Stresses and deformations induced during manufacturing. Part II: A study of the spring-in phenomenon

It has been observed that residual stresses always build up during the fabrication of composite components. Such stresses can change the shape of a component when it is removed from the mould. This paper examines the spring-in induced during fabrication of composite angle components by such residual stresses. The sample composite components were fabricated from unidirectional carbon/epoxy pre-preg tape and plain-weave carbon/epoxy pre-preg fabric, as well as from dry carbon fabric and resin using the resin transfer moulding (RTM) technique. The effects of lay-up, orientations, part thickness, tool angle, tool material, etc. were investigated. The results show that (1) the tool material has an insignificant effect on the degree of spring-in, (2) spring-in is insensitive to the lay-up sequence for symmetric lay-ups, (3) spring-in does not depend on ply orientation angles in the case of fabric laminates, (4) spring-in remains constant for almost all radius/thickness ratios and (5) spring-in decreases with an increase in the tool angle. Comparison with the theoretical model developed by Jain and Mai is provided and good agreement is found.