超超临界锅炉含微裂纹HR3C受热面J积分数值模拟

采用有限元软件ANSYS对超超临界锅炉含径向裂纹的HR3C受热面管道在不同温度、压力作用下的应力应变以及J积分进行了数值模拟计算。根据裂纹尖端区域发生塑性应变分布情况,估算了塑性区域的大小。通过在裂纹尖端定义4条不同的积分回路,对J积分值进行了数值计算。结果表明,在裂纹尖端存在应力突变,易发生屈服;裂纹尖端塑性区的大小与裂纹区域特征尺寸属于同一个级别;压力和温度对断裂参数J均有影响,但压力的影响较大。     

断裂力学在电力工业部门的应用 试验方法概要

正如前九节所述,对有裂纹状缺陷的部件材料运用断裂力学来分析它的抗断裂性能时,一方面要了解裂纹尖端附近应力强度系数K、张开位移δ和J积分值的表答式,并计     

各向异性材料属性对发电机定子锥环模态分析的影响

使用不同材料模型对锥环模态分析的影响各不相同,对此进行了深入研究。以1 000MW汽轮发电机定子锥环为例,分别对使用各向同性材料模型及各向异性材料模型的锥环模态进行分析。结果显示,使用各向同性材料模型的计算数据无法与试验值相吻合,说明将锥环复合材料等效为各向同性材料是不合理的;使用各向异性材料模型的计算数据与试验值十分吻合,说明将锥环复合材料等效为横观各向异性材料是合理的。     

瞬态电热作用下金属材料断裂行为的仿真研究

带预制裂纹的金属试件在强脉冲电流和机械力的作用下,会产生裂纹扩展、裂尖熔洞和熔洞递进增大等一系列现象。为此,基于断裂力学理论模型和扩展有限元计算模块,提出了一种多物理场解耦分析的数值方法,通过有限元软件ABAQUS的扩展有限元XFEM来模拟裂纹的动态扩展,采用直接耦合和载荷传递耦合方式实现电-热-力多物理场之间的相互作用过程。应用上述方法模拟了带预制裂纹试件裂纹扩展、裂尖温度场的变化以及熔洞等动态损伤行为,最后通过裂纹的扩展量、熔洞的半径与实验结果的对比,验证了该方法的有效性。     

汽轮机转子弹性槽三维表面裂纹的边界元分析

本文在对弹性槽应力分布数值解分析的基础上,将弹性槽表面缺陷作为三维表面裂纹处理,进行线弹性(考虑塑性修正)断裂力学分析,用边界元法进行了权函数和应力强度因子的计算,得出了权函数及沿裂尖的应力强度因子分布(K-θ关系),并与转子中心孔表面裂纹计算结果进行了对比。分析了机组启停工况下转子不同表面裂纹可能的开裂方式。     

30Cr1Mo1V转子钢应力强度因子有限元分析

通过采用20节点solid186退化奇异单元,利用ANSYS软件,对三维断裂参量进行计算和分析,结果表明位移法和J积分法确定应力强度因子是可行的;对一定尺寸的紧凑拉伸试样三维裂纹进行分析,得出30Cr1Mo1V转子钢裂纹尖端KI随裂纹长度和载荷水平改变时的变化规律,为研究汽轮机转子裂纹扩展规律提供了合理、有效的方法.     

超声电机定子的简化复合梁模型裂纹扩展分析与实验

超声电机工作环境非常复杂,压电陶瓷极易发生断裂失效。为了分析研究电场、预压力及裂纹位置对压电陶瓷断裂失效的影响,将超声电机的定子沿周向简化为弹性复合梁模型,并在压电陶瓷上预制贯穿裂纹。首先用Ansys有限元软件对简化模型进行仿真,分析得到增大电场、预压力能增加裂纹尖端应力值,裂纹更加容易扩展。然后通过实验验证得到增大电场强度裂纹更加容易扩展。     

绕纤维环形裂纹界面处的应力奇异性

基于弹性力学空间轴对称问题的通解 ,研究了长纤维增强复合材料中绕纤维且垂直于纤维的环形裂纹位于界面处裂纹尖端的应力奇异性 .研究结果表明 ,应力奇异性特征方程与平面应变状态下相应模型的结果一致 ,只与Dundurs组合参数有关 ,材料性能对裂纹尖端附近奇异应力场的影响可用三个组合参数描述     

汽轮机转子材料蠕变裂纹的抗裂特性研究

本文对发电设备中关键部件汽轮机转子的抗裂性能进行了实验研究。在温度550℃下,用直流电位法进行了紧凑拉伸试样的裂纹启裂和扩展试验。通过理论分析和实验结果,得到了蠕变裂纹扩展的断续模型;得到了在高温蠕变条件下,描述裂纹启裂和扩展的合理参数;提出了“临界应变准则”,对估算汽轮机转子的工作寿命提供了依据.     

基于广义塑性模型的高心墙堆石坝反演计算分析

高堆石坝工程在填筑、蓄水和运行过程中,堆石料常经历复杂多变的应力路径,它所表现出的各向异性和颗粒破碎对其力学特性有明显的影响。采用现有的方法计算高堆石坝变形误差大,其主要原因是目前本构模型在反映堆石料的本质特性方面有待完善。本文构造了各向异性状态参量,定义了参考各向异性状态参数替代基于固定临界状态线的状态参数,可将各向异性、颗粒破碎、复杂应力路径的影响综合考虑到与参考状态线的相对空间位置中。基于参考各向异性状态参数,发展了考虑各向异性和颗粒破碎的堆石料弹塑性本构模型。最后,采用所发展的堆石料广义塑性模型MPZR对已建的糯扎渡高心墙堆石坝进行了应力变形有限元计算分析,并与堆石体内测点的监测值进行对比,验证了模型的可靠性和实用性。     

TLM simulation of electromagnetic wave propagation in anisotropic moving media

A transmission line matrix (TLM) model suitable to simulate the propagation of waves in moving anisotropic continuous media is presented. As is well known, an electromagnetic wave propagating in a general medium, moving with respect to its source, experiences a drag by the own medium, which involves a wave velocity dependent on the direction of propagation. In this work, we present a first approach for the case of uniform movement of an anisotropic dielectric medium with respect to an electromagnetic source. Although the technique allows for quantitative results, special attention is devoted to the simulation of wave fronts, distorted elliptical fronts, because a particular kind of ‘anisotropy’ appears, even in an isotropic medium. Copyright © 2005 John Wiley & Sons, Ltd.     

Advanced models for transient analysis of lossy and dispersive anisotropic planar layers

A new model is proposed for the transient analysis of the electromagnetic field propagation through anisotropic lossy and dispersive layers. The propagation equations of the electromagnetic fields are solved as a Sturm–Liouville problem leading to identify its dyadic Green's function in a series rational form. Then, the corresponding poles and residues are obtained and a reduced order macromodel is generated, which can be easily embedded within existing three dimensional solvers. The model is applied to lossy and dispersive anisotropic layers with differently polarized plane–waves. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterizations of fatigue and crack growth of ferroelectrics under cyclic electric field

The behavior of fatigue and crack growth of PZT based ferroelectrics under electric field was characterized. It is found that the crack growth shows an anisotropic effect. Under cyclic electric field, crack in the direction perpendicular to the polarization direction grows very fast, whereas in the direction parallel to the polarization direction no clear crack propagation is observed. Low cyclic electric field can also result in crack growth. The results also show that high electric field leads to degradation of the ferroelectric property more quickly than low electric field. The mechanism of the phenomenon is discussed.     

换流变压器极性反转试验的数值模拟

换流变压器绝缘结构中的油浸纸、纸板的电导率呈各向异性、非线性特性.从利用罚函数法获得的有限元状态方程出发,应用龙格库塔法对状态方程进行求解,计算了一个实际换流变压器模型在极性反转试验电压下绝缘结构中瞬态电场的变化.计算结果表明,各向异性非线性媒质中的电场分布与各向同性线形媒质中的电场分布有很大不同.为了准确的进行换流变压器绝缘结构设计,需要考虑媒质的各向异性非线性特性.     

Electromagnetic wave propagation in anisotropic metamaterial waveguides

In this paper, we present the formalism of the transverse operator method (TOM). A rigorous study of propagation in anisotropic and multi‐layer medium using the tensor character of the permeability and permittivity is presented. With the application of the Galerkin method, the propagating modes in metallic rectangular waveguides filled with anisotropic metamaterial are exploited. The results are compared with those previously published and show a good agreement. The complex modes have been obtained. The advantages of the techniques used in this paper lie in the proper analytical formulation of the problem studied, on the one hand, and the speed of convergence, on the other hand. TOM offers a fast convergence of the propagation constant. This shows the effectiveness of our numerical model. As such, the formulation of the transverse operator could be a useful tool for microwave engineers. This type of materials known as metamaterial is widely used and needed by industries and information technology, especially in microwave and radiofrequency devices such as patch antennas, antennas waveguides, resonators, circulators, isolators, phase shifters, and filters. Copyright © 2014 John Wiley & Sons, Ltd.     

Fundamental electromagnetic characteristics of magnetically anisotropic damper-wedges

A magnetically anisotropic conductor was applied to the damper-wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper-clad steel wires of 1.6 mm diameter aligned in the same radial direction. This means permeability in the direction of the wires, i.e., the thickness direction of the damper-wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good. To evaluate the electromagnetic characteristics, a trial damper-wedge, 1.2 m in length and with a steel space factor of 40 percent to total volume, was manufactured and maintained in a standstill model iron core. Test results were as follows when the magnetically anisotropic damper-wedge was employed. (1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the nonmagnetic or magnetic isotropic conductor is used. (2) The damper-wedge had a smaller skin effect for ac current than a conventional copper damper bar. The losses concentration for the damper system was relieved so that better machine performance under heavy load condition would be obtained.     

Measurement of propagation velocity driven by current microstimulation in the mouse auditory cortex in vitro

All sensory cortical areas, including the auditory cortex, are considered to be wired according to the same general laminar structure schema, commonly referred to as the canonical model of cortical circuitry. The auditory cortex in vivo , however, is functionally anisotropic; the functional organization along the tonotopic axis is qualitatively different from that orthogonal to this axis. In the current study, we examined whether the functional anisotropy of the auditory cortex observed in vivo is reflected in propagation activity driven by electric stimulation in the local microcircuitry in vitro . Using in vitro preparations of coronal and angled horizontal brain slices, we directly investigated their isotropic versus anisotropic properties using microstimulation and multi‐site recording with a multielectrode array substrate. Our results clearly demonstrated the isotropic properties of the circuits in slice preparations of the auditory cortex. Additionally, we found that driven by stimulation current in layer 4, the horizontal velocity of activity propagation in layer 2/3 was faster than the vertical velocity from layer 4 to layer 2/3 and the horizontal velocity in layer 4. On the basis of these results, we discuss the local network and its possible functions in the auditory cortex. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

各向异性非线性直流电场数值算法研究

油纸复合绝缘中的直流电场与交流电场在数值算法上有很大不同,其中油浸纸的层叠结构使其电导率呈各向异性。本文应用Ｇａｌｅｒｋｉｎ法建立了各向异性直流电场的有限元模型,通过一个算例验证了模型的正确性;针对材料的非线性特征,给出了合理的收敛判据和松驰因子;最后应用所建模型计算了一种典型的换流变压器绕组端部绝缘中的直流电场的分布,并与线性各向同性、非线性各向同性电场的计算结果进行了比较,所得结论与已有的试验结论一致。     

长期恒荷载作用下混凝土断裂过程的时变特性

大体积混凝土结构的时变断裂行为关系到结构的安全。为研究在长期恒荷载作用下混凝土的时变断裂特性,采用三种尺寸的楔入式紧凑拉伸试件,进行了荷载水平为85%最大荷载的恒定荷载作用下的时变断裂试验。试验结果表明,时变裂缝口张开位移、时变裂缝尖端张开位移与时变裂缝口张开速率均呈现出减速、稳定发展和加速破坏三个阶段的发展特征。与单调加载静态断裂试验相比,在试件尺寸相同时,时变断裂试验的临界裂缝口张开位移更大。时变裂缝口张开位移与时变裂缝尖端张开位移具有较强的线性相关性。裂缝张开位移与裂缝扩展长度间的几何关系较好符合铰链模型。     

Reliability Estimation for Large-Area Solder Joints Using Explicit Modeling of Damage

The issues of available cyclic fatigue models in life prediction of large-area solder joints using finite-element analysis (FEA) are discussed. In this paper, a new FEA approach called successive initiation (SI) is modified and introduced in conjunction with energy partitioning (E-P) damage model to resolve some of the issues with available damage models such as geometry and scale dependency and provide a solution to large-area solder joints. This new technique models damage explicitly, meaning that it separates initiation from propagation by monitoring the plastic and creep damage at the tip of the crack successively. The SI technique could be easily used with continuous loadings of different types and frequencies. The modeling approach is then implemented on a power device with large-area solder. Sensitivity study is conducted with the help of the experiment to determine the right initiation threshold for smooth crack initiation and propagation. The results of modeling are then compared with available experimental data for the same power device. The comparison shows that using the damage model constants generated for small solder joints such as ball-grid array or chip-scale package could significantly overpredict the life of larger area solders. New E-P damage model constants for large-area solder joints are obtained and presented by calibrating the modeling to the experiment.