Assessment of Stringer Debonding by Guided Wave Inspection in Composite Structures

Composite structures have been increasingly adopted for designing high performance airframes. However, the critical fracture mechanics prevents a smooth integration of composites in safety designed aircraft. Some compensation strategies are needed to face the occurrence of barely visible damage, including interply delamination and disbonding of stringers adopted to stiffen the airframe. The latter evidences the necessity of crack stoppers in form of rivets or similar connections between the skin and the stringer although composite allow one-piece manufacturing. This brings to light the necessity of crack identification, localization and size estimation to achieve the stringer monitoring and make use of less connections possible. To this end, a novel and promising approach based on guided wave propagation and scattering in composite media is investigated thoroughly using finite element modeling. Firstly, the potentiality of this approach is highlighted making use of a design formulation applied to a linear sensor network located alongside the stringer. Secondly, the interaction between the wave and the stringer is further investigated to achieve simultaneous inspections by an asymmetric design of the sensor network. Theoretical findings demonstrate the ability of guided waves to achieve a local monitoring of the structural performance. The wave focusing can be achieved by locating the sensors appropriately. Numerical outcomes show how a good level of inspection can be achieved making use of fewer sensors possible.