A fiber optic strain gage sensor for measuring preload in thick composite bolted joints

Mechanical fastening is a popular choice in joining composites because of the ability to transfer high loads and the ease of assembly and disassembly. In this study, the failure behavior of composite–aluminum single lap bolted joint is investigated. In particular, the effects of varying the preload on the bolt are examined. In order to accurately measure the preload, a specialized sensor that uses a fiber Bragg grating sensor embedded in the bolt is proposed and created. This sensor is realized for the current tests but can be expanded to other applications. An experimental study of bolted single-lap joints varying the tightening torque value has been carried out and, in order to validate the experimental tests, several finite element analyses conducted in ANSYS environment with explicit solver are performed. Comparison between numerical results and experimental tests allows us to determine the effect of bolting parameters on the strength of joint and to verify the effectiveness of the use of the specialized preload sensor.