Impact area and debonding line detection assessment by cross-correlation analysis and distributed sensing

Debonding at two components interface (f.i., skin & stringer) is a common defect of composite stiffened structures. It may result from inefficient manufacturing or impacts from foreign objects. Discontinuities within an elastic solid medium under mechanical loads may cause local anomalies in the strain field. On this basis, the current work investigates disbonding at skin/stringer interface of an aeronautical plate, generated by low/medium energy impacts. Distributed fiber optics records longitudinal strain values; data are then elaborated by a methodology using different deformation-based features providing Local High Edge Observation (LHEO) in both time and space domains. Cross correlation is implemented to improve signal to noise ratio. Proposed LHEO algorithm proves its capability to detect impact area and occurred skin-stringer debonding, without reference to applied loads or a certain baseline. A dedicated Matlab routine elaborates the output further, with the aim of visualizing and estimating impact region extension.