Abstract: This paper studies the surface profile changes around the crack tip in an attempt to predict the crack path based on the surface roughness indices. Center crack specimens prepared from nickel 200 were polished, etched, and subjected to fatigue cycling. During fatigue testing, the surface of these samples were imaged with an in-situ scanning white light interferometer (SWLI). Surface profile images were taken using a 10X lens at intervals of every 5000 cycles at the pre-cracking stages, followed by images taken with a 50X lens at every 200 cycles. An image processing algorithm was developed to analyze the surface profile images. The 10X images indicated that the Ra (arithmetic average of absolute values) and Rt (maximum height) changes are highest at the area ahead of the crack tip. The 50X images revealed that the locations with the highest changes in Ra and Rt coincident with the path along which the crack eventually propagated. These results indicated the aforementioned surface indices can predict future propagation path of a fatigue crack.
Authors: Jalal Fathi Sola, Randall Kelton, Haiying Huang, and Efstathios I. Meletis
Keywords: Crack Growth Path, Surface Index, Scanning White Light Interferometry