Microstructural modeling approach applied to rock material

The importance of the microstructural parameters in rock mechanical behavior has been investigated by several authors. Moreover, the Weibull statistical model has been used to characterize the heterogeneity of several materials on the basis of the concept that the microscopic defects within the material determine their mechanical strength. The modeling of different rocks is a topic that is fundamental for the prediction of rock fragmentation. In this article, the analysis of rock microstructure is performed using the microstructural modeling approach, which consists of the simplification, quantification, and modeling of the main properties of rock microstructure. The grain size, grain shape, and microcracks are modeled by means of statistical density functions, namely, Cauchy, chi-squared, exponential, extreme value, gamma, Laplace, normal, uniform, and Weibull. It is found that the Weibull distribution is the most appropriate statistical model of the grain size and grain shape, when compared with the other eight statistical models. Regarding microcracks, the results show that the gamma distribution is the most appropriate model. The Weibull and gamma distributions are then used to analyze the heterogeneity of the microstructure. This is done by comparison of the statistical models of each microstructural property evaluated in several thin sections of the same rock. It is found that with respect to grain size and grain shape, the rock is homogeneous, while the size distribution of the microcracks shows a clear trend toward less homogeneity. The microstructural modeling approach is important for modeling, characterizing, and analyzing the microstructure of rock material. Among other applications, it can be used to explain differences in the mechanical behavior obtained in testing several specimens.     

一种Cr—Mn—Mo—B低碳低合金钢的热变形行为

利用ＴＨＥＲＭＣＭＡＳＴＯＲ－Ｚ热处理机对一种Ｃｒ－Ｍｎ－Ｍｏ－Ｂ钢的热变形行为进行了研究，绘制了真应力－应变曲线，得到了各变形工艺参数之间的定量关系，得出试验用钢的Ｑ值为３７３．７ｋｊ／ｍｏｌ。在此基础上给出了试验用钢的动态再结晶图，试验发现，试验用钢９００℃以上变形后，在奥氏体区冷过程中发生静态再结晶与晶粒长大，相变前晶粒尺寸与变形条件Ｚ的关系：ｄｒｅｃ＝２．８８×１０＾４×Ｚ＾－０．２０５。     

CERTAIN CRITERION FOR THE FORMATION OF AMORPHOUS SOLIDS

<正> 根据成核理论,当仅考虑均匀核化时,在过冷熔体中结晶成核率可用下式表示: I=N_v~°kT/(3πα_°~3η)exp(-16πα~3β/3T_rΔT_r~2) (1)其中α=(N_v~°)~(1/3)σ/ΔH_m,β=1ΔH_m/RT_m=T/T_m, ΔT_r=T_m-T/T_m.各参量分别表示:I,成核率(cm~(-3)·s~(-1);N_v~°单位体积中的分子数(cm~(-3);η,粘滞系数(P);σ,比表面能(cal·cm~(-2));ΔH_m,熔化时的焓变(cal·mol~(-1));N,阿佛加德罗常数;v,克分子体积;T,熔体温度(K);T_m,熔点(K);k,玻尔兹曼常数;R,气体常数;α_0,分子直径。     

GMAW熔滴过渡数值模拟的研究进展

熔化极气体保护焊熔滴过渡数值模拟作为焊接学科的前沿领域和研究的热点之一,近年来已经取得了较大的进展。本文在综述了熔化极气体保护焊熔滴过渡数值模拟理论发展的基础上,详细的分析了目前最为广泛用于熔滴过渡数值模拟的流体动力学理论建模的关键技术,并展望了未来的发展趋势。     

人工智能在冷轧带肋钢筋工艺参数优化中的应用

论述了人工智能在冷轧带肋钢筋工艺参数优化中的应用,首先利用神经网络建立起冷轧带肋钢筋工艺参数与产品抗拉强度之间关系的数学模型,然后用遗传算法对工艺参数优化。按优化后的工艺参数在某拉丝加工厂进行了大批量生产试验,产品的合格率达到98%以上,从而为控制冷轧带肋钢筋工艺参数提供了一条行之有效的途径。     

二辊轧机轧辊堆焊新技术应用

介绍了二辊粗轧机轧辊利用堆焊新技术开展堆焊修复试验与应用，并介绍了堆焊材料的选择、堆焊工艺以及取得的良好效果。     

1420铝锂合金的各向异性

以1420铝锂合金为对象，研究了轧板的各向异性在时效过程中的演化，并探讨了δ′相强化的各向异性机制。研究结果表明：随着时效的进行，合金的各向异性逐渐增强，合金的拉伸断裂特征也出现各向异性；且随着时效的进行，合金的断裂方式由沿晶分层断裂向沿亚晶分层断裂转变。可以认为，δ′相是通过共面滑移来软化滑移面、减少滑移系数目，从而增强合金的各向异性。     

EQUILIBRIA OF SYSTEM MoO_3-MoO_2-H_2O-H_2 AND PHASE DIAGRAM FOR SYSTEM Mo-O BETWEEN 400 AND 700℃

使用自行设计的受控气氛热重装置研究了MoO_3—MoO_2-H_2O—H_2系平衡.在P_(H_2O)/P_(H_2)从0.412至0.609,温度从400至534℃范围内直接测定了反应:MoO_3+H_2=MoO_2+H_2O(g)的平衡常数与温度间的关系为1gK_p=0.702-739.8/T获得298.15K下MoO_3标准生成焓及绝对熵分别为:-845.75kJmole~(-1)及78.1 J·K~(-1)mole~(-1) 实验表明,存在于MoO_2-MoO_3系中的一些Magneli相在本研究条件下不能作为热力学稳定相而存在.并绘制了400-700℃下Mo-O系相图.     

A study of the corrosion properties of plasma nitrocarburized and oxidized AISI 1020 steels

Plasma nitrocarburized AISI 1020 steels were oxidized for 15, 30 and 60 min to evaluate their corrosion and microstructural properties. After plasma nitrocarburizing for 3 h at 570°C in a gas mixture comprising 85 vol.% N₂, 12vol.% H₂ and 3 vol.% CH₄, the compound layer composed of ɛ-Fe_2–3(N,C) and γ’-Fe₄(N,C) phases and the diffusion layer above the matrix were observed. The top oxide layer, consisting mainly of magnetite (Fe₂O₄) and hematite (Fe₂O₃) phases, forms after post-oxidation treatment at 500°C. However, the oxide layer was severely degraded by spallation as a result of increases in post-oxidizing time. The difference in corrosion resistance should be attributed to the thickness of the top oxide layer, which was governed by post-oxidizing time.     

球磨改性处理对Ti0．9Zr0．1Mn1．5合金相结构及储氢性能的影响

系统研究了Ti0．9Zr0．1Mn1．5储氢合金经不同时间（t=0min，10min，30min，60min）球磨改性处理后对其相结构及储氢性能的影响。结构分析表明，Ti0．9Zr0．1Mn1．5合金在球磨改性处理前后均由单一的六方结构的C14型Laves相组成；随着球磨时间的延长，合金粉的平均粒度减小，并出现了部分团聚现象。储氢性能测试表明，铸态合金经4次吸放氢循环后活化，室温最大吸氢量和有效放氢量分别为209．3ml／g和157．6ml／g，放氢率为75．3％；随着球磨时间的延长，合金的活化性能得到改善，室温最大吸氢量和有效放氢量均先升后降，且都在球磨30min时达到相应最高值231．4ml／g和203．8ml／g，放氢率达到88．1％。由此可见，适当的球磨改性处理能有效地改善Ti0．9Zr0．1Mn1．5合金的综合储氢性能。