Effect of Molding Conditions on Process-Induced Deformation of Asymmetric FRP Laminates

It is well known that process-induced deformation of laminates affected dimensional accuracy of FRP components strongly. It is very important for manufacturing of FRP laminates to investigate cure shrinkage and thermal strain during molding process. In the present paper, in order to investigate effect of molding conditions on process-induced deformation of asymmetric GFRP laminates, several molding patterns of temperature and pressure and two types of interfacial conditions between FRP and a mold were employed for manufacturing of the laminates by a hot press molding method. Single-hold pattern or double-hold patterns of temperature were applied to the molding process. The highest molding temperature was 140 degrees C and the first hold temperature of double-hold patterns were 90 degrees C, 110 degrees C and 120 degrees C. Fiber optic strain sensors and refractive index sensors were used for measurement of strain and degree of cure. It was confirmed that prepreg was cured perfectly at the first holding step. Curvature of the specimen were measured after demolding and drying processes. From the experimental results, it was found that the first holding temperature of double-hold patterns did not affect the curvature of warping deflection after demolding. The results of strain measurements suggested that the strain during cure process was governed mainly by friction between laminates and deformation of molding plates. Moreover, it was found that Interfacial constraint between the laminates and molding plates strongly affected process-induced deformation of asymmetric GFRP laminates.