COMPOSITES SCIENCE AND ENGINEERING

DAMAGE ANALYSIS AND EXPERIMENTAL STUDY OF OPEN-HOLE CFRP COMPOSITE LAMINATES

SUN Zhen-hui, TIE Ying, LI Cheng, HOU Yu-liang

2019, 0(1): 5-10.

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In this paper, the hole-edge stress and damage of open-hole CFRP laminate plate were studied by means of analytical calculation and tensile test. Based on the complex variable function method and the Tsai-Hill failure criterion, the principal stress distribution and the first damage load coefficient of each layer of the laminate plate are calculated. In order to determine the in-plane tensile properties of the plate and verify the analytical results, tensile tests on the plate were carried out based on the ASTM D5766-07 test standard. The results show that 0 degree and ±45 degrees layers are the main bearing layers when the open-hole laminate plate is subjected to the tensile load along the long axis direction, and the maximum value of the principal stress, σ₁, occurs in the range of 65 to 115 degrees and 245 to 295 degrees along the center of the hole, the minimum first damage load coefficient of each layer is within the range of 65 to 115 degrees and the damage load coefficient of 45 and -45 degrees is the smallest. When the load reaches the initial damage load, the internal damage and the parameter degradation begin to occur. After the tensile test, the damage of the laminate plate is mainly based on the matrix cracking and the fiber fracture, the damage region is within the range of 61 to 90 degrees and 241 to 270 degrees around the hole, the results of the test are in agreement with the analytical results.

INFLUENCES OF GRAPHENE NANOSHEETS ON THERMAL CONDUCTIVITY AND MECHANICAL PROPERTIES OF CARBON FIBER/POLYPROPYLENE COMPOSITES

XIA Xue, MEI Qi-lin, WANG Cong, ZHOU Xiao

2019, 0(1): 11-14.

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Polypropylene (PP) is a high strength thermoplastic with low thermal conductivity which limits its application in many fields. So it is necessary to improve the thermal conductivity of PP composite material.Graphene nanosheets (GNSs) are a kind of layered micro-scale materials with excellent mechanical properties and thermal conductivity, but few research has been done. Carbon fiber (CF) is a high-strength and high-modulus fiber which can improve the PP/GNSs/CF mechanical properties and thermal conductivity. PP/GNSs/CF composites were prepared by melt blending to study the effect of different GNSs mass fractions on the mechanical properties and thermal conductivity of composites. The results show that the mixed use of GNSs and CF not only has obvious synergistic effect on the thermal conductivity, but also improves the mechanical properties. The thermal conductivity of PP/GNSs (3 phr)/CF (2 phr) composites is 0.42 W/(m·K), which was increased by 110% compared with pure PP. The tensile strength and flexural strength of the composites were increased to 38.0 MPa and 56.7 MPa, respectively, which were increased by 12% and 13%, respectively, compared with pure PP.

MECHANICAL PROPERTIES OF HYBRID FIBER COMPOSITE SHAFT REINFORCED BY Al₂O₃ PARTICLES MANUFACTURED BY MICROWAVE CURING

ZHENG Wei-feng, ZHOU Lai-shui, YUAN Tie-jun, AN Lu-ling

2019, 0(1): 15-22.

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Aiming at improving the bearing capacity of composite transmission shaft manufactured by microwave curing, the material enhancement method with hybrid fiber as reinforcement and alumina particle reinforced epoxy as matrix was proposed. The microwave curing process was optimized simultaneously. The optimal hybrid volume ratio, Al₂O₃ content and microwave curing parameters were determined by comparing the interlaminar shear, tensile and dynamic impact properties of plate specimens. On that basis, the reduced transmission shaft was manufactured by wet winding with fabrics. The mechanical property difference between thermal and microwave curing was compared by bending and torque test. The experimental results showed that ① the interlaminar shear strength of specimen could be enhanced by low-power preheat and high-power curing on the premise of efficiency. ② With the increase of CF/GF hybrid ratio, the interlaminar shear strength and tensile properties increased, while the impact toughness was reduced. ③ When the Al₂O₃ content increased from 0 to 30%, the interlaminar shear strength, tensile strength and module increased by 8.7%, 27.9% and 12.5%, respectively. However, further increase in Al₂O₃ content resulted in the reduction of properties. ④ The maximum torque, bending strength and module of composite transmission shaft manufactured by microwave curing showed the same level with those by thermal curing.

RESEARCH ON THE EFFECT OF MATERIAL LAYING SEQUENCE ON STRESS OF ENERGY STORAGE FLYWHEEL

REN Zheng-yi, ZHANG Shao-wu, YANG Li-ping, HUANG Tong

2019, 0(1): 23-27.

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Taking the composite energy storage flywheel as the research object, this paper analyzed the influence of the material layout on the flywheel stress. Aiming at the structural characteristics of the flywheel, a stress analysis model of a multi-layer interference fit composite material rim was established, and the radial and hoop stress distribution of composite material flywheel under different material placement sequence was analyzed by ANSYS Workbench software. The results show that when the rim material is the same in all layers, the stress of using glass fiber is the largest, and the stress of using carbon fiber T800 is the least, which the rotating speed is constant. When the rim material of each layer is different, the inner layer is a lower cost glass fiber, the middle layer is a carbon fiber T300, and the outer layer is a higher cost carbon fiber T800, so that the force of the flywheel is the most uniform and the stress gradient is the smallest. The research results will have certain reference value for the design and optimization of composite energy storage flywheels.

EFFECTS OF TITANIUM SURFACE TREATMENT ON ADHESIVE PROPERTY OF TITANIUM-COMPOSITE JOINTS

DONG Wei, LI Zeng-shan, CUI Hai-chao

2019, 0(1): 28-35.

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The Titanium/Graphite Hybrid Laminates (TiGr) have been widely used in aeronautical structures for their excellent performance. The adhesive properties of the titanium plate and the composite in the TiGr laminates will affect the stiffness and failure modes of the TiGr laminates. However, the adhesive property of the titanium plate and the composite are greatly influenced by the processing technology. In this paper, adhesive property of titanium-composite joints with different surface treatments on titanium surface was investigated based on floating roll peeling methods and range analysis. The peeling results show that the titanium-composite joints with twice plasma treatment have the highest peeling resistance of 6.914 kN/m, but the titanium-composite joints with twice plasma treatment and resin protection have the the lowest peeling resistance, which is 2.139 kN/m. Three failure patterns of the adhesive interface between titanium and composite happen during the peeling process. That is the adhesion failure between the titanium plate and the adhesive film, the cohesion failure of the adhesive film, and the adhesion failure between the adhesive film and the composite. The peel resistance reaches the highest when the cohesion failure of the adhesive film occurs. According to the experimental results, the adhesive property is weakened with the resin protection applied on the titanium surface. In addition, the grit blasting prior to the plasma treatment weakens the adhesive property, as compared to the property with no grit blasting prior to plasma treatment.

STUDY ON SHEAR RESISTANCE OF BFRP REINFORCED CONCRETE DEEP BEAMS WITHOUT STIRRUPS

ZHANG Zhi-jin, LIU Hua-xin, LI Qing-wen, WANG Xue-zhi

2019, 0(1): 36-41.

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In order to study the influence of different shear span ratio, reinforcement ratio and basalt fiber volume fraction on the deflection, cracking load and ultimate bearing capacity, 7 basalt fiber reinforced polymer (BFRP) reinforced concrete deep beams without stirrups were investigated, and the crack development and failure mode were analyzed. The research results can be obtained as follows. The failure mode of all beams is shear failure; Under the same load, the mid-span deflection of specimen can be improved by the increase of shear span ratio, while will be reduced by the increase of BFRP reinforcement ratio and basalt fiber volume fraction. The cracking load and ultimate load of beams are weakened with the shear span ratio increases, and will be increased with the increase of longitudinal reinforcement ratio and basalt fiber volume fraction. Calculation of shear capacity of test beams was performed by reference to relevant specifications, and it is found that shear design equations of the ACI 440. 1R-06 code were better predictions, the predications of CSA. S 806-12 code were more stable and the GB 50608—10 were relatively conservative. The ACI440.1R-06 code is suggested to be used to calculate the shear capacity of BFRP reinforced concrete deep beams without stirrups.

PREPARATION AND PROPERTIES OF THIOUREA-MODIFIED POLYAMIDE CURING AGENT

HUANG Yuan-zheng, HUANG Zhi-yong, DAI Hai-feng

2019, 0(1): 42-46.

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In order to prepare room-temperature curing polyamide curing agent with similar viscosity to E-51, thiourea was used to modify the self-made low-viscosity polyamide curing agent, and the optimal reaction conditions were explored. The non-isothermal DSC method was used to study the curing reaction kinetics of the modified curing agent/E-51, and the thermal stability of the cured system before and after the modification was tested. The results showed that, to meet the application requirements, the viscosity of the modified curing agent was 10.9 Pa·s, the gelling time was 23 min, and the curing time was 47 min when the thiourea was 8%, the reaction temperature was 100 ℃, and the reaction time was 1 h. According to the Kissinger method, the activation energy of the modified curing agent/E-51 curing reaction was calculated to be 38.79 kJ/mol, the Arrhenius constant was 9.68×10⁴ and the reaction rate constant was 0.0154 at 25 ℃. According to the FWO method, the activation energy was 42.73 kJ/mol. The thermal decomposition temperatures before and after the modification were 347.46 ℃ and 350.72 ℃, respectively.

PYROLYSIS CHARACTERISTICS AND KINETICS OF SCRAP CARBON FIBER REINFORCED EPOXY RESIN MATRIX COMPOSITES

SONG Jin-mei, LIU Hui, WANG Lei, WANG Ying-ming

2019, 0(1): 47-53.

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The pyrolysis process of a scrap carbon fiber reinforced epoxy resin matrix composite has been studied under different heating rates of 6.67 ℃·min^-1, 10 ℃·min^-1 and 13.33 ℃·min^-1 using thermogravimetric methods. The effects on pyrolysis of the composite of varying atmosphere and heating rate were studied. The results show that the pyrolysis heating rate and atmosphere both have a significant effect. In a nitrogen atmosphere the scrap carbon fiber reinforced epoxy resin matrix composite has only one thermal decomposition stage and follows a first-order reaction model. In air there are two decomposition stages following a second-order reaction model and a 0.5-order reaction model. The apparent activation energy and frequency factor of the thermal decomposition of the scrap carbon fiber reinforced epoxy resin matrix composite are both increased significantly when the heating rate is increased. In the nitrogen atmosphere the apparent activation energy is 55.84 kJ·mol^-1. In air the apparent activation energy of the first weightlessness phase is 39.24 kJ·mol^-1, and the apparent activation energy of the second weightlessness stage is -8.62 kJ·mol^-1.

SOUND ABSORPTION PROPERTIES OF SINGLE-HOLE HOLLOW POLYESTER REINFORCED RUBBER COMPOSITES

HONG Jie

2019, 0(1): 54-60.

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A series of single-hole hollow polyester (abbreviated SHHPF) reinforced hydrogenated carboxyl nitrile rubber (abbreviated HXNBR) composites were fabricated. The sound absorption properties were investigated. The results indicate that the sound absorption property of HXNBR/SHHPF composite with thickness of 1 mm was remarkably improved with increasing SHHPF content. At SHHPF content of 40%, the sound absorption property is the best. The sound absorption coefficient at frequency 2500 Hz was increased to 0.671, and the effective bandwidth was 1800 Hz~2500 Hz for sound absorption coefficient larger than 0.2. However, sound absorption property was degraded when the SHHPF content grows to 50%. While, with the HXNBR/SHHPF mass ratio of 80/20, the sound absorption property was improved by increasing thickness of composites from 1 mm to 5 mm. However, the improvement through increasing thickness was relatively small after 3 mm, and the improvement was moved to medium frequency. At the same time, tensile mechanical property of HXNBR/SHHPF was also improved significantly, which benefits for its practical application.

ELECTROTHERMAL ICE MELTING PROPERTIES OF NICKEL COATED GLASS FIBER/EPOXY RESIN COMPOSITES

QIN Wen-feng, YOU Wen-tao, FAN Yu-hang, HAN Xiao-qiang

2019, 0(1): 61-65.

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A dense and uniform Ni-P coating was prepared on the treated glass fiber surface by electroless plating. The electrothermal properties of nickel-coated glass fiber and the melting properties of the composites were studied. SEM showed that the surface of the glass fiber was smooth before nickel plating, and the nickel particle distribution was uniform and its diameter was between 150 nm and 300 nm. The resistance test shows that the resistance of the sample decreases with the increase of nickel plating time, and the surface resistance of the sample is 1.4 Ω/□ when the nickel plating time is 25 min. The cyclic electrothermal experiment shows that the nickel-coated glass fiber has good electrothermal properties, and the heating capacity increases rapidly with the increase of input power. The maximum equilibrium temperature is reached within 40 s. The conductivity of the sample was improved after several electrothermal cycles, which may be related to the crystallization transition caused by high temperature. The deicing experiment showed that the best deicing effect was obtained by using Ni-coated glass fiber/epoxy resin conductive FRP material, and the shortest time of ice falling off on the surface of Ni-coated glass fiber/epoxy composite was 112 s under the input voltage of 5 V.

PROPERTY STUDIES OF HIGH-TEMPERATURE EPOXY RESIN FOR RTM

QIAN Jian-hua, FU Jian-hui, HUANG Rui

2019, 0(1): 66-70.

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The structures, properties and fracture image of one-component high-temperature epoxy resin suitable for RTM process were studied. FTIR and ¹H NMR shows that MERICAN 3768 and CYCOM 890 have similar structural components. Viscosity of MERICAN 3768 is 240 mPa·s at 80 ℃ and is increased to 300 mPa·s after 12 h at 80 ℃, which meets the requirements of RTM process. Thermal stability of MERICAN 3768 is similar to that of CYCOM 890 from thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) analysis. Mechanical properties of MERICAN 3768 are similar to those of CYCOM 890.

STUDY ON METAL SANDBLASTING PROCESS FOR BONDING OF COMPOSITES

ZHANG Yu-jie, ZHAO Xin, GUO Jin-hai, SHI Wen-feng

2019, 0(1): 71-74.

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The paper introduces metal materials and their surface treatment for bonding of composites, and tests the sandblast parameters of TC4 titanium alloy, 5052 aluminum alloy, 304 stainless stell and 4J36 invar stell. Taking sandblast time as variable as well as tensile shear strength between metal and composite after bonding to verify the surface condition under metal sandblasting. The test demonstrates that appropriate sandblasting parameter of TC4 titanium alloy is 30 s±5 s/15 cm² and 20 s±5 s/15 cm² for 052 aluminum alloy, 45 s±5 s/15 cm² for 304 stainless stell, 25 s±5 s/15 cm² for 4J36 invar stell under the condition of 40 mesh quartz sand, the sandblasting distance of 150 mm, the sandblasting angle of 45°, the sandblasting pressure of 0.5 MPa.

RESEARCH ON THE TECHNOLOGY OF POLYMERIZING NYLON 6 ON THE SURFACE OF CARBON FIBER BY IN-SITU IMPREGNATING

ZOU Xue-xue, LI Jin-huan, ZHAN Dong-zhi, XIAO Jun

2019, 0(1): 75-81.

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A new method was explored to synthesize nylon 6 on the surface of carbon fiber by fiber activating and in-situ impregnating polymerization in order to equip with carbon fiber/nylon 6 composite on line production line on the carbon fiber production line. Firstly, the surface of carbon fiber was coated with a layer of TDI (2,4-toluene diisocyanate) which was used as activator to make the fiber activate. Then the activated fiber was passed through the monomer anion melt which was obtained from the system of caprolactam and an initiator sodium hydroxide by previously removing water. Finally, a layer of nylon 6 is formed on the surface of the fiber through diffusion and polymerization of monomer anion. The results showed that nylon 6 could be successfully formed on the surface of carbon fiber through fiber activating and in-situ impregnating polymerization process. However, the polymerization temperature has great influence on the conversion rate, melting crystallization behavior and molecular weight of nylon 6. And the excess activator also has an adverse effect on the conversion rate of nylon 6. If the ratio of activator could be improved, the conversion rate of polymer will be improved. Finally, the functional group distribution and microstructure of the material were detected by infrared spectroscopy and scanning electron microscopy (SEM).

INFLUENCE OF PEEL PLY SURFACE TREATMENT ON ADHESIVE BONDING OF COMPOSITES

CHEN Lu-yuan, GU Ling-cong, WANG Xu

2019, 0(1): 82-86.

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The adhesion properties depend on several physical and chemical factors, such as peel ply component, microstructure of adhesive surface, ambient humidity. This paper aimed at the effect of surface morphology characteristics of composite materials and surface freedom energy on adhesion performances of corresponding surfaces assemblies. In order to achieve this purpose, scanning electron microscopy (SEM) and surface tension meter were performed, and the relationships between surface characteristics and results from GIC tests were established. We concluded that the surface cleanliness apparently increases the interlaminar fracture toughness. However, the influence of surface free energy on the adhesive quality has not been found.

CHARACTERIZATION OF UNIFORMITY OF WINDING COMPOSITE MATERIALS BY BACKSCATTERING

ZHENG Shan-pu, LU Ming-hui, LIU Mo, JIANG Xian-rong

2019, 0(1): 87-90.

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By studying the acoustic characteristics of filament winding composites and the difficulty of detecting the material by conventional ultrasonic bottom wave method, this paper presents a non-destructive testing method using ultrasonic backscattering signals to characterize the homogeneity of materials. High-power ultrasonic pulse reflection method was used to extract the echo signals from multiple regions of the glass fiber-wound composite material. The ultrasonic backscatter integral was used as a parameter to analyze the time-domain and frequency-domain of the backscatter signal. Finally, the ultrasonic nonlinearity was used. The coefficient validates its characterization effect. The results show that the time-domain backscatter integral is more sensitive to defects than the frequency domain integral and lower than the ultrasonic nonlinearity coefficient. The backscatter integral is an effective and accurate parameter for evaluating the internal quality uniformity of the material.

STUDY ON THE ELECTRIC PROPERTIES OF PAN-BASED CARBON FIBER ELECTRIC HEATING DEVICE

YANG Miao, TONG Yao-yao

2019, 0(1): 91-94.

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Carbon fiber is a versatile functional and structural material. The PAN-based carbon fiber produced by wet process has the advantages of uniform heat and stable heat. In order to study the electric properties of PAN based carbon fiber cloth, an electrical heating device is designed and made with PAN-based carbon fiber cloth as the heating material. We test the resistance-temperature characteristic, voltage-temperature relation and time-temperature relation. The result shows that when the device is electrified, the rate of resistance change increases slightly with the increase of temperature, but the change is very small. The device has good thermal stability under low pressure, and the surface temperature is proportional to the voltage and input power. The device temperature rises faster, which reaches thermal equilibrium after 5 minutes of electricity, the temperature fluctuation is less than 0.5 ℃. It is proved that PAN-based carbon fiber cloth can replace resistance wire as heating material. It provides experimental evidence for the popularization and use of PAN-based carbon fiber as heating material for electric heating device.

RESEARCH ON THE USE OF ADVANCED PULTRUSION TECHNOLOGY TO ASSIST IN FORMING EQUAL-SECTION SPIRAL STRUCTURE PRODUCTS

LI Shi-cheng, ZHAO Xin, ZHAN Guang-liang, YE Qi-fei

2019, 0(1): 95-98.

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In order to improve the forming efficiency and automation of the equal-section spiral products, the forming process was studied. For the structural product section size and the process characteristics of the preform, the molding parameters design and process tests were performed. Equal-section preforms were prepared using advanced pultrusion process (ADP), and the preforms were twisted and filled into a spiral groove and vacuum-cured to prepare the related products. Studies have shown that the use of ADP has assitted the formation of equal-section spiral structure products with high degree of automation, compactness, and improved the appearance quality.

RESEARCH STATUS AND PROSPECT OF GFRP ANCHOR IN ANTI-FLOATING ENGINEERING

LI Jing-wen, QIAO Jian-gang, FU Xu, LIU Xiao-li

2019, 0(1): 99-105.

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GFRP anti-floating anchor is one of the effective ways to solve the corrosion problem of the rod body and it has a broad application prospect in the anti-floating engineering of underground structures. In this paper, the basic composition, working characteristics and design method of GFRP anti-floating anchor in recent years are analyzed. The research progress of inner and external anchorage of GFRP anti-floating anchor is introduced in detail. The anchoring mechanism characteristics of GFRP anti-floating anchor are summarized and analyzed. Under the action of tension load, the main failure modes of the inner anchorage are the bar pull-out and shear displacement. The bearing capacity is positively correlated with the diameter and length of anchorage segment, but there is a critical anchorage length. The distribution range of axial force and shear stress is between 0 and 3 m from the aperture. The failure modes of external anchorage section are three kinds of pullout, splitting and sliding. Anchor anchorage provides higher bearing capacity than straight anchor, and the bending radius and bending length of flexural anchorage have a direct bearing on the bearing capacity. The load-slip relationship curve of the external anchorage section presents a three stage change form. Finally, the research work about the bearing and deformation characteristics of GFRP anti-floating anchor in anti-floating system, the stability calculation based on groundwater level prediction and GFRP anti-floating anchor fabrication/design/construction integration technology are prospected.

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