Identifying Debonding Regions in a Composite Radiative Cooling Film Bonded to a Steel Plate

Abstract

This study presents a method to map the regions of debonding of a thin composite film attached to a steel plate based on the changes in Lamb wave signatures. The film in discussion is a passive radiative cooling film that can be coated on the top of metallic roof shingles to reflect the sunlight and subsequently cool the building. It is an energyefficient building material that can potentially reduce building energy consumption by up to 30%. Its effectiveness can, however, be decreased by damage or debonding of the film from the substructure. Hence, it is essential to identify the regions of debonding/ damage in a timely manner for rectification. Here, we demonstrate a method to map the regions of debonding based on changes observed in Lamb waves when they pass through a debonded region. When the Lamb waves pass through this film, they get attenuated and arrive with a slight delay. By quantifying the changes in the wavepackets, the debonded regions can be mapped tomographically. With this as the basis, experiments were conducted on a steel plate bonded with the film to demonstrate the mapping of debonded regions. A small section of the film was removed to simulate a damaged scenario. PZT discs were bonded to the structure along the edges of the square to create a dense network of paths passing through the film. Along each path, signals are acquired in pristine and damaged conditions to estimate the damage index for each path. The Reconstruction Algorithm for Probabilistic Inspection of Damage (RAPID) technique was employed to construct the map, where high-intensity regions denoted areas with a higher likelihood of debonding. The obtained map was compared with the structure to validate the method and establish it as a viable option. Through a successful demonstration, this work lays the foundations for identifying and quantifying regions of film debonding.