【作者】 王明珠；

【导师】 姚卫星；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2009， 博士

【摘要】 航空航天、风能利用、公路铁路以及海洋运输等领域的很多结构都是在振动载荷环境下工作的,然而由于振动疲劳本身存在的复杂性,目前在试验和理论方面对振动疲劳的研究还很不成熟。因此,对振动疲劳寿命进行系统深入的研究具有重要的理论意义和工程实用价值。本文采用试验和理论相结合的研究方法。振动疲劳试验提供了验证数据,以全寿命区疲劳S-N曲线作为寿命分析依据,从振动疲劳寿命估算方法和振动疲劳寿命的影响因素两方面,对结构振动疲劳寿命分析方法进行了比较系统的研究。采用锤击法对LY12CZ铝合金悬臂梁结构的U形槽和圆形槽缺口试验件进行了模态分析试验;采用基础振动的加载方式对U形槽缺口试验件悬臂梁结构进行了三种不同疲劳载荷谱下的振动疲劳试验,对圆形槽缺口试验件悬臂梁结构进行了两种不同疲劳载荷谱下的振动疲劳试验。研究了频率对金属材料疲劳寿命曲线的影响,提出了金属材料疲劳S-N曲线模型。疲劳S-N曲线模型在全寿命区域内很好的描述了循环应力和疲劳寿命之间的关系。统计分析了大量的试验结果,对疲劳S-N曲线模型以及频率的影响进行了验证,为结构振动疲劳寿命估算提供了重要的依据。提出了随机过程的雨流幅值分布模型和时域振动疲劳寿命估算的样本法。提出的改进三角级数法解决了频域内非均匀采样随机过程的时域模拟问题,并基于改进三角级数法提出了时域振动疲劳寿命估算的样本法;提出了限带白噪声、单峰谱、双峰谱、斜谱和一般宽带随机过程的雨流幅值分布模型,给出了模型的参数和随机过程谱参数之间的半经验计算公式,并据此发展了频域振动疲劳寿命估算方法。结合振动疲劳试验结果对常用的频域疲劳寿命估算方法进行了评述和比较。经试验验证,得出本文提出的振动疲劳寿命预测方法能给出令人满意的寿命预测结果,且偏于安全。研究了阻尼、应力集中和平均应力对结构振动疲劳寿命的影响。建立了模态阻尼比与结构振动疲劳寿命之间的关系;定义了均方应力集中系数,引入疲劳缺口系数计算缺口件的振动疲劳寿命;提出了随机过程雨流均值分布模型,基于雨流幅值和雨流均值相互独立的假设,解决了平均应力影响下结构的振动疲劳寿命估算问题,给出了总体疲劳载荷和振动疲劳载荷共同作用下结构疲劳寿命估算过程。通过模态分析试验和振动疲劳试验的验证,表明本文的方法能很好的预测阻尼和应力集中影响下结构的振动疲劳寿命。更多还原

【Abstract】 Many components usually undergo vibration loading, which are used in aircrafts, wind energy utilizations and automobiles. However, vibration fatigue is more complicated than general cycle fatigue. Up to now, little experimental work has been done for vibration fatigue, and many theoretical problems have not been solved completely. Thus the systematical study on the vibration fatigue life has not only the important significance, but also a practical value.A combined theoretical and experimental study method for vibration fatigue life prediction was used. The vibration fatigue life research was consisted of the research on fatigue life prediction methods and the effect factors in fatigue life. The fatigue S-N curve was used as computation basis of fatigue life prediction. The vibration fatigue test was provided the datas for experimental verification.Modal analysis test and vibration fatigue test were conducted on cantilever structure of LY12CZ aluminum alloy. Two types of notch specimens were used, one was U grooved and the other was circular grooved. Hammering method was used in modal analysis test. Three different fatigue loadings were used on vibration fatigue test of U grooved specimens, and two different fatigue loadings were used on vibration fatigue test of circular groove specimens.The all life model of fatigue S-N curve for metal materials was presented. The effect of frequency on fatigue life curve of metal materials has been analyzed. The all life model of fatigue S-N curve describes the relationship between cycle stress and fatigue life very well. The statistics and analysis of test results show that the S-N curve model and frequency effects are in good agreement with the experimental ones.The models of rainflow amplitude distribution for random process and the sample method for vibration fatigue life prediction in time domain were presented. An improved trigonometric series method for time domain simulation of random process was proposed to solve the time domain simulation of random process on non-uniform sampling in frequency domain. The sample method was proposed and used for vibration fatigue life prediction in time domain, which based on the improved trigonometric series method. The models of rainflow amplitude distribution for limited band white noise, unimodal resonance spectrum, bimodal stress spectrum and general broadband random process were proposed, and the experiential formulas of model parameters were given in this paper. New methods of vibration fatigue life prediction in frequency domain were developed. Several common frequency domain methods of vibration fatigue life prediction and our methods of vibration fatigue life prediction were examined with the test data. It is demonstrated that the proposed life prediction methods give better satisfactory results for all experimental samples.The effect of damping, stress concentration and mean stress on structure vibration fatigue life has been analyzed. The relationship formula between modal damping ratio and structure vibration fatigue life has been given. The stress concentration factor of root mean square has been defined in this paper. And the prediction method for vibration fatigue life of notch sample based on fatigue notch factor has been proposed. The model of rainflow mean distribution for random process was proposed. The prediction method for vibration fatigue life taken into account effect of mean stress was presented, and this method based on the assumption of mutually independent between rainflow amplitude and rainflow mean. The effect of damping and stress concentration on vibration fatigue life are examined with the results of modal analysis test and vibration fatigue test. The analyzed results show good agreement with experimental results.更多还原