Key Engineering Materials Vol. 748

Abstract: In recent years, more and more attention has been paid to the effect of stray current on the properties of cement-base materials in subway engineering. In the actual service process, reinforced cement-based systems suffer from various erosive conditions, the degradation mechanisms in reinforced cement-based systems due to the combined effects of stray current and environmental multi-factors have been a serious problem in civil engineering for many years. This paper reviews the research achievements on the properties of cement-based materials under the multi-factor coupling conditions such as stray current and soft water, chloride ion, sulfate, stress, freezing and thawing cycle and so on. Furthermore, the improvement of cement-based materials on stray current resistance is also generalized in it. Prospects of cement-based materials for durability under environment multi-factor coupling actions are also presented.

Abstract: The hydroxy-aluminum solution is prepared by alkali neutralization titration and the subsequent cross-linking tests are designed by mixing the hydroxy-aluminum solution and expansive soil, followed by the discussion on the influence of the molar ratio of OH^- to Al³⁺ and ratio of total aluminum to expansive soil on the swelling behavior of the cross-linked soil. The free swelling ratio of the cross-linked soil decreased significantly, indicating that the main aluminum species that changes the expansion properties of the cross-linked soil is [Al₁₃]⁷⁺.

Abstract: A non-suction controlled method of wetting-drying cycles for unsaturated compacted loess material has been studied in this paper. The specimen was wetted by a sprayer and dried by air and the moisture content was controlled by measuring the specimen mass. Calculated moisture content was investigated and compared with measurement data. It can be indicated from the results that the method is effective, accurate and time-saving for controlling moisture content of compacted loess.

Abstract: In this study, a newly materials based on copper–benzene-1,3,5-tricarboxylate/polyaniline (PANI/Cu-BTC) composite was investigated for NH₃ sensing. Cu-BTC was grown on the PANI a hydrothermal process. The sensing performance of as-grown product was studied for different concentrations of NH₃ at room temperature. The results reveal that Cu-BTC/PANI composite exhibit high sensitivity toward NH₃. The good sensing performance of the composite was attributed to high surface area and good affinity of Cu-BTC for NH₃, which can act like preconcentrator for the NH₃ gas sensing.

Abstract: The 2, 4, 6-trinitrotoluene (TNT) vapor detection by quartz crystal microbalance (QCM) coated with 18-crown-6 ether film is introduced. The film acts as selective or sensitive layer for detecting TNT molecule. The frequency shift response is depend on the amount of mass of molecule adhere on the coated film surface. In this study, the concentrations of TNT vapor which is related to responses are studied. It shows that the TNT vapor concentration is related to the time for steady state condition and the frequency shift response. The high concentration vapor will increase the frequency shift response but increase the steady state time.

Abstract: The preparation and adsorption capacity of a methane based sensor probe based on lead-free piezoelectric resonance ceramics were investigated in this paper. The zeolite X which synthesized via hydro-thermal process was used to modify the sensor probe surface. The phase structure and microstructure of the zeolite membranes was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM).Due to the special crystal structure, the zeolite X molecular contain a regular form, uniform pore, larger surface area and a strong surface polarity. In order to test the sensor probe sensitivity, the impedance spectrum of methane adsorption sensitivity was measured at a methane concentration range from 0 to 5%. The results indicate that the sensor probe exhibits enhanced sensitivity with an offset resonant frequency of 590Hz especially at the lower methane concentration found in coal mining. The sensitivity can reach 165 Hz/1% CH4 at the concentration of methanol below 3%. With further increase of methane concentration from 3% to 5%, the sensitivity of sensor probe dropped slightly to 120Hz/1% CH4.

Abstract: The new relations in kinematics of the magnetoplasticity phenomenon in nonmagnetic materials based on the experimental studies and the computer simulations are presented. The movement of the crystal dislocations, the fundamental crystal defects responsible for plastic deformations, through the random distribution of the point defects, being the obstacles for the motion of the dislocation, is discussed. It is shown that the mean value of the obstacles on the dislocation line does not depend on their concentration C in the sample and the critical dispatching force is proportional to √C.

Abstract: Molecular dynamics simulations were carried out to investigate the change in the crystal orientation of polycrystalline materials placed under an external load. Two models were prepared, both comprising four grains but with different grain arrangements. Each grain had a face-centered cubic structure with (001) face on the x-y plane, whereas each grain had a different rotation of orientation around the z-axis. A tensile load was applied by extending the edge length in the y direction while the other directions were kept stress-free. As a result, a significant change in the microstructure was observed, with changes in both crystal orientation and shape along with the formation of subgrains. The structure and direction of the grain boundary against the external load were also found to affect the change in the microstructure.

Abstract: Thermally sprayed tungsten carbide-based coatings deposited by High Velocity Oxygen Fuel (HVOF) has been widely developed for its high corrosion and wear resistance. The finishing of the coated surface by grinding process is essential because of the high surface roughness of carbide coatings. Residual stresses existing in most hard coatings have significant influence on the adhesion, mechanical properties and tribological performance. The present study investigated the effect of grinding process on the residual stress of WC-10Co-4Cr coating by HVOF. The residual stress of coating was measured by the X-ray diffraction (XRD) technique using sin²ψ method. In addition, the effect of diffraction peak positioning method on the accuracy of residual stress of WC-10Co-4Cr coating was determined in the XRD technique. Four peak positioning methods and their effects on the accuracy of X-ray diffraction (XRD) residual stress measurement are considered. The results showed that the compressive residual stress of the WC-10Co-4Cr coating increase after grinding process. The parabolic method was selected for the peak positioning to measure the precise residual stress of HVOF-deposited WC-10Co-4Cr coating.

Abstract: Crack propagation around the stress concentration area causes fatigue failure. Non-destructive method is necessary for monitoring structure fatigue before destruction. We focused on a magnetic non-destructive evaluation method for crack growth. In order to understand the relation between crack propagation and changes in magnetic flux density, we observed the position of the positive and negative magnetic flux density distributions around the crack of tool steel (SCM440) plate using a scanning Hall probe microscope (SHPM). We found that the vertical component of the three-dimensional magnetic flux density moved as the crack growth. Furthermore, the magnetic component which is parallel to the tensile stress appeared just before destruction of the specimen.