Characterization and 3-D modeling of Ni60Ti SMA for actuation of a variable geometry jet engine chevron

Abstract

This work describes the thermomechanical characterization and FEA modeling of commercial jet engine chevrons incorporating active Shape Memory Alloy (SMA) beam components. The reduction of community noise at airports generated during aircraft take-off has become a major research goal. Serrated aerodynamic devices along the trailing edge of a jet engine primary and secondary exhaust nozzle, known as chevrons, have been shown to greatly reduce jet noise by encouraging advantageous mixing of the streams. To achieve the noise reduction, the secondary exhaust nozzle chevrons are typically immersed into the fan flow which results in drag, or thrust losses during cruise. SMA materials have been applied to this problem of jet engine noise. Active chevrons, utilizing SMA components, have been developed and tested to create maximum deflection during takeoff and landing while minimizing deflection into the flow during the remainder of flight, increasing efficiency. Boeing has flight tested one Variable Geometry Chevron (VGC) system which includes active SMA beams encased in a composite structure with a complex 3-D configuration. The SMA beams, when activated, induce the necessary bending forces on the chevron structure to deflect it into the fan flow and reduce noise. The SMA composition chosen for the fabrication of these beams is a Ni60Ti40 (wt%) alloy. In order to calibrate the material parameters of the constitutive SMA model, various thermomechanical experiments are performed on trained (stabilized) standard SMA tensile specimens. Primary among these tests are thermal cycles at various constant stress levels. Material properties for the shape memory alloy components are derived from this tensile experimentation. Using this data, a 3-D FEA implementation of a phenomenological SMA model is calibrated and used to analyze the response of the chevron. The primary focus of this work is the full 3-D modeling of the active chevron system behavior by considering the SMA beams as fastened to the elastic chevron structure. Experimental and numerical results are compared. Discussion is focused on actuation properties such as tip deflection and chevron bending profile. The model proves to be an accurate tool for predicting the mechanical response of such a system subject to defined thermal inputs.

Aerospace applications of shape memory alloys

“…In this case the goal is to optimize the trade-off between noise mitigation at take-off and landing and performance at altitude [26][27][28][29]. Such engine noise levels are often highly regulated by various civil agencies.…”

“…Figure 11 illustrates the results of current efforts to model the Boeing chevron system. Here, complex behaviours such as elastic laminate response of the composite substrate, sliding contact, and threedimensional non-homogeneous SMA loading have all been considered [28,29].…”

Optimal design of rotary manipulators using shape memory alloy wire actuated flexures

“…Thus SMA actuators of one-way effect, especially wire and strip type alloy, are more attractive in aerospace and robotic applications. Repetitive motion is achieved by passive elastic force [9][10][11][12][13][14] or opposing (antagonistic) SMA actuator pairs [15][16][17][18]. Regardless the applications of SMA, it is limited by its hysteresis and slow response time.…”

Characterization of Ni 19.5 Ti 50.5 Pd 25 Pt 5 high-temperature shape memory alloy springs and their potential applications in aeronautics

“…10,11 SMAs have also been used to develop a variable geometry chevron for noise pollution reduction, capable of optimum positioning for both take-off and cruise conditions. 12 The actuators used in these demonstrations and applications have been made from commercially available NiTi SMAs. The primary limitation when considering alloys that are commercially available today for use in the field of aeronautics is their temperature capability.…”