结构振动疲劳特性及其试验方法研究

图
分类号 TB534 密 级
学校代码 10699 学 号 066016006
西 北 工 业 大 学
硕 士 学 位 论 文
（学位研究生）
题目：结构振动疲劳特性及其试பைடு நூலகம்方法研究
作
者：
史展飞 固体力学 李玉龙
学科专业： 指导教师：
2009 年 3 月，西安
Northwestern Polytechnical University
Thesis for the Degree of Master
Title： A study on the fatigue properties and experimental method of structure vibration fatigue
Author：
Zhanfei Shi
Subject： Solid Mechanics Advisor： Yulong Li
III
西北工业大学硕士学位论文
Abstract
resonant frequency, the resistance of the structure to fatigue failure was the best. When the vibration frequency was lower than the resonant one, the resistance fatigue of structure was poor. The worst resistance fatigue for structure occurred at the resonant frequency. Fatigue fracture surface showed that the crack source was initiated from scratch or defects in the edges and surface of rectangular section beam. Besides conventional resisting fatigue design method, four other aspects such as alleviating vibration source, reducing vibration transfer, vibration control and optimizing the structure and technology should also be considered in order to improve the vibration fatigue resistance. (3) In order to accomplish the vibration experiment of LY12 aluminum alloy cantilever beam under high stress, non-resonance exciting frequency, mechanical excitation equipment was designed, which was drove by an dc driver motor. The test sample was loaded by cam-lever arm equipment. In this equipment, the frequency could be adjusted by controlling the rotational speed of the an dc driver motor and the amplitude adjusting could be achieved by applying the cams with different outlines. The debugging result showed that this equipment can be used to carry out experiments with high stress and non-resonance frequency vibration. Keywords: Vibration fatigue, frequency effect, mechanical exciting equipment, Vibration fatigue resistant design
March, 2009 in Xi`an City
西北工业大学硕士学位论文
摘要
摘要
振动疲劳是指交变激励频率与结构的某阶固有频率接近或一致时使结构产 生的疲劳失效。振动疲劳因其具有突发性，往往造成灾难性后果，特别在航空航 天结构设计中成为一个不可回避的问题。 振动疲劳的首要研究问题是分析振动频 率对疲劳特性的影响。 本文讨论了振动频率对合金高周疲劳寿命和裂纹扩展模型 的影响， 通过试验研究了铝合金悬臂梁结构在同一应力水平不同频率激励时的疲 劳特性，提出了结构抗振动疲劳破坏的设计方法，并设计了可调幅、调频的机械 式激励装置。本文拟为航空结构安全性设计提供参考。具体工作总结如下： （1） 通过对国内外文献报道的学习，发现加载频率对不同材料高周疲劳特性 的影响存在差异。钢材的高周疲劳特性受加载频率的影响较大，其高频 试验下得到的振动疲劳 S-N 曲线结果须加以修正才可使用；铝合金的高 周疲劳特性受加载频率的影响较小，其高频试验下得到的振动疲劳 S-N 曲线结果可直接使用。同时，加载频率对疲劳寿命的影响导致了不同的 裂纹扩展模型。 （2） 本研究针对 LY12 铝合金悬臂梁结构在不同频率进行了同一应力水平的 振动疲劳试验，结果表明该结构的疲劳特性在一定范围内，不同频率激 励下表现不同。且在共振曲线的共振频率两侧，用对称频率激励时得到 的结果不同。在激励频率高于共振频率振动时，结构抵抗疲劳失效的能 力最好；激励频率低于共振频率振动时，结构抵抗疲劳失效的能力较弱； 在共振频率振动时，结构抵抗疲劳失效的能力最差。疲劳断口形貌表明 裂纹源产生于矩形截面梁的棱边和梁表面的划痕、缺陷处。提高结构的 抗振动疲劳性能，除了常规的抗疲劳设计方法，还应从减轻振源、减少 振动传递、振动控制、结构及工艺优化四个方面为原则进行设计。 （3） 为了完成 LY12 铝合金悬臂梁结构高应力、非共振频率激励的振动试验， 设计了机械式激励设备。该设备由直流调速电机提供动力，采用凸轮— 杠杆机构完成对试样的加载。通过控制电机转速实现调频及不同轮廓线 的凸轮实现调幅。设备调试结果表明，该激励设备用于高应力、非共振 频率的振动试验是可行的。 关键词：振动疲劳，频率效应，机械激励设备，抗振动疲劳设计
I
西北工业大学硕士学位论文
摘要
II
西北工业大学硕士学位论文
Abstract
Abstract
Vibration fatigue is a kind of fatigue failure, which occur when the alternate excitation frequency is close to or the same with the natural frequency of the structure. Vibration fatigue usually happens suddenly, and therefore often leads to catastrophic consequences. Hence , it becomes an unavoidable problem for structural design in the fields of aeronautics and astronautics. The primary research issue of vibration fatigue is to analyze the effect of vibration frequency on fatigue properties. In this paper, we discussed the influence of vibration frequency on the high cycle fatigue life and crack propagation, investigated the fatigue property of aluminum alloy projecting beam structure under the same stress but different frequency excitation, the design methods for resisting failure of vibration fatigue in structural material were proposed, and designed a amplitude-modulated and frequency-modulated control mechanical excitation installation. The paper could provide actual reference for the sake of aerospace structure safe design. The main works were as follows: (1) By systematically investigating the open literatures and reports, we discovered that loading frequency had different influence on the high cycle fatigue life of different material. The high cycle fatigue properties of steel were greatly influenced by loading frequency. Its results from vibration fatigue S-N curve under high frequency should be properly modified before using. While for aluminum alloys, the high cycle fatigue properties were influenced less and the results obtained from vibration fatigue S-N curve under high frequency could be used directly for engineering application. Meanwhile, we also found that different effects of loading frequency on fatigue life lead to different crack propagation models. (2) Vibration fatigue experiment on a cantilever beam made of LY12 aluminum alloy was carried out at the same stress level but different vibration frequency. During a certain exciting frequency range, the fatigue properties of the tested structure were very sensitive to the exciting frequency. On both sides of the resonant frequency of the resonant curve, the experimental results were different when the exciting frequency was asymmetric. When vibration frequency was higher than the