Papers by Keyword: Pore

Abstract: Complex characteristics of pore structure of rock mass, such as limestone, are difficult to describe by means of general mathematics and physics. While, the fractal geometry can describe some simple rules behind complex phenomena; and these simple rules can describe the complex phenomena. Therefore in this paper, the fractal theory is applied to study the complexity of the limestone pore structure. Through calculating the fractal dimension of the limestone pore microscopic images of different zoom scales, the scale-independence is proved to be possessed by complexity of pore, which indicates that the limestone is a good fractal body, and its complexity can be studied by means of fractal dimension.

Abstract: Using polycarbosilane(PCS) as precursor materials, 2.5D、3D3d、3D4d、3D5d braided structure Cf/SiC composites were prepared by Precursor Infiltration and Pyrolysis (PIP). The result showed that different braided structure Cf/SiC composites had dissimilar change tendency of density and porosity. The braided structure and pore position influenced mechanical properties of Cf/SiC composites obviously. 2.5D Cf/SiC composites had the lowest mechanical properties compared others braided structure via PIP process, 3D5d Cf/SiC composites had the highest mechanical properties for the bending strength reached 334MPa, modulus 99.5GPa. Furthermore, the microstructure and properties of different braided structure Cf/SiC composites has been investigated by means of SEM.

Abstract: Concrete is the most widely used building material and due to its use, water tightness is one of the factors essential for many constructions. Materials applied on concrete surface as secondary protection can have various forms. One of the material group with waterproofing ability, are materials on so called "crystalline technology base". As this material is cement-based its wide world production brings significant effect on environment. To bring on building materials market new materials should be considered its environmental friendlier production. One of the ways for this group of materials with crystalline abilities is replacing cement by other substituent, at best by secondary raw material. This would bring double advantage, lowering usage of cement and on the other hand use of already produced secondary raw material. This article deals with new developed materials based on "crystalline technology" with cement partly replaced by fly-ash substituent. At this article are presented results of new developed screed and coating modifications and its effectiveness on concrete waterproofing.

Abstract: Electromagnetic stirring (EMS) is an important method to homogenize the hard phase of the cladding layer. Rotary Permanent magnet electromagnetic stirring (PEMS) is adopted during the experiment. The changes of heat affected zone, solidification character, microstructure and hardness of TA15 Laser Metal Deposition (LMD) based on PEMS have been researched during the experiment. The results show that the PEMS can refine the grain, homogenize the microstructure, eliminate the disfigurement and enhance the hardness.

Abstract: In order to confirm the surface fractal dimension of the internal pore of complex porous materials by means of the FHH model and nitrogen adsorption method. Study the change rule on fractal characteristics of the pore of cement based materials further. The results shows that, surface area of the complex internal structure of cement based materials has the fractal characteristics observably. Testing and evaluating the fractal characteristics on surface area of the pore of cement-based materials is effective by nitrogen adsorption method. It is good for analyzing surface characteristics of pore structure further. Surface fractal dimension of pore structure and surface area have not good correlation. The characteristics and conclusion that quality fractal dimension of powder and surface area evaluating fineness of powder have not very good correlation is consistent.

Abstract: This work compared the densification behavior and pores evolution of two kinds of samples (15% and 35% initial porosity stainless steels parts) prepared by selective laser sintering. The results show that post microwave sintering process results in an increase of the density of sample. At the low sintering temperature (1200°C, 1300°C), the low porosity can lead to high density in the final sintered sample. As the sintering temperature reaches 1400°C, however, the sample with 35% initial porosity could be sintered to the higher final density than that of the sample with 15% initial porosity. The results also indicate that the initial porosity has a great effect on the number of pores, pore size, pore shape and the distribution of pores during post sintering process.

Abstract: In order to obtain better understanding of the resistance spot weldability of magnesium alloy and provide some foundational information for improving mechanical properties of the magnesium alloy joint, the influencing factors of pore formation during resistance spot welding of magnesium alloy, such as preexisting pores in base material, hydrogen rejection, shrinkage strain and expulsion, were analyzed; the corresponding restraining measures were discussed. The analyses reveal that the shrinkage strain and expulsion are important factors in contributing to the formation of pores during resistance spot welding of magnesium alloy, and that the pore formation could be suppressed by adjusting welding parameters.

Abstract: For further research on durability of concrete material under salt frozen conditions in cold area, the non air-entraining concrete with water-binder ratio of 0.4 and 0.28, air-entraining concrete with water-binder ratio 0.28 and the air content 7.0% are studied respectively. The fractal dimension of three kinds of concrete pore at different pore diameter range were determined by MIP(mereury intrusion porosimetry) before and after salt freezing and were studied in a comparative way. The research shows that the fractal dimension of pore diameter at range of 50nm ~ 550nm after salt freezing changed remarkably, namely salt frozen process has greater influence on pore within this range. Objectively the pore within this range in concrete suffered supercooled water osmotic pressure is the greatest. In addition, the total porosity reduced after salt freezing injury while fractal dimension changed more obviously. The fractal dimension of concrete pore could be a good reflection of concrete structure after salt freezing injury, showing that the diameter at 50nm ~ 550nm after salt frozen injury coarsening is obvious. Thus the fractal dimension of diameter within this range can be used as a key parameters after salt freezing injury.

Abstract: The present paper gives a detailed inferential reasoning to a new mathematical model for structural strength indicator of soil under dynamic load, which is established on the base of law of conservation of energy and strain energy transformed principle. Through dynamic triaxial test, it points out that the relation of principal stress difference and accumulation subsidence quantity exists threshold value and calculates the structural strength indicator change rule. According to the analysis of structural strength indicator variation rule, it lays emphasis on uniformity of structural strength indicator variation rule under different vibration times and draws the conclusion which is the increasing of the structural strength indicator.

Abstract: The effect and the ways of removal of the segregation of alloying elements within the dendrite cell in single-crystal nickel-base superalloys are discussed. The peculiar features of Re and Ru behavior are underlined.