聚四氟乙烯/碳纤维增强聚酰亚胺复合体系的摩擦学性能

研究评价了不同PTFE含量的碳纤维增强PI复合材料的力学和摩擦学性能 ,并分析了在干摩擦和水润滑 2种不同条件下的磨损表面形貌和磨损机理。研究表明 :PTFE以 10 %添加时PI CF PTFE体系的机械性能最佳 ,而摩擦学性能以 5 %添加为佳 ;随PTFE含量的增加 ,复合材料的摩擦系数降低 ,磨损率增加。水润滑下 ,摩擦系数和磨损率比干摩擦下的都有相应的降低。干摩擦下 ,材料的磨损均以塑性变形、微观破裂及破碎为主导 ;水润滑下 ,这一机制显著减弱 。

碳纤维增强地聚物混凝土韧性评价指标的对比研究

采用经波形整形技术改进后的100分离式Hopkinson压杆试验装置,开展了碳纤维增强地聚物混凝土(carbon fiber reinforced geopolymeric concrete,CFRGC)的冲击压缩试验,基于峰值韧度和比能量吸收2种评价指标研究了CFRGC的冲击韧性,并进行了对比分析和机理探究.结果表明:从峰值韧度的评价指标来看,CFRGC在碳纤维体积分数为0.3%时能发挥出明显的冲击增韧优势;从比能量吸收的评价指标来看,CFRGC的增韧特性在碳纤维体积分数为0.2%和0.3%时相对较优异;2种表征冲击韧性的方法所反映的发展趋势存在一致性,一是冲击韧性指标存在明显的应变率效应,二是碳纤维对于地聚物混凝土而言具有一定的增韧效果;在评价碳纤维增强地聚物混凝土的冲击韧性时,采用比能量吸收指标更加有效、合理.

PMR型耐高温聚酰亚胺基体树脂及复合材料的制备与性能研究

分别以3,4′-二氨基二苯基醚(3,4′-ODA)和3,3′,4,4′-二苯甲酮四羧酸二酐(BTDA)作为二胺和二酐单体、5-降冰片烯-2,3-二甲酸酐(NA)作为封端剂,通过调节3种原料的化学计量比,在无水甲醇溶剂中合成了具有不同分子量的预聚体,并通过不同温度下的热处理获得了一系列聚酰亚胺(PI)树脂。结果表明:随着预聚体分子量的增加,固化后PI树脂的热稳定性得到提高,5%热失重温度(T_(5%))由460℃升至513℃,10%热失重温度(T_(10%))由513℃升至554℃;但是由于交联密度的降低,PI树脂的玻璃化转变温度(Tg)随预聚体分子量的增加从309℃降低至271℃。同时发现,合理的后固化可使PI树脂的耐高温性能得到提高。以该系列PI树脂为基体,采用手糊法制备了一系列碳纤维增强聚酰亚胺(CF/PI)复合材料,它们表现出优良的耐热性能(T_(5%):532~595℃,T10%:631~840℃,Tg:346~422℃)和机械性能(弯曲强度:559~811MPa,弯曲模量:46.3~59.9GPa,层间剪切强度:29.3~36.7MPa,冲击强度:88~104kJ/m^(2)),可实现在航空航天领域的耐高温应用。

废铅蓄电池存储材料的改性开发与性能测试研究

对废铅蓄电池存储用纤维进行了浓硝酸和过氧化氢+超声波联合改性处理,考察了改性处理对纤维单丝表面形貌和拉伸性能的影响。基于此制备了碳纤维/聚酰胺自增强复合材料,分析了热压压强和热压温度对复合材料的拉伸性能影响。结果表明,碳纤维/聚酰胺自增强复合材料适宜的热压温度为180℃、热压压强为5 MPa,此时复合材料取得抗拉强度、断后伸长率和弹性模量最大值,分别为141.7 MPa、46.9%和943.4 GPa;改性后的复合材料改善了碳纤维复合材料的综合使用性能。

Durability of concrete beams reinforced with CFRP sheet under wet-dry cycles and loading

The test results of eight concrete beams reinforced with carbon fiber reinforced polymer （CFRP） sheets subjected to an aggressive environment under a sustained load are presented. The beams are 1 700 mm long with a rectangular cross-section of 120- mm width and 200-mm depth. The beams are precracked with a four-point flexural load, bonded CFRP sheets, and placed into wet-dry saline water（ NaCl） either in an unstressed state or loaded to about 30% or 60% of the initial ultimate load. The individual and coupled effects of wet-dry saline water and sustained bending stresses on the long term behaviour of concrete beams reinforced with the CFRP are investigated. The test results show that the coupled action of wet-dry saline water and sustained bending stresses appears to significantly affect the load capacity and the failure mode of beam strengthened with CFRP, mainly due to the degradation of the bond between CFRP and concrete. However, the stiffness is not affected by the coupled action of wet-dry cycles and a sustained load.

纤维网格增强超高韧性水泥复合材料加固混凝土圆柱受压性能试验

为提升纤维增强聚合物复合材料(FRP)在加固材料中的优势和发挥效率,同时克服传统纤维网格增强砂浆的抗裂性差的缺点,将超高韧性水泥基材料(ECC)替代砂浆作为FRP网格无机黏结剂的新型复合材料已被提出,但仍缺乏相关的基础研究。本文以新型聚乙烯型ECC为基材,重点研究FRP grid/ECC加固混凝土柱的加固机制。以标准混凝土圆柱为试验对象,采用新型ECC材料为基材的FRP grid/ECC复合材料,以不同强度素混凝土、不同网格材料(玄武岩纤维增强聚合物复合材料(BFRP)与碳纤维增强聚合物复合材料(CFRP)网格)为试验变量,研究了该加固方式下对混凝土轴心受压性能的影响。试验结果表明,该加固方法可有效改善素混凝土脆性压溃破坏模式,提高峰值强度及受压延性。基于FRP grid/ECC材性特征,提出两阶段FRP grid/ECC加固机制,并基于该机制提出加固素混凝土圆柱承载力计算方法。

Thermal-mechanical properties of short carbon fiber reinforced geopolymer matrix composites subjected to thermal load

Short carbon fiber preform reinforced geopolymer composites containing different contents of α-Al2O3 filler （Cr（a-Al2O3）/geopolymer composites） were fabricated, and the effects of heat treatment temperatures up to 1 200 ℃ on the thermal-mechanical properties were studied. The results show that the thermal shrinkage in the direction perpendicular to the lamination of the composites gradually increases with the increase of the heat treatment temperatures from room temperature （25 ℃ ） to 1000 ℃. However, the composites in the direction parallel to the lamination show an expansion behavior. Beyond 1 000℃, in the two directions the composites exhibit a larger degree of shrinkage due to the densification and crystallization. The mechanical properties of the composites show the minimum values in the temperature range from 600 to 800 ℃ as the hydration water of geopolymer matrix is lost. The addition of α-Al2O3 particle filler into the composites clearly increases the onset crystalline temperature of leucite （KAlSi2O6） from the amorphous geopolymer matrix. In addition, the addition of α-Al2O3 particles into the composites can not only help to keep volume stable at high temperatures but also effectively improve the mechanical properties of the composites subjected to thermal load to a certain extent. The main toughening mechanisms of the composites subjected to thermal load are attributed to fiber pulling-out.

Strengthening reinforced concrete beams using prestressed glass fiber-reinforced polymer-Part I: Experimental study

This work is aimed at studying the strengthening of reinforced concrete (R. C.) beams using prestressed glass fi- ber-reinforced polymer (PGFRP). Carbon fiber-reinforced polymer (CFRP) has recently become popular for use as repair or rehabilitation material for deteriorated R. C. structures, but because CFRP material is very stiff, the difference in CFRP sheet and concrete material properties is not favorable for transferring the prestress from CFRP sheets to R. C. members. Glass fi- ber-reinforced polymer (GFRP) sheets with Modulus of Elasticity quite close to that of concrete was chosen in this study. The load-carrying capacities (ultimate loads) and the deflections of strengthened R. C. beams using GFRP and PGFRP sheets were tested and compared. T- and ⊥-shaped beams were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before being bonded to the T- and ⊥-shaped R. C. beams. The prestressed tension in the PGFRP sheets caused cambers in the R. C. beams without cracks on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacity. The test results indicated that T-shaped beams with GFRP sheets increased in load-carrying capacity by 55% while the same beams with PGFRP sheets could increase load-carrying capacity by 100%. The ⊥-shaped beams with GFRP sheets could increase load-carrying capacity by 97% while the same beams with PGFRP sheets could increase the loading-carrying capacity by 117%. Under the same external loads, beams with GFRP sheets underwent larger deflections than beams with PGFRP sheets. While GFRP sheets strengthen R. C. beams, PGFRP sheets decrease the beams’ ductility, especially for the over-strengthened beams (⊥-shaped beams).

Effect of fiber angle on LYP steel shear walls behavior

Steel shear wall(SSW) was properly determined using numerical and experimental approaches.The properties of SSW and LYP(low yield point) steel shear wall(LSSW) were measured.It is revealed that LSSW exhibits higher properties compared to SSW in both elastic and inelastic zones.It is also concluded that the addition of CFRP(carbon fiber reinforced polymers) enhances the seismic parameters of LSSW(stiffness,energy absorption,shear capacity,over strength values).Also,stress values applied to boundary frames are lower due to post buckling forces.The effect of fiber angle was also studied and presented as a mathematical equation.

Performances of super-long span prestressed cable-stayed bridge with CFRP cables and RPC girder

To discuss the applicability of advanced composite carbon fiber reinforced polymer(CFRP) and ultrahigh performance concrete reactive powder concrete(RPC) in super-long span cable-stayed bridges, taking a 1 008 m cable-stayed bridge with steel girders and steel cables as an example,a new cable-stayed bridge in the same span with RPC girders and CFRP cables was designed,in which the cable's cross section was determined by the principle of equivalent cable capacity and the girder's cross section was determined in virtual of its stiffness, shear capacity and local stability. Based on the methods of finite element analysis,the comparative analysis of these two cable-stayed bridge schemes about static performances,dynamic performances,stability and wind resistance behavior were carried out. The results showed that it was feasible to form a highly efficient,durable concrete cable-stayed bridge with RPC girders and CFRP cables and made its applicable span range expand to 1 000 m long around.

Bonding Characteristics and Flexural Stiffening Effect of Carbon Fibre Reinforced Plastics Strand Sheets Bonded to Steel Beams

Corrosion of steel structures is unavoidable and the structural performance decreases dramatically due to the corrosion. As a repairing method for corroded steel members, bonding carbon fiber sheets with resin had been developed. The purpose of this study is to propose the flexural strengthening method for steel members by using CFRP （carbon fiber reinforced polymer） strand sheets. In order to clarify the stiffening effect and the debonding characteristics of CFRP strand sheets, and to optimize the strengthening design specifications, the flexural tests using high tension steel beams strengthened with CFRP strand sheets are performed. Two cases of experiments are carried out. In Experiment 1, the result from previous research is reflected in the strengthening design. Moreover in Experiment 2, the debonding characteristics obtained from Experiment 1 are reflected. As a result, it was clarified that CFRP strand sheets have stiffening effect equivalent to the theoretical value and its debonding property is practically high enough when FRP （fiber reinforcement polymer） sheets have an appropriate bonding length.

Strengthening of Concrete Box Girder Bridges under Close-in Detonations

The response of a bridge superstructure under blast loading might depend largely on the extent of the local damage experienced due to close-in explosion threats. This paper investigates the local and structural response of box girder bridge decks strengthened using CFRP （carbon fiber reinforced polymers） under close-in detonations. Due to the lack of experimental research on this topic, the study is conducted using the explicit finite element computer program LS-DY-NA. The numerical study will be verified using the results of strengthened reinforced concrete slabs under field detonations. The blast load was assumed to be detonated above the bridge deck. The key parameters investigated are the charge size, and the strengthening location on the deck. This paper will present the results of this investigation and provides recommendations for predicting the local damage level based on the CFRP strengthening design under blast threat.

Improvement of the CFRP Mechanical Properties Using Taguchi Method to Optimize the Formation Conditions

Carbon fiber composites have high strength, high stiffness and light weight characteristics to apply to many fields, such as leisure, energy and transportation industries. The CFRP （carbon fiber reinforced polymers/plastics） composites made of carbon fibers as reinforcement and epoxy resins as matrix were prepared by drum winding process. Various parameters such as molding temperature, molding pressure and pressing time were selected as the pre-pregs were laminated to be the CFRP. The effects of fabricating parameters which affected the mechanical properties of CFRPs were analyzed by Taguchi method in this study. The results showed that molding temperature was the main factor to influence the mechanical properties of composites.

Nonlinear Elastic Buckling of CFRP Reinforced Steel Cylinders under Axial Compression

In this paper, the strengthening of thin-walled metallic shells with the application of CFRP （carbon fibre reinforced polymer） has been investigated. To lower down the downside of the lower stiffness exhibited by CFRP shells and to diminish the major problem associated with steel shells, a new composite sandwich structure has been introduced in this paper and effect of CFRP reinforcements under axial compression has been studied through three kinds of analytical procedures; the linear Eigen value problem, the modified RS （reduced stiffness） analysis and the fully nonlinear numerical experiment. With these multiple treatments it has been suggested that recently developed modified RS analysis which effectively compute the lower bounds provides the significant information to evaluate the buckling capacity of reinforced shells that display the unstable behaviour and imperfection-sensitivity than the general RS Analysis. This paper also illustrates the application of the methodology to cases of axial loaded shells with the varying thickness of veneers of CFRP.

Near Surface Mounted Application for the Strengthening of Rectangular Reinforced Concrete Slender Columns under Eccentric Load

The behavior of slender columns under the effect of eccentric loading has always taken the attention of researchers. When investigating the strengthening of reinforced concrete columns, mainly short and circular columns are the targeted elements. This is why the data about slender columns with rectangular sections is limited and infrequent specially when loaded eccentrically. This paper aims to increase the available experimental data in this specific area. The experimental program consisted of twenty seven specimens. The specimens were divided into three groups; one control group and two groups strengthened using two strengthening schemes. Scheme 1 implied the use of near surface mounted （NSM） longitudinal steel bars, while in scheme 2, NSM longitudinal steel bars partially wrapped with one ply of carbon fibers reinforced polymers （CFRP） sheets was used. The test specimen had an overall length of 2000 mm and a 100 x 200 mm rectangular cross section. In addition to the strengthening schemes, the test parameters included three ratios for the internal longitudinal steel bars ＂μ＂ 1%, 1.57% and 2.26%. The parameters were extended to cover three stirrups＇ volumetric ratio ＂ρv＂ 0.73%, 0.49% and 0.37%. The specimens were tested under the effect of eccentric loading with eccentricity-to-section height e/h equals 0.25. The research revealed that the strength gain in specimens strengthened with scheme 2 was higher than with scheme 1. Analytical modeling of the stress strain relation of the strengthened RC columns considering the effect of strengthening scheme, internal reinforcement ratio μ, and stirrups＇ volumetric ratio ＂ρv＂ was proposed. Verification was made using available experimental data. The proposed model showed a reasonable agreement with the experimental results.

Improvement of Impact Absorbed Energy of CFRPs on Adding the Nanoparticles into Epoxy Resins

The present study investigates the effect of the addition of nanoparticles into epoxy resins as the matrix on the impact absorbed energy of CFRP （carbon fiber reinforced polymer）. Impact absorbed energy is one of the main properties to evaluate the CFRP＇s performance for transportation and aerospace structures. Two types of nanoparticle, namely nanofibers and nano-silica beads, were added into the epoxy resin to improve the impact absorption capacity of the CFRP. Two modified additives and conventional epoxy resins were quantitatively compared. The impact test results showed that impact absorbed energy for nanofibers was higher than nano-silica beads, and nanofibers as the additive promoted about 11% of impact absorbed energy compared with neat epoxy resin.

Bond Performance of Fiber Reinforced Polymer （FRP） Bars in Autoclaved Aerated Concrete （AAC）

This paper concerns the bond strength of FRP bars in AAC by the concentric pullout test. Specimens were subjected to compare with mild steel bars. The bond performance including the mode of failure and bond strength was investigated with varying embedment length and surface treatment. Regarding the bond performance, embedment depth has influenced on bond strength as well as the sanded surface. Carbon fiber reinforced polymer （CFRP） pronounced the most promising results with the highest bond strength attained.

Experimental and Stowing/Deploying Dynamical Simulation of Lenticular Carbon Fiber Reinforced Polymer Thin-Walled Tubular Space Boom

The stowing and deploying experiment was conducted for three 700 mm long thin-walled tubes,and the structural behavior characteristics parameters were measured clearly,including strain,deformation and wrapping moment.3D finite element models(FEM)were built subsequently and explicit dynamic method was used to simulate the stowing and deploying of the lenticular carbon fiber reinforced polymer(CFRP)thin-walled tubular space boom,which was designed as four-ply(45°/-45°/45°/-45°)lay-up.The stress and energy during the wrapping process were got and compared with different wrapping angular velocity,the reasonable wrapping angular velocity and effective method were conformed,and structural behavior characteristics were obtained.The results were compared and discussed as well,and the results show that the numerical results by 0.628 rad/s velocity agree well with the measured values.In this paper,the numerical procedure and experimental results are valuable to the optimization design of CFRP thin-walled tubular space boom and future research.