The effect of surface preparation on the bond interface between FRP sheets and concrete members

Fiber-reinforced polymer (FRP) composite wraps have been established as an effective method for rehabilitation and strengthening of concrete structures. They are being increasingly used as an alternative to steel for reinforcing and strengthening of concrete structures. This paper presents the experimental and analytical results of the influence of concrete surface treatment and the type of FRP sheets on the bonding strength of concrete-FRP sheet. The FRP sheets were bonded to concrete beams in two opposite sides using an epoxy resin. Variables included the type of fiber (C1, C5, and GE) and the surface treatment (water jet and sanding). With changing the surface treatment of concrete surface preparation and the type of fiber sheets, the bonding strength, bonding load–strain response and failure modes were investigated. The concrete specimens with surface roughened with water jet showed much better bonding strength than those roughened with an ordinary sander. Equations for predicting the bond load failure of concrete specimens externally bonded with carbon and glass fiber sheets compared well with those of experimental.     

Effects of super plasticizer and curing conditions on properties of concrete with and without fiber

In this study, effects of super plasticizer (SP) and curing conditions on properties of concrete with and without fiber were investigated. In the concrete mixtures, Portland cement, artificial aggregate, SP and steel fibers were used. SP in concrete mixtures was used with ratios of 1.0%, 1.5%, and 2.0% by weight of cement and so C25 concrete was produced with and without fiber. Specimens were cured under two different curing conditions being continuous moist curing and open-air curing. Produced concrete with and without fiber were compared with each other as well as with Portland cement concrete. The highest compressive and flexural strength were obtained with 1.0% and 1.5% SP fiber reinforced concrete, respectively.     

炭黑填充Lyocell纤维的制备及其用于炭纤维原丝的研究初探

为了提高Lyocell基炭纤维的得率及其力学性能，制备了不同含量炭黑填充的Lyocell纤维用做炭纤维原丝。采用X-衍射(WAXD)、热重分析(TGA)、扫描电镜(SEM)、强度仪等分析了试样的结构与性能。WAXD表明炭黑填充的LyoceH纤维仍然具有纤维素Ⅱ晶型的结构，同时还保留了炭黑的特征衍射峰；TGA表明该纤维热稳定性不变，添加质量分数为10％和30％炭黑的LyoceH纤维在1000℃时的碳得率可分别提高4．4％和17．1％：SEM显示该纤维表面光滑且截面为圆形，符合优质炭纤维原丝的要求；炭黑填充的Lyocell基炭纤维的WAXD图谱与一般Lyocell基炭纤维图谱不同。选择质量分数为10％的炭黑添加量制备出的Lyocell基炭纤维其强度和模量分别比未填充炭黑的Lyocell基炭纤维提高22％和42％，大样实验已制备出强度和模量分别为0．8GPa和70GPa的炭纤维。     

Experimental study on dynamic damage evolution of concrete under multi-axial stresses

The effect of stress state on the dynamic compressive strength and the dynamic damage evolution process of concretes are investigated by use of a Spilt Hopkinson Pressure Bar (SHPB) and the ultrasonic technique. The columned concrete specimen is encircled by a steel sleeve. The multi-axial loading includes the axial and the radial loadings. The axial loading is supplied by the incidence bar, and the radial ones are produced by the steel sleeve. Analysis of the dynamic damage evolution of the samples is based on the measurement of the changes of ultrasonic wave velocities before and after the impact tests. The waveforms in the test bars, the stress strain curves, the confining pressure of the specimen, the dynamic compressive strength and other information about the samples are obtained during the SHPB experiments. The results of the tests show that the loading rate and stress states of the specimen apparently influence the damage evolution process in concretes. The dynamic damage evolutions are accelerated with the increase of the strain rate and are delayed significantly under the confined pressure.     

Free vibration analysis of continuous grading fiber reinforced plates on elastic foundation

The free vibration characteristics of rectangular continuous grading fiber reinforced (CGFR) plates resting on elastic foundations have been studied, based on the three-dimensional, linear and small strain elasticity theory. The foundation is described by the Pasternak or two-parameter model. The CGFR plate is simply supported at the edges and is assumed to have an arbitrary variation of fiber volume fraction in the thickness direction. Suitable displacement functions that identically satisfy the simply supported boundary conditions are used to reduce the equilibrium equations to a set of coupled ordinary differential equations with variable coefficients, which can be solved by differential quadrature method (DQM) to obtain natural frequencies. Convergence studies have been performed on CGFR plates on the elastic foundations. It is shown that the present method has a rapid convergent rate, stable numerical operation and very high accuracy. Besides results for CGFR plate with arbitrary variation of fiber volume fraction in the plate’s thickness are compared with discrete laminated composite plate. The main contribution of this work is to present useful results for continuous grading of fiber reinforcement in the thickness direction of a plate on elastic foundation and comparison with similar discrete laminate composite plate. Results indicate the advantages of using CGFR plate with graded fiber volume fractions over traditional discretely laminated plates.     

Experimental investigations on the ballistic impact performances of cold rolled sheet metals

This study focuses on the ballistic performances of 1 and 2 mm-thick and 2 × 1 mm-thick cold rolled sheet metal plates against 9 mm standard NATO projectile. The velocity of the projectile before and after perforation, the diameter of the front face deformation, the depth of the crater and the diameter of the hole were measured. The fracture surfaces of the plates near the ballistic limit were also microscopically analyzed. The highest ballistic limit was found in 2 mm-thick plate (332 m s⁻¹) and the lowest in 1 mm-thick plate (97 m s⁻¹). While, the ballistic limit of 2 × 1 mm-thick plate decreased to 306 m s⁻¹. Typical failure mechanism of the projectile was the flattening and mushrooming at relatively low velocities and the separation from the jacket at relatively high velocities. In accord with the ballistic limits, 2 mm-thick target plate exhibited the highest hardness value. Microscopic investigations showed the significant reductions in the grain size of the targets after the test.     

The effect of anchorage on the effectiveness of the shear reinforcement in the punching zone

All building codes require well anchored shear systems in the punching zone. The enforced experimental investigation of 10 symmetric punching tests with conventional stirrups and stirrups made of fabric reinforcement shows, that the effectiveness of the shear reinforcement depends on the quality of the anchorage. This result could be confirmed by tests from the literature too. In addition, the punching design approach of DIN 1045-1, 2001 [Tragwerke aus Beton, Stahlbeton und Spannbeton, Teil1: Bemessung und Konstruktion. Beuth Verlag, Juli 2001] is presented.     

Influence of ultrasonic treatment on the characteristics of epoxy resin and the interfacial property of its carbon fiber composites

To enhance the interfacial property between a carbon fiber and epoxy matrix, an ultrasonic technique was used to treat the resin liquid and the impregnated fibers respectively. The effects of the treatments on the characteristics of the resin system and the fiber surface, as well as fiber/matrix interfacial bonding strength, were analyzed and discussed. The results indicated ultrasonic treatments significantly decreased the viscosity and surface tension of the resin system, and increased the wettability and the oxygen content of the fiber surface due to the ultrasonic cavitation effects. Microbond tests revealed much more increase of interfacial shear strength when the ultrasound was applied to the impregnated fibers, and combination failures of interface and matrix layer were observed from the pulled-out fiber surface.     

Analytical and experimental investigations on the fracture behavior of hybrid fiber reinforced concrete

In the present study, Mode-I fracture tests of hybrid fiber reinforced concrete (HFRC) composite beams were conducted and the fracture properties and other post peak strength characteristics of the HFRC composites were evaluated and analyzed. The HFRC composite was produced using three types of fibers namely steel, Kevlar and polypropylene. A total of 27 HFRC composite beam specimens were cast and tested using the RILEM recommended three point bending test. The main variables were the fiber volume content and combinations of different fibers. The load versus crack mouth opening displacement (CMOD) curves of HFRC composite beams were obtained. Inverse analysis was carried out to determine the tensile strength and crack opening relationship. Analytical models based on comprehensive reinforcing index were developed for determining the influence of the fibers on fracture energy, flexural tensile strength, equivalent tensile strengths and residual tensile strengths of HFRC composites. Based on the experimental results and inverse analysis, a model for predicting the tensile softening diagram of HFRC composite mixes was also developed. The analytical models show conformity with the experimental results.     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

Effect of fiber orientation on the structural behavior of FRP wrapped concrete cylinders

In this study, 27 concrete cylinders with a diameter of 152.4 and a height of 304.8 mm were prepared. Among them, 18 cylinders were wrapped using two layers of fiber reinforced polymer (FRP) with six fiber orientations; six cylinders were wrapped using four layers of FRP with fibers in axial or hoop direction only; the remaining three cylinders were used as control. The FRP used was E-glass fiber reinforced ultraviolet (UV) curing vinyl ester. Fifteen coupon specimens were prepared to experimentally determine the tensile strength of the FRP with fibers oriented at 0°, 45°, and 90° from the loading direction. Co-axial compression tests were conducted on the wrapped cylinders and control cylinders. The test results were compared with existing confinement models. It is found that the strength, ductility, and failure mode of FRP wrapped concrete cylinders depend on the fiber orientation and wall thickness. Fibers oriented at a certain angle in between the hoop direction and axial direction may result in strength lower than fibers along hoop or axial direction. A larger database is desired in order to refine the existing design-oriented confinement models.     

分布式光纤传感技术应变测量试验研究

基于布里渊散射原理的布里渊光时域反射技术利用布里渊散射光的光谱技术和光时域测量技术,可对光纤沿线的温度、应变进行分布式监测。通过试验研究了分布式光纤传感技术在应变测量中的空间分辨率、应变分辨率、应变测量精度。研究结果表明,分布式光纤传感技术应变测量能够较准确地测得被测量结构上任何一点的应变,空间最小分辨率0.1m,应变测量分辨率和精度满足工程监测要求,可以在工程监测中作为一种新型分布式应变监测技术加以推广。     

Experimental study on the improvement of CO2 air conditioning system performance using an ejector

Several preceding researches have evidenced that the transcritical air conditioning system using CO₂ as a refrigerant has an inherent inefficiency resulting in degraded steady-state system performance of a CO₂ air conditioning system compared with that of a conventional air conditioning system. As a practical improvement, two-phase ejector was considered in place of expansion device in this study. The two-phase ejector for CO₂ air conditioning system was designed and developed considering the non-equilibrium state for evaluating the sonic velocity and the critical mass flux. The experiments of performance with respect to variation of ejector geometry such as the motive nozzle throat diameter, mixing section diameter and the distance between motive nozzle and diffuser were carried out. There exist optimum design parameters in each test. Experiments showed that the coefficient of performance of the system using an ejector was about 15% higher than that of the conventional system.     

Experimental and computational study on the separation performance of an electrostatic precipitator with curved transvers collecting plates

Aiming at the problems of low collection efficiency of fine particulate matter and large area occupied by existing electrostatic precipitators (ESP), a new type of horizontal electrode ESP is proposed. It has the advantages of accelerating turbulent coalescence, increasing the effective dust collecting area and increasing the particle driving speed. The performance of the new type of ESP is systematic studied through simulation and experiment at the same time, and the results matches well. By comparing the dust removal effect of the horizontal electrode ESP and the conventional ESP, it can be concluded that the horizontal electrode ESP has a better dust removal efficiency, and can still maintain a better dust removal effect under high air velocity. The dust removal efficiency of new ESP can reach above 98% under the experimental conditions.     

超高分子量聚乙烯纤维增强对木材破坏形貌及承载性能影响

选用PUR木材层压胶,设计"刨光锯材-超高分子量聚乙烯(UHMWPE)纤维-单板"3层结构木质复合材,探索研究了UHMWPE纤维增强对木材抗弯性能、剪切性能以及单板厚度对其增强效果影响,并利用红外光谱(FT-IR)对脱粘纤维进行表征,进而对UHMWPE纤维增强机理进行了分析。结果表明,PUR木材层压胶可用于UHMWPE纤维/木材的复合,UHMWPE纤维增强明显改变了木材破坏过程和破坏形貌,提高了木材的承载性能,同时UHMWPE纤维增强效果与单板厚度密切相关。UHMWPE纤维的加入降低了胶合界面的剪切性能。     

Experimental investigation on test methods for mode II interlaminar fracture testing of carbon fiber reinforced composites

In this paper, experimental investigation on the test methods for mode II interlaminar fracture testing of carbon fiber reinforced composites are carried out. Mode II interlaminar fracture testing of unidirectional composite of carbon fiber reinforced epoxy (T800/#3631) are conducted using four kinds of test methods, namely end notched flexure (ENF) test, end loaded split (ELS) test, four-point bend end notched flexure (4ENF) test, and over notched flexure (ONF) test. An analytical model based on a point-friction assumption and classical beam theory is proposed to evaluate the effect of friction between crack faces on the mode II interlaminar fracture toughness in the 4ENF and ONF tests. The analytical model is validated by the comparison of analytical results with previous ones obtained from finite element analysis. Experimental results show that the ENF test gives reliable initiation value of fracture toughness with a small scatter and that the average value of fracture toughness obtained from 4ENF test is about 2% higher than that obtained from the ENF test. The effect of friction in the 4ENF test is much lower than that in the ONF test in which the effect of friction increases with the crack growing. It is concluded that the 4ENF test method is an effective test method for the experimental evaluation of mode II propagation interlaminar fracture toughness of carbon fiber reinforced composites.     

铝纤维混合燃料破岩激波管作用机理研究

为了验证非炸药爆炸破岩新方法的可行性,利用铝纤维和常用燃料作为能源,在密闭管道内反应产生高压气体激波和射流,冲击炮孔孔壁岩体,产生初始裂缝并使裂缝继续扩展,达到破岩的目的。根据实验设计及情况,使用动载系数法校核了破岩管的强度,给出了许用的管内反应压力。最后,用水泥砂浆试件检验该方法的实际破岩能力,结果表明:在1 g铝纤维、10 mL乙醇、1 MPa氧气的情况下能破碎试件1;在2 g铝纤维、15 mL乙醇、2 MPa氧气的情况下能破碎试件2和试件3,并在试件2和试件3沿着以及垂直于泄能口连线的方向上产生了4道主要裂缝,裂缝在高压气体作用下延伸、扩展,使试件开裂破碎。     

Experimental investigation on the mechanical behaviour of the fiber reinforced high-performance concrete tunnel segment

The main objective of this paper is to investigate the composite effect of macro steel fiber and steel rebar on the mechanical behaviour of tunnel segment with fiber reinforced high-performance concrete (FRHPC). A new experimental method is used for simulating the loading state of the tunnel segment. The experiment including several symmetric-inclination beams with various steel ratios and fiber contents has been carried out. The results indicate that the addition of 50 kg/m³ steel fibers can partly replace the shear reinforcement, and increases the ultimate load and the energy absorption capacity as well as the toughness. The combination of steel fibers and steel rebars illustrates synergistic response and indicates an optimal choice of reinforcement for tunnel segment.     

Lung counting: Comparison of a four detector array that has either metal or carbon fiber end caps, and the effect on array performance characteristics

This study described the performance of an array of HPGe detectors, made by ORTEC. In the existing system, a metal end cap was used in the detector construction. In general, the natural metal contains some radioactive materials, create high background noises and signals during in vivo counting. ORTEC proposed a novel carbon fiber to be used in end cap, without any radio active content. This paper described the methodology of developing a model of the given HPGe array-detectors, comparing the detection efficiency and cross talk among the detectors using two end cap materials: either metal or carbon fiber and to provide a recommendation about the end cap material. The detector's counting efficiency were studied using point and plane sources. The cross talk among the array detectors were studied using a homogeneous attenuating medium made of tissue equivalent material. The cross talk was significant when single or multiple point sources (simulated to heterogeneous hot spots) were embedded inside the attenuating medium. With carbon fiber, the cross talk increased about 100% for photon energy at about 100 keV. For a uniform distribution of radioactive material, the cross talk increased about 5-10% when the end cap was made of carbon instead of steel. Metal end cap was recommended for the array of HPGe detectors.     

Experimental study of heat transfer additive influence on the absorption chiller performance

The influence of 2-methyl-1-pentanol (2MP) on the cooling effect of pilot absorption chiller has been studied experimentally. In one experimental series the additive was injected into LiBr solution. The enhancement ratio up to 20% was observed at the optimum additive concentration. In the second experimental series the additive was injected into the refrigerant. The enhancement ratio became 32% at higher additive concentration. Different additive concentrations have been tested in both series. These experimental results clearly showed that the presence of the additive in the vapour phase, even in very small amounts, favours the enhancement more than the additive in the LiBr solution. Also, it has been noticed, that the additive travels around the absorption cycle during long-term operation.