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设计附录C 英文翻译振动故障分析中的微动磨损轴模拟器Young-Ho Lee *, Jae-Yong Kim, Hyung-Kyu Kim韩国原子能研究所，150 Dukjin-dong, Yuseong-gu, Daejeon 305-353,，出版于韩国。文章信息文章历史：收到于2008年7月11日 接受于2008年8月1日 公布于2008年8月15日 摘要最近，微动磨损模拟器被开发，以评估微动磨损的的核部件行为在高温和高压（高温高压）水条件下。经过500h后的测试，然而，四个振动轴中的两个骨折，其中一个轴通过螺栓被连接到一个试样座夹具。断裂表面研究同时使用光学显微镜（OM）和扫描电子显微镜（SEM）来确定未能启动和故障模式。据发现，失败开始于振动轴与燃料棒夹具架接触区之间和疲劳裂纹的传播，虽然它的传播很难证明这个结论，由于重氧化断裂面。然而，在失败的近地点，螺纹孔受到重复载荷，导致一个事实，试样架夹具进行了圆周运动来模拟振动运动。这表明，轴振动故障产生于腐蚀疲劳现象，因为微动测试被进行在高温度（320 C）和蒸馏水加压（15兆帕）的条件下。本文对失败和断裂机理的原因被揭示和讨论，利用光学显微镜和扫描电镜表面的破坏面和在振动轴与试样架夹具之间的接触区应力分析。最后，上述结果被应用到振动轴的设计变更。2008年爱思唯尔版权所有关键字：失效分析；微动磨损模拟器；振动轴；高温高压水；断裂面1简介机械结构在极端环境下通过材料的退化的破坏现象经常在各种行业中被报告。这些例子之一，是核电厂（核电站）。一般而言，核电厂的运作在高温度（320丙），压水（15 MPa）和放射性环境。这种状况在材料降解过程中必然导致如腐蚀，疲劳，辐照脆化，蠕变等现象。另一严重的结构材料的降解情况被称为由于主副冷却剂导致的流激振动相对细长结构（FIV），它在微动细长的损害结果之间快速流动速度结构及其支持结构。这些种类的微动已经损伤主要成分如对核电站的核燃料棒，蒸汽发生器（SG）的管和控制棒1。在这些项目中，我们实验室以研究和开发微动磨损机制和无缺陷的燃料组件（法），对核燃料棒微动磨损现象进行调查，一般来说，燃料组件由若干16x17 或17x 16的核燃料棒组成，其中外径9.5毫米，0.6毫米壁厚，约1 4米长度。由于受主冷却剂的FIV的现象，这些细长的燃料棒可以很容易地震动，因此，他们是几个格架结构，如图1所示的支持。每间隔电网结构单元由两个弹簧和4个韧窝。因此，核燃料棒依赖于一定量的的弹簧来保证它的形状和刚度。根据一项在高温条件下核电站运行的资料，由于弹簧放松，燃料之间的接触力杆和弹簧/韧窝正逐渐下降，此外，由于发车间弹簧/韧窝辐照脆化，弹簧刚度也逐渐增加。尽管弹簧是运作在其最初的阶段，但对接触面比较小幅度下滑燃料棒是不可避免的产生。下一个严重的FIV条件，接触力正逐步下降，最后，打开了一个缺口。该微动磨损模式可以改变，由随滑动磨损营运的撞击磨损手段时间决定。另一个重要的一点是，由于一个接触条件变化的燃料棒，核燃料棒的振动特性也发生了变化。因此，研究核燃料微动磨损机理棒核电站的运行条件是相当困难的。 Y.-H. Lee等人。 /工程失效分析16（2009）1238-1244 1239一台微动磨损试验机（FRETONUS核系统测试仪）的高温高压水条件垂直类型发展以评估核部件微动磨损性能2。经过500h后的测试，但是，两个振动其中有四个轴断裂，其中连接到试样座使用，如图2所示螺栓夹具。有必要评估其失败的原因，以及改善振动轴的设计，长期试验以确认可靠性微动磨损。在这项研究中，对于失败和断裂机制的原因，揭示并讨论了利用光学显微镜和扫描电镜对振动轴断口微维氏硬度和测量应力分析的结果。最后，上述结果应用到振动轴的设计变更中去。Wnzhng xnxWnzhng lsh:Shu do 2008 nin 7 yu 11 rJishu 2008 nin 8 yu 1 rZi wngshng tgng 2008 nin 8 yu 15 r图 1 一个核燃料组件，16x16或17x 17燃料棒，并组成若干格架组装示意图图2在高温高压水条件试验500h后，振动棒试样座轴与夹具和振动轴之间断裂组装方法示意图2断口分析2.1 光学显微镜观察振动轴是一个传统的高碳马氏体不锈钢做出（技能提升计440C），用于广泛的工具或刀片在相对腐蚀性气体中使用3。材料的化学成分和力学性能列于表1。图3显示了对振动轴断裂面分析的结果。由于高温高压的条件下，断裂表面氧化严重，而且很难通过光学显微镜观察金相获得证明。然而，预计该故障是在一轴和振动之间的接触区，因为这两个部分是通过使用一个如图2所示螺栓装配在微动磨损测试中，4轴的振动回旋在轴向方向为 200m，频率30赫兹，在一个90度角的排列执行器上。要生成一个圆周运动对燃料棒样本是作为一个实际经营核电站的燃料杆振动仿真视为保守，该执行器的两个信号波形正弦震动相位差设置为90度，如图4所示。试样的燃料棒振动的圆周运动，与燃油棒振动槽夹具持有人的接触区预计经历疲劳载荷。一般来说，如果是结构材料的疲劳加载条件下裂隙，条纹痕迹是明显的疲劳破坏可以找到证据表面上很容易断裂，。但是用扫描电镜对氧化振动轴断裂面进行了洗牙检查，可以预期没有任何痕迹的条纹，消除氧化过程（如酸洗）。2.2 硬度变化SEM观察之前，有必要审查振动轴力学性能的变化，因为它被暴露在高温高压水条件在500h内测试。因此，一个轴断裂的振动微维氏硬度测量，其结果如图5所示。很明显，微维氏硬度值根据振动轴暴露温度增加。这一结果符合很好地与回火温度体外对力学性能的SUS 440C 4。在这项研究中，高碳马氏体不锈钢有可能保留大量的未转奥氏体。据认为，可能会出现延迟转变温度波动在几个微动磨损试验，因为在320度的条件下实验500 h测试振动轴的材料对纾解压力的影响甚微。此外，它有可能发生氢脆现象影响其塑性。就是在热处理中导致马氏体不锈钢含有的氢元素以蒸馏水的形式散发。化学成分（重量）CMnSiPSCrMoFe1.01.01.00.040.03170.75Bal机械性能屈服强度抗拉强度伸长率弹性模量密度泊松比1280 Mpa1750 Mpa4%200 Gpa7.8g/cm0.3图3奥姆结果为振动轴断裂面：箭头指示的预期裂纹萌生区域。Y.-H. Lee等人。 /工程失效分析16（2009）1238年至1244年图4 通过使用两个驱动电磁在FRETONUS：注意执行器，该议案是善变的燃料棒由燃料棒机制调整振动的振幅和相位两个驱动器之间的差异。图5 测量结果的微维氏硬度根据暴露温度的振动轴。2.3 SEM结果 图.6显示了用电子显微镜镜扫描的断口形貌。很明显，断裂面几乎覆盖了氧化物，这是很难以察觉的痕迹，如条纹的疲劳破坏的证据。从仔细观察结果，条纹痕迹出现在外表面。另外，裂纹扩展跟踪被发现振动轴与夹具的燃料棒之间，即使其特点不能确定接触区 由于在高温高压水条件严重氧化。有趣的结果之一是，撞击磨痕出现在振动轴断裂面。这一结果意味着，影响两者之间的磨损断裂表面因为断裂振动轴不断来回运动，无轴驱动器故障。因此，预计疲劳条纹痕迹已经消失，被覆盖受冲击磨损议案和磨损碎片严重氧化，分别。因此，振动轴故障预计将发起一个在接触区域的接触疲劳的接触力，将逐渐减少。此时，初始裂纹扩展逐渐迟缓和接触条件轴之间的振动和燃料棒之间将改为夹具，如图7所示。因此，有必要审查通过使用新的裂纹应力分析，这可能验证了该振动轴的最大应力区在一个圆周运动的启动区。3应力分析 为了分析轴的振动的应力分布，在新的裂缝进行了有限元模型分析，直径10毫米，长度233.5毫米通过使用商用三维建模，如图9所示。气缸的约束在左侧位移为0.2毫米，在右边与连通区域电磁致动器是固定的。 4个节点的线性四面体分子的振动轴的有限元模型中使用包括约10,100 47,200节点和元素。所使用的弹性模量，屈服强度，密度和泊松比提升计划440C比例列于表。 1。商业代码，ABAQUS的标准版本。 6.6-3 5，是使用后处理的模式，以计算出振动轴应力。在振动轴应力分布表明，高浓度的压力在目前的螺纹孔和边缘作为如图9所示侧外表面。特别是，面对经横向应力的大小约 640兆帕斯卡。该值是对振动轴的屈服应力的一半。据认为，这是高应力集中受诸多因素影响的有限元分析保守的边界条件。因此，电镜扫描观测揭示了应激的立场浓度与裂缝产生痕迹的关系。根据这一结果，修改振动轴的设计，以减少接触面间的应力集中，增加疲劳寿命周期。4总结使用电子显微镜扫描有机物的微维氏硬度和有限元分析来调查模拟器中的微动磨损轴振动故障原因。由于大量氧化断口以及两者之间的断裂面磨损冲击失败后，很难利用光学显微镜观察获得金相证明 然而，失败是预期开始在振动轴之间的接触区和燃料棒夹具持有人的疲劳载荷条件下。轴的振动故障，预计将在启动接触疲劳在接触区域的接触力，然后由一个螺栓螺钉的压力，将逐渐减少。后初始裂纹扩展逐渐迟缓，对在新的裂纹萌生接触条件的结果改变一个侧面 外表面。从有限元分析结果，扫描电镜观测显示了在应力集中的位置与裂缝产生良好的痕迹。在此基础上修改对振动轴的设计，以减少应力之间的接触面和它的螺纹孔大小的降低，增加疲劳寿命 鸣谢这项研究在韩国科技部核武器的研发计划下进行。参考文献1Fisher NJ,Weckwerth MK,Grandison DAE,Cotnam BM.Fretting-wear of zirconium alloys.Nucl Eng Des 2002;213:79-90.2Kim HK,Lee YH Ryew SM,KIM CH,Kim MH.Development of vertical type high temperature and pressure fretting wear tester(FRETONUS).In:Proceedings of KSTLE spring meeting;2008.3Ojima M,Ohnuma M,Suzuki J,Ueta S,Narita S,Shimizu T,et al.Origin of enhanced hardness of a tempered high-nitrogen martensitic steel.Scripta Mater 2008;59:313-6.4Davis JR.ASM specialty handbook-stainless steels,ASM interational-The Materials Information Society;1996.5Hibbit HD,Karlsson GI,Sorensen EP.Analysis users manual(version6.6).USA;200- 66 -致 谢经过三个月的忙碌和工作，本次毕业设计已接近尾声，作为本科毕业设计，由于缺乏工作经验，有许多考虑不周全的地方。但在老师的指导下，以及同学们的帮助下，最终圆满完成了设计。感谢我的指导老师在我做毕业设计的每个阶段，从开题报告到查阅资料、设计草案的确定和修改、中期检查、后期详细设计、装配草图等整个过程中都给予了我悉心的指导。感谢大学四年来所有的老师，为我们打下机械技术专业知识的基础。 感谢和我一起在做毕业设计的同学们，他们在本次设计中勤奋工作，克服了许多困难来完成此次毕业设计。我们共同努力，使得毕业设计完成得很快并且很愉快。感谢学校微机房和图书馆对我们的特殊开放，让我们有足够的资料可供参考。本设计由于时间紧迫和本人对知识掌握不足，在设计上不很周详，许多应该考虑的因素，可能没在设计上体现出来。在这次设计过程中，我得到老师的精心指导和各方面的帮助，我再次深表谢意。Failure analysis of a vibrating shaft in a fretting wear simulatorYoung-Ho Lee*, Jae-Yong Kim, Hyung-Kyu KimKorea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong-gu, Daejeon 305-353, Republic of Koreaa r t i c l ei n f oArticle history:Received 11 July 2008Accepted 1 August 2008Available online 15 August 2008Keywords:Failure analysisFretting wear simulatorVibrating shaftHigh temperature and high pressure waterFracture surfacea b s t r a c tRecently, a fretting wear simulator was developed in order to evaluate the fretting wearbehavior of nuclear components in high temperature and high pressure (HTHP) water con-ditions. After 500 h tests, however, two vibrating shafts among four were fractured, whichwere connected to a specimen holder jig by using a bolt. The fracture surface was examinedusing both an optical microscope (OM) and a scanning electron microscope (SEM) to deter-mine the failure initiation and failure mode. It was found that the failure had initiated at acontact region between the vibrating shaft and the fuel rod holder jig and a fatigue crackwas propagated although it was difficult to prove it conclusively due to the heavily oxi-dized fracture surface. Near the failure locations, however, the thread hole was subjectedto a repeated loading due to the fact that the specimen holder jig had a circular motionfor simulating a vibration motion. This suggests that the vibrating shaft failure resultedfrom corrosion fatigue phenomenon because the fretting test had been performed at hightemperature (?320 ?C) and pressurized distilled water (?15 MPa) conditions. In this paper,the reasons for this failure and the fracture mechanisms are revealed and discussed byusing the OM and SEM results of the failure surface and the stress analysis of the contactregions between the vibrating shaft and the specimen holder jig. Finally, the above resultswere applied to a design change of the vibrating shaft.? 2008 Elsevier Ltd. All rights reserved.1. IntroductionThe failure phenomena of mechanical structures by material degradations in extreme environments have been reportedfrequently in various industries. One of these examples, is in nuclear power plants (NPPs). Generally, NPPs operate in a hightemperature (?320 ?C), pressurized water (?15 MPa) and radioactive environment. This condition inevitably results inmaterial degradations such as a corrosion, fatigue, irradiation embrittlement, creep, etc. during their operation. Anothersevere condition for degrading structural materials is known as a flow-induced vibration (FIV) of relatively slender structuresdue to the rapid flow velocity of primary and secondary coolants, which results in fretting damages between these slenderstructures and their supporting structures. These kinds of fretting damages have been experienced in the major componentsof NPPs such as the nuclear fuel rods, steam generator (SG) tubes and control rods 1. Among these components, in ourlaboratory, the fretting wear phenomenon of nuclear fuel rods has been investigated in order to examine and develop a fret-ting wear mechanism and a defect-free fuel assembly (FA), respectively. Generally, a FA consists of 16 ? 16 or 17 ? 17nuclear fuel rods, which have the following dimensions; 9.5 mm outer diameter, 0.6 mm wall thickness and about a 4 mlength. Because of the FIV phenomenon by a primary coolant, these slender fuel rods could easily vibrate, thus they aresupported by several spacer grid structures as shown in Fig. 1. Each cell of a spacer grid structure consists of two springsand four dimples. Therefore, a nuclear fuel rod is supported by a certain amount of spring force, which depends on the springshape and its stiffness. Under a high temperature in an operating NPP condition, however, the contact force between the fuel1350-6307/$ - see front matter ? 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.engfailanal.2008.08.013* Corresponding author. Tel.: +82 42 68 8761; fax: +82 42 863 0565.E-mail address: leeyhkaeri.re.kr (Y.-H. Lee).Engineering Failure Analysis 16 (2009) 12381244Contents lists available at ScienceDirectEngineering Failure Analysisjournal homepage: /locate/engfailanalrod and spring/dimple is gradually decreased due to a spring relaxation. In addition, the spring stiffness is also graduallyincreased because of an irradiation embrittlement of a spacer grid spring/dimple. Even though a certain amount of springforce is exerted on the fuel rod at its initial operation, a relatively small slip amplitude on the contact surface is unavoidableunder a severe FIV condition. Consequently, the contact force is gradually decreased and finally, a gap is opened up. Thismeans that the fretting wear mode could be changed from a sliding wear to an impacting wear with increasing operatingtime. Another important point is that the vibration characteristics of a nuclear fuel rod also changed due to a contactcondition change of a fuel rod. Therefore, it is quite difficult to examine the fretting wear mechanism of a nuclear fuelrod in NPP operating conditions.A vertical type of a fretting wear tester (FRETONUS, FRTtting Tester Of NUclear Systems) for a HTHP water condition wasdeveloped in order to evaluate the fretting wear behavior of nuclear components 2. After 500 h tests, however, two vibrat-ing shafts among four were fractured, which were connected to a specimen holder jig by using a bolt as shown in Fig. 2. It isFig. 2. Schematic views of the assembling method between the vibrating shaft and rod specimen holder jig and the fractured vibrating shaft after 500 htests at high temperature and pressurized water condition.Fig. 1. The schematic view of a nuclear fuel assembly that consists of 16 ? 16 or 17 ? 17 fuel rods and several spacer grid assembly.Y.-H. Lee et al./Engineering Failure Analysis 16 (2009) 123812441239essential to evaluate the reason for their failure and to improve the vibrating shaft design to confirm the reliability of thefretting wear tester for a long experiment. In this study, the reasons for the failure and the fracture mechanisms are revealedand discussed by using the OM and SEM results of the fracture surface, measurement of the micro-vickers hardness and thestress analysis of the vibrating shaft. Finally, the above results were applied to a design change of the vibrating shaft.2. Fracture surface analysis2.1. OM observationThe vibrating shaft is made of a conventional high-carbon martensitic stainless steel (SUS 440C) and this material iswidely used as tools or blades for use in relatively corrosive atmospheres 3. The chemical composition and mechanicalproperties are listed in Table. 1. Fig. 3 shows the OM result of the fracture surface for the vibrating shaft. Due to the HTHPwater condition, the fracture surface was heavily oxidized and it was difficult to obtain metallographic proof by using theOM observation. However, it is expected that the failure was initiated at a contact region between the vibrating shaft andthe fuel rod holder jig because these two parts was assembled by using a bolt as shown in Fig. 2. During the fretting weartests, four vibrating shafts were reciprocated in their axial direction with a range of 200lm, a frequency of 30 ?Hz and asinusoidal motion by two electro-magnetic actuators that were arrayed at an angle of 90o. To generate a circular motionof the fuel rod specimen which is regarded as a conservative simulation of an actual fuel rod vibration in operating NPPs,the phase difference of the sinusoidal waveform for the shake signals of two actuators is set to 90oas shown in Fig. 4. Whenthe fuel rod specimen is vibrated with a circular motion, the contact region of the vibrating shafts with the fuel rod holder jigis expected to experience fatigue loads. Generally, striation traces that are distinct proof for a fatigue failure could be foundeasily on a fracture surface, if the structural materials are fractured under the fatigue loading conditions. However, the oxi-dized fracture surface of the vibrating shaft was examined by using SEM without any cleanings because the striation tracescould be expected to remove by the oxide removal process (i.e. acid cleaning).2.2. Hardness variationBefore the SEM observation, it is necessary to examine the mechanical property changes of the vibrating shaft, because itwas exposed to the HTHP water condition during 500 h tests. So, a micro-vickers hardness of the fractured vibrating shaftwas measured and its result is shown in Fig. 5. It is apparent that the micro-vickers hardness value increased accordingto the exposed temperature for the vibrating shaft. This result corresponds well with the tempering temperature effectTable 1Chemical compositions and mechanical properties (room temperature) of a conventional high-carbon martensitic stainless steel (SUS 440C) 4CMnSiPSCrMoFeChemical compositions (wt%)1.01.01.00.040.03170.75Bal.Yield strengthTensile strengthElongationElastic modulusDensityPoissons ratioMechanical properties1280 MPa1750 MPa4%200 GPa7.8 g/cm30.3Fig. 3. OM result of the fracture surface for the vibrating shaft: arrows indicate the expected crack initiation region.1240Y.-H. Lee et al./Engineering Failure Analysis 16 (2009) 12381244on the mechanical properties of SUS 440C 4. In this study, the higher carbon martensitic stainless steel is likely to retain alarge amount of untransformed austenite. It is thought that a delayed transformation may occur as temperature fluctuationsin several fretting wear tests because the 500 h tests at about 320 ?C did not have a negligible effect on the stress relieving ofthe vibrating shaft material. In addition, it is possible that some loss in ductility may result from a hydrogen embrittlementthat is an important concern in martensitic stainless steels in a heat-treating atmosphere containing hydrogen in the form ofdistilled water.2.3. SEM resultsFig. 6 shows the morphology of the fracture surface by using SEM. It is apparent that the fracture surface was almost cov-ered with oxides and it is difficult to detect evidence of a fatigue failure such as striation traces. From a careful inspection ofthe results, however, weak striation traces appeared near a lateral outer surface. Also, a crack propagation trace was found atthe contact region between the vibrating shaft and the fuel rod holder jig even though its characteristic could not be defineddue to the severe oxidation in the HTHP water condition. One of the interesting results is that an impacting wear scarappeared in the fracture surface of the vibrating shaft. This result means that the impacting wear between the two fracturedsurfaces is generated after a fracture because the fractured vibrating shaft is continuously reciprocated by an electro-mag-netic actuator regardless of the shaft failure. So, it is expected that the fatigue striation traces had disappeared and were cov-ered by the impacting wear motion and by the wear debris with a severe oxidation, respectively. Consequently, the vibratingshaft failure is expected to be initiated by a contact fatigue at the contact region and then the contact force exerted by a boltFig. 4. Actuating mechanism of the fuel rod by using two electro-magnetic actuators in FRETONUS: note that the fuel rod motions are changeable byadjusting vibration amplitudes and phase difference between two actuators.Fig. 5. Measurement result of the micro-vickers hardness according to the exposed temperature for the vibrating shaft.Y.-H. Lee et al./Engineering Failure Analysis 16 (2009) 123812441241screw will be decreased gradually. At this time, the initial crack propagation is gradually retarded and the contact conditionbetween the vibrating shaft and the fuel rod holder jig will be changed as shown in Fig. 7. So, it is necessary to examine thenew crack initiation region by using a stress analysis, which could verify the maximum stress region of the vibrating shaftduring a circular motion.3. Stress analysisIn order to analyze the stress distribution that the vibrating shaft experienced during the initiation of the new crack, theFE model with 10 mm in diameter and 233.5 mm in length was created by using the commercial 3D modeler, SolidEdge V.19as shown in Fig. 8. The displacement of the constrained cylinder at the left side is 0.2 mm and the connected region with theelectro-magnetic actuator at the right side is fixed. The 4 node linear tetrahedron elements were used for the vibrating shaft.Fig. 6. SEM micrograph of the fractured vibrating shaft surface.1242Y.-H. Lee et al./Engineering Failure Analysis 16 (2009) 12381244The FE model consisted of about 10,100 nodes and 47,200 elements. The used elastic modulus, yield strength, density andPoissons ratio of the commercial SUS 440C are listed in Table. 1. The commercial code, ABAQUS Standard ver. 6.63 5, wasused to post-process the model in order to calculate the Von-Mises stress of the vibrating shaft. The Von-Mises stress dis-Fig. 7. Variation of contact condition between the vibrating shaft and the fuel rod holder jig after the retardation of initial crack propagation.Fig. 8. FE model of the vibrating shaft generated by using a commercial 3D modeler.Fig. 9. Model of Von-Mises stress distribution in the vibrating shaft.Y.-H. Lee et al./Engineering Failure Analysis 16 (2009) 123812441243tribution in the vibrating shaft showed that the high stress concentrations were present at the edge of the thread hole andthe lateral outer surfaces as shown in Fig. 9. In particular, the lateral face experienced stresses in the magnitude of approx-imately 640 MPa. This value is about half of the yield stress of the vibrating shaft. It is considered that these high stress con-centrations are affected by the conservative boundary condition of the FE analysis. Consequently, the positions of the stressconcentration are in good accord with the crack generation traces revealed in the SEM observation. Based on this result, thedesign of the vibrating shaft was modified to reduce the stress concentration between the contact surfaces and the threadhole size of it was decreased to increase the fatigue life cycle.4. SummaryThe reason fo