关于材料疲劳强度分布函数的实例分析

材料的疲劳强度分布函数及其与疲劳寿命分布函数之间的关系是近年来引起国内外学者强烈兴趣的研究课题。本文应用文献〔3〕的工作具体研究了某些材料的疲劳寿命分布与疲劳强度分布函数之间的关系。从实验上支持了在一般情况下疲劳寿命与疲劳强度不为同一种分布的结论。     

桥式起重机焊接箱形梁的疲劳试验

作通过常幅疲劳试验，得到了焊接箱形梁的疲劳强度Ｐ－Ｓ－Ｎ曲线和曲线方程：以及给定寿命下疲劳强度的分布；进行了变幅疲劳试验，根据得到的Ｐ－Ｓ－Ｎ曲线论证变幅与常幅疲劳试验的相互关系；在试验过程中，收集了焊接箱形梁疲劳破坏裂纹的扩展历程数据，探讨了断裂的机理。     

起重机焊接箱形梁的疲劳试验

通过常幅及变幅疲劳试验，得出焊接箱形梁的疲劳强度Ｐ－Ｓ－Ｎ曲线方程及给定寿命下疲劳强度分布，论证变幅与常幅疲劳试验的相互关系；试验中取得了焊接箱形梁疲劳破坏殂纹的扩展历程数据并分析断裂的机理。     

疲劳强度的频率分布和疲劳强度特征函数

本文根据疲劳破坏的基本特性,利用概率论方法建立了疲劳强度频率分布与疲劳寿命频率分布之间的数学关系式,从而由已知的在给定应力水平下的疲劳寿命频率函数推导出在给定寿命下的疲劳强度频率函数,与威布尔早期的设想完全相同。理论与实验研究结果表明:在给定寿命下的疲劳强度一般不遵循(对数)正态分布或威布尔分布,而遵循一偏态分布[见本文式(25)或式(34)]。经数学变换后的疲劳强度特征函数遵循标准正态分布。这样,利用疲劳强度特征函数便于进行可靠性分析。     

16Mn钢疲劳强度的概率分布

提出了一种研究指定寿命下疲劳强度概率分布问题的新的统计分析方法。用这种方法可以在不能求得寿命分布的长寿命区,求得疲劳强度的分布。用16Mn 钢的疲劳试验结果和新方法研究了其疲劳强度分布。结果表明,疲劳强度系数遵循对数正态分布理论疲劳极限遵循正态分布,疲劳强度遵循正态分布和对数正态分布。     

装甲车辆侧减速器齿轮接触疲劳寿命预测研究

通过对根据典型路面实车试验获得的载荷数据进行雨流计数处理,编制了装甲车辆侧减速器齿轮所承受的扭矩谱和应力谱;充分考虑残余应力对齿轮接触疲劳极限的影响,通过强度和硬度之间的转换关系以及疲劳强度与残余应力的作用关系,得到了齿面沿深度方向的静强度以及接触疲劳强度分布;结合疲劳寿命分析技术,进行了齿轮疲劳寿命预测,其预测结果与实际规律相符合。     

无限寿命的应力—寿命可靠度模型

根据疲劳强度试验过程，结合－３Ｓ－Ｓ－Ｎ曲线明确解释了无限寿命的疲劳强度可靠度的含义。说明了无限寿命的疲劳强度可靠度与寿命可靠度之间的关系。建立了恒幅常应力和恒幅变应力情况下疲劳寿命可靠度的计算公式。为系统的可靠性分析奠定了理论基础     

激光焊接对TC4钛合金静强度与疲劳性能的影响

采用静拉伸与等幅疲劳试验,对TC4钛合金母材试样和激光焊接(聚焦焊后进行散焦焊接)试样的静强度和疲劳寿命进行了对比研究,得到了两种试样的静强度、中值疲劳寿命S-N曲线和95%可靠度下的安全寿命P-S-N曲线,并获得了两种试样在指定疲劳寿命106次循环下所对应的中值疲劳强度和安全疲劳强度。结果表明:与母材试样相比,激光焊接试样的静强度虽然有所提高,但疲劳寿命或疲劳强度却大幅降低。     

变幅载荷下的有限寿命疲劳设计方法和设计数据

本文论述了变幅载荷下的有限寿命疲劳强度评价方法与寿命估算方法,给出了用Ｍｉｎｅｒ法则、修正Ｍｉｎｅｒ法则和Ｃｏｒｔｅｎ－Ｄｏｌａｎ理论进行疲劳强度评价和寿命估算的方法和计算公式。最后,还用４种零构件进行随机疲劳试验对三种累积损伤理论的疲劳强度评价和寿命估算精度和这生进行了验证和对比。     

随机应力谱下构件疲劳可靠性分析的Miner准则--寿命分布函数法

基于随机应力谱下的Miner准则和寿命分布函数，提出了一种随机应力谱下构件疲劳可靠性分析模型——Miner准则一寿命分布模型。该模型首先考虑构件疲劳强度影响系数，对材料的p-S-N曲线进行修正，以得到构件的p-S-N曲线；然后利用Miner准则导出构件在随机应力谱下的疲劳可靠寿命表达式，由疲劳寿命的概率分布函数，并考虑构件疲劳强度影响系数的随机性，求得构件在随机应力谱下给定疲劳寿命时的疲劳可靠度。     

长寿命区疲劳寿命概率分布

讨论了试件在低载长寿命区疲劳寿命概率分布问题,根据疲劳寿命与疲劳强度破坏率等同性原理,建立了一个疲劳寿命概率分布模型。文中给出了实例,并通过蒙特卡洛模拟验证了模型的正确。     

数控车床主轴低载强化试验数据处理

在高强度数控车床主轴低载强化试验结果的基础上,通过数值插值方法,补充了试验数据,得到强化载荷与强化后疲劳寿命之间、强化次数与强化后的疲劳寿命之间的数学关系,然后根据这两个二维关系式,通过数学插值,得到低载强化空间曲面的离散点三维坐标,再根据这些数据点,用Tablecurve3d软件拟合得到低幅交变载荷作用下的三维强化曲面方程。     

夹杂物尺寸及位置对51CrV4弹簧钢疲劳寿命的影响

用能谱仪、扫描电镜分析了51CrV4弹簧钢的疲劳断口,研究了夹杂物尺寸及位置对该钢疲劳寿命的影响规律。结果表明:51CrV4试验钢的疲劳强度为702.5MPa,在保证试样表面没有划痕和麻点的情况下,疲劳裂纹主要起裂于椭球状且塑性较低的复杂氧化铝夹杂;在夹杂物尺寸越大和距离表面越近的情况下,其疲劳寿命越低;在710MPa应力水平下近表面夹杂物的临界尺寸为5.47μm。     

Characterization of fretting fatigue crack initiation processes in CR Ti–6Al–4V

A study was conducted to quantify fretting fatigue damage and to evaluate the residual fatigue strength of specimens subjected to a range of fretting fatigue test conditions. Flat Ti–6Al–4V specimens were tested against flat Ti–6Al–4V fretting pads with blending radii at the edges of contact. Fretting fatigue damage for two combinations of static average clamping stress and applied axial stress was investigated for two percentages of total life. Accumulated damage was characterized using full field surface roughness evaluation and scanning electron microscopy (SEM). The effect of fretting fatigue on uniaxial fatigue strength was quantified by interrupting fretting fatigue tests, and conducting uniaxial residual fatigue strength tests at R=0.5 at 300 Hz. Results from the residual fatigue strength tests were correlated with characterization results.While surface roughness measurements, evaluated in terms of asperity height and asperity spacing, reflected changes in the specimen surfaces as a result of fretting fatigue cycling, those changes did not correspond to decreases in residual fatigue strength. Neither means of evaluating surface roughness was able to identify cracks observed during SEM characterization. Residual fatigue strength decreased only in the presence of fretting fatigue cracks with surface lengths of 150 μm or greater, regardless of contact condition or number of applied fretting fatigue cycles. No cracks were observed on specimens tested at the lower stress condition. Threshold stress intensity factors were calculated for cracks identified during SEM characterization. The resulting values were consistent with the threshold identified for naturally initiated cracks that were stress relieved to remove load history effects.     

柔性构架的动应力仿真研究

在 ANSYS 有限元分析软件中建立了转向架构架的柔性体模型,在 SIMPACK 多体动力学软件中建立了完整的车辆系统动力学模型,把 SIMPACK 中计算得到的构架载荷-时间历程引入 ANSYS 中得到构架各部位的应力分布以及关键部位的应力-时间历程,从而为构架的疲劳强度评估和疲劳寿命预测奠定了基础.这一方法不仅实现了有限元计算与多体动力学分析之间的有效结合,而且完成了多体系统动力学研究中刚体与柔性体之间的耦合,是构架设计新方法的尝试.     

变速箱齿轮低载强化微观机理的初步研究

疲劳试验表明工艺强化后的高强度变速箱齿轮经过低载强化,其单齿弯曲疲劳强度和疲劳寿命还能够得到一定程度的提高,而且疲劳寿命提高的幅度远大于疲劳后强度的提高幅度。本文参考未经过工艺处理的低强度前梁的低载强化微观分析结果,利用SEM和TEM对某汽车变速箱齿轮低载强化微观机理进行了初步研究,力图从微观上揭示工艺强化后高强度齿轮低载强化的成因和机理。结果表明,适当的强化载荷能够使高强度齿轮的疲劳扩展区域增加、裂纹扩展间距下降,低载强化使齿轮的微观组织得到进一步的锻炼、强度和硬度有所下降,但微观组织的整体机械性能得到提高。     

Investigating the effect of clamping force on the fatigue life of bolted plates using volumetric approach

In this paper, the effects of bolt clamping force on the fatigue life for bolted plates made from Al7075-T6 have been studied on the values of notch strength reduction factor obtained by volumetric approach. To attain stress distribution around the notch (hole) which is required for volumetric approach, nonlinear finite element simulations were carried out. To estimate the fatigue life, the available smooth S-N curve of Al7075-T6 and the notch strength reduction factor obtained from volumetric method were used. The estimated fatigue life was compared with the available experimental test results. The investigation shows that there is a good agreement between the life predicted by the volumetric approach and the experimental results for various specimens with different amount of clamping forces. Volumetric approach and experimental results showed that the fatigue life of bolted plates improves because of the compressive stresses created around the plate hole due to clamping force.     

发动机缸盖试验寿命趋势预测与分布规律研究

在发动机受热件高频感应式加速热疲劳台架试验研究的基础上，综合连续损伤力学及热强度、热疲劳研究的一些成果，推导了试验控制参数与零件试验寿命间的趋势预测模型，拟合了平均试验寿命的趋势预测模型参数；根据一定试验控制参数下的试验结果分析，验证了寿命分布服从威布尔分布，并对分布模型参数进行了参数估计；根据试验结果分析及威布尔分布的特点近似确定了安全寿命（可靠率大于99％）的曲线模型及参数值，得到了有实用价值的概率－－试验载荷－－寿命曲线（曲面）。     

W6Mo5Cr4V2钢轴承环冷轧芯辊的疲劳断裂与寿命分析

检测W6Mo5Cr4V2钢冷轧芯辊断口的宏观与微观形貌以及芯辊的表面质量与显微组织,并对芯辊的疲劳寿命进行理论分析.结果表明,低寿命冷轧芯辊的疲劳断裂源主要是表面缺陷,高寿命冷轧芯辊的疲劳断裂源主要是亚表层缺陷.冷轧芯辊的表面缺陷减少了疲劳裂纹萌生阶段的寿命,是导致芯辊过早疲劳断裂的主要原因,其对芯辊疲劳寿命的影响程度超过显微组织的影响程度,延长冷轧芯辊疲劳裂纹的萌生寿命是增加芯辊总寿命的主要方向.冷轧芯辊疲劳寿命的分布集中在两个不同的区域.     

Analysis of Fretting Fatigue of Cavitation Shotless Peened Ti–6Al–4V

Fretting fatigue behavior of cavitation shotless peened titanium alloy, Ti–6Al–4V coupons was investigated using finite element method and a critical plane-based multi-axial fatigue parameter. Cavitation shotless peening (CSP)-induced compressive residual stress, which was larger at the contact surface than its counterpart from the shot peening (SP). However, compressive residual stress decreased more sharply with distance from the contact surface in CSP than in SP. Analysis using a critical plane-based multi-axial fatigue parameter demonstrated that the crack initiation would occur inside the cavitation shotless peened specimen which matched with the experimental observations. On the other hand, crack initiation would occur on the contact surface in the shot peened specimen which again was in agreement with experiments. The analysis also showed that the crack propagation part of the total fretting fatigue life was longer in the shot peened specimen than in the cavitation shotless peened specimen while the crack initiation part was almost equal from both peening methods. Therefore, CSP could not improve the fretting fatigue life/strength as much as the SP did but it improved relative to the un-peened specimen.