残余应力和粗糙度对叶片振动疲劳性能的影响

为了研究叶片表面完整性对其振动疲劳性能的影响,本文模拟分析了某型高温合金叶片在振动疲劳实验过程中的动力学应力响应,获得叶片共振时应力幅值随时间的变化规律,分析了残余应力和粗糙度对叶片振动疲劳寿命和疲劳极限的影响规律.结果表明:叶片共振过程中的应力响应幅值先增大后减小呈周期性变化,属于"拍"现象,满足关系σ=1 046sin(242.83t)sin(5 828t);叶片的振动疲劳极限和疲劳寿命均随残余应力和粗糙度的增大而减小,振动疲劳极限和残余应力之间的关系满足σfat=510.9-0.31-70.93σrest;而疲劳极限和粗糙度之间的关系则满足σfat=9.67R2roughness-70.93Rroughness+713.23.     

砖块打包机摩擦焊接臂的振动特性分析

目的 减小共振疲劳对摩擦焊接机构的影响,提高砖块打包机的可靠性、性能及使用寿命。方法 建立摩擦焊接机构模型,分析不同振动频率下的摩擦振动臂位移振幅与应力振幅。以理想焊接温度为基础,焊接时间为参数,确定振动频率与马达转速。结果 在所测试的频率范围内,随着振动频率不断增加,Z方向位移振幅较大于X、Y方向,Y方向应力振幅较大于X、Z方向,3个方向位移振幅与应力振幅均呈上升趋势。振动频率为440 Hz时,焊接时间至少需要2.0 s;振动频率为450 Hz和460 Hz时,焊接时间至少需要1.9 s。摩擦振动臂底端温度分布基本一致且均达到理想焊接温度,最终选取振动频率为450 Hz,马达转速设定为27000r/min。结论 最终确定的转速不仅需要满足共振疲劳影响最小化,还需结合砖块打包机实际焊接温度及效率因素,以此提高砖块打包机的可靠性与使用寿命。     

用Lab VIEW分析采煤机滚筒转动惯量对振动的影响

采煤机滚筒在工况确定情况下,直径一般是给定的,但转动惯量是可以调整的。通过改变滚筒的筒毂和叶片厚度来增大滚筒的转动惯量,使滚筒起到飞轮的作用,贮存能量,稳定转速,降低机器的振动。并利用LabVIEW平台和数据采集卡,在质量和转动惯量增量已知的情况下,对振幅的变化进行量化,测试出转动惯量对振幅的影响。结果表明,当转动惯量约增大11 %时,振幅最大可减小9 %;当转动惯量约增大23 %时,振幅最大只减小约11 %。以此作为改变和叶片尺寸,减小采煤机滚筒振动的依据,可对滚筒进行综合设计,从而保证持采煤机工作的稳定性。     

悬索承重梁索耦合结构的垂向运动动力学模型及主共振分析

该文建立了描述结构大变形和主缆初始曲率产生的几何非线性对系统动力学影响的悬索承重梁索耦合结构垂向运动动力学偏微分方程组。通过Galerkin方法一次截断把偏微分方程组化为时域上的两自由度常微分方程组。使用多尺度法得到简谐激励下常微分方程组主共振时的一次近似解。结果显示,当外激励仅激发低频或高频主共振时,系统的振幅随激励的幅值或激励频率的变化出现突然的跳跃。当激励同时激发低频和高频主共振时则有两种情况：1) 若固定高频激励幅值和频率,则系统的低频和高频振动成分的振幅随低频激励参数变化同时增加或减小;2) 若固定低频激励的幅值和频率,则系统的低频和高频振动成分的振幅随高频激励参数变化以相反的趋势变化。即高频振动幅值增大时,低频振幅减小,反之亦然。     

高精度测量用的空气弹簧减振平台的建立

一、概述近年来国际上发展了一种新的减振技术,即用气垫式空气弹簧作为隔振元件,用这种元件建立的平台,具有自振频率低、阻尼系数可改变、减振效果明显等特点。我们所建立的空气弹簧减振平台,经过两年来的考查证明,当外界干扰振动的频率f=3f_0时,可使外界干扰振动的振幅衰减80％—90％,各项性能良好。     

振动管外流动与传热实验研究及场协同分析

采用实验与数值模拟相结合的方法研究了振动管外的流动及传热特性,利用正交设计方法分析了振幅、频率等参数对换热性能的影响,得到了低频区内换热效果与振动参数间的拟合关联式,并基于场协同理论得到了管外近壁区的协同角余弦值随频率、振幅的变化规律。通过分析发现：振动强化传热的效果随着频率和振幅的升高而显著增强,共振工况下换热最强。对比不同管型的换热性能,沿椭圆管短轴方向振动的传热效果最好,圆管次之,长轴最差,证明管型也为影响振动工况下对流换热性能的重要参数。     

不平衡转子扭转振动特征的测试

采用ＤＫ－Ⅱ型扭振测量系统，进行了不同转速下不平衡转子的弯曲，扭转振动的联合测量，得到了存在不平衡的故障转子的扭振特征和变化规律，即当转动频率小于一阶扭振固有频率时，扭振幅值随转速的升高而增大；当转动频率大于一阶扭振固有频率时，扭振幅值随转速的高而减小；当通过扭振界转速时，扭振相位翻转１８０°。     

疲劳振动对瓦楞纸板承载能力与缓冲性能的影响

对瓦楞纸板进行疲劳振动试验,测定分析振动次数、加速度对瓦楞纸板承载能力、缓冲性能的影响,并与未经振动材料进行比较.结果表明,随着振动次数、振动加速度的增加,瓦楞纸板剩余屈服应力减小,缓冲系数增大,其中在小应力阶段缓冲系数变化不大,在大应力阶段,缓冲系数显著增大.进行频率20Hz、加速度为2.0g、80000次振动试验后,瓦楞纸板承载能力下降了38.88%,静态应力0.012MPa下的缓冲系数增大了46.37%.缓冲包装设计时,应考虑疲劳效应对瓦楞纸板衬垫缓冲性能的影响,以确保实现预期缓冲包装的要求.     

斜拉索风致振动疲劳的分析

本文研究了斜拉索的风致振动疲劳问题。首先,假设在任一应力循环周期内, 考察点的最大与最小应力之差符合Rayleigh分布。其次,推导出斜拉索的疲劳可靠度计算公式;根据桥梁结构的疲劳目标可靠度, 给出简单明了的斜拉索疲劳寿命计算公式。第三,在目前既有研究的基础上,进一步评价不同的风攻角对疲劳可靠度和疲劳寿命的影响。最后,论文以松花江斜拉桥中的斜拉索为实例,计算分析了在不同的风攻角情况下斜拉索上各节点应力时程和位移时程,并得出在不同风攻角下各节点的应力响应根方差。于是,根据最危险工况作为疲劳寿命评估的考察点计算出斜拉索的最短疲劳寿命,以验证其风致振动疲劳的性能。     

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。     

基于疲劳寿命的旋翼气动弹性多目标优化研究

基于Hamilton原理基础上推导了旋翼桨叶有限元动力学模型和疲劳寿命计算模型。以动力学特性的固有频率,自转惯量为约束,以剖面特性参数的挥、摆、扭刚度及桨叶线性密度为设计变量,进行最小质量及最大疲劳寿命的多目标优化。采用满足溢出分析的优化算法（Satisficing Trade-off Analysis）。结果在满足各约束条件下,实现旋翼桨叶质量减少7.27％,疲劳寿命循环次数由3.98 108次到4.73 108次,寿命提高了18.7%,优化效果明显。     

A study of the low-cycle fatigue failure of a galvanised steel lighting column

This paper presents the results of a low-cycle fatigue test on a galvanised steel lighting column. The aim of the test was to simulate the behaviour of the column undergoing large amplitude resonant vibration caused by wind. A metallurgical study of the failure revealed the significant role of the galvanised coating in the failure process. Results from a detailed 3D finite element model are also used to explain the failure mechanism.The swage joint in the column was confirmed as a failure location by both experiment and finite element analysis. This in itself is not surprising and the position of the fatigue failure is consistent with those observed in the field. Of more importance is the fact that the experiment shows that galvanising can lead to premature failure of such columns. This is a highly significant conclusion as it implies that improving the weld detail in an effort to improve fatigue life may be ineffective for lighting columns coated in this manner.Given the detrimental effect of galvanising on fatigue performance and the fact that the most severe corrosion will be on the outside of columns, then the fatigue life of such structures may benefit if the inner surface was not galvanised in high stress regions. An alternative improvement would be the use of a galvanising coating with higher toughness and less susceptibility to cracking and damage.Attention is drawn to the need for a better understanding of the fatigue performance of galvanised steel columns resulting from large amplitude wind induced resonant vibration. The approach adopted so far for lighting column resonant vibration, has been to try and avoid it. While this is a laudable objective, clearly this has not always been possible, as designs push the limits permitted by Codes of Practice.     

Vibration fatigue analysis for multi-point spot-welded joints based on frequency response changes due to fatigue damage accumulation

This study conducted a vibration fatigue analysis that considered changes in frequency response resulting from the cumulative fatigue damage to multi-point spot-welded joints in an automotive body. The S–N curve was obtained using a fatigue test for tensile-shear spot-welded (single-point) joint under constant amplitude load and a finite element analysis based on the Rupp/LBF model. In addition, a vibration fatigue analysis that considered changes in the frequency response due to the fatigue damage was conducted on multi-point spot-welded joints. The fatigue life of the spot-welded joints was computed by combining the transfer function, the S–N curve of the tensile-shear spot-welded joint and the input PSD. Furthermore, a vibration fatigue test using an electronic dynamic shaker was conducted to verify the results of the analysis. The fatigue life by the proposed method was in conformance with the test results.     

Vibration analysis for failure detection in low pressure steam turbine blades in nuclear power plant

This paper presents an investigation of the failure of a low-pressure steam turbine blade in a pressurized water reactor (PWR) nuclear power plant. The dynamical behaviour of the blade is analyzed theoretically and experimentally. A three-dimensional finite element model is used to predict the blade resonances in the operational speed range. Natural frequencies and mode shapes of the blade at static condition are obtained, then natural frequencies of the blade at different rotational speeds are calculated with consideration of centrifugal force and steam flow forces. A Campbell diagram is plotted to predict the likely operational conditions that may cause resonant vibration of the blade. Vibration tests are conducted to determine the vibration characteristic of the blade. It is found that the 2nd natural frequency of the blade is very close to the 9th rotor speed harmonic. The experimental natural frequencies are in good agreement with the finite element predicted values. Fretting wear is observed at the concave root surfaces of the blade trailing edge caused by resonant vibration. The fracture surface of the cracked blade shows typical fatigue patterns. The fretting wear characteristics in the crack initiation regions are observed.Stress distribution of the blade at the 9th harmonic frequency is analyzed using an elastic-plastic finite element model. Fretting fatigue experiments indicate that the fatigue life of the blade is greatly reduced due to fretting wear. The results of the investigation show that the failure of the blade is attributed to a combination of high cycle fatigue (HCF) and fretting wear.     

大力矩径向驻波型超声波电机有限元分析与实验研究

提出了一种大力矩径向驻波型超声波电机,在实现电机大力矩输出的同时保持结构紧凑的特点。首先设计并分析了电机的结构和工作原理,采用有限元法分析了电机定子的振动特性。接着制作了超声波电机样机,样机直径为32 mm。采用激光测振仪测量了定子的共振频率及径向振动的振幅,测量结果与理论分析结果相吻合。最后,搭建了电机输出特性测试平台,测量了电机在不同电压下的转矩-转速特性。实验测试结果显示,定子工作模态的共振频率为73.3 kHz,当施加的电压幅值为100 V、频率为74 kHz时,电机的空载转速为45 r/min,堵转力矩达到0.41 N·m。与其他同尺寸的超声波电机相比,所提出的径向驻波型超声波电机具有更大的堵转力矩。     

考虑结构裂纹扩展的振动疲劳寿命计算方法

工程实践中任何结构都存在不同程度的裂纹损伤,振动激励下动响应与疲劳裂纹扩展之间互相耦合,直接影响结构振动疲劳寿命.为了考虑结构振动疲劳耦合效应对疲劳寿命的影响,提出了一种考虑结构裂纹扩展的振动疲劳寿命计算方法.分析时,通过建立若干个含不同长度裂纹的结构有限元模型模拟结构裂纹扩展,采用Paris方程分段计算结构振动疲劳裂纹扩展寿命,通过试验确定的固有频率降变化规律反推结构裂纹萌生寿命,最后累计得到结构疲劳总寿命.结论表明,仿真计算结果与试验结果比较吻合.     

不同频率比时立管两向涡激振动及疲劳分析

考虑四种不同频率比(流向荷载频率/横向荷载频率)情况下,立管两向涡激振动的幅值和疲劳的变化。结果表明：较低频率比且低约化速度条件下,流向自由度对横向振动具有一定的抑制作用;当6.3<约化速度<8.0时,考虑顺流向振动时横向振动幅值明显增加。随着频率比的增加,顺流向振动对横向振动的影响逐渐减弱。横向振动对顺流向振动的影响在四种情况下均较为显著,考虑横向振动时顺流向振动幅值急剧增大。两向自由度涡激振动的疲劳在低频率比时明显高于单自由度时的疲劳;顺流向振动疲劳随着频率比的增大受横向振动的影响越来越明显。     

Fatigue failure analysis of high speed train gearbox housings

The present work addresses the formation of fatigue cracks in gearbox housings of high speed trains. Systematic studies of fracture analysis, finite element analysis, and field tests under actual stress and acceleration conditions are employed. Time domain, frequency domain, and time-frequency domain analyses indicate that the first two natural vibration modes are excited by out-of-round wheels and rail-track irregularities, and the superposition of these vibration modes results in the occurrence of the beat phenomenon, where the amplitude of the vibration modulates periodically, which increases the likelihood of exceeding fatigue limits, and produces greater structural damage. Analyses reveal that the fatigue strength of the failure region is reduced by the casting process, which eventually leads to the formation of fatigue cracks. Our findings suggest that the gearbox housing casting process should be improved to reduce casting porosity, and the housing structure must be redesigned to avoid the resonance frequencies associated with wheel-rail excitation at operational speeds.     

风力机叶片载荷谱及疲劳寿命分析

研究了大型风力机玻璃钢叶片载荷谱和疲劳寿命的工程估算方法.运用片条理论分析了影响风力机叶片疲劳寿命的气动载荷分布;应用多体动力学方法,分析了旋转叶片动力刚化效应产生的原因及其对叶片振动模态的影响;根据模态叠加法,计算了叶片在气动力、重力和旋转惯性力等确定性载荷作用下的动应力响应;探讨了玻璃钢叶片的疲劳性能、破坏准则及疲劳寿命估计方法;提出了一种基于Palmgren Miner线性累积损伤法则的玻璃钢叶片安全寿命估计方法.通过所设计的1.5MW变速变桨距风力机叶片疲劳寿命估计的算例表明,该方法是可靠和实用的.