Monitoring of temperature and cure-induced strain gradient in laminated composite plate with FBG sensors

Unidirectional laminated composite plate composed of AS4/8552 prepregs was manufactured with autoclave processing, and the bare and encapsulated FBG sensors were longitudinally embedded into the composite plate along the through-thickness direction to monitor the development of temperature and strain gradient. Before the measurement, the coefficient of temperature sensitivity and axial strain sensitivity of FBG sensors were calibrated, and the results reveal that the coefficient of axial strain sensitivity is a constant but coefficient of temperature sensitivity depends on the magnitude of temperature. Subsequent data analyses on the monitored results by encapsulated FBG sensors show that temperature distribution is relatively uniform inside composite plate but temperature gradient still exists in the through-thickness direction during curing. Meanwhile the monitored results by bare FBG sensors indicate that strain gradient also occurs during curing, and further investigation demonstrates that tool-part interaction is the major cause for the formation of strain gradient within the unidirectional composite plate.