Monitoring of Marine Grade Composite Doubler Plate Joints Using Embedded Fiber Optic Strain Sensors

摘要

The objective of this paper was to develop a methodology for the structural health monitoring of composite joints based on strain measurements using distributed embedded fiber optic strain (FOS) sensors of the fiber Bragg grating (FBG) type. Secondary bonded woven E-glass/vinyl ester composite doubler plate joints were subjected to fatigue tension loading. The feasibility of monitoring delamination using embedded sensors was investigated. The fatigue experimental plan, the finite element (FE) modeling of the experiment, and the fabrication methodology of the composite joints through Vacuum Assisted Resin Transfer Molding (VARTM) processing are presented. Initial quasi-static tension tests showed a good correlation between the longitudinal strain measurement from the FOS sensors and finite element model predictions. The majority of the embedded sensors survived the fatigue loading and provided robust strain measurements. A progressive shift in the strain distribution in the vicinity of the crack was observed in most of the coupons. The experimental results, as well as the numerical study conducted prior to cyclic loading, showed that a strain-based methodology can be utilized to detect crack propagation in this type of composite joints. The proposed methodology allows detecting a one quarter inch delamination length, which is the criterion adopted by the U.S. Navy for damage tolerance in service conditions.