结构多轴疲劳寿命预测的场强法

发布时间：2018-05-13 05:38

本文选题：多轴疲劳 + 疲劳累积损伤　；参考：《南京航空航天大学》2016年博士论文

【摘要】：工程结构在服役期间通常受到多轴疲劳载荷的作用。疲劳累积损伤理论研究变幅载荷作用下疲劳损伤的累积规律,缺口件疲劳寿命预测方法研究缺口附近应力梯度对疲劳寿命的影响,它们对于工程结构的多轴疲劳寿命预测至关重要。本文按照载荷随机性,将多轴累积损伤理论研究中已有的多轴变幅载荷分为阶梯谱、块谱和随机谱。然后,按照损伤累积方式和对多轴疲劳损伤方向性的认识,将已有的多轴疲劳累积损伤理论分为四类:(a)不分方向的线性累积模型;(b)不分方向的非线性累积模型;(c)分方向的线性累积模型;(d)分方向的非线性累积模型。通过统计对比各模型的应用情况,对它们的适用范围、计算效果进行了初步分析。本文使用LY12CZ铝合金进行了一系列多轴两级阶梯谱试验。通过分析试验结果发现,载荷速率的变化与材料临界面上的多轴应力状态变化情况有关。本文提出了一种新的累积损伤模型用来描述多轴阶梯谱下的疲劳损伤累积规律。新模型的累积损伤计算结果与试验结果相比,准确率较高。本文使用LY12CZ铝合金进行了一系列多轴块谱、随机谱试验。试验结果表明,虽然载荷幅值和载荷路径的变化对损伤累积速率有影响,但是这种影响随着载荷随机性的增加而减弱。最终,Miner理论可以较好地描述多轴块谱和随机谱下的损伤累积规律。因此,对于工程结构,使用Miner理论计算多轴疲劳累积损伤是合理可行的。本文研究了薄壁圆管试件截面剪应力梯度对疲劳寿命的影响。然后,进一步通过考虑多轴疲劳损伤方向性和临界面上的应力梯度效应,对单轴缺口件疲劳研究中常用的应力场强法进行了改进。之后,本文使用LY12CZ铝合金进行了一系列多轴缺口件疲劳试验。试验结果表明,本文提出的改进模型有较好的寿命预测准确率。最后,本文结合上述多轴疲劳累积损伤理论和缺口件多轴疲劳寿命预测方法研究,给出了工程结构的多轴疲劳寿命分析流程,并依据分析流程对某型航空发动机轮盘、某型飞机起落架部件和新舟60某改型飞机机翼吊挂接头进行了疲劳寿命分析。分析结果表明,本文提出的多轴疲劳累积损伤理论和缺口件多轴疲劳寿命预测方法对实际结构的疲劳寿命预测结果均令人满意。
[Abstract]:Engineering structures are usually subjected to multiaxial fatigue loads during service. Fatigue cumulative damage theory is used to study the cumulative law of fatigue damage under variable amplitude loading. The prediction method of fatigue life of notched parts is used to study the effect of stress gradient near notch on fatigue life. They are very important to predict the multiaxial fatigue life of engineering structures. In this paper, according to the randomness of loads, the multiaxial variable amplitude loads in the study of multiaxial cumulative damage theory are divided into stepped spectrum, block spectrum and random spectrum. Then, according to the damage accumulation mode and the recognition of the direction of multiaxial fatigue damage, The existing multiaxial fatigue cumulative damage theory is divided into four kinds of linear accumulative models without any direction. Through statistical comparison of the application of each model, the scope of their application and calculation results are preliminarily analyzed. In this paper, a series of multi-axis two-step spectrum tests have been carried out using LY12CZ aluminum alloy. It is found that the change of loading rate is related to the change of multiaxial stress state at the interface of the material. In this paper, a new cumulative damage model is proposed to describe the fatigue damage accumulation law under multiaxial step spectrum. Compared with the experimental results, the accuracy of the new model is higher. In this paper, a series of multiaxial block spectra and random spectrum tests have been carried out using LY12CZ aluminum alloy. The experimental results show that the damage accumulation rate is affected by the change of load amplitude and load path, but the effect is weakened with the increase of load randomness. Finally, the Miner theory can well describe the damage accumulation law of multiaxial block spectrum and random spectrum. Therefore, for engineering structures, it is reasonable and feasible to use Miner theory to calculate multiaxial fatigue cumulative damage. In this paper, the influence of shear stress gradient on fatigue life of thin wall tube specimen is studied. Then, by considering the direction of multiaxial fatigue damage and the stress gradient effect at the interface, the stress field strength method, which is commonly used in the fatigue research of uniaxial notched parts, is improved. After that, a series of fatigue tests of multiaxial notched parts were carried out using LY12CZ aluminum alloy. The experimental results show that the proposed improved model has a better accuracy of life prediction. Finally, combined with the theory of multiaxial fatigue cumulative damage and the multiaxial fatigue life prediction method of notched parts, the multiaxial fatigue life analysis flow of engineering structure is presented, and the wheel disc of a certain aero-engine is analyzed according to the analysis flow. The fatigue life of landing gear parts of a certain aircraft and wing hangers of a modified aircraft Xinzhou 60 are analyzed. The results show that the multiaxial fatigue cumulative damage theory and the multiaxial fatigue life prediction method proposed in this paper are satisfactory for the prediction of fatigue life of real structures.
【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O346

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