Spring-in and warpage of angled composite laminates

The residual stresses that develop in fibre-reinforced laminates during autoclave processing while the laminate is confined to the process tool often lead to dimensional changes such as spring-in of angles and warpage of flat sections. A large number of experiments were performed to examine the effect of design and process parameters on spring-in and warpage of composite laminates with a symmetrical lay-up. The parameters studied include part angle, thickness, lay-up, flange length, tool material, tool surface, and cure cycle. This paper shows that both design and process parameters can have a significant effect on spring-in and warpage and that there are interactive effects between them. The paper also shows that spring-in of angled laminates is sensitive to the measurement technique as the measured spring-in often is compounded by warpage of flat laminate sections.