Spring-in analysis of CFRP thin laminates: numerical and experimental results

During the cure process of CFRP laminates, some geometrical unconformities can arise, due to several thermomechanical and thermochemical phenomena that make residual stress rise. Among these unconformities, one of the most studied is the spring-in, that is the deviation of the flange-to-flange angle from the design value. In this work a numerical model suitable to determine the spring-in value was developed and verified. The proposed model considered both the thermo-chemical and thermo-mechanical phenomena that happen during the cure process. Then, the numerical model was used for calculating the spring-in angle of lots of different laminates in order to evaluate the influence of the thickness, the corner radius and the layup sequence on the laminate deformation. For evaluating the influence of the above mentioned parameter on the spring-in a full factorial plan was designed, and the FEM analysis allowed a saving of time, energy and material. It was found that only the layup sequence influenced the spring-in. Finally, a preliminary analysis stated the possibility to extend the proposed model also to other geometries, such as U-shaped laminates.