Blade geometry and stiffness variations lead to advantages that have been proved in several fields, from aerospace to turbomachinery. The advent of innovative materials as Shape Memory Alloys (SMA), have allowed non-conventional design approaches, targeting adaptive, smooth and extensive modifications of aerodynamic shapes and local stiffness. The Project “Shape Adaptive Blades for Rotorcraft Efficiency” (SABRE) within the EU program H2020, has the main objective of maturing blade morphing technologies and related processes, moving from the assessment of predictive codes integrated with novel philosophies of geometry alterations, till experimental validation within lab and wind tunnel environments. In this paper, an SMA demonstrator for active twist is proposed, aimed at modulating spanwise blade torsion angle for rotorcraft performance improvement. The idea is to combine the reference structure with embedded torque actuators. Quasi-steady operations are targeted because of the low frequency bandwidth of the addressed devices (under 1 Hz). Thus, single flight regimes are considered (hover, climb, forward flight). Actuation authority is a critical aspect for the proper design of that system. It is influenced by many geometrical and physical parameters like the cross section geometry or the materials Young modulus. The presented demonstrator is made of three main elements: an SMA rod system, structural elements representative of the blade body stiffness, and the connecting fixtures. An experimental campaign is carried out to verify the relations among alloys activation temperatures, induced stiffness levels, and forces and installation angles (pre-twist).
Traditionally, metallic vessels have to comply with specific regulation rules (Pressure Equipment Directive from the European Parliament) involving periodic re-qualifications. However, for high pressure composite vessels, standards, and particularly non-destructive techniques, have to be developed, tested and validated. In this new frame, a research project has been set up for VECEP program (VEga launcher Consolidation and Evolution Preparation Programme) aiming at funding developments to set-up new control/monitoring techniques applicable to composite vessels, for both future regulatory and inspection needs. To reach the market, these techniques have also to be cost-effective in comparison with traditional ones. To monitor such vessels behavior and finalize the sensor system to the detection of structural defects, CIRA and AVIO have conducted R and D activities based on high resolution distributed strain profiles sensitivity analysis along single mode optical fibers. To elaborate this method, preliminary tests were carried out for testing different bonding agents and different surface finishing, on a set of representative coupon from composite overwrapped pressure vessels under bending incremental solicitation until reaching ultimate load. Additionally, their sensitivity, analyzed during the test, provided additional valuable data about structure integrity. A mechanical criterion based on OFDR (Optical Frequency Domain Reflectometry) differential strain profiles analysis was preliminarily implemented in order to evidence structural anomalies during the test.