随机载荷作用下动态应力-强度干涉模型

研究了随机应力作用下强度随时间退化时,随时间变化的应力-强度干涉模型。用泊松过程描述应力的作用过程,运用概率微分方程,建立了不考虑强度退化和考虑强度退化时的动态应力-强度干涉模型。在考虑强度退化时,分别将强度退化视为随机变量和随机过程。     

考虑载荷作用次数的零部件可靠性模型

研究随机载荷多次作用时零件的失效过程,建立载荷多次作用下的零件可靠性模型.从载荷作用的统计学意义出发,根据顺序统计量的性质,建立载荷多次作用时等效载荷的累积分布函数和概率密度函数.运用应力-强度干涉模型建立零件在单一失效模式下载荷多次作用时的可靠性模型.最后,运用Monte Carlo方法对可靠性模型进行仿真实验,证明模型的正确性.     

由剩余强度全域测试建立的疲劳可靠性估算模型

在全域疲劳加载下对处于不同损伤状态的材料进行剩余强度测试，得到剩余强度数据的函数曲线表达式，并由此建立剩余强度模型的一般形式，给出材料在常幅和变幅加载作用下的剩余强度退化模型。在此基础上研究常幅和多级加载下的疲劳可靠性分析方法。应用应力－强度干涉可靠性分析模型进行实例分析计算，结果与实验值较为符合，说明所提出的剩余强度模型是合理的。     

一个非线性强度退化模型

从疲劳过程本质上是材料静强度不断退化的过程的观点出发，建立了一个非线性的，连续性强度退化模型，该模型的参数可由Ｓ－Ｎ曲线来确定。将模型应用于两级及多级载荷下剩余寿命估算，并用１６Ｍｎ钢进行了试验验证，结果表明可以较准确地估算两级及多级载荷下的疲劳寿命。     

考虑剩余强度的焊接箱形梁动态可靠性分析

针对目前起重机金属结构可靠性的研究未反映出可靠度随时间动态变化的特性,考察其可靠度和失效率受多级的变幅载荷影响随时间的变化过程,推导出起重机金属结构的动态可靠度计算公式。研究表明：起重机金属结构的可靠度受到应力作用次数、应力峰值和剩余强度等因素的影响,并随时间的增加而呈非线性降低的特性。本研究为起重机的寿命评估和动态监测奠定了理论基础,具有重要的工程实用价值。     

基于剩余强度退化规律的疲劳损伤非线性演化模型

通过对正火４５钢的试验数据分析,提出了一个反映剩余强度退化的对数表达式,给出对称恒幅应力循环下疲劳损伤的定义与表达式。该表达工能够反映损伤演化的非线性特性。进一步分析了随机应力循环下结构的疲劳损伤,导出损伤演化的递推公式,并结合大量的计算给出结构在应力块重复循环下疲劳寿命估算的一个近似方法。     

载荷粗糙度对可靠性的影响

研究随机载荷粗糙度和作用次数对系统可靠性的影响,运用应力-强度干涉模型和数理统计理论,建立随机载荷多次作用下的应力-强度干涉模型.在此模型下,通过理论分析和实例计算,找到载荷粗糙度、安全裕度和失效概率三者之间的关系,并建立一种新的零部件尺寸的计算方法.     

应力-强度干涉模型下的滚动轴承可靠性评估与设计方法

针对滚动轴承可靠性低、缺乏设计依据等问题,提出一种应力-强度干涉模型下的滚动轴承可靠性评估与设计方法。考虑滚动轴承实际承载当量动载荷和规定当量动载荷的随机特性,假设两者为服从对数正态分布的随机变量,建立滚动轴承可靠性评估与设计模型。其次,对多型号多工况下的深沟球轴承和角接触球轴承进行仿真验证,结果表明:本文提出的滚动轴承可靠性评估与设计方法,通过分析当量动载荷的许用范围,结合轴承设计公式可以使优化后的轴承满足在该工况下的目标可靠性寿命,准确有效的实现滚动轴承的可靠性评估与设计。     

应力-强度干涉模型在系统失效概率分析中的应用及相关问题

研究一般串联、并联及K／N表决系统（不要求系统中各零件失效事件是相互独立的）的失效概率建模与失效概率预测。通过详细考察、深入分析应力-强度干涉理论、方法及其在零件失效概率和系统失效概率计算中的建模过程，介绍“系统级”的应力-强度干涉模型及其在系统失效概率分析中的应用，并给出应用实例及其与实验观测结果的比较。与传统的先计算零件失效概率，再在各零件失效相互独立的（不真实）假设条件下建立串联、并联、表决等系统失效概率模型的方法不同，文中提出应用“系统级”的应力-强度干涉分析直接建立系统失效概率模型的方法。为应用应力-强度干涉模型预测系统失效概率，首先详细分析传统的零件失效干涉分析过程中发生的系统可靠性信息损失问题。分析表明，零件失效概率的不确定性与载荷分散程度有关，在传统的应用应力-强度干涉模型计算零件失效概率过程中遗失的失效相关性信息对系统失效概率估算是十分重要的。在此基础上，指出无法通过传统的零件可靠度参数构建一般系统（具有失效相关性的非独立失效系统）可靠性模型的原因。最后，建立能根据系统低阶失效数据预测高阶失效概率的参数化模型。     

多级载荷作用下剩余强度的估算

针对现有方法在估算多级载荷作用下的剩余强度时存在的不足,文中在Schaff提出的剩余强度模型的基础上提出等损伤比剩余强度模型,并用于多级载荷作用下剩余强度的估算,给出多级载荷作用下剩余强度的退化模型公式.此剩余强度退化模型计算公式把后期计算建立在前期剩余强度的基础上,适于递归计算.由于采用等损伤比模型,适用于任意级载荷作用或随机载荷作用下的剩余强度估算,因此适用范围更广.     

The influence of stress concentration on creep rupture at non-stationary loading

A method is given for the calculation of creep rupture strength of parts containing stress concentrations. The creep theory takes account of the damage and anisotropy of materials. which arise during deformation. For the example of a plane specimen with a notch, results of calculations are compared with experimental data. The results of an investigation into the creep strength of the fir-tree root of a turbine blade at non-stationary loading is given.     

机载燃油泵复杂应力退化试验设计与应力影响分析

针对机载燃油泵可靠性高、寿命长,实际工作环境复杂,而试验应力因素单一等特点,设计搭建了复杂应力条件下燃油泵退化试验平台,并对应力因素影响进行了分析。首先通过对燃油泵失效机理的分析,选取了影响轴承磨损的电应力和机械振动作为主要应力,开展其性能退化研究;然后基于以上选取的应力搭建了燃油泵退化试验平台和振动试验装置,并对压力传感器和流量传感器进行了选型,介绍了信号采集控制系统,设计了燃油泵夹持装置并对其动态性能进行了分析;最后基于正交试验思想设计了试验方案,并采用极差分析和方差分析2种方法对试验结果进行了分析。所提方法缩减了2/3的试验次数,节省了试验时间,并得出电压对燃油泵可靠性的影响更为显著,其置信度可达99%。     

冲击作用下的载荷波形对动态应力集中系数的影响

本文从理论上证明了在一定条件下阶越波入射产生的最大应力集中系数是冲击作用下种瞬态波形入射时的极限值。有限元法计算结果不仅证实了这一结论，而且展示了在一般无理论解的情况下获得极值应力集中系数的可行性。     

The subsurface stress field caused by both normal loading and tangential loading

The subsurface stress field caused by both normal loads and tangential loads has been evaluated using the rectangular patch solution. The effect of tangential loading on the subsurface stress field has been investigated in detail for both the cylinder-on-cylinder contact and a spur gear teeth contact. For the cylinder-on-cylinder contact, the subsurface stress fields are moved more to the direction of tangential loads and the positions where the maximum stress occur are getting closer to the surface with the increasing tangential loads. The subsurface stress fields of the gear teeth contact are expanded more widely to the direction of tangential loads with the increasing tangential loads. The friction coefficient of a gear teeth contact is low because they are operated in a lubricated condition, and therefore surface tractions in the EHL condition hardly affect on the subsurface stress field.     

工作载荷对旋转叶片固有振动特性的影响研究

根据飞行中的工作状态建立某旋转叶片的振动模型,利用结构有限元方法进行模态分析,通过对比分析法分别研究了气动载荷和离心载荷对叶片固有振动特性的影响。确定了不同载荷组合下的各阶固有频率,给出叶片的共振-转速特性,并分析了转速对振型的影响,为叶片试验与分析提供依据。     

The influence of repeated loading,residual stresses and shakedown on the behaviour of tribological contacts

Most tribological pairs carry their service load not just once but for a very large number of repeated cycles. During the early stages of this life, protective residual stresses may be developed in the near surface layers which enable loads which are of sufficient magnitude to cause initial plastic deformation to be accommodated purely elastically in the longer term. This is an example of the phenomenon of ‘shakedown’ and when its effects are incorporated into the design and operation schedule of machine components this process can lead to significant increases in specific loading duties or improvements in material utilization. Although the underlying principles can be demonstrated by reference to relatively simple stress systems, when a moving Hertzian pressure distribution in considered, which is the form of loading applicable to many contact problems, the situation is more complex. In the absence of exact solutions, bounding theorems, adopted from the theory of plasticity, can be used to generate appropriate load or shakedown limits so that shakedown maps can be drawn which delineate the boundaries between potentially safe and unsafe operating conditions. When the operating point of the contact lies outside the shakedown limit there will be an increment of plastic strain with each application of the load—these can accumulate leading eventually to either component failure or the loss of material by wear.     

Development of improved Manson-Coffin model considering the effect of yield stress under asymmetrical cyclic loading

Journal of Mechanical Science and Technology - Life prediction of low cycle fatigue under asymmetrical cyclic loading is still open because the mean stress has complex effect on the fatigue life....     

The influence of the magnetoelastic effect on the hysteretic properties of medium-carbon steel during uniaxial loading

Hysteretic magnetic properties and longitudinal magnetostriction of planar specimens of air-hardened 45 steel were measured as functions of elastic tensile stresses along and perpendicular to the applied loading using a closed magnetic circuit and attachable transducers. Parameters that exhibit monotonic variations with increasing elastic tensile stresses, were found. It was shown that the maxima that were observed in the dependences of residual inductance and relative maximum magnetic permeability on applied stresses, as well as the minima that were observed in the dependences of the coercive force and demagnetizing current of an attachable electromagnet as measured with a sensor arranged along the tension axis on applied stresses, are related to the behavior of the magnetostriction curves of the steel under study.     

高频群脉冲电化学加工中频率对极间间隙的影响

给出了脉冲电化学加工极间平衡间隙的数学模型,并据此讨论了高频群脉冲电化学加工中,电源主脉冲频率与平衡加工间隙的关系.在模拟结果中,极间平衡间隙与主脉冲频率则呈严格的线性关系,即随频率增加平衡间隙线性减小.并根据设计的硬币花纹工艺试验表明,选择较高的主脉冲频率,可获得较小的加工间隙,进而获得良好的表面质量.由此可得出结论：良好的加工质量来源于高频所带来的较小极间间隙.     

弯曲剪应力对轴强度的影响

分析了弯曲剪应力对弯扭组合变形轴主应力强度的影响,推出了考虑该因素影响时第三、第四强度理论的相当应力,并给出了设计公式。结合实例进行了分析比较,指出当轴中传动点距支承较近且扭矩比弯矩大时,剪应力对轴的强度有较大的影响。