复合材料修补结构的疲劳寿命预测方法

针对复合材料修补结构应力分布复杂的特点,在剩余强度衰减模型的基础上引入局部应力应变法的分析思想,建立起复合材料修补结构的疲劳寿命预测模型.在剩余强度衰减模型和希尔提出的各向异性材料塑性条件基础上建立单向层合板在任意应力状态下的疲劳破坏准则.     

复合材料层合板疲劳寿命的可靠性分析

基于唯象的剩余强度衰减模型与蔡－希尔静强度判据,建立单向层合板在任意复杂面内应力作用下的疲劳失效准则。利用蒙特卡洛模拟方法计算层合板的疲劳寿命,并对其进行可靠性评估。根据Ｔ３００／ＱＹ８９１１的三种典型层合板［０］１６、［９０］２４和［±４５］３Ｓ的拉—拉疲劳试验结果,利用蒙特卡洛模拟方法计算层合板的疲劳寿命,结果表明寿命服从Ｗｅｉｂｕｌ分布。     

复合材料修补结构疲劳寿命分析方法研究

结合工艺方法,研究典型缺陷损伤的修理方法,针对复合材料修补结构应力分布复杂的特点,在剩余强度衰减模型的基础上引入局部应力应变法的分析思想,建立起复合材料修补结构的疲劳寿命预测模型。通过建立修补结构的力学分析模型,在分析了修补结构的危险部位和应力集中的基础上,利用寿命预测模型,分析和讨论补片直径和补片厚度两个修补参数对修补结构疲劳寿命的影响规律。     

基于累积损伤的三维复合材料层合板疲劳寿命研究

基于渐进疲劳损伤模型,建立复合材料层合板的三维疲劳寿命预测模型,模型以单向板单轴疲劳试验数据为基础,结合正则化剩余刚度模型、正则化剩余强度模型和等寿命曲线,通过层合板三维应力分析、失效分析和材料性能退化的循环迭代进行疲劳寿命计算,在Ansys软件平台上利用APDL语言编写相应的计算程序,估算不同铺层参数层合板在单轴和多...     

复合材料的疲劳寿命预测

较详细地介绍了疲劳寿命预测的剩余刚度，强度和疲劳模量模型，并且指出了这些方法的主要不足。在此基础上提出了一种基于疲劳损伤过程能量衰减的剩余能量模型，以及进行复合材料结构疲劳寿命预测的二元方法的构想。     

T700/3234碳纤维层合板的拉伸疲劳特性分析

通过对T700/3234碳纤维复合材料层合板进行静力拉伸试验和拉-拉疲劳试验,得到层合板的拉伸性能、疲劳寿命和刚度衰减规律,然后采用数值分析方法对层合板的拉伸强度进行预测,并对碳纤维层合板的疲劳S-N曲线以及疲劳刚度衰减进行了研究。结果表明:采用逐渐累积损伤的数值方法所得到的拉伸强度与试验结果较为吻合,根据疲劳理论拟合得到的S-N曲线和刚度衰减曲线很好地描述了材料的疲劳性能,为研究T700碳纤维层合板的疲劳损伤演化提供了重要参考。     

基于非线性连续疲劳损伤的再制造毛坯剩余寿命评估

在考虑裂纹闭合效应对疲劳损伤影响的情况下,对Chaboche提出的非线性连续疲劳累积损伤模型进行了修正,得到了疲劳累积损伤及再制造毛坯剩余寿命评估模型,并由对称循环拉压疲劳试验数据得出了修正模型的相关参数。通过二级加载(高低加载和低高加载)拉压疲劳试验对再制造毛坯剩余寿命评估模型进行了验证,结果表明模型计算值和试验值吻合良好,证明修正后的模型能够准确预测再制造毛坯的剩余寿命。     

基于低周热疲劳试验条件的活塞寿命预测研究

为了预测铝合金活塞在高温蠕变影响下的低周热疲劳寿命,根据活塞低周热疲劳试验反求确定其热边界条件,运用有限元法计算其温度场及应力场。考虑材料性能的温度效应,采用疲劳分析软件FE-FATIGUE中的E-N方法进行活塞低循环热疲劳寿命预测,经试验验证,软件预测与试验结果基本吻合。     

层压复合材料剪切疲劳寿命预估

将Iosipescu剪切强度测试方法推广到剪切疲劳试验.以碳纤维/树脂基T300/QY8911复合材料层压板为研究对象,对三种多向铺层试件进行剪切疲劳试验.用一种疲劳损伤累积模型和自行开发的有限元/疲劳寿命分析程序预测被试多向层压板的剪切强度,模拟局部疲劳失效演变的过程,给出疲劳寿命和剩余强度预估结果,比较两种静强度准则(Tsai-Hill准则和Puck修正准则)对预估结果的影响.寿命预测结果与试验结果基本相符.     

非比例载荷下304不锈钢低周疲劳寿命预测

在拉扭疲劳试验机上完成了一系列非比例加载下对304不锈钢的低周疲劳试验,对目前常用的几种多轴疲劳寿命预测模型进行了分析比较。结果表明,以单轴疲劳寿命分析方法为基础的等效应变法,不能预测多轴非比例加载下的低周疲劳寿命,以临界面法为基础的Socie剪切模型对非比例加载下304不锈钢材料的疲劳寿命预测较好。     

Fretting Fatigue Life Estimation of Al 7075-T6 Using Plain Fatigue Test

Fretting fatigue occurs in many engineering applications. Fretting fatigue life is estimated by experiment, which is tedious and requires special equipment and instrumentation. In this study, we attempt to introduce a method for estimation of fretting fatigue life from plain fatigue (normal fatigue without fretting) experiments. The method employs the critical distance theory for estimation of fretting fatigue life of Al7075-T6 under rotary bending loading. The approach uses the Fatemi-Socie parameter (FSP) as a multiaxial criterion to account for the stress multiaxiality on focus path. A comparison between the predictions of the new approach with the experimental results shows that the approach is quite accurate for low stress or high cycle fatigue regimes but for high stresses it is slightly conservative. This method considers only elastic behavior for materials and two characteristic diagrams that are obtained simply by testing two simple notched specimens under plain fatigue conditions. The method is therefore an applicable approach that can be used in the context of finite fretting fatigue life estimation with no need for fretting fatigue tests.     

电镀铜薄膜疲劳性能与寿命预测

利用MMT-11N微机械疲劳试验系统对11.5 μm厚无基体支持的电镀铜薄膜试件的拉伸疲劳特性进行了试验研究。试件采用准LIGA工艺制作。试验在室温条件下进行,采用载荷控制、脉动循环加载,载荷频率为20 Hz,得到了铜薄膜光滑试件和缺口试件的S-N曲线,根据传统宏观疲劳理论确定了铜薄膜循环应力—应变曲线和应变—寿命曲线。利用修正局部应力—应变法对缺口试件的疲劳寿命进行了预测,预测寿命与试验寿命误差在3.2倍因子之内,预测结果较好地符合试验结果。试验表明,取半寿命周期的迟滞回线作为稳定迟滞回线在微机械疲劳中仍是可信的,局部应力—应变法亦可应用于微机电系统疲劳寿命预测,宏观疲劳理论在一定程度上也适合于描述微机械疲劳。     

Fatigue life prediction by statistical approach under constant amplitude loading

In general, the experimental data of fatigue crack growth rates scatter very much even under identical experimental condition such as a constant amplitude loading condition. It is, thus, essential to take into account the data scatter of crack growth rates by using statistical approach for a reliable fatigue crack, propagation analysis. In this study, fatigue crack propagation tests were conducted on a 1.02 mm-thick 2024-T3 aluminum alloy under a constant amplitude loading condition. The distribution of the fatigue crack propagation life is estimated by using the stochastic Markov chain model based on a modified Paris-Erdogan equation to consider the variability of the fatigue crack growth. The fatigue lives estimated by using the Markov chain model are found to be agreed well with the experimental results.     

分层缺陷对复合材料结构疲劳寿命影响研究

介绍一种新研制的含缺陷复合材料压缩试验装置 ,并采用压缩疲劳试验方法研究中央分层和边缘分层缺陷对飞机复合材料结构疲劳寿命的影响。研究结果表明 ,试件疲劳破坏的起始位置与预制缺陷位置一致。含分层缺陷复合材料结构的疲劳寿命不仅与缺陷尺寸 ,而且与缺陷位置有关。该研究结果为制定生产和使用过程中缺陷或损伤的控制标准提供重要依据     

压力容器焊缝咬边疲劳裂纹的启裂寿命

针对某企业空气球罐焊缝咬边在压力波动时的受力情况,首先建立带咬边结构的受力模型,利用西田正孝的图表方法和有限元法分别计算咬边引起的弹性应力集中系数,然后计算出咬边尖端的名义应力,进而利用小缺口启裂寿命经验估算式估算咬边的疲劳裂纹启裂寿命。再采用与实物等厚度、与真实咬边等尺寸的模拟试样,进行与实际结构等应力范围条件下的模拟疲劳试验。结果表明,试验寿命与根据经验估算式得到的估算寿命非常接近,从而为咬边疲劳裂纹启裂寿命研究提供了理论依据和试验数据。在考虑一定的安全系数后,对所分析的球罐给出的剩余总寿命为9年,至启裂的剩余寿命为6年。     

Fretting damage in thin sheets: Analysis of an experimental configuration

A method for evaluating fretting damage in thin sheets was developed for AISI 301 stainless steel in full hard condition in contact with AISI 52100 steel and cast ANSI A356 aluminum. Samples were subjected to fretting and then were subsequently fatigue tested to determine the impact of the fretting damage on fatigue life. A finite element model of the experimental configuration was used to determine the response for the experimental conditions imposed. The values of Fatemi-Socie critical-plane fatigue damage parameter are shown to correspond to the trends in the observed residual fatigue life for contact with AISI 52100 steel.     

Fatigue resistance of SMA-martensite bars subjected to flexural bending

The fatigue resistance of Ni–Ti shape memory alloy (SMA)-martensite bars in bending subjected to large deformation cycles has been experimentally evaluated. Firstly, fatigue tests under constant displacement amplitude have been carried out, at two different frequencies of loading. Then, the cumulative fatigue damage and fatigue life prediction of specimens loaded under variable load conditions have been investigated. Finally, the effect of low-cycle-fatigue (LCF) and plastic deformations on subsequent high-cycle-fatigue (HCF) has been studied.The experimental results point out that the frequency of loading (i.e. temperature) significantly affects the fatigue life of the specimens. The damage accumulation process seems to follow the “Miner” linear damage theory for low-to-high (L–H) loading sequences, while the same does not hold for high-to-low (H–L) loading sequences. Surprisingly, a small fraction of LCF life consumption seems to enhance the subsequent HCF limits.     

FATIGUE LIFE PREDICTION THEORY OF COMPOSITE LAMINATES AND EXPERIMENTAL VERIFICATION

According to traditional phenomenological fatigue methodology and modem continuum damage mechanics theory, dual fatigue cumulative damage rules to predict fatigue damage formation and propagation lives of the notched composite laminates are presented. A 3-dimensional damage constitutive equation of anisotropic composites is also established. Damage strain energy release rate is interpreted as a driving force of the fatigue delamination damage propagation. A new damage evolution equation and a damage propagation σa-σm-N surface (stress amplitude-mean stress-life surface) are derived. Hence, using the method above, the fatigue life of composite components can be predicted. Finally, theoretically predicted results are compared with experimental data. It is found that the deviation of theoretic prediction from experimental results is about 22%.     

连接方式对紧固孔疲劳性能的影响

通过对紧固孔件的疲劳试验,研究不同连接方式对其疲劳性能的影响.对两种不同连接方式的紧固件的疲劳试验结果进行对比分析,对疲劳断口进行观察分析,基于当量初始裂纹(equivalent initial flaw size)理论计算不同连接方式下的原始疲劳质量.试验结果表明,采用沉头铆钉连接方式紧固孔的疲劳寿命略长于采用沉头螺栓连接方式的紧固孔,但沉头铆钉连接方式紧固件疲劳寿命的分散性较后者大;铆接紧固件的当量初始裂纹尺寸比螺接紧固件小,原始疲劳质量有所提高;在不同连接方式下,裂纹萌生位置不变,裂纹萌生寿命约为紧固件总疲劳寿命的80％.     

基于MSC.Fatigue的汽车横向稳定杆疲劳可靠性仿真及试验研究

基于传统汽车稳定杆疲劳可靠性设计偏于保守,造成疲劳设计缺乏科学依据、开发周期长、零件过于笨重、疲劳可靠性低等情况,提出将疲劳可靠性方法与疲劳有限元设计方法相结合,利用专业疲劳分析软件MSC.Fatigue,建立汽车稳定杆有限元模型,利用有限元方法计算其最小疲劳寿命和寿命分布,从而得到稳定杆的受力、危险部位、疲劳寿命等情况.稳定杆疲劳试验表明,预估结果与试验结果相吻合,为汽车稳定杆的材料选择、结构优化、疲劳设计提供了参考.