Characterization of the pseudoelastic damping behavior of shape memory alloy wires using complex modulus

Abstract

The pseudoelastic stress/strain hysteresis behavior observed in nickel-titanium (Ni-Ti) shape memory alloys (SMAs) above the austenite finish temperature can be exploited to provide passive structural damping in a variety of applications. The present study characterizes the damping behavior of Ni-Ti SMAs using the complex modulus approach, commonly used in structural dynamics for the characterization of damping materials. Results indicate that as excitation frequency increases, the loss modulus (a measure of the damping) undergoes a rapid initial decrease. The value of loss modulus (and available damping) at 6-10 Hz is approximately 50% of that at low frequencies, but does not show significant reduction thereafter. As the cyclic strain amplitude increases, the storage modulus (a measure of the stiffness) initially undergoes a rapid decrease, implying that the material softens with increasing motion amplitude. As the static strain offset increases, the loss modulus decreases, and the storage modulus increases. The loss modulus decreases at temperatures above , while the storage modulus shows a significant increase above associated with the SMA operating outside its ideal pseudoelastic temperature window. The experimental stress/strain hysteresis loops and the idealized loops based on complex modulus characterization compare very well for small cyclic strain amplitudes, but may differ for higher amplitudes. However, the energy dissipation estimates from the idealized and experimental hysteresis loops compare very well over the entire range of cyclic strain amplitudes, indicating that complex modulus characterization is well suited for estimating the damping capability of SMAs.

Auxetic compliant flexible PU foams: static and dynamic properties

“…Using the complex modulus approach [18], the constitutive relation between tensile stress σ and strain ε for a damping material subjected to steady-state sinusoidal (harmonic) excitation is given by:…”

“…Imposing a harmonic strain input 0 cos t e e w = and corresponding measured stress one obtains following [18]:…”

“…The hysteresis cycles have been measured and equivalent storage and loss modulus of the foams been detected at room temperature. The approach taken is similar to the one used by Gandhi and Wolons [18] to measure the complex modulus of the pseudo-elastic properties of shape memory alloy Nitinol wires. This approach has been deemed appropriate considering the significant dependence of the viscoelastic foam properties versus the excitation frequency and different levels of pre-strain for fixed temperature conditions [11,17].…”

Passive Damping Augmentation of a Vibrating Beam Using Pseudoelastic Shape Memory Alloy Wires

“…In addition, for non-linear materials the complex modulus also varies with excitation amplitude [17}19]. A complex modulus representation of SMA behavior, as presented in reference [20], can be easily integrated into structural analyses, and in#uence of the SMA on structural response or modal damping can then be readily calculated.…”

Rotor–bearing system integrated with shape memory alloy springs for ensuring adaptable dynamics and damping enhancement—Theory and experiment

“…When the rotor is not rotating, the system consists of two decoupled subsystems (α, x) and (β, y) as may be seen from the structure of the equations of motions (21). The two subsystems have two resonance frequencies each, and the first two modes consist of in-phase motion between rotor and bearing housings and the next two modes consist of counter-phase motion.…”