Experimental and numerical study of the effect of cure cycle, tool surface, geometry, and lay-up on the dimensional fidelity of autoclave-processed composite parts

Abstract Resin cure shrinkage and anisotropic thermal expansion cause process induced residual stresses in polymer composites. When relieved, the residual stresses cause reduction in enclosed angles of composite laminates; a phenomenon often called spring-in. Spring-in compromises the dimensional fidelity of composite parts and is often accounted for when designing the tool the part is made on. Spring-in is often estimated using past experience or simple analytical formulas that ignores many process parameters affecting the spring-in. This paper presents an experimental study that shows that spring-in can be strongly affected by a number of factors such as cure cycle, tool surface, part geometry, and lay-up. The paper also shows that by developing material models that accurately represent the stress transfer between the part and the tool at the tool-part interface, and by implementing a large deformation solution technique, the experimental results observed in this study can be predicted using finite element based process models.