ii
典型结构件的振动疲劳分析
图清单
图 1.1 基础激励振动疲劳试验装置 ........................................................................................ 4 图 1.2 铝合金疲劳裂纹扩展曲线及实物图.............................................................................. 4 图 1.3 复合膜材料疲劳寿命曲线............................................................................................ 5 图 1.4 有机塑料的 S-N 曲线 ................................................................................................... 5 图 1.5 LY12CZ 铝合金动态疲劳 S-N 曲线.........................................................................频率，模型修正，频率变化，裂纹扩展
i
典型结构件的振动疲劳分析
Abstract
At present, the conventional analytical methods of static fatigue has been formed a separate system, and in engineering applications are quite ripe. But in actual environment, the project structure is often working in the environment of the vibration loads, the principal loss of structure is caused by vibration. Only use the idea of static fatigue can not compeletly explain the vibration conditions of failure，because it omits the key role of the changes of frequency . As a result, we take the common typical structure of aircraft as analyzing objects. Futhermore, we use the finite element software of MSC.patran&nastran and fatigue as a platform building dynamic models to study its’dynamic features and fatigue life. This paper put forward a method which considers frequency as a main factor to predict the life of structure. All works of this paper includes: First, we choose unidirectional stiffened plate and linking slab which are widely used in aircraft as objects to complete the structural vibration fatigue experiments under resonant excitation, realizing band motivation of the incentive frequency tracking structure inherent frequency and studying structure life change rule and the dynamic change of natural frequency by the resonance conditions. Results show that structural dynamic characteristics have important influence on fatigue life and nature frequency with the fatigue process is drab degressive. Futhermore, all works Based on the MSC. Patran&nastran platform, establishing the typical structure finite element dynamic model to complete the modal analysis and validate the finite element model is correct. And we use the amended model to analysis structure dynamic response, so as to realize the fatigue life calculation. Moreover, considering frequency variation of structure damage effect, this paper puts forward the frequency as the main parameters of resonance fatigue longevity methods. Through reasonable simplification and assumptions, using the finite element software of ABAQUS to simulate the dynamic structure crack propagation (named frequency of dynamic decreasing process), dynamic analysis is studied on each stages. SN method and damage tolerance are picked to simulate the progress of Adopt SN method, damage tolerance is done by the way under the condition of simulation timely resonance fatigue life. The example shows that the method is simple and reasonable and provides reference for vibration fatigue analysis. Key words : vibration fatigue; typical structure; natural frequency; model modification; frequency change; crack propagation
图 3.1 连接板结构及尺寸 .................................................................................................... 15 图 3.2 1.6mm 加筋板结构及尺寸........................................................................................... 15 图 3.3 实验系统安装示意图................................................................................................. 16 图 3.4 ideas 中的识别模型 .................................................................................................... 16 图 3.5 第一阶振型及频率 ..................................................................................................... 17 图 3.6 第二阶振型及频率 ..................................................................................................... 17 图 3.7 第三阶振型及频率 ..................................................................................................... 17 图 3.8 第一阶振型及频率 ..................................................................................................... 17 图 3.9 第二阶振型及频率 ..................................................................................................... 17 图 3.10 第三阶振型及频率 ................................................................................................... 17 图 3.11 加筋板实验系统安装示意图..................................................................................... 18 图 3.12 连接板实验系统安装示意 ........................................................................................ 18 图 3.13 软件控制界面.......................................................................................................... 19 图 3.15 加筋板配重 ............................................................................................................. 21 图 3.16 连接板配重.............................................................................................................. 21 图 3.17 加筋板实验系统装夹 ............................................................................................... 21 图 3.18 连接板的实验系统装夹 ............................................................................................ 21 图 3.19 加筋板应变片黏贴位置............................................................................................ 22 图 3.20 连接板应变片黏贴位置 ............................................................................................ 22 图 3.21 实验系统的操作流程................................................................................................ 23 图 3.22 1.6mm 定应力应变寿命关系 ..................................................................................... 23 图 3.23 1.6mm 定应力载荷寿命关系 ..................................................................................... 24 图 3.24 1.6mm 定应力频率寿命关系 ..................................................................................... 24 图 3.25 2mm 定载荷载荷寿命历程........................................................................................ 25 图 3.26 2mm 定载荷应变寿命历程........................................................................................ 25