Water model simulation of tundish flow under varying conditions

Water model studies have been conducted to characterise the flow conditions in continuous casting tundishes under conditions of open and submerged nozzles. In this investigation simulations of practical problems of flow interruptions from the ladle, thermal inversions due to uninsulated ladle, and pneumatic agitation near the tundish end wall were conducted. The studies showed that incorporation of suitable flow control devices brings about homogenisation of temperature and composition between strands in the above cases. This study also showed that agitation of the liquid at the end wall reduces the extent of stagnant zone in the tundish.     

The simulation of hexavalent chromium formation under various incineration conditions

The formation of hexavalent chromium Cr(VI) during waste incineration processes is of interested because its carcinogenic characteristic. The objective of this study is to simulate the formation of Cr(VI) species under various operating temperatures and input waste compositions during incineration by a thermodynamic model. The results show that the major hexavalent chromium species are CrO2Cl2(g) and CrO3(g). Chlorine and oxygen can increase the formation of Cr(VI) species; while hydrogen, sulfur, sodium, and calcium can inhibit. The input waste composition has greater effect on the formation of hexavalent chromium species than operating temperature.     

不同地应力条件下含节理岩体爆破的数值模拟

将爆破损伤视为爆破应力波和爆生气体压力共同作用的结果,分别考虑不同的地应力条件(侧压力系数0.5、1和2,竖直方向地应力5 MPa和10 MPa)和节理角度(30°、45°、60°和90°),开展含节理岩体双孔爆破过程的数值模拟,研究爆生裂纹萌生—扩展—贯通过程的演化规律.无节理时,初始应力场对爆生裂纹的扩展具有一定的导向作用,裂纹扩展主方向趋于最大地应力方向.节理对裂纹的扩展方向具有一定的影响,节理角度为30°时,爆生裂纹与节理面连通,形成典型的‘之’字形断裂.节理对裂纹萌生和扩展具有明显的促进作用,有利于孔壁上下侧裂纹沿竖直方向的扩展.     

Effect of niobium on hot ductility of low C-Mn-steel under continuous casting simulation conditions

The effect of niobium on hot ductility of low C-Mn steel under continuous casting simulation conditions in the range from 700°C to 1 000°C was investigated on a Gleeble-1500 tester by using in-situ melting and solidification method. It was found that the ductility trough becomes deeper and wider as Nb content increases. The steel has more refined structure and is more sensitive to interdendritic fracture as Nb content gets higher. The segregation of impurities or alloy elements and formation of sulphides and Nb-compounds in the interdendritic regions promote the interdendritic fracture.     

高地应力硬岩下双孔并行隧道相似模型试验及数值模拟

基于相似模拟理论,通过试验台架设计、监测系统设计、加载系统设计和岩体模型制作等流程,完成了双孔并行隧道模型试验系统的研制工作;试验中实时监控模型各关键位置的位移变化、应力变化及隧道岩壁破坏情况.研究表明,试验观测结果与基于Mohr-Coulomb模型所得数值模拟结果相对误差较大,而基于Plastic-Hardening模型进行数值模拟计算时,所得岩土体屈服状态和变化规律与相似模型试验结果吻合度较高.综合各方面分析研究结果,认为Plastic-Hardening模型能够更为精确合理的反映实际工程及试验中岩土体状态的真实变化情况,可为相似地质条件下的双孔并行隧道施工及维护提供重要参考.     

Simulation of the hot-tension test under cavitating conditions

A theoretical analysis of the isothermal hot-tension test under cavitating conditions for sheet samples was performed using a “direct-equilibrium” approach. The effects of cavity growth rateη, initial cavity volume fractionC _v0, strain-rate sensitivity exponentm, and specimen taper on engineering stress-strain curves, strain profiles, and failure modes were established. For a given value ofm, it was predicted that the engineering stress-strain curves of cavitating and noncavitating samples are almost coincident except near failure. In fact, during quasistable deformation, the required load for a cavitating material is slightly higher than that for a noncavitating material because of strain rate and effective area effects. Model results also delineated the competition between failure controlled by localized neckingvs fracture, the latter being defined by a critical-volume fraction of cavities. Specifically, at low strain-rate sensitivitiesm and cavity growth ratesη, failure was predicted to be controlled by necking. By contrast, at high values ofm andη, fracture prior to localized necking was predicted to predominate; in these cases, the cross-sectional area at the failure site was appreciable, thus resembling a form of brittle fracture. The validity of the modeling approach was confirmed through the analysis of data in the literature. However, model results did suggest that caution should be taken in the interpretation of experimental data because various combinations ofC ^v0 and η can result in the same total elongation. Formerly Visiting Scientist, Metals and Ceramics Division, Materials Directorate, Wright Laboratory, WL/MLLN     

Occlusal considerations in the design of implant-assisted fixed prostheses

This paper introduces a classification system that enables the restorative dentist to design an appropriate occlusal scheme while restoring adult mixed dentition. The system guides the dentist in selecting an occlusal scheme based upon the number and location of osseointegrated implants and natural.     

Foaming of slags under dynamic conditions

Slag foaming under dynamic conditions has been studied in laboratory scale to examine the influence of properties commonly used to describe the foaminess and foam stability of slags under steady-state conditions. Synthetically produced slags with compositions relevant to tool steel and stainless steel production were studied through X-ray equipment in measurements simulating the dynamic conditions found in real processes. It is found that the dynamic systems display a more complex behavior than systems under steady state. Traditional theories for foaming do not seem to be valid for slag foaming under dynamic conditions. The foam displays a fluctuating behavior, which the presently available models are not able to take into account. The concept of a foaming index does not seem to be applicable, resulting in the need for alternative models.     

Biodegradation of atrazine under denitrifying conditions

Several significant advances in the understanding of the catalytic mechanisms, structures and evolution of glutathione transferases have occurred in the past year. These advances include new mechanistic information concerning the canonical soluble enzymes, the finding that the fosfomycin-specific enzyme, FosA, is a metalloglutathione transferase and a higher resolution projection structure of the microsomal enzyme.     

Stability of transition-metalcarbides under anodic-polarization conditions

Summary The stability of some carbides of the transition metals in sea-water and nitric-acid solutions was investigated. Chromium and tungsten carbides exhibited the highest stability. The decreased stability of the carbides observed in sea water is attributable to the effects of oxidizers (hypochlorous acid), which enhance the solubility of carbides. The improvement in the stability of the carbides with rise in nitric-acid concentration is ascribed to the formation of a surface oxide layer which protects the carbides against oxidation.Translated from Poroshkovaya Metallurgiya, No. 5 (77), pp. 75–78, May, 1969.     

Assessment of the danger of bronchological studies under polyclinic conditions

In 176 ambulatory patients with cancer and inflammatory diseases of the lung the initial parameters of acid-base balance and blood gases were studied. Metabolic acidosis was found in 29.5%, alkalosis--in 54.5%, the values of acid-base balance and blood gases were normal in 15.9% of patients. The degree of bronchoscopy risk under narcosis in ambulatory patients is directly proportional to the kind, character and intensity of disorders in oxidation-reduction processes. Deep, hardly compensated or decompensated disorders in acid-base balance and gas metabolism in pH values higher than 7.54 and lower the 7.26, BE (buffer base shift)--higher than 4.0 meq/1 and lower than 6.0 meq/l, and pO2 lower than 65 mm Hg are the criteria of high risk of bronchological investigation under anesthesia in ambulatory oncological patients.