The Effect of Curvature and Layup of Aircraft Type CFRP Laminate on the Springback After Curing Process

This paper deals with the investigation on the spring-back of CFRP composite laminate after curing process through autoclave manufacturing process. Two parameters are considered; curvature and stacking lay-up to reflect its application for Aircraft structure. The specimen consists of a 4 plies of UD laminate with a dimension of 500*500mm² and curvature angle of 30°, 45° and 90°. The analysis of experiments shows that the acute curvature angle until 90° influenced significantly the spring-back deformation with a linear correlation vis-a-vis curvature angle. A FE model is proposed where the laminate is divided into 2 regions; corner for curvature shape and flange for flat area. First attempt to simulate the effect of curvature is reducing the flange modulus of Young due to resin accumulation on flange area and FEA result showed the effect is insignificant. Therefore, the effect comes from the fact that the laminate behaves differently at the corner compared to the flange. The FEA simulation correlates the spring-back of all curved specimen by increasing the thermal expansion of 1st ply, α, of corner linearly with the flange. The proposed method is tested using other published data which were using the specimen with; 8 plies, 280*216mm² with curvature angle 45° and 90°. As for symmetrical laminate, specimens with a dimension of 300*300mm², 4 plies, and stacking layup [45/0]s [45/-45]s and [0/45]s are fabricated to investigate the effect of stacking lay-up of the laminate to the spring-back magnitude. The spring-back measurements indicate that the 1st ply fiber direction of laminate which is in contact with mold produces different shape of spring-back after curing. Therefore, the 1st ply of laminate, α, playes a significant role on the spring-back magnitude and shape of symmetrical laminate. FEA confirmed the phenomena by correlating the spring-back obtained from experiments.