乘用车排气净化器热疲劳分析方法

为探究温度循环载荷下排气净化器的热疲劳性能,结合传热分析和静力学分析,采用有限元软件HyperMesh和Abaqus,对某型乘用车排气净化器进行深入研究,考虑高温效应和材料硬化效应的影响,选择等效塑性应变幅值作为评价热疲劳的关键指标,分析得到危险点等效塑性应变幅值为0.0117,不满足热疲劳耐久要求.对原排气净化器的下支架进行翻边处理,得到的新排气净化器的等效塑性应变幅值最高为0.0087,满足热疲劳耐久要求.     

有限元法计算某钢结构件寿命

钢结构件在低于破坏载荷的反复作用下会发生疲劳断裂现象,周期性交变载荷对结构寿命影响最大。运用有限元方法,计算某结构件在特定载荷反复作用下的疲劳特性,确保试验件可靠性,使其在有限寿命范围内发挥最大功用。     

基于nCode Design-Life的某车架疲劳可靠性分析

针对某型半挂牵引车车架局部出现裂纹或者断裂现象,通过有限元理论和疲劳分析理论相结合进行了车架的有限元分析和疲劳可靠性分析。首先对该车架进行了建模和有限元静态特性分析,然后定义了特定的时间载荷序列数据和材料参数,选用了S-N疲劳设计和静态疲劳分析方法,利用疲劳分析软件nCode Design-Life对该车架进行疲劳可靠性分析,得出该车架的疲劳结果云图和各节点的疲劳寿命,并从相关云图中确定出车架容易破坏的位置和其寿命之后再进行样车实验验证。     

大型矿车用减速机齿轮系统的疲劳分析

提出一种基于"放大因子"、采用二维平面单元模拟三维实体动态工况的计算疲劳的方法,对某矿车减速机齿轮系统进行疲劳分析,得到太阳轮、行星轮和扭力管在不同抗拉强度下的疲劳寿命.结果表明:太阳轮和扭力管最易发生疲劳破坏;齿轮寿命对抗拉强度的依赖性较敏感;得出的齿轮系统热处理后的抗拉强度建议值能为设计提供参考,且该方法能大大提高计算效率.     

基于ANSYS排气吊耳刚度分析

本文首先建立了某汽车排气系统的有限元模型,然后利用排气系统的自由模态试验结果与仿真结果对比。验证了有限元模型的准确性。最后对排气系统进行静力学分析,得出排气系统的每个橡胶吊耳的受力和位移情况。基于整车设计及布置要求对排气吊耳刚度进行优化,得出满足整车要求的吊耳刚度。     

基于Pro/ENGINEER的某型排气歧管强度与模态分析

排气歧管是汽车发动机排气系统的重要部件,它的结构设计与发动机排气系统性能密切相关。文中采用有限元分析的方法对某品牌汽车发动机排气歧管关键部分进行排气压力下和温度载荷下的强度分析,对模型整体进行模态分析。对本产品的结构稳定性予以分析说明,为结构设计提供依据。     

D型打结器架体的随机振动分析与结构优化

针对D型打结器架体易断裂、寿命短等问题,采用动力学与疲劳分析相结合的研究方法.基于模态-谐响应分析,得到架体应变幅值曲线.采用随机振动分析与Miner线性损伤累加法则对架体进行疲劳寿命分析,结果得出架体的疲劳寿命不高.设计架体四因素三水平的正交试验,对架体进行结构优化.结果 表明优化后的架体疲劳寿命显著提高.     

曲轴疲劳寿命的三维有限元分析

针对影响曲轴疲劳寿命的众多复杂因素以及准确估计曲轴疲劳寿命难度大的问题,以某型柴油机组成的动力装置为原始模型,运用三维有限元模态分析计算柴油机曲轴的动态应力,应用动应力载荷谱疲劳计算方法分析曲轴疲劳寿命.实验比较不同情况的曲轴疲劳寿命,比较后的相对值非常可靠.     

飞机典型材料疲劳/断裂性能数据库设计 ——基于Java Applet

对我国百余种飞机典型材料疲劳/断裂性能试验数据进行了研究,在此基础上,探讨了该类材料疲劳/断裂性能SQL Server数据库的设计方法。采用ASP、JavaScript、Java等技术,建立了基于网络环境下的飞机典型材料疲劳/断裂性能数据库系统,实现数据表、图形图像的动态检索输出;为飞机结构的疲劳/断裂可靠性设计与结构寿命评定中材料性能数据的获得和分析带来极大方便。     

自适应局部迭代滤波在齿轮故障识别中的应用

针对齿轮实测信号因受噪声干扰而不能准确反映故障特征的问题,提出将自适应局部迭代滤波应用到齿轮故障识别中,与样本熵、灰色关联度相结合实现齿轮的故障识别。利用自适应局部迭代滤波将齿轮非平稳信号分解为有限个平稳的本质模态函数,通过计算各本质模态函数的样本熵,发现以齿轮系统的转频信号对应的本质模态函数的样本熵为界,前几个本质模态函数的样本熵能表征不同故障类型的特征;计算齿轮系统正常、齿面轻度磨损、齿面中度磨损和断齿4种工况下多个训练样本的样本熵的平均值,将其作为对应工况标准故障模式的参考值;计算待检测样本的样本熵与各状态下训练样本的样本熵平均值之间的灰色关联度,与待识别样本灰色关联度最大的标准故障模式即被认为是待识别样本的故障类型。实例分析结果表明,通过自适应迭代滤波能有效抑制模态混叠现象,发现明显的齿轮转频信号,而采用集合经验模式分解(EEMD)方法进行信号分解后,模态混叠现象比较明显,且在EEMD的分解结果中基本看不出齿轮的转频分量;4种工况的样本熵曲线形状存在明显差异,说明样本熵能有效表征齿轮故障特征的变化;灰色关联度方法能有效地将4种不同的故障类型进行分类识别,分类识别性能优于BP神经网络,对小样本数据具有较好的分类识别能力。     

基于有限元的杆端关节轴承结构优化

针对某型号杆端关节轴承在疲劳试验时发生断裂的问题,对其原结构进行有限元仿真分析,得到的最大应力位置与实际断裂位置吻合,圆柱段仿真结果误差与应力理论计算结果仅为0.5%,验证仿真结果的可靠性。对杆端体各结构参数依次进行单变量有限元仿真分析,获取各参数对杆端体最大应力和质量的影响,据此确定优化顺序并对关节轴承进行优化。优化后的杆端关节轴承质量增加9.8%,最大等效应力降低14.9%,计算疲劳寿命从500万次提高到4 600万次,大于目标疲劳寿命值3 000万次,优化后的样件均顺利通过疲劳试验。     

乘用车排气系统吊钩位置优化

使用模态分析和平均驱动自由度位移法,对某乘用车排气系统吊钩位置进行分析评估,提出优化方案,采用排气系统频响分析验证优化效果。优化后各吊钩振动位移和加速度明显降低,验证该排气系统吊钩位置优化方案的合理性和可行性。     

Study of TBM cutterhead fatigue crack propagation life based on multi-degree of freedom coupling system dynamics

Cutterhead is the core component of TBM tunneling equipment, which endures strong, multi-point distributed impact loads when the TBM tunnels, owing to the extreme surrounding rock environment of high hardness, high temperature and high quartz content. For this reason, the cutterhead works in an extremely severe vibration environment, which leads to engineering fault by a large area crack damage before the service life. Hence, the study on life prediction of TBM cutterhead under the impact loads is a core part of cutterhead design. This paper combines with the technology of system dynamics, linear elastic fracture mechanics and cumulative theory of fatigue damage, for the first time, proposes a method of fatigue crack propagation life prediction for the large and complex structures. In this paper, the TBM cutterhead of an actual project is taken as an example, to predict the fatigue crack propagation life of cutterhead piece and analyze the influences of plate thicknesses on fatigue life, then a new improved scheme of cutterhead structure is presented. The results show that the fatigue crack propagation life of actual cutterhead is 26.6 km, which is able to meet the requirement of 20 km service life. Moreover, the upper cover plate thickness has the greatest influence on cutterhead fatigue crack propagation life, with the thickness increasing 10%, the life increases nearly by 1.24 times. Then, the other influencing factors are as follows: thickness of the main support plate, thickness of the annular support plate and thickness of the support plate, whereas the influence of the lower cover plate thickness on fatigue life is minimal. Furthermore, the plate thickness limit sizes meeting the life requirement are obtained, and a new structure modified scheme of cutterhead is proposed. Compared with the original scheme, the new cutterhead scheme meets the requirements of structural strength and service life with 8.08% weight decrease, which achieves life determination design and lightweight design. The proposed method of fatigue crack propagation life prediction is feasible in the design and application stage of TBM cutterhead, besides, it is flexible enough and can also be applied in damage strength assessment, dynamic parameters optimization and establishment of nondestructive inspection cycle for the other large and complex structure, and takes on stronger project value and generality.     

高量程加速度传感器在测试中的失效分析

通过在不同测试环境对高量程加速度传感器进行测试,并对传感器在测试中出现的失效进行分析,在实验室环境测试中出现的主要失效模式为键合引线的脱落和微梁的断裂,其原因是不同金属的引线键合强度较低;重复性的冲击加速了材料的疲劳.在实弹测试环境测试中出现的传感器失效原因主要足在侵彻测试中传感器芯片与侵彻信号中高频分量发生共振导致过...     

轿车排气管挂钩刚度优化分析

针对某轿车在试车场进行耐久性试验时出现挂钩处开裂的问题,建立考虑动力总成的排气系统振动分析模型;通过频率响应分析发现挂钩开裂处的约束反力稍大,局部刚度偏低;通过结构优化使挂钩刚度得到加强.对2种优化方案的对比表明优化后的挂钩能减小排气系统传递到车身地板的振动,提高排气系统的疲劳寿命.     

Fatigue Life Prediction Criterion for Micro–Nanoscale Single-Crystal Silicon Structures

This paper describes fatigue damage evaluation for micro–nanoscale single-crystal silicon (SCS) structures toward the reliable design of microelectromechanical systems subjected to fluctuating stresses. The fatigue tests, by using atomic force microscope (AFM), nanoindentation tester, and specially developed uniaxial tensile tester, have been conducted under tensile and bending deformation modes for investigating the effects of specimen size, frequency, temperature, and deformation mode on the fatigue life of SCS specimens. Regardless of frequency and temperature, the fatigue life has correlated with specimen size. For example, nanoscale SCS specimens with 200 nm in width and 255 nm in thickness have showed a larger number of cycles to failure, by a factor of $10^{5}$, at the same stress level, as compared to microscale specimens with 48 $muhbox{m}$ in width and 19 $muhbox{m}$ in thickness. Deformation mode has also affected the lifetime; however, no frequency and temperature dependences have been observed unambiguously in the $S{-}N$ curves. The stress ratio parameter corresponding to the ratio of peak stress to average fracture strength has enabled us to estimate the lifetime for each deformation mode. To predict the fatigue life of SCS structures regardless of deformation mode and specimen size, we have proposed an empirical parameter that includes the resolved shear stress. The mechanism of fatigue failure of SCS structures is discussed from the viewpoint of dislocation slip, crack nucleation, growth, and failure through observations using AFM and scanning electron microscope.$hfillhbox{[2008-0072]}$      

Boundary element analysis of cracked homogeneous or bi-material structures under thermo-mechanical cycling

We present a sub-domain boundary element procedure to evaluate the failure capacity of cracked homogeneous and bi-material media under cyclic thermo-mechanical loads. The boundary integral equations of uncoupled, time-dependent thermo-elasticity are employed to account for the time-varying nature of the thermal load. If crack closure due to thermal distortion takes place, then the displacement and traction field may affect the heat flux between the crack faces, and the thermal and mechanical parts of the problem will need to be solved repeatedly until thermo-mechanical convergence is achieved. We present results from cases of pure mode-I fracture in homogeneous materials and for interfacial fracture in bi-materials. Our study discusses the influence of crack closure on quasi-static, sub-critical crack extension. Especially in case of interfacial cracks the type of loading, the thermal resistance between the crack faces, and the coefficient of friction are also taken into account. The results suggest that the above parameters may have a severe impact on the predicted failure capacity of cracked structures and should be considered in the evaluation of fatigue life.     

高速车辆结构振动的独立模态空间控制

铁路高速客车或轻型车辆的车体结构振动不仅影响车辆运行品质,而且导致车体结构动应力的增加和疲劳寿命的降低.本文在建立高速车辆的柔刚体系统动力学模型基础上,应用最优控制理论,提出了抑制车体的特定低阶垂直弯曲振动独立模态空间控制方法和已改善车辆运行平稳性为目标的控制策略,分析结果表明:该控制办法和策略可以较好地降低特定模态振动的幅度,改善车辆垂直运行平稳性.     

Notch Root Oxide Formation During Fatigue of Polycrystalline Silicon Structural Films

This paper investigates the fatigue behavior of n⁺-type 2-mum- thick polycrystalline silicon films that exhibit an initially thin (~2-3 nm) native oxide layer. The testing of kilohertz-frequency resonators provided accurate stress-life fatigue data at 30 and 50% relative humidity (RH) in the low (< 10⁶)and high (up to 10¹¹) cycle regimes. Long fatigue life specimens were associated with larger decreases in the natural frequency of the resonator and very smooth failure origins (at the notch) that encompassed several grains. Additional testing at various humidity levels highlighted the critical influence of humidity on the fatigue damage accumulation rate, which was measured via changes in the natural frequency. Finally, Auger electron spectroscopy (AES) characterized the formation of a nanometer-scale oxygen-rich reaction layer during cyclic loading. Although AES revealed a thin 2-3-nm initial oxide layer on a control specimen, measurements on a long-life fatigued specimen revealed an increased oxygen concentration over the first 10 nm of the material at the notch root. These findings demonstrate that the reaction-layer fatigue mechanism for silicon structural films operates even when reaction layers are initially very thin.