Stringer debonding edge detection employing fiber optics by combined distributed strain profile and wave scattering approaches for non-model based SHM

The paper presents a comparison of two novel damage detection approaches for interrogating stiffened composites. A guided wave assessed methodology based on piezoelectric patches is integrated with a distributed fiber optic sensor providing a cost-effective and time-saving monitoring system. Being the two techniques characterized by different sample ranges, they are prone to be integrated without any interference or cross talk effect and can be applied to provide a redundant inspection system. The structural health monitoring by distributed fiber optic is a non-model based damage detection method. The relative aspect ratio between shape profile at different time stamps or at different locations along the fiber segments are taken into consideration and the first order derivative is applied, both in time and spatial domain, correlating sensors values characterized by high gradient events. The occurrences of a such dispersed pattern can be associated to a structural non-linearity induced by damage. In order to make this approach effective the PZT guided wave scattering methodology is used as reference. Both systems are tested to the same specific target, nominally a composite stiffened plate undergoing to impact. Good results are reported when comparing the resolutions of the two methodologies, indeed verified by ultrasonic nondestructive investigation analysis.