随机载荷作用下结构低周疲劳可靠性研究

将影响结构低周疲劳寿命的不确定因素视为随机变量,基于可靠性分析理论,从概率论和数理统计的角度出发对随机载荷作用下的结构低周疲劳进行了可靠性分析.利用Neuber法得到低周疲劳结构的随机应力和应变响应.将随机载荷作用下的结构低周疲劳表示为材料参数、结构尺寸、载荷等随机变量的函数,并推导出了功能函数对随机变量偏导的表达式.算例显示了该方法的有效性和适用性.     

随机振动下机械产品广义可靠性评估

利用随机振动试验模拟使用环境可时构件进行可靠性考核，通过直接测量可获得薄弱部位的应变、加速度响应规律，再对相同振动条件下构件的可靠性进行评估。应力和应力循环次数是由平均功率谱密度通过离散计算得来，其计算精度由离散点间距、随机振动时间决定，因此获得的应力和应力循环次数具有模糊性。利用普通事件概率表示模糊事件概率，将模糊可靠性计算问题转化为普通可靠性计算。通过定义模糊安全状态的不同形式，建立了以状态变量表示安全状态时的广义可靠性计算模型。结合工程实际给出了算例。     

非正态随机参数的机械零部件可靠性灵敏度设计

将可靠性设计理论与灵敏度分析方法相结合,并应用4阶矩技术,提出了基于4阶矩方法的可靠性灵敏度设计计算方法,讨论了具有非正态随机参数的机械零部件可靠性灵敏度设计问题,给出了可靠性灵敏度的变化规律,研究了设计参数的改变对机械零部件可靠性的影响,为机械零部件的可靠性设计提供了理论依据.     

随机载荷下疲劳寿命估算的简便方法

针对工程实际中复杂随机载荷下疲劳寿命较难估算的情况，将载荷谱近似处理及利用剩余疲劳强度的概念。分别对窄带随机载荷以及缺乏工作载荷谱下的随机载荷的疲劳寿命进行了估算，方法简便，具有较强的工程实用性。     

随机载荷作用下微车车身结构疲劳寿命仿真分析

以微型车车身结构为研究对象,合理简化结构后建立车身有限元模型,确定载荷形式后,对车身进行静应力分析。以应力分析计算结果为基础,在动力学软件中计算获取车身承受的随机载荷,结合材料的S-N曲线和线性累积损伤理论,运用Goodman平均应力修正法,对车体进行全寿命疲劳分析,根据车身疲劳分析结果可知,该微型车车身结构疲劳寿命满足强度和疲劳性能要求。     

激光涂层多冲碰撞疲劳强度的正交分析

对激光涂层零件进行多冲碰撞疲劳试验,并用正交方法对试验数据进行了分析。发现涂层材料对激光涂层的多冲疲劳强度起主要作用,基体材料次之。涂层厚度对疲劳强度的影响随循环次数的增加而减小。     

弹性元件对受轴向工作载荷螺纹联接强度的影响

弹性元件作为一种常用的机械元件,经常应用于螺纹联接中。为了深入分析弹性元件对螺纹联接强度的影响,对不同联接方式下的螺栓联接进行了刚度分析和受力分析,从理论上提出弹性元件有增大螺栓相对刚度、增大螺栓受力的作用,由此得出弹性元件削弱螺纹联接强度的观点。同时,应用ANSYS仿真软件对不同联接方式下的螺栓联接进行有限元仿真分析,以螺栓的受力、变形的差异说明理论分析的正确性。将这一正确结果应用在实际工程中,有助于提高螺纹联接的强度。     

Relations between cavitation erosion resistance of materials and their fatigue strength under random loading

The paper contains results of tests on fatigue strength under uniaxial random loading and cavitation erosion resistance for three steels: 10HNAP, 18G2A and 15G2ANb. The obtained fatigue and cavitation characteristics were used for determination of relations between these two phenomena. From the analysis it appears that there is correlation between fatigue strength of the material under random loading and its cavitation erosion resistance. It has been shown that fatigue tests under random loading and tests on cavitation erosion of 10HNAP, 18G2A and 15G2ANb steels may be described with a mathematical model of the same type. It has been also found that there is a linear relation, in the dual logarithmic system, between cavitation erosion resistance of the steels tested and their fatigue strength under random tension—compression with zero mean value.     

Vibration and reliability of a rotating beam with random properties under random excitation

In this paper, vibration and reliability of a rotating beam with random properties under random excitations are studied. The rotating beam is under a stochastic load modeled as a stationary white noise. The cross-sectional area, elasticity modulus, moment of inertia, shear modulus, damping coefficient, mass density and rotational speed are modeled as random variables. To develop the equations of motion, the finite element method and space state analysis are applied. In order to consider the randomness of properties, a second order perturbation method is used. The effects of rotational speed, setting angle, hub radius, variances of random properties, correlation of random variables and damping matrix forms on the vibration and reliability of rotating beams, are studied completely.     

Improving machine reliability and efficiency by increasing the fatigue life of the components

Analytical determination of the γ life of machine parts in terms of parameters of a set of finite size is considered. The γ strength values of various steels obtained by the proposed method and by the Dubey method are compared.     

7140型客车车架随机振动特性及疲劳强度分析

通过建立7140客车车架的有限元模型,进行模态分析,得到车架的固有频率。采用模态叠加法计算车架在路面随机激励作用下车架的应力、车架位移随频率变化曲线及随机振动激励下最大振幅处的位移、速度、加速度响应曲线,分析掌握了车架的动态特性。并根据求解结果对车架进行了随机疲劳强度计算。为车架的改进优化提供理论参考依据。     

有限寿命下机械材料的疲劳强度近似等效正态分布研究

提出一种确定机械材料有限寿命下的疲劳强度近似等效正态分布的方法，该方法简单、准确、实用，对机械可靠性设计的广泛应用具有重要意义。     

Modal characteristics and fatigue strength of compressor blades

High-cycle fatigue (HCF) has been identified as one of the primary causes of gas turbine engine failure. The modal characteristics and endurance strength of a 5 MW gas turbine engine blade developed by Doosan Heavy Industries & Construction Co., Ltd. in HCF fracture were verified through analysis and tests to determine the reliability of the compressor blade. A compressor blade design procedure that considers HCF life was performed in the following order: airfoil and blade profile design, modal analysis, stress distribution test, stress endurance limit test, and fatigue life verification. This study analyzed the Campbell diagram and estimated resonance risk on the basis of the natural frequency analysis and modal test of the compressor blade to guarantee safe and operational reliability. In addition, the maximum stress point of the compressor blade was determined through stress distribution analysis and test. The bonding point of the strain gage was determined by using fatigue test. Stress endurance limit test was performed based on the results of these tests. This research compared and verified the modal characteristics and endurance strengths of the compressor blades to prevent HCF fracture, which is among the major causes of gas turbine engine damage. A fatigue life design procedure of compressor blades was established. The 5 MW class gas turbine compressor blade is well designed in terms of resonance stability and fatigue endurance limit.     

Determining the mechanical characteristics of nonlinearly elastic materials by vibrational tests

The equations of free vibration of a nonlinear system are solved numerically by the fourth-order Runge–Kutta method on the basis of vibrational tests of a rigidly fixed PVC cantilever beam. The solution is optimized by the Nelder–Mead method in terms of the key parameters. The dissipation and nonlinearity of the material are determined.     

Estimation for fatigue limit reliability of a metal with inhomogeneities under stress ratio

In this paper, by using statistical characteristics of hardness in a small region and statistical characteristics of mechanical condition in a small region based on a defect size distribution and a certain stress which is applied to a defect, a quantitative prediction method for fatigue limit reliability of a metal with inhomogeneities is proposed. Also rotating bending and push–pull fatigue tests under R=-1 are carried out on quenched-tempered 0.5% carbon steels, whose average hardness is about H_V600. Comparing a predicted fatigue limit reliability with experimental data, the applicability of the present proposed method is examined and confirmed.     

不同平衡率对曲轴动力学特性与疲劳强度的影响研究

以非道路高压共轨四缸柴油机为研究对象,通过曲轴模态试验模态仿真,验证了曲轴有限元模型的准确性;基于柔性多体动力学与弹性流体动力润滑理论,建立了轴系多体动力学仿真模型,研究了曲轴不同平衡率与不同平衡块数对额定转速工况下主轴承载荷与润滑特性、曲轴应力与疲劳强度的影响.研究结果表明:随着平衡率增加,曲轴质量增加,内弯矩减小,...     

Development of a method to calculate the strength reliability of tooth gears based on the fatigue resistance when the teeth bend

A verified method is discussed regarding how to calculate the strength reliability of tooth gears when they bend and thus resist fatigue. It is based on the computer simulation of random values and the mathematical apparatus of nonparametric statistics. The effective and tolerable bending stresses are described with samples generated by nonparametric sensors. It allows for the correct assessment of the probability of the failure-free performance of tooth gears under any loading conditions.     

随机道路谱作用下的汽车响应特性

针对驱动桥壳在随机道路谱作用下的响应特性问题,建立了汽车振动的7自由度动力学方程,应用随机振动理论求解出了汽车在路面不平度下的频率响应(FR),利用Matlab得到了不同速度下的后桥垂向振动加速度功率谱密度(PSD)。研究结果表明该随机道路谱作用下的汽车响应特性研究对驱动桥的动态设计具有一定的参考和应用价值。