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1.
点蚀是航空铝合金材料在服役环境下常见的损伤形式,点蚀损伤会导致材料性能的下降,严重地威胁着结构的承载能力.作为承力构件,航空铝合金不仅承受环境腐蚀的作用,还承受应力作用.论文根据点蚀基本原理,引入细观损伤变量孔隙率,考虑力学化学效应,建立了点蚀损伤弹性模量计算模型.使用2219铝合金,进行加速腐蚀试验和单向拉伸试验,利用显微扫描技术研究了点蚀坑深度随时间和载荷的变化,并对腐蚀后试验件的损伤宏观形貌进行观察分析.根据拉伸实验结果,对模型的正确性进行验证.模型计算与实验结果的对比证明了论文方法的可行性与正确性.  相似文献   

2.
随机疲劳累积损伤理论研究进展   总被引:40,自引:0,他引:40  
倪侃 《力学进展》1999,29(1):43-65
对疲劳载荷、应力、寿命和强度的随机性分别进行了明确分类.然后,针对在疲劳理论发展史上有代表性的、目前在国内外仍被大量引用的(主要用于裂纹起始阶段的)疲劳累积损伤准则,从力学、概率统计等方面进行了较深入系统的分析.提出疲劳损伤累积具有两类不同的概率机制,即损伤在单一个体内具有的随机性以及损伤在同一母体中不同个体之间具有的分散性.最后,重点介绍了二维概率Miper准则以及有关随机疲劳寿命、随机疲劳强度等方面的研究进展.   相似文献   

3.
The fatigue life prediction for components is a difficult task since many factors can affect the final fatigue life. Based on the damage evolution equation of Lemaitre and Desmorat, a revised two-scale damage evolution equation for high cycle fatigue is presented according to the experimental data, in which factors such as the stress amplitude and mean stress are taken into account. Then, a method is proposed to obtain the material parameters of the revised equation from the present fatigue experimental data. Finally, with the utilization of the ANSYS parametric design language (APDL) on the ANSYS platform, the coupling effect between the fatigue damage of materials and the stress distribution in structures is taken into account, and the fatigue life of specimens is predicted. The outcome shows that the numerical prediction is in accord with the experimental results, indicating that the revised two-scale damage evolution model can be well applied for the high cycle fatigue life prediction under uniaxial loading.  相似文献   

4.
应变疲劳强度概率分布   总被引:1,自引:0,他引:1  
利用概率论方法建立了应变疲劳强度概率分布与应变疲劳寿命概率分布之间的数学关系式,并根据应变-寿命转换关系,由已知的给定应变水平下的疲劳寿命概率分布求出给定寿命下的应变疲劳强度分布函数,便于进行可靠性分析。  相似文献   

5.
6.
Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF) test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.  相似文献   

7.
In this paper we introduce a peridynamic model for the evolution of damage from pitting corrosion capable of capturing subsurface damage. We model the anodic reaction in corrosion processes (in which electroplating is negligible) as an effective peridynamic diffusion process in the electrolyte/solid system coupled with a phase-change mechanism that allows for autonomous evolution of the moving interface. In order to simulate creation of subsurface damage, we introduce a corrosion damage model based on a stochastic relationship that connects the concentration in the metal to the damage of peridynamic mechanical-bonds that are superposed onto diffusion-bonds. We study convergence of this formulation for diffusion-dominated stage. The model leads to formation of a subsurface damage layer, seen in experiments. We validate results against experiments on pit growth rate and polarization data for pitting corrosion. We extend the 1D model to the 2D and 3D, and introduce a new damage-dependent corrosion model to account for broken mechanical bonds that enhance the corrosion rate. This coupled model can predict the pit shape and damage profile in materials with microstructural heterogeneities, such as defects, interfaces, inclusions, and grain boundaries.  相似文献   

8.
作为一种不可逆的热力学过程,腐蚀疲劳的点蚀演化受到体系应变能、表面能和电化学能的共同影响.基于能量学原理,对腐蚀疲劳点蚀演化过程中的能量问题进行探索性研究.引入双变量半椭球模型描述点蚀的演化过程,推导了点蚀形状参数在演化过程中的变化方程.基于应力强度因子准则建立点蚀向疲劳裂纹转化的临界条件,同时分析应力幅值对腐蚀疲劳裂纹成核寿命的影响.  相似文献   

9.
This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The criterion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S–N curves: tension–compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promising. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the nonproportionality of loading.  相似文献   

10.
Rotary bending fatigue tests were carried out by using smooth specimens of medium carbon steel with two ferrite grain sizes. In order to clarity the physical background of the scatter in fatigue behaviour, the statistical characteristics of the initiation and growth of short fatigue crack were investigated. Results show that the short crack initiation and growth life distribution can be express by two-or three-parameter Weibull distribution. The Weibull distribution of the mixed type is well fitted to the crack length distribution for both steels. The knee values of Weibull plots are related to the grain size. The crack length distribution before the knee point can be expressed by a two-parameter Weibull distribution, and that after the knee point can be represented by two-or three-parameter Weibull distribution. It was found that the initiation Life, growth life and crack length distribution were affected by the grain size.  相似文献   

11.
铝合金蚀坑损伤参量评述   总被引:1,自引:0,他引:1  
将蚀坑损伤参量分成4 类:尺寸、形状、统计和试验参数,回顾了蚀坑深度、投影面积、长宽比、矩形比、表面腐蚀率、分形维数、预腐蚀系数等影响剩余寿命的主要损伤参量,总结了蚀坑等效成初始裂纹的方法.  相似文献   

12.
试样尺度、缺口和加载方式通常对材料的疲劳性能具有重要影响. 因此,发展关联试样尺度、缺口和加载方式对疲劳强度影响的方法对于从材料疲劳性能到结构件疲劳性能的预测具有重要意义.首先,采用旋转弯曲加载和轴向加载方式对不同几何形状EA4T车轴钢试样进行了疲劳实验.实验结果表明, 由于试样尺度的增加,轴向加载下狗骨形试样的疲劳强度明显低于沙漏形试样; 相同寿命下,缺口显著降低试样的疲劳强度. 疲劳断口扫描电镜观测结果表明,疲劳裂纹均起源于试样表面.沙漏形试样和狗骨形试样疲劳断口大多只有一个裂纹源,而缺口试样疲劳断口均具有多裂纹源特征. 然后,采用概率控制体积方法研究了试样尺度、缺口和加载方式对疲劳强度的影响,并与临界距离和应变能密度方法进行了比较. 结果表明,概率控制体积方法能够更好地关联试样尺度、缺口和加载方式对EA4T车轴钢疲劳强度的影响.最后, 提出一种基于控制体积的结构件疲劳强度预测方法,并用于具有不连续高应力区域车轴钢试样的疲劳强度预测,预测结果与实验结果 吻合.   相似文献   

13.
既有铁路钢桥剩余疲劳寿命的概率性评估   总被引:1,自引:0,他引:1  
中国铁路线上大量既有钢桥承受着日益繁重的交通荷载,其疲劳剩余寿命与使用安全已受到桥梁管理部门的高度重视,为避免不必要的维护与更换,应建立合理的既有钢桥使用安全评估方法。在建立能反映铆接钢桥疲劳破坏机理的脆断和韧断概率失效模型基础上,给出了疲劳可靠性分析的极限状态方程,并合理确定了随机变量的参数取值。建立了铆接钢桥构件双角钢概率疲劳破坏模型,基于Monte Carlo算法实现了铆接钢桥构件双角钢疲劳断裂失效概率的计算,编制了相应的概率断裂分析程序DAPFF。进而将概率断裂力学评估方法应用于京九线赣江桥的时变疲劳可靠度分析,并给出了赣江桥概率疲劳剩余寿命评估结果与维护对策。  相似文献   

14.
基于韧性耗散模型的损伤定量分析方法   总被引:7,自引:0,他引:7  
胡明敏 《力学季刊》2000,21(3):387-391
材料的静力韧性便于工程测量,对疲劳损伤较其它宏观损伤变量更敏感。本文以材料静力韧性为宏观损伤变量,依据疲劳过程中金属材料韧性随疲劳循环加载而变化的实验结果的规律分析,得到了应力和循环数表达的损伤演化方程和损伤累积模型。该模型能较好地反映加载顺序的影响。推导出该疲劳损伤累积模型在多级加载下的递推公式。经四种金属材料疲劳试验数据验证结果表明,该模型预测疲劳寿命是较为满意的。由于疲劳试验数据分散性大,结果有待进一步验证。  相似文献   

15.
试验研究了铝合金切口件在4组变幅块谱下、3.5%NaCl溶液中腐蚀疲劳裂纹起始寿命.结果表明,变幅载荷谱中的大超载会显著延长腐蚀疲劳裂纹起始寿命,并且加载顺序具有明显的影响.根据反映大小载荷交互作用的超载腐蚀疲劳裂纹起始寿命曲线和Miner累积损伤定则,建立了变幅载荷下切口件腐蚀疲劳裂纹起始寿命估算模型,应用该模型估算的结果与试验结果相吻合.  相似文献   

16.
大型汽轮机部件低周疲劳安全寿命的设计和评定   总被引:1,自引:0,他引:1  
文中提出了汽轮机部件低周疲劳安全寿命的设计和评定方法。介绍了汽轮机部件低周疲劳安全寿命的含义和计算方法。该方法以概率论和统计学为基础,把汽轮机部件的低周疲劳寿命处理为随机变量,对低周疲劳试验数据进行统计分析来确定材料低周疲劳寿命的分布参数,使用可靠性理论来确定汽轮机部件的低周疲劳安全寿命。文中给出了低周疲劳寿命服从正态分布和对数正态分布时汽轮机部件低周疲劳安全寿命的计算方法和应用实例。该方法考虑了汽轮机运行参数随机性和材料低周疲劳特性离散性的影响,为汽轮机部件低周疲劳寿命的设计、评定和诊断提供了科学的依据。  相似文献   

17.
腐蚀疲劳是工业装备的主要失效模式之一.随着新技术的不断发展,航空航天、轨道交通、海洋设施等重大装备向着高可靠性、长寿命及智能化方向发展,亟需准确、高效的腐蚀疲劳寿命预测方法.论文对金属材料的腐蚀疲劳损伤机理进行了简要总结并对寿命预测模型进行了系统归纳与评述,提出未来的研究趋势与方向.具体地,首先介绍了腐蚀坑的萌生和生长、裂纹萌生及扩展的机理;其次总结了预腐蚀疲劳的断裂力学及损伤力学寿命预测模型,再次归纳了腐蚀疲劳的断裂力学、损伤力学及数据驱动寿命预测模型;进一步地,综合概括了现有寿命预测模型的优点和不足;最后,基于当前的研究指出未来可能的发展方向,一方面可以借助三维成像技术实现蚀坑向裂纹转变阶段和短裂纹扩展阶段的可视化研究,以改进现有的断裂力学模型;另一方面可以建立新型的多尺度多阶段寿命预测模型或利用新兴的数据驱动-物理融合方法实现腐蚀疲劳寿命预测.  相似文献   

18.
When the historic probabilistic S-N curves are given under special survival probability and confidence levels and there is no possible to re-test, fatigue reliability analysis at other levels can not be done except for the special levels. Therefore, the wide applied curves are expected. Monte Carlo reconstruction methods of the test data and the curves are investigated under fatigue life following lognormal distribution. To overcome the non-conservative assessment of existent man-made enlarging the sample size up to thousands, a simulation policy is employed to address the true production where the sample size is controlled less than 20 for material specimens, 10 for structural component specimens and the errors matching the statistical parameters are less than 5 percent. Availability and feasibility of the present methods have been indicated by the reconstruction practice of the test data and curves for 60Si2Mn high strength spring steel of railway industry.  相似文献   

19.
复杂应力状态镍基单晶合金低周疲劳损伤模型   总被引:1,自引:0,他引:1  
丁智平  陈吉平  尹泽勇 《应用力学学报》2005,22(2):310-314,i014
根据连续介质损伤力学理论,采用应变能释放率作为热力学广义力描述正交异性材料的疲劳损伤过程,引入取向函数考虑镍基单晶合金晶体取向对疲劳损伤的非线性影响,提出了一个各向异性疲劳损伤模型。应用多元线性回归分析方法,拟合疲劳试验数据可确定模型参数。从应变能释放率的应变空间表达式出发,导出了含有3个弹性常数的单晶合金应变三轴性因子,它既反映了材料性能的晶体取向相关性,又反映了正应力和剪应力的相互作用,并可退化为各向同性材料的应变三轴性因子。利用该模型对CMSX-2镍基单晶合金在应力控制对称循环拉-扭载荷作用下的低周疲劳寿命进行预测,预测值与试验值吻合的相当好,试验所得数据均落在2.2倍偏差的分布带内。  相似文献   

20.
IntroductionAsaspecialformofstructures,tubularjoints (multi_ductpipes)weldedbycircularcylindricalshells (circulartubes)havebeenwidelyusedinengineering .Oneoftheprimaryfactorsthatareresponsibleformanyseriousaccidentsistheinsufficientfatiguestrengthofthejo…  相似文献   

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