Cure monitoring of carbon–epoxy composites by optical fiber-based distributed strain–temperature sensing system

Abstract

This study establishes an innovative composite cure monitoring technique by utilizing a newly developed hybrid Brillouin–Rayleigh optical fiber sensing system. The new system can separately measure strain and temperature distribution with only one optical fiber. This study began by evaluating the measurement accuracy of the hybrid system in a composite application in a step-by-step manner. A single optical fiber was then embedded in a carbon–epoxy specimen, and thermal residual strain development and temperature change were measured during the cooling period of the curing process. The temperature and residual strain obtained by the hybrid Brillouin–Rayleigh system agreed well with the results measured by a conventional sensor set (i.e. fiber Bragg grating sensors and thermocouples). Furthermore, the system could identify a nonuniform thermal residual strain field induced by a nonuniform cure temperature. These results clearly demonstrated that the proposed technique is quite useful for cure monitoring of large-scale composite structures. Quality assurance for whole parts of actual products can be effectively accomplished by applying the proposed technique.