Key Engineering Materials Vol. 633

Abstract: The Impulse Excitation technique is a nondestructive and very convenient testing method. It could be applied at different circumstances such as high temperatures, low temperatures and controlled humidity. The Impulse Excitation technique is based on the analysis of the vibration of a test sample after it was impulse excited. The elastic properties of a test specimen are related to its mechanical resonance frequency. In this paper, the regular of resonance frequency changed with specimen’s size was discussed. Elastic modulus of glass with different length, width and thickness were measured, and ceramic composite material with small size was tested. The results indicate that the resonance frequency of specimen changed with its size regularly, and the specimen with small size has poor accuracy of elastic modulus measurement.

Abstract: The sliding friction behaviour of several ceramics, SiC,TiC,TiB₂ and their multiphase composite, had been studied under different humidity against Al₂O₃ ceramic ball. The results showed that, although the friction coefficients decreased along with humidity increased for all ceramics samples , the wear of ceramics had different performance. In high humidity condition, SiC can react with water in air to form oxide film enhance decreasing the wear. The wear rate of multiphase composite of SiC-TiC-TiB₂ are nearly not affect by humidity and are much smaller than for other ceramic.Key words: silicon carbide; titanium carbide; titanium boride; ceramic; oscillating sliding; humidity

Abstract: Vacuum insulation structure panel is the one type of the insulation materials. The characteristics of this material are not only low thermal conductivity, good sound insulation, energy efficient, environmental protection but also does not contain any ODS material. FLUENT software using Vacuum insulation structure panel of the temperature field of steady-state analysis. Comparative analysis of dynamic characteristics of the wall of the influencing factors。

Abstract: Mullite material is a material commonly used in honeycomb regenerator, because in the process of using material under big temperature difference effect, so have a great demand for its thermal shock resistance. The used mullite ceramics were made by the direct solid phase sintering method, and the modulus of elasticity of the mullite ceramics measured by ultrasonic pulse-echo method in a thermal shock and thermal fatigue experiment, respectively. In the air-cooling condition, the study found the mullite ceramic without thermal shock that the longitudinal wave velocity and shear wave velocity respectively 3970(m/s) and 2492(m/s). After 45 times thermal shock of temperature difference of 800°C, longitudinal wave velocity and shear wave velocity decreased to 3910(m/s) and 2457(m/s), and the value of the modulus of elasticity changed 1020MPa. By observing the change of the elastic modulus value rule, can know the elastic deformation of thermal shock on the material performance of thermal shock damage. Moreover, the results can provide the data basis for the calculation of the residual strength and the numerical simulation of thermal stress.

Abstract: It is generally believed that materials with high imaginary permeability and high imaginary permittivity are effective absorbers. For specific samples, however, the adjustment of input impedance is still necessary for the sample property optimization. By analyzing the relation between the diffraction rate and the input impedance, a method of absorption maximization for slab sample are presented in this sample. Medium choosing and volume rate controlling is the key of this method.

Abstract: Optical homogeneity is an important measurement of the optical materials, directly affects wavefront quality of the refractive optical system, changes the system wavefront aberration. As the traditional direct measurement method requires high precision surface shape machining for optical material (PV value < 0.1λ), it was gradually replaced by the method of Fizeau interferometer four step, which requires lower surface shape. This article used 600mm diameter Fizeau interferometer, a four step method tested the optical homogeneity of the same 500 mm diameter fused quartz material with a front surface shape respectively 3.719 λ and 0.427 λ (λ = 632.8nm). Comparison of the test results showed that the PV difference of optical homogeneity between the two was only 0.036 λ, △n inaccuracy was 10-7, and the homogeneity morphology matched exactly. To further analyze the factors affecting the optical homogeneity, the front surface shape of the other sample was sliced ​​in a predetermined direction. This artical analyzed the effect of morphology upon the slicing line on optical homogeneity. The conclusion was that the direct affecting factor on optical homogeneity was the slope of surface morphology, rather than the overall PV value.

Abstract: As the ultra high way and long distance pumping concrete became increasingly common, the engineers not only required the concrete have large liquidity but also increasingly concerned about the homogeneity of concrete. However, without effective and convincing method, currently the engineers had to assess and judge the homogeneity just by their sight, feel and experience. In order to test the homogeneity rapidly, exactly and quantitatively, a new device and method was developed relaying on the theory that the barycentre of the concrete which was filled in regular-shape container would deflect away from the shape-centre of the container more or less if the components with different density in concrete separated to stratifications. C30 and C40 concrete whose slump≥180mm and slump flow≥480mm were tested by this method and their homogeneity modulus (C_v) were figured out by the supporting formula. The result showed that the homogeneity of concrete was accredited if 0.90<C_v<1.10, and C_v was closer to 1.00, the homogeneity was better.

Abstract: This paper discusses the testing equipment of concrete deterioration under the coupled action of multiple factors. It discusses the classification, advantages and disadvantages which are related to the test system and studies the charge loading device design and the key problems. At last the paper forecasts the prospect of loading device design.

Abstract: The hydration of cement is known to be a complex phenomenon. Although the broad pattern of reactions and microstructural development are known, a number of important questions remain unanswered. How to select the proper techniques is what the research people think of for now. This paper reviewed the domestic and international research progress and presented the advantages and disadvantages of these methods and the application prospects. Nuclear magnetic resonance spectroscopy (NMR), nanoindentation and electron microscopy techniques of cements were expounded in detail. Furthermore, through analyzing the results obtained by different research methods, the paper predicted the development prospect of advanced testing method of cement-based materials.

Abstract: Fused cast Zirconia-Alumina-Silica material (AZS) is the key refractory to glass furnace. In order to reduce production cost and optimize production process, the influences of riser position and riser size on temperature gradient, solidification time, residual melt modulus, solidification fraction, and cooling rate of cast system were studied by the finite element simulation method according to the brick size of 600 mm × 400 mm × 300 mm. It turned out that it would be more efficient in feeding when riser located at the center of maximum surface of a brick or when the height of riser is 250 mm-270 mm, while the volume ratio of brick to riser is 2.95-2.74, on condition that the size of riser upper surface is 450 mm × 450 mm and the bottom 150 mm×150 mm.