弱配筋砼构件的裂缝宽度及相应最小配筋率的研究

弱配筋砼构件的裂缝宽度计算是一个急待解决的理论和工程应用问题,目前研究的资料很少。本文通过50多根受弯、大偏心受压弱配盘砼构件的试验研究及概率分析,提出了这种构件裂缝宽度及间距概率分布属性,提出特征裂缝宽度计算公式,并用模糊失效慨率进行了可靠度分析。找出现有计算公式存在的缺点和问题。建议公式与试验结果拟合性较好,可供规范修订和工程设计参考。     

非齐次马尔柯夫决策规划——折扣模型

本文是文献[3]、[4]的进一步深入、推广,所讨论的MDP模型具有最一般的非齐次性,即rt,qt都非齐次。证明了ε—最优马氏策略的存在性以及当最优策略存在时,最优马氏策略的存在性等。     

Isothermal grain growth of reactive spray formed 7075 alloys in semi-solid state

The grain growth behavior in reactive spray formed 7075 2.91vol%TiC AI alloy was studied and compared with that of spray formed 7075 AI alloy at semi-solid state. The effects of in-situ TiC particles on the microstructure of spray formed 7075 AI alloy were also investigated. The specimens were heat-treated isothermally at various temperatures between the solidus and liquidus of 7075 A1 alloy for times in the range of 10-60 rain, then quenched in water. The microstructure of reheated specimens was characterized using scanning electron microscopy and optical microscopy. The grain size was measured using a mean linear intercept method. Results show that the in-situ TiC particles can effectively retard grain growth and refine the grain at a limited size. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates that the in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solid state.     

Effect of Precipitating Phases on Tensile Strength and Microstructural Stability of a Spray-Deposited Al-Si-Fe-Mn-Cu-Mg Alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this study, AI-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by spray deposition technique. The aging process of the alloy was investigated by differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM). The results show that two kinds of phases, i.e. S(Al2CuMg) and σ(Al5Cu6Mg2), precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300℃). In addition, the σ-Al5Cu6Mg2 is a relatively stable phase which improves microstructural stability of the alloy.     

Win98注册表修改点滴

从注册表几个侧面的修改,帮助用户更方便地操作Windows.     

A Zr-RICH LOW MELTING POINT PHASE IN Ni_3Al ALLOY WITH Zr

A Zr-rich phase,Ni_5Zr,with low melting point has been fouhd in an Ni_3Al alloy doped withZr(1.2at.-%).It will cause the incipient melt of the alloy after being homogenized at 1300℃.This makes it difficult to homogenize the coarse casting structures completely and limits thefurther improvement of properties of the Ni_3Al alloy.     

复杂地区地震波场的正演模拟与反时偏移

本文用Fourier变换法精确地计葬了波动方程的空间导数项,导出了时一空域中只与时问导数有关的波动方程。对该方程用中心差分法求解,可得到适 于变速介质中地震波场的正演模拟和反时偏移的数位递推计葬会式。方法的关健在于对空问失量作多维Fourier变换之后,引入了两个分别与速度和空间 Fourier变换频率有关的翎助场。在理论上,本方法可适用于速度和构造形态任意变化的复杂地区地震波场的正演模拟与偏移。理论试葬的结果表明,该方法效果良好。     

Texture Evolution in a Warm-Rolled Ti-IF Steel During Cold Rolling and Annealing

The texture characteristics of a Ti-IF steel in ferritic hot-rolled (warm-rolled), cold-rolled, and annealed status were studied. The hot bands were obtained by finish rolling in ferrite region, coiling at very low temperature, and then directly annealing in industrial trial. It was found that dominates at the surface and is the main component at the midsection in the hot band. The α-fiber at the surface as well as at the midsection intensifies during cold rolling and weakens during annealing, while the changing of γ-fiber depends on the hot band texture during cold rolling, but it absolutely intensifies after a well-advanced state of annealing. Orientations concentrate on increasingly at the surface and continuously rotate to RD-fiber at the midsection as the reduction increases. The average plastic strain ratio, elongation, and strain hardening exponent measured for the cold-rolled and annealed steel increased with improving annealing temperatures.     

雾化喷射沉积成型凝固过程模拟Ⅱ.Al-Cu合金的计算结果

根据本文作者提出的喷射沉积成型沉积体内的凝固模型,对典型的Al-Cu合金进行了计算分析结果表明,工艺参数（如沉积速率和沉积时雾化锥的温度）和材料的热物性（如界面换热系数）对沉积体内的凝固过程有明显影响在沉积热力学条件（沉积前雾化锥的热力学状态）相同的情况下,沉积表面的温度随工艺参数和材料热物性发生显著变化所以,必须以沉积表面温度的变化作为工艺控制的参考、以往提出的以沉积前雾化锥热力学状态作为工艺控制标准的原则需要重新加以考虑     

喷射沉积快速凝固技术制备镁合金的研究现状及展望

喷射沉积是一种新型的快速凝固技术,被广泛用于研究和开发高性能的快速凝固材料.叙述了喷射沉积快速凝固技术的原理,综述了喷射沉积镁合金的特点和研究现状,并对其发展前景进行了展望.