Strain and damage monitoring in CFRP fuselage panels using fiber Bragg grating sensors. Part II: Mechanical testing and validation

This is the second paper of a two-paper series describing design, implementation and validation of a strain and damage monitoring system for CFRP fuselage stiffened panels based on Fiber Optic Bragg Grating (FOBG) sensors. The system was developed and tested on the basis of compression after impact response of the panel. The first paper describes the system design, the embedment of fiber sensors in the panel during manufacturing and the impact testing. In the present paper, mechanical testing of the panels and validation of the proposed monitoring system are described. The mechanical tests comprised three load-scenarios: compression to failure of undamaged panel, compression to failure of impacted panel and compression to failure of impacted and fatigued panel. In all cases the panel failed due to buckling. In order to monitor the panels’ behavior during testing and be able to validate the accuracy of the measurements of the FOBGs, a network of strain gauges were used. Impact damage and fatigue damage decreased the failure load and displacement at failure of the panel. The measurements taken from the FOBGs captured all changes in the buckling modes of the panel. Moreover, they showed a good correlation with the measurements taken from strain gauges. These findings validate the proposed monitoring system.