Damage Evolution of Ballastless Track Concrete Exposed to Flexural Fatigue Loads:The Application of Ultrasonic Pulse Velocity,Impact-echo and Surface Electrical Resistance Method

In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads,ultrasonic pulse velocity(UPV),impact-echo technology and surface electrical resistance(SR) method were used.Damage variable based on the change of velocity of ultrasonic pulse(Du) and impact elastic wave(Di)were defined according to the classical damage theory.The influences of stress level,loading frequency and concrete strength on damage variable were measured.The experimental results show that Du and Di both present a three-stages trend for concrete exposed to fatigue loads.Since impact elastic wave is more sensitive to the microstructure damage in stage Ⅲ,the critical damage variable,i e,the damage variable before the final fracture of concrete of Di is slightly higher than that of Du.Meanwhile,the evolution of SR of concrete exposed to fatigue loads were analyzed and the relationship between SR and Du,SR and Di of concrete exposed to fatigue loads were established.It is found that the SR of concrete was decreased with the increasing fatigue cycles,indicating that surface electrical resistance method can also be applied to describe the damage of ballastless track concrete exposed to fatigue loads.

Effects of surface nanocrystallization on corrosion resistance of β-type titanium alloy

Surface mechanical attrition treatment (SMAT) was performed on biomedicalβ-type TiNbZrFe alloy for 60 min at room temperature to study the effect of surface nanocrystallization on the corrosion resistance of TiNbZrFe alloy in physiological environment. The surface nanostructure was characterized by TEM, and the electrochemical behaviors of the samples with nanocrystalline layer and coarse grain were comparatively investigated in 0.9% NaCl and 0.2% NaF solutions, respectively. The results indicate that nanocrystallines with the size of 10-30 nm are formed within the surface layer of 30 μm in depth. The nanocrystallized surface behaves higher impedance, more positive corrosion potential and lower corrosion current density in 0.9%NaCl and 0.2%NaF solutions as compared with the coarse grain surface. The improvement of the corrosion resistance is attributed to the rapid formation of stable and dense passive film on the nanocrystallized surface of TiNbZrFe alloy.

Evaluation of surface textures and skid resistance of pervious concrete pavement

Surface textures had long been recognized as primary factors to provide the skid resistance on pavements; however, no measurement of skid resistance on pervious concrete pavement with various surface texture parameters had been made. Fractal geometry was introduced in the present work to accurately simulate transect contour curves of pervious concrete specimens through fractal interpolation. It is proved that its fractal dimension (D) can be adopted to measure the skid resistance on pervious concrete pavement, overcoming the shortcomings of both macrotexture depth (DT ) and British portable pendulum number (NBP). Combined with Fujikawa-Koike tire/road contact model, the optimization method of all surface textures was recommended for designing and constructing excellently skid-resistant and noise-absorptive pervious concrete pavement. In addition, evaluating of the abrasion process and attenuation of the surface textures on concrete pavement slabs was also the focus of this work based on accelerated abrasion test. Results show that the surface textures on pervious concrete pavement slabs is extremely durable, compared to those on conventional grooved or exposed aggregate concrete pavement slabs.

A proposed surface resistance model for the Penman-Monteith formula to estimate evapotranspiration in a solar greenhouse

Greenhousing is a technique to bridge season gap in vegetable production and has been widely used worldwide. Calculation of water requirement of crops grown in greenhouse and determination of their irrigation schedules in arid and semi-arid regions are essential for greenhouse maintenance and have thus attracted increased attention over the past decades. The most common method used in the literature to estimate crop evapotranspiration（ET） is the Penman-Monteith（PM） formula. When applied to greenhouse, however, it often uses canopy resistance instead of surface resistance. It is understood that the surface resistance in greenhouse is the result of a combined effect of canopy restriction and soil-surface restriction to water vapor flow, and the relative dominance of one restriction over another depends on crop canopy. In this paper, we developed a surface resistance model in a way similar to two parallel resistances in an electrical circuit to account for both restrictions. Also, considering that wind speed in greenhouse is normally rather small, we compared three methods available in the literature to calculate the aerodynamic resistance, which are the r_a^1 method proposed by Perrier（1975a, b）, the r_a^2 method proposed by Thom and Oliver（1977）, and the r_a^3 method proposed by Zhang and Lemeu（1992）. We validated the model against ET of tomatoes in a greenhouse measured from sap flow system combined with micro-lysimeter in 2015 and with weighing lysimeter in 2016. The results showed that the proposed surface resistance model improved the accuracy of the PM model, especially when the leaf area index was low and the greenhouse was being irrigated. We also found that the aerodynamic resistance calculated from the r_a^1 and r_a^3 methods is applicable to the greenhouse although the latter is slightly more accurate than the former. The proposed surface resistance model, together with the r_a^3 method for aerodynamic resistance, offers an improved approach to estimate ET in greenhouse using the PM formula.

Comparison on corrosion resistance and surface film of pure Mg and Mg−14Li alloy

To study different corrosion resistances and surface film types of hexagonal close-packed(HCP)pure Mg and body-centered cubic(BCC)Mg−14wt.%Li alloy in 0.1 mol/L NaCl,a series of experiments were conducted,including hydrogen evolution,mass loss,in-situ electrochemical testing combined with Raman spectroscopy and microstructural observation.The results indicate that the corrosion resistance of pure Mg is superior to that of Mg−14Li,and the protective function of the surface films on both magnesium systems is elevated within 16 h of immersion in 0.1 mol/L NaCl.An articulated,thick,and needle-like surface film containing Li2CO3 on Mg−14Li,different from the typically thin,flaky Mg(OH)2 film on pure Mg,is confirmed via scanning electron microscopy(SEM).However,both surface films can be broken down at a high anodic over-potential.Thus,different corrosion resistances of the two Mg systems are ascribed to various protective films forming on their surfaces.

Influence of Surface Treatment on the Corrosion Resistance of Stainless Steel in Simulated Human Body Environment

In the present research, the influence of chromium enrichment by surface treatment on corrosion resistance of type 316L stainless steel in body environment was investigated. For this study, weight loss test during 18 months, cyclic and liner polarization tests before and after surface treatment and metallography by electron and light microscopy were used to evaluate the effectiveness of the proposed method. In addition, X-ray photoelectron spectroscopy （XPS） method was used to determine the chromium concentration in the surface layer after surface treatment. Results show that the surface treatment has improved corrosion resistance of the type 316L stainless steel in body environment.

Self-repairing functionality and corrosion resistance of in-situ Mg-Al LDH film on Al-alloyed AZ31 surface

A novel Mg-Al LDH film was in-situ prepared hydrothermally in an alkaline aqueous solution on an Al-alloyed AZ31 substrate.The structural,chemical and functional characteristics of the film were explored by means of scanning electron microscope(SEM),X-ray diffraction(XRD),energy dispersive spectrometer(EDS),polarization curve,AC impedance and salt immersion tests,respectively.The anti-corrosion results indicated that the Mg-Al LDH film on the Al-alloyed AZ31 surface could effectively protect the AZ31 from corrosion attack even after 90 days of immersion in 3.5 wt.%NaCl solution.The protection performance is surprisingly better than most of the reported coatings on Mg alloys.More interestingly,when the Mg-Al LDH film was scratched,the exposed Al-alloyed surface might gradually release metal ions and re-generate dense LDH nano-sheets in the corrosive environment to inhibit the further corrosion there,exhibiting a self-repairing behavior.The combination of the benign long-term protection and desirable self-repairing performance in this new process of surface-alloying and LDH-formation may significantly extend the practical application of magnesium alloys.

Effect of RE on Cracking Resistance and Microstructure of Coatings Formed by Plasma Jet Surface Metallurgy

Metallurgical coatings of iron-based alloy with RE oxide were prepared on low-carbon steel using a home-made DC-plasma jet surface metallurgy equipment. Scanning electron microscope (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction analysis (XRD) were employed to observe the microstructure and analyze the chemical compositions of coatings. And the cracking susceptibility of coatings was studied in terms of RE addition. Experimental results show that addition of RE oxide (La_2O_3 and CeO_2) can refine and purify the microstructure, and can reduce the cracking susceptibility of coatings.

Chromizing treatment of the surface-nanocrystallized AISI H13 steel and the improved wear resistance

A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of the chromized layer were characterized by using the scanning and transmission electron microscopy,a nano-indenter and a tribo-meter.It was shown that a continuous chromized layer of approximately 30 μm in thickness was formed on the SNC specimen after a dual chromizing treatment at both 600℃ and 1050℃ consecutively,as thick as about 3 times of that on the coarse-grained specimen after the same chromizing treatment.In addition,the wear resistance of the SNC-chromized specimen was enhanced significantly,due to a smaller grain size and a higher hardness,as well as smoother gradient variations of the microstructure,composition and hardness across a greater depth in the formed chromized surface layer.

Experimental Investigation of the Effect of Bow Profiles on Resistance of an Underwater Vehicle in Free Surface Motion

In this paper, towing tank experiments are conducted to study the behavior of flow on a model of the underwater vehicle with various shapes of bows, i.e. tango and standard bows in free surface motion tests. The total resistances for different Froude numbers are considered experimentally. The towing tank is equipped with a trolley that can operate in through 0.05-6 m/s speed with ±0.02 m/s accuracy. Furthermore, the study is done on hydrodynamic coefficients i.e. total, residual and friction resistance coefficients, and the results are compared. Finally, the study on flow of wave fields around bows is done and wave filed around two bows are compared. The Froude number interval is between 0.099 and 0.349. Blockage fraction for the model is fixed to 0.005 3. The results showed that the residual resistance of the standard bow in 0.19 to 0.3 Froude number is more than the tango bow in surface motion which causes more total resistance for the submarine. Finally, details of wave generated by the bow are depicted and the effects of flow pattern on resistance drag are discussed.

Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.

Corrosion resistance of pulsed laser modified AZ31 Mg alloy surfaces

The effect of laser surface melting on the corrosion resistance of AZ31 Mg alloy in 0.1 M NaCl solution was investigated using different laser processing conditions(energy densities of 14 and 17 J cm^(-2)).Laser treatment induced rough surfaces primarily composed of oxidized species of Mg.XPS analysis revealed that the surface concentration of Al increased significantly as a consequence of LSM.Electrochemical impedance spectroscopy showed that the laser treatment remarkably increased the polarization resistance of the AZ31 Mg alloy and induced a passive-like region of about 100 mV,as determined by potentiodynamic polarization.Analysis of the results obtained provide solid evidence that within the immersion times used in this study,LSM treatment increased the corrosion resistance of AZ31 Mg alloy under open circuit conditions and anodic polarization.

Microstructure and corrosion resistance of Fe-Al intermetallic coating on 45 steel synthesized by double glow plasma surface alloying technology

A binary Fe-Al alloyed layer was synthesized on 45 steel by means of double glow plasma surface alloying technique. The corrosion-resisting layer prepared is composed of a sedimentary layer and a diffusion layer, with a total thickness of about 180 μm. The aluminum content of the alloyed layer shows gradual change from surface to the inside of substrate. The ideal profile is beneficial to the metallurgical bonding of the surface alloying layer with substrate materials. The microstructure of both layers consists of the Fe-Al intermetallic compound, which is FeAl with B2 structure in the sedimentary layer and Fe3Al with incompletely ordered DO3 structure in the diffusion layer. The protective film exhibits high micro-hardness. In comparison with the substrate of 45 steel, the corrosion resistance of the aluminized sample is much higher in 2.0% Na2S and 0.05 mol/L Na2SO4 + 0.5 mol/L NaCl mixed solutions.

An improved formula for the surface resistance of normal metals at millimetre wavelengths

A number of researchers haw reported discrepancies between surface resistance （SR） measurements and classical theoretical predictions in normal metals for millimetre wavelengths （MW）. In this paper, a rigorous model is developed for analysing SR of normal metals. This model is based on quantum mechanical analysis of the spatial dispersion within the metal. We use the model to predict SR and eliminate the discrepancies between SR measurements and classical theoretical predictions in normal metals for MW. Moreover, we have compared the results of this model with that of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency- but also wave-vector-dependent for MW. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals for MW.

Detection of Veneer Moisture Content by Surface-circle-shaped Resistance

This paper, with veneer as a particularly detected target, deals with a new method for detecting veneer moisture content. Surface resistance is measured by the fixed pressure, circle-shaped point and surface-touched detector. With the help of the computer, the veneer moisture and its distribution will be detected in a faster way with no harm to the veneer surface.

Numerical Investigation of the Effect of Surface Roughness on the Viscous Resistance Components of Surface Ships

Recently,computational fluid dynamics(CFD)approaches have been effectively used by researchers to calculate the resistance characteristics of ships that have rough outer surfaces.These approaches are mainly based on modifying wall functions using experimentally pre-determined roughness functions.Although several recent studies have shown that CFD can be an effective tool to calculate resistance components of ships for different roughness conditions,most of these studies were performed using the same ship geometry(KRISO Container Ship).Thus,the effect of ship geometry on the resistance characteristics of rough hull surfaces is worth investigating.In this study,viscous resistance components of four different ships are calculated for different roughness conditions.First,flat plate simulations are performed using a previous experimental study for comparison purposes.Then,the viscous resistance components of three-dimensional hulls are calculated.All simulations are performed using two different turbulence models to investigate the effect of the turbulence model on the results.An examination of the distributions of the local skin friction coefficients of the DTMB 5415 and Series 60 showed that the plumpness of the bow form has a significant effect on the increase in frictional resistance with increasing roughness.Another significant finding of the study is that viscous pressure resistance is directly affected by the surface roughness.For all geometries,viscous pressure resistances showed a significant increase for highly rough surfaces.

Effect of Pb content on the surface topography and corrosion resistance of hot dip Zn-Al-Mg coatings

In this study,the effect of Pb content on the surface morphology and salt spray corrosion resistance of hot dip Zn-AI-Mg coatings was investigated. The results showed that the coating surface easily formed small grains of zinc spangle structures and that the salt spray con＇osion resistance of the coating decreased when Pb content was greater than 0.01%. The microstructure and energy dispersive spectrum analysis of surface and cross-sectional areas was performed by scanning electron microscopy. Pb content present in the coating was analyzed by glow discharge spectrum. The results showed that the distribution of Pb in the coating was not uniform. The Pb content was segregated on the surface and at the cross-section of the Zn-A1-MgZn2 ternary eutectic structure,especially,on the surface of the Zn-A1-MgZn2 ternary eutectic structure.

Wear resistance of surface metal matrix composite produced by gas tungsten arc melt injection of Cr3C2 -NiCr particles into low carbon steel

Cr3 C2-NiCr particles were injected into the melted surface of Q235 low carbon steel to make a surface metal matrix composite （MMC） layer by gas tungsten are melt injection （GTAMI） process. Hardness of the surface MMC layer was tested. Wear resistance of the surface MMC was investigated with a ball-on-disk dry sliding setup. Microstrnetures of the surface MMC layer and morphology of the worn surfaces were investigated with scanning electron microscopy （SEM）. The results showed that the hardness of the MMC was as high as 1 960. 7 HV. Wear loss of the upper part of the MMC layer is onlyO. 8% of that of the substrate under the dry sliding condition given. Wear loss of the bottom part is 2. 5 % of that of the substrate.

Carbonation Resistance of Hybrid NanoSiO_(2) Modified Cementitious Surface Protection Materials

Hybrid nanoSiO_(2) (HNS) modified cement pastes were explored as a kind of surface protection material (SPM).The carbonation resistance and mechanical properties of SPMs coated samples were tested.Thermogravimetric analysis (TGA),X-ray diffraction (XRD),scanning electron microscope (SEM),and mercury intrusion porosimetry (MIP) were further employed to evaluate the chemical composition and microstructure characteristics of SPM.Besides,thermodynamic modeling was adopted to simulate the changes in the phase assemblages of SPM under the carbonation process.The results showed that SPM with 1 wt% HNS could effectively enhance the carbonation resistance.The incorporation of HNS could densify the microstructure and refine the pore structure.Moreover,the thaumasite can be stable at ambient temperature with the addition of HNS,which is beneficial to maintain alkalinity under the carbonation process.

Surface Temperatures Determination with Influencing Convective and Radiative Thermal Resistance Parameters of Combustor of Gas Turbine

Surface temperatures were determined with due consideration of the influencing thermal conditions of conductive, convective and radiative heat. A general condition of heat influx to a point was formulated with the end effect of such influx to the receiving point. It was noted that the heat flow will cause a rate of change of internal energy of the point. Based on the theory of the rate of change of internal energy, a combustor model of cylindrical cross-section was used to generate out the timely temperature equation. Further work was done on this model equation to convert it to non-dimensional. The conversion of this equation was very essential in summing up the parameters that can influence the timely generation of the temperatures. Interestingly, it is noted that when a material withstands temperatures, it will equally withstand the thermal stresses that inherently will be developed in it. From the results, the work came up with a table showing the range of these slope figures of equations, a point was also found for a vital recommendation for further studies, where such figures can be used to check the suitability for thermal stress levels and the lifetime of combustor of such thickness.