Anisotropy related "spring-in" of angled composite shells

During the manufacture of curved or angled shell composite structures, the enclosed angle of such structures tends to be reduced after cure. This phenomenon is referred to as "spring-in". It is believed that such distortion is caused mainly by the significant difference between the in-plane coefficient of thermal expansion (CTE) and the through-thickness CTE. This might result in a larger out-of-plane contraction than the in-plane contraction during the time that a composite structure is cooling down from the curing temperature. In this paper, a 3-D Finite Element Analysis procedure was developed to predict "spring-in" resulting from anisotropy for both thin and thick angled composite shell structures. The results of the FE analysis were evaluated together with those from the analytical study and experimental investigation conducted by Jain at the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) in Australia. It was concluded, based on these results, that the FE model gives more accurate results than the analytical model, particularly for thicker composite shells. The corner radius effect, shell thickness effect, and lay-up effect on "spring-in", together with the effect of tool/part interaction on the total distortion were also discussed. Comparison was made with the experimental results reported by Radford and Rennick.