Protection technology of optical fiber grating sensors embedded in fiber composite laminates

The survival rate and testing accuracy of embedded fiber Bragg grating (FBG) sensors are the precondition to on-line monitor the manufacturing and working status of fiber reinforced resin matrix composites. The stacking sequence of carbon fiber prepregs is90₁₁/0₁₁. The FBG temperature and strain sensors were embedded into the typical positions of the laminates along 0° and 45° directions, and then the composite laminates were manufactured by compression molding method. Four kinds of methods were used to protect fiber grating sensors when they were embedded into the laminates in direction of 45° where the fiber grating direction is not parallel to the carbon fiber direction. By the comparison of the experimental results, it can be concluded that the embedded FBG sensors which were not parallel to the carbon fiber direction were easily inactivated in the hot compression molding process without any additional protection; the method of laying several whole layers of synclastic prepregs to protect the FBG sensors which were not parallel to the carbon fiber direction has changed the mechanical performance of composites with specific layer parameters; the measurement error of the strain sensors would be enlarged if two narrow prepreg strips on both sides of the sensors were introduced to protect the sensors; the survival rate and testing accuracy of the fiber Bragg gratings would be significantly improved through the method in which two narrow prepreg strips on both sides of the sensors and opening grooves on the neighboring layers were used to protect the sensors.