轴类零件疲劳早期诊断的非线性超声检测关键技术研究

发布时间：2018-03-28 08:32

本文选题：轴类零件　切入点：疲劳　出处：《天津大学》2014年硕士论文

【摘要】：轴类零件在工程机械设备中广泛应用,作为支撑传动部件,在长期循环载荷作用下,不可避免地会产生金属疲劳,甚至使零件突然断裂,造成灾难性事故,带来巨大的人力、财力损失。45号钢是轴类零件常用材料,可作为基础研究对象,用于轴类零件疲劳检测的研究。本文采用非线性超声无损检测技术,利用超声波在结构中传播时所表现出来的非线性特征——谐波滋生,经分析计算,提取非线性系数β,进行材料性能评估和疲劳程度检测,能够对轴类零件进行疲劳早期的诊断和评价,预测其剩余使用寿命,从而发现潜在威胁,防范零件疲劳断裂事故于未然。本课题目的是进行材料疲劳早期的诊断与评价,该阶段试件并未产生裂纹等宏观损伤或缺陷,而只是材料性能的退化。因此,论文采用超声非线性最经典的表现形式——高次谐波,对不同拉伸加载次数的45号钢试件进行表征。针对试件早期疲劳诊断的非线性超声检测方法,主要对以下四项关键技术进行了研究:通过ABAQUS有限元分析,进行试件拉伸变形仿真;以与激励超声波脉冲相同时间作用下的微小压强载荷,模拟超声波在试件中的传播,可以实现精确跟踪超声应力波传播过程,并观察其波形衰减、反射等规律的目的。搭建非线性超声实验系统,通过多次重复测量,确定系统稳定性,并成功应用实验系统进行非线性超声检测实验。以A_2 vs.A_1~2数据点拟合直线的归一化斜率值,作为等效相对非线性系数,用于表征试件非线性特征,相当于对试件多次测量所得非线性系数的平均,可增加实验结果准确度和可靠性。以频谱直接提取法与脉冲反转提取法所得A_2 vs.A_1~2数据点拟合直线的归一化斜率值,作为试件非线性特征,以基波幅值A_1归一化系数作为超声线性特征。通过三种方法进行试件不同疲劳程度下测量结果的对比,说明只有采用脉冲反转法得到的归一化斜率值有增大趋势,可用于试件疲劳早期诊断与评估。
[Abstract]:Shaft parts are widely used in construction machinery and equipment, as supporting transmission parts, under the action of long-term cyclic load, metal fatigue will inevitably occur, and even parts will break suddenly, resulting in catastrophic accidents, and bringing huge manpower. Financial loss. 45 steel is a common material for shaft parts, which can be used as basic research object for fatigue testing of shaft parts. In this paper, nonlinear ultrasonic nondestructive testing technology is used. By using the nonlinear characteristic of ultrasonic wave propagating in the structure-harmonic breeding, the nonlinear coefficient 尾 is extracted through analysis and calculation, and the material performance evaluation and fatigue degree testing are carried out. It can diagnose and evaluate the shaft parts in the early stage of fatigue, predict their remaining service life, so as to find the potential threat and prevent the fatigue fracture accident of the parts. The purpose of this project is to diagnose and evaluate the material fatigue in the early stage. At this stage, the specimen does not produce macroscopic damage or defect, such as crack, but only the degradation of material properties. Therefore, the most classical expression of ultrasonic nonlinearity, high order harmonic, is adopted in this paper. The 45 steel specimens with different tensile loading times were characterized. The following four key techniques were studied: ABAQUS finite element analysis, the nonlinear ultrasonic testing method for early fatigue diagnosis of specimens. In order to simulate the tensile deformation of the specimen and simulate the propagation of the ultrasonic wave in the specimen under the same pressure load at the same time as the excited ultrasonic pulse, the ultrasonic stress wave propagation process can be tracked accurately and the wave attenuation can be observed. The purpose of this paper is to set up a nonlinear ultrasonic experimental system. The stability of the system is determined by repeated measurements, and the nonlinear ultrasonic testing experiment is carried out successfully by using the experimental system. The normalized slope value of the straight line is fitted with A-2 vs.A_1~2 data points. As an equivalent relative nonlinear coefficient, it is used to characterize the nonlinear characteristics of the specimen, which is equivalent to the average of the nonlinear coefficient obtained from multiple measurements of the specimen. The accuracy and reliability of the experimental results can be increased. The normalized slope value of the fitting line of A _ 2 vs.A_1~2 data points obtained from direct spectral extraction method and pulse inversion extraction method is regarded as the nonlinear feature of the specimen. The normalized coefficient of fundamental amplitude A _ 1 is taken as the ultrasonic linear characteristic. The comparison of the measured results under different fatigue degree by three methods shows that only the normalized slope obtained by the pulse inversion method has an increasing tendency. It can be used for early diagnosis and evaluation of fatigue of specimen.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TH133.2;TB559

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