COMPOSITES SCIENCE AND ENGINEERING

Characterization of pore structure and splitting tensile mechanical properties of carbonated basalt fiber concrete

ZHAO Zhe, LI Bin

2023, 0(6): 5-11. DOI: 10.19936/j.cnki.2096-8000.20230628.001

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Concrete buildings exposed to the air for a long time will be carbonized by CO₂ gas in the air. The mechanical properties of concrete materials will change under carbonation, which will affect the safety of concrete structures. Based on the test, this paper studies the internal pore structure and tensile strength of plain concrete and basalt fiber concrete under carbonation by using rapid carbonation. The two kinds of concrete were carbonized rapidly at 0 d, 3 d, 7 d, 14 d and 28 d. The carbonation depth of the specimens at different carbonation ages was measured. The pore structure changes of two kinds of concrete at different carbonation ages were measured by nuclear magnetic resonance (NMR) device, and the static load splitting tensile test was carried out on the specimens by electro-hydraulic press. The results show that the carbonation depth of plain concrete and fiber concrete increases with the increase of carbonation age. The carbonation depth and rate of basalt fiber concrete are always lower than that of plain concrete. The addition of basalt fiber reduces the carbonation rate of concrete. With the increase of carbonation age, the peak value of T₂ spectrum of the specimen decreases, and the spectrum shifts to the left. Carbonation reduces the number of pores in the concrete material, reduces the pore diameter, and then reduces the porosity. There is a good exponential correlation between carbonation age and porosity, and the porosity of plain concrete is always higher than that of basalt fiber concrete. The proportion of micropores and mesopores in the specimen is more than 85.89%. The longer the carbonation age, the larger the proportion of micropores and mesopores in the specimen. Carbonation generates carbonate crystals that fill the cracks, reducing the proportion of macropores and cracks in the specimen. With the increase of carbonation age, the tensile strength of the two kinds of concrete increases first and then decreases. The early carbonation will reduce the porosity of the specimen, enhance the whole specimen, and its tensile strength will increase. The expansion force generated by the late carbonation will damage the specimen, and the tensile strength of the specimen will decrease. The strength decline of basalt fiber concrete is significantly lower than that of plain concrete. The addition of fiber enhances the carbonation resistance of concrete materials.

Study on mechanical properties and impact resistance of short carbon fiber reinforced alumina composite ceramics

WANG Depan, LIANG Sen, ZHOU Yuesong, LIU Long

2023, 0(6): 12-16. DOI: 10.19936/j.cnki.2096-8000.20230628.002

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In this paper, carbon fiber/alumina multiphase ceramics were prepared by traditional alumina ceramic production process. In order to prevent the carbon fiber from being overoxidized in high temperature environment, a carbon powder protective layer and a silicon carbide protective layer were prepared on the surface of the carbon fiber. The effects of carbon fiber contents on mechanical properties and impact resistance of C_sf/Al₂O₃ composite ceramics and C_sf/SiC/Al₂O₃ composite ceramics were investigated. A drop hammer impact test platform was built, and the impact test of C_sf/SiC/Al₂O₃ multiphase ceramics was carried out. The results show that the maximum bending strength and fracture toughness of C_sf/Al₂O₃ composite ceramics and C_sf/SiC/Al₂O₃ composite ceramics are similar, and the maximum bending strength and fracture toughness are 321.78 MPa and 6.98 MPa· m^1/2 when the carbon fiber content is 0.3% and 0.1%, respectively, which are 35% and 45.2% higher than those of pure alumina ceramics. During the drop hammer impact process, the impact resistance of C_sf/SiC/Al₂O₃ composite ceramics increased by 4.15%, and the peak load increased by 10.05%.

Preparation of copolyamide water-based sizing agent for carbon fiber and interfacial modification of CF/PA6 composites

WANG Shaofei, XUE Kanghao, FAN Lin, YANG Qing, LÜ Yueen, DING Xiaoma, ZHAO Le, ZHANG Hui, LIU Yong

2023, 0(6): 17-22. DOI: 10.19936/j.cnki.2096-8000.20230628.003

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In order to improve the interfacial properties of carbon fiber reinforced polyamide 6(CF/PA6) composites, the CF/PA6 composites were prepared by vacuum molding process using copolyamide water-based sizing agent as surface modifier. The microstructure, elemental changes and mechanical properties of CF and CF/PA6 composites were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and universal testing machine. The experimental results show that the sizing process can successfully connect the copolyamide to the surface of carbon fiber and improve the binding ability between carbon fiber and polyamide 6. When the concentration of copolyamide waterborne sizing agent is 0.5%, the mechanical properties of CF/PA6 composite is the best. The bending strength and interlaminar shear strength of CF/PA6 composite are 1044.5 MPa and 70.6 MPa, which are increased by 64.4% and 97.8% respectively, compared with those without treatment.

3D textile composite mechanical properties prediction based on virtual modeling method of compact bundle-chain

ZHANG Jian

2023, 0(6): 23-29. DOI: 10.19936/j.cnki.2096-8000.20221128.031

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The accurate prediction of elastic constants of 3D textile composites is typically based on realistic unit cell geometry. This paper presents a compact virtual bundle-chain approach, utilizing a dynamic relaxation procedure, as applied to simulate real fiber bundle shape of a 3D woven composite preform. Then the deformed preform is applied to compress boundary condition to simulate the mold clamp process to the more accurate surface bundle shape. A mapping algorithm from beam elements to solid elements is developed to get the unit-cell FEA model that contains bundles and matrix. The fiber volume fraction of yarns is calculated based on the real fiber line density. The mechanical properties of the unit-cell FEA model is calculated after the period boundary condition applied. The results show that the compact virtual bundle-chain method can simulate the cross-section of the preform yarns accurately, and the predicted mechanical properties of the woven composite are in good agreement with the experimental results.

Research of the influence of high temperature pre-damage on the residual strength after impact of carbon fiber composites

CAO Yuhan, GUO Shuhan, OUYANG Junjie, KONG Fanqi, WANG Fusheng

2023, 0(6): 30-36. DOI: 10.19936/j.cnki.2096-8000.20230628.005

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Low-speed impact and post-impact compression test (CAI) were performed on 9A12 epoxy resin based T700 composite (CFRP) laminates at different pre-damage temperatures (180 ℃, 210 ℃, 240 ℃) and damage times (24 h, 72 h, 120 h, 168 h). Digital image technology (DIC) and micro-morphology were used to study the variation of weight loss and residual strength of CFRP laminates with damage temperature and damage time due to high temperature pre-damage. The results show that the relative weight loss rate and the decrease rate of compressive strength after impact of CFRP laminates at different temperatures are firstly fast and gradually slow, and finally tend to be stable. The relative weight loss and residual strength after pre-damage at 180 ℃ changed little with the damage time, and tended to be stable after 120 h of damage. When the temperature rises to 210 ℃ and 240 ℃, the residual strength of the laminate decreases rapidly at the initial stage of damage. After 40 h, the residual strength decreases by 20.4% and 25.1%, respectively, which is lower than that after 120 h of damage at 180 ℃. Based on the analysis of results, a linear relationship model of the weight loss caused by high temperature pre-damage of CFRP laminates and the residual strength after impact is established. The strain evolution law of the CFRP laminate in the compression direction was recorded by DIC technology, and the strain cloud map was obtained. Observing the microstructure, it was found that the high temperature damage reduced the encapsulation of the resin to the fiber, and scattered resin particles appeared between the layers. At 240 ℃, the damage form of the material changed from structural fracture to damage caused by oxidative decomposition of epoxy resin.

The bearing capacity and the damage process of the ceramic matrix composites L-shaped specimens with defects

ZHOU Junchen, GENG Qian, DUAN Yubin, WANG Dongliang

2023, 0(6): 37-43. DOI: 10.19936/j.cnki.2096-8000.20230628.006

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Based on the image reconstruction technology, we develop finite element models of the representative volume and L-shaped specimens of ceramic matrix composites, through which the elastic modulus of ceramic matrix composites is predicted. With a combination of numerical simulations and experiments, the bearing capacity and damage process of L-shaped specimens under tensile are studied. The results show that experiment and simulation results are in good consistency regarding the influence of defects on the bearing capacity, and the quantity difference is about 10%. The inner corner of specimens is mainly subjected to tension, while the outside area is subjected to compression. Defects on the inner corner affect the bearing capacity of specimens. The bearing capacity degrades as the defect area broadens. However, defects on the outside of specimens affect the damage process. Microscopic defects propagate and eventually lead to macroscopic failures of the specimen, mainly in the form of material delamination. This study can provide a reference for the testing and analysis of the bearing capacity of ceramic matrix composites.

Influence of the heating process on the scarf repair curing process of resin matrix composites

CHEN Shuxian, YAN Dengjie, DING Zhenyuan

2023, 0(6): 44-51. DOI: 10.19936/j.cnki.2096-8000.20230628.007

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Based on the time-dependent properties of the composite materials, a three-dimensional thermal-mechanical-chemical multi-field coupling model for thermal curing of resin matrix composites was established. The variation characteristics of temperature, curing degree and residual stress during the curing process were numerically studied. The results show that different thermal environments have little effect on the peak temperature of the patch, which is within 0.8%; for the curing method of the heat-blanket, increasing the heating rate can shorten the curing time of the patch, but it will increase the residual stress, and the time required to complete the curing is shortened by 23% with the residual stress increased by 9%, when the heating rate increases from 2 K/min to 6 K/min. For the autoclave curing mode, the residual stress in the patch can be reduced and the curing time will not be prolonged while decreasing the convective heat transfer coefficient in the autoclave, and the residual stress is decreased by 12.3% when the convective heat transfer coefficient decreases from 63 W/(m²·K) to 23 W/(m²·K); and the residual stress corresponding to the autoclave curing method is 7% smaller than that corresponding to the heat-blanket curing method, while the curing time is close for two curing methods. However, the curing cost for the autoclave is much higher than that for heat-blanket, so the curing process of the heat-blanket can be continuously optimized to achieve the goal of improving the curing quality and reducing the curing cost.

Research on topology optimization method of composite laminated plates with curvilinear fiber laying paths

WANG Tianli, YAN Chao, TONG Xinxing, FAN Jiahui, YANG Xiaokang, YUAN Zhenyi

2023, 0(6): 52-58. DOI: 10.19936/j.cnki.2096-8000.20230628.008

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Composite laminated plates with curvilinear fiber laying paths are taking as the research object in this paper. A model of curvilinear fiber laying path in single layer for the composite laminated plates was firstly constructed. Combined with the discretation and element equivalent principles of the laminated plates, the elemental equivalent constitutive relation of laminated plates with curvilinear fiber paths was established. Based on the material penalty model, a topology optimization model of composite laminated plates with curvilinear fiber paths under volume constraint was proposed to minimize the strain energy to evaluate the structural stiffness. The topology optimization model was solved based on finite element and moving asymptote method to obtain the optimal topological shape of laminated structures. Numerical examples were used to verify the accuracy of the design method. The results show that the topology optimization method can obtain effective topological shape, and the structural stiffness of cantilever beam and simply supported beam can be increased by 36.9% and 22.6% respectively. The performances are significantly improved by changing the curvilinear fiber laying paths.

Synthesis of a novel self-crosslinking flame retardant with phosphorus-containing and its thermal stability and combustion performance of solid epoxy resin

WANG Hengxu, XU Jinjia, LIN Zhiqian, XU Hanlin, LOU Gaobo, DAI Jinfeng, FU Shenyuan

2023, 0(6): 59-66. DOI: 10.19936/j.cnki.2096-8000.20230628.009

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A novel self-crosslinking flame retardant with phosphorus-containing (DPPN) was synthesized via substitution reaction, and its structure was characterized by ¹H-NMR and ³¹P-NMR. The results of self-crosslinking behavior and thermal stability for DPPN showed that DPPN has excellent self-crosslinking ability and thermal stability, which are evaluated by DSC and TGA respectively. The curing behavior, thermal stability, combustion behavior and morphology of char residue of the solid EP with DPPN were thoroughly investigated. It was found that the addition of 10% DPPN not only increased the curing temperature of EP, but also elevated the char residue (800 ℃) of EP from 11.0% for neat EP to 17.1%. Moreover, compared to neat EP, the peak heat release rate pHRR, total heat release THR, peak smoke producerate pSPR and total smoke production TSP of EP/10% DPPN composite were respectively reduced by 53.8%, 42.1%, 32.1%, 25.0%, and 10% DPPN EP has good fire resistance.

Study on curing deformation control of C-shaped composite beams

WANG Xuehua, CHEN Junlin, MAN Jiacheng, YUE Guangquan

2023, 0(6): 67-72. DOI: 10.19936/j.cnki.2096-8000.20230628.010

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Aiming at the curing deformation of the C-shaped beam structure of the civilian composite material, the simulation prediction models including heat transfer analysis model, curing kinetics analysis model, elastic modulus model, resin shrinkage model are established, and the C-shaped beam shrinkable. The curing deformation of the structure is predicted, and the prediction results have a small error compared to the test results. In this paper, the simulation prediction result of the curing deformation is used to guide the mold type correction adjustment of the C-shaped beam scaled-down component. The modification measurement of the C-shaped beam prepared by the mold adjustment is satisfied with the structural precision requirements, and the effective control of curing deformation of C-shaped beam structure is realized.

Research on mechanical properties of polypropylene fiber shotcrete under disturbed load

JIA Jingen, ZHANG Bin

2023, 0(6): 73-79. DOI: 10.19936/j.cnki.2096-8000.20230628.011

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Based on the test, the safety performance of fiber shotcrete in coal roadway support system under disturbed load is studied. The longitudinal wave velocity and damage degree of the specimen under different disturbance loads and times were measured by non-metallic ultrasonic measuring instrument. The uniaxial compression tests of specimens under different disturbance times are carried out by using the separated Hopkinson compression bar device. The relationship between longitudinal wave velocity, damage degree, peak stress, energy dissipation and disturbance load is analyzed. The results show that with the increase of disturbance times, the longitudinal wave velocity of the specimen first increases and then decreases. The early disturbance will reduce the porosity and increase the integrity of the specimen. With the increase of disturbance times, the damage of the specimen will accumulate, the damage degree will increase, the longitudinal wave velocity will decrease, and the increase of disturbance air pressure will increase the amplitude of wave velocity decrease. When the specimen is subjected to 0.15 MPa disturbing air pressure for 1~5 times, the peak stress is 39.6 MPa, 41.1 MPa, 38.7 MPa, 35.1 MPa and 33.7 MPa, respectively. The increase of the times of disturbance load increases the peak stress of the specimen first and then decreases. The appropriate impact disturbance will increase the peak stress of the specimen. With the increase of the times of disturbance, the decrease of the stress of the specimen increases significantly, and the damage degree of the specimen under the later disturbance load will be greater. The disturbance load will reduce the energy absorption effect of the specimen, and the greater the disturbance load is, the more the action times are, the more obvious the decrease of the energy absorption of the specimen is. In the operation and maintenance of coal roadway support system, the safety performance of fiber shotcrete should be regularly explored to ensure the safety of roadway support system.

Experimental study on mechanical properties of concrete confined by carbon fiber cloth under uniaxial compression at different strain rates

SONG Mengmeng, WU Wenfei, ZHOU Heng

2023, 0(6): 80-87. DOI: 10.19936/j.cnki.2096-8000.20230628.012

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The restraining and protective effect of carbon fiber cloth on concrete materials can greatly improve their mechanical properties. This paper analyzes the effects of strain rate, number of layers of carbon fiber cloth and concrete strength on the stress-strain curve, peak stress, DIF (dynamic increase factors) and toughness of carbon fiber cloth-constrained concrete based on the uniaxial compression tests with different strain rates using an electro-hydraulic servo press and a split Hopkinson pressure bar (SHPB). The test results showed that the peak stress of the specimens at different strain rates increased with the increase of the number of carbon fiber cloth layers, and the two were negatively correlated as an exponential function. The increase of strain rate makes the specimen DIF increase, and the two are positively correlated as an exponential function, and there is a significant strain rate effect on the specimen. C30 concrete is more sensitive to the strain rate effect of the specimen with the increase of the number of pasted fiber cloth layers, and the degree of influence of the number of carbon fiber cloth layers on the DIF of the specimen decreases with the increase of the concrete strength grade. The increase of strain rate, concrete strength grade and the number of layers of carbon fiber cloth paste increase the toughness of specimens. The restraining and protective effect of carbon fiber cloth can increase the ductility of the specimens and prevent the concrete structure from brittle damage, which is important to enhance the safety of the structure.

Experimental study on damping performance of typical marine composite materials

GONG Huashuai, MEI Zhiyuan, CHEN Guotao, SUN Zhaoyi

2023, 0(6): 88-94. DOI: 10.19936/j.cnki.2096-8000.20230628.013

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In order to study the influence of resin type, fiber layup angle, fiber type and its hybrid method on the damping performance of composite materials, this paper aims at two kinds of marine composite materials matrices, epoxy resin QC350 and vinyl ester resin 430LV, two reinforcing fibers, carbon fiber T700 and glass fiber G430S. Composite specimens with different fiber and resin combinations were prepared by vacuum forming, and DMA tests were carried out. The results show that the damping performance of QC350 pure resin is better than that of 430LV, the loss factor is η_{max (QC350)}≈0.094 and η_{max (430LV)}≈0.078 in the frequency domain from 1 Hz to 1 kHz, but in the frequency domain the damping performance of 430LV resin matrix composites is more stable under the same temperature range; the damping performance of carbon fiber composite CFRP is not as good as that of glass fiber composite GFRP, within 1 Hz~1 kHz frequency, η_(T700/QC350)≈0.025, η_{(G430S/QC350)}≈0.030; the effect of fiber layup angle on the damping performance of composites is obvious, but it does not change the change trend of loss factor in frequency and temperature domains. The composites with layup angles of 90° and ±45° have better damping performance, the loss factor of the two layup angles is about 2~3 times that of the 0° layup; when the carbon-glass hybrid method with glass fiber is used outside, the damping performance of the composite material is better, and with the number of layers of the glass fiber increases, the damping performance of the glass fiber increases gradually.

Mechanism and optimization of layer parameters on performance of Fe/CFRP hybrid structure

JING Shuowen, WANG Fazhan, HE Haoping, HUANG Kepeng

2023, 0(6): 95-103. DOI: 10.19936/j.cnki.2096-8000.20230628.014

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In order to study the Fe/CFRP (carbon fiber reinforced polymer) hybrid structure machine tool components that met the requirements of lightweight and high damping, in this paper, the three-dimensional structural topology optimization of integral metal beam was carried out by using the variable density method with constraint factors, and the damping characteristics are improved by laying CFRP free damping layer. Based on the response surface method, the regression equation of key pavement parameters on structural maximum deformation and damping loss factor was established, and the pavement parameters and beam performance were analyzed. Genetic algorithm was used to optimize the layer parameters of composite beam globally. The results showed that when the laying-angle was 46.03°,the 0° laying-thickness ratio was 25.39% and the laying-order was C₂,the composite performance of Fe/CFRP hybrid milling machine is best, and its stiffness was unchanged. The weight was reduced by 35.7%, and the damping performance was improved by 62.7%, the experimental results are consistent with the simulation results.

Numerical modeling and optimisaition in thermo-stamping process of unidirectional fiber reinforced thermoplastic composites

ZHANG Xuewen, WANG Jihui, CHEN Hongda, NI Aiqing

2023, 0(6): 104-114. DOI: 10.19936/j.cnki.2096-8000.20221028.031

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Based on the ultra high molecular weight fiber reinforced polyurethane (UHMWPE/PUR) unidirectional (UD) tape prepreg, the simulation modeling, experimental verification and process optimization of thermo-stamping process were studied. Firstly, the mechanical behavior of unidirectional reinforced thermoplastic composites during thermo-stamping was described, and the thermal-rate dependent non-orthogonal hypoelastic in-plane shear constitutive model was established. The thermal dependent in-plane tensile properties were considered. The commercial finite element software ABAQUS was used to simulate hemispherical thermo-stamping. Based on the principal curvature method, the out-plane wrinkling of the simulation results were qualitatively and quantitatively evaluated by MATLAB. The relationship between the three main parameters (blank holder pressure, prepreg initial temperature and die temperature)and the amount of wrinkling in thermo-stamping process was studied. Aim for the minimum amount of out-plane wrinkling, the response surface method was used to optimize the thermo-stamping simulation, and the best process parameters of blank holder pressure, prepreg initial temperature and punch temperature were determined. The results show that the pressure of blank holder and the initial temperature of prepreg have a great influence on the wrinkling. The response surface method can accurately predict the optimal molding parameters.

Structural design and experimental verification of the composite flexible thin rod

LIANG Xuhao, ZHANG Juanjuan, SHEN Feng, CHEN Yongxiao, WANG Xiaolei, BAI Ruixiang

2023, 0(6): 115-119. DOI: 10.19936/j.cnki.2096-8000.20230628.016

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The flexible deceleration brush de-rotation method is an existing contact active de-rotation technique for free tumbling targets in space. According to the technical requirements of the flexible brush tool for a certain type of deceleration brush de-rotation device, a kind of flexible thin rod of carbon fiber composites was designed. By carrying out finite element simulation analysis, the rationality of the structural design scheme was verified. Thin rod samples were prepared by rubbing-winding process. Randomly selected samples were tested for validation. The test results show that, both the bundling stiffness of 24 composite flexible thin rods and the maximum bending deflection of a single composite flexible thin rod meet the basic design requirements. The results of the simulation analysis are in accordance with the experimental results. This research work has laid the foundation for subsequent research into the application of the component on the deceleration brush de-rotation device.

Research on coupled mechanical properties of CFRP bolted connection force and temperature

WANG Weilong

2023, 0(6): 120-127. DOI: 10.19936/j.cnki.2096-8000.20230628.017

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In this paper, tensile tests of carbon fiber composite material (CFRP) bolted specimens with different connection modes (single screw double shear connection, double screw double shear connection), different tightening torques (2 N·m, 4 N·m, 6 N·m) and different temperature environments (normal temperature and low temperature) were carried out under static load. The effects of force, temperature and connection mode on the static tensile properties of bolted connected components were investigated. The results show that under the same experimental conditions, the tensile strength of the specimens with double screw connection is significantly improved. Properly increasing tightening torque can effectively improve bolt connection strength; the tensile strength of specimens was slightly improved under low temperature.

Research on the automatic spraying process of sealing glue for composite parts

QIU Yi, LIU Yanru, CHEN Jin, YU Ning, TANG Peng, ZHANG Kai

2023, 0(6): 128-132. DOI: 10.19936/j.cnki.2096-8000.20230628.018

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Spraying aluminum on the surface of composite parts with flame is one of the most commonly used conductive treatment methods for surface layer, and it is usually necessary to spray the sealing glue on the surface of the aluminum layer to protect it. At present, sealing glue is commonly used by hand brushing and manual spraying, which is inefficient and easy to produce hanging, and requires a lot of polishing work in the later stage. Automatic spraying of sealing glue robot has become a development trend, and this paper conducts a process parameter study on vertical automatic spraying of sealing glue robot. The results show that the automatic spraying of the robot can effectively improve the hanging phenomenon of the sealing glue, the thickness of the sealing adhesive layer is uniform, the surface quality is good, and the bonding strength between the sealing glue and the aluminum layer is as high as 30.28 MPa, far exceeding the industry standard.

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