The fractal effect of irregularity of crack branching on the fracture toughness of brittle materials

Microstructural observations of brittle materials indicated that a variety of microdefect events can be responsible not only for inelastic behaviour, but also for macroscopic crack front irregularity. This irregularity produces an increase in the fracture toughness of the material. In this paper, this irregularity is analysed by fractal geometry in a very simple manner; a fractal model of crack branching is established. Both microscopic and macroscopic analytical results show that the toughness can be raised appreciably as a fractal geometric effect of the irregularity.

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Résumé Des observations microscopiques sur des matériaux fragiles ont montré qu'une variété d'évènements à l'échelle du microdéfaut peuvent être responsables non seulement du comportement inélastique, mais aussi de l'irrégularité du front d'une fissure macroscopique. Cette irrégularité provoque un accroissement de la ténacité à la rupture du matériau. Dans cette étude, on analyse de manière très simple cette irrégularité par fractogéométrie (Mandelbrot) et on établit un modèle fractal relatif à une fissure qui se ramifie. Les résultats de l'analyse microscopique et macroscopique montrent qu'un effet fractogéométrique de l'irrégularité du front de fissure est d'accroitre de manière appréciable la ténacité.

     

CAD与CAPP集成研究回转体类零件特征识别

本文研究了回转体轴类,轴套类零件的特征识别。对这类零件常用的特征单元进行了定义,描述了这类零件的特征模型:介绍了它的识别方法和特征参数定义方法。     

Characterization of ultrafine La x Sr1−x MnO3 powder prepared by spray pyrolysis

The characterization of La _x Sr_1−x MnO₃ powders produced by spray pyrolysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation, specific surface area (Brunauer-Emett-Teller), and particle size distribution measurements shows that the resultant large particles are loose agglomerates consisting of many small particles. However, the sintered tiny particles can form hard agglomerates, and the particle size increases remarkably. The structures of the powders before and after sintering were identified by x-ray diffraction (XRD). The study of the electrical property of the powder shows that the powder is a metallic conductor. In a reducing atmosphere, the powder can be decomposed. When the powder is cofired with yttria-stabilized zirconia 5% (YSZ) powder at 1200 °C for 5 h, no new phase is produced, and the powder remains a single provskite hexagonal-rhombohedral structure.     

多元酚——甲醛树脂中游离酚,游离醛含量的测定

多元酚－－甲醛树脂是本院开发的热固粘接剂新产品，本文给出了这一产品技术指标中游离酚、游离醛含量的测定方法，并对方法进行了讨论。     

Cu2O/Cu Cermet as a Candidate Inert Anode for Al Production

Cu₂O/ x Cu ( x =0–25 wt%) cermets were evaluated as a novel partially inert anode for aluminum (Al) production. The physical and mechanical properties, including the compressive strength, flexural strength, thermal expansion coefficient, thermal conductivity, and dc electrical conductivity were tested at room temperature and at temperatures up to 950°C. The coefficient of thermal expansion, compressive strength, flexural strength, thermal conductivity, and electrical conductivity of Cu₂O/Cu cermets increased with increasing Cu content. High-temperature electrical conductivity measurements showed that with increasing temperature, the electrical conductivity increased when the Cu content was below the percolation threshold, while it decreased when the Cu content was above the percolation threshold. A relatively stable CuAlO₂ layer formed on the cermet surface during electrochemical testing, and the corrosion rate of this anode was estimated to be about 1.8–1.9 cm/year in Al production.     

顺酐化SBS的钠离聚体形式与丙烯酰胺的乳液接枝共聚

研究了顺酐化SBS的钠离聚体与丙烯酸胺以过氧化苯甲酰为引发剂的乳液聚合,得到了共聚的较佳条件.并以IR及DSC表征了试样的组成和多相结构.     

Effect of particle size on the surface oxidation and flotation behavior of galena particles in lime system

ABSTRACT

In this research, the effect of particle size on the surface oxidation and flotation behavior of galena in the lime system was studied. Coarse (?0.074 + 0.038 mm), intermediate (?0.038 + 0.025 mm) and fine (?0.025 mm) galena particles were used in the experiment. The dissolution tests, flotation tests, and sorption tests were accomplished. Through further analysis by XPS, the effect of particle size and lime was observed. The decrease of mineral particle sizes increased the adsorption ratio of collector and the dissolution of galena, while the hydrophilic product OH^?/Ca(OH)⁺ produced by dissolution occupied the dominant position, which led to the minerals hydrophilic.