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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.
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