可靠度理论在降雨入渗边坡工程中的应用——以元磨高速K253+(400~560)边坡为例

边坡工程是岩土领域研究的热点和难点,边坡工程的状态涉及众多参数,具有不确定性,可靠度理论能利用数学方法将边坡工程中随机不确定的参数与工程的安全性有机联系。以元磨高速公路K253+(400~560)段为例,通过Bishop法,运用极限平衡理论建立极限状态模型,进而推导极限状态方程;并利用Geo-studio对不同时段中边坡的降雨入渗情况进行分析,选取最不利状态为风险评价对象进行可靠度分析,验证JC法在边坡工程风险评价方法的可行性;同时对影响可靠度指标的变量进行敏感性分析,建议在此类地层相似的边坡加固方面,应该以主要提高土层整体的内摩擦角为主,在此基础上采取提高边坡岩土的黏聚力的治理措施更为有效。     

层状岩体受压力学特征结构面效应数值分析

煤层底板岩体是沉积岩,具有显著的层状结构特点。为研究层状岩体压缩强度的结构面效应,通过FLAC3D数值软件,结合改进的遍布节理本构模型,建立层状岩体压缩数值模型,分析单轴、三轴压缩情况下的应力应变响应以及强度特征。研究结果表明：层状岩体压缩强度具有显著的结构面倾角效应。随着倾角的增大,层状岩体的压缩强度呈现先减小后增大的趋势。当结构面倾角为40＆#176;～80＆#176;时,岩体强度整体较低,破裂面主要沿结构面展开。数值试验和理论分析反映的岩体强度随结构面倾角变化规律一致。层状岩体弹性模量沿平行于结构面方向最大,而垂直于结构面方向最小,并随结构面与水平面之间夹角的增加而增大。     

利用网络监控发现供电故障

网络监控通过网管平台实时监测的网络设备、链路的状态,一些网络监控管理管平台还增加了对主机、服务器等硬件设备的监控功能。可管理的网络设备端口供电时为激活状态,掉电时为非激活状态,可以利用网络设备这一特性结合网络监控平台来监控机房市电供电情况。     

SiC MOSFET短路失效与退化机理研究综述及展望

SiC MOSFET可以大幅提升变流器的效率和功率密度,在高频、高温、高压等领域有较好的应用前景。但是,由于其短路耐受时间短、特性退化现象严重以及失效机理模糊等因素,致使SiC MOSFET的普及应用受到了限制。因此,探究SiC MOSFET短路失效与特性退化的机理,可以为SiC MOSFET器件的应用及其保护电路的设计提供指导,具有重要的研究价值。该文首先归纳SiC MOSFET的短路故障类型,并针对其中一种典型的短路故障进行详细的特性分析。在此基础上,论述SiC MOSFET单次短路故障后存在的两种典型失效模式,综述其在两种失效模式下的失效机理以及影响因素。其次,对SiC MOSFET经历重复短路应力后器件特性退化机理的研究现状进行系统的总结。最后指出当前SiC MOSFET短路失效与特性退化的研究难点,展望SiC MOSFET短路特性研究的发展趋势。     

基于正负序矢量解耦控制的七相感应电机容错运行

现阶段多相电机已被各个领域广泛利用,在发生单相甚至若干相开路故障后,可以在不增加多余硬件的基础上确保多相电机维持平稳的运行。为了解决定子开路故障时空间谐波磁场耦合对电机转矩脉动的影响,本文提出了一种基于正负序矢量解耦控制的电机容错控制策略。以七相感应电机单相开路为例,引入对应的附加条件重新计算剩余各相电流。电流环采用双向比例积分控制算法,通过仿真在多相同步旋转坐标系下实现了对电流的无静差控制。最后通过实验对所提出的算法进行验证,表明该策略能保证故障前后基波磁动势不变,使电机在故障下获得较好稳态和动态性能。     

Mechanism and prediction of failure of diamond films deposited on various substrates by HFCVD

Diamond films were deposited on the WC-Co cemented carbide and Si3N4 ceramic cutting tool substrates by hot-filament-assisted chemical vapour deposition. The adherence property of diamond films was estimated using the critical load (Pcr) in the indentation test. The adhesive strength of diamond films is related to the intermediate layer between the film and the substrate. Poor adhesion of diamond films to polished cemented carbide substrate is owing to the formation of graphite phase in the interface. The adhesion of diamond films deposited on acid etched cemented carbide substrate is improved, and the peeling-off of the films often happens in the loosen layer of WC particles where the cobalt element is nearly removed. The diamond films' adhesion to cemented carbide substrate whose surface layer is decarbonizated is strengthened dramatically because WC phase forms by reaction between the deposited carbon and tungsten in the surface layer of substrates during the deposition of diamond, which results in chemical combination in the film-substrate interface. The adhesion of diamond films to silicon nitride substrate is the firmest due to the formation of chemical combination of the SiC intermediate layer in the interfaces. In the piston-turning application, the diamond-coated Si3N4 ceramic and the cemented carbide cutting tools usually fail in the form of collapsing of edge and cracking or flaking respectively. They have no built-up edge(BUE) as long as coating is intact.As it wears through, BUE develops and the cutting force on it increases 1 - 3 times than that prior to failure. This can predict the failure of diamond-coated cutting tools.     

热力管线中不锈钢波纹管破裂原因分析

采用金相显微镜和扫描电镜分析了热力管线中不锈钢 波纹管破裂原因.该波纹管破裂特征与一般环向开裂不同，裂纹沿轴向扩展.分析认为，破裂 属穿晶应力腐蚀.引起应力腐蚀的介质是土壤中的氯化物，而应力则来自环向工作应力和冷 加工残余应力，而环向工作应力起主导作用。     

Failure analysis of beta-C titanium alloy high-pressure vessels

An attempt has been made to apply the linear elastic fracture mechanics concept to Beta-C titanium alloy pressure vessels that exhibited brittle fractures during hydrotesting. Based on the results of stress analysis on the real structures and fracture surface examinations, a stress-intensity factor,K _IC, was estimated. TheK _IC value of the material in the cracking direction was measured by a surface semi-elliptical crack method. It was found that theK _IC value of the material is very close to the estimated stress-intensity factorK _I during failure, which places the pressure vessels in a critical condition in that a small variation in flaw size may cause a catastrophic failure. A compromise must be made betweenK _IC and the required yield strength. In this restricted case, the yield strength of the material should be controlled in the range of 1150 to 1200 MPa to avoid brittle fracture and the possible occurrence of yield during hydrotesting. Control of microstructure and other mechanical properties is also discussed in this investigation.     

汽车渗碳齿轮用钢的成分设计

根据汽车齿轮的工作状况，阐述了汽车渗碳齿轮的失效形式和影响失效的因素，提出了汽车渗碳齿轮用钢成分设计的主要依据：齿轮渗层表面淬硬性和心部淬透性、渗碳齿轮心部的强度和韧性、钢的切削加工性、热处理质量及钢的冶金质量。     

模糊理论在液压系统故障诊断中的应用

通常液压系统的故障诊断大多是根据专家经验来进行的,往往有些故障模糊不清,加上其诊断准确性受专家经验限制,系统故障误诊现象时有发生。本文应用模糊综合评价理论和方法对液压系统故障进行智能综合评价。该方法具有错容性好、评价方法简单等特点,能达到准确、高效地判断液压系统故障的目的。