April_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 0 6 1 In surveying existing materials, it was ap- parent that there were no commercially avail- able alloys that met these requirements. More- over, no torsional data was available given the actuation form was based on torque tubes to stay within the allocated footprint and in- stallation. As a result, the approach taken was to design a new alloy with specific attributes to fit this application, rather than modify existing alloys and settle for less than optimum perfor- mance. A Ni-rich Ni 50.3 Ti 47.7 (Hf,Zr) 2 (at.%) alloy was designed for this purpose following the ap- proach described by Benafan, et al. [8] . The alloy was vacuum induction melted in a graphite cru- cible and cast into 25.4 mm diameter rods. The ingots were vacuum homogenized at 1050°C for 72 hours and gas quenched, followed by hot ex- trusion at 900°C. Rods and tubes with an outer diameter of 3.175 mm and an active length of 89 mmwere cut from the extruded bars. The low levels of Hf and Zr not only proved to be critical in achieving the desired activation temperature, but also in stabi- lizing the alloy’s response during training in torsion. The rods were tested on a torsional frame with a custom heating and cooling setup to simulate the environmental temperatures during flight. Figure 2 shows the thermomechanical response of the material under constant shear loading. Transformation temperature shifts and transformation shear strains under varying shear stress are shown in Fig. 2a and b, respectively. By design, these responses were matched to the VG’s load, de- flection, and temperature requirements. Additionally, the alloy was designed with ample two-way capability of > ±3% shear strain to enable the VGs to move between the retracted and Fig. 1 — Shape memory alloy reconfigurable technology—vortex generators (SMART- VGs) flight testing on a 777-200 test aircraft as part of the 2019 Boeing EcoDemonstrator program. Fig. 2 — Thermomechanical response of NiTiHfZr alloy under constant shear loading: (a) temperature sensitivity as a function of stress, and (b) output shear strain as a function of stress. The solid symbols in (b) represent the two-way shape-memory effect after training. The trans- formation temperatures are indicated in the legend: martensite start (M s ), martensite finish (M f ), austenite start (A s ), and austenite finish (A f ). (a) (b) deployed configurations while under aerodynamic loading with-out the need of a return force. FLIGHT TESTING In-flight performance of three SMART-VGs was assessed on several flights over multiple weeks as part of Boeing’s 2019 EcoDemonstrator program on a 777-200 test aircraft. Figure 3 shows photographs of the three SMART-VGs deployed and retracted at altitudes below 3048 m and above 12,192 m (40,000 ft), respectively. Also, Fig. 3a shows the correspond- ing angular deflection-temperature response of the center VG under in-flight aerodynamic loading with mechanical limits at 0° and 90° deflection. These profiles are the result of a little over four hours of flight testing as shown in the altitude-time flight profiles in Fig. 3b. The flight test included ascending to 7 FEATURE