基于激光技术的振动和超声检测方法研究

发布时间：2018-03-05 19:30

本文选题：无损检测　切入点：激光技术　出处：《南京航空航天大学》2016年博士论文　论文类型：学位论文

【摘要】：开展面向航空结构的损伤检测方法研究是预防重大事故发生、提高飞行器经济效益、降低维护成本的重要手段。然而,常用的无损检测方法多以接触式的方式对结构进行检测,对于具有复杂曲面形式的航空结构,传统无损检测技术难以满足高自动化程度和高检测效率的要求。针对这一问题,本文开展了基于激光技术的非接触式、远距离无损检测方法研究。该方法的实质是采用激光传感或激光激励的方式提取损伤引起的结构动态响应变化,从而对损伤的位置和程度进行评估。在检测过程中,激光光路经过偏转镜的反射落在待测结构的表面。通过改变反射镜的转角就能够非常方便地实现激光大范围的移动和扫描。因此,该技术适合应用在检测面积很大的航空结构中。本文具体从激光振动和激光超声两个方面进行无损检测方法的研究。首先,激光振动损伤检测方法利用结构的低频振动响应,能够对损伤出现的位置进行识别;其次,采用激光超声损伤检测方法,激励结构中的高频Lamb波信号,实现对损伤具体形貌的成像。论文从理论推导、数值仿真、系统搭建和实验验证等多个方面开展了深入的研究,主要工作和创新点如下:1.提出了基于稀疏边界测量技术的虚拟激励检测方法。①建立了虚拟激励法在"弱"形式下的检测原理;②推导了损伤特征因子与虚拟单元边界振动响应之间的关系;③提出了激励频率和权函数的选择方法,避免了算法中使用数值差分求解振动位移高阶导数的过程;④采用数值仿真的手段验证了所提出方法的检测效果。这部分研究主要解决了传统严格形式下虚拟激励法抗噪能力弱的缺点,并采用了虚拟单元划分的方式,通过离散单元检测的手段减少了测量的点数。2.建立了激光振动与含金属芯压电纤维智能夹层组合的损伤检测系统。①以基于稀疏边界测量技术的损伤检测方法为理论基础,结合了激光多普勒测振和含金属芯压电纤维智能夹层两种测量方式进行了系统搭建;②提出了含金属芯压电纤维智能夹层的封装方法及其标定流程;③通过欧拉-伯努利梁的实验,验证了所提出方法的有效性。这部分研究主要解决了结构分布式高频应变的测量问题,并采用多传感系统融合的方式实现了虚拟单元边界振动情况的测量,实现了所提出检测方法的应用。3.提出了基于Lamb波波场数据分析的损伤成像方法。①在激光超声检测技术获取结构中Lamb波传播波场数据的基础上,建立了损伤附近Lamb波传播的简化模型;②提出了基于小波变换的Lamb波干涉能量提取算法;③提出了基于入射波异常信号能量提取的损伤成像方法。通过这部分内容的研究,从理论上分析了损伤对Lamb波传播产生的影响,并提取了能够用于表征损伤位置和形状的特征因子,为激光超声检测系统的建立与损伤成像技术的实施奠定了基础。4.研制了激光超声损伤检测系统。①采用二维扫描振镜控制脉冲激光在待测结构表面的扫描,实现了可移动的Lamb波激励方式。利用声发射传感器和激光多普勒测振仪对固定位置的Lamb波响应信号进行获取,通过声学互易原理,实现结构中Lamb波传播过程的可视化;②从面向实际工程应用的角度,开发了一套综合硬件驱动、扫描控制、信号处理和数据分析等功能的系统管理软件;③实验验证了该系统能够在金属和复合材料结构中实现自动化的Lamb波传播数据采集,并成功地在飞机机翼结构中得到了验证。5.开展了激光超声无损检测技术的应用与验证。①对典型的金属和复合材料结构进行了损伤成像方法的实施,实验结果验证了所提出方法在损伤成像分辨率上的提高;②实验研究了损伤延伸方向与损伤深度对检测效果的影响;③结合激光超声检测系统和疲劳拉伸试验系统对复合材料不同疲劳载荷周期数下的波场进行了获取,建立了 Lamb波传播相速度、传播衰减率和模态能量分布比与疲劳周期数间的关系。这部分研究解决了激光超声无损检测技术在实际应用过程中所面临的难题,为损伤识别和复合材料的疲劳评估提供了良好的实验基础。
[Abstract]:Study on damage detection method for aircraft structure is to prevent the occurrence of major accidents, improve vehicle economic efficiency, reduce the maintenance cost of the important means. However, nondestructive testing methods commonly used to contact the structure to detect the aircraft structure with complex surface form, the traditional nondestructive testing technology is difficult to meet the high degree of automation and the high detection efficiency. Aiming at this problem, this paper carried out the non-contact laser technology based on the research on nondestructive testing methods of long distance. The essence of the method is the use of laser sensors or laser excitation methods to extract damage structural dynamic response caused by changes in order to assess the location and extent of damage in the detection process., laser light reflected by mirror deflection falls on the surface to be measured. The structure through the corner reflector can be changed conveniently A large range of laser scanning and mobile. Therefore, this technique is suitable for application in the aviation structure detection area of great. This paper studied the NDT methods from two aspects of laser vibration and laser ultrasonic detection method. Firstly, the laser vibration damage by low frequency vibration structure dynamic response, able to identify the location of damage; secondly, using the ultrasonic detection method of laser damage, high frequency Lamb wave excitation structure, to achieve the specific morphology. The imaging damage from theoretical derivation, numerical simulation, carried out in-depth research on many aspects of system construction and experimental verification, the main work and innovation are as follows: 1. put forward the virtual excitation detection method sparse boundary measurement based on the detection principle. Established in the "weak" form of the virtual excitation method; the deduced damage characteristic factor and virtual boundary element vibration response The relationship between; the method is proposed to select the excitation frequency and weight function, to avoid the poor process of solving vibration displacement of high order derivative using numerical algorithm; the numerical simulations verify that the proposed detection method. This research is mainly to solve the pseudo excitation method is the traditional form of strict anti noise the ability of the weak, and the use of virtual cell division, through the discrete unit detection means to reduce the measurement points.2. established laser vibration and metal core piezoelectric damage detection system of electric fiber smart layer combination. With the damage detection method based on sparse boundary measurement technology as the theoretical basis, combined with laser Doppler the vibration and the metal core piezoelectric fiber smart layer two ways to measure the system; the encapsulation method of piezoelectric fiber smart layer with metal core and its standard A process; through the Euler Bernoulli beam experiments verify the effectiveness of the proposed method. This part mainly resolves the problem of measuring the structure of distributed high frequency strain, and the fusion of multi sensor system to realize the measurement of vibration of the virtual boundary element, realizes the application of the proposed.3. detection method is proposed damage analysis of Lamb imaging method based on wave field data acquisition. In the laser ultrasonic detection technology in the structure of Lamb wave propagation based on wave field data, establishes a simplified model of damage near the Lamb wave propagation is proposed based on wavelet transform; Lamb wave interference energy extraction algorithm; the proposed damage imaging method of incident wave anomaly based on the extraction of signal energy. Through the study of this part, from the theoretical analysis of the effect of damage on Lamb wave propagation, and extraction can be used to characterize damage The characteristic factor of the position and shape of the implementation for the establishment of the laser ultrasonic detection system and damage imaging technology laid the foundation of the.4. has developed a laser ultrasonic damage detection system. Using the two-dimensional scanning mirror control pulse laser in the structure of the measured surface scanning, realize the Lamb wave mobile incentives. The use of acoustic emission sensor and laser Doppler vibrometer for fixed Lamb wave response signal acquisition, through acoustic reciprocity principle, realize the visualization of Lamb wave propagation process of the structure; the practical engineering point of view, the development of a comprehensive set of hardware drivers, scanning control function, signal processing and data analysis system management software; experiment verify the Lamb wave data acquisition system can realize the automation in the structure of metal and composite materials, and successfully in the aircraft wing structure to test Application and validation of.5. to carry out the laser ultrasonic nondestructive testing technology. The implementation of the damage imaging method on typical metal and composite structures, the experimental results verify that the proposed method to improve the resolution of the injury in the experimental study; damage extension direction of impact and damage depth of the effect of the 3; combined with the laser ultrasonic detection system and fatigue tensile test system of composite fatigue load cycles under wave field are obtained, a Lamb wave phase velocity, attenuation rate and modal energy distribution ratio and the number of fatigue cycles. The relationship between this part of the study to solve the problem of laser ultrasonic nondestructive testing technology in the face of in the practical application, provides a good experimental foundation for the evaluation of damage identification and composite material fatigue.

【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN249;TB559

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