COMPOSITES SCIENCE AND ENGINEERING

Numerical analysis on trapezoidal tearing of fabric membrane based on a nonlinear constitutive model

MA Junjie, CHEN Jianwen

2024, 0(5): 5-11. DOI: 10.19936/j.cnki.2096-8000.20240528.001

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In order to improve the accuracy of the numerical analysis for the tearing mechanical response of fabric composites, a nonlinear damage constitutive model for PVDF-coated fabric was developed based on the continuous damage mechanics theory. The accuracy of the nonlinear constitutive model is verified by combining the off-axis tensile test with a gradient of 15°. The nonlinear constitutive model was added to the numerical analysis. The results were compared with the conventional folding line model and the trapezoidal tearing test with a gradient of 15° to verify the accuracy of the nonlinear constitutive model in terms of tearing mechanical response. The results show that the nonlinear constitutive model can effectively track the actual stress-strain curve of the fabric. In terms of tearing mechanical response, both models can reflect the effect of series parameter changes on tearing performance and the corresponding tearing mechanism.But the numerical results of the nonlinear constitutive model have a better representation of the complex stresses of tensile-shear coupling during the tearing process.

Study of acrylic copolymer modified liquid acrylate resin and its composite mechanical properties

CHEN Shuhui, MEI Qilin, DING Guomin, WANG Rui, CAI Yongqi, JIANG Duanyang

2024, 0(5): 12-18. DOI: 10.19936/j.cnki.2096-8000.20240528.002

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In order to solve the problem of insufficient tensile strength of acrylate resin and its weak bonding with fiber interface. In this paper, liquid acrylate low polymerization resin (AOLM) was modified by copolymerization of acrylic acid (AAc) to significantly improve the overall mechanical properties of the resin matrix and its glass fiber (GF) reinforced composites after curing by increasing the intermolecular force of polyacrylate resin matrix (PAOLM). The results show that the introduced AAc causes the appearance of vibrational absorption peaks for intramolecular hydrogen bonding (3 545 cm^-1) and intermolecular hydrogen bonding (3 294 cm^-1) in the infrared spectrogram of PAOLM. Compared with the unmodified PAOLM, the tensile strength and modulus of resin P(AOLM-AAc) are improved by 20.86% and 32.65%, respectively. The bending strength and modulus are increased by 18.14% and 25.73%, respectively. The impact toughness is improved by 24.03%, and the glass transition temperature is increased by 10.03% after copolymerization modification. Compared with the composite with AOLM (GF/PAOLM), the tensile strength and flexural strength of the composite with AAc-modified AOLM [GF/P(AOLM-AAc)] are increased by 11.62% and 37.18%, respectively.

Synthesis of melamine solid waste modified phenolic resin and its influence on the properties of moulding compounds

ZHAI Suyu, HUANG Shijun, CHEN Weiting, ZHANG Zhenwei, LUO Yaosen, LI Chenhui, SU Zhizhong

2024, 0(5): 19-24. DOI: 10.19936/j.cnki.2096-8000.20240528.003

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The green disposal of solid waste and the resource modification of traditional materials are of great significance to the healthy development of chemical and material industries. In this paper, solid waste OAT(oxiaminothriazine)was used to modify phenolic resin, the feasibility of reactive introducing OAT into phenolic resin was discussed, and the modified resin was used as the matrix to prepare phenolic moulding compounds (PMC). The influence of modified resin on the properties of PMC was studied. The results showed that OAT had a certain reactivity with formaldehyde, and the viscosity of phenolic resin decreased with the introduction of OAT, but with the further increase of the dosage, the viscosity and polymerization speed increased, but the fluidity decreased significantly, the optimal dosage of OAT was about 8%. PMC prepared with OAT modified phenolic resin have better thermal stability and electrical strength, and other properties are comparable to those of ordinary mouldings.

Dynamic properties of damping layer composite sandwich beam

ZHAO Xiaojun, YANG Yiting, WU Lei

2024, 0(5): 25-29. DOI: 10.19936/j.cnki.2096-8000.20240528.004

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The partial differential vibration equations of damping layer composite sandwich beam were deduced combined with the principle of Hamiltons Principle. Then, these vibration equations were solved by means of the closed-form Navier method, and the calculated result was validated versus the data of the published literature. Finally, the influence of changing parameters of the damping layer composite beam on its dynamic properties was studied. The results show that: The natural frequency decreases gradually and the loss factor tends to go from ascent to descent with the increase of length of beam, and there is an optimal value of length in the dynamics design. The natural frequency increases gradually and the loss factor tends to go from ascent to descent as the shear modulus of the damping layer is increased, and there is an optimal value of shear modulus in the dynamics design. With the increase of thickness of damping layer, the natural frequency decreases gradually, the first-order loss factor increases gradually and the other loss factors tend to go from descent to ascent. The loss factor of damping layer has less influence on the natural frequencies.

Ablation resistance of potassium hexafluorotitanate whisker-modified epoxy silicone resin

LI Xuan, ZHOU Dedong, HE Yu, ZHANG Lijing, SU Jing, LI Wei, XIAO Kui, MENG Weigang

2024, 0(5): 30-35. DOI: 10.19936/j.cnki.2096-8000.20240528.005

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The epoxy-silicone resin composites modified with potassium hexafluorotitanate whiskers (PHW) were prepared, and their oxygen-acetylene ablation performance was investigated, focusing on the impact of varying PHW content. The results indicate that addition of PHW can effectively enhance the anti-spalling capability and high-temperature ablation resistance of the epoxy organosilicon resin. When the PHW concentration is 20wt%, the composite material exhibits the lowest linear ablation rate and mass ablation rate, which are 0.136 mm/s and 1.143 g/s, respectively. These values are approximately 53.74% and 47.04% lower than those of the epoxy organosilicon resin alone. However, when the PHW content exceeds 20wt%, further increasing its amount is no longer significantly improving the ablation resistance of the composite material. Thermal gravimetric analysis (TGA) results reveal that the addition of PHW significantly decreases the weight loss rate of the epoxy-silicone resin. Specifically, when the PHW content is 20wt%, the weight loss rate of the composite material is approximately 38.57%, which is roughly 19.89% lower than that of the epoxy-silicone resin. Beyond a PHW content of 20wt%, further increases in its concentration within the composite material no longer yield a significant improvement in weight loss rate.

Study on surface flashover and failure mechanism of EP/AlN composite insulator rod

ZHANG Xinwei, ZHOU Liying, WANG Bo, DAI Yuwei, DUANMU Tianxiang, WANG Bin, XING Yunqi

2024, 0(5): 36-42. DOI: 10.19936/j.cnki.2096-8000.20240528.006

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Epoxy resin for composite insulator rod has the advantages of high mechanical strength and good insulation performance, but it is easy to produce electric tracking damage under the condition of heating and temperature rise, which leads to the decrease of long-term operation stability and safety of power grid. Therefore, in this paper, epoxy resin/aluminum nitride (EP/AlN) composites with different micro-nano ratios are prepared. The surface flashover and surface tracking resistance characteristics are tested, and the trap distribution characteristics and surface damage parameters are analyzed. The results show that with the increase of the doping ratio of nanoparticles, the charge trapping ability of surface traps decreases, the surface conductivity increases, the surface discharge process is accelerated, the flashover voltage decreases, and the single release energy decreases. Combined with the increase of thermal conductivity, the surface temperature rise of epoxy resin is effectively inhibited, and the tracking resistance of epoxy resin is improved.

Study on high speed impact performance and damage mechanism of 3D fabric structural composites

ZHANG Gen, HE Zekan, XUAN Haijun, MAO Runfeng, JIA Wenbin

2024, 0(5): 43-51. DOI: 10.19936/j.cnki.2096-8000.20240528.007

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3D fabric composites exhibit promising application potential in the field of impact-resistant aerospace structures. This study conducted over 30 ballistic impact tests using a titanium alloy cylindrical projectile and 3D fabric composite plates, with projectile velocities ranging from 160~280 m/s. Various impact test results such as rebound, embedding, and penetration were obtained, along with different damage forms of the composite target plate. Based on these test results, the impact properties and damage mechanisms of three different structural composites (3D 4 direction braided, 3D 5 direction braided, and 3D orthogonal woven) were analyzed. It is indicated that after being impacted by the projectile body, all three structures exhibit similar damage patterns characterized by local fiber fracture and matrix cracking at the point of impact without any lamination. The damage region of the 3D 4 direction braided structure is a sharp angle cross shape, while the damage spread along the braided direction. The damage region of the 3D 5 direction braided and 3D orthogonal woven structure are diamond-shaped, while the damage spread along the 90° and 0° direction. Comparing the three structures of specimens in this paper, it is found that the ballistic limit of 3D orthogonal woven structure is highest while its corresponding damage area is smallest.

Preparation and properties of ethylene-acrylic acid copolymer modified epoxy/UHMWPE fiber composite

ZHOU Dianrui, WANG Weihan, GAO Liang, DU Yu, WU Tianyu, ZHANG Baoyan

2024, 0(5): 52-57. DOI: 10.19936/j.cnki.2096-8000.20240528.008

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A novel composite based on ethylene-acrylic acid copolymer(EAA) modified epoxy, reinforced by ultra-high molecular weight polyethylene(UHMWPE) fiber, was manufactured by means of impregnating through aqueous emulsion. The influences of various EAA contents on composite characteristics in terms of wettability, thermal property of resin, mechanical property of composite, interface adhesion as well as fracture morphology were compared and discussed. The results indicated that the blend system could retain both strong adhesions to UHMWPE fiber attribute to EAA as well as presentable thermal properties due to the rigid epoxy crosslink network. Best comprehensive performances with inter-laminar shear strength of 8.7 MPa and flexural strength retention rate at 60 ℃ of near 80% were presented by the sample composed of 25% EAA proportion.

Effect of SiC fiber preforms structure on densification and mechanical properties of SiC_f/BN/SiC composites

WANG Mengqian, JIA Lintao, LI Aijun, PENG Yuqing

2024, 0(5): 58-65. DOI: 10.19936/j.cnki.2096-8000.20240528.009

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In order to study the effect of silicon carbon (SiC) fiber preform structure on the densification process of SiC matrix by chemical vapor deposition (CVI) process, the pore structure evolution of SiC preform with 2D, 2.5D and 3D structures during the densification process was analyzed using simulation method; and SiC_f/BN/SiC composites with three kinds of SiC fiber preform structures were prepared by CVI process using boron trichloride-ammonia-hydrogen-nitrogen (BCl₃-NH₃-H₂-N₂)and trichloromethylsilane-hydrogen (MTS-H₂) gas mixture as precursor. The results show that the densification efficiency of SiC_f/BN/SiC composites varies with SiC fiber preforms structure. The densification rate of 2.5D preform and 3D preform is the fastest and the slowest, respectively. After 120 h, the density of three kinds of structure SiC_f/BN/SiC composites was more than 2.3 g/cm³ and the porosity was about 10%. The tensile strength of the three kinds of SiC_f/BN/SiC composites was 130~170 MPa. In the process of interlaminar shear, 2D SiC_f/BN/SiC composites and 2.5D SiC_f/BN/SiC composites showed fiber stripping in XY plane, while 3D SiC_f/BN/SiC composites showed the highest interlaminar shear strength and the fracture of orthogonal Z-direction fibers occurred. Therefore, the densification process and mechanical properties of the composite were affected by the SiC fiber preform structure.

Experimental and theoretical calculation of cracking resistance in the negative moment zone of steel concrete composite beams strengthened with CFRP-PCPs composite reinforcement

DENG Yu, LING Daoyuan, NI Miao

2024, 0(5): 66-75. DOI: 10.19936/j.cnki.2096-8000.20240528.010

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In order to overcome the industry problem that the concrete slab in the negative moment region of the steel-concrete composite beam is prone to cracking causing weakening of stiffness. Prefabricated CFRP-PCPs (carbon fiber reinforced polymer-prestressed concrete prisms) composite reinforcement is used as the web reinforcement of the middle support. Five steel-concrete composite continuous beams with composite reinforcement and one ordinary composite continuous beam are designed and manufactured with the number of composite reinforcement, prestressed tension level and section size as the main parameters, the crack resistance in the negative moment zone under single-span single-point load is studied. The results show that: The composite reinforcement can significantly enhance the section stiffness of the middle support, the crack control ability in the negative bending moment zone is significantly improved; compared with ordinary composite beams, the cracking load of composite reinforcement beams is increased by nearly 30%, the number and width of cracks are reduced by nearly 50%; the area of composite reinforcement is the main factor to improve the crack control ability, the influence of prestress level and section size on cracking load is weak; the cracking load of composite reinforcement is positively related to the level and area of prestress. Among them, the level of prestress is the key factor affecting the effective duration of composite reinforcement. Based on the existing theoretical and experimental data, in this paper, the calculation formulas of the cracking load in the negative moment region of the steel-concrete composite continuous beam with CFRP-PCPs composite reinforcement and the cracking load of the composite reinforcement are proposed, the calculated results are in good agreement with the test values, it can provide reference for the practical engineering application of composite reinforcement in steel-concrete composite beam bridges.

Improving the resistance welding strength of carbon fiber/polyphenylene sulfide thermoplastic composite materials by modifying metal heating elements with silane coupling agents

WANG Huanxiang, ZHAO Gang, XU Jian

2024, 0(5): 76-84. DOI: 10.19936/j.cnki.2096-8000.20240528.011

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This article focuses on carbon fiber resin based materials, namely carbon fiber polyphenylene sulfide (CF/PPS) thermoplastic composites with carbon fiber as reinforcement and polyphenylene sulfide as resin matrix. The resistance welding process is studied, and the optimal process parameters are explored. The heating element (metal mesh) is modified using silane coupling agent. When exploring the optimal process parameters, Taguchi experimental method was used and orthogonal experiments with three factors and three levels were designed to obtain the optimal parameters for CF/PPS resistance welding experiment (current 42 A, pressure 2.0 MPa, time 10 s), and the maximum lap shear strength (LSS) was 24.5 MPa. In resistance welding experiments, the heating element generates heat due to the Joule effect after being energized, melting the resin in the welding area, and cooling and solidifying under pressure to generate a welded joint. The surface modification of heating elements using silane coupling agents has improved the adhesion between polyphenylene sulfide and metal mesh. Compared with the welded joints of untreated heating elements, the LSS of the welded joints of heating elements treated with silane coupling agent was 31.1 MPa, increased by 27%.

Experimental study on rapid evaluation of CFRP plate strengthening bridges based on macro-strain

HUANG Zhigang, WU Bitao, YIN Xiang, WU Gang, OUYANG Yao

2024, 0(5): 85-91. DOI: 10.19936/j.cnki.2096-8000.20240528.012

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In order to realize the rapid quantitative assessment of the strengthening effect of existing highway bridges without interrupting the normal traffic, this paper takes the prestressed CFRP plate strengthened hollow slab footbridge as the test object, and derives the formula of the long-gauge strain influence line for simply supported beam bridge under moving vehicle load based on the long-gauge fiber grating strain sensing technology. On this basis, the performance characteristics of the long-gauge strain influence line before and after the bridge strengthening with prestressed CFRP plates were studied, and the evaluation index of the bridge strengthening effect based on the long-range strain time-area envelope under the moving vehicle load was proposed. Finally, a footprint test study of prestressed CFRP plate reinforced hollow slab girders was carried out, and the reinforcement effect was rapidly evaluated and monitored. The test results showed that the bridge reinforcement effect based on the long-gauge strain influence line of the bridge under moving vehicle load can effectively evaluate the bridge reinforcement effect of prestressed CFRP plate, and the long-gauge strain time range area decreases with the increase of the prestressing level of CFRP, and the bridge reinforcement effect in this reinforcement test is 7.07% and 6.90% respectively through the evaluation and analysis.

Research on bonding quality detection of adhesively bonded structure in composite plates based on guided wave and Y-Net

ZHANG Xiaoyan, ZENG Zhoumo, LI Jian, CHEN Shili, LIU Yang

2024, 0(5): 92-99. DOI: 10.19936/j.cnki.2096-8000.20240528.013

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In order to detect the interface bonding quality of the adhesively bonded structure in composite plates, this paper proposed an inversion imaging method for interface weak bonding defects based on ultrasonic guided wave detection technology and Y-Net convolutional neural network. In this paper, the phase velocity dispersion curve and wave structure of the ultrasonic guided wave propagating in adhesively bonded structure in composite plates were calculated, from which the optimal excitation frequency and excitation mode suitable for detection were selected. A data set based on finite element simulation was created. The Y-Net was built, trained, verified and generalized ability tested, while the defect guided wave detection data and reconstruction algorithm for probabilistic inspection of defects (RAPID) imaging results were used as input, and the real bonding quality results were used as label data. Structural similarity index measure (SSIM) and peak signal-to-noise ratio (PSNR) were used to evaluate the inversion ability of Y-Net quantitatively. The experimental system was built, and the adhesively bonded structure in composite plates detection experiment was carried out. The results show that the method proposed in this paper can realize the bonding quality detection by means of inversion imaging of weak bonding defects, and the imaging results can accurately and high-quality characterize the position, shape, size and degree of weak bonding of weak bonding defects and other characteristics.

Research on the influence of hygro-thermal effects on matrix-dominated mechanical properties of T800S/M21 CFRP composites

CHEN Cheng, LI Chen, WANG Yan, GAO Limin, XU Jifeng

2024, 0(5): 100-106. DOI: 10.19936/j.cnki.2096-8000.20240528.014

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This work studies the hygro-thermal effects on matrix-dominated mechanical properties of T800S/M21 CFRP laminates. Experimental tests are performed on 90°and ±45° laminate test coupons to investigate the hygro-thermal effects on matrix dominated tension and shear mechanical behaviors. Laminate interface properties under fracture mode Ⅰ and mode Ⅱ considering different hygro-thermal conditions are evaluated by DCB and ENF tests. Based on ±45° tension test, crack density on specimen edge is measured to support the analysis of shear modulus degradation and crack density evolution under different moisture absorption conditions. In conclusion: Hygro-thermal conditions show significant effects on matrix dominated in-plane and interface properties. The nonlinear response of in-plane shear is strongly dependent on hygro-thermal conditions. Test results show that moisture absorption accelerates the crack density evolution and shear modulus degradation, and moisture content plays an important role in the contribution of crack density to the shear modulus reduction.

Study on thermal expansion behavior and pressure balance of soft mode during soft-die forming process

MA Tengfei, GUO Zimin, LI Guiyang, ZHENG Guodong, Li Weiming

2024, 0(5): 107-113. DOI: 10.19936/j.cnki.2096-8000.20240528.015

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The matching of the expansion and pressurization of soft modes was the key to the soft molding of composites. In order to control the pressure of soft die in the process of soft die forming, the compression Poisson’s ratio, expansion behavior and pressure balance characteristics of soft mold were studied. The expansion and pressurization processes was demarcated into three steps, including free expansion, semi-free expansion and pressurization and volume-limited expansion and pressurization of soft mold. The deformation and pressure theory of different stages of soft modes were studied, and the size and pressure changes of soft modes was measured by soft mode heating system. The size of the soft die was designed based on the above theory, and the curing process was optimized. The C-beam and I-beam were fabricated by soft-mold forming technology, and the internal quality and dimensional accuracy were characterized. The experimental results show that the compression Poisson’s ratio of soft mold material is 0.495, and the expansion behavior and pressure balance characteristics of the soft modesare consistent with the theoretical analysis in different stages. The precise control of pressure in the process of composite soft die molding is realized through the size design and curing process optimization, and the C-beam and I-beam with excellent quality and high dimensional accuracy are successfully fabricated.

Analysis of edge delamination damage of CFRP based on Lamb wave and improved Bayesian fusion algorithm

LÜ Wei, WEN Xue, FU Weigang, TANG Jingkun

2024, 0(5): 114-120. DOI: 10.19936/j.cnki.2096-8000.20240528.016

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Bayesian fusion method has good positioning results on damage of CFRP, but there will be obvious positioning errors in the sensor network edge area. In order to solve the problem that the original algorithm is inaccurate in the layered damage localization of the sensor network edge, firstly, the localization effect of Bayesian fusion algorithm composed of two different damage factors on damage of CFRP is analyzed in this paper, and the feasibility of Bayesian fusion algorithm formed by ToF damage factor on the damage localization and accurate for the edge layereddamage localization are verified. Then, on the basis of the probabilistic imaging algorithm formed by the damage factor DI, the linear weight is replaced by the exponential weight with faster attenuation, and the improved probabilistic imaging algorithm is re-substituted into the algorithm framed by Bayesian to form a new Bayesian fusion algorithm. The results show that compared with the existing fusion reconstruction algorithm, the improved fusion reconstruction algorithm reduces the error by at least 58%, and the positioning error is not more than 5 mm.

Analysis of rain erosion testing technology for wind turbine blades

YANG Dexu, LAN Haijin, YIN Xiuyun

2024, 0(5): 121-128. DOI: 10.19936/j.cnki.2096-8000.20240528.017

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Wind turbine blade is one of the core components of wind turbine, affected by rain, snow, wind and sand, hail and other harsh weather factors, the leading edge of wind turbine blade in long-term operation will produce serious erosion damage, resulting in delamination cracks at the leading edge joints, thus seriously affecting the structural stability of the blade. In order to develop a better coating for blade protection and to maintain the blade better, it is necessary to study the rain erosion test of the blades. This paper systematically introduces the process of wind turbine blades and their coatings affected by rain erosion, rain erosion mechanism, rain erosion test methods, types of test equipment, and rain erosion assessment methods, hoping to provide a reference for the industry to carry out research on rain erosion protection of wind turbine blades.

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