Effect of interfacial nanostructure on mode mixity in directly bonded carbon fiber reinforced thermoplastic laminates and aluminum alloy considering thermal residual stress

In recent years, for the aim of weight reduction of transportation equipment, carbon fiber reinforced thermoplastics (CFRTPs), which have high recyclability and formability, are becoming suitable for mass production.Additionally, with the development of multi-material structures, excellent technologies are required for joining metals and CFRTPs. Presently, adhesive bonding and mechanical joining methods are employed for joining dissimilar materials,however, these methods still have some problems. Therefore, an alternative bonding method that does not use adhesives or employ mechanical joining is required for joining CFRTPs and metals. This study focuses on direct bonding between the CFRTP laminate and an aluminum alloy by fabricating a nanostructure on the aluminum alloy surface. The nanostructure penetrates the CFRTP matrix, causing an anchoring effect that improves the bonding strength significantly. The influence of the nanostructure on the energy release rateof the directly bonded CFRTP and aluminum was evaluated bystatic double cantilever beam testing. Because of the difference in thermal expansion coefficients of the CFRTP laminate and the aluminum alloy, significant residual stresses are generated. The effect of the thermal residual stresses on the energy release ratealong with the resulting mode mixity (mode I and II) was determined. Results reveal that the critical energy release rate is improved by the nanostructure and mode I contribution of the energy release rate is increased for the nanostructure case.