Thermal fatigue estimation due to thermal stratification in the RCS branch line using one-way FSI scheme

The scheme and procedure for thermal fatigue estimation of a thermally stratified branch line were developed. One-way FSI (fluid and structure interaction) scheme was applied to evaluate the thermal stratification piping. Thermal flow analysis, stress analysis and fatigue estimation were performed in serial order. Finally, detailed monitoring locations and mitigation scheme for the integrity maintenance of piping were recommended. All wall mesh and transient temperature distribution data obtained from the CFD (computational fluid dynamics) analysis were directly imported into the input data of stress analysis model without any calculation for heat transfer coefficients. Cumulated usage factors for fatigue effect review with nodes were calculated. A modified method that combines ASME Section III, NB-3600 with NB-3200 was used because the previous method cannot consider the thermal stratification stress intensity. As the results of evaluation, the SCS (shutdown cooling system) line, branch piping of the RCS (reactor coolant system) line, shows that the CUF (cumulative usage factor) value exceeds 1.0, ASME Code limit, in case thermal stratification load is included. The HPSI (high pressure safety injection) line, re-branch piping, shows that temperature difference between top and bottom of piping exceeds the criterion temperature, 28°C, and that the CUF value exceeds 1.0. Therefore, these branch pipings require a detailed review, monitoring or analysis. In particular, it is recommended that the HPSI piping should be shifted backward to decrease the influence of turbulent penetration intensity from the RCS piping. This paper was recommended for publication in revised form by Associate Editor Jae Young Lee Kwang-Chu Kim received his B.S., M.S. and Ph.D degrees from department of mechanical engineering, Kyunghee University in 1993, 1995 and 2000, respectively. He has worked for Korea Power Engineering Company since 1995 and he is now a senior researcher. Dr. Kim’s research area includes CFD analysis, flow control, plant design and simulator. Jong-Han Lim received his B.S. degree from department of mechanical engineering, Chosun University in 1981, M.S. and Ph.D degrees from department of mechanical engineering, Kyunghee University in 1986 and 1992, respectively. He worked for Hyundai Motors Company during 1986-95. He is now a professor in department of mechanical & automotive engineering, Kyungwon University. Dr. Lim’s research interests are in the area of thermal flow, internal combustion and liquid atomization. Jun-Kyu Yoon received his B.S. degree from department of mechanical engineering, Chosun University in 1981, M.S. degree from department of mechanical engineering, Kyunghee University in 1987 and Ph.D degree from department of mechanical engineering, Myongji University in 2001. He worked for Hyundai Motors Company and Asia Motors Company during 1985–96. He is now a professor in department of mechanical & automotive engineering, Kyungwon University. Dr. Yoon’s research interests are in the area of flow control, heat transfer, liquid atomization, spray and combustion.     

Experiments on the thermal stratification in the branch of NPP

The thermal stratification phenomena, frequently occurring in the component of nuclear power plant system such as pressurizer surge line, steam generator inlet nozzle, safety injection system (SIS), and chemical and volume control system (CVCS), can cause through-wall cracks, thermal fatigue, unexpected piping displacement and dislocation, and pipe support damage. The phenomenon is one of the unaccounted load in the design stage. However, the load have been found to be serious as nuclear power plant operation experience accumulates. In particular, the thermal stratification by the turbulent penetration or valve leak in the SIS and SCS pipe line can lead these safety systems to failure by the thermal fatigue. Therefore in this study an l/lO scaledowned experimental rig had been designed and installed. And a series of experimental works had been executed to measure the temperature distribution (thermal stratification) in these systems by the turbulent penetration, valve leak, and heat transfer through valve. The results provide very valuable informations such as turbulent penetration depth, the possibility of thermal stratification by the heat transfer through valve, etc. Also the results are expected to be useful to understand the thermal stratification in these systems, establish the thermal stratification criteria and validate the calculation results by CFD Codes such as Fluent, Phenix, CFX.     

热循环下热障涂层结构不稳定性的数值模拟

针对多次热循环工作条件下热障涂层的结构不稳定问题,采用热弹塑性有限元方法,对不规则界面形貌的涂层结构进行安定性分析.分析了不同的BC层屈服强度对涂层循环不稳定性的影响.结果表明,在温度场和界面形貌相同的条件下BC的屈服强度决定系统的稳定性.该结果对分析涂层体寿命及失效机制有指导意义.     

Effects of area discontinuity at nozzle inlet on the characteristics of self-resonating cavitating waterjet

The current research on self-resonating cavitating waterjet(SRCW) mainly focuses on the generation mechanism and structure optimization. Researches relating to the influences of disturbances at nozzle inlet on the characteristics of the jet are rarely available. In order to further improve the performance of SRCW, effects of area discontinuity(enlargement and contraction) are experimentally investigated using three organ-pipe nozzles. Axial pressure oscillation peak and amplitude as well as aggressive erosion intensity of the jet are used to evaluate the effects. The results reveal that area enlargement and contraction affect the peak differently, depending on the inlet pressure, nozzle geometry, and standoff distance; while area contraction always improves the amplitude regardless of these factors. At inlet pressures of 10 MPa and 20 MPa, area discontinuity improves the peak at almost all the testing standoff distances, while this only happens at smaller standoff distances with the inlet pressure increased to 30 MPa. The capability of area discontinuity for improving the amplitude is enhancing with increasing inlet pressure. Moreover, the cavitation erosion ability of the jet can be largely enhanced around the optimum standoff distance, depending on the type of area discontinuity and nozzle geometry. A preliminary analysis of the influence of area discontinuity on the disturbance waves in the flow is also performed. The proposed research provides a new method for effectively enhancing the performance of SRCW.     

低雷诺数音速喷嘴临界背压比的实验研究

音速喷嘴是气体流量标准装置中最常用的标准流量计,喷嘴临界背压比直接关系到装置的准确度,喉部雷诺数低于2×105的喷嘴需要进行临界背压比测试。建立了一套基于喷嘴串联方法的临界背压比测试系统,将不易准确测量的质量流量转换为较易准确测量的压力,实现了临界背压比的准确高效测量。研究表明,低喉部雷诺数喷嘴临界背压比小于其设计值,且喉部雷诺数越小,临界背压比越低;另外可能出现一种"非临界状态提前"现象,引起临界背压比的进一步降低,且降低程度与喷嘴加工水平有关,更加说明了临界背压比测试的必要性。     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

电子电路中焊点的热疲劳裂纹扩展规律

采用试验方法研究表面贴装结构焊点在热疲劳过程中的疲劳裂纹扩展规律。试验研究中选用两种不同尺寸的焊盘及两种不同的钎料(包括传统的锡铅钎料和锡银铜无铅钎料SAC305),通过观测焊点截面上的裂纹萌生及扩展过程来研究焊点中的热疲劳裂纹扩展规律。研究结果表明,在热疲劳过程中,焊点经历热疲劳裂纹萌生和扩展的两个不同阶段,其中裂纹萌生所占的时间比例较小。在热疲劳后期,裂纹贯穿整个焊点从而造成焊点结构失效。研究发现,焊点结构失效过程中存在着两种不同的裂纹扩展模式,并且锡铅钎料焊点和SAC305无铅钎料焊点的裂纹扩展规律表现出明显的差异。另外研究还发现,当焊盘尺寸较小时,焊点的抗热疲劳性能相对较差;SAC305无铅钎料焊点的抗热疲劳性能优于传统锡铅钎料焊点。     

Numerical simulation of displacement instabilities of surface grooves on an alumina forming alloy during thermal cycling oxidation

Displacement instability of the thermally grown oxide (TGO) is a fundamental source of failure in thermal barrier systems. In this work, a finite element analysis has been performed to analyze the displacement instability occurring at a heat resistant metal with superficial TGO subjected to thermal cycling. Lateral and in-plane growth of the TGO which happens during high temperature is simulated by means of material property change from the substrate metal to the TGO. Most of the material properties including the TGO growth are based on the results experimentally obtained in-house. Results of the finite element analyses agree well with the experimental observation, which proves the accuracy and validity of this simulation. The technique will be useful for future work on more complicated phenomena such as deformation under thermo-mechanical cycling. This paper was recommended for publication in revised form by Associate Editor Maenghyo Cho Jun Ding received his B.S. degree in Mechanical Engineering from Chongqing Institute of Technology, China, in 2000. He then received his M.S. degree from Chongqing University, China, in 2004. Currently a Ph. D candidate at the Graduate School of Mechanical Systems Engineering at Chonnam National University in Gwangju, Korea, he is mainly working on the theoretical and numerical analyses of mechanical behaviors of various materials. Feng-Xun Li received his B.S. degree from the Department of Mechanical Engineering of Yanbian University, China, in 2005. He then received his M.S. degree from Chonnam National University, Korea, in 2007. He is currently a Ph. D candidate at the Graduate School of Mechanical Systems Engineering at Chonnam National University in Gwangju, Korea and is mainly working on the deformation mechanism of thermally grown oxide. Ki-Ju Kang received his B.S. degree in Mechanical Engineering from Chonnam National University, Korea, in 1981. He then received his M.S. and Ph.D. degrees from Korea Advanced Institute of Science and Technology in 1983 and 1988, respectively. Dr. Kang is currently a Professor at the School of Mechanical Systems Engineering at Chonnam National University in Gwangju, Korea. His laboratory is designated as a national research laboratory. His research interests include the optimal designs and manufacturing technologies of various types of porous cellular metal and mechanical behaviors of a thermally grown oxide at high temperature.     

The influence of oil additives on spread cracks in silicon nitride

The properties of ceramic materials (high hardness, high-temperature capability, low coefficient of thermal expansion) are of interest to rolling element materials. One of the most interesting materials is silicon nitride.The paper presents an experimental study of the influence of oil additives (Cl, S, P, cerium dioxide (CeO₂)) on spread cracks in silicon nitride. The additives Cl, S, P are bound in molecules in liquid form soluble in the base oil. The CeO₂ is purely in powder form in suspension. The use of CeO₂ powder was made based on the good results of polishing of silicon nitride. A ceramic angular contact ball bearing was modelled using a four-ball machine. Silicon nitride, -in diameters balls were artificially damaged with pre-cracks. Ring formed pre-cracks were propagated on the ball surface by a blunt impact load using a tungsten carbide ball under five various impacts.Rolling contact fatigue failure modes were studied under high contact stresses and speed. The surface of silicon nitride balls before and after failure was examined using scanning electron microscopy.The research of the present paper shows that fatigue failure under rolling contact loading is markedly sensitive on the size of pre-cracks and oil additives. Propagations of surface pre-cracks takes place under fatigue load. Primary and secondary surface crack propagation are described.     

磨料射流切割钻杆的喷嘴设计

在高含硫油气田中,为避免剪切闸板发生硫化物应力腐蚀开裂,采用前混合磨料射流替代剪切闸板切割钻杆.将S135钻杆51/2″作为研究对象,选取圆锥带圆柱段型喷嘴.通过分析磨料粒子在喷嘴内的加速过程,对喷嘴的结构参数进行了系统研究,得出啧嘴的加速性能和收敛性能达到最佳时的具体结构尺寸.并且计算出磨料颗粒与钻杆材料接触时的最大剪应力,校核了设定参数在理论上的可行性.     

基于ANSYS的蒸汽发生器机械堵管接触分析

为了分析蒸汽发生器传热管维修时机械堵管过程中的堵头材料受力与形变,研究堵头滑块滑动距离对套筒与传热管的径向膨胀及接触压力的影响,验证堵头结构参数设计的合理性,借助有限元软件ANSYS接触分析工具,模拟实际堵管过程中堵头滑块、堵头套筒与传热管及管板的接触情形,得到接触区域的径向位移与接触压力随时间变化图像。经仿真分析,证明堵头结构及堵管工艺设计合理,接触分析为堵管物理实验的开展与我国蒸汽发生器传热管堵管技术的开发奠定了基础。     

蒸汽发生器给水管嘴低周疲劳损伤分析评定研究

给水管嘴是蒸汽发生器关键部件之一,蒸汽发生器运行期间给水过程中的运行瞬态使得给水管嘴承受着复杂的疲劳载荷作用。利用有限元法对压水堆蒸汽发生器给水管嘴在典型运行循环下的累积损伤系数进行了计算,在不考虑热分层现象的情况下,分析了相关因素对给水管嘴疲劳寿命的影响。     

加工中心热误差补偿的研究

热误差是加工中心的最大误差源。通过对机床热特性的实验和分析，利用神经网络模型对热误差进行了补偿，取得比较好的效果。     

Effect of Thermal Cycling on Properties and Microstructure of SnAgCuCe Soldered Joints in QFP Devices

Increasing global concern about the environment is bringing regulatory (European directives) and consumer (green products) pressure on the electronics industry in Europe and Japan to reduce or completely eliminate the use of lead (Pb) in products. Among all lead-free solder alloys, SnAgCu solder system, which has better thermo-mechanical properties compared with those of SnPb solder, is proven to be one of the promising candidates for electronic assembly. Previous work also revealed that adding a small amou...     

数控机床热变形关键点的辨识与补偿方法的研究

阐述了数控机床热误差补偿的基本概念,提出了基于人工神经网络对热变形关键点进行辨识的通用方法,最后对补偿方法进行了讨论。     

压力容器非正交接管区表面裂纹疲劳扩展特性研究

对一台压力容器非正交接管区表面裂纹的疲劳扩展进行了试验研究和计算机模拟跟踪，获得了非正交接管区表面裂纹疲劳扩展的特性、形貌、速率及寿命。试验与计算机跟踪结果比较表明：在相同循环次数下，有限元的扩展深度大于实测值，但二者基本吻合，误差为10％左右；二者的裂纹扩展方向是不一致的。     

The effect of bridging on fatigue crack growth behavior in Aramid Patched Aluminum Alloy(APAL)

A new hybrid composite (APAL: Aramid Patched Aluminum Alloy), consisting of a 2024-T3 aluminum alloy plate sandwiched between two aramid/epoxy laminate (HK 285/RS 1222), was developed. Fatigue crack growth behavior was examined at stress ratios of R=0.2, 0.5 using the aluminum alloy and two kinds of the APAL with different fiber orientation (0°/90° and 45° for crack direction). The APAL showed superior fatigue crack growth resistance, which may be attributed to the crack bridging effect imposed by the intact fibers in the crack wake. The magnitude of crack bridging was estimated quantitatively and determined by a new technique on basis of compliances of the 2024-T3 aluminum alloy and the APAL specimens. The crack growth rates of the APAL specimens were reduced significantly as comparison to the monolithic aluminum alloy and were not adequately correlated with the conventional stress intensity factor range(ΔK). It was found that the crack growth rate was successfully correlated with the effective stress intensity factor range (ΔK _eff =K _br -K _ct ) allowing for the crack closure and the crack bridging. The relation between da/dN and theΔK _eff was plotted within a narrow scatter band regardless of kind of stress ratio (R=0.2, 0.5) and material (2024-T3 aluminum alloy, APAL 0°/90° and APAL±45°). The result equation was as follow:da/dN=6.45×10⁻⁷(ΔK _eff )^2.4.     

The effect of an oscillatory entrainment velocity on the film thickness in thermal EHL point contact

In this study, the mathematical model for transient thermal elastohydrodynamic lubrication (EHL) was established and the effect of tangential vibration on thermal EHL was investigated. The pressure calculation was carried out by a multi-grid technique, the elastic deformation was evaluated by a multilevel multi-intergration method, and the temperature was calculated by a single-direction sequential column sweeping process. The present study aims to explain the multi-dimple phenomenon observed experimentally by Ehret and Bauget [Proc Inst Mech Eng Part J: J Eng Tribol 2001; 215: 289–300]. The results show that a tangential vibration produces significant change of pressure and film thickness and it seems to be the most possible mechanism of the movement of multi-dimples observed by Ehret and Bauget [Proc Inst Mech Eng Part J: J Eng Tribol 2001; 215: 289–300]. Furthermore, the effect of the curvature radius, viscosity–pressure coefficient, load and the parameters of vibration was also investigated.     

Effect of rotation and thermal relaxation on Rayleigh waves in piezothermoelastic half space

The present paper represents an analysis of Rayleigh surface waves in a homogeneous, transversely isotropic, generalized piezothermoelastic half-space rotating with uniform angular velocity about normal to its boundary and subjected to stress free, electrically shorted/charge free and thermally insulated/isothermal boundary conditions. The secular equations for stress free, generalized piezothermoelastic half-space in closed form and isolated mathematical conditions are derived. The characteristics of surface waves propagating in generalized piezothermoelastic solid half-space and their dependence upon various geometric and physical parameters have been investigated. Finally, in order to illustrate and compare the theoretical results, numerical solution of various secular equations and other relevant relations are derived for cadmium selenide (6 mm) class material by adopting functional iteration scheme after employing Descartes’ algorithm to compute the characteristic roots of coupled differential equation system. The corresponding simulated results of various physical quantities such as phase velocity, attenuation, specific loss, frequency shifts and electromechanical coupling have been presented graphically for rotation and non-rotation cases. The study will be useful in design and construction of gyroscope, rotation sensors, temperature sensors and other pyro/piezoelectric SAW devices.     

Effect of fluid rheology on the thermal EHL under ZEV in line contact

In this study, thermal EHL performances in line contact under zero entrainment velocity (ZEV) are investigated theoretically by employing Newtonian and Ree–Eyring fluid models. From high to modest surface velocity, both rheology models predict large classical surface dimple and the depth of the surface dimple increases with decrease of the surface velocity. However, if the surface velocity is further decreased, a smaller centralized dimple is obtained by using Ree–Eyring model similar to those point contact oil film shape observed in optical interferometric experiments. At lower surface velocity, the Newtonian model shows too poor convergence to predict such film shape. At last, the influence of the applied load on the centralized dimple is also studied.