Real-time cure and health monitoring of FW FRP by using built-in FBG sensors

Abstract

Recently real-time monitoring technique by using built-in sensors of FRP is expected to reduce the cost and enhance the reliability. In the present paper, built-in FBG fiber optic sensors were applied to cure and health monitoring of filament winding (FW) glass/epoxy pipes. FW pipes were wound by ±45° helical ±5° parallel winding methods. The FBG sensors were embedded between helical and parallel layers along axis direction of the pipes. Internal strain monitoring of the FW pipes was conducted during cure and fatigue tests. From the results of the cure monitoring, it was found that FBG sensors could be used for measurement of the curing shrink as well as the thermal residual strain. The results of the fatigue tests showed that strain from the FBG sensors had very good agreement with that from the attached strain gauges. Young's modulus of the pipes measured by the FBG sensor was almost constant during the fatigue tests although transverse cracks occurred in the parallel layers. However, the spectral shape reflected from the FBG sensor was affected by existence of the fatigue cracks. In order to evaluate degree of damages near the sensor, correlation coefficient calculated from the spectral shape was introduced. The experimental results showed that the correlation coefficient was useful for evaluation of damages.