## 1 Introduction  
In recent years, the use of composite fiber-reinforced plastic (CFRP) for the manufacturing of aerospace primary structures has unquestionably increased. However, despite the undeniable advantages in terms of weight related to composites, metal parts are still widely used because of the criticalities related to the damage management of the new outstanding composites [1; 2; 3; 4; 5; 6]. Therefore, for several structural components, metal/composite hybrid solutions are adopted, due to the effective reduction in weight and costs without strong compromises in terms of safety [7; 8]. In the literature, the damage behavior of composite materials has been widely investigated, pointing out the effects in terms of induced damage of impacts with foreign objects [9; 10; 11; 12; 13; 14], of the manufacturing or the assembly processes [15; 16; 17; 18] and, finally, the effects of service loading conditions. Indeed, in order to exploit the advantages related to the adoption of composite-metal hybrid solutions, it is mandatory to understand the issues related to the manufacturing and the joining of these different materials [19]. In [20], a comprehensive review on the methods, commonly adopted, to join CFRP and aluminum alloys parts was presented. Among the several methods described, adhesive joints, bolts, and self-piercing rivest (SPR) are, of course, the most affordable. In particular, bonded joints have been found to be the method most adopted to join CFRPs and aluminum alloys parts. Indeed, bonded joints avoid undesirable stress concentrations and does not require an intrusive application, being at the same time weight saving with respect to other joining techniques. However, since the bonding is an irreversible process, the separation of joined components often results in critical material damage, as demonstrated by several investigations on bonded joints found in the literature [21; 22; 23; 24; 25]. A CFRP/aluminum double lap-bonded joint was presented in [26] where a non-linear cohesive material model was used to investigate the bonded interface behavior. In [27], the strain distribution in CFRP/aluminum double lap joints was experimentally and numerically investigated. The surface strain within the adhesive layer was measured by using high-magnification Moire interferometry. Hence, the spatial variation of longitudinal, peel, and shear strains was evaluated in detail and compared to numerical predictions. Moreover, due to the different thermal expansion coefficients of metal and composite sub-components, the effects of the thermal residual stress in terms of curvature of the composite/metal assembly should be addressed. This issue was investigated in [28], where a thermo-chemical-mechanical constitutive model was used to simulate the curing process of the composites and to evaluate the thermal residual stresses of a metal/CFRP plate. In [29], the mode I and II interfacial fracture behavior of a titanium/CFRP bonded joint was studied by considering the bending-extension coupling induced by the presence of the aluminum beams and the manufacturing-induced residual thermal stresses. Bolts and rivets are a common alternative to bonded joints [30; 31; 32; 33; 34; 35]. The bolt is inserted in a uniaxial common hole in components to be joined. However, the hole drilling may generate damage and defects in the CFRP components, which can evolve due to the service load, affecting the life of the components themselves. In [36], an experimental study on the manufacturing defects induced by drilling aluminum/CFRP stacks was performed, aimed to determine the critical geometric parameters of a carbide drill in order to reduce the fragmentation of the metallic chips while avoiding damages on the composite components. This issue was also addressed in [37], where nano-coated carbide drills were used to reduce the damages resulting in drilling multimaterials made of aluminum alloy and CFRP.