FABRICATION OF SECONDARY BONDED VARTM COMPOSITE DOUBLER-PLATE JOINT PANEL WITH EMBEDDED FIBER BRAGG GRATING STRAIN SENSORS FOR FATIGUE CRACK MONITORING

摘要

In the present work a methodology to fabricate secondary bonded composite doubler-plate joints with embedded Distributed Strain Sensors (DSS) arrays of the fiber Bragg grating (FBG) type, through Vacuum Assisted Resin Transfer Molding (VARTM) processing was developed. The embedding technique, egress points, and some fabrication issues are discussed. Four doubler-plate joint panels of 36 inches in length by 18 inches in width were fabricated. Ten 2 inch by 30 inch specimens with three embedded DSS arrays in different locations were projected to be fabricated. Five specimens with three embedded sensors, one with two sensors, and two with only one sensor were obtained. Of the twenty-nine embedded DSS, ten were broken during the fabrication process. Of nineteen successfully embedded DSS, only one was found to be inoperable after the fabrication process was completed. The embedded DSS are intended to monitor longitudinal crack initiation and propagation in the doubler-plate joint specimens under fatigue tension loading. A description of the fatigue test plan and the finite element modeling which supports the design of the experiment are also presented.