多轴随机载荷下疲劳寿命预测方法的研究

发布时间：2018-01-01 02:12

本文关键词：多轴随机载荷下疲劳寿命预测方法的研究　出处：《东北大学》2012年硕士论文　论文类型：学位论文

【摘要】：多轴随机载荷是工程实践中大量遇到的实际情况,经典的疲劳理论远远满足不了当代机械产品强度和寿命设计要求,因此多轴随机载荷作用下结构构件的疲劳强度分析和寿命估算是近年来国内外疲劳研究的主要对象。从理论上对随机载荷下的疲劳寿命预测方法进行全面系统深入地研究,将会有效地提高疲劳寿命预测精度,保证机械设备安全可靠地运行,减少事故的发生。同时也可以提高产品的设计水平、延长使用寿命,增强机械产品在市场的竞争力,不仅具有深远的理论意义,而且也具有重大的应用价值和经济效益。本文在综述国内外多轴疲劳研究发展概况的基础上,根据目前已有的多轴疲劳理论研究成果,采用时域与频域相结合的方法,对随机载荷下多轴疲劳寿命预测方法进行深入研究。首先,建立根据载荷幅值的方差所确定的参考坐标系,将偏量空间中的载荷路径沿参考坐标系各轴投影,原载荷等效成为多段单轴载荷历程,依据向量范数的概念,定义和求解剪应力的等效幅值。由于疲劳损伤与载荷幅值的方差密切相关,所以通过这种方法求得的剪应力的等效幅值反映了载荷对材料损伤的影响。其次,考虑平均应力的影响,计算等效的单轴载荷历程造成的疲劳损伤。这个过程需要对两段载荷时间历程进行同步计数,基于此,给出了多轴随机载荷的压缩方法与多轴循环计数方法。本方法不但能够有效地简化随机载荷历史,而且还能实现载荷取舍的同步性,使同时对两段载荷进行循环计数成为可能。再次,利用修正S-N曲线方法,建立了时域多轴疲劳寿命估算模型。该模型也适用于单轴、多轴比例、非比例,多轴变幅等加载情况。通过引用三种材料的试验数据进行验证,预测结果与试验结果的误差较小,并偏于安全。最后,在时域多轴疲劳寿命估算模型的基础上,结合频域疲劳的研究方法,建立了频域多轴疲劳寿命估算模型。该模型也适用于单轴、多轴平稳高斯应力过程。经过引用文献中的试验数据进行验证,预测结果均在2个因子范围内,预测能力较好。
[Abstract]:Multi-axis random load is a large number of practical situations encountered in engineering practice. The classical fatigue theory can not meet the requirements of strength and life design of modern mechanical products. Therefore, fatigue strength analysis and life estimation of structural members under multiaxial random loads are the main objects of fatigue research at home and abroad in recent years. Ground study. It will effectively improve the prediction accuracy of fatigue life, ensure the safe and reliable operation of mechanical equipment, reduce the occurrence of accidents, improve the design level of products, and prolong the service life. Enhancing the competitiveness of mechanical products in the market not only has profound theoretical significance, but also has great application value and economic benefit. On the basis of summarizing the development of multiaxial fatigue research at home and abroad, this paper adopts the method of combining time domain and frequency domain according to the existing research results of multiaxial fatigue theory. The prediction method of multiaxial fatigue life under random load is studied. Firstly, the reference coordinate system is established according to the variance of the load amplitude. The load path in the offset space is projected along each axis of the reference coordinate system, and the original load is equivalent to the multi-section uniaxial load history. According to the concept of vector norm, the equivalent amplitude of shear stress is defined and solved. The fatigue damage is closely related to the variance of load amplitude. So the equivalent amplitude of shear stress obtained by this method reflects the effect of load on material damage. Secondly, considering the effect of average stress, the fatigue damage caused by the equivalent uniaxial load history is calculated. The compression method and the multiaxial cyclic counting method of multiaxial random loads are presented. This method not only simplifies the history of random loads effectively, but also realizes the synchronicity of load selection and selection. It is possible to carry out cyclic counting of two loads at the same time. Thirdly, using the modified S-N curve method, a time-domain multiaxial fatigue life estimation model is established, which is also applicable to uniaxial, multi-axial proportional and non-proportional. By using the test data of three kinds of materials for verification, the error between the prediction results and the test results is small, and it is more safe. Finally, based on the time-domain multiaxial fatigue life estimation model and the frequency-domain fatigue research method, a frequency-domain multiaxial fatigue life estimation model is established, which is also suitable for uniaxial fatigue. The multiaxial stationary Gao Si stress process is verified by citing the experimental data in the literature. The predicted results are within the range of two factors and the prediction ability is good.
【学位授予单位】：东北大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH114

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