【作者】 张妮；

【导师】 姜伟； 高红俐；

【作者基本信息】 浙江工业大学 ， 机械电子工程， 2009， 硕士

【摘要】 高频疲劳试验机是一种基于共振原理的电磁谐振式金属材料试验机,它用于测定金属及其合金在室温状态下拉伸、压缩的疲劳性能,其特点是高负荷、高频率、低消耗,从而缩短试验时间,降低试验费用,是我国工业发展的主要测试设备之一。目前,高频疲劳试验机存在的主要问题是试件刚度变化过程中系统的控制:固有频率的实时跟踪和振动载荷的精确控制。为了实现这一目标必须建立精确的系统动力学模型,并在此基础上对系统的动态特性进行相应的理论、仿真及实验研究,本文所做的主要研究工作如下:1、提出了标准紧凑拉伸试件的悬臂梁模型,从应力函数出发建立了试件等效刚度的表达式,最后分析了试件尺寸、材料等因素对刚度的影响。2、利用有限元分析软件对试件的模态和谐响应进行分析,计算试件本身的固有频率并得出裂纹扩展时固有频率随裂纹长度的变化规律。3、阐述了高频疲劳试验机的工作原理,建立了试件未出现裂纹时系统的动力学模型;分析了系统的固有频率、振动振幅和小阻尼系统的最大振幅;最后在此基础上对系统的动态特性进行了仿真分析。4、建立了疲劳扩展时变系统的动力学方程,利用疲劳裂纹检测系统记录裂纹长度和时间的关系,并根据实验数据对试件出现裂纹时的系统固有频率、试件最大振幅进行了理论分析。5、搭建了基于虚拟仪器技术的实验平台,进行了系统未知参数的辨识,并验证了刚度、固有频率和最大振幅随裂纹长度及时间的变化趋势。本论文对高频疲劳试验机动态特性的分析和研究工作,为高频疲劳试验的频率和载荷的高精度控制提供了理论基础,为疲劳试验技术的发展做出了贡献。更多还原

【Abstract】 High-frequency fatigue testing machine is a metal material testing machine based on the resonance theory. It is used to measure the fatigue property of tension and compression of material and its alloy under the normal temperature, it can realize high-load, high-frequency, low-consumption, so the experiment time is shortened, the experiment cost is reduced, it is one of main testing equipments of our industrial development. So far, the main problem existed in the high-frequency fatigue testing machine is the system control in the process of the changing of sample stiffness. The concise dynamic model of system must be built in order to realize the aim. This thesis mainly deals with the theoretical analysis, simulation and experimental research of dynamic characteristics of system. Main contents of the thesis are listed as follows:1. Put forward a cantilever beam model of standard compact tension sample, the formula of stiffness of sample is set up from stress function, at last, the influence of dimension and material of sample to stiffness is analyzed.2. The modal and harmonic of sample are analyzed by the ANSYS software, the natural frequency of sample and the natural frequency change along the crack length when crack extends are calculated.3. The working principle of high-frequency fatigue testing machine is introduced, the dynamic model of system is built when the crack don’t appear in the sample; The natural frequency, vibrating amplitude and sample maximum amplitude of small damper system are analyzed; At last, the dynamic characteristics of system is simulated.4. The dynamic equation of time-varying crack extending system is built; the relationship of crack length and time is recorded by on-line fatigue crack monitor system, based on the experiment data, the natural frequency and sample maximum amplitude of system is analyzed when the crack appears in the sample.5. The experiment platform based on virtual instrument is built, the identification of unknown parameter of system is operated, besides, the change trend of stiffness, natural frequency and sample maximum amplitude with crack length and time is verified.The analytical and research work on dynamic characteristics of high-frequency fatigue testing machine in the thesis, provides a theoretical basis for the high-precision control of frequency and load of high-frequency fatigue tester and contribute the development of the fatigue test technology.更多还原