Q345B钢轧后拉伸分层试样的显微组织研究

利用金相检验，扫描电镜，能谱分析以及元素分布原位分析等手段，研究了Q345B钢轧后拉伸试样中的夹杂物和显微组织，寻求产生拉伸分层的原因。结果表明，Q345B钢连铸坯中主要微合金元素C、Mn、Nb等的偏析，造成轧后试样中存在大量的长条状MnS夹杂物，块状铌、钛的碳化物和条带状马氏体组织，致使局部力学性能差异过大，容易在缺陷集中分布的显微组织层面上产生开裂和分层。     

X42与330CL钢冷弯裂纹成因分析

针对新产品X42管线钢与330CL车轮钢冷弯性能不合的原因进行了可能性分析。结果表明：X42管线钢不合试样的带状组织严重而夹杂物级别较低,带状组织可能是导致冷弯不合的主因;330CL车轮钢不合试样的夹杂物级别较高,而带状不甚明显,夹杂物可能是导致冷弯裂纹的主因。     

Vacuum-induced Bubble Formation in Liquid-tempered Chocolate

ABSTRACT: Bubble inclusion is one of the fastest growing operations practiced in the food industry. A variety of aerated foods is currently available in supermarkets, and newer products are emerging all the time. This paper aims to combine knowledge on chocolate aeration with studies performed on bubble formation and dispersion characteristics. More specifically, we have investigated bubble formation induced by applying vacuum. Experimental methods to determine gas hold-up (volume fraction of air), bubble section distributions along specific planes, and chocolate rheological properties are presented. This study concludes that decreasing pressures elevate gas hold-up values due to an increase in the number of bubble nuclei being formed and release of a greater volume of dissolved gases. Furthermore, bubbles are observed to be larger at lower pressures for a set amount of gas because the internal pressure needs to be in equilibrium with the surrounding pressures. Temperature-induced changes to the properties of the chocolate have less of an effect on bubble formation. On the other hand, when different fats and emulsifiers are added to a standard chocolate recipe, milk fat was found to increase, significantly, the gas hold-up values and the mean bubble-section diameters. It is hypothesized that this behavior is related to the way milk fats, which contain different fatty acids to cocoa butter, crystallize and influence the setting properties of the final product. It is highlighted that apparent viscosity values at low shear rate, as well as setting behavior, play an important role in terms of bubble formation and entrainment.     

Quantifying the dispersion of mixture microstructures

A general method to quantify the inclusion dispersion of mixture microstructures has been developed. The dispersion quantity, D, is defined as the probability of inclusion particle free‐path spacing falling into a certain range of the mean spacing μ, according to the particle spacing data frequency distribution. Two quantities, D_0.1 and D_0.2, are proposed, which are the probabilities of the particle free‐path spacing falling into the ranges of μ± 0.1 μ and μ± 0.2 μ, respectively. Both normal and lognormal distributions are discussed, and in both cases, the quantities D_0.1 and D_0.2 are specified as monotonous increasing functions of μ/σ, where μ and sigma; are the mean particle free‐path spacing and standard deviation, respectively. Examples of composite are presented to quantify the dispersion of foreign reinforcements based on the proposed method.     

Si－Al－Ba脱氧剂应用的试验研究

本文研究了一种Ｓｉ—Ａｌ－Ｂａ脱氧剂在实验室条件下的应用效果，试验发现：Ｓｉ－Ａｌ－Ｂａ优于铝及Ｓｉ－Ａｌ－Ｆｅ脱氧剂，铝利用率高，有利于控制钢中夹杂物，钢的力学性能也有所提高，有较好的经济效益和应用前景。     

夹杂物控制技术在阀门弹簧钢生产中的应用

介绍了国外为适应阀门弹簧的高疲劳寿命对氧化物夹杂的苛刻要求,采用夹杂物形态控制理论使夹杂物无害化的生产技术,这种技术生产的超清洁阀门弹簧钢,细化和软化了氧化物夹杂,从而消除了氧化物夹杂对材料疲劳性能的危害,提高了阀门弹簧疲劳极限和寿命     

导模法生长蓝宝石单晶光纤的缺陷和光学特性研究

通过导模法(EFG)成功生长了蓝宝石单晶光纤(直径400~1000 μm, 长度500 mm)。光纤的横截面大致为圆形, 侧面无明显的小面, 直径变化小于40 μm。本研究对晶体缺陷, 例如微气泡, 包裹物和生长条纹等进行观察与分析, 得出: 大多数微气泡是球状的, 且存在于光纤的外侧缘; 在蓝宝石光纤外侧面也观察到少量的钼包裹物元素; 新模具在前几次使用中往往会产生更多的钼夹杂物, 在多次使用后降低。通过对熔体膜流体流动的实验和数值模拟, 研究蓝宝石光纤中微气泡尺寸和分布, 实验和数值模拟的结果显示出良好的一致性。微气泡的分布取决于熔体膜处的流体流动模式, 流体流动的涡流使微气泡在热毛细对流作用下移动到蓝宝石光纤外侧缘。633 nm处的吸收损耗为9 dB/m, 包裹物和表面不规则性会增加散射损耗。     

非金属夹杂物特性对钢铁材料疲劳性能影响的研究进展EI北大核心CSCD

本文综述了非金属夹杂物对钢铁材料疲劳性能的影响及研究现状,从夹杂物的角度出发,首先介绍非金属夹杂物特征提取的最新研究进展,分别从实验测量方法和数学公式科学统计方法两方面进行论述;其次根据夹杂物对于疲劳损伤的主要原理,介绍5种应用较为广泛的定量化分析夹杂物特征参数与钢材疲劳性能的数学模型;然后以夹杂物的形貌特征、力学性能以及与基体之间的相互作用为出发点,探究非金属夹杂物的特性对重载零件钢材疲劳性能的影响。最后指出从多角度解析非金属夹杂物对钢材疲劳性能的主要作用机理,构建非金属夹杂物对钢材疲劳寿命预测模型是未来该领域的研究重点。     

Influence of carbon dioxide shielding gas on microstructure and corrosion property of welds

The microstructures and corrosion properties of weld joints are studied during 10 kW high power fiber laser welding of 304 stainless steel with shielding gases of 100 % argon, 80 % argon containing 20 % carbon dioxide and 100 % carbon dioxide, respectively. As the content of carbon dioxide in argon shielding gas increases from 0 % to 20 % then to 100 % during 10 kW high power fibre laser welding, the interdendritic δ‐ferrite in weld joints changes from lathy, short strip and trivial structures to thick‐long strip with short secondary dendrite arms then to skeletal‐network structure. Oxide inclusions, observed in 100 % carbon dioxide shielded weld, promote the formation of the skeletal‐network structure of δ‐ferrite and the homogenization of chromium and nickel in weld joint. The 100 % argon shielded weld joint has a highest initial corrosion current density, the 80 % argon containing 20 % carbon dioxide shielded weld has a lowest pitting potential, while the 100 % carbon dioxide shielded weld has a highest initial corrosion potential. The microstructures and element distribution play important role in determining the corrosion properties of the weld joints.     

Lie-algebraic stability conditions for nonlinear switched systems and differential inclusions

We present a stability criterion for switched nonlinear systems which involves Lie brackets of the individual vector fields but does not require that these vector fields commute. A special case of the main result says that a switched system generated by a pair of globally asymptotically stable nonlinear vector fields whose third-order Lie brackets vanish is globally uniformly asymptotically stable under arbitrary switching. This generalizes a known fact for switched linear systems and provides a partial solution to the open problem posed in [D. Liberzon, Lie algebras and stability of switched nonlinear systems, in: V. Blondel, A. Megretski (Eds.), Unsolved Problems in Mathematical Systems and Control Theory, Princeton University Press, NJ, 2004, pp. 203–207.]. To prove the result, we consider an optimal control problem which consists in finding the “most unstable” trajectory for an associated control system, and show that there exists an optimal solution which is bang-bang with a bound on the total number of switches. This property is obtained as a special case of a reachability result by bang-bang controls which is of independent interest. By construction, our criterion also automatically applies to the corresponding relaxed differential inclusion.