Modeling of the interface delamination process when machining hybrid multi-material assemblies

Thanks to their high mechanical properties, structures involving assembled materials such as titanium/composite are suitable for many applications in the aeronautical industry. However, the machining process used for these structures to achieve dimensional tolerance and assembly requirements often entails difficulties due to their poor machinability. A numerical model considering different phases of the assembly has been developed for machining in the present work. The behavior of the composite phase is governed by a mesomechanical model coupling the effect of the drop in stiffness, plasticity, damage initiation, and its progression. The well-known thermoviscoplastic constitutive Johnson-Cook law and evolution of the damage energy criterion were considered for the titanium phase. Debonding of the CFRP/Ti interface was modeled using cohesive elements. The cutting sequence was found to be a key factor to prevent the interface delamination process; the cutting from Ti to CFRP phase induced permanent damage at the interface between these two materials while the cutting from CFRP to Ti phase exhibits a smooth transition between phases and almost no delamination was observed. It has been also found that during the orthogonal cutting process, two levels of cutting forces related to ductile behavior for the titanium phase and brittle behavior for the composite phase, respectively. The chip formation mechanisms were correctly reproduced in comparison with experimental observations.