Microcapsule-Based Visualization Smart Sensors for Damage Detection: Principles and Applications

The smart sensor is an effective way to detect damage and improve structural safety in structural health monitoring. Microcapsule-based visualization sensors stand out from the smart sensors. Here, the research progress of microcapsule visualization materials in recent years is summarized and the sensing principles, influence factors, performances, applications, and future prospects are introduced. The way to achieve the visualizing function of microcapsule visualization sensors is the fabrication of microcapsules that are encapsulated with solutions of dyes or indicator. When the protective shell of microcapsules is broken, the dyes will be released and activated under optical, chemical, or mechanical conditions. These visualized microcapsules can be added to the interior of the structure or prepared as a coating to provide structural health monitoring of the interior and surface of the structure. They can accurately detect microcracks and highlight them in bright colors. Additionally, the structural health monitoring applications of microcapsule visualization sensing coatings in concrete, asphalt, and steel are presented with detailed examples. The development and application of these microcapsule visualization sensors are of great significance in improving the structural life and avoiding structural failure in engineering.