Evaluation on estimation in characteristics of fatigue crack using micro-encapsulated dye mixing paint

There are various ways to detect the fatigue crack in structural members, but it is difficult to find the initiation, characteristics of fatigue cracks, its length, and propagations due to the cost and effectiveness from the structural members under service condition. This study quantitatively examined the efficiency of estimating the characteristics of fatigue crack of notch crack and gusset welded joint specimens with micro-encapsulated dye mixing paint according to its layers, protective coating, surface conditions. Initial fatigue crack length and propagations were measured by digital images and compared with colored fatigue cracks, which appeared on micro-encapsulated dye mixing paint. And also, fatigue tests were carried out on structural member with perpendicular welding joint to verify its applicability for actual structural members. It was shown to be a good inspection in visual inspection perspective, and the inspection errors were lowered when fatigue crack length increased. The micro-encapsulated dye mixing paint can be considered as an easily applicable inspection method of fatigue crack and propagations through a close inspections around colored crack line after detecting structural defects, despite of difficulty in detecting the initial crack and short fatigue crack.