## 10 Conclusions and Further Steps
In this regard, even if room temperature is foreseen for the tests, the requirement of an activation over 90 \({}^{\circ}\)C was considered and met in view of an application within a real operational scenario. The encouraging results achieved in this application led to the realization of the prototypes for the WT and WhT experimental campaigns. After the completion of the functionality and commissioning tests, the devices were delivered and tests executed in the facilities, generally confirming the modeling predictions and the effectiveness of the concept that was considered worth intellectual protection. One of the most important aspects of the modeling approach herein developed is represented by the simulation of the different phases that characterize the realization and the functioning of the SMA twist device. At first, the preload phase was modeled. The peculiar nature of the SMA, requiring enough martensite for the strain recovery, led to considering a specific integration approach, consisting of pre-twisting and then connecting the SMA to the structure to achieve the elastic equilibrium. This process is strictly non-linear for the SMA constitutive law and the impact of the stress level on the global stiffness matrix. A nonlinear solver was necessary to simulate the process. Moreover, passing from the pretwist operation to the connection with the structure, specific dofs were connected. In this way, the process was faithfully replicated. After the integration phase, the effect of the applied loads was simulated. The sequence of the operations occurring during the test campaigns was respected in the simulation. Thus, first, the external loads (aerodynamics for the WT and aerodynamics + centrifugal forces for WhT) were applied, and their effect was predicted within a dedicated simulation step. Then, the SMAs were actuated, and their effect on the deformed shape and in the presence of the external loads was evaluated. This approach was inspired by the specific integration process that was ideated. Its scope was essentially to allow the pre-twist and connection operations, minimizing the needed tools and the forces to be applied. This has a relevant impact both in terms of implementation costs and safety. Another important aspect is represented by the sensor layout, whose definition, as discussed, was driven by the necessity, from one side, of intensifying the magnitude of the measured strain and, from the other side, of minimizing its impact on twist performance. The role of this system is to support the logic of shape reconstruction even in the presence of multiple load sets and monitor the level of solicitation of the structure during the operative life. Despite the promising outcomes and the attractive peculiarities, it is worth stressing that the present architecture is not yet suited for real applications. As discussed in [48], some specific aspects should be further matured before arriving at a TRL compliant with an industrial application. First of all, as already mentioned, even if the stiffness falls within the order of magnitude typical of a real blade structure, only a device with a rigidity of 20% of the real one was considered for safety restrictions. The development of a more rigid structure is compliant with the present architecture since it can be obtained, for example, by just thickening the spars and the ribs. However, to keep the same performance of twist, the authority of the SMA actuators should be increased. Also, in this case, the operation is feasible by, for example, increasing the radius of the cross-section. Moreover, a tubular configuration could be considered to optimize the available room within the blade and ensure the maximum exploitation of the SMA martensite phase.