## 1 Introduction
The hybridization of thermoplastic matrices was also investigated, showing positive interactions in static and dynamic behavior both in the case of glass and carbon fibers with polypropylene [21], as well as for carbon fibers and metallic braided wire mesh with poly-ether-ether-ketone [22]. In this case, an important contribution to damping is made by the matrix, too, but problems with optimal matrix-fiber adhesion may arise for such non-traditional fibers. In other cases, hybridization is used as a tool of sustainable development by integrating traditional fibers with natural ones, such as jute [23, 24, 25], flax [26], kenaf [27], banana fibers [11], cellulose [15], or sisal [28]. For these studies, the aspect of aging is most significant because of the strong sensitivity of natural fiber to the environment. As a consequence, final composite performances are often low, and not attractive for highly demanding application fields. Hybridization is also exploited in terms of structures if the interface between the different elements occurs at the macro-scale. Examples are the hybrid panels of 7075-T6 aluminum alloy and CFR laminate, manufactured using the thermoforming process [29], pultruded rods [30], hybrid joints [31], and sandwic [32]. These structures are easier to implement into the design and manufacturing procedures of the aerospace sector, but attention has to be paid at the interface in order to detect unexpected adhesion or corrosion problems. Dealing with structures, hybrid assemblies can be produced by joining thermoplastic (TP) and thermosetting (TS) matrices [33]. Co-bonding generally occurs during composite laminate molding. Nevertheless, co-bonding of TP and TS matrices remains as a challenge in the manufacturing of hybrid composites [34]. During curing, TP films, in contact with TS layers, can partially penetrate, leading to macro-mechanical interlocking as the main connection mechanism [35]. These hybrid composites, also known as \"multi-material composites\", combine the damage tolerance characteristics of thermoplastics with the strength and stiffness of TS composites, resulting in more reliable structures with an extended lifetime [36]. In fact, TP matrices are more ductile than TS, leading to higher damping, toughness and impact resistance at low speed. The same hybrid effect of TS-TP systems is proposed in this study by combining an elastomeric matrix with the traditional epoxy matrix of CFR prepregs. The use of a thermosetting elastomer is expected to improve co-bonding with the prepreg epoxy matrix. Moreover, commercial raw materials and conventional molding procedures used in aerospace have been used to manufacture the samples. This study aims to show that hybrid elastomer-rigid CFR TS laminates can be produced by using already-available materials and equipment. For the first time, hybrid composite laminates have been manufactured by interposing uncured rubber interlayers between CFR thermosetting prepregs during the lamination procedure. Another novel aspect is that hybrid composites have been produced by using state-of-the-art aeronautical materials and molding technologies. This study has been carried out to develop new smart structures for enhanced vibration mitigation. In fact, aeronautic structures experience vibration and impulsive loads that can be propagated and amplified, thus reducing their lifespan. Structural dampers are used to address this issue, but smart structures could integrate this capability into the material. However, very stiff structures behave poorly under dynamic loads, and a compromise is necessary between static and dynamic performances. The insertion of viscoelastic interlayers between composite plies during the lamination process is a smart manufacturing solution for these multi-functional structures [37]. Lightweight composite sandwich beams have been manufactured using this technique. The elastomeric sheet has the additional role of mitigating the thermal expansion mismatch between composite plies and aluminum sheets [38].