Modelling the propagation of a radar signal through concrete as a low-pass filter

The knowledge of how a dispersive, dielectric medium such as concrete affects a propagating short electromagnetic pulse used in ground penetrating radar (GPR) is helpful both in the interpretation of radar results and in the prediction/modelling of expected radar measurements. Although there are a number of published results on the frequency-dependent, dielectric properties of media such as concrete and soils, the use of this information is still relatively small, primarily due the lack of a reliable method of applying these properties to propagating radar pulses. Modelling the dielectric medium as low-pass filter is one solution to this difficulty. In this paper the propagation of short pulses in concrete with known frequency-dependent properties is studied. The extent of how the pulses are attenuated and distorted is analysed and the implications on GPR applications are also discussed.     

含水率对受损混凝土超声波波速的影响

为了揭示含水率对受损混凝土的超声波波速的影响规律,研究了不同损伤程度的混凝土试块在不同含水率下的超声波波速。研究结果表明,含水率〈1．5％时,含水率对混凝土超声波波速的影响较小,可以忽略;含水率〉1．5％时,超声波波速随含水率的提高而明显增大;损伤越大,这种影响就越明显。     

Corrosion of reinforcing steel in neutral and acid solutions simulating the electrolytic environments in the micropores of concrete in the propagation period

Steel embedded in concrete passivates due to the alkaline nature of the concrete pore solution. Reinforcement corrosion develops when the alkalinity is neutralized. Corrosion, in turn, induces acidification of the surrounding pore solution. In the present paper, corrosion rate of corrugated steel bars is studied and measured at different pH values in solutions simulating chloride environments. The media considered consists of saturated calcium hydroxide solutions containing Na and K⁺, neutralized with ferrous chloride. This latter substance is the soluble compound produced during the corrosion of steel after chloride attack. Hydrochloric acid solutions of different pHs were prepared in order to compare the steel corrosion rates in these solutions with those observed in ferrous chloride solutions of the same pH. A comparison of polarization resistance measurements (R_p) with gravimetrically weight loss determined is presented. Tafel slopes results are also included. Additionally, a comparison is made between measurements of AC impedance with those of the R_p method. The results indicate that the corrosion rate in the studied media follows the general trend found in other media of similar pH values: corrosion increases in acidic solutions, remains rather stable for pH range 3-11 and decreases significantly in highly alkaline solutions.     

零保温两次加热淬火对25MnV钢组织与性能的影响

研究零保温两次淬火对25MnV钢组织性能的影响。结果表明:对于零保温一次淬火,在870~910℃的奥氏体化温度范围,强度和硬度随淬火温度的升高而增加,高于910℃,强度和硬度逐渐下降;在试验温度范围内,25MnV钢零保温两次淬火的强度和硬度优于零保温一次淬火,且经910℃零保温一次淬火和900℃零保温二次淬火后,力学性能最佳,其组织为隐针马氏体。     

零传动机床高速直线数控进给单元的速度与加速度特性研究

高速直线进给单元是零传动机床的重要组成部分,文章介绍了GD-3直线电机高速数控进给单元的基本结构和组成特点,分析了这种新型进给单元控制系统的特点,并对其速度、加速度和位移精度进行了实验研究,结果表明,它的最大进给速度可达到80m/min,其加(减)速度可达到16.8m/s2,定位精度可达到0.004mm,并且运动过程平稳.     

Dielectric properties of concrete and their influence on radar testing

Sub-surface radar is becoming increasingly popular as an inspection method. Interpretation can be enhanced if uncertainties about the dielectric properties of the concretes under investigation are removed. The need for reliable data to identify possible variations of the dielectric properties of different concrete mixes and their condition on site has led to a systematic laboratory based experimental programme under the auspices of a major European Commission (Brite-Euram III Framework 4) funded project. Some key results from this recently completed work are presented in this paper with practical implications related to field surveys of structural concrete.     

Application of radar technology to reinforced concrete structures: a case study

The radar technology, used to perform investigations on the civil buildings, derives from that used for investigations of the ground known with the name of Georadar. This is diffusing rapidly among the investigation methodology not destructive in the field of the structural engineering. It is based on the sending of electromagnetic waves of very short length and the recording of the time of arrival and of the breadth of any signals reflected on the interface between materials with a different dielectric constant. The aim of this paper is to present the operating methodologies and the results achieved by the application in the field of radar methodologies to map utilities, and for applications to civil building with special regard to the determination of the intern morphology, to the lack of homogeneity research and defectiveness and to the determination of the location of the steel reinforcements.Specifically, the system used, made up of one apparatus of field acquisition and another of delayed processing, seems to be able to provide good planimetric and three-dimensional restitution with regard to location and placement. In this paper, special attention has been paid to the processing of the acquired data and on the interpretation of experimental tests conducted on a civil building.     

Measurement and numerical simulation of particle velocity in cold spraying

The velocity of cold spray particles was measured by a diagnostic system designed for thermal spray particles that is based on thermal radiation. A laser beam was used to illuminate the cold spray particles in cold spraying to obtain a sufficient radiant energy intensity for detection. The measurement was carried out for copper particles of different mean particle sizes. The particle velocity was also estimated using a two-dimensional axisymmetric model developed previously. The simulated velocity agreed well with the measured result. This fact indicates that particle velocity in cold spraying can be predicted reasonably by simulation. Therefore, it is possible to optimize the cold spray process with the aid of the simulation results. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Corrosion properties of HVOF-coated steel in simulated concrete pore electrolyte and concentrated chloride environments

The corrosion susceptibility of steel and HVOF-coated steel in solutions simulating the alkaline concrete pore environment and with the addition of chloride was investigated using potentiodynamic polarization and potential step techniques. The surface characterization was performed using SEM and the surface elemental analysis was determined by EDS. The concentration of chloride was 2.8 M to simulate the concentration of chloride spread in many local regions of Saudi Arabia and called Sabkha. It was found that, in the case of the simulated concrete pore electrolytes, the HVOF coating resulted in an anodic shift of the corrosion potential with marginal effect on the corrosion current. However, upon addition of 2.8 M chloride solution, the corrosion rate of the HVOF-coated steel was found to increase by a factor of two. SEM showed a network of pores within the coating which provides a path for the electrolyte. This would result in preferential corrosion around splat boundaries and confirmed by EDS which showed that the corroded splats have higher oxide contents. Potential step experiments at 400 mV above open circuit potential showed a suppressed current of the HVOF-coated steel compared to the steel substrate alone. The corrosion potential versus time experiments resulted in a more anodic Ecorr which decreased with time and became equal to the Ecorr of the bare steel after 34 h. After that, the corrosion potential of the HVOF-coated steel decreased due to the increase in galvanic coupling between the steel and the HVOF coating.     

Effect of the reinforcement bar arrangement on the efficiency of electrochemical chloride removal technique applied to reinforced concrete structures

This paper reports on the research done to find out the effect that different bar arrangements may have on the efficiency of the electrochemical chloride removal (ECR) technique when applied to a reinforced concrete structural member. Five different types of bar arrangements were considered, corresponding to typical structural members such as columns (with single and double bar reinforcing), slabs, beams and footings. ECR was applied in several steps. We observe that the extraction efficiency depends on the reinforcing bar arrangement. A uniform layer set-up favours chloride extraction. Electrochemical techniques were also used to estimate the reinforcing bar corrosion states, as well as measure the corrosion potential, and instant corrosion rate based on the polarization resistance technique. After ECR treatment, a reduction in the corrosion levels is observed falling short of the depassivation threshold.     

Study on microstructure and properties of high velocity arc sprayed Fe3 Al intermetallic coating

Coating structural materials with Fe3Al based intermetallics may rapidly lend to industrial application of their environment and wear resistant features. In the present study, high velocity arc spraying (HVAS) was used to in-situ synthesize Fe3Al intermetallic coating. The microstructural characterization and properties of the coating have been investigated. The microstructure was found to consist of Fe3A1 based intermetallic ( 1303 and B2 ) and a-Fe regions together with fine oxide ( ct-Al2 03 ) layers. TEM images of coating show that the solidified lamellae are polycrystalline and have a grain size of the order of about 150 rim, and there also exists amorphous state in some areas. It can be concluded that a very high cooling rate has been obtained during HVAS process. Moreover, the coating has relatively higher ndhesion strength and microhardness, as well as lower density and porosity.     

热处理对AlFeCrTi粉末铝合金组织性能的影响

用气雾化铝合金粉为原料,通过高速压制和烧结工艺获得高密度铝合金,然后对其进行热处理,研究了固溶处理对合金性能的影响,并分析讨论其机理。结果表明,高速压制法制备的铝合金组织均匀、致密。经过固溶和时效处理,合金的强度明显提高,塑性略有下降。经过500℃×30 min的固溶+180℃×360 min的时效,合金的抗拉强度可达206 MPa,屈服强度165 MPa,伸长率2%。     

Effect of particle size of iron on reaction velocity of combustion synthesis of Ti-C-Fe system

Four Ti-C-Fe powder mixtures, with a same molar ratio but different particle sizes of Fe and Ti, were used to measure the reaction velocity of the combustion synthesis. The results show that in the case of the finer Ti powder used, the reaction velocity of mixture with the finer Fe powder is higher than that with the coarser Fe powder. However,in the case of the coarser Ti powder used, the reaction velocity of mixture with the finer Fe powder is lower than that with the coarser Fe powder. The effect of particle size of Fe powder on reaction velocity can be explained with the previously proposed mechanisms of the combustion synthesis of Ti-C-Fe system.     

Effect of stress corrosion cracking on stress-strain response of steel wires used in prestressed concrete beams

This paper presents an experimental study of the stress corrosion cracking (SCC) process on 8-mm-diameter wires which are used industrially in precast concrete prestressed by pre-tension. The service life of steel wires under accelerated SCC and the reduction of their mechanical performance are studied. A dynamic analysis to detect the damage to corroded wire due to SCC before brittle failure and the influence of internal defects on the service life of stress corroded wire are also presented. The study shows that stress corrosion cracking is characterized by an evolution to SCC from pitting corrosion attacks that result in the development of both micro-cracking and micro-voids in the steel bulk. The stress level does not influence the composition of corrosion products. It is a major factor of SCC development, leading to a considerable reduction in the ultimate strain and thus to brittle failure of the corroded wires. Local defects on the steel surface increase the SCC effect due to stress corrosion concentration. A reduction in the elastic modulus and the elastic limit, which may reach 25% and 15%, respectively, can be expected due to steel micro-cracking. No damage detection through mechanical analysis seems possible before the brittle failure occurs as the corrosion is very localized and so does not globally reduce the tension in the wires.     

稀土元素对SnAgCu钎料性能的影响

综合评述了无铅化背景下SnAgCu系钎料合金的性能特点和研究现状,着重讨论分析了微量稀土元素的添加对SnAgCu系钎料润湿性能、力学性能、蠕变性能和显微组织的影响及其作用机理,并对具有广阔发展前景的SnAgCuRE系无铅钎料的研究与发展趋势进行了展望.     

微合金化元素对7005铝合金铸态组织与性能的影响

采用金相显微镜、SEM、EDS等试验方法研究了Al-10Ti中间合金、细晶铝锭、Sc-Zr以及Ti-Sc-Zr等细化方式细化的7005铝合金铸态组织和铸态力学性能.结果表明,由Al-10Ti中间合金细化的合金晶粒最大,平均晶粒直径约为330μm;由细晶铝锭细化的合金晶粒明显变小,平均直径在170μm左右,抗拉强度由Al-10Ti细化时的280MPa提高到了304MPa,伸长率由3.2%提高到4.2%.由Sc-Zr细化的合金的晶粒直径约为50μm,抗拉强度达到了330MPa,但伸长率只有2%;由Ti-Sc-Zr细化的合金的晶粒直径约为35μm,力学性能最好,抗拉强度达到338MPa,伸长率达到4.5%.     

Effect of vanadium and other carbide-forming elements on the properties of rotor steels

It is important to solve the problem of obtaining a fine-grain structure and the related improvement in the properties of rotor steels. Accordingly, we have investigated the effect of additives of vanadium and also zirconium, niobium, and tantalum on the properties of 25Kh2N2M rotor steel.Scientific Industrial Association TsNIITMASh. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 33–35, October, 1994.     

时效时间对7150铝合金组织和性能的影响

通过维氏硬度测试、电导率测试和拉伸、晶间腐蚀等测试方法,研究了预时效、回归及再时效三个阶段中的时效时间对7150铝合金组织和性能的影响,借助透射电镜观察时效处理各阶段合金的微观组织演变。结果表明:120℃×20 h欠时效作为预时效工艺,比120℃×24 h峰时效的晶内析出相更细小,高温回归时更利于回溶。在190℃短时回归5、15和30 min中,15 min回溶效果最好,硬度最低,再经120℃×24 h再时效后合金抗拉强度Rm、屈服强度RP0.2、伸长率A分别为622 MPa、573 MPa、10.8%,显微硬度为204 HV,力学性能与120℃×24 h单级峰时效时相近。经120℃×20 h+190℃×15 min+120℃×24 h处理后7150铝合金综合性能好,耐晶间腐蚀性能佳。     

Effect of alloying elements on austempered ductile iron(ADI) properties and its process:Review

Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.     

Effect of extrusion wheel angular velocity on continuous extrusion forming process of copper concave bus bar

The continuous extrusion forming process for producing large section copper concave bus bar under different extrusion wheel angular velocities was studied by three-dimensional finite element technology based on software DEFORM-3D. The rigid-viscoplastic constitutive equation was employed in the model. The numerical simulation results show that the deformation body flow velocity in the die orifice increases gradually with the increase of the extrusion wheel angular velocity. But slippage between the rod and extrusion wheel occurs when the extrusion wheel angular velocity is high. The effective stress near the die orifice enhances gradually with increasing extrusion wheel angular velocity. High stress is concentrated in adjacent regions of the flash gap. The effective strain gradient is greater near the abutment than that near the die orifice. The effective strain of the product increases gradually with increasing extrusion wheel angular velocity. In the deformation process, the deformation body temperature increases remarkably due to friction and deformation. So the cooling is necessary in the region of the die and tools.