Improvement of Composite Drape Forming Quality by Enhancing Interply Slip

Diaphragm forming such as hot drape forming (HDF) is a cost effective method that has been used to manufacture large composite aircraft structures with relatively low geometrical complexity. This technique improves production rate by laying multiple prepregs to create an uncured laminate preform first and then forming it into a desired shape, instead of the time consuming manual ply-by-ply lay-up process. However, the disadvantage of this method is that out-of-plane wrinkles occur during forming, which makes this method challenging. This undesirable defect is generated by high interfacial friction between the plies due to the tacky surface resin preventing ply slippage. Therefore, the process usually needs to be carried out at an elevated temperature to enhance the ply slippage by reducing the resin viscosity, however the cost of heating energy and processing time can be significant in manufacture of large aircraft components, such as wing spars. In this research, a new method using interleaving materials to reduce the interply friction was developed, which could effectively minimise the wrinkles during forming. Additionally, the effect of interleaving material on the interlaminar fracture toughness was investigated experimentally.