Cure strain in thick CFRP laminate: optical-fiber-based distributed measurement and numerical simulation

This study seeks to clarify the mechanism of strain development in curing a thick composite structure with a temperature distribution in the thickness direction. Strain developed during curing can be separated into two parts according to the causes. One is chemical cure shrinkage of the matrix; the other is thermal shrinkage (or expansion) of the cured composite. Therefore, this study consists of a cure-shrinkage part and a thermal-shrinkage part. In both parts, the curing was monitored with an embedded distributed optical-fiber sensor (pulse-pre-pump Brillouin optical-time-domain analysis, PPP-BOTDA) and analyzed. In the cure-shrinkage strain part, the strain distribution caused by different temperature histories was observed. We confirmed that the lower viscosity part was influenced by the cure shrinkage of the other part and that these phenomena can be analyzed by the visco-elastic cure model. In the thermal-strain part, the amount of total shrinkage strain and the apparent coefficient of temperature expansion distribution were observed in the thickness direction. Warpage of the specimen was also observed. These results were confirmed to be caused by the distribution of temperature and of the fiber volume fraction, V-f.