2025 Volume 74 Issue 4 Pages 158-165
The purpose of this study was to develop a method for the early detection of corrosion in under coating using the Digital Image Correlation (DIC) method and the Acoustic Emission (AE) method. Accelerated corrosion tests were conducted on one-layer coated steel sheets (barrier corrosion preventive steel sheets) and monitored using the DIC and AE methods. Corrosion was detected at approximately the same timing using both methods. However, for the 2-layer coated steel plate (sacrificial corrosion protection and barrier corrosion protection), DIC could detect corrosion at an early stage, while AE did not detect it during the test. The results of the two types of specimens were evaluated in combination with the results of SEM and EDS analyses. In the one-layer specimen, rust initially formed under the coating film, followed by the swelling of the coating film. Then, rust cracking occurred due to the growth of rust, and it was presumed that the growth of rust damaged the coating film. Alternatively, in the two-layer sample, moisture penetrated into the coating film and white rust formed on the coating film, followed by the swelling of the coating film. It was presumed that the rust then grew and cracked the coating film. Therefore, this method can be applied to the early detection of corrosion under the coating.
