Fractal analysis of crack initiation in polycrystalline alloys using surface interferometry

Microstructural degradation is a predominant source of damage in polycrystalline alloys that are commonly used in diverse applications. For early diagnosis and prognosis of failures, it is essential to understand the mechanisms of damage growth specifically in the crack initiation phase, which is still an intriguing phenomenon for scientists due to sensing inaccuracies and modeling uncertainties. Measurements of gradually evolving deformations on the material surface during crack initiation provide early warnings of forthcoming widespread damage. In this paper, a surface interferometer is used to generate 3-D surface profiles of polycrystalline alloy specimens under oscillating load. The concepts of fractal geometry are used to quantify the changes in the 3-D surface profiles as early indicators of damage evolution in the crack initiation phase.