Delamination in rotary ultrasonic machining of CFRP composites: finite element analysis and experimental implementation

Delamination, an inter-ply debonding failure phenomenon, is considered as the most undesirable and challenging failure mode in hole making of carbon fiber-reinforced plastic (CFRP) composite laminates. The existence of delamination, even small ones, noticeably damages the strength and stability of the assembled products. It is reported that delamination is responsible for up to 60% of composite components' rejection during assembling. In order to reduce delamination, rotary ultrasonic machining (RUM) has been studied and utilized in hole making of CFRP composites. Existing investigations on delamination of CFRP composites in RUM hole making are experimental studies, in which several methods (such as adjusting input variables and the use of supportive plate) to reduce delamination are reported. To understand delamination generation mechanisms and predict delamination initiation, theoretical investigations are needed. Cutting force models in RUM of CFRP composites have been developed, and it is well accepted that delamination is correlated to thrust force. However, there are no reported investigations to predict delamination initiation and study the impact of thrust force on the delamination of CFRP composites in the RUM hole-making process. Finite element analysis (FEA) could be an effective way to study the delamination in the RUM process. In this paper, FEA was conducted to predict delamination initiation and establish the relationship between the thrust force and delamination thickness in RUM, for the first time. In addition, experiments were conducted to validate the FEA model. The proposed model was proved to be effective in predicting delamination initiation, and the trends of the FEA results agreed well with those of the experimental results.