【作者】 李志远；

【导师】 杨栋； 伍贤智；

【作者基本信息】 合肥工业大学 ， 建筑与土木工程（专业学位）， 2021， 硕士

【摘要】 桥梁吊杆在自然环境的不断侵蚀和长时间的高张拉作用下,表面会产生疲劳微裂纹,如何有效识别微裂纹对于桥梁结构的安全状态、劣化行为、承载力评估等均具有重要的理论意义和工程应用价值。对于杆件的这种接触性缺陷,传统超声检测的回波很难识别出缺陷波信号,而非线性超声检测技术具有非常好的效果。振动声调制技术是非线性超声检测技术的一种,其对于接触型的缺陷尤其是疲劳性的裂纹格外敏感,但非线性检测技术只能判断损伤是否存在,无法识别出微裂纹的具体位置。因此,本文引入时间反转法,将振动声调制技术检测得到的非线性信号进行聚焦处理,实现杆件微裂纹的检测及定位。论文的主要研究工作与结论如下:1.对振动声调制技术和时间反转法的基础理论进行了研究,并对直杆和螺旋杆的频散曲线公式进行了推导,为试验的开展提供了理论基础。2.利用多组不同频率的低频激励对直杆进行了调制分析,证明了在低频激励作用下裂纹的运动状态为开合型。把杆件的右端面白噪声响应与Z方向裂纹面相对位移量进行对比分析,发现了低频激励频率越接近杆件共振频率,其调制的效果也就越好。3.对含有微裂纹的杆件以及无损杆件进行了数值仿真分析,结果表明有损杆件检测信号的频谱图中出现了明显的一阶旁瓣、二阶旁瓣、谐波等非线性信号。对非线性信号进行时反聚焦处理,实现了杆件微裂纹的定位,为后续试验验证工作的参数设置提供了参考。4.搭建了振动声调制的试验检测平台,对直杆和螺旋杆进行了基于振动声调制方法的微裂纹检测及定位试验验证。振动/超声在裂纹界面上信号发生调制,试验结果中出现了非线性损伤信号,证明振动声调制技术可较好适用于直杆及螺旋形杆件的微裂纹检测。同时在有限元软件中进行时反聚焦处理,微裂纹位置不相同的三根杆件均出现了时反聚焦点,且误差在6%以内,振动声调制试验检测与有限元时反聚焦相结合的方式可以有效实现杆件微裂纹的定位。作为一种新型超声无损检测技术,振动声调制和时反过程的自适应聚焦能力为桥梁吊杆小损伤的增强检测和局部定位提供了新的思路和途径。更多还原

【Abstract】 The bridge suspender is composed of several steel bars with uniform thickness.Under the continuous erosion of the natural environment and long-time high tension,the surface of the suspender will produce fatigue microcracks.How to identify micro-cracks effectively has important theoretical significance and engineering application value for the evaluation of the carrying capacity of the deterioration behavior of the bridge structure in the safety state.For this kind of contact defects of the bar,the echo of traditional ultrasonic test is difficult to identify the defect wave signal,and the nonlinear ultrasonic testing technology has a very good effect.Vibro-acoustic modulation technology is one of the nonlinear ultrasonic detection technology,which is particularly sensitive to contact type defects,especially fatigue cracks.However,the nonlinear detection technology can only judge the existence of damage,and cannot identify the specific location of microcracks.Therefore,the time reversal method is introduced in this paper,the nonlinear signals detected by vibro-acoustic modulation technology were focused to realize the detection and location of microcracks in bars.The main research work and conclusions of the paper are as follows:1.The basic theory of vibro-acoustic modulation technology and time reversal method is studied,and the dispersion curve formula of straight and spiral rods are deduced.2.The modulation analysis of straight bar is carried out by using several groups of low frequency excitations with different frequencies,and it is proved that the motion state of the crack under low frequency excitation is open-close type.By comparing the white noise response of the right end of the rod with the relative displacement of the crack surface in the Z direction,it is found that the closer the low frequency excitation frequency is to the resonant frequency of the rod,the better the modulation effect is.3.The bars with micro cracks and non-destructive bars are simulated and tested.It is found that there are obvious first-order sidelobes,second-order sidelobes,harmonics and other nonlinear signals in the spectrum of the detection signal of the damaged bars.Then,the time reversal focusing processing of the nonlinear signal is carried out to locate the microcracks of the bar,which provides a reference for the parameter setting of the subsequent experimental detection.4.An experimental detection platform for vibro-acoustic modulation was built,the microcrack detection and location tests for straight and screw rods were carried out based on the vibro-acoustic modulation control method.The ultrasonic signal is modulated at the crack interface,and the nonlinear damage signals appear in the test results.It is proved that the vibro-acoustic modulation technique is suitable for the detection of micro-cracks in straight and spiral rods.At the same time,the time reversal focusing processing is carried out in the finite element software.The three bars with different microcrack positions all have time-reverse focusing points,and the error is less than 6%.The method of combining vibro-acoustic modulation test with finite element time reverse focusing can effectively realize the location of microcracks in the rod.As a new type of ultrasonic nondestructive testing technology,the adaptive focusing ability of vibro-acoustic modulation and time reversal process provides a new idea and approach for enhanced detection and local localization of small damage of bridge suspender.更多还原