COMPOSITES SCIENCE AND ENGINEERING

Preparation and characterization of low temperature co-curing composites of nitrile rubber with different acrylonitrile contents

TIAN Cheng, LIANG Sen, WU Zhaoqi, WANG Fengquan

2023, 0(12): 5-11. DOI: 10.19936/j.cnki.2096-8000.20231228.001

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In order to explore the co-curing conditions of rubber and matrix resin composites at 80 ℃ in low temperature environment, the free energy of chemical reaction between nitrile butadiene rubber (NBR) and E51 epoxy resin at 353.15 K (80 ℃) is simulated and calculated, and the co-curing of NBR N41 and NBR N220S damping composites is realized through experiments. A viscoelastic damping material component with excellent performance and co-curing with carbon fiber/epoxy resin matrix prepreg at 80 ℃ is determined by orthogonal test. The viscoelastic damping material component is dissolved by tetrahydrofuran solvent, and N41 and N220S damping composite specimens are prepared by brush coating and co-curing process. The scanning electron microscope is used to analyze the micro damage morphology of the composite. The damping properties and shear properties of different adhesives are obtained by testing the damping DMA and interlaminar shear tests. The data shows that the damping interlaminar properties of the composite made of butadiene acrylic rubber with high acrylonitrile content are better, and NBR N220S is more suitable as a viscoelastic damping material.

Effect of two impact distances on impact damage and residual compressive strength of CFRP laminates

XU Liang, HU Hongming, ZHOU Song, SONG Wanwan

2023, 0(12): 12-18. DOI: 10.19936/j.cnki.2096-8000.20231228.002

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In order to study the influence of pre-damage impact on the secondary impact and post-impact compression behavior of composite materials, pre-damage impact test, secondary impact test and post-impact compression test of composite laminates were carried out. The relationship between the distance between the pre-damage impact and the secondary impact and the impact damage and the residual compressive strength was investigated. Based on the three-dimensional Hashin criterion and progressive damage stiffness degradation scheme, a pre-damage impact-secondary impact-compression simulation model is established in ABAQUS/Explicit. The first impact damage is prefabricated into the second impact model by the method of prefabricated layered damage. The results show that the simulation results of the established model agree well with the experimental results. When the two impact distance is less than 125% of the longitudinal radius sum of the two impact damage area, the secondary impact damage extends along the fiber direction to the pre-damage impact location. When the distance between the second impact and the pre-damage impact is 150% of the longitudinal radius sum of the two damage impact areas, the residual compressive strength is the smallest and the damage to the laminated plate is the largest.

Shear performance of concrete beams with BFRP-reinforcement and steel bar combination reinforcement

XUE Xin, CHEN Jian, PENG Junzhen

2023, 0(12): 19-27. DOI: 10.19936/j.cnki.2096-8000.20231228.003

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Due to the excellent corrosion resistance property of FRP (fiber reinforced polymer) bars, the durability problem caused by steel bar corrosion can be fundamentally solved by using FRP reinforcement as a substitute for ordinary steel bars. However, there are still many topics needed to be made clear regarding the load-carrying performance of FRP-reinforced concrete members or structures. By using hybrid reinforcement of FRP bars and steel bars, this paper experimentally studied the effects of elastic modulus and steel ratio of reinforcement on the shear performance of concrete beams with BFRP-reinforcement and steel bar combination reinforcement. In addition, based on the test results, this paper further performed a validation of the shear strength evaluation formula proposed by codes of various countries. It is hoped that this paper could contribute to the further understanding of the shear performance of FRP-reinforced concrete beams.

Effect of material type on mechanical properties of bonded joint based on cohesive model

XIAO Xiao, YUE Tao, ZHANG Tieshan

2023, 0(12): 28-37. DOI: 10.19936/j.cnki.2096-8000.20231228.004

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To explore bonding material type on the mechanical behavior and failure mechanism of adhesive joint, cohesive zone model (CZM) and Hashin failure criteria were used to model adhesives and carbon fiber reinforced polymer (CFRP) composite laminates, respectively. The accuracy of the model is verified by the simulation of the CFRP laminate bonding joint test,which extracted from the literature. In addition, based on the verified model, the tensile numerical models of the single-lap adhesive joint with the same material (CFRP, steel plate, aluminum plate) and different materials (CFRP/ steel plate, CFRP/ aluminum plate) were established, and the tensile damage and stiffness degradation characteristics of different parts of the adhesive joint were analyzed. The results showed that the ultimate load of all lap joints increases with the increase of bond length. When steel plate and aluminum plate were lapped with CFRP, the strength of steel plate is higher than that of aluminum plate, resulting in greater tensile strain and stripping strain of aluminum plate for hybrid lap joints. Therefore, the ultimate load of steel plate mixed lap is higher than that of aluminum plate. The initial damage of adhesive layer and CFRP laminate was affected by bonding material type during loading. This paper provided the basis for the design of the adhesive joint by studying the adhesive joints of different bonding materials.

Effect of ultrasonic vibration on the mechanical properties hand lay-up molded of carbon fiber composites

ZHANG Jintong, YANG Tao, DU Yu, ZHANG Lintao

2023, 0(12): 38-43. DOI: 10.19936/j.cnki.2096-8000.20231228.005

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In order to improve the mechanical properties of the carbon fiber composites prepared by the hand lay-up molding process, the fiber cloth was pretreated with various parameters of ultrasound before curing, and the specimens were tested in bending and tension after curing and molding. The effects of various ultrasonic times and powers on the mechanical properties of the hand lay-up molded carbon fiber composites were investigated by using digital image correlation (DIC) and scanning electron microscope (SEM) for characterization. The results showed that the bending and tensile loads of the specimens were 854.02 N and 31 351.10 N, respectively, when the ultrasonic time was 15 min and the ultrasonic power reached 300 W. The bending and tensile strengths of the specimens increased by 32.05% and 25.39%, respectively, compared with those of the un-sonicated specimens. At this sonication parameter, both the range of strain value variation and the number of voids were significantly reduced compared to the specimens without sonication. This indicates that ultrasonic vibration-assisted hand lay-up molding can effectively reduce the stress concentration phenomenon and the generation of voids, thus improving the mechanical properties of the prepared materials.

Preparation, heat resistance and mechanical properties of silica aerogel/aluminum silicate composite fiber paper

HOU Yu, SONG Zixuan, XUE Jundong, ZHANG Guotao, WU Jianfeng, TANG Xiuping

2023, 0(12): 44-49. DOI: 10.19936/j.cnki.2096-8000.20231228.006

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Aluminosilicate fiber paper is a traditional kind of thermal insulation material. When it is used at a relatively high temperature, its structure easily collapses, resulting in the significantly deteriorated mechanical properties. In this paper, silica (SiO₂) aerogel/aluminum silicate composite fiber papers were prepared on the structure of aluminum silicate fibers with SiO₂ aerogel by a sol gel process. The heat resistance of the as-prepared composite fiber papers was obvious increased from 800 ℃ to 1 100 ℃, and their structures began to collapse until 1 100 ℃. The tensile strength of the SiO₂ aerogel/aluminum silicate composite fiber papers was increased from 9.01 MPa to 20.41 MPa, and the elongation at break was increased from 2.36% to 3.52%. By comparing the micro morphology of the composite fiber papers prepared under different pH (8, 9 and 10), the combination between the SiO₂ aerogels and aluminum silicate fiber was the best at pH of 8.

The effect of twisting on tensile properties of high modulus carbon fiber impregnated filament

HUANG Wei, ZHOU Dong, HUANG Wenyu, SHI Wenfeng, SUN Ziqi, CHEN Yubin

2023, 0(12): 50-54. DOI: 10.19936/j.cnki.2096-8000.20231228.007

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In order to improve the tensile properties of high modulus carbon fibers, the tensile strength and elongation at break of CCM40J and CCM55J carbon fibers before and after resin dipping were studied. It is found that twisting can improve the tensile properties of carbon fiber. Compared with CCM55J carbon fiber, the tensile strength and elongation at break of CCM40J carbon fiber increased by 17% when the twisting was 10 n/m. In order to improve the tensile properties of two high modulus carbon fibers, the optimal twist and dipping method were determined.

Research on compressive residual strength of composites after impact based on random forests algorithm

HUANG Yubing, LI Chen, LI Shuo

2023, 0(12): 55-62. DOI: 10.19936/j.cnki.2096-8000.20231228.008

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The aircraft composite structure will inevitably be damaged by the impact of foreign objects in service, which will reduce the bearing capacity of the structure to a certain extent, and will also affect the flight safety of the aircraft. Compared with tensile properties, composites are more sensitive to compressive loadings, so it is of great significance to study the compressive properties of the composites after impact. In this paper, the compression residual strength test of composites after impact is studied, and the test data are analyzed by engineering method and artificial intelligence modeling. The results of this paper show that the predicted precision for the post impact compressive residual strength of the composite materials based on artificial intelligence analysis established in this paper is significantly improved compared with the existing engineering methods.

Numerical study on hysteresis behavior of PVC-CFRP confined concrete column-RC ring beam interior joint

YU Feng, MAIMAITI Nuermaimaiti, FANG Yuan, ZHANG Nannan

2023, 0(12): 63-71. DOI: 10.19936/j.cnki.2096-8000.20231228.009

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Based on the experimental study, the appropriate constitutive models are selected and the fiber model method is adopted to analysis the load-displacement and moment-curvature skeleton curves of PVC-CFRP confined concrete column-RC ring beam interior joints under low cyclic loading. The influence of the concrete strength of joint area, ring beam height, column diameter and longitudinal reinforcement ratio of frame beam on the skeleton curves of the specimens are investigated on the basis of the verified accurate numerical model. The results show that the bearing capacity and ductility of the specimens increase with the increase of frame beam height, column diameter and longitudinal reinforcement ratio of frame beam. The bearing capacity of the specimens increases while the ductility decreases with the improvement of concrete strength of joint area. On the basis of the analysis results of the test and numerical simulation, considering the economy and rationality of the ring beam joints, it is suggested that the concrete strength of the joint area should not exceed C60, the height of the ring beam should be 340~440 mm, and the ratio of the ring beam width to the column diameter should be controlled between 0.33~0.50.

Impact resistance and optimization of damping composite multilayer soft bulletproof target plate

GUO Jian, LIANG Sen, HUANG Haojie

2023, 0(12): 72-79. DOI: 10.19936/j.cnki.2096-8000.20231228.010

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With the upgrading of firearms and weapons, the penetration ability of bullet is increasing. The impact finite element model of surface damping/carbon fiber/UHMWPE fiber soft bulletproof target plate is established by ANSYS/LS-DYNA. Based on the finite element model, the experimental platform of ordinary bullet penetrating UHMWPE fiber laminate is set up. By comparing the experimental results with the simulation results, the validity of simulation method is verified. By changing the laying mode of fiber layer through ANSYS, four different laying angles and eight laying sequences are designed. The genetic algorithm is used to optimize the approximate model to obtain the lightweight and high-strength soft bulletproof target plate. The results show that when the fiber laminates are [0°/30°/60°/90°/120°]_n, the fiber laminates are placed on the projectile surface, and the UHMWPE fiber laminates are placed on the back projectile surface, and the proportion of UHMWPE fiber laminates is high, the bulletproof performance of the target plate is better. The optimized target plate of 0.6 mm surface damping/5.1 mm CF laminated plate/9.4 mm UHMWPE laminatedplate can effectively resist the penetration of 7.62 mm ordinary projectile. Compared with the armored steel target plate, the surface density of the target plate decreases by more than 53.4% under the same bulletproof performance.

Research on flow velocity monitoring technology of resin flow front based on parametric curve model

YAO Wensheng, WANG Fenghuai, XIE Haoping, YU Yue

2023, 0(12): 80-87. DOI: 10.19936/j.cnki.2096-8000.20231228.011

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Vacuum assisted resin transfer molding (VARTM) is often used to manufacture large and complex composite components. Monitoring the resin flow in the fiber preform in real time and human intervention in the manufacturing process can effectively avoid the formation of internal defects in composite products. Among them, real-time monitoring of the flow rate of the resin flow front provides a key technical basis for accurately controlling the negative pressure level in the molding process and intervening in the resin infiltration process. In this paper, the flow velocity parameters of resin flow front in VARTM process will be studied. Through the ultrasonic propagation theory, an ultrasonic monitoring characteristic model based on circular piezoelectric chip active sensor will be established to monitor the changes of ultrasonic pulse echo at the mold resin interface to identify the arrival position of resin flow front. Gaussian and elliptic curve parametric models are introduced to calculate the flow velocity of flow front. Finally, piezoelectric wafers with different frequencies are selected to conduct experiments on plexiglass plates with various thicknesses. Combined with the data, the accuracy and effectiveness of the flow velocity calculation model are evaluated. Finally, it was found that the results of velocity calculation through the parametric curve model were in good agreement with the actual situation, and the accuracy was in line with expectations. Moreover, the comprehensive performance of the Gaussian curve model was better than the elliptic curve model, but the elliptic curve model performed better in small thickness molds.

Buckling analysis of glass/carbon fiber hybrid composite laminates under thermal-mechanical loading

WANG Xiugang, SUN Shuangshuang, ZHANG Shengqi, MA Jiabin

2023, 0(12): 88-95. DOI: 10.19936/j.cnki.2096-8000.20231228.012

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In this paper, glass/carbon fiber hybrid composite (G/CFHC) laminates are considered as the research object, and the buckling load of G/CFHC laminates is calculated by the finite element software ABAQUS on the basis of considering the dual influence of composite material property degradation and thermo-stress induced by temperature. The effects of ambient temperature, ply sequence, ply thickness and fiber hybrid ratio on the buckling characteristics of G/CFHC laminates are discussed. The results show that in the environment of 20~120 ℃, the temperature has great influence on the G/CFHC laminate. The buckling load of the laminate decreases continuously with the incresing of temperature and the downward trend tends to be flat after the temperature reaches a certain value. Under the premise of the same ply angle, the buckling load changes with the change of the position of carbon fiber laminas. The buckling load decreses gradually when the position of carbon fiber lanimas moves from the outer layers to the middle layers. And the ply thickness affects the buckling load tramatically which shows the buckling load increases with increasing the thickness of laminates. In addition, the fiber hybrid ratio has great influence on the buckling load of G/CFHC laminates. Increasing the numbers of carbon fiber laminas can improve the capability of buckling resistance of G/CFHC laminates effectively and increase the stability when the thickness and layer numbers are kept unchanged.

Research on ballistic impact characteristics of carbon/aramid fiber hybrid laminates

LIU Yating, XIE Jiang, MOU Haolei, FENG Zhenyu

2023, 0(12): 96-104. DOI: 10.19936/j.cnki.2096-8000.20231228.013

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In order to explore the impact resistance characteristics of carbon fiber, aramid fiber and carbon/aramid fiber hybrid plates, ballistic impact tests were conducted on T700SC-12K-50C carbon fiber laminate, 1000D629T aramid fiber laminate and two kinds of carbon/aramid fiber hybrid plates respectively, and their ballistic impact characteristics were evaluated through the impact resistance evaluation parameters. At the same time, with the help of CT scanning results, the internal damage of the laminated plate was analyzed, the mechanism of energy absorption was revealed, and the influence of fiber hybrid on ballistic impact characteristics was further explored. The results show that the energy absorption capacity of the flat plate increases with the increase of the projectile incident velocity until the saturation reaches the peak value. When the projectile incident velocity exceeds the ballistic limit, the energy absorption of the flat plate remains stable or slightly decreases with the increase of the incident velocity, while the energy absorption rate gradually decreases. The impact resistance of the pure aramid fiber plate is better than that of the pure carbon fiber plate. Replacing the carbon fiber layer on both sides of the pure aramid fiber plate can improve the overall energy absorption effect, but the impact resistance of the plate decreases when more carbon fibers are replaced. Under the impact of cylindrical projectile, the damage of pure carbon fiber plate is notch type, mainly shear failure, and the damage is concentrated near the impact part of the projectile. The pure aramid fiber plate and carbon/aramid fiber hybrid plate are explosion damage. The shape of the bullet hole is round near the projectile attack surface, while the damage area on the projectile back surface is conical. The damage formation process includes three stages: extrusion deformation, shear penetration and tensile penetration.

Study on toughening modification and mechanism of phenolic resin matrix composite for evacuation platform

WEN Jingbo, WANG Shuxia, ZHENG Shihong

2023, 0(12): 105-111. DOI: 10.19936/j.cnki.2096-8000.20231228.014

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This paper focuses on the comparison of the effects of three kinds of tougheners, namely, silicic acid (TEOS), polyvinyl butyral (PVB) and nitrile rubber (NBR), on the tensile properties, impact toughness, bending properties and other mechanical properties of phenolic resin matrix composites. Based on the actual needs of evacuation platform products, the effects of tougheners on the thermal value of composites are investigated. Finally, the possible toughening mechanisms of each toughener are analyzed. The results show that the three kinds of toughening agents have significant toughening effects on phenolic resin matrix composites, and their toughening effects are related to the amount of addition and their toughening mechanisms are different.

Experimental study on pore structure and mechanical properties of basalt fiber high strength concrete under multiple impact loads

XIE Liang

2023, 0(12): 112-118. DOI: 10.19936/j.cnki.2096-8000.20231228.015

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In order to explore the safety of basalt fiber high strength concrete under multiple impact loads, the longitudinal wave velocity and internal pore structure of the specimen under different strain rates and impact times are measured by non-metallic ultrasonic analyzer and nuclear magnetic resonance test device. The dynamic compression test of the specimen was carried out by using the separated Hopkinson compression bar device with a diameter of 74 mm. The changes of longitudinal wave velocity, damage factor, T₂ spectrum, pore structure and stress-strain with impact pressure and impact times are analyzed. The test results show that the longitudinal wave velocity decreases with the increase of impact times, and the damage factor increases with the increase of impact times, and there is a good quadratic linear positive correlation between them. The T₂ spectrum of the specimen is mainly three peak type, and the increase of impact times will shift the spectrum to the right and increase the peak value. With the increase of impact times, the pore diameter and the number of pores increase, the porosity of the specimen increases, and the subsequent impact is more conducive to the expansion of cracks. The contents of micropores and mesopores in the specimen account for more than 95% of the total porosity. The impact load reduces the proportion of micropores and mesopores in the specimen, and increases the proportion of macropores and cracks. Under the action of multiple impact loads, the peak stress of the specimen will be reduced and the stress variable will be increased. There is a good quadratic function negative correlation between the impact times and the peak stress.

Review of shear behavior of FRP reinforced concrete beams

JIANG Jitong, GAO Yu

2023, 0(12): 119-128. DOI: 10.19936/j.cnki.2096-8000.20231228.016

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As a new kind of high performance material, fiber reinforced composite (FRP) bars have become an important supplement to traditional building materials due to the advantages of high strength and corrosion resistance, and are gradually applied in the field of civil engineering. Therefore, the combination of FRP bars and concrete will be a hot topic in the field of civil engineering in the future. However, there is no unified theory on the shear mechanism of FRP reinforced concrete beams, which greatly limits the application and promotion of FRP bars in the field of practical engineering. In this paper, the research results of the shear performance of FRP reinforced concrete beams are sorted out from three aspects, namely experimental research, numerical simulation and theoretical analysis by tracing the relevant research results and norms at home and abroad. The calculation formulas for shear bearing capacity obtained under different research objects and methods are summarized, expecting to provide reference and suggestions for the future research and design of FRP reinforced concrete beams.

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