Forming quality prediction and evaluation of polymer composite laminates under different autoclave curing pressures based on FBG sensors

Abstract

To study the effect of curing pressure on the strain change of composite components during autoclave curing process. A combination of fiber Bragg grating (FBG) and thermocouple sensors is employed to monitor temperature and strain data of the laminates during the curing process. On this basis, the effect of curing pressure on strain change at different process stages is investigated, and the forming quality is predicted online by the states of strain change at each stage. The external forming precision and internal microscopic defects of the samples are used to verify the predicted results. Results show that the strain change is mainly divided into heating, holding and cooling stages. In the heating/holding stage, the overall strain tends to increase, while in the cooling stage, the strain decreases and is accompanied by a jump phenomenon. The effect of curing pressure on the strain change is obvious. The higher the curing pressure, the better the bonding quality between fibers and resin, and the more significant the inhibition of strain changes by fibers. In order to obtain the good forming quality, the curing pressure should not be lower than 0.4 MPa. When the curing pressure is above 0.4 MPa, the thickness deviation of the laminate is limited to ±0.06 mm. Meanwhile, there is basically no defect within the laminate, which verifies the accuracy of using FBG sensors to monitor the strain change for online prediction of forming quality in composite components.