基于数字图像相关法的扣件弹条模态特征识别试验研究

Experimental study on the modal characteristics identification for the clip based on the digital image correlation

为解决传统测试方法中附加质量过大,无法准确及时获取弹条真实模态振型这一难题,本文基于高速数字图像相关法(DIC)测量弹条表面位移场。结合小波变换法,识别弹条在不同边界条件下的模态特征参数,分析边界条件对弹条动力学行为的影响。试验中采用京沪高铁常用的Vossloh300-1型扣件弹条,通过改变边界条件确定三类弹条试件:自由状态下的弹条、组装状态下的弹条(标准安装在钢轨上)以及施加不同钢轨下压位移的组装弹条。试验结果显示,高速数字图像相关法既能准确获得弹条模态频率,也能通过获取弹条动态位移场提取弹条模态振型。对比自由及组装状态下的弹条模态特征发现,边界条件对弹条动力学行为有很大影响。当弹条标准安装在钢轨上时,因弹条中肢约束导致部分自由模态振型消失,部分模态频率显著上升。随着钢轨下压位移增加,振型为弹条趾端及前拱被板下部件牵引,纵向振动的弹条第一阶组装模态频率显著降低,最终影响弹条实际共振频率。上述结果表明,高速数字图像相关法可用来测量弹条的模态特征参数,并有望为诊断及预报弹条或扣件系统的故障、减振降噪等提供借鉴和依据。

To solve the problem that the added mass in the traditional test method is too large to accurately obtain the real modal shape of the projectile,the surface displacement field of the projectile is measured based on the high-speed digital image correlation(DIC)technology.Combined with the wavelet transform method,the modal characteristics of rail clips under different boundary conditions were identified,and the influence of boundary conditions on dynamic behaviors of rail clips was analyzed.In the tests,the clips for fastner Vossloh 300-1,commonly used in Beijing-Shanghai high-speed railway,were chosen,and three kinds of specimens were determined by changing the boundary conditions:the clips in the free state,the clips in the assembled state(standard installed on the rail)and the assembled clips in the state of different rail downward displacements.The test results show that the high-speed DIC can not only measure the modal frequencies of clips,but also capture the dynamic displacement and strain fields of the clips,and extract their modal shapes.By comparing the modal characteristics of the clips in free and assembled states,it is found that the boundary conditions have a great influence on the dynamic behavior of clips.When the clip is standard-installed on the rail,part of the modes will disappear due to the restraint of the center leg,and the modal frequencies of rest modes increase significantly.With the increase of the rail downward displacement,the frequency of the first order assembly mode,which is the longitudinal vibration of the toe and the front arch caused by the components under the plate,decreases significantly,finally affecting the actual resonant frequencies of the clip.The above results indicate that the high-speed DIC can be used to measure the modal characteristics parameters of rail clips,which is expected to provide reference and basis for diagnosis and prediction of fault of rail clips or fastening systems,vibration and noise reduction,etc.