An experimental study of the feasibility of phase-based video magnification for damage detection and localisation in operational deflection shapes

Optical measurements from high-speed, high-definition video recordings canbe used to define the full-field dynamics of a structure. By comparing thedynamic responses resulting from both damaged and undamaged elements,structural health monitoring can be carried out, similarly as with mountedtransducers. Unlike the physical sensors, which provide point-wise measure-ments and a limited number of output channels, high-quality video recordingallows very spatially dense information. Moreover, video acquisition is a non-contact technique. This guarantees that any anomaly in the dynamic behav-iour can be more easily correlated to damage and not to added mass orstiffness due to the installed sensors.However, in real-life scenarios, the vibrations due to environmental input areoften so small that they are indistinguishable from measurement noise if con-ventional image-based techniques are applied. In order to improve the signal-to-noise ratio in low-amplitude measurements, phase-based motion magnifica-tion has been recently proposed.This study intends to show that model-based structural health monitoring canbe performed on modal data and time histories processed with phase-basedmotion magnification, whereas unamplified vibrations would be too small forbeing successfully exploited. All the experiments were performed on amultidamaged box beam with different damage sizes and angles.