Abstract
In this study, Computer Vision and Phase-Based Motion Magnification (PBMM) are validated for continuous Structural Health Monitoring (SHM) purposes. The aim is to identify the exact instant of occurrence for damage or abrupt structural changes from video-extracted, very low amplitude (barely visible) vibrations. The study presents three experimental datasets: a box beam with multiple saw cuts of different lengths and angles, a beam with a full rectangular cross section and a mass added at the tip, and the spar of a prototype High-Aspect-Ratio wing. Both mode-shape- and frequency-based approaches are considered, showing the potential to identify the severity and position of the damage as well A high-definition, high-speed camera and a low-cost commercial alternative have been successfully utilised for these video acquisitions. Finally, the technique is also preliminarily tested for outdoor applications with smartphone cameras.
Highlights
Vibration-based Inspection (VBI) represents, to the present day, the standard framework for the assessment of civil structures and infrastructures and mechanical systems
Structural Health Monitoring (SHM) resorts to several features to detect the presence of damage in a target structure [4]. is allows classifying the techniques mainly as Frequency-Based Damage Detection (FBDD) and Mode-shape-Based Damage Detection (MBDD) [5]. e resonant frequencies and the mode shapes have their own advantages and limitations, yet both are modal parameters, which are widely considered among the best choices for a Damage Sensitive Feature (DSF) [6]
Attached sensors like accelerometers or strain gauges vary locally the mass and the bending stiffness of the investigated system. is has been proved to significantly alter the dynamic response of slender and flexible structures since these pointwise changes produce effects that can be mislabeled as damage [7]. erefore, there is an urge for noninvasive acquisition techniques; this issue has gained more and more interest in recent years, with a flourishing of noncontact measurement techniques [8]
Summary
Vibration-based Inspection (VBI) represents, to the present day, the standard framework for the assessment of civil structures and infrastructures and mechanical systems. They provide insight into the mechanical parameters which govern the local and global dynamic response of the target system [2, 3]. E resonant frequencies and the mode shapes have their own advantages and limitations, yet both are modal parameters, which are widely considered among the best choices for a Damage Sensitive Feature (DSF) [6]. The acquisition of the necessary vibration measurements is not free from practical issues. Many SHM algorithms, while theoretically valid, require many output channels to record the structural response, to ensure the robustness of the results, and/or to provide a high spatial resolution (which is essential for damage localisation and severity assessment [9,10,11,12,13])
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