Structural Damage Detection and Evaluation Using a Scanning Laser Vibrometer

对老化的土木结构、震后建筑物和桥梁、老化的飞机以及疲劳载荷下的机械系统进行检测，需要一种能够对大型结构进行现场快速准确的损伤检测的方法。 传统的无损检测方法大多是局部检测方法，用于大型结构的现场检测速度慢、成本高。 由于结构的动态响应中往往包含有损伤信号，因此本研究旨在发展一种基于动力学的整体检测方法，用于大型复合材料和组合结构的缺陷检测和评估。为了实现全球检查方法，将使用扫描激光测振仪对结构的运行挠度进行准确和密集的测量，并将使用新开发的边界效应评估方法从ODS中提取损伤引起的边界效应，以揭示损伤位置。 BEE方法是一种与模型无关的方法，它使用滑动窗口最小二乘曲线拟合方法将ODS分解为中心解和边界解。 由于损伤引入了新的边界，边界解存在于损伤和结构边界周围，因此可以揭示损伤位置。 此外，裂纹尺寸可以通过使用断裂力学的应力强度因子来估计。 通过实验验证了BEE方法在定位表面槽、边缘槽、表面孔、内部孔、疲劳裂纹和加筋段等方面的能力。 数值和实验结果表明，BEE方法是更灵敏和可靠的比其他动力学或变形为基础的方法。通过研究ODS的噪声模式、使用低阶横向ODS、使用锁定放大器的新数据采集方法以及选择ODS进行检查的系统方法，将提高BEE方法的准确性和能力。该项目将产生一种有效可靠的损伤检测和估计方法，用于对大型民用、机械和航空航天结构进行基于状态的结构安全检查。

Inspection of aging civil structures, after-earthquake buildings and bridges, aging aircraft, and mechanical systems under fatigue loading requires a method that can perform on-site quick and accurate damage detection of large structures. Unfortunately most of conventional non-destructive inspection methods are local methods; it is slow and expensive to use them for on-site inspection of large structures. Because damage signals are always contained in dynamic responses of structures, this research project is to develop a dynamics-based global inspection method for the detection and estimation of defects in large composite and built-up structures. Toward a global inspection method a scanning laser vibrometer will be used to provide accurate and dense measurement of Operational Deflection Shapes (ODSs) of structures, and a newly developed Boundary Effect Evaluation (BEE) method will be used to extract damage-induced boundary effects from the ODSs to reveal damage locations. The BEE method is a model-independent method; it uses a sliding-window least-squares curve-fitting method to decompose an ODS into central solutions and boundary solutions. Because damage introduces new boundaries to a structure, boundary solutions exist around damage and structural boundaries and hence can reveal damage locations. Moreover, crack sizes can be estimated by using stress intensity factors from fracture mechanics. Experiments have been performed to verify the capability of this BEE method in locating surface slots, edge slots, surface holes, internal holes, fatigue cracks, and stiffened sections. Numerical and experimental results indicate that the BEE method is more sensitive and reliable than other dynamics- or deformation-based methods. The accuracy and capability of this BEE method will be improved by investigating the noise patterns of ODSs, the use of low-order transverse ODSs, a new data acquisition method using a lock-in amplifier, and a systematic method of selecting ODSs for examination. This project will result in an efficient and reliable damage detection and estimation method for performing condition-based structural safety inspection of large civil, mechanical, and aerospace structures.