A Case Study of Cure Cycle Shrinkage Deformations

A case study of curing deformations in square struts laminated from unidirectional prepreg is presented that uses laminate and three-dimensional finite element analyses to analyze critical shrinkage behavior. The manufacture of square graphite epoxy struts is complicated by twisting deformations during cooling from autoclave cure temperatures that are not predicted by laminate analyses. Three-dimensional finite element analyses are presented that correctly predict the twisting but not its amplitude which appears to be dependent on a geometric nonlinearity. The three-dimensional and laminate results both show large self equilibriating stresses in individual plies caused by local shrinkage and stiffness property differences. This is a key finding that identified the source of shape instability and confirmed design changes to minimize twisting deformations that were first determined experimentally.