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The Frequency Domain Assurance Criterion as a Tool for Damage Detection

机译：频域保证标准作为损伤检测工具

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The aging of large civil and aerospace structures, the increasing operational demands of industry and the satisfaction of quality standards have contributed to the need of continuous monitoring and global health condition assessment techniques. Since structural damage alters the dynamic characteristics of a structure, namely its natural frequencies, modal damping and modes of vibration, and because it is possible to measure vibrations while the structure remains in service, various damage identification techniques based upon experimental modal analysis have been developed in the last 30 years. The main objective of damage identification is to provide answers to the following questions: (ⅰ) is there any damage? (detection), (ⅱ) where is it? (localization), (ⅲ) how much damage is there? (quantification), (ⅳ) what kind of damage is it? (classification) and (ⅴ) for how long is it safe to keep the structure in operation? (prediction). Among the existing methods there are those based on the comparison between the parameters extracted from experimental observation and the ones predicted from an analytic or numerical model of the structure, and there are those based on the comparison between parameters identified from experimentally-only observations. These modal parameters are usually the natural frequencies, the modes shapes, the dynamically measured flexibility matrix and the stiffness matrix, identified through a curve fitting process known as modal identification or system identification. The main objective of the authors' previous work was the elimination of the modal identification stage in the practical implementation of some of the existing methods. In that sense, it has been proposed the generalization of the methods based on the modes shapes to the operational deflection shapes. Most of the methods focus their attention in the localization of damage, some go further to the quantification but almost none classify, predict or even assess the existence of damage. In fact, it is common practice in the published scientific work to test the methods in the presence of damage but not so much in its absence (to evaluate the possible occurrence of false alarms). In this paper the problem of damage detection and the distinction of a positive occurrence from a false alarm are assessed. Some developments concerning the detection and also the relative severity of damage are presented. A new method is proposed, the Detection and Relative damage Quantification indicator (DRQ), based on the use of the Frequency Domain Assurance Criterion (FDAC), as an effective damage indicator. To illustrate the procedure, the authors present some numerical simulations, as well as an experimental example taken on a beam.
机译：大型民用和航空结构的老化，行业不断增长的操作需求以及对质量标准的满足，促使了对持续监测和全球健康状况评估技术的需求。由于结构损伤会改变结构的动态特性，即其固有频率，模态阻尼和振动模式，并且由于可以在结构保持使用状态下测量振动，因此开发了各种基于实验模态分析的损伤识别技术在过去的30年中。识别损坏的主要目的是为以下问题提供答案：（ⅰ）是否有损坏？ （检测），（ⅱ）在哪里？ （本地化），（ⅲ）有多少损坏？ （量化），（ⅳ）这是一种什么样的损害？ （分类）和（ⅴ）将结构保持运行状态安全多长时间？ （预测）。在现有方法中，有一些是基于从实验观察中提取的参数与从结构的解析模型或数值模型预测的参数之间进行比较的方法，还有一些是基于从仅用于实验的观察中识别出的参数之间的比较方法。这些模态参数通常是固有频率，模态形状，动态测量的柔韧性矩阵和刚度矩阵，它们通过称为模态识别或系统识别的曲线拟合过程来识别。作者先前工作的主要目的是在实际实施某些现有方法中消除模式识别阶段。从这个意义上说，已经提出了将基于模态形状的方法推广到工作偏转形状的方法。大多数方法将注意力集中在损害的定位上，一些方法更进一步地量化，但几乎没有方法对损害的存在进行分类，预测甚至评估。实际上，在已发表的科学著作中，通常的做法是在有损坏的情况下测试这些方法，而在没有损坏的情况下进行很多测试（以评估错误警报的可能发生）。在本文中，评估了损坏检测的问题以及误报警与正事故之间的区别。介绍了有关检测以及损坏的相对严重性的一些进展。提出了一种新方法，即基于频域保证标准（FDAC）作为有效损害指标的检测和相对损害量化指标（DRQ）。为了说明该过程，作者提供了一些数值模拟，以及在光束上进行的实验示例。

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