Dimensional analysis of the impact toughness test for synthetic diamond grits

The method, in which a few carats of diamond grits are placed inside a capsule together with a steel ball, shaken for a number of times, and the unbroken ratio of the grits is then used to evaluate the quality of the diamond, has been well established for many years. However, the unbroken percentage, in an equivalent view, represents the impact toughness of the grits and cannot reflect the value of the crushing energy. Most of the previous empirical formulas obtained from experiments by scholars cannot be applied to practical tests. In this paper, a dimensional analysis was applied to investigate the impact toughness experiment, and the dimensionless relationship has been built among those variables such as the toughness index, the impact time, the impact frequency and the crushing energy per unit area. According to the results of a large number of experiments with synthetic diamond grits of mesh size 45/50, the percentage of the broken grits H is proportional to the impact time T^1.14 when the impact frequency is 2400 r/min, and the impact frequency f^2.576 when the number of impacts is 2000.     

复合岩体的TBM破岩机理数值模拟

为了指导TBM刀盘刀具的研制和不同地质条件下刀盘刀具的选型,TBM破岩机理的研究成为核心。在TBM滚刀的作用下,岩体中裂纹的生成、扩展和连接规律是深刻理解TBM破岩机理的前提,因此,TBM滚刀破岩机理的研究具有重要的工程应用价值。目前,TBM滚刀破岩机理的研究主要集中在单一岩体中,但在TBM施工过程中会遇到各种复杂的地质条件。笔者采用离散元方法,研究了复合岩体的破岩机理,复合岩体中岩片的形成不同于单一岩体,其裂纹的最终连接是由起裂于复合岩体交界面上的微裂纹的扩展,将两滚刀之间的赫兹裂纹连接,最终形成岩片。因此,在一定情况下复合岩体更有利于TBM隧道施工。     

石材加工用金刚石带锯锯条的应力分析

针对金刚石带锯锯条在使用中易产生疲劳裂纹这一问题,较详细地分析和计算了锯条的受力状况及内应力状况,并应用有限元法对锯齿局部应力进行了计算,最后提出了防止产生疲劳裂纹的有关措施.     

金刚石刀具前角对超精密切削过程影响的有限元分析

基于大变形有限元理论和更新的拉格朗日方程式,建立热机械耦合的平面应变正交切削模型,并利用通用的商业有限元软件,对6061铝合金的超精密切削过程进行有限元仿真．分析金刚石刀具前角对切削力、切屑变形、切屑根部最大应变、作用于前刀面最大压应力和切削温度分布的影响．结果表明：随前角由负向正变化,切屑厚度变小而长度变长、切屑的曲率半径随着变小,切削力和切屑一刀具接触面上最大压应力则随之下降,刀尖附近的切削温度逐步上升,但切屑根部的最大应变则保持不变．以此优选金刚石刀具前角．     

岩坡稳定性优势面分析法 ———以太湖度假区休体公园渔洋山边坡为例

运用优势面理论层次分析法,确定岩坡的控稳优势面,通过对太湖度假区休体公园渔洋山边坡 的研究得出F1和软弱夹层是控稳优势面,通过优势面组合分析,得出4组优势分离体,其中F1、软弱夹 层和边坡临空面组合为试算安全系数最小优势分离体。最后用Sarma法进行稳定性计算,得出各种优 势分离体组合模型在考虑地下水和地震加速度为0.15g的情况下均是不稳定的。结果表明,采用层次 分析法对岩坡稳定性进行评价的方法是可行的。     

Failure analysis used for remanufacturing of steel rolling components

The guide-pieces, used in the process line of steel roiling, were the important components. The guidepieces, which were slide contacting with the rolled-piece, had a high temperature and high speed. The wear was very serious. The results from failure analysis showed that there were three failure forms in the guide-pieces: the first was the wear during heat friction, the second was the heat fatigue under the cycle of deep heating and deep cooling, and the third was the impact rupture. Among them, the wear was the main reason. To the wear of guidepieces, there were four mechanisms, namely abrasive wear, adhesive wear, fatigue wear and corrosion wear. The failure analysis to the guide-piece laid the foundation for its remanufacturing.     

Failure analysis used for remanufacturing of steel rolling components

The guide-pieces, used in the process line of steel rolling, were the important components. The guidepieces, which were slide contacting with the rolled-piece, had a high temperature and high speed. The wear was very serious. The results from failure analysis showed that there were three failure forms in the guide-pieces: the first was the wear during heat friction, the second was the heat fatigue under the cycle of deep heating and deep cooling, and the third was the impact rupture. Among them, the wear was the main reason. To the wear of guidepieces, there were four mechanisms, namely abrasive wear, adhesive wear, fatigue wear and corrosion wear. The failure analysis to the guide-piece laid the foundation for its remanufacturing. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China     

Theoretical analysis on bending behavior of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

Ultrahigh toughness cementitious composites (UHTCC) obviously show strain hardening property under tensile or bending loading. The failure pattern of the UHTCC components exhibits multiple fine cracks under uniaxial tensile loading with prominent tensile strain capacity in excess of 3%, with merely 60 μm average crack width even corresponding to the ultimate tensile strain state. The approach adopted is based on the concept of functionally-graded concrete, where part of the concrete, which surrounds the main longitudinal reinforcement in a RC (reinforced concrete) member, is strategically replaced with UHTCC with excellent crack-controlling ability. Investigations on bending behavior of functionally-graded composite beam crack controlled by UHTCC has been carried out, including theo- retical analysis, experimental research on long composite beams without web reinforcement, validation and comparison between experimental and theoretical results, and analysis on crack control. In addition to improving bearing capacity, the results indicate that functionally-graded composite beams using UHTCC has been found to be very effective in preventing corrosion-induced damage compared with RC beams. Therefore, durability and service life of the structure could be enhanced. This paper discusses the development of internal force and crack propagation during loading process, and presents analysis of the internal force in different stages, moment-curvature relationship from loading to damage and calculation of mid-span deflection and ductility index. In the end, the theoretical formulae have been validated by experimental results.     

竖向荷载下弹性支承直墙拱反弯点理论分析

在工程实践中,直墙拱应用较多。由于拱脚位移的存在,合理假设拱脚约束为转角约束、竖向约束和水平弹性约束,应用力法推导出了在弯矩、剪力和轴力共同作用下直墙拱沿弧长的弯矩公式。研究了竖向均布荷载、竖向三角形荷载和竖向集中力荷载作用下,直墙拱沿弧长的弯矩分布及反弯点形成的规律;发现在3种荷载作用下,使得拱脚弯矩为零时的圆心角依次减小。取弹簧支座刚度为等效的下端固支、上端允许水平位移的直墙的抗推刚度,得出了随着直墙高度增加,圆弧拱拱顶弯矩增大而拱脚弯矩减小的变化规律。在直墙拱的设计中,建议选取合适的直墙高度和使得圆弧拱拱脚弯矩为零的圆心角大小,从而有利于提高结构抗弯承载力及拱脚抗剪承载力。     

Non-probabilistic fuzzy reliability analysis of pile foundation stability by interval theory

Randomness and fuzziness are among the attributes of the influential factors for stability assessment of pile foundation. According to these two characteristics, the triangular fuzzy number analysis approach was introduced to determine the probability-distributed function of mechanical parameters. Then the functional function of reliability analysis was constructed based on the study of bearing mechanism of pile foundation, and the way to calculate interval values of the functional function was developed by using improved interval-truncation approach and operation rules of interval numbers. Afterwards, the non-probabilistic fuzzy reliability analysis method was applied to assessing the pile foundation, from which a method was presented for non- probabilistic fuzzy reliability analysis of pile foundation stability by interval theory. Finally, the probability distribution curve of non- probabilistic fuzzy reliability indexes of practical pile foundation was concluded. Its failure possibility is 0.91%, which shows that the pile foundation is stable and reliable.     

Theory of random energy analysis for train derailment

1　INTRODUCTIONTrainderailmenthasbeenstudiedformorethanonecenturybothabroadandathome .Agreatnum berofachievementshavebeenmade ,however ,nosatisfactorysolutionhasbeenfound .Thebasicreasonliesinthefactthattherestillexistthreefundamentalproblemsinthecalculationoftrainderailment[1 4 ] :1)Propersolutiontotransversevibrationequationgroupsofthetraintracksystemcannotbeobtainedbyseparatelyestablishingthemofthetrainandtrack .2 )Thetransversetrackirregularityismostlytreatedastheexcitingsourceoftrans…     

梁弯曲和振动问题的一种新解法

将固体力学中具有两个广义位移的梁弯曲问题和振动问题的高阶方程组，转换成正则方程的形式，以矩阵分析为数学工具，求解此正则方程组得到他们的通解。与传统的分析方法相比，本文方法的求解过程清晰，并能得到通解的解析表达式，有一定的理论价值。     

按无量纲屈服准则分析正交异性板的极限荷载

为得到正交异性板极限荷载分析的简单实用的计算方法，建立了正交异性板的无量纲屈服准则，得出了用量纲力矩表示的正交异性板曲率速率公式。利用转轴公式和沿塑铰线曲率速率应满足的条件得出正交异性板中沿任意方向塑性铰截面弯矩的普遍算式，得出用无量纲力矩计算内力功的计算方法，最后根据能量原理得出正交异性板极限荷载上限估计的一般计算方法。并通过实例对理论公式做了验算。     

结构能量分析非线性地震反应的理论研究

采用能量分析方法，对抗震结构地震总输入及分配进行了理论研究，从地震动三要素，结构自身动力特性两方面探讨了抗震结构总输入能量及其影响因素．最后，通过能量的抗震设计准则检验了结构各层在大震下的安全性．计算结果表明，采用考虑和不考虑负刚度退化三线型恢复力模型，对结构破坏指数D影响较大．在结构分析中，若不考虑负刚度的影响，可能会掩盖结构的倒塌危险．     

Y岔圆形调压井洞室围岩稳定和锚杆支护分析

采用三维非线性有限元弹塑性损伤力学对琅琊山地下电站的Y岔圆形调压井的洞室围岩进行了分析计算,对各种工况下的围岩稳定和支护参数的合理性进行了评述.根据岩体损伤开裂后的应力应变关系,提出了变损伤刚度迭代计算方法,有效地反应了岩体损伤开裂后的围岩破坏特性;采用隐式锚杆柱单元模拟锚杆的支护效应,合理地反应了洞室开挖过程中的锚杆支护受力特性.通过对地下Y岔圆形调压井洞室围岩稳定分析计算,论证了该方法的可行性与合理性,为同类地下工程问题演示了一套完整的分析计算方法.     

某空腹式双曲拱桥承载力现场测试与分析

为检验在役双曲拱桥的承载能力与动力特性,对某净跨为36 m空腹式双曲拱桥进行了静载试验、动载试验及空间有限元分析。测试结构的静态应变、动态应变、挠度、自振频率、振型及加速度等结构反应,计算得出冲击系数。将实测结果与有限元结果进行对比分析,结果表明：应变校验系数为0.5~0.9,结构具有较好承载力。实测的各阶频率及相应振型与有限元计算结果比较吻合,桥梁整体竖向刚度较好。     

套管式地下换热器传热模型及其特性分析

通过对套管式地下换热器传热过程的分析,在已有套管式地下换热器传热模型基础上,考虑管内流动和传热,提出了集管内流动与土壤导热相耦合的传热分析模型,并利用有限元数值计算方法进行了传热特性的分析。讨论了埋管管径组合和流体流速对流体出口温度及单位埋管换热量的影响。此外,还系统地研究了连续运行模式和可变负荷运行模式的地下传热特性,阐述了地下换热器高效运行的控制策略和影响。     

Elastoplastic analysis for infinite plate with centric crack loaded by two pairs of point shear forces

The near crack line analysis method was used to investigate a crack loaded by two pairs of point shear forces in an infinite plate in an elastic-perfectly plastic solid, and the analytical solution was obtained. The solutions include: the unit normal vector of the elastic-plastic boundary near the crack line, the elastic-plastic stress fields near crack line, law that the length of the plastic zone along the crack line is varied with an external loads, and the bearing capacity of an infinite plate with a center crack loaded by two pairs of point shear forces. The results are sufficiently precise near the crack line because the assumptions of the small scale yielding theory have not been made and no other assumption have been taken.