基于弹性波传播特性的大型旋转机械主轴裂纹检测方法研究

Shaft crack detection for large rotating machinery is of great significance to avoid the occurrence of shaft fracture. Traditional feature extraction method based on vibration signal and based on vibration modal analysis for crack detection, studied the vibration signals but did not consider the effect of vibration propagation process. Based on the wave model that the double ends free, infinite and no reflection components of the elastic waves, this project establishes an elastic wave model for the variable multi-step shaft on the basis of a fixed-fixed boundary condition and finite length, the influence of discontinuity of the cross-section, crack and speed fluctuation on elastic wave propagation characteristics is studied; In the presence of reflected wave component as well as the environmental noise, the method to improve the SNR of elastic wave is to be researched; Through comparison between the change of elastic wave propagation characteristics with and without cracks, this project establishes the relationship between the crack and the changes of propagation characteristics of the elastic wave, and then the crack is researched; An experiment rig is built up for the crack detection, so as to validate the methods of this project. By the study to propagation characteristics of the elastic waves in shafts, this project proposes a crack detection method based on elastic wave propagation characteristics, and reveals the mechanism of elastic wave propagation, solves the problem of the transverse crack detection in shafts of large rotating machinery.

大型旋转机械主轴的裂纹检测对于避免发生主轴断裂的重大事故来说具有重要意义。传统的基于振动信号特征提取及基于振动模态分析来进行裂纹检测的方法，对振动特性进行了研究但没有考虑振动传播过程的影响。本项目在双端自由、无限长且无反射成分的弹性波波动模型的基础上，建立弹性波在固定-固定边界条件下且长度为有限的变截面阶梯转轴中的波动模型，研究主轴截面不连续、裂纹及转速波动对弹性波传播特性的影响；在环境噪音以及存在反射波成分的干扰下，研究提高弹性波信噪比的方法；通过对比有、无裂纹两种情形下弹性波传播特性的变化，建立裂纹对应传播特性变化的特征数据库，并以此对裂纹进行分析和研究；搭建基于弹性波传播特性的主轴裂纹检测实验系统，验证本项目方法的有效性。本项目提出基于弹性波传播特性的主轴裂纹检测方法，通过对主轴中弹性波传播特性的研究，揭示弹性波的传播机理，解决大型旋转机械主轴裂纹检测的问题。

本项目以大型旋转机械主轴的横向裂纹检测为背景，针对目前基于振动的检测方法存在的无法获取振源的真实振动等问题，研究了振动的传播机理以及基于弹性波的裂纹检测方法。首先将横向裂纹简化成局部弹簧，然后利用广义哈密顿原理、平衡方程、叠加原理等建立了存在轴向载荷以及含横向裂纹的变截面转轴的运动方程，并利用分离原则和分段方法得到了弹性波在含一个或多个横向裂纹转轴中的传递矩阵。随后利用数值分析，有限元方法、试验验证等手段，研究了复杂噪音条件下弹性波信号的降噪问题，提出了基于频谱比较和边际谱比较的弹性波通带、阻带以及中心频率等传播特性的分析方法，得到了截面变化形式、端面面积比、转轴转速、裂纹模式、裂纹位置、裂纹深度以及轴向载荷等因素对弹性波通带、阻带以及中心频率等特性的影响规律，并进一步提出了基于EMD和弹性波的转轴横向裂纹检测方法。解决了振动在大型旋转机械主轴中的传播机理问题以及基于振动传播的主轴横向裂纹检测问题。