Abstract
In recent years, several research projects have focused on life extension techniques utilizing fatigue crack closure. This paper describes the experimental work for the fatigue life extension utilizing corrosion products and quantitative measurements of the corrosion volume with the 3D shape measurement tool. In the experiment of life extension, the SENT specimens, made from the rolled steels for welded structure SM490A, are adopted for the investigation. Fatigue tests are conducted under the different stress ratios R = -1.0 / 0.1. A corrosion accelerator, 35% HNO3 liquid, is injected into the crack faces of the specimen with a crack length of corrosion aco. = 0.4 / 3.0mm. Finally, the tests are resumed for the final fracture. Regarding the investigation of the accumulated corrosion products, precise measurements for the opposite fractured surfaces are performed. The volume of corrosion products is obtained by utilizing the notion of FRASTA to exclude the effect of plastic deformation along the crack faces.
The obtained results show considerable life extensions containing crack arrest by accumulated corrosion products on crack faces under the different stress ratios R and the crack length of corrosion aco., which suggest the applicability of this technique regardless of R and aco.. Furthermore, a positive correlation is confirmed between the accumulated corrosion products on crack faces and the level of the life extension.
