Impact Responses of the Carbon Fiber Fabric Reinforced Composites

To study the response characteristics of the carbon fiber fabric reinforced composites under impact loading, one dimensional strain impact test, multi gauge technique and Lagrange analysis method are used. The decaying rule of the stress σ , strain ε , strain rate ε · and density ρ with time and space is obtained. By the theory of dynamics, the impact response characteristics of the material is analyzed and discussed.

The properties of flax fiber reinforced wood flour/high density polyethylene composites

Flax fiber(FF) was used to reinforce wood flour/high density polyethylene composites(WF/PE).WF/PE particles were uniformly mixed with FF via high-speed mixing and then extruded with a single screw extruder to prepare FF reinforced WF/PE composites(FF/WF/PE).Mechanical testing,dynamic mechanical analysis,scanning electron microscopy(SEM),creep measurement and Torque rheology were used to characterize the resulting composites.The results indicate that the mechanical performance of the composites could be remarkably improved by adding a limited amount of FF.The flexural strength and modulus increased by 14.6 and 51.4%,respectively(FF content of 9 wt%),while the unnotched impact strength could be increased by 26.5%(FF content of12 wt%).The creep resistance and toughness of thecomposite was markedly improved without changing the plastic content of the composite material.

Experimental study on ductility improvement of reinforced concrete rectangular Columns retrofitted with a new fiber reinforced plastics method

Reinforced concrete （RC） columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics （FRP） confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP （CFRP） sheets and glass FRP （GFRP） bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.

Experimental Investigation of Natural Fiber Reinforced Polymers

The potential usage of virgin Low density polyethelyne (LDPE) reinforced with different concentrations (2%, 5% and 6% by weight) of treated rice straw with different lengths (2 mm, 4 mm and 6 mm) is investigated to produce high value products that have technical and environmental demand. The two treatment methods used for rice straw are alkali and acidic treatments of rice straw. The removal of impurities and waxy substances from fiber surface avoid creation of rougher topography after treatment and improves the quality of fiber, also content of hemi cellulose and lignin decrease so increase effectiveness of fiber due to dispersing of fiber in matrix. The reinforcing material is embedded in the matrix material to enhance tensile and flexural behaviors of the synthesized composite. The result of investigating these two mechanical properties, using statistical analysis & design of experiments, showed an enhancement in the mechaniccal properties of the virgin polymer composite compared to the virgin polymer. The flexural stress of the composite increased three times the virgin flexural stress, while the tensile stress increased eight times the original tensile stress.

Structural Performance of Light Weight Multicellular FRP Composite Bridge Deck Using Finite Element Analysis

Fiber reinforced polymer （FRP） composite materials having advantages such as higher strength to weight than conventional engineering materials, non-corrosiveness and modularization, which should help engineers to obtain more efficient and cost effective structural materials and systems. Currently, FRP composites are becoming more popular in civil engineering applications. The objectives of this research are to study performance and behavior of light weight multi-cellular FRP composite bridge decks （both module and system levels） under various loading conditions through finite element modeling, and to validate analytical response of FRP composite bridge decks with data from laboratory evaluations. The relative deflection, equivalent flexural rigidity, failure load （mode） and load distribution factors （LDF） based on FE results have been compared with experimental data and discussed in detail. The finite element results showing good correlations with experimental data are presented in this work.

GFRP约束ECC短柱偏压试验研究

纤维增强复合材料(Fiber Reinforced Polymer,FRP)约束工程纤维增强水泥基复合材料(Engineered Fiber Reinforced Cementitious Composites,ECC)轴压柱可显著提高其承载能力和延性,但偏压作用下FRP约束ECC柱的性能提升程度和作用机理有待研究。基于此,以偏心距(0、10、30、50 mm)和FRP层数(0、2、4层)为试验变量,对玻璃纤维增强复合材料(Glass Fiber Reinforced Polymer,GFRP)约束ECC短柱展开了竖向加载试验,并对试验结果进行了分析。研究结果表明:小偏心破坏时受压侧FRP断裂、混凝土被压碎,大偏心破坏时受拉侧FRP撕裂与混凝土横向裂缝近乎同时出现。轴压作用下,轴向变形和抗压强度显著增大;偏压作用下,抗压承载力随着偏心距的增大而减小,而极限位移无明显变化规律。此外,承载力和延性都随着FRP层数的增加而增大。

Reinforcement of Plastic Waste with Treated Natural Fibers

Plastic wastes are a major environmental concern that needs to be dealt with to minimize the amount of municipal solid waste and depletion of natural resources thus enhancing the sustainability concept for future generations. The objective of this study is to enhance the properties of plastic products using plastic wastes reinforced with treated natural fibers such as rice straw as well as carbonized rice straw, using a simple and efficient technology.

Detection of stacking orientation error of CFRP composite laminates using ultrasound waves

A jig was developed for generating a shear wave. A pyramid with an isosceles triangle with two 45o was made of aluminum to generate shear waves using two longitudinal transducers based on ultrasonic-polarized mechanism. Also, the signal splitter was connected to the pulser jack on the pulser/receiver and to the longitudinal transducers. Therefore, an experimental way was performed in order to make shear wave on the bottom of aluminum alloyed pyramid. Also, a jig was manufactured and developed for generating a shear wave based on the computer numerical simulation. It is found that the experimentally shear wave variation of newly-designed jig is consistent with computer numerical simulation results and shear wave ultrasonic application can be very useful to detect the defects in CFRP composites.

基于修正混凝土塑性损伤模型的大应变FRP约束混凝土有限元分析

精确的有限元分析(FEA)依赖于材料的准确定义。通过编写用户子程序UMAT实现了大断裂应变纤维增强聚合物(LRS FRP)在纤维方向上拉伸特性的定义。基于Abaqus中混凝土塑性损伤模型的理论框架,提出了一种改进的混凝土塑性损伤模型用于定义LRS FRP约束混凝土的材料特性。这些改进包括:通过LRS FRP约束混凝土的实验数据校准了与屈服准则相关的参数K;硬化/软化准则与约束刚度相关;流动法则与轴向塑性应变相关。采用修改后的材料模型进行FEA,结果表明:FEA预测的应力-应变曲线与实验结果吻合。基于FEA的结果,讨论了矩形柱截面上应力分布的不均匀性,根据约束效果可分为有效约束区域和弱约束区域,且在约束有效区域上应力分布不均匀性随着截面比(长边/短边)的增加而增加。

DELAMINATION FORMATION AND DELAMINATION PROPAGATION OF COMPOSITE LAMINATES UNDER COMPRESSIVE FATIGUE LOADING

Fatigue tests of the smooth composite laminates and the notched composite laminates under compressive cyclic loading have been carried out. The damage mechanism is discussed and analyzed. Damage evolution is monitored using stiffness decay. From these tests, it is found that the initial delamination occurs at the free boundary of smooth specimens, or the notch boundary of notched specimens, subjected to the compression-compression cyclic load. A point of view in relation to two-phases of compression fatigue delamination of composites is proposed, namely, compression-compression delamination consists of the delamination formation phase and the delamination propagation, and there is a 'damage transition point' to separate this two-phases. Furthermore, an empirical modulus degradation formula and its parameters fitting method are presented. According to the test data handling results, it is shown that this formula is univocal and can fit the test data conveniently. In addition, two kinds of new anti-buckling devices are designed for these tests. At last, the E-N curves, the D-N curves and the S-N curve of the smooth carbon fiber reinforced composite laminates of T300/648C are determined to predict the fatigue life of the notched composite laminate. And the E-N curve of the notched specimens at the given load ratio R = 10 and minimum load Pmin = -0.45 kN is also measured to verify the estimated result of fatigue life.

CFRP加固损伤钢筋混凝土梁抗冲击性能数值研究

为探究碳纤维增强复合材料(carbon fiber reinforced plastics,CFRP)加固损伤钢筋混凝土(reinforced concrete,RC)梁的抗冲击性能,利用有限元分析软件LS-DYNA,对不同CFRP加固方式下损伤梁的动态响应进行了数值模拟研究,并与物理试验结果进行对比验证.对加固梁的破坏模式、裂缝扩展规律和动态时程响应进行分析.结果表明,U型CFRP加固梁能显著抑制剪切斜裂缝的发展,大幅减小裂缝开展范围;在第1次冲击时,相较于未加固梁,平直型、U型和复合型CFRP加固梁的峰值冲击力分别提高了15.4%、16.6%和13.1%,跨中峰值位移分别降低了4.8%、8.3%和10.1%;在第2次冲击时,U型和复合型CFRP加固梁仍表现出较好的抗冲击性能.研究结果可为CFRP加固损伤RC梁的优化设计提供参考.

不同冷却方式对激光加工CFRP的影响研究

为了探索不同冷却方式对激光加工的影响,采用水、气体以及水气复合3种不同冷却方式辅助激光加工碳纤维复合材料进行了对比研究,同时采用单因素实验研究了不同工艺条件对加工质量的影响,并分析了作用机理。结果表明,在3种冷却方式下,热影响区、槽深均随着功率、频率的降低而降低,随着扫描速率的增加而降低;在相同工艺参数下,水气复合辅助激光加工产生的热影响区最小,气体辅助激光加工产生的热影响区次之,水辅助激光加工产生的热影响区最大;当激光功率为2250 W、频率为1200 Hz、速率为120 mm/s时,水、气体以及水气复合3种不同冷却方式的热影响区分别为378μm,283μm,196μm,槽深分别为401μm,789μm,647μm;采用水气复合辅助激光加工可以在加工过程中实现较好的冷热平衡,获得最好的加工质量。该研究为更好地实现碳纤维复合材料低损伤加工提供了参考。

Debonding Patch Detection in FRP-Strengthened Materials with Fiber-Optic Interferometer

The interfacial debonding in fiber-reinforced plastic(FRP)strengthened repair material will affect the bonding strength and lead to failure of the repair without warning.Unfortunately the interfacial damage is normally invisible and often in the form of a patch rather than a through-width crack.Therefore,a debonding patch detection technique based on fiber optic interferometry is proposed.A quasi-impulse loading is applied with a rubberhead hammer and the total elongation of a surface-mounted optical fiber along the length of the repair material is measured as a function of load position.When a debonding patch is present,the induced sudden slope or sign change on the plot of fiber integral strain v.s.load position will reveal the extent and the location of the debonded area.The results of the study indicate that the proposed technique is applicable for debonding patch detection in repaired members under various support conditions.

Quasi-Static Mechanical Properties of a Novel Hybrid Composites Wrapped Rebar

A novel hybrid composites wrapped rebar is developed to overcome the brittleness of fiber reinforced polymer( FRP) rebars.Theoretical and experimental studies are carried out on two types of rebars wrapped by FRP and hybrid composites,respectively. The stress-strain curves under quasi-static loads are given. The results show that FRP or hybrid composites outside rebars improve the ultimate tensile stress and the rebar in the core improves the ductility. It is also observed that hybrid composites wrapped layer can provide higher compatibility and lower interlaminar shear stress than FRP wrapped layer.

钢-CFRP异质复合B柱的弯曲实验分析

目的为提高B柱的抗弯性能,通常会在B柱上额外焊接补丁板,但同时也增加了B柱的重量。在原始B柱上铺设碳纤维增强复合材料(CFRP),获得钢-CFRP异质复合B柱,取消B柱的钢制加强板,实现B柱的轻量化。方法通过热冲压制备原始B柱及带补丁板B柱,并以原始B柱为凹模,采用真空袋压工艺制备钢-CFRP异质复合B柱。基于2018版C-NCAP侧面碰撞实验要求,设计B柱三点弯曲夹具,进行原始B柱、带补丁板B柱及钢-CFRP异质复合B柱的三点弯曲实验,并对其重量及弯曲性能进行分析。结果原始B柱重量4.1kg,三点弯曲实验测得其刚度为0.763k N/mm,最大载荷为21.59k N,平均力为14.52 kN;带补丁板B柱质量为5.6 kg,三点弯曲实验测得其刚度为1.095 kN/mm,最大载荷为31.08 kN,平均力为18.38 kN;钢-CFRP异质复合B柱总质量4.7 kg,三点弯曲试验测得其刚度为1.071 kN/mm,最大载荷为31.76 kN,平均力为19.58 kN。结论在保持刚度、最大载荷及平均力等弯曲力学性能不变的前提下,相对于带补丁板B柱,钢-CFRP异质复合B柱可以减轻质量0.9 kg,并且吸能更优,实现了B柱的轻量化。

FRP加固木梁的受弯性能研究

为考察纤维增强复合材料（fiber reinforced plastics/polymer,FRP）对木梁的加固效果,对比分析了6根普通木梁和21根FRP（包括CFRP和GFRP）加固木梁的极限荷载与抗弯刚度等结构性能,并探讨了构件的破坏形态与破坏机理.结果表明：FRP可避免或延缓木梁的受拉脆性破坏,降低木材缺陷对其受弯性能的影响,充分利用木材的抗压强度并显著提高构件的刚度和延性性能;当配筋率为0.37%~1.13%时,FRP加固木梁比未加固木梁的极限承载力提高了17.7%~77.3%.基于极限应变分析方法,提出了构件极限承载力的计算公式,经国外试验结果初步验证后发现,该计算公式简便且结果精度较高.

FRP-螺栓联合加固RC梁粘结性能试验研究

通过对17根跨中留有预切缝的试验梁进行破坏性加载试验,研究了FRP-螺栓联合加固技术的粘结性能、锚固间距和合理锚固长度。结果表明,HB-FRP(FRP-锚钉联合加固技术)体系较EB-FRP(外贴FRP加固法)体系的延性、承载力、FRP的剥离应力等都有较大的提高。在试验数据及理论分析的基础上,提出了HB-FRP和EB-FRP中部裂缝引起的剥离强度计算公式以及较为合理的锚固间距估算公式,计算结果与试验结果吻合较好。所得结果可为联合加固的进一步研究及工程上的应用提供一定的依据。

FRP片材加固混凝土梁温度应力的计算与分析

文章分析了FRP片材加固混凝土结构的温度应力,研究表明当温度降低时,在碳纤维内部会产生较大的正应力,而处在粘贴位置的混凝土会产生较大的拉应力。应力的大小主要与FRP片材的弹性模量、热膨胀系数、碳纤维厚度和温差值的大小等参数有关。

FRP强约束混凝土配筋柱稳定承载力的试验研究

通过长细比Lb为4.5～17.5的6根截面经圆弧化处理、外包FRP后的矩形截面的钢筋混凝土柱的轴心受压试验,研究了长细比对稳定承载力的影响。结果表明:长细比对FRP约束混凝土柱的稳定承载力影响远比螺旋配筋柱和普通钢筋混凝土严重,但当长细比不大于17.5时,其稳定承载力仍比未包裹柱高20%(约束比ξ=0.188)以上。讨论了影响稳定系数φ的因素,给出了稳定系数的参考值,可供工程设计人员参考。