NASA Glenn Research Center (GRC), in collaboration with GE Aviation, has begun the development of a smart
adaptive structure system with piezoelectric transducers to improve composite fan blade damping at resonances.
Traditional resonant damping approaches may not be realistic for rotating frame applications such as engine blades. The
limited space in which the blades reside in the engine makes it impossible to accommodate the circuit size required to
implement passive resonant damping. Thus, we have developed a novel digital shunt scheme to replace the conventional
electric passive shunt circuits. The digital shunt dissipates strain energy through the load capacitor on a power amplifier.
GE designed and fabricated a variety of polymer matrix fiber composite (PMFC) test specimens. We investigated the
optimal topology of PE sensors and actuators for each test specimen to discover the best PE transducer location for each
target mode. Also a variety of flexible patches, which can conform to the blade surface, have been tested to identify the
best performing piezoelectric patch. The active damping control achieved significant performance at target modes. This
work has been highlighted by successful spin testing up to 5,000 rpm of subscale GEnx composite blades in GRC's
Dynamic Spin Rig.
Piezoelectric materials have been proposed as a means of decreasing turbomachinery blade vibration either through a
passive damping scheme, or as part of an active vibration control system. For polymer matrix fiber composite (PMFC)
blades, the piezoelectric elements could be embedded within the blade material, protecting the brittle piezoceramic
material from the airflow and from debris. Before implementation of a piezoelectric element within a PMFC blade, the
effect on PMFC mechanical properties needs to be understood. This study attempts to determine how the inclusion of a
packaged piezoelectric patch affects the material properties of the PMFC. Composite specimens with embedded
piezoelectric patches were tested in four-point bending, short beam shear, and flatwise tension configurations. Results
show that the embedded piezoelectric material does decrease the strength of the composite material, especially in
flatwise tension, attributable to failure at the interface or within the piezoelectric element itself. In addition, the sensing
properties of the post-cured embedded piezoelectric materials were tested, and performed as expected. The piezoelectric
materials include a non-flexible patch incorporating solid piezoceramic material, and two flexible patch types
incorporating piezoelectric fibers. The piezoceramic material used in these patches was Navy Type-II PZT.
Researchers at NASA Glenn Research Center have been investigating high temperature shape memory alloys as potential damping materials for turbomachinery rotor blades. Analysis shows that a thin layer of SMA with a loss factor of 0.04 or more would be effective at reducing the resonant response of a titanium alloy beam. Two NiTiHf shape memory alloy compositions were tested to determine their loss factors at frequencies from 0.1 to 100 Hz, at temperatures from room temperature to 300°C, and at alternating strain levels of 34-35x10<sup>-6</sup>. Elevated damping was demonstrated between the M<sub>s</sub> and M<sub>f</sub> phase transformation temperatures and between the A<sub>s</sub> and A<sub>f</sub> temperatures. The highest damping occurred at the lowest frequencies, with a loss factor of 0.2-0.26 at 0.1 Hz. However, the peak damping decreased with increasing frequency, and showed significant temperature hysteresis in heating and cooling.