渗流作用下井筒周围岩石内弹塑性应力分布规律及井壁稳定条件

将地层岩石视为多孔介质,考虑了孔隙压力和渗流作用的影响,根据弹性理论和摩尔一库仑屈服条件以及岩石损伤后的软化特性,对井筒周围岩石进行了弹塑性力学分析,给出了井壁稳定条件。     

大曲率圆弧深拱平面弹性稳定分析

大曲率拱中,截面形心轴与中性轴不重合,其截面抗弯惯性矩与不考虑曲率影响的截面面积二阶矩有一定的差别;当截面尺寸相对拱弧长来说较大时,此时拱为深拱,剪切变形的影响不能忽略。基于此认识,提出了考虑曲率、剪切变形影响的深拱平面弹性稳定分析方法,讨论了圆弧拱在径向均布荷载作用下的面内稳定问题,导出了临界荷载计算公式,比较了不同理论结果的差别,给出了弹性失稳与塑性屈曲的临界系数和临界圆心角,得出了一些重要结论。     

大塑性变形工艺制备纳米晶过饱和固溶体的研究进展

合金在大塑性变形过程中能够形成纳米晶过饱和固溶体,呈现出不同于传统粗晶材料的微观结构和独特性能。近年来,纳米晶过饱和固溶体的形成机制及其热稳定性已成为国内外的一个研究热点。综述了大塑性变形工艺(如机械合金化法、高压扭转法等)制备纳米晶过饱和固溶体的研究概况,着重讨论分析了大塑性变形诱导纳米晶形成和固溶度扩展的几种机制及其局限性,简要介绍了纳米晶过饱和固溶体的热稳定性及其影响因素,最后对该领域今后的研究方向做出了分析和展望。     

Paradoxes of Severe Plastic Deformation

Severe plastic deformation (SPD) can lead to emergence of microstructural features and properties in materials which are fundamentally different from the ones well known for conventional cold deformation. In particular, the instances of unusual phase transformations resulting in development of highly metastable states associated with formation of supersaturated solid solutions, disordering or amorphization and their further decomposition during heating, high thermal stability of the SPD‐produced nanostructures, and the paradox of strength and ductility in some SPD‐processed metals and alloys are discussed.     

Mechanical stabilisation of retained austenite in δ-TRIP steel

Recent research suggests that extraordinary combinations of strength and ductility can be achieved in the so-called δ-TRIP steels, which contain ferrite, bainite and austenite. A part of the reason for the ductility of almost 40% elongation at a strength of some 900 MPa, is believed to be the optimal stability of the austenite to plastic deformation. We demonstrate here that mechanical stabilisation plays an important role in preserving the austenite to large plastic strains.     

矩形板在双向压力与剪切力复合加载下的塑性屈曲

依据Prandtl-Reuss增量理论和Mises屈服准则,推导出完整的复合加载平板的塑性分支屈曲微分方程。应用特征值分解技术,计算了双向压力与剪力复合加载铰支矩形板在塑性流动区和应变强化区的稳定参数,绘制了相应的塑性分支应力曲线。计算结果和理论分析有较好的相关性。     

Influence of external stress and plastic strain on morphological evolution of precipitates in Ni-based superalloys

An analytical method is proposed to investigate the morphological evolution of γ^′ precipitates in Ni-based superalloys. Two types of superalloys are considered with different ratio between the Young’s moduli of the precipitates and the matrix. Based on Eshelby’s equivalent inclusion theory and Mori–Tanaka’s mean field method the elastic energy is calculated as a function of the particle shape. The plastic strain induced by the formation of dislocation networks at the phase interface is taken into account. The results show that the external stress and the plastic matrix strain play a significant role for shape stability and the rafting mechanism of the precipitates. The elastic–plastic analysis provides a satisfactory explanation for all available experimental observations superalloys undergoing plastic creep.     

弯曲梁柱结构平面外失稳的研究

研究了两节梁组成的弯曲梁在受竖向集中载荷作用下的平面外稳定问题,通过建立每节梁临界状态下弯曲和扭转变形微分方程,根据变形协调关系,得出了一端固定一端悬臂的弯曲梁平面外失稳的特征方程,并以等截面等长度梁构成的弯曲梁为对象,探讨了弯曲梁上拱和上翘对其平面外稳定性的影响,以及抗扭刚度对稳定性的影响。结果表明,同样的载荷作用幅度和梁高度,采用上拱的弯曲梁比直梁具有更高的侧向稳定性,并且存在一个最佳的弯曲角度,而上翘弯曲梁的侧向稳定性要低于直梁的侧向稳定性。当弯曲梁上翘时,增大抗扭刚度可以提高侧向稳定性,弯曲梁上拱时,增大抗扭刚度却会降低其侧向稳定性。     

泡沫塑料的单轴压缩力学性能(上)

泡沫塑料具有优良的缓冲减震性能、良好的温湿度稳定性以及机械性能,仍是目前应用最普遍的缓冲材料之一,是大中型产品包装或高安全防护包装的首选.以EPS、EPP与EPE 3种具有较大性能差异的低密度发泡塑料作为主要研究对象,分析讨论了其在静态单轴压缩条件下的应力-应变关系及材料静压力学性能的影响因素.     

A Rate-Dependent Crystal Plasticity Analysis of Orientation Stability in Biaxial Tension of Magnesium

The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets.In this study,the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes.The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions.However,relatively stable orientations with zero rotation velocity and an overall convergence are found.They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction,depending on the slip modes involved in the deformation.It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension.The simulation results are briefly discussed in comparison with pre-existing experiments.     

扁拱的非线性稳定验算

本文研究用煤矿钻井法钻凿竖井时钢板-混凝土复合井壁内钢板的非线性失稳问题。研究的结果对国内实际工程中多次出现的内钢板“鼓包”现象给予了力学上的解释。文中相应地导出了非线性稳定计算的具体公式,编制了计算程序,并提供了六个有代表性的示例及计算结果。     

Correlation of austenite stability and ductile-to-brittle transition behavior of high-nitrogen 18Cr-10Mn austenitic steels

Ductile-to-brittle transition behavior of high-nitrogen 18Cr-10Mn austenitic steels containing different contents of Ni, Mo, Cu as well as nitrogen is discussed in terms of austenite stability and associated deformation-induced martensitic transformation (DIMT). Electron back-scattered diffraction and transmission electron microscopy analyses of cross-sectional area of the Charpy impact specimens fractured at −196 °C indicated that the brittle fracture planes were almost parallel to one of {1 1 1} slip planes and some metastable austenites near the fracture surface were transformed to α′-martensite by localized plastic deformation occurring during crack propagation. Quantitative evaluation of deformation-induced martensite together with characteristics of true stress-strain and load-displacement curves obtained from tensile and Charpy impact tests, respectively, supported that DIMT might take place in high-nitrogen austenitic steels with relatively low austenite stability. The occurrence of DIMT decreased low-temperature toughness and thus increased largely ductile-to-brittle transition temperature (DBTT), as compared to that predicted by empirical equations strongly depending on nitrogen content. As a result, the increased DBTT could be reasonably correlated with austenite stability against DIMT.     

离散动力系统稳定性的判别条件

本文讨论了一类多项式系统的D-稳定性,给出了一类离散动力系统稳定或渐近稳定的充要条件,解决了其稳定性的判别,推广了XycaИHOB和HИKИФopoBa等人近期获得的结果。然后引入辅助多项式,获得了多项式系统新的D-稳定性判据和Scher稳定性判据。     

钛酸钾晶须增强铝基复合材料的热循环尺寸稳定性

用挤压铸造工艺制备了钛酸钾晶须增强铝基复合材料,研究了其热膨胀系数和热循环尺寸稳定性。复合材料的热膨胀系数低于ZL109合金且随晶须含量的增加而降低。50℃~280℃热循环实验中,ZL109合金和复合材料中都观察到应变滞后现象。ZL109合金的热循环曲线具有最大的应变滞后和残余塑性应变,而30 vol%复合材料热循环前后几乎没有尺寸变化,具有很高的尺寸稳定性。最后,我们认为可以用热循环曲线来分析工作在变温环境下的结构材料的尺寸稳定性和失效。     

波纹腹板钢梁受弯稳定性研究

对于波纹腹板钢梁的稳定性从两个层次进行了探讨:弹性稳定和弹塑性稳定。其中,弹性稳定分析的重点是截面的翘曲常数,所提出的翘曲常数计算方法与其他研究者有所不同,通过有限元证明该方法具有较高的准确性,而且形式简单、应用方便。对于波纹腹板H型钢梁弹塑性稳定问题,采用大量的数值模拟,研究了不同的参数对稳定承载力的影响,包括梁的跨度、腹板波纹的波高、波纹倾斜段的倾角等。经过与有限元弹塑性稳定承载力模拟结果的对比,可以证实所提出计算方法是准确有效的,同时也比较了现有设计公式差异。     

Er对ZrCuNiAl非晶合金结构、力学性能、热稳定性及非晶形成能力的影响

以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x=0,0.5,1,1.5,2,2.5,3,原子分数,下同)系块体非晶合金为研究对象,通过改变微量元素Er的含量来研究Er对非晶合金的结构、力学性能、热稳定性及非晶形成能力的影响。结果表明:添加Er元素所制备出的试样都是完全非晶结构的合金。随着Er含量的增加,各试样的弹性模量呈现出先增大后减小,压缩塑性应变呈台阶式上升,x=0,x=0.5,x=1试样的塑性应变在4%的范围内波动;x=1.5,x=2,x=2.5试样的塑性应变在11%的范围内波动;x=3试样的塑性应变最高,其值为23.19%,弹性模量为37.76GPa,屈服强度为1604MPa,抗压强度为2068MPa,断裂强度为2060MPa;随着Er含量的增加,锆基非晶合金的热稳定性和非晶形成能力均先减小后增大。     

基于ADAMS的着陆器软着陆稳定性仿真分析

基于土壤Bekker承压模型、Janosi剪切模型和塑性大变形原理分别建立着陆器足垫-月壤相互作用模型及铝蜂窝的力学模型,在此基础上应用ADAMS软件构建准确的着陆器整体的多体动力学模型,并结合力-角稳定性度量法,为着陆器安全软着陆提出了合理的稳定性判据.针对不同月面环境与着陆器着陆初始状态,通过数值计算模拟了着陆器在刚性或模拟月面上的软着陆冲击过程,着重分析了月面着陆环境和初始条件对软着陆稳定性的影响,并获得了着陆器发生倾覆时不同着陆偏航角与极限水平速度关系的稳定性边界曲线.同时,根据其边界稳定性曲线,找出了最恶劣工况,即偏航角为22.5°时的工况所容许的极限水平速度最小,工况最为恶劣.以上研究为着陆器实现软着陆月面环境和初始条件的选择或类似的工程设计提供指导方案.     

Stability aspects of bulk nanostructured metals and composites

The requirement of thermal stability of nanocrystalline materials can be fulfilled with a composite approach. However, utilizing a two-phase approach includes additional constraints concerning the synthesis and processing, especially of massive nanostructured materials. Here, the potential of deformation processing for synthesizing nanoscale composite structures with uniform microstructures in bulk shape is analyzed for a series of Cu-rich alloys. The results are discussed with respect of governing materials properties that determine the feasibility of a composite approach in combination with severe plastic deformation to obtain massive nano-composite materials with high thermal stability.     

烧结Nd-Fe-B系永磁材料的稳定性研究现状

材料性能的稳定性是材料使用过程中的一个重要质量指标,对于功能材料更是如此.作为一种广泛应用的功能材料,烧结Nd-Fe B系永磁材料的稳定性就更加值得我们去研究和探讨.对该类材料的温度稳定性和化学稳定性进行了详细的阐述.     

一类固定时刻脉冲微分系统的Φ-变差稳定性

本文借助Φ-有界变差函数理论,以及一类不连续系统的Φ-有界变差解的稳定性理论,讨论了一类固定时刻脉冲微分系统的Φ-变差稳定性,给出了该类脉冲微分系统的Φ-变差稳定、Φ-变差吸引以及渐近变差稳定的定义,建立了该类脉冲微分系统Φ-有界变差解的Φ-变差稳定性和渐近Φ-变差稳定性的Lyapunov型定理.