Shape Memory Alloy Torque Tube Research Articles

A shape memory alloy torsion actuator for static blade twist

Active blade twist is an option to increase helicopter performance, for instance moving its condition from hovering to cruise. Shape memory alloys give the possibility of realizing compact devices, with high energy density. Several devices have been proposed in literature, showing limitations in terms of effectiveness and necessary room. In this article, the capability of a shape memory alloy torque tube to induce a certain twist law along the blade, while preserving its integrability within the structure, has been exploited. The study refers to a complex theoretical model, made of different specialized modules. In detail, transmitted twist action by the shape memory alloy actuators, aerodynamic effects caused by the induced geometrical change, inertial impact following the motor system integration, and system layout influence on the blade response have been taken into account. Through this model, a parametric investigation has been organized to highlight the importance of selected design variables. Tube thickness, mass, and length have been considered. Two different configurations have been initially taken into account, distinguished for the twist transmission mode and their outline. In the first hypothesis, a pre-stressed wire system converts tensile stress into a rotary action. In the second sketch, a pre-twisted solid tube connects two different stations of the blade, transmitting relative rotation. After the first trade-off, the second architecture has been selected for further analysis, focusing on its performance in terms of net transmitted twist, aerodynamic effects, while paying attention to a proper mass balance. In the chosen approach, the actuator has been installed at the torsion center. A finite element model has been used to validate the assessed analytical representation and has permitted establishing the applicability domain. Apart elastic forces, acting both in the shape memory alloys and the blade components, centrifugal forces have been taken into account by considering an increased stiffness of the reference structural element. Aerodynamic forces have been evaluated after the target configuration has been reached; helicopter trim has been considered to this purpose. The researchers aim at developing this concept by integrating the reverse action of the aerodynamic field and evaluating the importance of the actuator position along the chord. The research herein presented has been carried out within the SABRE project, project ID 723491, gratefully funded by the European Union within the Horizon 2020 program.

A simplified model for high-rate actuation of shape memory alloy torque tubes using induction heating

Shape memory alloy actuators deliver high forces while being compact and reliable, making them ideal for consideration in aerospace applications. Induction heating of shape memory alloy actuators, specifically tubes that twist about the longitudinal axis, has recently been studied experimentally and computationally using finite element analysis. Reduced-order models for the torsional behavior of shape memory alloy tubes and induction heating of general metallic tubes exist, and thus, it is possible for these thermal and mechanical models to be combined and numerically solved. This work develops and implements an engineering model for inductively heated shape memory alloy tubes based on the reduction of the governing partial differential equations in space and time to an ordinary differential equation in time. An example solution is compared to finite element analysis results and agrees well. Finally, the ordinary differential equation is linearized and solved analytically. The linearized model agrees well with the nonlinear ordinary differential equation and finite element model.

A validated model for induction heating of shape memory alloy actuators

Shape memory alloy (SMA) actuators deliver high forces while being compact and reliable, making them ideal for consideration in aerospace applications. One disadvantage of these thermally driven actuators is their slow cyclic time response compared to conventional actuators. Induction heating has recently been proposed to quickly heat SMA components. However efforts to date have been purely empirical. The present work approachs this problem in a computational manner by developing a finite element model of induction heating in which the time-harmonic electromagnetic equations are solved for the Joule heat power field, the energy equation is solved for the temperature field, and the linear momentum equations are solved to find the stress, displacement, and internal state variable fields. The combined model was implemented in Abaqus using a Python script approach and applied to SMA torque tube and beam actuators. The model has also been used to examine magnetic flux concentrators to improve the induction systems performance. Induction heating experiments were performed using the SMA torque tube, and the model agreed well with the experiments.