ORIGINAL ARTICLE Numerical and experimental study of the drilling of multi-stacks made of titanium alloy Ti-6Al-4V: interface and burr behavior Nawel Glaa 1,2 & Kamel Mehdi 3 & Kamel Moussaoui 4 & Redouane Zitoune 2 Received: 3 November 2019 /Accepted: 18 February 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020 Abstract Machining and especially drilling of multi-stacks is a challenge task. In fact, drilling of multi-layers generates several damages such as burr at the hole exit and the decohesion of the interface of the layers. It is important to note that the decohesion phenomenon favors the accumulation of the chips at the interface of the layers. In this case, it will not be possible to use the automated system (such as robots) for drilling and fastening in the aeronautical field. This work gives focuses on the numerical and an experimental study during drilling of a multi-stack made of titanium alloy (Ti/Ti), which is usually encountered during the assembly of the aircraft door at Boeing Company. The impact of the machining parameters on the thrust force, responsible of the decohesion of the layers as well as the burr size, has been investigated experimentally and numerically. The proposed model is based on the behavior law of Johnson-Cook for the titanium parts and the cohesive zone for the interface. The main experimental and numerical results have shown that the feed rate and the thickness of the bottom layer have a great influence on the size of the decohesion zone. However, the burr at the hole exit is strongly influenced by the feed rate. Keywords Drilling . Damage interfaces . Decohesion . Quality 1 Introduction Many researchers and industrialists are working on cutting pro- cesses in order to predict machining performance, surface in- tegrity, chip formation, tool life, tool wear and breakage, cut- ting, and temperature distribution [1–8]. The major advantages of these works have resulted to step increase in productivity and lower manufacturing cost of the machined components [6]. For many years, materials with low density and important mechanical characteristics of supporting large loads are increas- ingly used in aeronautic and automotive industries. Composite materials made of carbon fibers (CFRP) have recorded signif- icant growth in the field of mechanical engineering [4]. The aerospace industry as well as many others is increasingly using materials of different mechanical and geometric characteristics in order to strengthen, lighten, and improve the aesthetic aspect of mechanical structures [9, 10]. It is important to notice that, for a design and dimensioning reasons in the aircraft, the pres- ence of multi-stacks made of CFRP, titanium, and aluminum is commonly encountered [11]. Numerous experimental, numerical, and analytical studies have focused on the study of the drilling of multilayer mate- rials in order to improve the quality of the holes [11–14] by analyzing the influence of the cutting parameters as well as the geometry and the tool material [15–20]. Due to the different mechanical properties of the materials constituting the com- posite plate, their machinability remains an open problem [13, 21–26]. It should be noted that the drilling of certain metal parts (titanium or aluminum), replaced by parts made of monolithic composite materials (CFRP) with an organic ma- trix or by parts made of multilayer materials CFRP/Al or CFRP/Ti, remains a major problem. For example, when dril- ling a carbon/epoxy monolithic composite material (CFRP), * Kamel Mehdi kamel.mehdi@ipeiem.utm.tn 1 Engineering National High School of Tunis (ENSIT), Mechanics, Production and Energetics Laboratory ‘LMPE’, University of Tunis (UT), Tunis, Tunisia 2 Institut Clément Ader, CNRS UMR 5312, ‘INSA, UPS, Mines Albi, ISAE’, Université de Toulouse, 133 c Avenue de Rangueil, 31077 Toulouse, cedex 04, France 3 Preparatory Institute for Engineering Studies El Manar (IPEIEM), University of Tunis EL Manar (UTM), PB. 244, 2092 Tunis, Tunisia 4 Altran Sud Ouest, Département recherche, 4 avenue Didier Daurat, 31700 Blagnac, France The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-020-05116-0