Table of Content

28 December 2019, Volume 0 Issue 12

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EXPERIMENTAL STUDY ON AXIAL COMPRESSION BEHAVIOR OF ELLIPTICAL HIGH-STRENGTH CONCRETE-FILLED GFRP TUBULAR STUB COLUMNS

WANG Yan-lei, ZHANG Yi-nan, LIU Qing, XU Qing-feng

2019, 0(12):  5-10. 

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In order to investigate the axial compressive behavior of elliptical high-strength concrete-filled GFRP tubular stub columns and verify the applicability of Teng et al. 2016 model for the stress-strain relationship of FRP confined elliptical concrete, a total of four series of eight elliptical high-strength concrete-filled GFRP tubular stub column specimens were tested. One test parameter of the major axis-to-minor axis length ratio (abbreviated as aspect ratios), were considered in this experimental investigation. The test results revealed that the failure mode of elliptical specimens is the rupture of GFRP tube at around the apex of long axis of elliptical section. The confinement of elliptical GFRP tube can significantly improve the compressive strength and ultimate axial strain of concrete core, and the compressive strength and ultimate axial strain decrease with the increase of aspect ratios. The model of Teng et al. 2016 is in good agreement with the test results of this paper, which indicates that the model can be used to predicate the behavior of elliptical high-strength concrete-filled GFRP tubular stub column specimens.

VISCOELASTIC CONSTITUTIVE RELATIONS OF HIGH STITCH DENSITY BIAXIAL WARP KNITTED FABRIC REINFORCED PVC

HOU Jia-jia, CHEN Nan-liang, JIANG Jin-hua, LIU Yi-wen

2019, 0(12):  11-17. 

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In this paper, the creep and stress relaxation tests of high stitch density biaxial warp knitted fabric reinforced PVC were carried out, and the action law of tensile rate and initial stress level on the viscoelastic behavior of the material was investigated. The relaxation modulus and creep compliance were obtained and their curves as a function of time were drawn. The test results show that the high stitch density biaxial warp knitted fabric reinforced PVC has typical viscoelastic behavior; the membrane has reached the steady-state relaxation stage in the test period, and the stress level has a significant effect on the static viscoelasticity of the PVC membrane. In particular, the creep phenomenon occurs with the increase of the initial stress level, and the tensile rate plays a role in the stress relaxation behavior of the sample, but it is not obvious. By comparison, the long-term transformation relationship between creep and stress relaxation of high stitch density biaxial warp knitted fabric reinforced PVC deduced by the principle of aging creep and time effect force relaxation of metal materials is deviated from the experimental results.

STUDY ON FATIGUE DAMAGE AND FATIGUE LIFE OF WIND TURBINE BLADES COMPOSITES WITH MICRO-DEFECTIVE

WANG Lin-lin, CHEN Chang-zheng, ZHOU Bo, KANG Shuang

2019, 0(12):  18-23. 

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The wind turbine blade specimens with micro-defects were carried out tension-tension fatigue testes. The surface temperature change and infrared thermogram change of blade specimens were monitored by infrared thermography under fatigue tests. The fatigue damage evolution process of specimens was found out by infrared thermography pictures. The entropy production and entropy accumulation of specimen were studied in the fatigue tests. The wind turbine blade with micro-defects had three stages of temperature change in the fatigue test i.e., rapid temperature rise, steady temperature rise, and sharp temperature rise. The three stages of temperature change were account for about 10%, 70%, and 20% of the total fatigue life in the fatigue test. It is found that the position of the micro-defect in the test piece first appears as a bright heat source by the infrared thermal images. The heat source range increases with the load time when the temperature rose sharply. The cumulative entropy production of specimens with three stages of change was the same as the temperature change trend. The entropy accumulation showed nonlinear variation with load under fatigue test. The fatigue fracture entropy of blade specimen was an independent parameter which was not affected by any parameters at the fatigue test. A new predicting fatigue life model of blade was established based on the thermodynamic fatigue fracture entropy failure criterion.

STUDY ON VIBRATION PROPERTIES OF CFRP AT HIGH TEMPERATURES BASED ON FBG

XIA Ping, YANG Hai-ru, TAN Yue-gang

2019, 0(12):  24-28. 

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Based on experimental strain modal tests,the vibration properties of carbon fiber reinforced polymer (CFRP) plate at different elevated temperatures from 25 ℃ to 190 ℃ were investigated using fiber Bragg grating (FBG) as dynamic strain sensors. The 1st and 2nd frequency and vibration mode of CFRP cantilever beam at room temperature were obtained by finite element method. Bending vibration tests were conducted on CFRP cantilever beam at different temperatures through pulse hammer hitting and the 1st and 2nd natural frequency at different elevated temperatures were obtained by Fast Fourier Transform (FFT). The results showed that, the 1st and 2nd natural frequency decreased with the temperature rise, and the stiffness has changed permanently compared with those before heating.

EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF SUPER ABSORBENT RESIN BASALT FIBER CONCRETE

LI Tong, ZHANG Xiao-dong, FAN Jin-ze, CHEN Chen

2019, 0(12):  29-33. 

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In order to study the mechanical properties of SAP basalt fiber concrete, cubic compressive, splitting tensile and flexural tests were carried out on SAP basalt fiber concrete with different basalt fiber length (6 mm, 18 mm, 30 mm), different basalt fiber content (0.1%, 0.2%, 0.3%) and different SAP content (0.1%, 0.2%, 0.3%). The test results show that the compressive strength of concrete is improved by adding basalt fibers with length of 18 mm and content of 0.1%, and the increase rate is 9.67%. The effect of adding basalt fibers with length of 18 mm and content of 0.2% on the tensile and flexural properties of concrete is remarkable, which is 20.82% and 18.04% higher than that of plain concrete, respectively. For SAP basalt fiber reinforced concrete, with the increase of SAP content, the compressive, tensile and flexural strength of SAP basalt fiber reinforced concrete increases first and then decreases. Based on the experimental data, the optimum length, content of basalt fiber and the optimum content of SAP were obtained.

EFFECTS OF DIFFERENT FACTORS ON THE ULTIMATE LOAD OF BONDED DCB

LI Zhan-ying, LU Xiao-feng, YANG Miao-yuan

2019, 0(12):  34-38. 

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In order to get a more accurate method for predicting the ultimate load for thick bond joint in wind turbine blade, a modeling method for bond joint using the finite element method based on virtual crack closure technique (VCCT) is presented, and the effect of adhesive thickness and adherends bending stiffness on the ultimate load of the bonded double cantilever beam (DCB) is analyzed. First, the modeling method of bonded DCB is described. Then, the finite element model of test coupon is established, and the ultimate load is predicted. Finally, the ultimate load for different bond thickness and adherent bending stiffness is calculated. It is found that the simulation ultimate load is in good agreement with the experimental result. VCCT can then be used to predict the ultimate load of bonded DCB. The ultimate load of the bonded DCB will increase, as the thickness of adhesive increases. The ultimate load of the bonded DCB will increase, as the adherends bending stiffness increases. The modeling method using VCCT can be used to simulate the failure behavior for the thick bond joint in wind turbine blade.

VARIATION COEFFICIENTS MODEL FOR CREEP OF POLYMER MATRIX

LIANG Na, ZHU Si-rong

2019, 0(12):  39-42. 

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The dashpot of standard three-element viscoelastic model is extended to the generalized based on the assumption that the coefficient of viscosity is a function of time. A variation coefficients model for creep is established. The creep strain is obtained by resolving the variable parameter constitutive relation. The parameter determination method was established by the principle of the least square. The theoretical analysis shows that the model is suitable for describing the creep behavior of GFRP composites in the first two stages. The creep tests of glass-fiber reinforced plastic (GFRP) unidirectional plate has been conducted, and the proposed model was verified through the experimental data.

STUDY ON THE CROSS-SECTIONAL FLATTENING PHENOMENON OF GFRP PIPES

GENG Shuai

2019, 0(12):  43-46. 

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A method of classical structural mechanics is used to study the cross-sectional flattening phenomenon of pipes under pure bending. The formula for the cross-sectional flattening deformation is deduced and then verified by finite element analysis. The relationship between the transverse and longitudinal maximum bending stress of the pipe under pure bending is derived to guide the design of the GFRP pipe material to ensure that its longitudinal flexural strength can be fully utilized.

STUDY ON THE INFLUENCE OF INJECTION PARAMETERS ON RESIN FLOW IN RTM POROUS INJECTION MOLDING

XIANG Lin-tong, ZHAO An-an, YU Fei, LU Shi-hong

2019, 0(12):  47-53. 

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In order to improve the efficiency of resin transfer molding, porous injection molding is often used. In the process of porous injection molding, the location of injection and outlet, injection pressure and other process parameters will affect the flow of resin, and then affect the quality of final parts. At present, the porous injection molding is often used for large and complex structural parts, so it is necessary to obtain the influence of injection parameters on the resin flow. In this paper, based on the numerical simulation by Fluent software, the influence of the number of injections, the distance between adjacent injections and the injection pressure on the resin flow were analyzed by using the control variable method, and the relationship among the three parameters and the length of weld lines and filling time was obtained. The simulation results show that the filling time is inversely proportional to the number of injection ports, the distance between adjacent injection ports and the injection pressure, and the length of weld line is proportional to the number of injection ports and the distance between injections, and not related to injection pressure.

ALUMINIUM LINED, CARBON COMPOSITE OVERWRAPPED NON-GEODESIC PRESSURE VESSEL WINDING AND STRENGTH ANALYSIS

YUNUSA Mujaheed, ZU Lei, TAPA Arnauld Robert

2019, 0(12):  54-61. 

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In this paper, non-geodesic winding linear design, finite element simulation and filament winding and hydraulic blasting experiments were carried out on carbon fiber wound composite pressure vessels. The optimal winding parameters of the composite pressure vessel were determined according to the non-geodesical trajectory. Validity of the trajectory was verified as well, the stress and strain values under pressure were analyzed by finite element software ABAQUS. The stress state of the pressure vessel at 35 MPa internal pressure was studied, and its blasting was predicted. The strength is 92.2 MPa. The winding experiment is carried out on a five-axis CNC winding machine. The T800 carbon fiber wound aluminum alloy inner liner is used to complete the development of the composite pressure vessel. The fiber winding layer has 26 layers, and the fibers are arranged neatly and evenly after winding without slippage phenomenon. After curing, the blasting strength is 87.5 MPa, the actual value differs from the predicted value by 5.1%, and the feasibility numerical analysis was verified. In conclusion the present analysis result of both numerical and experimental were in good agreement. Meanwhile, the manufacture foundation for the preparation of eminent performance and prominent specification filament wound products was laid.

RESEARCH ON MICRO-DRILLING OF CARBON FIBER COMPOSITES

ZHAO Qi-di, WANG Gong-dong, WANG Meng, LI Ying-chi

2019, 0(12):  62-66. 

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In the hole-making process of carbon fiber composites, micro-hole processing is an important processing technology. The delamination in micro-hole machining is mainly caused by the spalling effect of the inlet bit and the pushing effect of the outlet. The damage of hole wall is mainly caused by too high drilling temperature, which leads to the softening of interlayer resin and adhesion of the cutter, and affects the cutting quality of the cutter. In this paper, the effects of spindle speed and feed speed on axial force and interlaminar temperature of carbon fiber composites with a diameter of 1 mm were studied experimentally, and the micropore quality was evaluated by SEM. The results show that controlling spindle speed and feed speed can effectively reduce axial force and interlayer temperature and improve the quality of hole forming.

ACOUSTIC PROPERTIES OF POROUS FIBER ASSEMBLY-FILLED NOMEX HONEYCOMB SANDWICH STRUCTURE

XIAO Hong-bo, QU Hang, LAN Guo-yong

2019, 0(12):  67-71. 

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In order to improve the sound absorption and noise reduction performance of nomex honeycomb sandwich structure, the effects of honeycomb height, the filling content of porous fibers and the opening of microporous skin on the sound absorption coefficient (SAC) and sound transmission loss (STL) of honeycomb sandwich structures are explored. The experiment results indicate that SAC of sandwich structure can be effectively changed by filling sound absorption cotton and skin opening in 0.8 kHz~2.5 kHz. SAC can be improved by the increase of the fiber content. When the filling content of fiber material is 300 g/m², the peak of SAC is 0.84, which increases by 0.16. But the influence of fiber material on STL is weak. Microporous skin is beneficial to play the role of sound absorption of microperforated board and porous fiber, and SAC is greatly improved.

MODELING THE CURING KINETICS OF FM94 ADHESIVE BASED ON MF/MALEK METHOD

PEI Shi-kai, LI Yi-bo, YANG Yuan-cheng, LI Jian

2019, 0(12):  72-76. 

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The curing kinetics of epoxy resin FM94 adhesive was studied by differential scanning calorimetry (DSC) at different heating rates. The activation energies of the curing reaction were calculated based on Model-Free method by analyzing DSC curves at different heating rates, and the curing mechanism of FM94 adhesive was explained. The most probable curing mechanism function was determined by Malek method. The results indicated that the two-parameter (m, n) autocatalytic model can well describe the curing reaction process of FM94 adhesive. The fractional conversion of DSC curves obtained using the experimental data showed a good agreement with the curves calculated theoretically under 2 K/min~10 K/min heating rates.

THE EFFECT OF FIBER TYPE ON THE SHRINKAGE OF MORTAR

CHENG Cong-mi, HE Jian-hui, HE Juan, ZHANG Ya-fang

2019, 0(12):  77-82. 

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In this paper, the effects of glass fiber, steel fiber, basalt fiber and lignin fiber on the autogenous shrinkage and drying shrinkage of mortar were studied. Through the study of autogenous shrinkage, dry shrinkage and wet swelling after drying shrinkage of mortar reinforced with different fibers, the results show that glass fiber has the best effect on restraining the shrinkage of mortar and the volume stability in four kinds of fibers. Lignin fibers have better inhibition effect on the early shrinkage of mortar, but the inhibition ability on the long-term shrinkage of mortar is the worst among the four kinds of fibers. The drying shrinkage of fiber mortar in 90 days is as follows: lignin fiber mortar>reference mortar>steel fiber mortar>basalt fiber mortar>glass fiber mortar. The autogenous shrinkage of fiber mortar is much lower than that of dry shrinkage. The autogenous shrinkage of fiber mortar in 90 days is as follows: reference mortar>lignin fiber mortar>steel fiber mortar>basalt fiber mortar>glass fiber mortar.

STUDY ON MECHANICAL AND INTERFACIAL PROPERTIES OF GLASS FIBER REINFORCED COMPOSITES CONTAINING MWCNTs

ZHENG Yi-fei, SHEN Ming-xia, DUAN Peng-peng, ZENG Shao-hua

2019, 0(12):  83-88. 

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In order to improve the comprehensive properties of glass fiber reinforced epoxy composites (GFRE), industrial multi-walled carbon nanotubes (MWCNTs) were dispersed uniformly in EP by adding dispersant B60T, and then glass fiber reinforced epoxy composites containing MWCNTs (MWCNTs/GFRE) were fabricated. The effects of functional groups and content of MWCNTs on the macro and micro mechanical properties of GFRE were further studied, and the interfacial adhesion of the composites was also evaluated. The results showed that functionalized MWCNTs can significantly improve the mechanical properties and interlaminar bonding strength of GFRE, and the hydroxylated MWCNTs (MWCNTs-OH) has the most obvious improvement in mechanical properties and interlaminar shear strength (ILSS) of GFRE. When the addition amount of MWCNTs-OH was 0.1wt%, the tensile strength and flexural strength of MWCNTs-OH/GFRE were increased by 51.9% and 31.2%, respectively, the tensile modulus and flexural modulus were improved by 9.1% and 5.2%, respectively, and the ILSS was raised by 23.9%, as compared with pure GFRE composites. Dynamic viscoelastic studies showed that the initial storage modulus (E′) and the glass transition temperature (T_g) of MWCNTs-OH/GFRE were increased by 10.1% and 4.8 ℃ compared with GFRE, respectively. The increase of interfacial adhesion and temperature resistance of MWCNTs/GFRE is suggested to be related to the content and type of functional groups of MWCNTs, the difficulty of reaction with epoxy molecule and the freedom of chemical bonds formed between MWCNTs and EP.

RESEARCH OF OUT OF AUTOCLAVE COMPOSITE POROSITY

YUAN Chao, CHENG Wen-li, CHEN Jing

2019, 0(12):  89-93. 

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The influence of out of autoclave(OOA) process is researched and influencing factor of different prepreg, curing process and sealing ways on the porosity of OOA composite is analyzed. The result shows that the resin film coating method of prepreg has great influence on the porosity of products with OOA process. The porosity of products is lower than that double-sided covering when the resin film is one-sided covering. Increasing temperature platform properly is propitious to the air out before the resin gelated and the porosity of final products is lower than that without temperature platform. Using the sealing way of more material to guide air is propitious to squeezing the air produced in the prepreg folding and volatilizing, which will and finally get products with lower porosity.

RESEARCH ON PROPERTIES OF POLYACRYLATE THERMOPLASTIC RESIN AND ITS VACUUM-ASSISTED INFUSION GLASS FIBER REINFORCED COMPOSITES

ZHANG Ping, MU Shu-xiang, ZHU Jin-chun, PIEERE Gerard

2019, 0(12):  94-100. 

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The reaction characteristics of Arkema polyacrylate thermoplastic resin Elium190M were analyzed, the basic properties of thermoplastic resin and the mechanical properties of the glass fiber reinforced thermoplastic composite by vacuum infusion were studied, and compared with the thermosetting resin and its vacuum infusion glass fiber reinforced composite which is used in batch in wind turbine blade industry. The results show that polyacrylate resin Elium190M has low viscosity, long open time, low curing temperature and short curing time, which is suitable for vacuum assisted resin infusion process. The mechanical properties of glass fiber reinforced thermoplastic composite are comparable to those of thermosetting composite used in batch for manufacturing of the wind turbine blade. At the same time, the interface property between thermoplastic resin Elium190M and its thermoplastic composite material is higher than that of the thermosetting resin used in batch in wind blade, indicating that the thermoplastic resin can also be molded partially by prefabricated parts, then formed large composite parts by integrated infusion molding.

THE CONTROL OF THE EPOXY RESIN CONENT ON SATELLITE SOLAR BATTERY′S GRID HARD SUBSTRATES

SU Qing-yun, LIU Hai-xin, WEI Shi-hou, ZHENG Jian-hu

2019, 0(12):  101-105. 

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The HM40-3K carbon fiber produced by the foreign company and the BSCHM40-3K carbon fiber made by China were selected as research objective. The scanning electron microscope (SEM) was applied to characterize the surface morphologies and roughness of these carbon fibers. The contact angle, surface energy and wettability of the two type fibers were investigated by surface tension-meter. Experiment of HM40-3K/epoxy resin TDE-86 and BSCHM40-3K/epoxy resin TDE-86 bleeders′ system to analysis the epoxy resin content of the products. The experimental results showed that the wettability was closely related to the tow size of carbon fiber, contact angle, surface energy and the polar components of surface energy. The wettability was increased with the tow size of carbon fiber and rose from the surface energy and the polar components of surface energy. In addition, the wettability became better by decreasing the contact angle. As a result, the better of the wettability, the epoxy resin was more difficult to absorb by bleeder materials. According to the resin content′s formula of the HM40-3K/epoxy resin TDE-86, the formula of the BHM3-3K/epoxy resin TDE-86 was summarized and an important rule supporting this formula was found.

RESEARCH PROGRESS ON PROPERTIES OF FIBER RAC

WANG Xing-guo, CHENG Fei, WANG Yi-xin, A Lata

2019, 0(12):  106-113. 

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Recycled aggregates and their products are an effective way to promote the healthy development of the building materials industry. However, recycled aggregates are difficult to apply to structural member of engineering structure, due to their low apparent density and high porosity. As an engineering technology, the performance of fiber-modified recycled concrete materials can greatly improve the mechanical properties of recycled aggregate concrete (RAC), reducing the demand for natural sand and gravel resources in the construction industry, and effectively saving natural sandstone resources. The performance of fiber recycled concrete materials was mainly introduced, and its high temperature resistance was discussed. The durability test results were summarized. The mechanism of fiber modified recycled concrete performance was analyzed. The existing problems in the research were also proposed. Its future development direction is further prospected.

RESEARCH SITUATION OF CONTINUOUS QUARTZ FIBER REINFORCED SILICA COMPOSITES

GAO Long-fei, WAN Ye-qiang, LU Qiu-mian, LI Song

2019, 0(12):  114-117. 

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At present, the Sol-gel method is the main method for preparing continuous quartz fiber reinforced silica (SiO_2f/SiO₂) composites. In this paper, the factors affecting the densification of SiO_2f/SiO₂ composites are introduced. The research progress of SiO_2f/SiO₂ composites is reviewed. Some suggestions for the preparation of SiO_2f/SiO₂ composites and moisture-proof coatings are proposed. And the future application of the SiO_2f/SiO₂ composites are prospected.