Electro-thermomechanical characterization of Ti-Ni shape memory alloy thin wires

Abstract

The use of shape memory alloys (SMA) as smart structures and other modern applications require a previous evaluation of its performance under load as well as a training procedure. In general, these requirements lead to the design and assembly of a specific test bench. In this work, an experimental set-up was specially designed to perform the electro-thermomechanical characterization of SMA wires. This apparatus was used to determine the strain-temperature (epsilon - T) and electrical resistance-temperature (R - T) hysteretic characteristics curves of a Ti-Ni shape memory wire (90 mm in length and 150 µm in diameter) under mechanical load. The SMA wire is loaded by means of constant weights and a controlled system for injection of electrical power allows performing the heating-cooling cycles. The obtained hysteretic epsilon - T and R - T characteristics curves for some levels of applied loads are used to determine important shape memory parameters, like martensitic transformation temperatures, temperature hysteresis, temperature slopes and shape memory effect under load. These parameters were in accord with the ones found in literature for the studied SMA wires

Electrical Resistance and Natural Convection Heat Transfer Modeling of Shape Memory Alloy Wires

“…The literature lacks accurate thermal models developed specifically for SMA wires. The thermal models available in the literature cannot be used to calculate natural convection heat transfer coefficients for the SMA wires precisely since they are based on approximations or are developed for other types of wires or cylinders [6][7][8][9]. Therefore, this work proposes a heat transfer correlation for SMA wires that can be used to predict the temperature of current-carrying wires.…”

“…Nascimento et al [9] studied electrical resistance of NiTi wire for different applied 21 stresses and reported that the electrical resistance decreases by 17 to 18% during phase transformation from martensite to austenite for all applied loads. where and are constant coefficients [5].…”

“…There is very little published literature about the relation between SMA wire strain and its electrical resistance [4,9]. The strain of SMA wire is a function of phase transformation and can be used to detect the phase state of the wire during heating and cooling [41].…”

Online fatigue detection of a SMA-based control valve using CUSUM algorithm

“…The polynomial models were used in this work as F (-) because of their linear-in-the-parameters which allows simple algorithms of least squares family to be used in the identification process. The deterministic part of the polynomial NARX model can be expanded from the following notation [7] : p m X IIy( k -n k ) II u(k-nJ k=J k=p+J (2) where O:S; m :s; I is the degree of nonlinear, I is the maximum degree of nonlinearity, each mth order term is the product of a pth order factor in y, a (m-p)th order factor in u and a C p , m-p (n1 ,00', nm) coefficient.…”

“…Functional fatigue is a primary contributor to working displacement degradation of SMA-based actuator systems and thus must be understood and monitored [2][3]. The fatigue life and characteristics is highly dependent of the amount of applied stress/strain and the number of cyclic loadings.…”