Investigation on the parameter determination and implementation of a dual-pulse shock test machine using a MR damper

The characteristics of a dual-pulse shock caused by an UNDEX (underwater explosion) are described through many standards. Shock signals required to evaluate the survivability of equipment by a shock test machine are also described. To generate various types of shock signals described in the standard, Shock test machines (STMs) require adjustment to various levels of shock occurring in surface ships and submarines. Therefore, the characteristics of each component of a STM should be changeable to generate various shock signals. This paper describes the concept of a STM that can generate various types of dual-pulse shocks. Moreover, this paper suggests an analytic method to determine the characteristics of each component of a STM to generate the required shock signal for various specimens. A method for adjusting the shock signals using a magnetorheological damper is specifically suggested. The results of dynamic analysis using the characteristic values of each component determined by this method shows that the required shock signal can be generated by this concept of the shock test machine.     

基于模糊理论的PMT水下防爆试验故障树分析

为解决光电倍增管（photomultiplier tubes,简称PMT）水下防爆试验系统的故障诊断问题以及故障发生概率存在模糊不确定性的特点,应用模糊集数学方法和可能性理论,把模糊数学和故障树模型相结合,提出一种基于三角形模糊数算法的PMT试验系统失效模式分析方法。根据试验系统工作原理,采用下行法建立故障树并对其进行定量分析,获得了顶事件的结构函数及多种失效模式,进而利用专家语言评价法,计算顶事件发生的模糊概率和各底事件的模糊重要度,得到了PMT试验中故障发生率较高的环节,最后对故障分析结果进行改进测试。结果表明,该方法能够准确地诊断出存在的故障,为PMT防爆试验系统进行故障诊断以及提高PMT保护罩的水下防爆性能提供参考依据。     

一种分析受爆炸冲击的水下圆柱壳结构强度的方法

根据小型水下圆柱壳状结构受爆炸冲击后散射现象严重的特点，提出一种新的冲击载荷的近似计算方法。首先把带加强筋的实际柱壳状结构简化为与实际结构外形尺寸和低阶振动模态都相同的理想柱壳，并将冲击波分解为不同频率谐和平面波的迭加，然后，采用耦合模态法分析受爆炸冲击水下圆柱壳状结构周围的散射场，求出圆柱壳状水下结构的表面总压，再通过积分求得表面平均总压，并探讨结构的弹性变形、材料特性对它的影响，最后用有限元软件分析某水下工程实际结构受到爆炸冲击后的弹塑性变形时间历程。结果表明，结构的弹塑性变形的时间历程明显落后于表面平均总压的时间历程，即前者的峰值到达时间迟于后者的峰值。工程实例分析的结果表明，本文方法具有物理概念清晰，运用方便，准确度较高的特点，可适用于水下圆柱壳状结构受到冲击后的强度分析。     

ExLO: A three-dimensional total shock physics FEM code

A unified shock physics code, ExLO, in which Lagrangian, ALE and Eulerian solvers are incorporated into a single framework, has recently been developed in Korea. It is based on the three-dimensional explicit finite element method and written in C++. ExLO is mainly designed for the calculation of structural responses to highly transient loading conditions, such as high-speed impacts, high-speed machining and explosions. In this paper the numerical schemes are described. Some improvements of the material interface and advection scheme are included. Details and issues of the momentum advection scheme are provided. Numerical predictions are in good agreement with the existing experimental data. Specific applications of the code are discussed in a separate paper in this journal. Eventually, ExLO will provide an optimum simulation environment to engineering problems including the fluid-structure interaction problems, since it allows regions of a problem to be modeled with Lagrangian, ALE or Eulerian schemes in a single framework. This paper was recommended for publication in revised form by Associate Editor Heoung Jae Chun Minhyung Lee. Professor in the Mechanical and Aerospace Engineering at the Sejong University, Seoul, Korea, holds a PhD from the University of Texas at Austin. His research interests include Lagrangian, Multi-material Eulerian and arbitrary Lagrangian-Eulerian (ALE) finite element methods for high strain rate of large deformation problems (eg, high speed impact/pene-tration, air blast/underwater explosion and bubble dynamics). Prior to joining Sejong University, he was with the US Naval Postgraduate School, Monterey, CA. as a research professor working on the UNDEX problems. He was also with the Institute for Advanced Technology, Austin, TX. (federated with Army Research Lab.) working on the highly transient dynamics.     

粗糙云模型与PROMETHEE的航发主轴轴承失效模式重要度评估

针对目前航空发动机主轴轴承关键失效模式确定困难的问题,提出了一种粗糙云模型与偏好顺序结构评估（PROMETHEE）的航发主轴轴承失效模式重要度评估方法。结合失效模式与影响分析（FMEA）方法,通过专家系统构建主轴轴承各失效模式的风险评估矩阵;运用粗糙集理论与云模型理论,将风险评估矩阵转换为粗糙云评估矩阵,描述专家评价信息中存在的主观性、模糊性和随机性问题;运用PROMETHEE计算各失效模式的流出量、流入量与净流量,根据净流量的大小对航发主轴轴承的6种失效模式进行风险排序,为制定预防措施和降低风险提供可靠依据。     

某水下热动力系统热爆事故的润滑失效原因分析

针对某水下热动力系统换速试验中多次出现的旋转燃烧室头部的热爆事故，基于流体力学、传热学以及数值计算的理论和方法，充分考虑了密封环节在整个系统中的工作环境变化，给出了一种关于旋转密封失效原因的工程分析方法。得出以下主要结论：(1)缓慢的系统升速过程不会引起摩擦面处温度的超调，系统的安全性可以得到保证；(2)过快的系统升速过程会造成摩擦面处的温度超调，超调量随换速过程的加快而增大，且较大幅度的温度超调会造成润滑失效，从而引发热爆事故。根据以上分析将系统过渡过程放慢，热爆事故得以有效地避免，多次热乍试验证明了文中理论和分析的正确性。分析方法和采取的措施已经应用于工程实践。     

纤维金属层板铆接剩余强度影响因素研究

为研究单搭铆接接头中纤维金属层板耦合损伤行为,运用金属硬化Johnson-Cook失效准则、纤维增强复合材料三维Hashin损伤准则、脱层B-K失效理论以及刚度退化失效准则建立了纤维金属层板铆接渐进失效模型,并结合实验验证了模型的合理性。考察了单搭铆接二次弯曲效应、层板铝合金体积分数、预紧力、层板孔边距对纤维金属层板铆接强度和失效模式的影响,为提高纤维金属层板铆接剩余强度提供可靠建议。分析结果表明：二次弯曲效应加速损伤发生,从而降低层板铆接强度,其中偏心加载可以削弱二次弯曲效应,更好地提高铆接强度;层板铝合金体积分数的增大能够提高层板铆接强度,但当体积分数大于50%时层板铆接比刚度和比强度反而下降;预紧力的增加能够提高层板铆接强度和增强层板损伤抗力;随着孔边距的递增,铆接剩余强度有所提高,破坏模式由灾难性拉断失效模式逐渐转化为理想的挤压失效模式,但当孔边距达到一定数值时,铆接强度不再明显提高,而失效模式也维持为挤压破坏。     

Modeling high-speed impacts and explosions with ExLO code

Korea has recently developed a total shock physics code, ExLO, based on the three-dimensional finite element method in order to calculate highly transient events involving large deformations. One special feature of the code is that the Lagrangian, ALE and Eulerian schemes are integrated into a single framework. The details of the numerical schemes are described in a previous paper [1]. In this paper, the modeling capability of ExLO has been described for two extreme loading events: high-speed impacts and explosions. Results of three-dimensional calculations for penetration of long rods and segments (L/D < 1) into thick target show a good agreement with experimental results and other finite difference solutions. Next, we include the free field air blast modeling by two approaches, one-dimensional spherical coordinates and three-dimensional rectangular coordinates. The predictions are compared with an analytic solution of air blast. For large scale simulations required for complex design problems, some advances in the field of parallelization and adaptive meshing are demanded. This paper was recommended for publication in revised form by Associate Editor Heoung Jae Chun Minhyung Lee. Professor in the Mechanical and Aerospace Engineering at the Sejong University, Seoul, Korea, holds a PhD from the University of Texas at Austin. His research interests include Lagrangian, Multi-material Eulerian and arbitrary Lagrangian-Eulerian (ALE) finite element methods for high strain rate of large deformation problems (eg, high speed impact/penetration, air blast/underwater explosion and bubble dynamics). Prior to joining Sejong University, he was with the US Naval Postgraduate School, Monterey, CA. as a research professor working on the UNDEX problems. He was also with the Institute for Advanced Technology, Austin, TX. (federated with Army Research Lab.) working on the highly transient dynamics. Wanjin Chung. Professor in the Die and Mould Engineering at the Seoul National University of Technology, Seoul, Korea, holds a PhD from Korea Advanced Institute of Technology. His research interests include the development of finite element methods for large deformation problems and its application to metal forming problems (eg, sheet metal forming, forging, high-velocity forming). Prior to joining Seoul National University of Technology, he works at Samsung Advanced Institute of Technology, Kiheung, Korea, as a senior researcher.     

大深度潜器冲吸复合清淤工具研制

坝面的裂纹、凹坑可能被大坝表面附着的泥沙覆盖,影响水下作业人员对大坝实际安全情况的判断。为大坝安全,水下检测时必须清除坝面泥沙,并保证坝面附近水域清澈。根据实际需求,设计出一种大深度潜器冲吸复合清淤工具,由水下电机、离心泵、射流泵、控制阀组、冲洗与抽吸复合喷头组成。对作业工具不同的工作模式进行了CFD模拟仿真,并开展了作业工具陆地环境的模拟试验。结果表明,所设计的装置可以有效实现不同工作模式的转换,已装备于我国首艘大坝检测载人潜水器。     

水下目标自主连续跟踪与定位算法研究

针对水下无人航行器进行纯方位目标运动分析时难以获取精确稳定的目标方位的情况,研究了实时有效的方位预处理方法。针对水下环境噪声起伏变化的特点,采用自动阈值检测和抛物线波束内插方法获取精确的目标方位;提出了一种预置跟踪算法实现对目标方位的连续检测跟踪,克服了方位历程中可能出现的野值和漏检现象,确保基于修正极坐标的扩展卡尔曼滤波算法(modified polar extended Kalman filter,MPEKF)正常工作。试验结果表明,该方法能够对移动目标进行运动分析,正确获取目标距离、速度信息,误差较小,具有很高的工程价值和军事应用前景。     

海上储油技术现状及水下无污染储油模式探讨

概括介绍了海上开发储油模式和水下储油技术发展现状,探讨了油水隔离置换水下无污染储油的几种模式,对近海边际油田的开发具有参考价值。     

多失效模式下电阻制动系统的可靠性建模与分析

针对电阻制动系统在多种失效模式下的建模问题,对电阻制动系统的建模方法和可靠性模型参数估计方法进行了研究,对电阻制动系统易损件及相应的失效模式进行了统计,提出一种基于故障树的多失效模式可靠性建模方法和基于最小二乘法和遗传算法的参数估计方法,利用系统整体及各部件的可靠度模型进行了可靠度分析和寿命预测。分析结果表明,考虑失效模式建立可靠性模型可以直观地揭示失效模式对产品可靠性的影响趋势,有利于产品的维护和寿命预计,为可靠性提高制定有效措施提供了依据。     

基于系统功能-结构-故障模型的[WTHZ]FMMEA[WTBZ]分析方法

针对传统故障模式及影响分析（failure mode and effects analysis,简称FMEA）不能识别装备或零部件的故障机理,其故障原因分析、故障影响推理及潜在故障模式识别能力较弱,故障信息描述不规范等导致的分析效率低、可信度差、分析结果重复使用性差等问题,提出一种新的故障机理、模式及影响分析（failure mode, mechanism and effects analysis,简称FMMEA）方法。首先,根据系统结构、功能及其内部物质流、能量流、信号流、部件故障等信息建立系统的功能-结构-故障模型;其次,采用模糊认知图推理分析各故障模式的传播途径及影响,得到规范化的故障模式及影响分析表格,可为系统的可靠性、测试性设计与分析提供基础数据;最后,以某燃油供给系统为例进行了FMMEA分析,验证了该方法的可行性和有效性。     

基于本体和FTF的风力发电设备维护优化

为满足优化风电设备维护计划的需求,提出了用本体将故障模式影响及危害性分析(FMECA)与故障树分析(FTA)相结合的方法,即FTF方法。该方法根据风电设备故障模式的特点,分四个步骤建立了风电FMECA领域本体,然后利用本体推导出故障树,计算故障树最小割集的风险顺序数以优化维护计划。该方法解决了FMECA不能研究多故障的问题,并实现了知识的共享、重用和推理,能有效提高风电设备维护效率。     

Efficient force prediction for incremental sheet forming and experimental validation

Incremental sheet forming (ISF) has been attractive during the last decades because of its greater flexibility, increased formability and reduced forming forces. However, traditional finite element simulation used for force prediction is significantly time consuming. This study aims to provide an efficient analytical model for tangential force prediction. In the present work, forces during the cone-forming process with different wall angles and step-down sizes are recorded experimentally. Different force trends are identified and discussed with reference to different deformation mechanisms. An efficient model is proposed based on the energy method to study the deformation zone in a cone-forming process. The effects of deformation modes from shear, bending and stretching are taken into account separately by two sub-models. The final predicted tangential forces are compared with the experimental results which show an average error of 6 and 11 % in respect to the variation of step-down size and wall angle in the explored limits, respectively. The proposed model would greatly improve the prediction efficiency of forming force and benefit both the design and forming process.     

多失效模式机械零部件可靠性灵敏度设计

基于应力-强度干涉模型,应用概率摄动法及四阶矩技术,讨论多失效模式下机械零部件可靠性分析问题.利用灵敏度分析的梯度算法,确定各个随机参数对机械零部件可靠性灵敏度.在随机参数前四阶矩已知的情况下,放松对随机参数的分布概型限制,使之更接近于工程实际,从而为多失效模式作用下机械零部件可靠性分析和可靠性设计等方面提供理论依据和方法参考.     

Failure mode maps in the thin film scratch adhesion test

The scratch test has been used to assess thin coating adhesion for some time now. In this test a diamond indenter is drawn across the coated surface under an increasing load (either stepwise or continuous) until at some load, termed the critical load, L_c a well-defined failure event occurs; if this failure event represents coating detachment then the critical load can be used as a qualitative measure of coating-substrate adhesion. However, it is well known that a range of possible failure modes can occur and only some of these are dependent on adhesion. Other failure modes which depend on plastic deformation and fracture within the coating, rather than any adhesive failure at the coating substrate interface, may be just as useful in the assessment of coating quality particularly for tribological applications. In this paper the load regimes in which the main adhesion-related failure modes (spallation and buckling) occur as a function of coating thickness will be presented for thermally grown oxide and sputtered nitride coatings. The origin of the observed failure modes and the use of the scratch test to assess coating/substrate adhesion in a more quantitative fashion is discussed in the light of these observations.     

MEMS可靠性与失效分析

主要探讨目前微电子机械系统（micro-electro-mechanicalsystem,MEMS）中采用的分别以费用和以失效分析,质量保证为主的两种可靠性分析方法,并介绍其他相关的分析方法;对国内外广泛运用的众多失效分析基本单元结构进行详细分析;叙述MEMS中各种不同的失效模式、失效机理、失效分析应用范围及采取的相应措施;并就MEMS可能出现的失效模式提出相关的微分析技术,为MEMS提供可靠性保障。有利于MEMS的可靠性设计。     

Identification of bearing dynamics under operational conditions for chatter stability prediction in high speed machining operations

Chatter is a major problem causing poor surface finish, low material removal rate, machine tool failure, increased tool wear, excessive noise and thus increased cost for machining applications. Chatter vibrations can be avoided using stability diagrams for which tool point frequency response function (FRF) must be determined accurately. During cutting operations, due to gyroscopic moments, centrifugal forces and thermal expansions bearing dynamics change resulting in tool point FRF variations. In addition, gyroscopic moments on spindle–holder–tool assembly cause separation of modes in tool point FRF into backward and forward modes which will lead to variations in tool point FRF. Therefore, for accurate stability predictions of machining operations, effects of operational conditions on machine tool dynamics should be considered in calculations. In this study, spindle bearing dynamics are identified for various spindle rotational speeds and cutting forces. Then, for a real machining center, tool point FRFs under operating conditions are determined using the identified speed dependent bearing dynamics and the mathematical model proposed. Moreover, effects of gyroscopic moments and bearing dynamics variations on tool point FRF are examined separately. Finally, computationally determined tool point FRFs using revised bearing parameters are verified through chatter tests.     

航空发动机诊断知识的动态获取与柔性诊断技术

针对军用航空发动机的状态监测与故障诊断问题，研究了航空发动机的诊断知识动态获取模型及柔性诊断技术。建立了可扩展诊断样本库，实现样本库中故障征兆和故障模式的动态增减，以增加系统的柔性和可扩展性；运用粗糙集理论对样本集进行处理，实现冗余属性的约简、冗余样本的去除及样本冲突的消除；用神经网络通过对处理后的样本集进行学习以动态获取知识，将实际诊断样本输入到训练好的神经网络模型即可得到诊断结果。整个诊断过程具有充分的可扩展性和柔性，当有新样本加入时，按上述步骤进行处理即可实现诊断知识的动态获取和诊断。算例表明了方法的正确性和有效性。