Failure Analysis of a Launch Vehicle Umbilical Shutter Mechanism During Vibration Qualification

Payload fairing (PLF) of a launch vehicle is exposed to harsh vibration environments due to jet noise during liftoff and in-flight aerodynamic noise. Accordingly, the systems mounted on the payload fairing are to be qualified for the vibration levels, predicted corresponding to the envelope of acoustic spectrums at critical instants of atmospheric flight. This paper presents a detailed study of a failure observed on the payload cooling umbilical system, mounted on the cylindrical portion of the PLF structure, during its design qualification vibration testing. The umbilical shutter inadvertently opened during the test. The vibration responses on the shutter, the dynamic behavior of the system, and the forces and moments on the mechanism are analyzed, and the physics of failure is understood. The design marginality is identified, and the shutter locking mechanism reconfigured to achieve the desired level of robustness in the system.     

Fatigue curves of a low carbon steel obtained from vibration experiments with an electrodynamic shaker

This paper presents an original contribution for the establishment of the high-cycle fatigue curves ε–N_f (strain versus cycle number to failure) of low carbon steel under vibratory testing. These curves are obtained thanks to a vibrational fatigue bench composed of an electrodynamic shaker and a closed loop vibration control system. The main advantage of this is the high frequency excitation compared to conventional fatigue systems. Three criteria based on strain gauge measurements are implemented to provide cycle numbers to failure N_f and to plot the fatigue curves. Furthermore, cycle numbers to failure are also assessed from two modal parameters (resonant frequency and loss damping factor) and compared with the results obtained from these three criteria. Some micrographies of fractured samples observed by scanning electron microscope reveal fatigue striations but also intergranular fracture.     

电动振动台模型辨识方法及其应用的研究

电动振动台是振动与冲击环境试验的主设备,对其模型的辨识与估计是开展振动控制技术研究和振动试验仿真的必要环节。本文基于电动振动台的动力学和电学耦合模型,提出了一种以冲击信号作为激励的振动台模型传递函数进行系统辨识与参数估计的方法。并应用其模型参数完成了冲击波形的生成。仿真结果与试验结果一致性很好,表明本文所提出的模型辨识方法有效可行,对电动振动台试验波形的生成具有一定的实用价值     

Ultrasonic Evaluation of Bolted Connections in Satellites

Prolonged periods from conception to deployment of a satellite can undermine a time dependent mission. Currently, the timeline for a new satellite to reach deployment is on the order of years. The need for a more efficient process is evident and has lead to innovations at every aspect of satellite design and pre-launch testing. One such example is the development of panels and components that are prefabricated for space flight and capable of assembly in a variety of configurations. However, all final systems regardless of component qualification must be validated for space flight. Current qualification testing can take weeks to years. An ultrasonic technique based on the energy of a transmitted wave across the connection is intended either as an alternative to traditional vibration/qualification testing or as a precursor to in-situ monitoring of panel-to-panel connections. Transmitted elastic wave energy is used to assess the integrity of the connection in reference to an initially established baseline. An experiment was conducted on a functional satellite to test the feasibility of deploying this test method under realistic circumstances. A second experiment was conducted to test the repeatability of the test method and to find an appropriate range of test parameters.     

Failure analysis of cast-on-strap in lead-acid battery subjected to vibration

Lead-acid batteries (LAB) are widely used in transportation sector for starting, lighting and ignition application. The possibility of vibration mode of failure occurs in this application due to wear and tear of the road. These vibration causes fatigue failure, particularly between the cast on strap and pillar post leading to loss of electrical connection. In this paper vibration test is conducted on a 12 V/75 Ah AGM Valve Regulated Lead-Acid Battery (VRLAB) used for above mentioned application in India. The test is carried out using Electrodynamic Vibration System model SD-10-240/GT500M/DA-10. The shaker is performed with a sinusoidal excitation, with an acceleration of 2.143G and a fixed frequency of 16.7 Hz. The peak to peak displacement is 4 mm. The deformation and crack propagation features on the surface and cross sectional area of pillar post and strap in both positive and negative group are observed with Scanning Electron Microscope (SEM). The material is yielded due to improper fusion between pillar post and strap which could not stand the vibration force. During vibration this region is vulnerable for fatigue failure.     

MIMO随机振动试验频响估计中激励和响应的同步方法

频响函数估计是多输入多输出随机振动试验控制算法中的必要环节。在振动环境试验中,通常不采集振动台的实际激励信号,而用实测的响应信号和计算机内存中的激励信号来进行系统频响函数估计。由于计算机内存中的激励信号与实际振动台上的激励信号之间在相位上存在着差异,从而导致实测的响应信号和计算机内存中的激励信号不同步。这给系统频响函数的估计带来了较大困难。为此,根据线性系统中激励和响应之间的关系,结合随机减量法,提出了一种二次相关法用于系统频响函数的估计。用该方法进行频响函数估计只需要采集响应信号。在三轴振动台上进行了对比试验,结果验证了本文所提出的二次相关法的正确性。     

力限控制在振动试验中的应用研究

传统航天器加速度响应控制振动试验是根据特定的加速度规范,控制振动台台面加速度,这种试验方法会在试件固有频率处产生过试验现象,力限振动试验可以有效地缓解这种过试验.本文基于简单二自由度模型给出了详细计算力限条件的方法,在此方法基础上,推导出了航天器试件支架与振动台台面间力谱和加速度谱,并对试件支架进行力限正弦振动试验和力限随机振动试验,实验结果表明：与传统加速度响应控制方法相比,基于简单二自由度模型力谱条件的力限振动控制试验能够更加真实模拟动力学环境,有效缓解振动过试验,可以为航天器振动试验提供很好的试验依据。     

Failure Analysis of AISI 304 Stainless Steel Sleeve Used in High-Pressure Hose Assembly of Actuation System of a Satellite Launch Vehicle

Hydraulic control actuation systems in launch vehicles use flexible hoses for transmission of forces to actuators at different locations. The hose ends are connected to the interface adapters by AISI 304 stainless steel sleeves. These sleeves are assembled to nipple end fittings of the high-pressure hose by a swaging operation to obtain leak-proof hose assemblies. The swaging operation is carried out at room temperature by a hydraulically operated swaging machine. Performance of the system as a whole requires strict adherence to the quality standards maintaining the critical interface dimensions within specified tolerances and ensuring the compression given to the swaged joint through the sleeve. If the joining forces are less, this can result in loose joints and gross leakage, whereas excessive compression can cause damage to the parts of the system namely the sleeve, stainless steel braid, PTFE or the adapter. The swaged joint is a single-point failure mode, indicating that a failure in the joint can lead to mission failure. It has to withstand harsh environments such as high pressure, low and high temperature extremes, fatigue loading due to pressure cycling as well as vibration. Therefore, as part of design verification, a detailed qualification plan has been prepared and the hoses were tested as per the plan. As per the test plan, these hoses undergo acceptance tests which include pneumatic and hydraulic pressure testing. During acceptance testing of hoses, one of the hose sleeves was found to be cracked. The cracking was observed after carrying out the pneumatic test when the assembly was being prepared for hydraulic pressure set-up. This paper describes the detailed metallurgical investigation carried out to understand the cause of failure and actions taken to avoid similar failures.     

钢丝绳隔振器综合力学性能试验研究

针对某电子器件同时承受强振动和过载的隔振设计要求，通过试验研究三种不同刚度的钢丝绳隔振器兼顾隔振、隔冲和抗过载的综合能力。试验结果表明，刚度较大的隔振器在承受高量级随机激励时具有一定的隔振能力、抗冲击和过载的性能较好。钢丝绳隔振器具有明显的非线性特性，只能对其进行特定条件下的参数识别。     

砖墙抗爆炸冲击震动效应模型试验研究

为研究砖墙在爆炸冲击震动作用下的破坏模式及阈值,据工程内砖墙实际情况建立简化的底部固定、周边无约束砖墙模型,在模拟爆炸震动冲击试验台上进行三方向单独作用的冲击试验,研究砖墙模型的动态响应及破坏时加速度峰值、作用时间。结果表明,遭水平向冲击时模型均表现为水平通缝破坏。破坏主要由受拉而非剪切所致。通过对试验结果分析,获得三个冲击方向独立作用下的破坏阈值。     

Failure analysis for vibration-based energy harvester utilized in high-speed railroad vehicle

This study aims to analyze the failure mechanism and improve the structural design of a vibration-based energy harvester (VEH), which intends to replace or extend the service life of batteries for condition monitoring systems of high-risk structures such as railroad vehicles and wind turbines. The observation of a fractured VEH under service condition of high-speed railway vehicle reveals several cracks originating on the surface of the VEH. A vibration test in the laboratory, conducted by using an electromagnetic exciter, identifies the resonant frequency, displacement-frequency, and acceleration-frequency plots of the VEH. A comparison of the surface fractured during vibration testing with that under service condition indicates that the major failure mechanism is static brittle fracture. The failure critical location and stress states are identified through frequency response analysis. Several measures are recommended to prevent the failure of VEHs, including selecting materials and redesigning the moving component of VEH.     

Reliability-based optimization of fibrous laminated composites

This paper is concerned with the optimum design of multiaxial fiber reinforced laminate systems under probabilistic conditions of loads and material properties. A multiaxially laminated composite is treated as a structural system with each ply contained in the composite as one element. The Tsai-Wu failure criterion is adopted as the limit state function of a unidirectional ply. It is assumed that the system failure occurs when any one of the plies in a laminate system fails. The multiple-check-point method is successfully applied to evaluate the system reliabilities of multiaxial laminates under probabilistic in-plane stresses. An optimization problem is defined to find the optimal number of fiber orientation axes, optimum orientation angles, and optimum ply ratios which yield the highest system reliability.     

基础位移激励下斜支承弹簧减振系统的振动

建立了基础位移激励下斜支承弹簧减振系统的几何非线性振动方程,研究了基础位移激励下斜支承弹簧减振系统的几何非线性振动问题。采用L-P法推导出了斜支承弹簧减振系统的非线性振动近似解,讨论分析了基础位移激励振幅、位移激励频率、斜支承弹簧倾角等因素对斜支承弹簧减振系统非线性振动的影响,得到了斜支承弹簧系统的减振效果优于垂直安装弹簧减振系统的减振效果,为斜支承弹簧减振器的设计提供了理论依据。     

Computational design of multiaxial tests for anisotropic material characterization

Although anisotropic materials provide more capabilities for mission‐ and application‐tailored design and functional flexibility to final structures than regular isotropic materials, the directional behavior of the anisotropic materials further complicates their inelastic and damage behavior. Such a non‐linear behavior can be effectively observed and characterized by multiaxial testing, but how to design a multiaxial test for material characterization given a specimen remains an untouched issue. This paper presents a methodology that numerically designs the loading path of a multiaxial testing machine to characterize anisotropic materials. The multiaxial test must be able to exhibit quantities used to characterize materials as distinctly as possible. The proposed methodology formulates distinguishability and uniqueness as such quantities by first analyzing the specimen on a continuum basis with finite element method and then applying singular value decomposition. Associating the distinguishability and uniqueness with the informativeness of the loading path, the design problem is formulated such that an effective loading path can be found efficiently by a standard optimization method. Numerical examples first investigate the validity of the distinguishability and the uniqueness as performance measures to evaluate loading paths. The efficacy of the proposed methodology has been then confirmed by analyzing it with and applying it to design problems. Copyright © 2007 John Wiley & Sons, Ltd.     

船舶管路中高频振动成因分析及控制策略研究

以分析管路减振工程实验实例为基础,阐述管路振动的特点,研究不同振动控制技术对管路中高频振动控制的功效,探讨针对管内流体激励产生的管路振动实施控制的策略。由此提出以控制振源为主的控制管路中高频振动的设计思想。     

不同频率激励下LY12铝合金悬臂梁的疲劳特性

为了研究激励频率对悬臂梁结构疲劳特性的影响,本文针对LY12铝合金悬臂梁在不同频率(139Hz、141Hz、143Hz)激励下进行了同一应力水平的振动疲劳试验。结果表明:该结构的疲劳特性在不同频率激励下存在差异。在激励频率高于固有频率振动时,结构疲劳寿命最长;激励频率低于固有频率振动时,结构疲劳寿命较短;在固有频率振动时,结构疲劳寿命最短。     

Application of continuum damage mechanics to vibration fatigue life prediction

It is pivotal to predict the multiaxial vibration fatigue life during mechanical structural dynamics design. An algorithm of the finite element method implementation for multiaxial high cycle fatigue life evaluation is proposed, on the basis of elastic evolution model of continuum damage mechanics. By considering structural dynamic characteristics, namely, resonant frequencies and mode shapes, this algorithm includes a modal analysis and harmonic analysis, which makes this different from existing fatigue life prediction methods. A 10% decrease in the resonant frequency is regarded as the failure criterion. A critical damage value was obtained, which indicates mesocrack initiation fulfilment. To validate the effectiveness of the algorithm, auto‐phase sine resonance track‐and‐dwell experiments were conducted on notched cantilever beams made of Ti‐6Al‐4V alloy. The life predictions are conservative and in good agreements with the experimental results, which are mainly distributed within a scatter band of 2. This investigation could provide technical support for structural dynamics design and the analysis of reusable spacecraft.     

土工二维振动离心机转臂的设计研究

土工二维振动离心机是岩土地震工程试验研究最有效的试验设备,转臂是支承和驱动吊篮、振动台、试验模型和配重等高速旋转并达到离心试验加速度要求的关键部件．常规土工离心机转臂结构已不满足二维振动试验工况要求．为了使离心机能在常规土工试验、一维振动试验和二维振动试验各工况下稳定运行,将其转臂设计成具有工字梁的焊接框架结构．在对该结构布局和工作原理介绍的基础上,针对某二维振动离心机技术指标,对转臂结构进行了优化设计,并对优化结构进行了力学分析．其结果表明,焊接的框架结构满足二维振动试验工况要求,是一种比较合理的土工二维振动离心机转臂结构．     

基于空气弹簧的振动离心机顺臂隔振技术研究

振动离心机是地震研究和飞行器离心振动复合环境试验研究的重要工具,顺臂振动是其重要的运行工况,而顺臂隔振是振动离心机在该工况下稳定运行的关键。在分析振动离心机顺臂振动工况的基础上,利用空气弹簧的动刚度小而轴向承载力大等特点,设计了一种安装于振动离心机转臂上可测不平衡力的顺臂隔振系统。基于隔振系统的力学模型,通过解析简化获得该系统的力传递率解析方程,并分析了影响该系统隔振能力的主要因素。针对某振动离心机,利用解析方程计算了其隔振系统的力传递率,并通过隔振系统力学模型对其传递力进行了仿真分析,理论计算及仿真所得的力传递率基本一致且均较小。结果表明：以空气弹簧为主体的顺臂隔振系统可有效隔离振动离心机的顺臂振动冲击,力传递率解析方程可用于隔振系统隔振能力评估计算。     

Vibration isolation of a symmetric rigid plate using struts under static and dynamic axial excitation

This paper presents vibration isolators in the form of post-buckled elastic clamped–clamped struts to relief the vibrating machines from the harmful effects of vibration. These vibrations are in most cases uncontrollable and lead to sudden failure. Therefore, mechanical engineers should control, isolate, and minimize such unwanted vibrations. A mathematical model is introduced consisting of pre-bent post-buckled struts acting as vibration isolators supporting a symmetric rigid plate. The model is subject to axial harmonic excitation at the base, and allowed to displace laterally with respect to axial center line of the isolated plate. The displacement transmissibility is the governing parameter of the isolator’s effectiveness at the mitigating vibrations transmitted from the base to the plate. The transmissibility is calculated over a wide range of frequencies and plotted in form of design charts. The transmissibility plots showed the ranges of frequencies, at which isolation can be maintained. The system resonance frequencies can be easily depicted from the design graphs. The present study reveals that at resonance frequencies the most effective transmissibility is well below unity. Vibration characteristics are determined under specific frequencies such that the physical behavior of the system can be thoroughly analyzed. All variables used are normalized, such that the results aren’t dependent on any material or geometric property, such as the modulus of elasticity of the material, section modulus of the used profile, or the length of the strut. In this way, the obtained results can be applied over a wide range of elastic materials, regardless of the material type or section properties.