear Lamb wave mixing detection technology

CONG Shi-fan, TIE Ying, ZHANG Chen-xi, YIN Zhen-hua

2021, 0(10): 26-33. DOI: 10.19936/j.cnki.2096-8000.20211028.004

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This paper aims at the invisible damage caused by low velocity impact in composites. A finite element model of mixing detection is established to predict the ultrasonic nonlinear mixing response of composites under different impact energy. The drop-weight impact test and RAM-5000 SNAP nonlinear ultrasonic testing system were used to study the interaction between nonlinear mixing Lamb waves and composites damaged with different impact energy, and the finite element model was compared and verified. The feasibility of detecting impact damage by mixing Lamb wave and the influence of different impact energy on the nonlinear coefficient of mixing Lamb wave sum frequency are discussed. The results show that mixing Lamb wave can be used to detect impact damage, and the sum frequency amplitude and sum frequency nonlinear coefficient increase with the increase of impact energy, and the sum frequency nonlinear coefficient can effectively evaluate the impact damage of composite plates.

Durability test of single limb with CFRP grid with elastic modulus as index

LI Jia-xing, YANG Yong-xin, JIA Bin, LI Biao, HUANG Hui, ZHAO Jin-jie, WANG Tao

2021, 0(10): 34-41. DOI: 10.19936/j.cnki.2096-8000.20211028.005

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The FRP durability test often takes the ultimate strength measured by the destructive test as the index to measure the performance degradation of the FRP. However, as a polymer material, the performance of FRP is affected by many factors such as the production process, composition ratio, etc. The individual difference of the material is great, and the data of the destructive test in different stages is relatively large. Therefore, in this paper, based on the elastic modulus as the index of the FRP durability test, the destructive test and the homogeneous test of the Same Non-failure durability of the CFRP grid under the three working conditions of aqueous solution, seawater solution and seawater dry and wet cycle were carried out. The conversion relationship between the elastic modulus and the tensile strength was established by using the principle of consistent strain in the corroded and uncorroded areas of materials. Compared with the traditional durability destructive testing method, the same non-failure testing method has the advantages of small data fluctuation, consistent data benchmark, low test cost and material saving, etc. The results show that after 360 days of aging, the retention rate of elastic modulus and tensile strength are 96.9%, 96.8% and 96.1%, and the retention rate of tensile strength are 93.8%, 89.8% and 89.1%, respectively. CFRP has good durability in water-immersed environment. The durability measured by elastic modulus is similar to the durability test results of tensile strength, and can be converted to each other through transformation relationship. It is more reasonable and scientific to evaluate the FRP durability by using the durability prediction model based on the relationship between elastic modulus and tensile strength measured by the same non-failure test method.

Experiment on basalt fabric reinforced polymer-fiber reinforced cementitious matrix tensile mechanical properties

LIAO Wei-zhang, WANG Jun-jie, WANG Qiu-wan

2021, 0(10): 42-50. DOI: 10.19936/j.cnki.2096-8000.20211028.006

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The excellent mechanical behaviors of Basalt Fabric Reinforced Polymer-Fiber Reinforced Cementitious Matrix (referred as to BFRP-FRCM) composite layer are tensile strain hardening, multi cracking, excellent deformation ability and so on. This makes BFRP-FRCM composite layer as a kind of preferred construction materials for the structural repair or reinforcement. Therefore, this paper presents an experimental study on the significant variables on the mechanical properties of BFRP-FRCM composite layers, including the mixed fibers, FRCM matrix water/binder ratio and basalt mesh layers. Experimental results indicated that BFRP-FRCM composite layers exhibited remarkable tensile strain hardening effect when PVA and PE fibers were mixed, but the layer mixed with PP fibers exhibited tensile softening effect. The maximum ultimate tensile strain of BFRP-FRCM composite layer mixed with PE fibers can reach to 3.95%, which is much larger than that of the mortar materials. The optimal amount of fiber mesh in the composite layers was also presented.

Influencing factors of laser ultrasonic thickness measurement technology for carbon fiber composite materials

CAO Wen-jia, CHEN You-xing, ZHAO Xia, CHAI Hua-qi

2021, 0(10): 51-55. DOI: 10.19936/j.cnki.2096-8000.20211028.007

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Carbon fiber composites have remarkable high specific strength and high specific modulus, and have become the first choice of aircraft structural materials. The uniformity of carbon fiber composite thickness will seriously affect the normal operation of aircraft. In this paper, the thickness of carbon fiber composite material is measured by laser ultrasonic pulse reflection method, and the non-contact measurement of composite material is realized. The effects of different lenses, different diameters of light spots and different power light sources on the thickness measurement signal are studied respectively. The test results show that the ultrasonic echo signal with higher amplitude can be excited by using small diameter spot under the excitation of laser pulse with the same energy. The amplitude of ultrasonic signal generated by focusing with convex lens is higher than that generated by focusing with cylindrical lens, and the relative error of measuring the thickness of carbon fiber composite material is less than 5.3%. The measurement experiment is carried out in a dark room without external light, and the background noise has little interference on the echo signal reflected from the bottom surface.

Research on hollow composites fabricated by 2D triaxial braiding technology

LUO Wei, CHENG Yong, YANG Yong-zhong, GUO Qiang, PENG Ke

2021, 0(10): 56-60. DOI: 10.19936/j.cnki.2096-8000.20211028.008

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Owing to the advantage of high automation, excellent integrity, neat-shaping and flexible designability, braiding technology can be used to fabricate complex composite tubes by typical liquid composite molding methods such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Infusion (VARI). Braided composites are now becoming a new trend of low-cost composites in the future. In this paper, the features and application of 2D triaxial braided composites (2DTBCs) are introduced. Meanwhile, typical 2DTBCs were fabricated by RTM process,and the basic mechanical properties of the composites were investigated. The results show that the performances of 2DTBC depend on the braiding angle. And the damage area of 2DTBCs after impact was much smaller than the classical laminate composite because of much effective force transferring routes of the fibers in the interfaced braiding structure. The development of a typical hollow composites barrel by braiding and RTM process verified the engineering feasibility of this method.

Effects of automated placement process of lattice structure with thermoplastic composites on the inter-laminar shear strength

LIANG Yi-nan, YANG Rui, WANG Jun-long, ZHANG Bo

2021, 0(10): 61-66. DOI: 10.19936/j.cnki.2096-8000.20211028.009

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In order to realize the fabrication of thermoplastic composite lattice structure based on the automated fiber placement and in-situ consolidation process, by taking the meso-scale thermoplastic composite laminate as a representative structure, aiming to improve its mechanical properties, this paper studies the meso-scale automated fiber placement and in-situ consolidation process through the experiment. Using interlaminar shear strength (ILSS) and micro morphology as characterization methods, the effect of automated placement and in-situ consolidation process parameters on the laminar mechanical properties were analyzed by a single factor experiments and response surface experiments, also a prediction model between parameters and mechanical properties was established. The results show that the influence of various processing parameters on ILSS in the test range was as follows: placement speed, placement pressure, placement temperature. And the interaction effects between the parameters were significant. The ILSS of specimen showed a trend of first increasing and then decreasing with the increase of placement pressure and temperature, and a trend of decreasing with the increase of placement speed. The optimal combination of process parameters in the test range was obtained, that is, placement pressure 14 N, placement temperature 408 ℃ and placement speed 60 mm/min.

Design and analysis of carbon fiber composite rail vehicle structure

WANG Cheng-yu, PENG Xiao-bo, YANG Jie

2021, 0(10): 67-73. DOI: 10.19936/j.cnki.2096-8000.20211028.010

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The lightweight of vehicle is one of the future development directions of railway vehicles. Carbon fiber composite material is the preferred material for the lightweight design of vehicle. This paper introduces a lightweight design of the whole carbon fiber composite vehicle, including the structure design and connection design of the whole vehicle. The strength, stiffness and modal of the composite vehicle structure were checked by the finite element method. Furthermore, the mechanical properties of carbon fiber composites were evaluated. According to the thought of integrated forming and modularization, the experimental part of composite vehicle was prepared by Vacuum Infusion Process under the environment of oven, which verified the feasibility of the structural design and manufacturing technology of vehicle. The results show that the design of composite materials vehicle should consider the material characteristics, vehicle structure and mode comprehensively, reduce the number of parts and connections, and realize the integration of vehicle forming. The carbon fiber composite material can greatly reduce the weight of vehicle in the manufacturing. Under the premise of meeting the standards of strength, stiffness and mode of the vehicle, the all-carbon fiber composite vehicle can reduce the weight by 42% compared with the traditional aluminum alloy vehicle.

Effect of plane rake faced twist drills with different drill geometric angle on CFRP

LIU Li-ping, LIAN Bo, ZHU Xue-ming, ZHOU Chang-geng, XIA Ping-feng

2021, 0(10): 74-82. DOI: 10.19936/j.cnki.2096-8000.20211028.011

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The delamination produced during CFRP drilling will affect its structural strength seriously. Delamination is closely related to the thrust force during drilling hole, which is closely related to the tool, so it is particularly important to choose the tools with appropriate geometric structure. In this paper, the research objects of drill geometry included the helix angle, point angle and clearance angle of plane rake faced twist drills, which was used to investigate the influence law of different geometric angles on the thrust force and drilling quality. What's more, the influence degree of different geometric angles on the delamination of drilling hole at entrance and exit was also analyzed. The results show that optimum geometry of plane rake faced twist drills for drilling CFRP is the helix angle of about 35°, the point angle of about 120° and the clearance angle of about 12°.

Effect of carbon fiber surface treatment on the mechanical properties of liquid-formed carbon fiber reinforced MC nylon composite

HU Bin-bin, WANG Shao-fei, CAI Chao-qian, HUANG Zhuang, MA Yu, ZHANG Hui

2021, 0(10): 83-88. DOI: 10.19936/j.cnki.2096-8000.20211028.012

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In this paper, a vacuum-assisted resin infusion molding process (VARI) was used to prepare continuous carbon fiber reinforced cast (MC) nylon composites by in-situ anionic polymerization of caprolactam. The O/C ratio detailed surface morphologies within the carbon fiber surface as well as the carbon fiber mechanical properties, the surface morphologies and fiber volume fraction of the composite materials were systematically studied in four different carbon fiber fabric surface treatment methods, i.e., acetone desizing treatment, gas phase oxidation treatment, coupling agent treatment and flame treatment. The results indicate that the surface of the carbon fiber is coated with a coupling agent, and the mechanical properties of the composite material prepared by this carbon fiber are better than those prepared by other treatment methods. In this case, the tensile strength reaches 595.5 MPa. The flexural strength reaches 330.7 MPa, and the interlaminar shear strength reaches 30.6 MPa. The carbon fiber surface O/C ratio reaches 44.51%, and the carbon fiber volume fraction of the composite material reaches 51.4%.

Finite element analysis and burst test of composite cylinder with plastic liner

HU Zheng-yun, CHEN Ming-he, WENG Yi-ming, PAN Bo

2021, 0(10): 89-95. DOI: 10.19936/j.cnki.2096-8000.20211028.013

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In this paper, the lay-up design, simulation analysis and burst test of 70 MPa carbon fiber fully wound cylinders with plastic liner are studied. Firstly, the lay-up design of the plastic liner cylinder is carried outbased on the grid theory. Then, the cylinder liner model and composite layer model were established by ABAQUS. The composite material properties of cylinder body and dome position were defined by UMAT subroutine, and the progressive damage model was defined based on Hashin damage theory to predict the burst pressure. Finally, the cylinder burst test is carried out, and the strain of the cylinder is collected by the strain gauge during the experiment. The results show that since the Young's modulus of plastic material is far less than that of composite material, there is no tensile yield situation, and the stress is three-way compressive stress. Plastic liner composite cylinders are also not self-reinforcing through the "self-tightening" process. The deviation between the predicted burst pressure and the test is less than 10%. The predicted burst position is consistent with the test results. The blasting mode of gas cylinders can be predicted by the relationship between axial displacement, radial displacement and pressure, and the inflection point (sudden change point) of the curve can be selected as the blasting load value. The main reason is that the damage of materials leads to stiffness degradation, which leads to the sudden change of macro displacement.

Research of double vacuum bag molding process for carbon fiber/vinyl resin prepreg

ZHANG Yi, YANG Rui-rui, GUO Wan-tao, TAO Hong-bo

2021, 0(10): 96-100. DOI: 10.19936/j.cnki.2096-8000.20211028.014

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In this paper, vinyl resin prepreg is used to form composite materials by double vacuum bag (DVB) molding process. The influence of the step curing system on the mechanical properties and porosity of the product was studied. The optimum mechanical properties have heen realized when being cured 3 hours at 100 ℃, then cured 4 hours at 140 ℃ and the vacuum degree of the inner bag film is maintained at -0.075 MPa for 2 hours in the early stage as a curing process to form a 4 mm thick laminate, and the porosity is the lowest, 0.45%. When forming 10 mm thick laminate, the porosity of the laminate is 1.75%, which is also less than 2%. It proves the feasibility of forming thicker laminates by this process.

Design and development of wind turbine blade automatic transfer vehicle equipment

CHEN Xiao-liang, LI Guo-liang, YAN Chen, CUI Jun-wei

2021, 0(10): 101-106. DOI: 10.19936/j.cnki.2096-8000.20211028.015

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With the large-scale development of wind turbine blades, it is more and more difficult for blades to be transported in wind turbine plants. At present, the traditional unpowered trolley is still used for blade transport, that is, the blade root trolley drives and steers with the forklift as the traction power source, while the blade tip trolley takes the manual steering as the steering power and the blade friction dragging as the traction force. The whole transit process employs a large number of workers, for which the safety risk is large, the transport operation is difficult, and the transport efficiency is low. In this case, the development of wind turbine blade automatic transfer vehicle has become the consistent goal of each wind turbine blade production enterprises. This paper mainly discusses a new kind of wind turbine blade automatic transfer vehicle equipment, the equipment mainly includes the root and tip of the blade transfer car body, car drive system, two-car control system, two-car linkage correction system, hydraulic automatic lifting system, safety obstacle avoidance system and other parts. The application of automatic transfer vehicle equipment can effectively reduce the difficulty of wind turbine blade transport, reduce the safety risk of blade transport, reduce the manufacturing cost of wind turbine blade, and improve the intelligent level of the blade manufacturing industry.

Effect of matrix resin and curing tension on tensile properties of carbon fiber multifilament

YUAN Chao, QIU Qi-yan, CHEN Jing

2021, 0(10): 107-110. DOI: 10.19936/j.cnki.2096-8000.20211028.016

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According to the sample preparation process of tensile properties test of carbon fiber multifilament, the influence factors of tensile properties test values of T300B, T700SC and T800H were studied by using different matrix resins and applying different tow curing tension. The results show that the test value of tensile properties of carbon fiber multifilament is not obviously related to the viscosity of matrix resin, but closely related to the elongation at break of matrix resin. Under the condition that the elongation at break of matrix resin does not exceed 4 times of the tested fiber, the higher the elongation at break of matrix resin is, the more accurate the test value of mechanical properties of carbon fiber multifilament is. The mechanical properties of carbon fiber multifilament can be improved by appropriately increasing the curing tension of carbon fiber during sample preparation. The larger the carbon fiber tow is, the higher the curing tension is required.

Preparation and performance of SiO₂-based rigid wave-transmitting insulation tile

XIAO Yuan-yu, CHAI Xiao-xiao, NIU Zuo-zhe, LI Song

2021, 0(10): 111-115. DOI: 10.19936/j.cnki.2096-8000.20211028.017

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In this paper, insulation tiles were prepared by dispersion stirring, wet suction filtration, and high temperature sintering, with quartz fiber, silica sol and BN powder as the main components. The effects of BN powder content and sintering temperature on the micro morphology, mechanical properties and thermal properties of insulation tiles were studied. In particular, the influence of high temperature environment on the thermal conductivity of the insulation tile and the hot and humid environment on the dielectric performance of the insulation tile are studied. The research results show that the fibers are effectively connected through the action of silica sol and the sintering aid BN. Changing the BN content and sintering temperature can adjust the material properties and obtain the optimal preparation process. Insulation tiles have extremely low thermal conductivity, but they will undergo changes such as sintering shrinkage under high temperature environments, which will significantly improve thermal performance parameters such as thermal conductivity. The hot and humid environment has a significant impact on the dielectric performance of the insulation tile, and the dielectric loss greatly increases. The moisture-proof treatment can reduce the water absorption rate of the insulation tile, so that its dielectric performance is stable.

Development of arc triangular cross-section CFRP structure truss

WANG Zeng-jia, WANG Xi-jie, KONG Na, SHI Hui, WANG Hua, LI Bo

2021, 0(10): 116-119. DOI: 10.19936/j.cnki.2096-8000.20211028.018

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Composites truss structure has the characteristics of light weight, high specific strength and specific rigidity and reasonable load distribution. In order to adapt to arc surface structure of airship and other aerostat, the arc triangular cross-section carbon fiber reinforced plastics (CFRP) truss structure was designed and its production process was studied. The truss chord pipe adopted the external mold and internal pressure forming, triangular web member and joint were integrative structure and integrated forming, and the integral unit truss was assembled and connected on the special tooling. The unit truss component produced by this method has high specific strength and specific rigidity, and its performance meets the requirements of design index, and has the characteristics of light weight and good load capacity. Finally, through the connection and combination of the unit truss components, the annular or arc integral composites truss structure can be formed, which can be used in the aerostat truss structure such as airship and high altitude balloon.

Research progress on forming process of continuous fiber reinforced thermoplastic composites

WANG Zi-jian, ZHOU Xiao-dong

2021, 0(10): 120-128. DOI: 10.19936/j.cnki.2096-8000.20210828.031

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Due to the unique advantages of continuous fiber reinforced thermoplastic composites (CFRTP) such as high impact resistance, high toughness, good heat resistance and electrical properties, no low-temperature storage and no storage period, high damage tolerance and recyclable waste, the proportion of thermoplastic composites in the market is increasing every day and has become one of the most widely used composites. According to the different types of CFRTP forming processes, this paper introduces the molding, winding, laying, pultrusion and 3D printing processes, expounds the research progress and application status of various forming processes, and looks forward to the future development direction of CFRTP forming process.

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