Performance Mapping of an Aluminum - Nitinol Composite Vibrating Beam

Abstract

Dynamic control of a vibrating beam is critical to the efforts of mitigation of high cycle fatigue, as it is a leading cause of component or engine failure. Recent advances in composite structures have afford the ability to control the eigenvalue, eigenvectors, and amplitude of vibration through the use of the shape memory effect of shape memory alloys (e.g. Nitinol). These "smart materials" are proven to create active damping and variable stiffness in engine components is an innovative concept. Research presented herein seeks to quantify the effectiveness of Nitinol as a HCF mitigation technique and map the frequency and damping performance. A composite beam consisting of a Nitinol topical actuator adhered to an aluminum alloy 6061 substrate was designed and fabricated. Test specimens comprised two configurations: (1) a composite beam with the topical treatment encompassing the full span of free length of the beam, and (2) a composite beam with the topical treatment encompassing half the span the free length of the beam. Benchtop tests allowed for the determination both modal frequency and damping of the aluminum-Nitinol composite beam with an 8 in. free length. Modal analyses were taken over a selected frequency range using a single point laser vibrometer, excited using a dynamic shaker. Experimental studies were completed over a frequency range which represented the second bending mode. Quality factor values, Q, of approximately 200 were observed. No correlation, however, with phase transformation was realized. The design space charts for temperature, modal frequency, and beam tip amplitude were compiled for both the full-span and half-span sample for second bending mode. These charts graphically depict how tip amplitude changes with varied temperature and illustrate the design capabilities created through the use of shape memory alloy components in dynamic applications.

Vibration Control of a Flexible Beam with Embedded Shape Memory Alloy Wire

“…An experimental study by Nakshatharan [24] using SMA wire applied externally to a clamped-free beam with a constant excitation frequency confirmed that beam tip amplitude reduction of approximately 60% can be achieved in first bending mode. The introduction of the shape memory effect, whereby the shape memory alloy material acts as both a damper and a means of variable stiffness have been confirmed for HCF mitigation [16,17,18,19] using thin sheet metal SMA topically adhered onto a clamped-free beam. This study highlights an amplitude reduction of 92% in the second bending mode with constant excitation frequency.…”